Touchstone File Guide: Read S2P Data

November 7th, 2026

A Touchstone file stores frequency-dependent network parameters in text form. An .s2p file normally describes a two-port network, with four complex S-parameters at each frequency. Before importing it into a PCB simulation, check the units, data representation, port map and reference impedance; a file that loads successfully can still describe a different setup from the one you intended.

This guide follows a hypothetical passive RF PCB coupon between two connectors. Numerical examples are teaching values, not measured performance. The reference specification is Touchstone 2.1, ratified January 26, 2024; importing software may support a narrower subset.

RF PCB coupon connected to coaxial cables on a laboratory bench — AI-generated RF measurement-context illustration, not a measured S-parameter result or factory test record.

What an S2P File Tells You—and What It Does Not

The data describes a network response at specified frequencies and reference conditions, not the complete physical design. For the coupon, S21 describes transmission toward port 2 from excitation at port 1, while S11 describes reflection at port 1 under the parameter definition.

The file may originate from a measurement or a simulation. That origin, the physical port locations and included fixtures need accompanying documentation. The filename alone does not establish temperature, calibration, geometry, manufacturing revision or validation quality. It also does not make a small-signal device model valid for every bias or large-signal operating condition.

Read the Option Line Before the Numbers

The option line explains how to interpret the data. For the example # GHz S MA R 50, read the fields separately rather than assuming a familiar instrument’s export defaults.

Field	Example	Meaning
Frequency unit	GHz	1 means 1 GHz
Parameter type	S	Scattering parameters
Pair format	MA	Linear magnitude and angle
Reference	R 50	50 Ω reference in this example
Angle unit	Degrees	Not radians

Version-specific keywords can affect the interpretation, including reference values and port ordering. Read the complete header and the applicable specification instead of treating this one example as a universal template.

Compare MA, DB and RI Using the Same Complex Value

All three formats can describe the same complex S-parameter, but the two stored numbers mean different things. Keysight’s S-parameter table documentation identifies these supported representations.

Format	Pair means	Teaching example
MA	Magnitude, angle	0.5, −90°
DB	dB value, angle	−6.0206, −90°
RI	Real, imaginary	0, −0.5

The example value is −j0.5. Its magnitude in dB is 20 log₁₀(0.5) ≈ −6.0206 dB. These are calculated representations, not three measurement results. Simply changing MA to DB in the header without converting the data changes the meaning of the file.

Check the Special Two-Port Data Order

Do not assume every two-port row is stored in the intuitive S11, S12, S21, S22 sequence. The legacy two-port convention is frequency followed by the S11, S21, S12 and S22 pairs. Versions 2.0 and 2.1 use the applicable [Two-Port Data Order] declaration to identify the permitted order.

For the teaching coupon, manually identify one frequency and its transmission pair, then compare that point with the imported plot. This spot check can catch an ordering mistake before the wrong column becomes a design conclusion. Preserve any original header instead of rearranging columns by visual intuition.

Map File Ports to Physical Connector Locations

A correct numeric matrix still needs a physical port map. Label the coupon ends in the review record, identify signal and reference conductors, and confirm the direction represented by S21. Do not assume the left side of a photograph is always port 1.

For a reciprocal uniform coupon, forward and reverse transmission can look similar, so a reversed connection may not be obvious from one magnitude plot. Connector launches or other asymmetric features can matter when the model is connected to the next network. Keep a simple physical connection sketch with the data, separate from the file’s numeric indexing.

Separate Reference Impedance from the Connected Load

The S-parameter reference defines the wave representation; it does not say that the actual trace has a constant 50 Ω impedance or that every future connected load must equal 50 Ω. The simulator must interpret the file with the correct reference before connecting other circuit elements.

When changing the S-parameter reference, use a valid renormalization operation rather than editing the R value alone. The scikit-rf renormalization example shows that the same physical load has a different reflection coefficient under a changed reference. More advanced complex-reference cases also require attention to wave definitions; do not improvise them from a simple real-resistance example.

Understand Why S4P Does Not Automatically Mean Differential Data

Four ports can represent two single-ended conductors at each end, but that physical arrangement must be established. A four-port file can also describe another network entirely. Even for a differential pair, single-ended data and mixed-mode data require the correct interpretation and pairing.

For a differential version of our coupon, identify the positive and negative conductors at both ends and check the file’s declared mode/order information. A mistaken pairing can produce misleading differential transmission or mode-conversion results. Do not rename .s4p to .s2p to make an import dialog accept it.

Four-port PCB coupon with SMA connectors and detached coaxial cable ends — AI-generated connection-planning illustration. Actual port numbering and differential pairing must come from the data provider.

Check the Frequency Band and Low-Frequency Treatment

The dataset supports its stated frequency range; behavior outside that range depends on the importing tool’s modeling assumptions. Record the first and last frequencies, point spacing and whether the intended analysis requires extrapolation or a DC estimate.

For the coupon, compare the planned simulation band with the data before running a time-domain analysis. Ask how the tool handles missing low-frequency data, interpolation and high-frequency truncation. A smooth-looking extrapolated curve is not an additional measurement. Keep any fitted or extended dataset distinguishable from the original supplied file.

Identify What the Measurement Reference Planes Include

The model boundary determines which physical effects are already in the data. A coupon file measured at coaxial reference planes may include launches that a trace-only electromagnetic model excludes. Cascading both without checking their boundaries can count the same transition twice.

Ask for the calibration or de-embedding description and a physical definition of each reference plane. For the teaching network, decide whether the connector bodies, launch pads and uniform line are included. This is different from the numerical impedance reference: both need to be correct, but they answer different questions.

Check Physical Plausibility for the Intended Network

Passing a syntax check does not demonstrate passivity, causality, reciprocity or measurement accuracy. A passive coupon and a biased amplifier are different model classes, so the applicable checks must match the object.

Use the simulator’s documented validation tools and investigate suspicious behavior against the original data and measurement setup. Do not judge full multiport passivity solely by looking at one S21 magnitude. Likewise, do not “repair” a model automatically without understanding how the correction changes its response. Save the original and document any authorized fitted or corrected version.

Diagnose an Import Failure Without Corrupting the File

Identify the reader’s supported version and the exact reported problem before altering the data. Common review areas include the option line, frequency units, port count, pair format and required version-specific keywords.

Keep an unchanged original, test the file with a suitable independent reader, and compare at least one known point. If a format conversion is required, use a tool that actually converts the data and preserves the intended network meaning. Deleting unfamiliar header lines until the error disappears can remove information the importer needed to interpret the file correctly.

Release the Dataset with a Short Model Record

A usable handoff includes enough context to connect the network correctly and understand its limits.

File identity, revision and measured or simulated origin.
Format version, parameter type and pair representation.
Frequency range and any fitting or extrapolation.
Physical port map, reference planes and impedance convention.
Relevant bias, temperature and construction conditions.
Import spot check and applicable model validation results.

For interpretation of reflected signals, see the related PCB return loss and S11 guide. Reading the file correctly is the starting point for that interpretation, not proof that the manufactured channel meets its requirement.

FAQ

Can a CSV export be renamed to .s2p?

No. The content must follow the supported Touchstone syntax and contain the required complex network data. A spreadsheet of frequency and one magnitude curve is not a complete two-port network. Use an appropriate export or conversion method, then verify units, ordering and a known data point in the receiving tool.

Why does a file open in one tool but not another?

The tools may support different versions or subsets of the format, or may handle nonconforming input differently. Compare their documented capabilities with the actual header and data. A tolerant reader accepting the file does not prove full conformance, and a rejected file should not be fixed by removing required information blindly.

Can the file contain Y or Z parameters instead of S parameters?

Yes, the declared parameter type matters. Do not interpret every pair in a file as an S-parameter just because the workflow uses the word Touchstone. Check the option line and the receiving tool’s support for that parameter type. A conversion to scattering parameters must use the appropriate definitions and reference conventions.

Does a negative S21 dB value mean negative power?

No. It is a logarithmic representation of the magnitude of a complex transmission parameter under the stated reference definition. In the teaching example, magnitude 0.5 corresponds to about −6.02 dB. Interpreting delivered power additionally requires the relevant network and termination conditions; the sign alone is not a power measurement.

Can I recover phase from a magnitude-only screenshot?

Not as a complete replacement for the original complex dataset. A plot of magnitude omits phase information and usually lacks the full numeric precision and context needed for a network model. Ask for the original file rather than reconstructing a production simulation from a screenshot and assuming the missing phase is zero.

Does an S2P file fully describe an operational amplifier?

Not across every operating condition. Device data depends on how the part was biased, connected and characterized, and a small-signal network description does not replace all nonlinear, stability or supply behavior. Check the manufacturer’s intended model use and conditions before applying a two-port representation to an amplifier circuit.

Should I delete comment lines to improve compatibility?

Only if a documented conversion or troubleshooting step justifies it and the original is preserved. Comments may carry essential human-readable context such as port names or measurement conditions, even when they do not alter numeric parsing. Keep that context in the handoff record rather than stripping it simply to make the file smaller.

Is a supplier’s simulated file equivalent to a measured production coupon?

No. Both can be useful, but they answer different evidence questions. A simulated file depends on the model assumptions; a measurement depends on the specimen and test setup. Label the origin clearly and compare the construction and conditions with the intended PCB. Do not present simulation output as a manufacturing test certificate.

For a Best Technology RF PCB enquiry, send the stackup, conductor requirements, model boundary and intended validation scope to sales@bestpcbs.com. Keep the supplied network file paired with its physical port map and construction revision.

Tags: RF PCB Validation, S Parameters, S2P Data, Touchstone Files
Posted in bestpcb | No Comments »

Huray Roughness Model: Input Guide

November 7th, 2026

The Huray roughness model represents copper surface texture using an idealized nodule geometry to modify conductor surface impedance. In Ansys HFSS 3D Layout, its inputs include a nodule radius and a dimensionless Hall-Huray surface ratio. They are not interchangeable with a foil datasheet’s Rz roughness height.

This guide follows a hypothetical RF microstrip coupon from material selection to simulation review. Its useful output is a traceable input record: which copper face each value describes, where that value came from, which solver convention was used, and how the model was checked. It does not supply universal roughness settings for an unspecified PCB.

Matte and more reflective copper foil swatches on a laboratory tray — AI-generated physical-material illustration. Visible sheen does not measure micron-scale roughness or identify Huray parameters.

What the Huray Model Does to a PCB Simulation

The model accounts for electrical consequences of surface texture without requiring the mesh to reproduce every microscopic feature. A smooth-copper calculation and a roughness-enabled calculation can therefore differ even though the drawn trace geometry is unchanged.

Ansys documents a causal modification that also handles phase effects, rather than only a real-valued loss increase. See its Huray Surface Roughness Model documentation, 2025 R2. Record the actual implementation and version; the name “Huray” alone is not a complete description of a simulation setup.

Why Copper Texture Matters More as Frequency Rises

At increasing frequency, skin effect concentrates current nearer conductor surfaces, making the condition of those surfaces relevant to loss. Skin depth is the characteristic penetration distance, not the physical foil thickness. That is why a thick copper layer can still need a surface model.

For the RF coupon, first define the operating frequency range and acceptable channel behavior. Do not ask whether roughness matters in isolation from frequency, geometry and field distribution. The current in both the signal conductor and its return path matters. A visual inspection of a shiny top surface does not characterize the less visible copper-dielectric interface.

Key Huray Parameters and Their Units

Keep physical dimensions, dimensionless factors and software defaults in separate fields. This avoids a numerically plausible entry acquiring an unsupported physical meaning.

Input	Unit	Interpretation
Nodule radius	Length, e.g. µm	Radius in the idealized surface model
Hall-Huray ratio	None	Surface-area relationship under the model convention
Rz or Rq	Length	Measured profile statistic, not automatically either input above
Conductivity	S/m	Conductor property, separate from roughness
Frequency	Hz and stated sweep	Range over which the response is evaluated

The current PyEDB StackupLayer API reference shows default Huray inputs of 0.5 µm and 2.9. These are API defaults, not measured values for your copper. Explicitly supply reviewed inputs and record their source rather than accepting a default because the solver runs.

Why Rz Cannot Simply Be Pasted into Nodule Radius

Rz describes a surface-profile measurement, while nodule radius describes the geometry assumed by the model. A numerical conversion requires an identified method and assumptions; equal units do not make two quantities equivalent.

A Cannonball-Huray derivation is one published route for estimating model inputs from foil roughness information. It introduces a close-packed-sphere assumption rather than proving that a real copper surface consists of identical spheres. Use the method as a documented estimate within its limits, not as an exact measurement. Keep the original roughness metric, measurement convention and derived parameters together so another engineer can reproduce the choice.

Huray vs Groiss and a Smooth-Copper Baseline

Compare models as modeling choices, not as three interchangeable fields accepting the same number.

Choice	Role	Review caution
Smooth copper	Diagnostic baseline	Not a claim that the physical copper is smooth
Groiss in Ansys 2025 R2	Legacy roughness correction	Frequency-domain limitation documented by Ansys
Huray in Ansys 2025 R2	Causal roughness model	Requires radius and surface-ratio convention
Cannonball-derived inputs	Parameter-estimation approach	Not a separate measurement of the finished interface

These statements refer to the named Ansys implementation. The layer roughness settings documentation explains its available choices. Other solvers may use different names, conventions or corrections, so do not translate settings solely by matching menu labels.

Map Model Values to the Correct Copper Faces

Assign values by physical interface, not merely by a layer name such as “top copper.” A microstrip trace has a face toward the dielectric, a face away from it and etched sidewalls. Its reference plane also participates in the electromagnetic problem.

Draw a simple face map for the hypothetical coupon and identify which supplied value belongs to each interface. Ansys permits separate top, bottom and side settings. “Set all” is a convenience command, not evidence that the three physical surfaces are identical. If only one face is characterized, record the uncertainty rather than quietly copying it everywhere.

Ask for Data That Matches the Manufactured Interface

Request foil identity, side identity, roughness metric and processing context together. The laminate name alone may not identify the exact copper supplied or the state of the surface after subsequent fabrication.

For the coupon, distinguish incoming foil data from information representing the finished stackup. Ask what treatment or processing stage the value describes and whether the modeled face corresponds to it. Keep an input marked “supplier data” separate from one derived by an engineer or fitted to a coupon. Our related microstrip PCB guide provides the wider geometry and reference-plane context.

Build a Sensitivity Study Before Claiming a Prediction

A sensitivity study asks how much the result depends on uncertain inputs; it does not establish which input is true. For the hypothetical RF coupon, hold the verified trace geometry, dielectric model and ports fixed while comparing a smooth baseline with separately documented candidate roughness sets.

Save the baseline model and complete input record.
Change only the selected roughness parameters for each comparison.
Review insertion loss and phase across the same frequency sweep.
Mark which candidates are measured, supplied, derived or hypothetical.
Investigate whether the resulting spread changes the design decision.

No numerical outcome is implied here. If the acceptable design depends on one unverified roughness setting, the next action is better characterization, not a more confident caption on the plot.

RF microstrip test coupons with straight traces and edge connectors on a laboratory bench — AI-generated coupon illustration, not a measured comparison or evidence of factory test capability.

Use Coupon Measurements Without Hiding Other Errors

Measurement comparison must use a defined reference plane and a controlled geometry before it can usefully constrain a material model. A connector transition, calibration issue or incorrect trace width can otherwise be mistaken for roughness loss.

Two line lengths can support a suitable extraction method, but subtracting two arbitrary S21 magnitudes is not automatically a rigorous de-embedding procedure. Check the chosen method’s assumptions, matching, fixture repeatability and frequency behavior. Use independent geometry and dielectric information where possible. Save the measured data, extraction steps and model version so the apparent agreement can be reproduced.

Do Not Fit Roughness and Dielectric Loss Blindly

A good-looking total-loss fit does not prove that the separate loss mechanisms were identified correctly. If both dielectric loss and roughness are freely adjusted, different parameter combinations may explain similar attenuation over a limited band.

Constrain one mechanism with independent evidence before interpreting the other. Review phase as well as loss, and test against a different length or suitable validation structure not used for fitting. If changing geometry or reference-plane assumptions destroys the fit, investigate those assumptions first. Describe a fitted parameter set as a model effective for its validation conditions, not as a universal copper material certificate.

Check Plating, Vias and Return Surfaces Separately

Do not use a roughness factor as a catch-all correction for every conductor-related effect. Surface finishes, plated conductors, etched geometry, vias and reference planes need their own modeling decisions and appropriate evidence.

For the RF coupon, write down which metal stack and interfaces the solver actually represents. If a later design adds a different finish or via transition, revisit the model instead of copying the coupon’s fit unchanged. Applying a trace-surface setting to every conductor is not automatically conservative: it may misrepresent where the fields and currents are concentrated.

Release a Traceable Roughness Model, Not Just a Screenshot

The release record should let another engineer rebuild the same assumptions and identify what remains uncertain.

Solver, version, roughness model and unit convention.
Material and foil identity with source document revision.
Face-by-face assignment and treatment state.
Radius and ratio, labeled supplied, measured, derived or fitted.
Geometry, frequency range, dielectric model and port setup.
Validation data, limits and triggers for rechecking substitutions.

The practical decision is whether that evidence supports the design margin. A completed simulation proves that a model was solved, not that the finished PCB has been validated.

FAQ

Can I use the same Huray values in two different solvers?

Only after checking each solver’s parameter definitions, units, causal treatment and surface assignments. Similar field names do not establish equivalent implementations. Reproduce a simple controlled structure and compare the expected behavior before transferring a production model. Keep the original source and conversion assumptions with both projects rather than copying two unexplained numbers.

Does a lower foil Rz guarantee lower finished channel loss?

No. It is one potentially relevant input, not a channel-level guarantee. Dielectric loss, geometry, copper processing, finishes and transitions can also affect the measured response. Compare matched constructions and methods before attributing the difference to foil texture. Do not replace a complete channel requirement with one roughness statistic on a purchase order.

Should I increase mesh density until the microscopic texture appears?

Not as a substitute for understanding the selected surface model. A model-based correction represents effects that are not explicitly drawn as physical nodules. Follow the solver’s meshing and boundary guidance for the actual structure, then demonstrate convergence. Increasing computational effort does not repair unsupported material parameters or an incorrect face assignment.

Is a fitted roughness value valid for a different surface finish?

Not automatically. The fit may include effects that were not separately identified in the original coupon. A changed finish or metal stack can invalidate that interpretation. Review what the original model represented and repeat the relevant validation rather than treating the fitted value as an intrinsic property independent of manufacturing conditions.

Why can a model match loss but miss resonance frequency?

A loss match does not prove that phase delay and stored-energy behavior were modeled correctly. Geometry, dielectric dispersion, roughness implementation and transitions may need review. Use suitable phase or resonant measurements as additional constraints. Do not change dielectric constant solely to hide a mismatch before checking the physical construction and reference planes.

Can I use a single model for all fabrication lots?

Use it only within the construction and variation envelope that your evidence supports. A material substitution, changed foil treatment or altered fabrication process should trigger review. Define that envelope in the release record and ask how the relevant material identity is controlled. One successful coupon does not establish unlimited lot-to-lot equivalence.

Does the model predict DC resistance accurately from roughness alone?

No. DC resistance still depends on conductor dimensions, conductivity, temperature and the actual current path. A high-frequency surface correction is not a replacement for those inputs. Check the solver’s low-frequency treatment and compare against an appropriate baseline rather than interpreting a Huray radius as a standalone resistance specification.

What should I do when the supplier provides only Rz?

Ask which face and measurement method the value describes, then request a supported model parameter set if available. If you use a published derivation, record its assumptions and label the result as estimated. Carry the uncertainty into sensitivity and validation work; do not relabel the original Rz value as a measured sphere radius.

Technical References

Bert Simonovich: Practical Method for Modeling Conductor Surface Roughness Using Close Packing of Equal Spheres, original method discussion and validation context.
Altium OnTrack interview: Copper Roughness and Signal Integrity, discussion with the model-method developer.

For a Best Technology RF PCB enquiry, send the stackup, foil requirements, simulation assumptions and intended validation scope to sales@bestpcbs.com. Confirm the proposed construction before treating the analysis as representative of the manufactured board.

Tags: Copper Roughness, Huray Model, Insertion Loss, RF PCB Simulation
Posted in bestpcb | No Comments »

PCB Return Loss Guide: Read S11 Correctly

November 7th, 2026

For an ordinary passive PCB interconnect, S11 displayed as log magnitude is usually negative, while return loss is conventionally reported as the corresponding positive number. S11 of −20 dB means 20 dB return loss and 1% reflected power at that frequency and reference plane. It does not mean 20 dB of forward signal loss.

This guide follows a hypothetical RF coupon between two coaxial launches. An engineer receives a plot and needs to determine whether it meets a specified reflection limit. The task is to read the quantity, sign, frequency range, and measurement boundary correctly—not to judge a PCB from one attractive marker value.

Illustrative RF PCB coupon with opposing coaxial edge launches — AI-generated physical-product illustration. No measured impedance or RF performance is represented.

What Does S11 Describe on a PCB?

S11 describes the reflected wave at port 1 relative to the incident wave at port 1 under the defined network conditions. It is a complex quantity, carrying magnitude and phase. The familiar negative-dB curve shows a transformation of its magnitude, not the complete complex result.

Keysight’s measurement-parameter documentation distinguishes reflection parameters S11 and S22 from transmission parameters S21 and S12. The port labels matter: a curve cannot be interpreted reliably without knowing where excitation and measurement occur and how the other ports are terminated.

Detailed S11 and Return-Loss Parameters

Write down the parameter definition before comparing a plot with a requirement. For equal real reference impedances in the usual passive interconnect context, use the following relationships. Here Γ denotes the input reflection coefficient and log means base 10.

S11 log magnitude: 20 log(|Γ|), in dB.
Return loss: −20 log(|Γ|), in dB.
Reflected power fraction: |Γ|² = 10^−RL/10.
Record the reference impedance, frequency, calibration plane and termination conditions with every result.

S11 (dB)	RL (dB)	\|Γ\|	Power back
−6 dB	6 dB	0.5012	25.12%
−10 dB	10 dB	0.3162	10%
−20 dB	20 dB	0.1000	1%
−30 dB	30 dB	0.03162	0.1%

These are calculated conversions, not PCB acceptance limits or measured results. The Teledyne LeCroy explanation of S-parameter terminology discusses the sign convention and the distinction between reflection and transmission.

Why More Negative S11 Means Less Reflection

A smaller reflected-to-incident wave ratio has a more negative logarithm. Therefore −30 dB S11 indicates less reflected power than −10 dB S11 at the same measurement conditions. Under the positive return-loss convention, the same comparison becomes 30 dB versus 10 dB.

Avoid saying only “lower return loss is better” or “higher S11 is better.” Name the plotted quantity. For our coupon, a specification of RL ≥20 dB corresponds to S11 log magnitude ≤−20 dB. These are the same reflection requirement written in two conventions, not competing performance targets.

Return Loss vs Insertion Loss

Return loss concerns reflected signal; insertion loss concerns reduction in forward transmission under the stated reference conditions. Their desirable directions differ. A positive return-loss value should usually be large, while a positive insertion-loss value should usually be small for a transparent interconnect.

Quantity	Usual passive log-magnitude view	What a transparent path aims for
S11	Negative dB reflection trace	Small reflection magnitude
Return loss	Positive counterpart of S11 log magnitude	Larger positive value
S21	Forward transmission, often negative dB	Near 0 dB within the intended band
Insertion loss	Positive loss derived under stated conditions	Smaller positive value

For the broader forward-loss question, see the RF PCB insertion-loss guide. Do not substitute that quantity for the reflection criterion.

A Worked Power Example for an RF Coupon

Suppose a hypothetical passive two-port coupon has S11 = −20 dB and S21 = −3 dB at one frequency, with equal real reference impedances and a matched output. The calculated reflected fraction is 10^−20/10 = 0.01, or 1%. The forward transmitted fraction is 10^−3/10 ≈0.5012, or 50.12%.

About 48.88% remains outside those reflected and transmitted terms in this example. Do not automatically call all of it dielectric heating: losses, radiation, unmodelled paths and measurement limitations need consideration. The lesson is that little reflection does not guarantee nearly complete forward transmission. This is a teaching calculation, not a test report.

Judge the Whole Required Frequency Band

A reflection limit applies over the specified band unless the requirement says otherwise. One deep S11 minimum can coexist with poor matching elsewhere. A marker placed at the best point cannot demonstrate compliance across an operating range.

For the coupon, record the band endpoints and the worst result within that interval. Under the positive return-loss convention, the weakest point is the smallest RL. Under the negative S11 log-magnitude convention, it is the point closest to 0 dB. Check the same band when comparing two revisions or suppliers.

Keep the Reference Impedance Attached to the Result

S11 is referenced to a defined port impedance. A result normalized to one reference cannot be compared casually with a different reference. The relevant value should come from the measurement setup, model, or supplied network data rather than an assumption based on connector appearance.

A nominally 50-ohm test system does not prove that every part of the physical coupon is 50 ohms. It defines a reference for evaluating the structure. If data are renormalized, record that transformation and its basis. Do not describe a changed reference as a physical improvement to the board.

Know Whether the Launches Are Inside the Measurement

The calibration and de-embedding boundary determines which structures the reported network includes. A measurement can contain cable adapters, connectors, launches and PCB traces, or represent a narrower region after an appropriate correction.

In our example, decide whether the requirement applies to the entire connectorized coupon or the trace region alone. Do not blame laminate properties from a launch-inclusive reflection result without further evidence. The related PCB fixture de-embedding guide explains the separate boundary question. A correction must be validated; it is not merely a cosmetic plot adjustment.

Illustrative RF coupon, coaxial cable and calibration accessories on a lab bench — AI-generated laboratory illustration, not an actual calibration or measurement record.

Why S11 and S22 Can Tell Different Stories

S11 looks into port 1; S22 looks into port 2. A structure with different launches or asymmetric discontinuities can present different reflection behavior from its two ends. Label the physical ports clearly before comparing curves.

Do not assume that similar forward and reverse transmission establishes identical input and output matching. In the controller’s RF path, the installed orientation can make the relevant end especially important. Record both reflection parameters when the test plan requires them and use the specified termination conditions rather than an undocumented open connector.

Single-Ended S11 Is Not Differential Return Loss

A differential interconnect needs the appropriate mixed-mode parameter and port definition. An individual single-ended S11 trace does not by itself describe the differential pair’s reflection behavior. Confirm the pairing, polarity and normalization used in the model or measurement.

Do not relabel a single-ended curve as SDD11 to match a requirement. Request the correct data or a documented conversion from a complete suitable multiport dataset. Keep the scope of this guide clear: the earlier numeric example is an ordinary single-ended two-port example, not a differential-channel qualification.

Investigate a Poor Result Without Guessing the Cause

Check the measurement configuration and repeatability before assigning a PCB defect. Verify connections, calibration applicability, port labels, data format, band and reference plane. Then compare the structure with its released design and any validated model.

A reflection feature can be associated with launches, geometry changes, vias, termination or other discontinuities. The S11 magnitude alone does not uniquely identify which one is responsible. Use additional evidence—such as a controlled comparison or an appropriate time-domain analysis—rather than announcing a root cause from the curve’s shape.

Report a Reflection Requirement Without Sign Ambiguity

A useful report names the quantity, inequality, band, reference impedance and measurement boundary. For example: “Calculated teaching requirement: return loss ≥20 dB across the stated band; equivalent S11 log magnitude ≤−20 dB.” Replace the example threshold with the actual approved requirement.

Include the dataset, setup notes and relevant uncertainty or validation limitations. For our coupon, release requires the agreed evidence across the band, not a universal “good S11” number. Keep forward transmission and other channel requirements in their own acceptance checks so one passing metric cannot conceal another failing one.

FAQ

Is −10 dB S11 better or worse than −20 dB?

For the ordinary passive reflection comparison at the same frequency and conditions, −20 dB indicates less reflection. It corresponds to 1% reflected power, versus 10% at −10 dB. Whether either result is acceptable depends on the actual requirement and operating band. Do not turn these conversion examples into universal PCB pass limits.

Why does a report call a negative trace return loss?

People sometimes use return loss informally to refer to an S11 log-magnitude plot. Read the axis, instrument format and stated formula before applying an inequality. If the report is ambiguous, ask the author to name the quantity explicitly. Changing a label without clarifying its definition can reverse an acceptance decision.

Does a 20 dB return loss mean 99% reaches the output?

No. It means 1% is reflected under the stated conditions. The remaining power is not necessarily all delivered through the intended output; dissipation, radiation or other paths may matter. Check the relevant transmission measurement separately. A well-matched attenuating structure is a useful reminder that input matching and forward transmission are different properties.

Can I add return-loss dB values along a channel?

Not as a general channel calculation. Reflections interact with phase and multiple discontinuities, so scalar return-loss numbers do not preserve enough information to predict the cascade. Use suitable complete network data and a validated connection model. Keep reference impedances, port orientation and measurement boundaries consistent when evaluating the combined structure.

Is dB the same as dBm on an RF plot?

No. A ratio expressed in dB is not an absolute power level in dBm. S11 log magnitude describes a wave ratio, while a receiver power readout can be an absolute quantity. Check the selected measurement and units before converting numbers or comparing them with a reflection specification. Similar-looking axes can represent different physical questions.

What if S11 appears above 0 dB?

First establish the device and measurement context. An active network is not covered by the simple passive assumptions used here. For an expected passive interconnect, examine calibration, processing, reference definitions and uncertainty before drawing conclusions. Do not merely flip the sign or delete inconvenient points to make the curve resemble a typical passive result.

Does a Smith chart contradict the negative-dB trace?

Not necessarily. A Smith chart displays complex reflection information in a different representation. A log-magnitude plot discards phase and shows only a magnitude transformation. Verify that both use the same frequency, port, reference impedance and dataset before comparing them. One view may reveal information that the other deliberately does not display.

What should a supplier send with a return-loss plot?

Request the measured structure identity and revision, port map, frequency range, reference impedance, calibration or de-embedding boundary, and the underlying data where available. Ask how the reported quantity and limit are defined. This makes the plot reviewable and prevents confusion between a connectorized coupon, a corrected trace model and a complete installed channel.

References and RF Enquiries

The linked Keysight and Teledyne LeCroy documentation supports the parameter definitions and sign conventions; the numerical examples are calculated and explicitly hypothetical. For a Best Technology RF PCB enquiry, send the stackup, geometry and measurement requirement to sales@bestpcbs.com. Specific fabrication and verification scope require confirmation.

Tags: PCB return loss, RF measurement, S11, Signal Integrity
Posted in bestpcb | No Comments »

AlN Cleaning Guide: Check Water and pH Compatibility

November 7th, 2026

Aluminum nitride, or AlN, should not be treated as a ceramic that tolerates every water-based cleaner. Cleaning compatibility depends on the material grade, exposed surface, chemistry, temperature, contact time, and the other materials in the assembly. Obtain supplier guidance and qualify the complete process before using a new cleaner on production substrates.

This guide is a planning tool, not a chemical recipe. It follows a hypothetical power-electronics substrate with residue near copper metallization. The objective is to remove the residue without damaging the ceramic, metal, joints, or later bonding surface. A clean-looking part is not automatically an undamaged or electrically acceptable part.

Illustrative dry ceramic substrate coupons with copper metallized islands — AI-generated physical-product illustration, not a photograph of a tested or certified AlN product.

1. Why AlN Cleaning Needs a Compatibility Check

AlN is used where heat transfer and electrical insulation must coexist. Its value does not make its exposed surface chemically inert. Research on aqueous treatment and guidance from cleaning manufacturers both show why the specific exposure matters.

For example, Alconox’s AlN cleaning guidance warns about alkaline attack and prolonged or repeated exposure. Its product-specific recommendations should not be copied into a universal recipe for a metallized or assembled substrate. Compatibility must cover every exposed material, not only the ceramic named in the article.

2. Identify Which Form of AlN You Have

Powder, dense sintered ceramic, a coated substrate, and a single-crystal research sample are different test subjects. Their surface area, structure, additives, and exposed interfaces can differ. A cleaning method described for one form is not automatically suitable for another.

Start with the purchased substrate’s exact designation and supplier documentation. Identify whether the cleaning step reaches bare ceramic, a protective layer, metallization, or all three. If the grade or coating is unknown, that is a missing input to resolve—not a reason to use a familiar cleaner and hope for the best.

3. Detailed Cleaning Parameters to Record

A compatibility study needs a reproducible exposure description. Record the following parameters before comparing trial results. This table specifies what to document; it does not prescribe safe numerical limits.

Parameter	What to record	Why it matters
Material and surface	Grade, supplier, finish, coating, metallization	Defines the actual test subject
Chemistry	Product, concentration, water quality, measured pH	Names the real exposure, not a broad cleaner category
Temperature	Controlled range and measurement point	Prevents an unrecorded process change
Contact	Time, immersion or spray, agitation	Distinguishes different exposure conditions
Rinse and dry	Method, sequence, limits, delay	Extends the process beyond the wash bath
Repeat exposure	Normal and permitted rework cycles	Checks cumulative processing

Write the actual pH measurement conditions rather than relying only on a bottle label. A controlled process should also identify how solution condition and concentration are maintained under the approved procedure.

4. What Water-Exposure Research Does and Does Not Prove

A 2026 study of AlN under prolonged pool boiling observed surface degradation under its specific heated-water conditions. That supports taking water compatibility seriously even for bulk material. It does not establish a universal room-temperature cleaning lifetime.

Do not convert a severe laboratory exposure into a rule that a short rinse always fails—or that it is always safe. Use research to identify mechanisms and questions, then test the proposed substrate and process. Temperature, duration, surface preparation, and the exact material form must remain attached to any reported result.

5. Why pH Alone Cannot Select a Cleaner

pH describes one aspect of an aqueous solution. It does not fully describe its ingredients, residue-removal ability, interaction with metals, or effect on coatings. Two products with similar pH can still have different compatibility and rinsing behavior.

Likewise, “neutral” is not a qualification certificate, and “acidic” does not mean safe for every assembly. Compare candidate processes using the complete exposure record in the parameter table. If a proposed cleaner changes both chemistry and operating temperature, evaluate that combined change rather than approving it from a pH comparison alone.

6. AlN vs Alumina: Do Not Transfer a Cleaning Approval

Alumina and aluminum nitride are different materials. Their shared use as insulating substrates does not establish shared chemical behavior. A process approved for an alumina part therefore needs review before being applied to an AlN part.

Comparison	What may look similar	What still needs verification
AlN vs alumina	Ceramic substrate function	Grade-specific chemical and surface response
Bare vs metallized AlN	Underlying ceramic designation	Metal, interfaces, coatings and exposed edges
Powder vs dense AlN	Chemical name	Material form and relevance of the study
Unassembled vs assembled substrate	Same starting substrate	Joints, components, adhesives and trapped solution

For the hypothetical power substrate, changing only the ceramic while keeping the old wash program is a process change to evaluate, not a clerical substitution.

7. Check Metallization and Assembly Materials Too

A cleaner reaches whatever is exposed. Copper, surface finishes, bonding layers, solder joints, adhesives, markings, and component packages may impose limits different from those of the ceramic. A process that leaves bare AlN unchanged can still be unsuitable for an assembled product.

List all affected materials and obtain the relevant compatibility guidance. Pay particular attention to crevices and interfaces that may retain solution. Do not infer that a clean coupon proves compatibility with a complete power module. Test articles should represent the production surfaces and geometry that create the risk.

8. Start with the Residue You Need to Remove

Identify the contamination before choosing a process. Handling contamination, machining debris, flux residue, and an unknown white surface deposit are not interchangeable problems. Their removal and verification may require different approaches.

In our example, first establish whether the deposit is assembly residue or a change to the substrate itself. Repeatedly increasing wash strength can make the evidence harder to interpret. Preserve an uncleaned reference and document the starting condition so that the trial can distinguish removal of contamination from creation of new surface damage.

Illustrative dry ceramic coupon and sealed laboratory sample bottle for compatibility planning — AI-generated laboratory illustration. No cleaning chemistry, procedure, or successful test result is implied.

9. Design a Small, Controlled Compatibility Trial

Use representative material and retain untreated controls. Define the wash, rinse, drying, and permitted repeat-cycle conditions. Decide in advance what measurements will demonstrate residue removal and what observations would indicate damage. Include appropriate handling and chemical safety controls under the organization’s approved procedures.

A staged trial makes discrepancies easier to interpret. If several variables change at once, a failure may not identify its cause. Do not assign production limits from one attractive photograph. Record the sample identity, process settings, inspection method, and acceptance criteria so the result is reviewable and repeatable.

10. Inspect More Than Cosmetic Appearance

Visual inspection can reveal discoloration, deposits, or obvious damage, but it cannot answer every surface or electrical question. Select verification methods according to the product’s risk: surface condition, dimensions, cleanliness, adhesion or bonding behavior, and relevant electrical performance may need separate checks.

Do not impose an arbitrary universal threshold for roughness, residue, or insulation. Use the product’s specifications and a suitable measurement method. Where qualification requires specialist analysis, involve the responsible laboratory or materials engineer before interpreting a change as harmless or assigning a chemical cause.

11. Common Failures in Cleaning Qualification

Common reasoning failures include testing the wrong ceramic grade, omitting a rinse from the trial, ignoring repeat cleaning, and checking only an unassembled coupon. Another is declaring that no visible change means no relevant change. Each can leave the actual production exposure untested.

Also avoid presenting a solvent as universally safe because it is not water-based. Solvents can introduce their own material compatibility, residue, fire, and handling constraints. This guide deliberately does not prescribe acids, alkalis, solvent mixtures, or temperatures for unknown assemblies. Supplier guidance and controlled qualification must come first.

12. Release the Process with Clear Boundaries

An approved cleaning instruction should identify the permitted material and assembly state, controlled chemistry, operating window, rinse and dry sequence, repeat-cycle allowance, inspection criteria, and change triggers. Define who reviews deviations and what to do when the starting contamination is outside the qualified scope.

For the power-substrate example, the useful result is a bounded process supported by representative evidence—not a general claim that AlN can or cannot be washed. For broader material background, see the AlN PCB substrate guide; use this cleaning checklist for the separate compatibility decision.

FAQ

Can I rinse AlN with deionized water?

Do not assume that deionization alone establishes compatibility. Confirm the substrate supplier’s guidance and assess the proposed temperature, duration, exposed materials, and drying sequence. A brief approved rinse and prolonged immersion are different exposures. Qualification should cover the actual process, including repeated cycles where those can occur in production or rework.

Is a neutral-pH cleaner automatically safe?

No. pH does not identify every ingredient or interaction with ceramic, metallization, coatings, and assembly materials. A neutral label is one input, not a complete compatibility assessment. Obtain product-specific guidance and verify cleaning effectiveness and absence of unacceptable damage under the intended conditions before releasing the process for production use.

Can an alumina cleaning instruction be reused?

It can be considered as a candidate process, but it should not be treated as already approved for AlN. Confirm the new material and all exposed surfaces, review supplier guidance, and qualify the proposed process. Similar appearance or a shared role as an insulating substrate does not establish equivalent chemical behavior.

Does a white deposit prove hydrolysis?

No. Appearance alone cannot reliably identify a deposit’s composition or origin. Contamination, dried cleaner, process residue, and material changes may need different investigation methods. Preserve a reference sample, document the exposure history, and use appropriate analysis before declaring a mechanism or trying a more aggressive wash that could alter the evidence.

Can ultrasonic cleaning be added to an approved wash?

Not without reviewing the change. Ultrasonic exposure changes the process and may interact with part geometry, surfaces, joints, and components. Ask the relevant suppliers for limitations and evaluate representative samples under controlled conditions. An approved chemistry does not automatically approve every agitation method, exposure duration, or assembled configuration using that chemistry.

Does an AlN powder study apply to my dense substrate?

It may highlight a mechanism worth investigating, but it does not automatically establish a rate or safe exposure window for a dense substrate. Material form, surface area, grade, and test conditions matter. Use the study within its stated scope and obtain evidence relevant to the actual purchased substrate and proposed cleaning process.

Is alcohol a universal alternative to water?

No. A nonaqueous route still needs compatibility, cleanliness, drying, and safety review. It may not remove the target contamination and may affect other materials or leave unacceptable residue. Follow the chemical supplier’s safety information and the assembly’s approved process requirements rather than selecting a solvent solely because it avoids an aqueous label.

When should a qualified cleaning process be reviewed again?

Review it when the substrate grade, supplier, coating, metallization, assembly materials, cleaner, concentration, equipment, exposure window, or rework allowance changes. New residue types or unexplained inspection failures are also reasons to reassess. Keep change control linked to the qualification’s boundaries so that an old approval is not silently extended to a different process.

Sources and Technical Support

The linked cleaning-manufacturer guidance and original surface-reaction studies support the compatibility cautions; they do not establish a universal production recipe. Send the substrate identification, assembly materials, residue description, and proposed process to sales@bestpcbs.com for a Best Technology technical enquiry. Specific review and manufacturing scope require confirmation.

Tags: AlN cleaning, aluminum nitride substrate, ceramic PCB, cleaning compatibility
Posted in bestpcb | No Comments »

CPW vs GCPW: Why Bottom Copper Changes the Model

November 7th, 2026

Conventional coplanar waveguide (CPW) has a signal conductor between two same-layer ground conductors without a metal plane beneath the substrate. Grounded CPW (GCPW), also called conductor-backed CPW, adds a lower ground plane electrically connected to the side grounds. The same top-layer width and gap do not make these two structures electrically equivalent.

In a teaching example, a designer calculates a 50-ohm antenna feed, then adds bottom copper and stitching vias to the board. The trace has not changed on screen, but the cross-section has. This guide explains how to select a model that represents the board, rather than assuming that any calculator labeled “coplanar” will do.

Illustrative RF coupon with a straight signal strip between two same-layer copper grounds — AI-generated physical illustration. Top copper alone cannot establish whether a structure is CPW or GCPW; inspect the layers beneath it.

Identify the Cross-Section Before Naming the Line

Start with where copper exists above, beside and below the signal, not the label attached to a CAD rule. Sonnet’s CPW documentation distinguishes conventional, grounded and floating structures. In its definitions, lower copper that is not connected to the side grounds is a different case from grounded CPW.

Sketch the actual layer stack through the antenna feed. Mark the nearest plane, side-ground extents, vias and nearby metal enclosure. If two engineers use CPW to mean different cross-sections, a discussion about trace width can appear precise while comparing different physical objects. Keep the drawing with the model so the topology is unambiguous.

CPW vs GCPW vs Microstrip: Compare the Copper

The distinction is the ground geometry surrounding the signal. A simple comparison helps select the initial model, but it does not replace reviewing discontinuities along the entire route.

Structure	Side grounds	Lower metal
Conventional CPW	Part of the line	No plane beneath substrate
GCPW / CBCPW	Tied to lower ground	Connected ground plane
Floating CPW	Not tied to lower metal	Separate lower conductor
Microstrip	Not part of the ideal model	Reference plane below

A real layout may transition between these structures. A coplanar connector launch can lead into a microstrip route. The transition itself then needs review. Calling the whole route “50 ohms” does not show that its launch, straight section and destination share the same local geometry.

Detailed Parameters Needed for a Useful Model

Record conductor dimensions and the complete electromagnetic environment before solving for width. The entries below are required input descriptions, not a universal 50-ohm recipe. Use the fabricator’s proposed stackup and relevant material data for an actual design.

Input	Unit or form	What to identify
Signal width w	mm or µm	Finished top and base widths
Side gap s	mm or µm	Left and right clearances
Plane distance h	mm or µm	Actual dielectric separation
Copper thickness t	µm	Finished conductor section
Material model	Dk, loss; frequency	Relevant grade and method
Ground geometry	Widths, vias, plane shape	Finite physical conductors
Coatings and metal	Thickness; material; distance	Mask, finish and enclosure
Analysis scope	Hz; Ω; reference planes	Band, target and ports

Use one length unit consistently. In a multilayer board, h usually means the distance to the relevant reference plane, not the total board thickness. Confusing those two values can invalidate a calculation before any discussion of fine tolerance begins.

Why Adding a Lower Plane Changes the Answer

The lower conductor changes how electric and magnetic fields occupy the surrounding space. It is not an electrically invisible support sheet. For a low-loss transmission-line approximation, characteristic impedance is related to per-length inductance and capacitance by Z₀ ≈ √(L′/C′). Changing surrounding conductors can change those quantities.

This explains the teaching example without inventing a numerical shift: a width found for a no-backplane CPW must be checked again when a connected backplane is added. The size of the change depends on the complete geometry. Do not claim a fixed percentage correction or declare the added plane harmless merely because it is on the other side of the board.

Select the Calculator by Its Assumptions

Choose a model whose illustrated stackup and boundary conditions match the proposed board. A page title saying “CPW calculator” is not enough to establish whether it includes finite substrate thickness, a lower plane or finite-width side grounds.

Check the equations or documentation, required inputs and cross-section drawing. If the board has a connected plane below the line, a conventional no-backplane result is not automatically applicable. If a tool omits a relevant feature, use it only as a clearly limited starting estimate. Record what it leaves out and move to an appropriate field model before treating its output as a release dimension.

A Worked Input Check for an Antenna Feed

Compare assumptions before comparing impedance outputs. Suppose the teaching board has w = 0.30 mm, s = 0.15 mm, h = 0.20 mm and t = 0.035 mm. These are arbitrary example dimensions, not a calculated 50-ohm structure or a Best Technology capability statement.

For Model A, remove all lower metal to represent conventional CPW. For Model B, add the intended connected lower plane to represent GCPW. Hold the specified material and top geometry constant so the comparison isolates that topology change. Then solve each case and check convergence. No impedance result is supplied here because material properties, side-ground width and frequency-dependent modeling choices have not been specified.

The useful output is a discrepancy identified before fabrication: “our calculator assumed no bottom plane, but our released board has one.” Resolve that mismatch rather than adjusting width until two unrelated tools happen to display the same number.

A DC Ground Connection Is Not the Whole RF Structure

A shared ground net name does not describe the positions and geometry of its physical connections. Review how the side grounds connect to the lower plane along the route and at the ports.

Sonnet warns that electrically long grounded structures without suitable connecting vias can show unexpected resonances. That is a reason to analyze the intended via arrangement, not a universal instruction to place the largest possible number of vias. For connector-specific detail, use the separate RF via-fence launch guide. Check the transition and reference path rather than adopting a pitch from an unrelated board.

Illustrative RF coupons showing coplanar top copper and a separate continuous copper back face — AI-generated physical illustration of top and back faces. Connectivity and impedance must come from design records and verification, not this image.

Finite Ground Width and Nearby Metal Need Attention

Real ground conductors have edges, and nearby metal can become part of the electromagnetic environment. An ideal model with infinitely wide grounds is not automatically representative of a narrow coupon inside an enclosure.

For the teaching feed, compare the side-ground width in the model with the actual copper remaining after component clearances and board cutouts. If the line is near a metal lid, include that boundary where it matters. A useful convergence check changes the modeled boundary distance or ground width and asks whether the answer has stabilized sufficiently for the design’s accuracy needs. Do not confuse solver precision with proof that omitted metal has no effect.

Use the Finished Etched Geometry, Not Only the Artwork

Etching can produce a conductor cross-section different from the ideal rectangle entered into a simple calculator. The gap that interacts with the fields is part of that finished geometry, not just an artwork dimension.

The Rogers–Sonnet comparison study discusses trapezoidal conductor shape and surface roughness in measured and modeled coplanar structures. Use that as evidence to request realistic geometry, not as a source of universal loss values. Ask which finished width and gap ranges the proposed process can support, then analyze those actual bounds rather than silently assuming the drawing’s nominal values are exact.

Keep Coatings and Finish Consistent With the Model

A model of bare copper and air does not fully describe a coated surface line. State whether mask covers the signal, the gaps and the nearby grounds, and what material model is being used.

Do not change a mask opening merely to make a calculator easier to use. Review electrical behavior, environmental protection and assembly needs together. The separate GCPW solder-mask guide focuses on that coating question. Here the first decision is still topology: a correct coating input does not rescue a calculation built on the wrong lower-plane assumption.

Verify the Straight Line and the Launch Separately

A uniform cross-section calculation does not verify a connector pad, bend, component discontinuity or the complete antenna match. Those features can require a different level of model and measurement.

Define the intended electrical acceptance before ordering: impedance, reflection, insertion loss and operating band are related but different requirements. If using a coupon, make its construction representative and state the measurement reference planes. When simulated and measured results differ, investigate the launch, fixture, material and finished geometry before assigning every discrepancy to trace width. The microstrip guide provides an adjacent reference for routes that do not intentionally use nearby side grounds.

Release a Cross-Section, Not Just a 50-Ohm Label

The release package must let the designer, fabricator and test team describe the same structure. A target number without topology and construction inputs leaves room for incompatible interpretations.

Identify conventional CPW, connected GCPW or another explicit structure.
Record the layer pair, lower-plane continuity and side-ground geometry.
Confirm finished width, gap, copper and dielectric ranges.
Keep mask, finish and material assumptions tied to the revision.
Review vias, launch and discontinuities over the required band.
Define coupon scope, measurement conditions and acceptance criteria.

For the teaching antenna feed, the correct next step is to rerun the appropriate model after adding bottom copper, not to preserve an old width because its original calculation said 50 ohms. Approve the resulting construction only after the required validation.

FAQ

Are CPWG, GCPW and CBCPW always different structures?

They are often used for the connected, conductor-backed coplanar arrangement, but naming conventions vary. Ask for a cross-section rather than resolving the design from an acronym alone. Verify the lower conductor, its connection to the side grounds and the model’s boundary assumptions before deciding that two calculators describe the same line.

Does copying a reference-board trace width guarantee 50 ohms?

No. The copied width must be considered with its original gap, dielectric separation, material, copper, coatings and ground geometry. A reference board may also use a different launch or stackup revision. Use its dimensions as design context, then validate the actual proposed construction instead of treating the width as a standalone component value.

Can a very short feed ignore the distinction?

Electrical length and the allowed error influence how much a discontinuity matters, but short physical length is not proof of equivalence. Review the operating band, surrounding structures and system requirements. A model mismatch should be understood and bounded even when the final engineering judgment accepts its effect as sufficiently small.

Does passing the CAD design-rule check verify the impedance?

Only the checks actually configured and implemented are verified. A clearance or connectivity rule can pass while the impedance model uses the wrong plane distance or topology. Inspect the rule’s purpose and the exported geometry. Treat electromagnetic validation and fabrication checks as complementary tasks, not interchangeable evidence for one another.

Is adding top ground beside microstrip always an improvement?

No automatic improvement follows from more copper. Nearby side conductors can change the line being built, especially when their gap is relevant to the fields. Review the revised structure and its connections. Keep a microstrip assumption only when the chosen analysis supports neglecting those conductors for the required accuracy and operating conditions.

Can a hatched lower plane be modeled as a solid plane?

Do not make that substitution without justification. The actual lower conductor pattern and its scale relative to the electrical behavior must be considered. A solver or calculation that assumes a continuous sheet may not represent the patterned structure. Use an appropriate model and validation plan rather than quietly changing the physical geometry in the analysis.

Why might two GCPW tools disagree with identical input numbers?

They may not use identical definitions or assumptions. Check whether gap and width refer to finished dimensions, how conductor thickness is represented, whether side grounds are finite, and which dielectric and coating models are used. Align those details before attributing the difference to numerical accuracy or selecting the more convenient answer.

Does good return loss prove low transmission loss?

No. A path can have limited reflection while still dissipating or radiating energy. Evaluate the separate performance requirements and use measurements appropriate to each. State the operating band, fixture and reference planes so a return-loss result is not presented as evidence that insertion loss or the complete antenna system also meets its target.

Discuss the RF Stackup

For a Best Technology manufacturing inquiry, send the proposed cross-section, layer stack, target impedance, operating band and coupon requirements to sales@bestpcbs.com. Confirm the construction and acceptance scope before treating nominal calculator dimensions as released production data.

Tags: Coplanar Waveguide, GCPW, Impedance Modeling, RF PCB
Posted in bestpcb | No Comments »

100-Ohm PCB Pair Guide: Are Two 50-Ohm Traces Enough?

November 7th, 2026

Two traces that are each 50 Ω when modeled in isolation are not automatically a 100 Ω differential pair once placed close together. Mutual coupling changes the pair’s modal behavior. For a symmetric pair under differential excitation, the differential impedance is twice its odd-mode impedance—not necessarily twice the impedance of an isolated trace.

Two parallel exposed copper traces on a green PCB test structure — A pair of parallel copper traces. AI-generated illustration; geometry in a photograph does not establish impedance.

Follow a hypothetical interface whose specified differential target is 100 Ω. The designer initially selects a width that gives 50 Ω for one isolated trace, then places two such traces close together. We will distinguish what that calculation proves from what the actual pair still needs. The example does not assign a target or tolerance to every interface.

What Does a 100-Ohm Differential Target Describe?

It describes the transmission-line impedance associated with differential voltage and the corresponding loop current in the pair. It is not the DC resistance measured between the traces.

Each conductor has a voltage relative to the reference, while the receiver also sees the voltage difference between conductors. Those are different voltage definitions, so they produce different impedance definitions. AMD UG583’s transceiver guidance explicitly relates 50 Ω odd mode to 100 Ω differential. Its application-specific recommendation should not be copied as a requirement for an unrelated interface.

Which Impedance Parameters Must Stay Separate?

Name the excitation and current convention beside the impedance value. Otherwise, “50 ohms per trace” can refer to different calculations.

Quantity	Meaning for a symmetric pair	Example or relation
Isolated Z0	One trace without the coupled neighbor	Assume 50 Ω
Odd-mode Zodd	Per-line impedance under opposite excitation	Assume 45 Ω after coupling
Differential Zdiff	Between the pair under differential excitation	2 × Zodd = 90 Ω
Even-mode Zeven	Per-line impedance under equal excitation	Assume 60 Ω in that example
Common-mode Zcommon	Common voltage divided by total pair current	Zeven / 2 = 30 Ω

The numerical entries are illustrative model outputs, not results computed from the pictured board or a real stackup. The relationships follow the stated symmetric-line conventions.

Isolated-Trace vs Coupled-Pair Design

The isolated-line calculation omits the neighbor’s contribution, while the coupled-pair calculation includes it. Use the latter when checking the specified differential structure.

Design choice	Useful check	What not to assume
Choose width from isolated Z0	Single-line baseline	Pair remains twice that value at every gap
Set width and gap together	Actual coupled cross-section	One width works on every stackup
Increase separation	Recalculate both modes	“Three widths” proves a target
Change layer or dielectric	Re-solve the new structure	Same artwork keeps the same impedance
Check a transition	Use an appropriate transition model	Uniform-line results cover pads and vias

This distinction concerns model scope. It is not a demand that every differential signal be routed with the tightest possible coupling.

Derive the Factor of Two from Voltage and Current

The factor of two comes from the differential voltage definition for a balanced odd-mode excitation. It does not require adding two physical resistors to the PCB.

Suppose one trace is at +0.5 V and the other at −0.5 V, with equal and opposite currents of magnitude 10 mA. Each trace’s odd-mode ratio is 0.5 V / 0.010 A = 50 Ω. The differential voltage is 1.0 V, and its loop current magnitude is still 10 mA, so Zdiff = 1.0 V / 0.010 A = 100 Ω. These assumed traveling-wave quantities explain the definition; they are not a DC measurement prescription.

A Worked Example Shows How Two Isolated 50-Ohm Traces Miss

If coupling changes the per-line odd-mode impedance, doubling the old isolated result no longer describes the pair. Recalculate the actual cross-section.

Assume an isolated-trace model gives Z0 = 50 Ω, but a separate coupled-pair model for the intended gap gives Zodd = 45 Ω. The pair is then 90 Ω differential, not 100 Ω. The 10 Ω difference is 10% of the hypothetical target; whether it is acceptable depends on the actual specification. The 45 Ω value is an assumed teaching output, not a prediction from width alone. No fixed correction factor converts every isolated 50 Ω design into the right pair.

Why Does the Gap Change Odd-Mode Impedance?

The adjacent conductor changes the electromagnetic fields and coupling between the lines. Opposite-polarity excitation is therefore not equivalent to removing the neighbor.

Polar Instruments AP157 distinguishes the odd, even and isolated modes. For ordinary symmetric edge-coupled structures, narrowing the gap generally lowers odd-mode impedance relative to the isolated case; widening the gap reduces the coupling. Check the actual cross-section rather than treating that trend as a numerical design formula. Nearby copper, dielectric boundaries and reference-plane geometry also belong in the model.

Solve Width and Stackup Together

Width, copper thickness, dielectric geometry and material properties influence the solution along with the gap. A gap adjustment should be assessed within the complete manufacturing construction.

For the hypothetical interface, ask the fabricator for the proposed cured stackup and achievable trace geometry, then solve the candidate pair using appropriate material data. Do not keep a width selected for a different layer height merely because its old calculation said 50 Ω. Record whether the dimensions describe artwork, finished top width or another geometry convention. A clearly named input is more reproducible than a screenshot of an unlabeled calculator result.

Can a Weakly Coupled Pair Still Be 100 Ohms?

Yes. In the weak-coupling limit, two equal lines approach independent behavior, and a pair of isolated 50 Ω lines can approach 100 Ω differential. Tight coupling is not the definition of differential signaling.

That limiting case does not remove the need for suitable references, balanced routing and interface-specific constraints. Evaluate whether the available routing geometry preserves the intended behavior along the path. A long uncoupled region, connector breakout and closely coupled region can each have different cross-sections. Avoid turning a general “route together” recommendation into an arbitrary universal gap requirement.

Even Mode Is Not Another Name for Differential Mode

Even-mode excitation drives the two lines with equal polarity, while odd mode uses opposite polarity. The same physical pair therefore has different modal quantities.

Using the assumed table value Zeven = 60 Ω, a common voltage of 0.6 V produces 10 mA on each line in the idealized mode. Total current is 20 mA, so the pair’s common-mode impedance under this convention is 30 Ω. This explains why Zeven and Zcommon differ by a factor of two. It does not prove that a real link has no common-mode noise or that an arbitrary termination is appropriate.

Bare PCB differential test coupon with two separate coaxial launches — Illustrative two-port coupon connection. AI-generated, not a validated launch geometry or impedance test record.

Recognize Where the Uniform-Line Model Stops

A two-dimensional cross-section describes a uniform line, not every pad, via, connector or reference transition on the route. Those discontinuities need an appropriate additional assessment.

Inspect where the teaching pair changes gap, enters a connector or moves layers. Do not infer that a correct straight-section result proves the entire channel meets its requirements. For relevant via geometry, the Best Technology differential-antipad guide addresses a separate design decision. Keep transition effects and line-target errors distinguishable so a local mismatch does not lead to unnecessary changes across the whole board.

Write the Fabrication Requirement in the Correct Mode

State the differential target, tolerance, layer, referenced structure and test expectations explicitly. Do not ask for “50 ohms on each trace” if the actual acceptance requirement is a differential pair.

A coupon and measurement plan should represent the intended construction within their agreed scope. Confirm the instrument’s mode and reporting convention before comparing values. A single-ended observation of one conductor is not automatically a differential result. The Best Technology differential-pair design guide covers the wider routing and manufacturing handoff; this article clarifies the impedance definitions within it.

Close the Design with a Reproducible Verification Basis

Retain the input construction, mode definitions, calculated result and agreed manufacturing evidence together. The objective is a controlled, verifiable pair—not a favorable number obtained by changing unnamed assumptions.

For the hypothetical link, verify that the final model satisfies its specified 100 Ω target and any other required channel criteria, then reconcile the production evidence with that basis. To discuss Best Technology fabrication requirements, send the stackup, routed layer, differential target and tolerance to sales@bestpcbs.com. Testing and modeling scope must be confirmed for the project rather than inferred from this educational example.

FAQ

Will a 100-ohm resistor make a 90-ohm pair become 100 ohms?

No. A termination sets the load seen at its location; it does not change the characteristic impedance of the distributed line geometry. Select termination according to the actual interface and analyze mismatches appropriately. Do not use a resistor substitution as evidence that an incorrectly modeled PCB cross-section now meets its fabrication target.

Why does my multimeter not read 100 ohms between the traces?

Characteristic impedance describes traveling-wave behavior, not simply DC resistance between two bare conductors. A multimeter can be affected by termination components or circuit paths, and an unconnected bare pair may appear open. Use an appropriate impedance measurement method and clearly identify the connected circuit before interpreting the reading.

Are all high-speed differential interfaces specified at 100 ohms?

No. Required impedance and tolerances depend on the interface and implementation guidance. The 100 Ω target in this article is a hypothetical teaching requirement, not a universal recommendation. Check the actual device and interface documentation before selecting geometry, termination or a fabrication acceptance limit for the project.

Can I double a single-ended TDR result to obtain differential impedance?

Not without establishing what the measurement represents. Exciting one line while treating its neighbor differently is not automatically a pure odd-mode measurement. Confirm the setup, terminations, calibration and conversion method. Doubling is valid for the defined odd-mode impedance, not every impedance trace displayed by a single-ended instrument.

Does correct differential impedance guarantee equal propagation delay?

No. Impedance and timing are separate design quantities. Geometry and materials influence both, but meeting one numerical target does not establish acceptable skew or total delay. Review the interface’s timing requirements and the actual path, including transitions, rather than treating an impedance pass as a complete channel qualification.

Does a symmetric drawing guarantee no mode conversion?

No. The manufactured structure, surrounding references, connectors and excitation can introduce imbalance even when two traces look symmetric in CAD. Maintain appropriate symmetry and analyze relevant discontinuities. A uniform-line impedance calculation is useful evidence for its own scope, but it is not proof that the assembled channel has zero conversion.

Can a solder-mask change affect the pair without changing its artwork?

It can alter the surrounding dielectric environment, particularly for outer-layer structures, so include the intended mask construction where it matters to the model. The size of any effect depends on the actual geometry and materials. Do not assume a fixed percentage change or approve a substitution without the relevant review.

Is impedance the only reason to keep a pair’s spacing consistent?

No. Consistent geometry also helps make coupling, propagation and the modeled structure predictable. Nevertheless, short constrained breakouts may require different spacing and a separate assessment. Apply the interface requirements and suitable analysis rather than forcing every segment into one gap at the expense of reference continuity or manufacturability.

Tags: Differential Impedance, Odd Mode, pcb stackup, Signal Integrity
Posted in bestpcb | No Comments »

PCB Antenna Detuning Guide: Why the Case Changes Range

November 7th, 2026

PCB antenna enclosure detuning occurs when the assembled product changes the antenna’s electrical environment enough to shift its response. A plastic wall, battery, screw, cable or changed ground geometry can matter. However, reduced range after closing a case is not proof of detuning: radiation loss, a changed pattern, receiver noise and an uncontrolled test can produce similar symptoms.

Wireless sensor PCB with edge antenna beside an open plastic enclosure — A wireless board and its housing. AI-generated illustration, not a validated antenna layout or tested product.

Use a hypothetical battery-powered 2.4 GHz sensor as the running example. It communicates on the bench but becomes unreliable inside its enclosure. The goal is to identify what changed, test that hypothesis and verify the complete assembly. It is not to copy a universal keepout distance or guess a new matching capacitor.

What Changes When the Case Closes?

Closing the case changes the materials and objects surrounding the radiator, and sometimes the positions of the board, battery and cables. The antenna is part of that assembled electromagnetic system, not an isolated copper shape.

Antenova’s detuning discussion describes how nearby conductive parts and enclosure materials can affect the antenna environment. For the sensor, begin with a mechanical comparison: what moves toward the antenna when the lid is secured? A newly routed battery lead is a different suspect from the lid material itself.

Which Antenna Parameters Help Diagnose the Change?

Use measurements that distinguish port matching from radiated performance. A single range number is useful as a symptom, but it does not identify the mechanism.

Parameter	Meaning	Diagnostic boundary
Frequency response	How the antenna behaves across the band	A single point can miss a shifted response
S11	Reflection at a defined reference plane	Does not directly measure radiated efficiency
Return loss	Positive loss measure from reflection magnitude	Check sign convention against S11 in dB
Radiation efficiency	Radiated fraction of accepted power	Needs suitable radiated measurement
Radiation pattern	Direction-dependent response	One orientation is not the entire pattern
Packet error result	Link outcome under defined conditions	Also depends on radio and interference

These are diagnostic quantities, not promised sensor specifications. Record the operating band, setup and device configuration alongside each result.

Detuning vs Absorption vs Receiver Noise

Separate these candidate mechanisms before changing the antenna. More than one can exist in the same product.

Candidate	Possible observation	Useful next check
Impedance detuning	Port response shifts after assembly	Compare calibrated sweeps in both states
Loss or shielding	Weak radiated link despite acceptable match	Assess radiated performance and nearby materials
Pattern change	Some orientations worsen more than others	Repeat controlled orientation comparisons
Receiver noise	Performance changes with internal activity	Compare power and operating modes
Test variation	Results move without a design change	Control position, traffic and surroundings

The table is a diagnostic starting point, not a rule that one observation proves one cause. Preserve the baseline while investigating each hypothesis.

Respect the Radiator Keepout and Its Ground Reference

Follow the actual antenna’s reference layout, including its ground geometry and layer-specific keepout. “Ground is useful” and “no ground beneath this radiator” can both be correct for different parts of a design.

For common monopole-style board antennas, the ground region participates in antenna behavior while the designated radiator area requires its specified clearance. Infineon AN91445, revision H discusses enclosure and ground-plane effects for its illustrated antenna systems. Do not transfer one drawing’s distances to every antenna type. In the sensor review, inspect every copper layer and the assembled mechanical model.

Why Can a Plastic Lid Affect a PCB Antenna?

Nonmetallic does not mean electromagnetically invisible. Material close to the radiator can change its loading, even when it does not fully shield the signal.

The relevant question is not simply “Is the case plastic?” Record the wall position, material and nearby internal features. AN91445 explains how nearby plastic can lower resonance in its discussed antenna context. The direction and magnitude in the sensor still need measurement; do not assign a fixed frequency shift from the material name. Compare the actual production-intent lid rather than assuming a loosely placed prototype cover represents the same geometry.

Check Batteries, Screws, Cables and Coatings

Review all nearby objects as possible contributors, not just the outer wall. Conductive hardware and wiring can change coupling, current paths or radiation behavior.

For the sensor, photograph the cable route and battery position before and after closure. Check whether a mounting screw, shield or metallic coating approaches the antenna region. If one object can be moved in an engineering sample, compare controlled configurations without changing everything else. Do not conclude that a removed screw is unnecessary for the final product; mechanical retention, safety and production requirements still apply. The diagnostic result should inform a reviewed redesign.

Small enclosed wireless sensor beside its open reference unit on a test bench — Open and enclosed unit configurations. AI-generated illustration, not evidence of a measured range or matching result.

Build a Controlled Open-and-Closed Comparison

Compare the same radio configuration and physical setup while changing only the assembly state you intend to investigate. Otherwise, a changed result can have several explanations.

Keep firmware, channel, transmit power, battery state, peer device, separation and orientation fixed for an initial comparison. Use a repeatable nonconductive fixture where appropriate and record the environment. Compare more than one unit before deciding the effect is systematic. The hypothetical sensor’s “works on my desk” observation is a useful starting point, but it is not a reproducible acceptance test. Define what constitutes an improvement before trying corrective changes.

Use a VNA with a Defined Reference Plane

A vector network analyzer can compare antenna input response, but the connection and cable become part of the measurement problem. Establish where the calibrated result applies and how the radio is isolated for that measurement.

Use an RF specialist’s suitable fixture and calibration method rather than attaching a cable anywhere convenient. Record its route and keep it consistent between assembly states. A cable that cannot pass through a fully closed lid without changing the geometry may limit the comparison. Treat an observed shift as evidence within that setup, and confirm it with a representative assembled configuration before choosing corrective components.

What Does a Better S11 Actually Prove?

It proves a change in reflection at the measured port under those conditions, not automatically a better radio link. Matching and radiation are related but different.

For a calculated example, S11 = −10 dB corresponds to a reflected-power fraction of 10%, while −6 dB corresponds to about 25.1%, using 10 raised to S11/10. The remainder is accepted at the port; it is not necessarily all radiated. These are mathematical examples, not measured sensor data or universal acceptance limits. A well-matched lossy structure can still perform poorly over the air, so do not stop the investigation at an attractive dip.

Correct the Mechanism Before Guessing Matching Parts

Choose the correction from the evidence: geometry, clearance, component placement, material or matching may need attention. A matching network is not a guaranteed cure for shielding or loss.

TI AN043, revision D is a specific 2.4 GHz PCB antenna reference, not a universal shape that remains unchanged in every host board. Likewise, TE’s embedded-antenna design note discusses ground-plane and tuning limitations. For the sensor, select candidate changes, document them and measure again instead of repeatedly swapping components without a baseline.

Verify the Link in the Final Product Configuration

After correcting the suspected cause, verify radio behavior with the intended enclosure, battery, cable routes and operating modes. The best open-board result is not the delivery configuration.

Use the project’s agreed link criteria and controlled tests across relevant channels, orientations and use conditions. Include internal high-activity modes if they might affect the receiver. Retain the measurement setup and configuration identifiers so another unit can be compared. Check any required radio-compliance implications with the responsible specialist; neither this article nor an improved laboratory response establishes regulatory approval. A range claim requires its own documented conditions.

Freeze the RF-Relevant Mechanical and PCB Details

Release the validated combination, not just the antenna trace artwork. Capture the board outline, stackup, copper keepout, matching population and surrounding mechanical configuration.

The Best Technology PCB antenna manufacturing guide explains why manufacturing handoff matters. Flag a later case, battery or ground change for RF review rather than treating it as purely cosmetic. For a Best Technology fabrication discussion, send the controlled board files and antenna constraints to sales@bestpcbs.com. Any tuning, radiated testing or assembly service must be confirmed within the actual project scope.

FAQ

Can I copy a working antenna into a smaller PCB?

Not with an assumption of unchanged performance. A different board outline and ground region can alter the antenna system even if the radiator artwork is identical. Use the reference design’s complete constraints, then evaluate the actual host board and enclosure. Treat copying as a design starting point rather than validation.

Is there one safe distance between an antenna and every enclosure?

No universal distance covers every antenna, frequency, material and geometry. Use the actual antenna documentation and verify the assembled product. A distance from a particular module guide belongs to that guide’s conditions; it is not a general clearance rule for every trace antenna, chip antenna or external antenna.

Does a metal case always require the same antenna solution?

No. The appropriate solution depends on the complete RF and mechanical design. An external antenna or a deliberately designed RF-transparent region may be considered, but both need engineering evaluation. Do not assume that a small opening, plastic insert or stronger transmitter automatically restores the required coverage and compliance.

Why does touching the unit change its range?

A person’s hand changes the antenna’s nearby environment and may alter both loading and propagation. That makes handling an uncontrolled variable in a bench comparison. Use repeatable fixtures for diagnostic measurements, then include representative handling in the product’s intended-use validation rather than judging performance from one hand-held position.

Can increasing transmit power solve the problem?

It does not identify or correct the underlying mechanism and may not improve the reverse link. It can also affect battery consumption, thermal behavior and regulatory obligations. First determine whether the issue is matching, radiation, interference or the test setup. Use permitted radio settings and validate the complete link.

Why can one channel work while another fails?

The assembled antenna response and the interference environment can vary across frequency. A shifted or narrow response can affect channels differently, but that is not the only explanation. Compare channel-dependent port and link evidence under controlled conditions before attributing the result solely to the antenna or changing its geometry.

Does a pre-certified radio module remove the need for enclosure checks?

No. Follow the module’s integration instructions and the conditions of its approvals, and assess the actual host product. Antenna placement and nearby materials can still affect performance. Consult the responsible compliance specialist about allowed changes; a module’s prior approval is not an unrestricted approval of every enclosure and antenna configuration.

Should the production line repeat the complete antenna tuning exercise?

Not necessarily. Development characterization and production screening serve different purposes. Define a practical production test and controls based on the validated design and project requirements. Keep component population, board geometry and mechanical assembly controlled, and specify what result or change triggers investigation rather than improvising a full retuning procedure for every unit.

Tags: Antenna Detuning, Enclosure Design, PCB Antenna, RF Layout
Posted in bestpcb | No Comments »

PCB Trace Resistance Guide: Check the Hot Voltage Drop

November 7th, 2026

A copper PCB trace becomes more resistive as its conductor temperature rises. If the load current stays constant, its voltage drop and resistive power loss rise as well. A room-temperature resistance calculation is therefore only the starting point for a hot power-distribution path.

Broad exposed copper power trace on a bare green PCB. AI-generated illustration, not a measurement or production record.

Use this guide to estimate the change and decide what to measure. The worked example describes a uniform trace at a specified temperature; it does not calculate its final operating temperature or establish a current rating.

What does PCB trace resistance describe?

Trace resistance is the opposition a copper path presents to direct current. For a uniform rectangular section, R = rho × L/(w × t), where rho is electrical resistivity, L is length, w is width and t is copper thickness.

Longer paths have more resistance. Wider or thicker paths have less resistance when the other inputs stay equal. This is a DC geometric model: it leaves out connector contacts, vias, local neck-downs and high-frequency effects unless they are separately included. That boundary matters before comparing a calculated trace with a measured complete power route.

Which electrical and geometry inputs are required?

Record conductor dimensions and temperature, not just nominal copper weight. Use consistent units throughout the calculation.

Input	Unit	Basis used in the teaching example
Length L	m	0.100
Width w	m	0.002
Thickness t	m	0.000035
Resistivity at 20°C	Ω·m	1.68 × 10^-8
Temperature coefficient	1/°C	0.00393 at a 20°C reference
Conductor temperature	°C	20 or 80
Constant load current	A	5

The material constants are the approximate copper values used in TI’s FPD-Link ADAS Power-Over-Coax Design Guidelines, section 3.3. The dimensions and operating points are hypothetical. Actual finished copper geometry and material properties can differ; none of these entries is a manufacturing guarantee or a safe-current recommendation.

Calculate the cold resistance first

The hypothetical 100 mm long, 2 mm wide, 35 µm thick uniform trace has a 20°C resistance of 0.024 Ω, or 24 mΩ. Its cross-sectional area is 0.002 × 0.000035 = 0.00000007 m², and 1.68 × 10^-8 × 0.100 divided by that area gives the result.

At a constant 5 A, V = I × R gives 0.120 V across this trace. P = I² × R gives 0.600 W of electrical loss. Those are calculated values for this section alone. They exclude its return path and all other series elements.

Apply the temperature correction to the copper

Use the approximate linear relationship R(T) = R20 × [1 + alpha × (T − 20°C)]. For 80°C copper and alpha = 0.00393/°C, the multiplier is 1.2358, so 24 mΩ becomes about 29.66 mΩ.

The reference temperature belongs to the coefficient and resistance data; do not silently substitute a resistance measured at a different temperature. TI presents this correction for the PCB portion of its example system. For materials, alloys or temperatures outside the intended approximation, obtain the appropriate data rather than treating one copper coefficient as universal.

Compare cold and hot voltage drop at the same current

At a fixed 5 A, the hypothetical 80°C trace drops about 0.148 V and dissipates about 0.741 W. Both are approximately 23.6% higher than their 20°C values because the current is held constant.

Condition or change	Trace resistance	Drop at 5 A
Original geometry, 20°C	24.00 mΩ	0.120 V
Original geometry, 80°C	29.66 mΩ	0.148 V
Twice the width, 80°C	14.83 mΩ	0.074 V
Half the length, 80°C	14.83 mΩ	0.074 V
Twice the thickness, 80°C	14.83 mΩ	0.074 V

The last three rows hold conductor temperature at 80°C to isolate geometry. They do not predict the new equilibrium temperature or imply equal fabrication cost, routing space or thermal behavior.

Why conductor temperature is not ambient temperature

The copper can be warmer than the air surrounding the board because it dissipates energy and exchanges heat with components, nearby copper and cooling structures. Entering ambient temperature into the correction is valid only if it represents the conductor closely enough for the intended estimate.

For a board inside a closed enclosure, the air itself can differ from the laboratory room. Measure or model the relevant conductor condition under the intended load. A datasheet’s maximum material temperature, a chosen temperature rise and an observed copper temperature are three different inputs, not interchangeable labels.

Separate current and sense connections on a PCB test coupon. AI-generated illustration, not a measurement or production record.

Include the return path and other series elements

A load sees the voltage available between its supply and return terminals. That depends on the whole current loop, not only the positive trace. Add the relevant return conductor, vias, connectors, protection devices and joints with their own appropriate resistance models.

If the example had an identical return trace at the same 80°C and current, the two copper traces together would drop about 0.297 V. That remains an illustrative copper-only subtotal. Do not apply the copper temperature coefficient automatically to semiconductor switches or contacts, whose behavior requires different data.

Handle neck-downs and changing cross sections

Divide a varying route into sections and add their resistances. A wide pour connected through a narrow segment does not have the resistance of the wide pour over its full length.

Use each segment’s relevant width, thickness and temperature. If current spreads through a large irregular plane, a simple one-dimensional rectangle may be inadequate. The BestPCBs trace neck-down guide discusses the associated local heating risk. Do not average a narrow bottleneck away by substituting the route’s widest width.

Separate electrical loss from the thermal solution

Calculating I²R tells you heat generation at the stated current and resistance. It does not tell you the final temperature without the thermal path. Temperature changes resistance, and resistance changes heating, so the electrical and thermal calculations are coupled.

A useful design process starts with an estimated temperature, evaluates loss and then checks the resulting temperature using an appropriate thermal model or measurement. Iterate as necessary. Do not use the example’s assumed 80°C as evidence that this trace will settle there, or that its surroundings can safely tolerate it.

Check how the load responds to falling voltage

The constant-current example does not describe every load. A regulated downstream converter serving approximately constant power can draw more input current as its input voltage falls, while a simple resistive load behaves differently.

Use the real load characteristic and input-voltage limits. Recalculate the operating point when route loss changes the load current materially. Startup, load steps and undervoltage behavior may also govern the design. The right question is not only “what is the trace resistance?” but “what current and voltage does this complete system reach under the required conditions?”

Verify small resistance without measuring the test leads

Use an appropriate low-resistance measurement method and defined endpoints. A four-wire arrangement separates current injection from voltage sensing, reducing the influence of lead resistance on the sensed voltage. It does not remove errors caused by incorrect probe locations or an unintended parallel path.

Measure an isolated route or account for the rest of the circuit. Record current, polarity, settling and temperature; test current itself can warm the coupon. Follow instrument limits and safe test procedures. A continuity beep is not a quantitative milliohm measurement or evidence of adequate voltage at the operating load.

Release the power route against a voltage budget

Allocate the allowed distribution drop from source to load, then verify the copper and other series elements under the relevant operating conditions. Check both the cold model and hot evidence, including the return path.

Preserve the finished copper requirement, geometry, current waveform, measurement endpoints and thermal conditions. Choose wider, shorter or thicker routing on that basis, not from copper weight alone. For a Best Technology review, send those inputs and the required load voltage to sales@bestpcbs.com. Manufacturing review does not replace complete-system thermal and electrical validation.

FAQ

Is trace resistance the same as trace impedance?

No. DC resistance describes resistive opposition in the stated path. Transmission-line impedance also depends on geometry, reference conductors and frequency-dependent behavior. A 50-ohm RF trace is not normally a 50-ohm DC resistor. Use the electrical model that matches the measurement and signal or power problem being investigated.

Can I convert a resistance measured at 25°C using the 20°C formula?

Do not treat the 25°C reading as R20. First relate it to the stated reference using the same applicable approximation, or use a coefficient and reference formulation appropriate to that measurement. Record the actual conductor temperature so the comparison does not hide a systematic reference-temperature error.

Does doubling copper weight guarantee half the measured route resistance?

Not for the entire route. The simple model halves resistance only when the actual trace thickness doubles and other relevant inputs remain equal. Vias, contacts, neck-downs, temperature and finished copper variation can prevent the complete path from following that ratio. Compare the same endpoints and operating conditions.

Can I use voltage drop to infer conductor temperature?

Only with a sufficiently characterized path, current measurement and resistance-versus-temperature relationship. Contacts, parallel current paths and nonuniform temperature can distort the inference. For a complex route, resistance represents a combined response rather than one guaranteed local hot-spot temperature. Validate the method before using it for protection decisions.

Why does my multimeter disagree with the geometric calculation?

Check units, actual copper thickness, etched shape, probe endpoints, temperature and parallel connections first. Lead and contact resistance can dominate a small trace value in a two-wire measurement. A discrepancy is not automatic evidence of bad copper; isolate the measured object before assigning a manufacturing cause.

Does low DC voltage drop prove that a power path handles a fast load step?

No. Fast behavior also depends on inductance, capacitance, regulator response and distribution geometry. A route can have low DC resistance yet show a transient voltage excursion. Check the time-domain requirement separately and do not use this uniform DC trace calculation as a power-integrity qualification.

Can I use a standard copper coefficient for a copper-alloy busbar?

Not without verifying the alloy’s properties. Its resistivity and temperature behavior can differ from the pure-copper approximation used here, and joints add their own behavior. Use the material supplier’s relevant data and the complete connection geometry rather than transferring one coefficient based only on the word copper.

Is adding solder a predictable substitute for a wider copper route?

Not by itself. Solder geometry and material properties differ from the finished copper trace, and the resulting cross section can be uneven. A controlled design change requires characterized electrical and manufacturing evidence. Do not assume an informal solder layer delivers a specified resistance, temperature rise or repeatable current capability.

Tags: copper trace, heavy copper pcb, Power Distribution, Voltage Drop
Posted in bestpcb | No Comments »

Microvia Aspect Ratio Guide: Which Depth and Diameter?

November 7th, 2026

Microvia aspect ratio compares a blind microvia’s depth with a defined hole diameter. The calculation is simple, but the dimension definitions are often not. A tapered opening, an entry diameter and a target-side diameter can give different ratios, while a notation such as 1:0.8 may place diameter first rather than depth first.

Fine HDI pad array with small via openings. AI-generated illustration, not a measurement or production record.

This guide shows how to read the convention, calculate a comparable ratio and review a proposed stackup change. It does not present one ratio as a universal manufacturing or reliability guarantee.

What does a microvia aspect ratio describe?

Here, aspect ratio A means depth h divided by reference diameter d: A = h/d. A depth of 60 µm and a diameter of 100 µm give 0.60, often written 0.60:1 when depth is listed first.

The ratio describes a geometry, not every condition needed to fabricate it. The opening shape, bottom condition, material and metallization process still matter. Always state the convention beside the value instead of relying on the word aspect ratio alone.

Which dimensions must be defined?

Use a cross-sectional definition agreed with the fabricator. Nominal CAD dimensions, laser-process dimensions and finished measurements are not automatically identical.

Dimension	Unit	Definition to confirm
Depth h	µm	Start surface to target
Entry diameter	µm	At specified process stage
Target-side diameter	µm	At bottom of tapered opening
Dielectric thickness	µm	Actual laminated construction
Outer copper	µm	Whether included in depth
Ratio A	None	Named depth and diameter

Keep units consistent. Dividing a depth in micrometers by a diameter in millimeters without conversion creates a thousandfold error, even if the resulting number is formatted neatly in a report.

Read the order of the ratio before comparing it

Some published guides write diameter first. For example, Würth Elektronik’s HDI design guide expresses its microvia example as diameter/depth = 1:0.8. Expressed as depth divided by diameter, that relationship is 0.8. Check the supplier’s current design rules separately before applying the published example to an order.

This is a supplier-specific published example, not Best Technology’s capability statement or a universal limit. It shows why comparing “0.8:1” and “1:0.8” without reading the axis order can reverse the intended relationship.

A worked example with a tapered hole

Assume a hypothetical depth of 60 µm, an entry diameter of 100 µm and a target-side diameter of 70 µm. The entry-based ratio is 60/100 = 0.60. The bottom-based ratio is 60/70, about 0.86.

Both calculations describe the same hypothetical hole using different reference diameters. You cannot call one supplier more capable by comparing its entry-based number with another supplier’s bottom-based number. First establish the common definition.

Why total board thickness is the wrong depth

A blind microvia connects a limited layer span, so its depth is not normally the complete multilayer board thickness. A thicker central core does not necessarily change an outer microvia’s depth, while a thicker outer buildup dielectric can change it directly.

Identify the start and target layers on the stackup. Read the relevant local construction, including the agreed copper reference, rather than dividing total board thickness by the small via diameter as if it were a through hole.

Compare three geometry changes

If a proposed geometry is outside the agreed process envelope, compare changes in the complete layout and stackup.

Option	Geometric effect	Other checks
Increase diameter	Reduces h/d	Pad size and escape routing
Reduce buildup depth	Reduces h/d	Impedance and dielectric requirements
Change layer connection	Changes required span	Routing and lamination sequence
Use another via structure	Different fabrication problem	Space, cost and qualification

A smaller numerical ratio is not automatically a better overall PCB design. The revised construction still has to satisfy electrical, mechanical and manufacturing requirements.

Mounted PCB section specimen on a metallurgical microscope stage. AI-generated illustration, not a measurement or production record.

Why a stackup change can invalidate the old check

A material substitution or thickness change can alter the actual distance to the target layer. Suppose the same hypothetical 100 µm reference diameter remains, but the agreed depth grows from 60 to 80 µm. The ratio changes from 0.60 to 0.80.

Do not assume the CAD via definition automatically records that construction change. Recalculate against the proposed laminated stackup and ask the supplier to confirm the referenced depth rather than reusing an approval from a thinner buildup.

Keep target-pad capture separate from aspect ratio

Aspect ratio does not prove that the laser opening lands on enough target copper. Registration, target-pad dimensions and material movement affect capture. A via can satisfy a ratio requirement and still have inadequate landing geometry.

The BestPCBs microvia target-pad guide covers that separate check. Review both the depth/diameter definition and the target capture evidence when evaluating a dense escape pattern.

Why cleaning and plating still matter

A geometry within the agreed envelope does not establish the condition of the blind bottom or the deposited copper. Residue, interface preparation and plating quality can affect the finished connection. Those conditions need process and inspection evidence, not an arithmetic ratio alone.

An IPC-hosted microvia reliability presentation discusses several interacting failure mechanisms. Treat it as technical background, not a substitute for the applicable current procurement requirements or a universal pass/fail ratio.

Check stacked and staggered structures separately

For multiple buildup levels, evaluate each microvia and the full interconnect structure. A stack is not qualified simply because every individual hole has an acceptable nominal h/d. Interfaces between levels and the fabrication sequence introduce additional review needs.

Do not describe a tall stack as one ordinary microvia unless the construction and calculation explicitly define it that way. Keep the individual layer spans and the intended reliability evidence visible in the stackup review.

Request measurements that match the drawing

A cross section can show the measured depth, taper, bottom and copper condition at the section location. It does not prove every via across every panel has the same geometry. State the sampling and acceptance requirements along with the dimension definitions.

Ask the report to identify the board revision, stackup, specimen location and measurement stage. If the section is offset from the intended hole center, its apparent opening may not represent the diameter you meant to evaluate.

Release the construction, not just the ratio

Approve the actual layer span, material construction, dimension references, via and pad geometry, and required inspection or reliability evidence together. Keep a change trigger for revised dielectric thickness, laser geometry or interconnect structure.

For a Best Technology HDI review, send the stackup, start and target layers, intended microvia dimensions and product requirements to sales@bestpcbs.com. Ask which diameter and depth the fabricator uses before interpreting a quoted aspect-ratio capability.

FAQ

Is a microvia ratio of 1:0.8 the same as 0.8:1?

It can describe the same geometry if the first notation lists diameter before depth and the second lists depth before diameter. It can also mean something different if the conventions are not stated. Read the definition and convert both to the same h/d expression before comparing.

Should I use the entry diameter or the bottom diameter?

Use the diameter defined by the applicable design rule or supplier agreement. A tapered hole has more than one meaningful diameter, and each produces a different ratio. Do not switch definitions to make a borderline geometry appear compliant; clarify the reference and keep the measured evidence consistent.

Does a ratio below one guarantee reliable plating?

No. Geometry is one input to a fabrication process. Bottom preparation, metallization, copper deposition, interfaces and the required qualification evidence also matter. Check the supplier’s actual process envelope and the applicable inspection requirements rather than treating a numerical threshold as a complete reliability test.

Can I use the full board thickness in the microvia calculation?

Not for an ordinary blind microvia spanning only part of the stack. Use the depth between the stated start and target references. Total board thickness is relevant to other structures, such as a through hole, but it can badly misrepresent a shallow outer buildup connection.

Does increasing the hole diameter solve every aspect-ratio problem?

No. It may reduce h/d, but it also uses more pad and routing area and can affect the escape design. Check the target capture, spacing and finished interconnect requirements. Sometimes a thinner buildup or a different layer connection is a better option, subject to the full stackup review.

Can a material change affect the ratio without changing my drill file?

Yes. A change in laminated buildup thickness can change the distance to the target while the nominal opening data remain the same. Recalculate using the proposed actual construction and confirm whether copper is included in the stated depth. Keep the revised approval with the material change.

Does a microsection establish every hole’s exact diameter?

No. It measures a particular section through a particular specimen, and the cutting plane and preparation affect what is visible. Use the agreed sampling plan and interpret the apparent dimensions against the measurement method. A report should identify the location and construction instead of presenting one image as universal proof.

Can I compare different fabricators using only their aspect-ratio numbers?

Not safely. First align the ratio convention, reference diameter, depth definition, material and via structure. Then compare the relevant fabrication and verification scope. Two similar headline numbers can describe different holes or different evidence, so a dimensioned cross section and stackup are more useful comparison inputs.

Tags: Aspect Ratio, HDI PCB, Microvia, pcb stackup
Posted in bestpcb | No Comments »

PCB Copper Skin Depth Guide: Does Thicker Copper Help?

November 7th, 2026

Copper skin depth describes how far alternating current penetrates into a conductor at a particular frequency. At high frequency, current density falls with depth instead of remaining uniform through the copper. This means thicker PCB copper can reduce DC resistance without producing the same proportional reduction in RF conductor loss.

Copper foil beside the edge of a copper-clad laminate. AI-generated illustration, not a measurement or production record.

Use this guide when comparing copper thickness or foil for an RF line. It explains the calculation, gives a frequency table and separates skin depth from the other effects that determine the loss of the finished transmission line.

What does one skin depth mean?

In the ideal good-conductor model, current-density amplitude falls to 1/e, about 37% of its surface value, at one skin depth. Current does not stop at a sharp boundary. The field and current distribution continue to decay into the metal.

Skin depth is therefore not a layer of copper that can be peeled away or a fixed property independent of frequency. It is a calculated length for stated material properties and excitation conditions.

Which inputs define the copper calculation?

The model uses frequency, conductivity and permeability. For the following teaching calculations, assume smooth bulk copper with conductivity 5.8 × 10^7 S/m, relative permeability approximately 1, and μ0 approximately 4π × 10^-7 H/m. These are illustrative near-room-temperature model inputs, not guaranteed foil specifications.

Here f is frequency in hertz (Hz), σ is conductivity in siemens per meter (S/m), and μ is permeability in henries per meter (H/m). The calculated skin depth δ and conductor thickness t must use the same length unit when comparing t/δ.

Use δ = √[1 ÷ (π f μ σ)]. Conductivity can change with temperature and material condition. If the application depends on a supplier’s actual foil properties, use those values and retain the model assumptions.

Calculate a frequency table before choosing thickness

For the stated smooth-copper assumptions, the calculated values are approximately:

Frequency	Skin depth	Interpretation
1 MHz	66.1 µm	Can exceed thin foil thickness
10 MHz	20.9 µm	Comparable with some PCB foil
100 MHz	6.61 µm	Smaller than 35 µm copper
1 GHz	2.09 µm	Surface effects become prominent
10 GHz	0.661 µm	Surface texture deserves review

These are calculated penetration depths, not insertion-loss predictions. Rogers’ copper-foil technical article provides a corresponding high-frequency skin-depth table and discusses foil surface effects.

Why frequency changes the result by a square-root law

With conductivity and permeability held constant, skin depth is proportional to 1/√f. Raising frequency by a factor of 100 reduces the calculated depth by a factor of 10. Moving from 100 MHz to 10 GHz therefore changes 6.61 µm to approximately 0.661 µm in the example.

Do not extrapolate a linear relationship such as “ten times the frequency means one tenth the depth.” Check the units before calculating: 1 GHz is 10^9 Hz, not 10^6 Hz.

Compare DC resistance with high-frequency conductor loss

DC and high-frequency current distribution lead to different thickness trade-offs.

Question	DC or low frequency	High-frequency line
Used cross-section	More nearly the full thickness	Nonuniform distribution
Extra thickness	Can reduce resistance strongly	Benefit depends on t/δ and geometry
Surface texture	Not a skin-depth issue	Can affect conductor loss
Verification	Resistance and thermal checks	Line model and loss measurement

The comparison does not mean copper thickness becomes irrelevant at RF. It means the DC cross-sectional-area argument cannot be used alone to predict RF improvement.

A worked comparison of 35 and 70 µm copper

At 1 GHz, the example skin depth is 2.09 µm. Copper thicknesses of 35 and 70 µm are roughly 17 and 33 skin depths. Both are well beyond a single penetration depth, so doubling thickness does not justify claiming that conductor loss will be halved.

A real line also changes when thicker copper alters its cross-section. If width and dielectric spacing stay unchanged, impedance may change. Compare the complete line geometry rather than treating copper weight as an isolated loss-control knob.

Microstrip PCB coupon with coaxial connectors at both ends. AI-generated illustration, not a measurement or production record.

Why the current is not spread equally over every surface

The signal and return geometry determines the electromagnetic fields around a PCB trace. Current can concentrate on the face toward a reference plane and near edges; the exact distribution depends on the structure. Do not assume equal current on the top, bottom and sidewalls.

Keysight’s Momentum documentation distinguishes conductor-loss models with different surface-current assumptions. Choose a model appropriate to the line rather than dividing the total copper perimeter into equal current shares by hand.

What copper roughness changes

When texture dimensions become relevant to the field penetration scale, a smooth-conductor model may underpredict loss. But a roughness statistic is not itself a universal loss multiplier. The foil face, treatment, measurement and roughness model must correspond to the real copper-to-dielectric interface.

Do not compare an Rz number directly with an Rq-based model input or a fitted surface parameter without checking the definitions. Keep the foil specification with the stackup and use representative line data when the loss budget is tight.

Why surface finish needs its own model

The exposed copper may carry another conductive layer or finish, while buried copper has a different interface. A plated layer can have different conductivity and magnetic behavior from bulk copper. The effect depends on layer thickness, frequency and current distribution.

Do not apply the bulk-copper table unchanged to every finish stack or assume that all the RF current flows only in a named outermost layer. Use a multilayer conductor model or applicable measured evidence for the actual construction.

Do not confuse skin depth with total transmission loss

A line loses and reflects energy through more than conductor resistance. Dielectric loss, launches, vias, mismatch and radiation can also contribute. A better conductor surface will not necessarily remove a loss dominated by another mechanism.

Keep the observation ports and fixtures consistent when comparing coupons. The BestPCBs fixture-de-embedding guide concerns separating fixture effects from the line under test; it is a measurement step, not a skin-depth correction.

When thicker copper still makes sense

Thicker copper can still be useful for DC current, heat spreading or another mechanical and electrical requirement even when the RF conductor-loss benefit is limited. Balance those needs against the trace geometry, fabrication process and impedance target.

For a mixed power-and-RF board, evaluate the power path and RF path as separate design tasks. A copper change that helps the supply path can require a revised RF line width and a new stackup review.

Verify the proposed foil and geometry together

Compare candidate lines with the same electrical target, operating band and reference conditions. Include actual copper thickness, foil surface, finish and dielectric construction. If the candidates use different dimensions to maintain impedance, preserve those dimensions in the comparison.

For a Best Technology RF stackup review, send the frequency band, impedance and loss targets, proposed foil and finished copper geometry to sales@bestpcbs.com. Use the skin-depth calculation to ask better questions, then verify the complete line rather than treating the table as a production result.

FAQ

Does current flow only within one skin depth?

No. In the ideal model, current-density amplitude decays continuously into the conductor and is about 37% of its surface value at one skin depth. There is no hard cutoff. A one-depth illustration can explain concentration near the surface but should not be mistaken for a boundary containing all current.

Can I use the same table for copper at a different temperature?

Only as an approximation if the change is acceptable for the task. Conductivity changes with temperature, which changes the calculated depth and conductor resistance. Use material properties appropriate to the operating condition when a quantitative loss or thermal decision depends on the result.

Does doubling copper thickness halve RF loss?

Not generally. That simple scaling resembles a DC area argument, whereas high-frequency current is distributed nonuniformly. When thickness is already many skin depths, additional thickness does not produce the same proportional gain. Include the changed trace geometry and impedance when comparing the complete line.

Is skin depth the same as dielectric penetration?

No. Skin depth here describes the decay of current and fields into a conductive metal. Transmission-line fields also occupy the surrounding dielectric, but that is a different part of the model. Keep conductor properties separate from dielectric constant and loss tangent when calculating the PCB line.

Can I apply the copper formula to a nickel-containing finish?

Not by keeping the copper properties unchanged. A finish introduces another material and layer thickness, and its electrical or magnetic behavior may differ. Use the properties and structure of the actual stack in a suitable model rather than labeling the whole conductive path as bulk copper.

Does a thinner skin depth always mean a board will fail?

No. It identifies a frequency-dependent conductor behavior, not a pass/fail limit. The design passes or fails against the applicable impedance, loss, thermal and link requirements. A line can operate successfully with a small skin depth if its complete construction meets those requirements.

Can a DC resistance measurement validate my RF loss model?

It can verify a low-frequency resistance input, but it does not validate the surface-current distribution, roughness correction or high-frequency fixture. Use a suitable line measurement over the relevant band as well. Keep DC resistance evidence and RF insertion-loss evidence as separate checks.

Should I choose the smoothest available foil for every PCB?

Not automatically. Surface profile, adhesion treatment, dielectric compatibility, cost and the actual loss budget all matter. A less demanding line may not need a premium foil. Select the construction against the design requirements and confirm the supplier’s exact foil and process rather than relying on a generic smoothness label.

Tags: Conductor Loss, Copper Foil, RF PCB, Skin Effect
Posted in bestpcb | No Comments »

Cookie	Duration	Description
cookielawinfo-checkbox-analytics	11 months	This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Analytics".
cookielawinfo-checkbox-functional	11 months	The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional".
cookielawinfo-checkbox-necessary	11 months	This cookie is set by GDPR Cookie Consent plugin. The cookies is used to store the user consent for the cookies in the category "Necessary".
cookielawinfo-checkbox-others	11 months	This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Other.
cookielawinfo-checkbox-performance	11 months	This cookie is set by GDPR Cookie Consent plugin. The cookie is used to store the user consent for the cookies in the category "Performance".
viewed_cookie_policy	11 months	The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. It does not store any personal data.