Fretting-induced electrical degradation is a major reliability issue in current-carrying electrical contacts. For sputtered contact coatings, the degradation process is affected not only by hardness or wear resistance, but also by the coupled evolution of plastic deformation resistance, residual stress, debris behavior, interfacial oxidation, and metallic a-spot stability. In this study, AgNi composite coatings with different Ni contents were prepared by magnetron sputtering to investigate the role of yield strength–residual stress coupling in fretting-induced electrical degradation. A dimensional inverse analysis combined with finite element simulation and nanoindentation was used to estimate the effective elasto-plastic parameters of the coatings. Current-carrying fretting tests showed a significant overall composition effect and a non-monotonic variation in electrical contact lifetime. Ag92Ni8 exhibited the highest observed mean lifetime of 157.07 ± 17.34 k cycles, approximately 2.68 times that of Ag99Ni1. Although its mean lifetime was not statistically distinguishable from that of Ag90Ni10, Ag90Ni10 exhibited a substantially broader lifetime distribution, indicating poorer lifetime consistency. Morphological and compositional analyses indicated that the post-test interfacial state resulted from the coupled evolution of plastic deformation, wear, debris redistribution, oxygen-enriched interfacial products, possible substrate participation, and metallic a-spot instability. The results show that yield strength and residual stress are complementary mechanical descriptors of the coating state, but do not independently determine electrical contact lifetime, which reflects coupled mechanical, chemical, and electrical interfacial processes.
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, Jc, at the crack tip based on the experimentally measured critical loads. The mean Jc was 20.52 J/m2 for the dry interface and decreased to 16.92 J/m2 after moisture conditioning, corresponding to an approximately 18% reduction. The measured Jc 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.
