Thermomechanical Stress Analysis, Characterization, and Optimization for Double-Side Cooled Power Modules With Ceramic Substrate

Benefiting from the high thermal performance and low parasitic parameters, double-side cooled (DSC) power modules are promising in high-power-density applications. However, as the structure of DSC power module differs from that of conventional power module, the theoretical description of the interaction mechanisms of components in the DSC power module is still lacking and the effect of ceramic substrate structure on its reliability remains unclear. In this article, we propose a thermomechanical stress model for DSC power modules, whose accuracy is evaluated by a finite element analysis (FEA). Based on the model, we reveal the interaction mechanism of components in the DSC power module, including the spacer with a special focus on the ceramic substrate. Combined with a 650-V/30-A gallium nitride (GaN) full-bridge DSC power module, different ceramic substrate structures are evaluated. By optimizing the ceramic substrate structure, i.e., the ceramic thickness and the ratio of metal thickness to ceramic thickness, the stress of GaN die and the plastic strain change of attachments are lowered by 13% and 56%, respectively. Finally, strain experiments are performed to verify our analysis with errors of less than 4%.