Pyralux

DuPont Pyralux LF8515 is a flex-circuit material callout that needs a complete copper specification. For LF8515R, DuPont lists ½ oz/ft² rolled-annealed copper on each side, a 1 mil Kapton® polyimide core and 1 mil of modified acrylic adhesive on each face of the film. The 1 mil film entry alone does not give the distance between the copper layers. That distinction matters when a replacement core has to fit an existing connector or preserve a controlled-impedance trace.

Where Is LF8515R Used in a Flex PCB?

LF8515R supplies the two copper foils that a fabricator patterns into circuits. A designer can use both faces for routing, or use one face for signal traces and the other for a return path. The inner film insulates the two conductors. A connection between faces requires a designed interconnect, such as a plated hole.

In a rigid-flex circuit, the flex core can run through a rigid component area and continue into a thin connecting tail. The FR-4 laminate in the rigid area adds support there. A drawing should identify where that rigid buildup ends and where the exposed flex begins. The product photographs show examples of these features; the material grade of the pictured circuits is unspecified.

Which DuPont Datasheet Lists LF8515R?

Use Table 2 of DuPont publication H-73244 (September 2002) for the exact LF8515R row. Its heading identifies double-sided copper-clad products. The copper column gives weight per unit area, while the adhesive and Kapton columns give thickness. Reading across the same row avoids accidentally using a single-sided construction from Table 1.

DuPont’s March 2020 LF copper-clad laminate datasheet, EI-10117 explains foil suffixes and lists standard offerings. LF8515R does not appear in those standard tables. The older row establishes the documented construction. For a new order, obtain current confirmation of the complete code, available sheet size and lot documentation before committing the build.

LF8515R Material Specifications

LF8515R feature	Nominal value in H-73244	How to use it
Cladding	Double-sided	Assign a copper artwork layer to each face.
Copper on each face	½ oz/ft² (153 g/m²), rolled-annealed	Specify as starting foil. State any finished copper requirement separately.
Modified acrylic adhesive	1 mil (25 µm) on each face	Include both bond lines when estimating conductor separation.
Kapton polyimide film	1 mil (25 µm)	Count the center film once.
IPC entry in the historical row	Certified to IPC-4204/1 at publication	Ask for the current material lot’s certificate if the order requires it.

How Are the Five Layers Arranged?

Read the unetched core from the top down: copper, adhesive, Kapton film, adhesive, copper. Both adhesive layers are inside the laminate. After etching, the remaining copper traces still rest on their respective bond lines. A drawing that shows copper directly against the film on either face describes a different construction.

How Thick Is the Finished Flex Circuit?

Consider a nominal estimate before etching. The dielectric between foils is about 3 mil: 1 mil of adhesive on each side plus 1 mil of polyimide. Using the datasheet’s rounded metric values gives about 75 µm. With nominal 18 µm half-ounce copper on each face, the example bare core totals about 111 µm. These are layer sums; thickness tolerances and measurements on a supplied lot are separate matters.

For a connector tail, specify the finished thickness and tolerance where the contacts engage. A reading over coverlay, a reading on an exposed contact and a reading over a stiffener can differ on the same part. Mark the measurement zone on the drawing and identify any plating, coverlay and stiffener included there.

Does the Flex Stackup Need a Separate Coverlay?

Etching leaves copper on the outside faces of the core. If traces need insulation or environmental protection, specify the coverlay separately and draw its openings around contacts, pads and test points. The adhesive inside LF8515R cannot protect exposed traces. Conversely, an LF coverlay code in a bill of materials does not identify the copper-clad core.

At a connector, an opening that is too short can cover part of the mating contact. Show the opening edge relative to the contact area and dimension the stiffener on its own layer. That gives the fabricator two independently checkable features.

What Determines the Bend Radius?

A one-time installation fold and a tail that moves on every operating cycle pose different design problems. For an installation bend, show the installed radius and whether the bend will be reopened during service. For repeated motion, also specify the travel, direction and target number of cycles so the finished construction can be evaluated under those conditions.

The R suffix identifies rolled-annealed foil. It does not establish a cycle rating. A bend that starts at the stiffener edge or passes through a plated hole concentrates strain differently from a bend through a uniform tail. Mark the bend zone relative to these features on the mechanical drawing.

Which Dielectric Data Can You Use for Impedance?

For an impedance-controlled PCB, start with the signal layer, its reference conductor and the dielectric between them. A trace over the opposite foil sees the polyimide and both acrylic layers. Entering only the 1 mil film as the separation would model a different circuit. Copper coverage on the reference face and the coverlay above the trace also matter.

EI-10117 Table 3 identifies LF9110R as its test product. Its dielectric constant and loss values at the listed frequencies are typical for that specimen. For an LF8515R design, request construction-specific modeling inputs at the operating frequency, then agree on trace geometry, impedance tolerance and coupon verification with the fabricator.

LF8515R vs LF8510R

Historical construction	LF8515R · Table 2	LF8510R · Table 1
Copper-clad faces	Two	One
Starting copper per clad face	½ oz/ft² RA	½ oz/ft² RA
Kapton film / adhesive per clad face	1 mil / 1 mil	1 mil / 1 mil
Consequence for artwork	Copper available for two patterned faces	No reverse-side foil for a second circuit or reference plane

A drawing with a signal on the front and a continuous return on the back cannot use LF8510R unchanged. The shared film thickness and copper weight would pass a superficial comparison, yet the return conductor would be missing. Check the face count before comparing the finer details of an alternative.

What Qualifies as an LF8515R Equivalent?

Ask the supplier for a cross-section and data sheet for the proposed code. Compare both foil types and weights, both bond lines, center film, dielectric thickness and the tolerance that matters to the assembly. A thinner adhesive can change trace-to-plane spacing even if foil weight and film thickness match. An adhesiveless laminate changes the dielectric construction even when its overall thickness looks close.

Identify what must be rechecked for the particular design. A connector interface needs a finished-tail thickness check. An impedance-controlled pair needs an updated stackup model. A moving tail may need a bend test on representative circuits. Obtain the design owner’s approval for the named substitution before production.

How Should LF8515R Be Specified on a Drawing?

A usable example for a legacy DuPont Pyralux LF8515 drawing is: “Flex core: Pyralux LF8515R, double-sided, ½ oz/ft² RA starting copper each face, 1 mil Kapton film, 1 mil acrylic adhesive each face. Any material substitution requires written approval.” Add the finished copper and thickness requirements where the design depends on them. The example is a material note, not a finished-board acceptance specification.

Send with the PCB drawing	What it resolves
Layer order and copper artwork for both faces	Identifies which nets or return planes use the reverse foil.
Coverlay openings, stiffener outline and connector tolerance	Defines thickness and exposed copper in the mating area.
Bend location, radius and service duty	Distinguishes installation forming from repeated motion.
Approved material revision and substitution restrictions	Defines whether an alternative can be quoted for engineering review.

At EBest Circuit (Best Technology), we can review the flex and rigid regions together against your stackup. Send the fabrication drawing, copper artwork, quantity and material approval requirements to sales@bestpcbs.com so we can confirm the construction and check availability for your order.

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