Modeling of SiC power modules with double sided cooling

Abstract

Silicon Carbide (SiC) based transistor devices have demonstrated higher efficiency switching operation compared to silicon-based, state-of-the-art solutions due to the superior electrical and thermal properties of the SiC material. The improved current density and thermal conductivity allows SiC-based power modules to be smaller than their silicon counterparts for comparable current densities. The active chip area can be reduced further by effectively cooling the devices. In this work, a new power module including SiC bipolar junction transistors (BJT) and diodes and integrated double sided cooling will be introduced. The target application of these modules is a new drive-train system for commercial electric vehicles. The double sided cooling concept (named 2Cool) is a feasibility study with the goal to further compact the inverter system. More efficient removal of heat from the junction leads to a higher power rating per die, which in turn leads to fewer die and reduced system volume. Since temperature is a main driver in expected failure modes an increase in cooling capability will also enhance margins of the SiC device reliability. In addition, the removal of wirebonds on the top side of the die will result in lower electrical inductance. Several geometries of the heat exchanger cooling structures have been modeled in terms of thermal performance. The best geometry was a staggered pin-fin structure, which resulted in a junction temperature increase of 74 K at 400 W thermal loading. Also, thermomechanical modeling was used to make an estimation of stress in the power module materials.