Direct liquid cooling of high performance Silicon Carbide (SiC) power modules

Silicon Carbide (SiC) wide band gap power devices are capable of operating at extremely high current densities and switching frequencies. Systems embracing these benefits can achieve a substantial increase in power density. However, cooling becomes exponentially more difficult as the size of the modules lessens. Direct cooling of the power electronic modules, in which the liquid coolant flows over the surfaces of the base plate, is a highly effective approach to improve the thermal performance of a conversion system. Notably, it allows for a reduction of layers in the thermal stack-up and completely eliminates the need for a thermal interface material (TIM). In this work, Wolfspeed has taken the commercial CAS325M12HM2 SiC power module, which was specifically designed to take advantage of wide band gap power semiconductors, and developed a prototype variant to enable direct liquid cooling of the base plate. High surface area pin fins are formed in a concentrated density directly on the base plate, providing a quality means of heat removal as close to the semiconductor devices as possible. High thermal conductivity materials and attaches, including silver sintering paste and film, were utilized to achieve an optimized heat transfer path. The discussion presents the design, analysis, and testing of this direct cooled module. It focuses on various physical factors influencing the thermal performance and a comparison between different direct structural configurations and power levels.