As chip components and SMT (Surface Mount Technology) are widely accepted by the electronics industry, traditional PCBs (printed circuit boards) based on organic laminates are moving towards high precision, high density and high reliability. As a relatively new circuit board, ceramic PCB is regarded as an effective solution for miniaturization of modern electronic products and electronic assembly technology, so it has attracted great attention from the industry.
Compared with the traditional PCB based on epoxy glass fiber, polyimide, polystyrene and phenolic resin, ceramic PCB has the following characteristics:
1. Excellent thermal conductivity;
2. Chemical resistance;
3. Satisfactory mechanical strength;
4. Compatible with the CTE of the component;
5. Easy to realize density track.
Due to more and more functions, the miniaturization and high-speed of electronic equipment and the large-scale IC, in terms of CTE, thermal conductivity, loss, dielectric constant and band resistance, more stringent requirements are placed on ceramic PCBs. It can be estimated that there is an increasing need for ceramic PCBs based on aluminum nitride, mullite and glass-ceramics.
According to the manufacturing method of ceramic PCBs, they can be divided into three categories: high temperature co-fired ceramic PCB, low temperature co-fired ceramic PCB and thick film ceramic PCB.
1. High temperature co-fired ceramic (HTCC) PCB
As a traditional manufacturing method, high-temperature co-firing is made by mixing alumina with binders, plasticizers, lubricants and solvents, forming green ceramics through roll forming and curtain coating processes, and it is realized by drawing circuits on refractory metals such as tungsten and molybdenum. Then, put it in a high-temperature oven at a temperature of 1600°C to 1700°C, and bake it for 32 to 48 hours after cutting and lamination. To prevent tungsten and molybdenum from being oxidized at high temperatures, baking should be carried out in a reducing gas (such as hydrogen or mixed gas).
The ceramic PCB made by high temperature co-firing can be applied to small circuit boards, derivative circuit boards, or carrier circuits. However, on large circuit boards, high-temperature co-fired ceramic PCBs face the challenges of shrinkage tolerance, warpage, and relatively high traceability of refractory metals.
2. Low temperature co-fired ceramic (LTCC) PCB
The low-temperature co-fired ceramic PCB is made by mixing crystal glass, glass composite materials and non-glass and adhesives with the resulting flakes, and circuit tracking will be achieved by gold paste with high conductivity. After being cut and accurately shaped, it is placed in an oxidizing gas oven at 900°C for baking. The low-temperature co-fired ceramic PCB provides a circuit tracing a path to the precious metal paste, and as long as a few improvements are made to the thick film baking, the PCB baking can be completed. Product accuracy and shrinkage tolerance can also be improved, and further optimization of mechanical strength and thermal conductivity is required.
3. Thick film ceramic PCB
The thick film gold paste and dielectric paste are repeatedly printed alternately on the ceramic substrate and baked at a temperature lower than 1000°C. Although this type of manufacturing technology is the best choice for large-scale ceramic PCB manufacturing and has a relatively high assembly base, its application is limited due to the high cost of gold (which also prevents the precipitation of solder paste). As a result, a multilayer thick film copper circuit technology was developed, which is the most eye-catching and popular ceramic PCB. In order to prevent copper from being oxidized, this type of ceramic PCB must be baked in nitrogen, which is the key to this technology. In addition, depending on the complex multilayer interconnection structure, a dielectric paste is generated in nitrogen, which is also a core technology.
Ceramic PCB is widely used due to its high thermal conductivity, low CTE, chemical resistance and low dielectric constant.
1. Memory bank
Can be used in extreme environments. The multilayer ceramic PCB and the packaging components on it have sufficient strength and resistance to shock and vibration.
2. Receiving/transmitting module
Aluminum nitride has the characteristics of high thermal conductivity and low CTE, laying a solid foundation for the application of ceramic PCB in transceiver modules.
3. Multilayer interconnection board
In order to be compatible with the miniaturization of electronic products, ceramic PCBs can accommodate more components in the same board area, which adds more possibilities for ceramic PCBs in multilayer interconnection board applications.
4. Analog/digital PCB
The use of PCB to produce analog/digital PCB boards can reduce parasitic capacitance by approximately 90%. It not only effectively overcomes the crosstalk of circuit track, but also reduces the volume and weight of the circuit.
All in all, ceramic PCB has a wide range of applications due to its high thermal conductivity, low CTE and low dielectric constant. They will undoubtedly play an important role in applications requiring high reliability, high air tightness and high thermal conductivity.
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