Nonconchoidal Fracture in Power Electronics Substrates due to Delamination in Baseplate Solder Joints

Power Electronic (PE) modules for inverter applications in electric and hybrid electric vehicles are often built on Direct Bonded Copper (DBC) or Active Metal Brazing (AMB) substrates. For adequate thermal management, these substrates are soldered onto liquid cooled metallic heat sinks (baseplates). While passive temperature cycling (pTC) leading to delamination in the baseplate solder layer is relatively well known, this paper documents the occurrence of a lesser known nonconchoidal fracture in the ceramic layer of AMBs/DBCs. Interestingly, such cracks are strongly coupled to the delamination of the substrate-solder interface and substrate design. Using experimental and Finite Element Method (FEM) tools, this study also clarifies the mechanism through which these cracks initiate, potentially leading to possible design solutions to avoid such cracks.