Hygrothermal delamination assessment of EMC/Cu interfaces in molded power modules

Interfacial delamination at epoxy molding compound/copper (EMC/Cu) interfaces compromises the reliability of molded power modules (MPMs) under hygrothermal loading. In this study, EMC/Cu interfacial specimens were excised from an MPM, and interface precracks were introduced by femtosecond-laser machining. The specimens were tested in the dry state and after conditioning at 85 °C/85% relative humidity (RH) for 168 h. Finite element analysis was employed to determine the critical J -integral, J c , at the crack tip based on the experimentally measured critical loads. The mean J c was 20.52 J/m 2 for the dry interface and decreased to 16.92 J/m 2 after moisture conditioning, corresponding to an approximately 18% reduction. The measured J c values for the dry and conditioned EMC/Cu interfaces were incorporated into a hygrothermal fracture analysis of the MPM to evaluate the critical delamination areas in high-risk regions subjected to a cooling from 175 °C to −40 °C. For sector-shaped corner delaminations and slim rectangular defects near the substrate edge, the predicted critical areas in the conditioned state were 45.61% and 48.16% smaller, respectively, than those in the dry state. These results indicate that moisture absorption significantly degrades the interfacial fracture resistance and markedly increases the propensity for EMC/Cu interfacial delamination under subsequent thermal loading. The findings demonstrate the necessity of incorporating moisture-induced interfacial degradation into the reliability assessment and design of MPMs.