Comparison of fatigue strength of interfacial cracks between molding resin and metallic substrate in a power module under thermal cycle test and mechanical cycle test

Abstract

Power module is sealed with molding resin to protect from the environment. A large residual stress is generated along the interface between the substrate and the resin due to the difference of the Young's modulus and the coefficient of linear thermal expansion. The delamination between the substrate and molding resin due to the thermal residual stress is one of the serious reliability problems. The fracture toughness of interface cracks between a copper substrate and three types of molding resin was measured under various temperatures. Furthermore, we analyzed the stress intensity factors of an assumed crack on an interface between the substrate and molding resin in a test package, and evaluated the possibility of the fracture during thermal cycle tests. We compared the thermal cycle tests and mechanical fatigue tests of cracked specimens, and investigated the possibility to predict the life of thermal cycle test from the mechanical fatigue test.