3. Aluminum nitride ceramic PCB
AlN has two very important properties worth noting: one is high thermal conductivity, and the other is the expansion coefficient matching with Si. The disadvantage is that even if there is a very thin oxide layer on the surface, it will affect the thermal conductivity. Only by strictly controlling the materials and processes can AlN substrates with good consistency be manufactured. There are few AlN production technologies in China that can be produced on a large scale like Sliton, and the price of AlN is relatively high compared with Al2O3, which is also a small bottleneck restricting its development. However, with the improvement of economy and technology, this bottleneck will eventually disappear.
From the above reasons, it can be known that alumina ceramics are widely used because of their superior comprehensive performance, and they are still in a dominant position in microelectronics, power electronics, hybrid microelectronics, power modules and other fields.
AlN can be stabilized up to 2200℃. The strength is high at room temperature, and the strength decreases slowly with the increase of temperature. Good thermal conductivity, small thermal expansion coefficient, and is a good thermal shock-resistant material. With strong resistance to molten metal erosion, it is an ideal crucible material for melting and casting pure iron, aluminum or aluminum alloy. Aluminum nitride is also an electrical insulator with good dielectric properties, and it is also promising to be used as an electrical component. The aluminum nitride coating on the surface of gallium arsenide can protect it from ion implantation during annealing. It is also a catalyst for converting aluminum nitride from hexagonal boron nitride to cubic boron nitride. It reacts slowly with water at room temperature. It can be synthesized from aluminum powder at 800~1000℃ in ammonia or nitrogen atmosphere. The product is white to gray powder blue. Or synthesized by reaction of Al2O3-C-N2 system at 1600~1750℃, and the product is off-white powder. Or aluminum chloride and ammonia are prepared by gas phase reaction. The coating can be synthesized from AlCl3-NH3 system by gas phase deposition.

4. Silicon nitride ceramic PCB
Rogers Company introduced the new curamik® series silicon nitride (Si3N4) ceramic PCB substrate in 2012. As the mechanical strength of silicon nitride is higher than that of other ceramics, the new curamik® substrate can help designers achieve a long life in harsh working environment and HEV/EV and other renewable energy applications.
The flexural strength of the new ceramic PCB substrate made of silicon nitride is higher than that of the substrate made of Al2O3 and AlN.
The fracture toughness of Si3N4 even exceeds that of zirconia doped ceramics.
Up to now, the reliability of copper-clad ceramic PCB substrate used in power modules has been limited by the low flexural strength of ceramics, which will reduce the thermal cycle capability. For those applications that combine extreme thermal and mechanical stress, such as hybrid vehicles and electric vehicles (HEV/EV), the commonly used ceramic PCB substrate is not the best choice. The thermal expansion coefficients of the substrate (ceramic PCB) and the conductor (copper) are very different, which will exert pressure on the bonding area during the thermal cycle, thus reducing the reliability. This curamik® series silicon nitride (Si3N4) ceramic PCB substrate introduced by Rogers Company at this year's PCIM exhibition will prolong the life of power electronic modules by 10 times.



With the growth of HEV/EV and renewable energy applications, designers have found new ways to ensure the reliability of these electronic components needed to promote the development of challenging new technologies. Since the service life is 10 times or more longer than that of other ceramics used in power electronics, the silicon nitride substrate can provide mechanical strength which is essential to meet the necessary reliability requirements. The life of the ceramic PCB substrate is measured by the number of thermal cycles that the substrate can bear without peeling and other faults that affect the circuit function and safety. This test is usually done by circulating the sample from-55 C to 125°C or 150 C.
Manfred Goetz, Curamik product marketing manager, said, "Our current test results (-55 C to 150°C) show that the service life of Curamik silicon nitride substrate is more than ten times longer than that of the substrate commonly used in automobile market, especially HEV/EV. Similarly, the life of the whole module is greatly improved by using the silicon nitride substrate. "
The extension of service life is very important for all power module applications where large semiconductor wafers are directly bonded to the substrate, especially for SiC and GaN wafers with high junction temperature (up to 250°C). The thermal conductivity of curamik® silicon nitride substrate is 90 W/mK, which exceeds the average value of other substrates on the market.

The mechanical strength of the new substrate enables us to use thinner ceramic PCB layer, thus reducing thermal resistance, increasing power density and cutting system cost.

Compared with Al2O3 and AlN substrates, its flexural strength is much improved, which will benefit designers. The fracture toughness of silicon nitride is even higher than that of zirconia doped ceramics, reaching 6.5~7 MPa/√m at the thermal conductivity of 90 W/MK.

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