Failure Analysis and Shape Optimization of Bonding Wire for SiC Power Module Encapsulated with Epoxy Resin

Two typical SiC power modules, one sealed with silicone gel and the other encapsulated with epoxy, are widely used in electric vehicles. The reliability and shape optimization of bonding wires in silicone gel modules have been extensively investigated. Heel cracking and lifting-off have been identified as the two primary failure modes of bonding wires. However, the epoxy modules, which introduce additional constraints on bonding wires, have rarely been studied. In this paper, the reliability of the bonding wires in the two types of modules is systematically analyzed through the finite element simulation using the bilinear kinematic hardening model. The results reveal that the equivalent plastic strain is much smaller in epoxy modules, indicating a higher lifetime. Lifting-off is the predominant failure mode of bonding wires in epoxy modules resulting from the larger equivalent plastic strain at the bonding interface than the heel. Two samples with 8 bonding wires are tested through power cycling, and all wires occurred lifting-off failures after about 30 K cycles. The influences of bond wire geometry parameters, specifically loop height and length, on bond wire reliability are studied. The larger loop height and the smaller length lead to the smaller equivalent plastic strain range. Based on the main effect analysis, the loop height has a bigger impact on the equivalent plastic strain range. Furthermore, the ratio of loop height to length is approximately linear to the equivalent plastic strain range, indicating that a larger ratio enhances the reliability of bonding wires. These findings provide guidance for power module packaging designers in the design of bonding wire shapes for epoxy power modules.