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.

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 P6_3mc, 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.

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)
0.31	130
0.24	146
0.19	165
0.13	171
0.12	185

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-Dy₂O_3, 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.

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.

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.