- Substrate

The substrate, as the backing of SiC chips, must meet the material requirement with characteristics of excellent thermal conductivity, high mechanical strength, high flexural strength, and the similar coefficient of thermal expansion (CTE) with SiC. The direct-bond-copper (DBC) substrate presents a sandwich structure, which consists of two layers of copper, lying on the top and bottom, and with insulation ceramics in between. The available materials for insulating ceramics could be quantized as Al2O3, AlN, BeO, and Si3N4, and Table 3 shows the thermal mechanical characteristics. As it can be seen, the CTE of AlN is close to that of SiC material with the value of approximately 4–6 ppm/◦C, and the mechanical stress resulted by heat expansion can be significantly reduced by the uniformity of parameters. Moreover, the thermal conductivity of AlN is highly relative to two other materials like Al2O3 and Si3N4, which will significantly promote the cooling capacity of power modules. Therefore, AlN is one of the most appropriate choices for the substrate to encapsulate SiC power modules, and the relevant power modules can endure in the high-temperature environment which is above 250 ◦C [33].


**Table 3.** The thermal mechanical characteristics of materials for the substrate.
