Application of Nonlinear Fracture Mechanics Parameter to Predicting Wire-Liftoff Lifetime of Power Module at Elevated Temperatures

Abstract

Power modules are utilized for electric power control and play a key role in efficient energy conversion. A structural reliability problem of wire bonding, wire-liftoff, in power modules becomes important at high-temperature operation. Wire-liftoff is a thermal fatigue phenomenon caused by thermal stress due to mismatch of coefficients of thermal expansion between a wire and a chip material. According to experimental studies, a saturation phenomenon of wire-liftoff lifetime was observed in power modules above the maximum junction temperature of 200 °C. In this paper, we examine the failure models for predicting wire-liftoff lifetime proposed in the previous studies and also propose a new failure model based on the nonlinear fracture mechanics parameter $T^\ast $ -integral range $\Delta T^\ast $ . Among various failure models, the proposed model is the best to represent a saturation phenomenon of wire-liftoff lifetime. For practical use of the failure model based on $\Delta T^\ast $ -integral range, we propose a simple calculation method of $\Delta T^\ast $ -integral range that can be calculated by using the commercial finite element computer code such as Marc, Ansys, and so on.