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Can I Design Via Holes in Thick Film Ceramic Boards?

Tuesday, April 18th, 2023

May some engineers or designers who be interested in thick film ceramic circuit are curious about can thick film ceramic boards design with via holes like FR4 PCB? Herein, we will explore the feasibility of using thick film ceramic boards for via holes, including the materials and processes involved, as well as the advantages of this approach.

What is thick film ceramic board?

The “Thick Film” refers to the thickness of conductor layer on a Ceramic PCB. Normally the thickness will be at least 10um, around 10~13um, which is thicker than spurting technology in Thin Film Ceramic PCB. And of course thickness is less than DCB Ceramic board or FR4 board.

Thick film ceramic circuit enables to put resistor, electric capacitor, conductor, semi-conductor, and interchangeable conductor on ceramic board, after manufacturing steps of printing and high temperature sintering. The more important thing is by using thick film technology, we can make all the resistors with the same value, or different value for different resistor on the same board.

Materials and processes for via holes

In general, thick film ceramic circuit is not suitable for designing via holes. Because the characteristics of thick film ceramic board mainly depends on the insulation properties of its ceramic substrate, rather than conductive properties. The conductivity of thick film ceramic plate is not good than Metal Core PCB, or even we can say it has a very poor conductivity, usually can’t meet the requirements of the via hole.

But, designing via holes in thick film ceramics is available in Best Technology. Generally speaking, the fabrication of via holes in thick film ceramic boards typically involves several key materials and processes.

From the designer’s perspective, a conductive material is used to create a continuous conductive path from one side of the ceramic board to the other. Common conductive materials include gold paste, silver paste, and copper paste. These materials are usually screen printed onto the ceramic board in the desired pattern, and then fired at high temperatures to achieve sintering and form a conductive layer.

Once the conductive layer is formed, the via holes are created by drilling or punching small holes through the ceramic board at the desired locations. These holes are then filled with a conductive material, such as silver paste or copper paste, to establish electrical connections between the different layers of the circuit.

Finally, the via holes are fired again at high temperatures to achieve sintering and ensure good adhesion and electrical performance.

Advantages of Via Holes in Thick Film Ceramic Boards

These via holes offer several advantages in the design and fabrication of thick film ceramic boards, including as following:

  • Electrical connectivity

Via holes provide electrical connectivity between different layers of a thick film ceramic board. They allow for the interconnection of different circuitry or conductive layers, enabling the flow of electrical signals or power between different parts of the board. This allows for complex and multi-layered circuit designs, which can be highly beneficial in applications that require intricate circuitry or high-density interconnects.

  • Space-saving

Via holes can provide a means of vertical interconnection, allowing for more efficient use of board real estate. Instead of routing traces or conductors on the surface of the board, which can take up valuable space, via holes can be used to route connections through the board, freeing up surface area for other components or functions. This is especially advantageous in compact or miniaturized electronic devices where space is limited.

  • Thermal management

Via holes can aid in thermal management in thick film ceramics. They can be used to transfer heat from one layer of the board to another, helping to dissipate heat generated by components or circuits. This can be particularly important in high-power or high-heat applications, where efficient thermal management is crucial for preventing overheating and ensuring reliable performance.

  • Mechanical stability

Via holes provide additional support and reinforcement to the board, reducing the risk of warping, bending, or cracking. Via holes can also help improve the overall mechanical integrity of the board by reducing stress concentration points and enhancing its structural rigidity.

  • Design flexibility

Via holes offer design flexibility in thick film ceramic boards. They can be designed and placed according to the specific requirements of the circuit or system, allowing for customized and optimized designs. Via holes can be used to route traces, create vias for component mounting, or provide grounding or shielding, among other functionalities. This flexibility in design allows for more efficient and effective circuit layouts, which can lead to improved performance and reliability.

As previously mentioned, designing via holes in thick film ceramic boards offers various benefits. However, when it comes to choosing the appropriate paste for via holes, silver paste is often recommended to our customers. But why is that? Can I use gold or copper? In our upcoming article, we will delve into the reasons behind this recommendation and provide you with valuable insights. Stay tuned to uncover the answers!

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“TEN Q & A” about Ceramic Printed Circuit Board

Monday, February 27th, 2023

Q1: What do the abbreviations DBC and AMB stand for?

A: DBC means “Direct Bond Copper” while full name of AMB is “Active Metal Brazed”. Both abbreviations refer to bonding technology of attaching a relatively thick copper (generally more than 0.2mm) on the ceramic substrates. These two technologies can be used to fabricate metalized ceramic substrates.

Q2: What is the mainly difference between DBC and AMB?

A: The mainly difference is AMB need to braze the copper to a ceramic board by active metal while DBC can directly connect the copper and substrate without any additional materials.

Q3: Which kind of ceramics are suitable for DBC and AMB?

A: DBC technology is suitable for oxide ceramics such as Al2O3 and ZTA. Non-oxide ceramics must be oxidized before they can be bonded to copper by DBC technology. ALN can be made into DBC or AMB ceramics, but Si3N4 only can be used as AMB substrates.

Q4: What is the function of metalized ceramic PCB?

The metallized ceramic substrate needs to carrier and interconnect multiple power semiconductor devices. The resulting electronic components are called power modules or multi-chip packages, most commonly LED packages or semiconductor packages. 

Q5: Does AMB can be used with oxide ceramics?

A: Yes, but the effective of DBC technology is better and the cost is relatively lower.

Q6: What is the most important performance need to be considered when design a new ceramic PCB?

A: It depends on the end application of product will be used in. Ceramics are chemically inert substances that are resistant to corrosion, moisture, and high temperatures, making them preferable to organic dielectrics that degrade in corrosive environments. Electrical, thermal and mechanical properties are equally important in the design of a new substrate. Dielectric strength is an important factor to meet the isolation requirements, which should be set according to the standards, specifications and regulations of the target application. Low thermal conductivity is not conducive to the heat transfer between the chip and the surrounding environment. The bending strength and fracture toughness play an important role in prolonging the service life of the substrate under thermal-mechanical stress.

Q7: How to choose a suitable substrate?

A: First, the heat dissipation of power semiconductor devices should be understood. Then, based on the chip and the ambient temperature, the required substrate thermal resistance is calculated. However, the combination of copper and ceramic may not always achieve the desired thermal resistance.  For one thing, the isolation voltage determines the minimum thickness of the ceramic. On the other hand, the thickness ratio of copper to ceramic has a great effect on the reliability. Finally, the set of applicable standards will be very limited.

Q8: Are DBC and AMB substrates suitable for high voltage applications?

A: The DBC substrate is ideal for applications with operating voltages up to 1.7 kV.  For higher operating voltages, a thicker ceramic layer is required to meet the relevant isolation requirements.  Silicon nitride (ALN) is often used because its high thermal conductivity offsets the increased thickness. In addition, resistance to partial discharge is particularly important in this application. Thus, AMB is superior to DBC techniques for this purpose unless the interfacial gap between copper and ceramics can be eliminated.

Q9: Are DBC and AMB substrates copper plated only on both sides?

A: No, both of two technologies can plate copper only on one side. But this is not a standard combination of materials, however, because the resulting flatness of the substrate is critical in multiple applications.

Q10: What are the shapes of substrates?

A: The rectangle is the cheapest and most common shape to produce. Other shapes are also available, but may incur additional production costs.

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What is the DBC Ceramic Copper Oxidation Technology

Monday, February 20th, 2023

DBC (Direct Bond Copper) ceramic PCB also known as DCB ceramic, which is widely used in various type of high-power semiconductor, especially in IGBT package material by means of its excellent electricity and thermal conductivity of copper and the advantages of high mechanical strength and low dielectric loss of ceramics. DBC technology uses the oxygen-containing eutectic solution of copper to directly apply it to the ceramic. The key factor in the preparation process is the introduction of oxygen element, so the copper foil needs to be pre-oxidized in advance. Do you want to know what is the copper foil oxidation technology during the DBC ceramics manufacturing? Hereinbelow, we will introduce the oxidation process for you.

Oxidation technology of copper foil

Copper oxidation is divided into Wet Air Oxidation (including soaking oxidation and spraying oxidation) and Dry Oxidation.  Both oxidation methods can form CuO or Cu2O on the surface of copper foil.

  • Wet Air Oxidation (WAO)

i. Soaking oxidation

First, the copper is pickled with 3% dilute sulfuric acid, and then washed by the spray washing machine after overflow. Next, sent the copper into the mixed solution of potassium permanganate and copper sulfate (the concentration of potassium permanganate is about 31.6mg/L and the copper sulfate is about 95.4mg/L) for soaking and oxidation.  The oxidized copper is then washed with water and three-stage countercurrent washing, and then slowly pulled for dehydration and drying (the temperature is about 100℃) to complete soaking and oxidation.

ii. Spraying oxidation

Spraying oxidation is a kind of WAO, only the oxidation method become spraying. Spray oxidation is to spray copper with mixed solution of manganese nitrate and copper nitrate (concentration of about 3%) after pickling and washing.  The sprayed copper is dried directly in the tunnel kiln (the temperature is about 200℃).  In the drying process of tunnel kiln, the manganese nitrate and copper nitrate sprayed on the copper sheet are decomposed into copper oxide and manganese oxide.  The ratio of soaking oxidation and spraying oxidation treatment of copper sheet is about 5:5.

  • Dry Oxidation

Dry oxidation is very easy to process, put the copper into oxidation oven firstly, then heating up to 600~800oC for oxidizing around 30mins and then subjected to air cooling annealing.

Wet Air Oxidation VS Dry Oxidation

At present, the existing industry is widely used to finish the high-temperature annealing oxidation of copper then sintering with ceramic substrate, that is dry oxidation.  But this high temperature annealing, oxidation in one way has some drawbacks as following:

  1. Uneven oxidation. It will directly cause sintering defects during sintering, and the peeling strength will change greatly.
  2. Leaving conveyor belt marks.  Because the high temperature and oxidation process is transported by the conveyor belt, the existence of the conveyor belt mesh will affect the temperature distribution of the entire copper is not uniform, leaving marks/traces of the conveyor belt.  The result of sintering is to leave the corresponding trace on the bonding surface of CuAl2O3.
  3. High temperature annealing and oxidation will accompany the grain growth of copper. In the subsequent sintering process, the grain will continue to grow, which brings adverse effects on the mechanical properties and surface treatment of copper.  The copper surface grain produced by wet oxidation is fine, which is conducive to improving the mechanical properties of copper and eliminating the traces of conveyor belt. The main difference between wet oxidation and dry oxidation is shown in the bending resistance, heat resistance cycle performance and peeling strength, and these three indicators are significantly better than dry oxidation. Wet oxidation products can better meet the requirements of bending strength and heat resistance cycle performance.

So, this is the end of this post, Best Technology specialized in fabricating ceramic PCB (including DBC, DPC, AMB, HTCC and LTCC technology) for more than 16 years, we have rich engineering team and professional sales team can provide one-stop service for you. Welcome to contact us if you have any inquiries about ceramic PCB.

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Everything you should know about Tg in PCB

Wednesday, January 4th, 2023

Working temperature changes can have a significant influence on the operation, reliability, lifetime and quality of products. Temperature rises results in materials expanding, however, the substrate materials that PCB are made of have different thermal expansion coefficients, this causes mechanical stress that can create micro-cracks that may be undetected during electrical tests carried out at the end of production.

Due to the policy of RoHS issued in 2002 required lead-free alloys for soldering. However, removing lead directly results in the rise of melting temperature, printed circuit boards are therefore subject to higher temperatures during soldering (including reflow and wave). Depending on the chosen reflow process (single, double…), it is necessary to use a PCB with appropriate mechanical characteristics, especially one with suitable Tg. 

What is Tg?

Tg (glass transition temperature) is the temperature value that guarantees the mechanical stability of the PCB during operational life time of the PCB, it refers to the critical temperature at which the substrate melts from solid to rubberized liquid, we called the Tg point, or melting point for easy to understanding. The higher the Tg point is, the higher the temperature requirement of the board will be when laminated, and high Tg board after laminated will also be hard and brittle, which benefits for next process such as mechanical drilling (if any) and keep better electrical properties during use.

The glass transition temperature is hard to be measured accurately in considerate many of factors, as well as each material have its own molecular structure, therefore, different materials have a different glass transition temperature, and two different materials may have the same Tg value even they have different characteristics, this enable us to have an alternative choice when the needed material is out of stock.

Features of High Tg materials

  • Better thermal stability
  • Good resistance to moisture
  • Lower thermal expansion coefficient
  • Good chemical resistance than low Tg material
  • High value of thermal stress resistance
  • Excellent reliability

Advantages of High Tg PCB

In general, a normal PCB FR4-Tg is 130-140 degrees, the medium Tg is greater than 150-160 degrees, and high Tg is greater than 170 degrees, High FR4-Tg will have better mechanical and chemical resistance to heat and moisture than standard FR4, here are some advantages of high Tg PCB for your reviewing:

  1. Higher stability: It will automatically improve the heat resistance, chemical resistance, moisture resistance, as well as stability of the device if increasing the Tg of a PCB substrate.
  2. Withstand high power density design: If the device has a high power density and a fairly high calorific value, then high Tg PCB will be a good solution for heat management. 
  3. Larger printed circuit boards can be used to change the design and power requirements of the equipment while reducing the heat generation of ordinary boards, and high Tg PCBS can also be used. 
  4. Ideal choice of multi-layer and HDI PCB: Because multi-layer and HDI PCB are more compact and circuit dense, it will result in a high level of heat dissipation.  Therefore, high TG PCBs are commonly used in multi-layer and HDI PCBs to ensure the reliability of PCB manufacturing.

When do you need a High Tg PCB?

Normally to ensure the best performance of a PCB, the maximum operating temperature of the circuit board should be about 20 degrees less than the glass transition temperature. For example, if the Tg value of material is 150 degrees, then the actual operating temperature of this circuit board shouldn’t more than 130 degrees. So, when do you need a high Tg PCB?

  1. If your end application requires to bear a thermal load greater than 25 degrees centigrade below the Tg, then a high Tg PCB is the best choice for your needs.
  2. To make sure the safety when your products require an operating temperature equal or greater than 130 degrees, a high Tg PCB is great for your application.
  3. If your application requires a multi-layer PCB to meet your needs, then a high Tg material is good for the PCB.

Applications that require a high Tg PCB

  • Gateway
  • Inverter
  • Antenna
  • Wifi Booster
  • Embedded Systems Development
  • Embedded Computer Systems
  • Ac Power Supplies
  • RF device
  • LED industry

Best Tech has rich experience in manufacturing High Tg PCB, we can make PCBs from Tg170 to maximum Tg260, meanwhile, if your application need to use under extremely high temperature like 800C, you’d better use Ceramic board which can go through -55~880C.

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Suitable Choice of Ceramic Substrate for Your Application

Wednesday, December 7th, 2022

With the rapid development of ceramic industry, Ceramic Circuit Board is widely used in semi-conductors and electronic packages fields because it provides an excellent electric conductivity, low thermal expansion and good insulation properties over standard FR4 based PCBs. As you can see from our website: https://www.bestpcbs.com/products/ceramic-substrate.htm, there are various kinds of ceramic substrate materials in the market, different materials have different functions and properties. Here we illustrated the different kinds of materials in the market as below for you to choose which one is ideal for your designs when needs come out.

Common ceramic substrate materials

Nowadays, the most commonly material in the market is oxidation material, it always used in automobile products as its wear resistance and good strength.

Besides, there are some nitrides and silicious can be used in high power products.

For a quick look, here I listed as following:

  • Alumina Oxide (Al2O3)
  • Alumina Nitride (ALN)
  • Beryllium Oxide (BeO)
  • Silicon Nitride (Si3N4)
  • Zirconium Oxide (ZrO2)
  • Silicon Carbide (SiC)

Characteristics of different substrate materials

Alumina Oxide (Al2O3)

Alumina substrate characterize as a pure white substrate and the most commonly used ceramic substrate material in the electronics industry because of its high strength and chemical stability compared to most other oxide ceramics in terms of mechanical, thermal and electrical properties, and the richful source of raw materials is suitable for a variety of technical manufacturing and different shapes. The most commonly used Alumina Oxide are 96% alumina and 99.6% alumina.

  • 96% alumina can be used to fabricate Thick Film Ceramic Circuits as it has excellent electrical insulation, mechanical strength, good thermal conductivity, chemical durability and dimensional stability. The surface roughness is generally 0.2~0.6μm, and the maximum using temperature of the substrate can reach 1600℃
  • 99.6% alumina is the mainstay of most Thin-film electronic substrate applications, commonly used in circuit generation for sputtering, evaporation and chemical vapor deposition of metals. 99.6% alumina has higher purity, smaller grain size, and excellent surface smoothness than 96% alumina (the surface roughness is generally 0.08~0.1μm), and it can withstand maximum 1700°C temperature when applied in applications.

Alumina Nitride (ALN)

Currently, Alumina Nitride won the high attention of the public by means of two key excellent properties: one is high thermal conductivity. Alumina nitride offers a big increasing in thermal conductivity (170Wm.k), which is approximately 100-200 times than FR4 substrates did, while alumina oxide only offers 24W/m.K.

Another characteristic is silicon-matched expansion coefficient of 4.7ppm/°C 20~300°C, this makes it suitable for used in extremely harsh environments likely in high temperatures. The disadvantage is that even an extra thin oxidation will affect the thermal conductivity. Only by strictly controlling the material and process, can aluminum nitride substrate be produced with good consistency. That’s why the alumina nitride is expansive than alumina oxide.

By visually, alumina nitride has an off-white color, that give us a chance to distinguish it with alumina oxide easily.

Beryllium Oxide (BeO)

Beryllium Oxide has a high thermal conductivity than alumina, therefore, it almost used where high thermal conductivity required.  But when the temperature exceeds 300°C, it drops quickly. It is not as widely used as alumina oxide or aluminum nitride, the most important thing is that its toxicity limits its development.

Silicon Nitride (Si3N4)

Silicon Nitride is a material with high fracture toughness and strong heat resistance are often used as alternative materials for modules in recent years. With strong mechanical, high temperature resistance, corrosion resistance and wear resistance, it is widely used in automotive shock absorber, engine, especially automotive IGBT products, as well as traffic track, aerospace and other fields.

Zirconium Oxide (ZrO2)

Zirconium Oxide is popular as its exceptional strength, toughness, biocompatibility, high fatigue and wear resistance (15times of alumina oxide) render it optimal for dental applications.

Silicon Carbide (SiC)

The essence of silicon carbide ceramic substrate is a silicon material, which determines its high current density characteristics due to its superior thermal conductivity.

In the meantime, the higher band gap width determines the higher breakdown field and higher operating temperature of silicon carbide (SiC) ceramic circuit board. 

The core advantages of silicon carbide are high temperature resistance, high pressure resistance, wear resistance, low loss and high frequency work.  Therefore, it is used for products with high heat dissipation, high thermal conductivity, large current, large voltage and high frequency operation.

Send us inquiry for fabrication

At present, you should have a brief acknowledge about different ceramic substrate materials and their characteristics, and you should be able to decide which materials is most suitable for you. If you still have some concerns or different opinions about substrate for Ceramic pcb, welcome to contact us, Best Tech will offer you free advice and technical support for ceramic substrate choice.

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Why ENEPIG More Suitable for Ceramic PCB Wire Bonding?

Thursday, October 20th, 2022

There are many surface treatment choices that can be used on Ceramic PCB, but why ENEPIG is one of options we always recommend to our customers whom have wire bonding demands?

In the application of Ceramic PCB, COB or wire bonding was widely used for the packaging technology in thin, short, high speed of electronic products. The Chip On Board (COB) technology refers to a technology in which bare chips are directly attached to the PCB board and then connected electronically through metal wires, namely “Wire Bonding”. Due to gold wire has an excellent electrical conductivity, thermal conductivity, corrosion and oxidation resistance, gold wire is often used as a main bonding material in microelectronics packaging.

What is ENEPIG?

ENEPIG, is a type of surface treatment on Printed Circuit Boards and ceramic PCB, the full name of it is Electroless Nickel – Electroless Palladium – Immersion Gold, now it is widely used in wire bonding field.

How does it work and what’s the standard thickness of each layer?

  • Electroless Nickel: Nickel acts as a barrier layer, preventing copper from interacting with the other metals involved in this plating technology, particularly gold. The layer is deposited on the catalytic copper surface using an oxidation-reduction reaction. The result is a layer that is between 2.0 to 5.0 microns thick.
  • Electroless Palladium: Palladium is a relatively stable metal at room temperature, and it is difficult to be oxidized within 400℃. The chemically deposited palladium layer has a neat lattice arrangement, uniform grain size and compact structure. Adding palladium layer between nickel layer and gold layer can effectively prevent the diffusion of nickel layer to gold layer. The Palladium is a layer with a thickness between 0.03 to 0.10 microns, it also depends on the final applications.
  • Immersion Gold: The main function of the gold layer is to bond with the gold wire. If there is no palladium layer as a diffusion barrier between the nickel layer and the gold layer, the gold layer can also bond with the gold wire after reflow, as long as the gold layer reaches a certain thickness. For example, when the thickness of the electroplated nickel gold reaches 0.3um, it can bond with the gold wire. In addition, gold itself has a good bonding ability with gold wire, and in ENEPIG process, due to the palladium layer protects the gold layer from the pollution of nickel, only a thin gold layer (0.03um~0.05umm) is needed to have a good bonding property. This’s why there’s cost advantage of ENEPIG than that of thicker ENIG.
(ENEPIG product)

Why choose ENEPIG?

ENIPIG has a good wiring bonding ability, solder joint reliability, multiple reflow soldering and excellent storage time, can correspond to and meet the requirements of a variety of different assemblies.  Below is a comparison about performance of different surface treatments:

(Comparison-about-performance-of-different-surface-treatments)

Advantages  of ENEPIG

  • “Black Nickel” free — The palladium layer separates the Nickel layer from the gold layer, it can prevents the mutual migration of gold and nickel, so no black nickel will appear
  • Excellent gold wire bondability — the gold plating/coating is very thin, can be used for gold wire bonding as well aluminum wire bonding
  • Palladium acts as an additional barrier layer to further reduce copper diffusion to surface, thus ensuring good solderability
  • Cost-effective than ENIG
  • Lead-free nickel
  • Good compatibility between coating and solder paste
  • Very suitable for packaging components such as SSOP, TSOP, QFP, TQFP, PBGA

Best Technology is a 16+ years PCB manufacturer and we made many ENEPIG PCBs and ceramic PCBs for our customers, welcome to contact us if you have demands on ENEPIG PCB.

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What are the Factors Affecting the Thermal Conductivity of AlN Ceramic Substrate?

Tuesday, May 31st, 2022

The Introduction of AlN Ceramic

With hexagonal wurtzite structure and no other homomorphic isomers, AlN, aluminum nitride, is a structurally stable covalent bond compound, whose crystal structure is AlN4 tetrahedron formed by the dismutation of aluminum atom and adjacent nitrogen atom. And its space group is P63mc, belonging to hexagonal system.

The Features of AlN Ceramic

  1. High thermal conductivity, which is 5 to 10 times than that of aluminum oxide ceramic.
  2. Coefficient of thermal expansion (4.3*10-6/℃) matches the semiconductor silicon material (3.5-4.0*10-6/℃).
  3. Great mechanical properties.
  4. Excellent electrical performance, with high insulation resistance and low dielectric loss.
  5. Multi-layer wiring can be carried out to achieve high density and miniaturization of packaging.
  6. Non-toxic, conducive to environmental protection.
Ceramic PCB

Factors Impacting on the Thermal Conductivity of AlN Ceramic

At 300K, the theoretical thermal conductivity of AlN single crystal material is as high as 319 W/(m·K). But in the actual production process, its thermal conductivity will still be affected, which is often lower than the theoretical value due to the influence of various factors such as the purity and internal defects (dislocations, pores, impurities, lattice distortion) of material, grain orientation and sintering process.

Effect of Microstructure on Thermal Conductivity

The heat conduction mechanism of single crystal AlN is phonon heat transfer, hence the thermal conductivity of AlN may be mainly influenced by the scattering control of grain boundary, interface, second phase, defect, electron and phonon itself. In accordance with the solid lattice vibration theory, the relation between phonon scattering and thermal conductivity “λ” is as follows: λ= L / 3CV.

In the formula, C is the heat capacity; V represents the average velocity of phonons; and L stands for the mean free path. And it can be seen from the equation that the thermal conductivity (λ) of AlN has direct ratio with the mean free path (L), for which the larger “L” is, the higher the thermal conductivity is. From the perspective of microstructure, the scattering can be caused by the interaction between phonons and phonons, phonons and impurities, and phonons and grain boundary.  It will affect the mean free path of phonons, and thus impact on the thermal conductivity.

It can be learnt from above that the microstructure of AlN has a great influence on its thermal conductivity. Therefore, it is necessary to make AlN crystals with fewer defects and impurities in order to obtain AlN ceramics with high thermal conductivity.

Effect of Oxygen Impurities Content on Thermal Conductivity

There are studies show that AlN has a strong affinity with oxygen so that it is easy to be oxidized, leading to the formation of aluminum oxide film on its surface. Owing to the dissolution of oxygen atoms in Al2O3, the nitrogen in AlN is replaced, resulting in aluminum void and oxygen defect. In this way, it will bring about the increase phonon scattering and decrease of mean free path hence the thermal conductivity will be reduced.

Oxygen Content in AlN (wt%)Thermal Conductivity (W/m·K)
0.31130
0.24146
0.19165
0.13171
0.12185

So, it can be concluded that the types of defects in AlN lattice are related to the concentration of oxygen atoms.

  • When the oxygen concentration is lower than 0.75%, oxygen atoms evenly distributed in the AlN lattice, replacing the position of nitrogen atoms. And then the aluminum void is accompanied by it.
  • When the oxygen concentration is not less than 0.75%, the position of Al in aluminum nitride lattice will have a change. Then the aluminum void will disappear, causing octahedral defects.
  • When the oxygen concentration is higher, the lattice will produce extension defects such as polytype, inversion domain and oxygen-containing stacking fault. Moreover, based on thermodynamics, it is found that the amount of oxygen in AlN lattice is under the influence of Gibbs free energy (ΔG°). The larger the ΔG° is, the less oxygen is in the lattice, hence there will be a higher thermal conductivity.

Therefore, the thermal conductivity of aluminum nitride is seriously affected by the existence of oxygen impurities, which is a key point resulting in the decrease of thermal conductivity.

Thermal Conductivity can be Enhanced by Suitable Sintering Aids

In order to improve the thermal conductivity of AlN, the required sintering aids need to be added to lower sintering temperature and remove oxygen in lattice.

As matters stand, the addition of multiple composite sintering additives is followed with more interests. And the experiment shows that relatively dense AlN samples with less oxygen impurities and the secondary phase can be obtained by adding the composite sintering aids, Y2O3-Li2O, Y2O3-CaC2, Y2O3-CaF2, Y2O3-Dy2O3, to aluminum nitride.

In a word, selecting appropriate composite sintering additives can help to get lower sintering temperature and effectively purify the grain boundary, so as to obtain AlN with high thermal conductivity.

In case if you have any other questions about ceramic PCB or MCPCB, you are welcome to contact us via email at sales@bestpcbs.com. We are fully equipped to handle your PCB or MCPCB manufacturing requirements.

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Pros and Cons of the Ceramic PCB

Friday, May 27th, 2022

Ceramic PCB is used in various fields because of its high-quality thermal and mechanical advantages. The board’s unique features and high thermal conductivity have enabled it to be used in devices big and small. But meanwhile, it is not flawless. There are also some disadvantages.

Ceramic PCB

Pros of ceramic PCB

It is supposed that you are familiar with the features below that the ceramic PCB has.

  • Excellent thermal conductivity.
  • Good insulation.
  • High temperature resistance.
  • Great mechanical properties.
  • Compatible with CTE (Coefficient of Thermal Expansion) of components.
  • High-density assembly possible.
  • Non-toxic, conducive to environmental protection.

Cons of ceramic PCB

There are also a few disadvantages that can be found in ceramic PCB. Some of the disadvantages are stated below.

  • Cost—It has a higher cost compared to other printed circuit boards.
  • Handling—Since ceramic is fragile, it entails careful handling. As ceramic PCB is made for tight spaces, it is very small and this makes it even harder to handle.
  • Availability—It is not as widely available.

Everything has two sides. And ceramic PCB has no exception. But if considering all the advantages and disadvantages, ceramic PCB still takes the win amongst all other boards.

So, this is the end of the article about the advantages and disadvantages of the ceramic PCB. In case if you have any other questions about ceramic PCB or MCPCB, you are welcome to contact us via email at sales@bestpcbs.com. We are fully equipped to handle your PCB or MCPCB manufacturing requirements.

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Thermal Conductivity—Aluminum PCB vs Ceramic PCB Series 2

Tuesday, April 19th, 2022

Last time we have talked about the structure difference between the aluminum PCB and ceramic PCB. So, based on the different structures, whose thermal conductivity is better?

We have known that a single layer aluminum PCB is made up of copper layer, dielectric layer and aluminum layer. Meanwhile, the dielectric layer is the decisive factor affecting the thermal conductivity.

Generally, its thermal conductivity ranges from 0.8 to 3.0 W/m-K, but can up to 8.0 W/m-K. So, in terms of heat dissipation, the aluminum substrate does much better than FR-4 substrate. And it is a good choice for LED lighting products with high power.

Aluminum PCB

However, the heat-conducting property of ceramic PCB is superior to that of the aluminum PCB.

Since ceramic itself is an insulating material with a great heat-conducting property, it does not need a dielectric layer. Therefore, the heat can be dissipated directly through the ceramic.

Because of its excellent performance in heat dissipation, it is particularly suitable for the lighting product with ultra high power and those products which have a high demand of heat dissipation.

Ceramic PCB

To summarize, clearly, we can know from the table below that ceramic PCB does better than aluminum PCB in terms of thermal conductivity and heat dissipation. And this is mainly because of the dielectric layer, which is related to the functions of bonding, insulation and heat conduction.

The better the heat conduction performance of the insulating layer, the more conducive it is to the diffusion of heat generated during the operation to the device, hence it will be more conducive to lower the operating temperature of the device. That is to say, aluminum PCB will be subject to the dielectric layer, while ceramic PCB will not be restricted.    

And, this is the end of the comparison of the thermal conductivity between aluminum PCB and ceramic PCB. If you still have any questions about them, please feel free to contact us.

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Differences in Structure——Aluminum PCB vs Ceramic PCB Series 1

Monday, March 21st, 2022

It is supposed that we are familiar with both aluminum PCB and ceramic PCB. But if juxtaposing them, which one will be better by one tally? So, we are about to talk about some differences between them in terms of structure.

Aluminum PCB

Aluminum substrate namely uses aluminum as substrate, which has a good heat dissipation capacity. Generally, it is single-sided, and also can be double-sided while multi-layer aluminum PCB is a little bit hard to manufacture. Besides, a single layer aluminum PCB is made up of copper layer, dielectric layer and aluminum layer.

Structure of Aluminum PCB

Ceramic PCB

Ceramic PCB namely uses ceramic as substrate. Apart from the material, the structure is the biggest difference between ceramic PCB and aluminum PCB. Since ceramic itself is an insulating material, it does not need a dielectric layer. Its structure is as follows.

Structure of Ceramic PCB

Therefore, whether there is a dielectric layer is the main difference in structure between aluminum PCB and ceramic PCB. And dielectric layer plays an important role in thermal conductivity. So, what is the relationship between dielectric layer and thermal conductivity? And whose thermal conductivity is better between aluminum PCB and ceramic PCB?

We will talk about it next time. And if you would like to know the answer, please feel free to contact us, or you can continuously follow our blog site, we will keep updating more information about the differences between aluminum PCB and ceramic PCB on it.

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