1. Why use ceramic circuit boards
Ordinary PCB is usually made of copper foil and substrate bonding, and the substrate material is mostly glass fiber (FR-4), phenolic resin (FR-3) and other materials, adhesive is usually phenolic, epoxy, etc. In the process of PCB processing due to thermal stress, chemical factors, improper production process and other reasons, or in the design process due to the two sides of copper asymmetry, it is easy to lead to different degrees of warping PCB board
PCB Twist
And another PCB substrate – ceramic substrate, due to the heat dissipation performance, current carrying capacity, insulation, thermal expansion coefficient, etc., are much better than ordinary glass fiber PCB board, so it is widely used in high-power power electronics modules, aerospace, military electronics and other products.
Ceramic substrates
With ordinary PCB using adhesive copper foil and substrate bonding, ceramic PCB is in high temperature environment, through the way of bonding copper foil and ceramic substrate pieced together, strong binding force, copper foil will not fall off, high reliability, stable performance in high temperature, high humidity environment
2. Main material of ceramic substrate
Alumina (Al2O3)
Alumina is the most commonly used substrate material in ceramic substrate, because in mechanical, thermal and electrical properties compared to most other oxide ceramics, high strength and chemical stability, and rich source of raw materials, suitable for a variety of technology manufacturing and different shapes. According to the percentage of alumina (Al2O3) can be divided into 75 porcelain, 96 porcelain, 99.5 porcelain. The electrical properties of alumina are almost not affected by the different content of alumina, but its mechanical properties and thermal conductivity change greatly. The substrate with low purity has more glass and larger surface roughness. The higher the purity of the substrate, the more smoother, compact, medium loss is lower, but the price is also higher
Beryllium oxide (BeO)
It has higher thermal conductivity than metal aluminum, and is used in situations where high thermal conductivity is needed. It decreases rapidly after the temperature exceeds 300℃, but its development is limited by its toxicity.
Aluminium nitride (AlN)
Aluminum nitride ceramics are ceramics with aluminum nitride powders as the main crystalline phase. Compared with alumina ceramic substrate, insulation resistance, insulation withstand higher voltage, lower dielectric constant. Its thermal conductivity is 7~10 times that of Al2O3, and its thermal expansion coefficient (CTE) is approximately matched with silicon chip, which is very important for high-power semiconductor chips. In the production process, the thermal conductivity of AlN is greatly affected by the content of residual oxygen impurities, and the thermal conductivity can be significantly increased by reducing the oxygen content. At present, the thermal conductivity of the process
Based on the above reasons, it can be known that alumina ceramics are in a leading position in the fields of microelectronics, power electronics, mixed microelectronics and power modules due to their superior comprehensive performance.
Compared with the market of the same size (100mm×100mm×1mm), different materials of ceramic substrate price: 96% alumina 9.5 yuan, 99% alumina 18 yuan, aluminum nitride 150 yuan, beryllium oxide 650 yuan, it can be seen that the price gap between different substrates is also relatively large
3. Advantages and disadvantages of ceramic PCB
Advantages
- Large current carrying capacity, 100A current continuously through 1mm 0.3mm thick copper body, temperature rise of about 17℃
- The temperature rise is only about 5℃ when 100A current continuously passes through 2mm 0.3mm thick copper body.
- Better heat dissipation performance, low thermal expansion coefficient, stable shape, not easy to warping.
- Good insulation, high voltage resistance, to ensure personal safety and equipment.
Disadvantages
Fragility is one of the main disadvantages, which leads to making only small boards.
The price is expensive, the requirements of electronic products more and more rules, ceramic circuit board or used in some of the more high-end products, low-end products will not be used at all.
4. Usage of ceramic PCB
a. High power electronic module, solar panel module, etc
- High frequency switching power supply, solid state relay
- Automotive electronics, aerospace, military electronics
- High power LED lighting products
- Communication antenna