Study on thermomechanical reliability of power modules and thermal grease pump-out mechanism

This paper focuses on two major thermomechanical reliability topics related to high power devices such as insulated gate bipolar transistor (IGBT) modules. Firstly, the stress-free status and the thermal residual stress of a typical power module are investigated by finite element method (FEM) analysis. After determining the thermal residual stresses at room temperature, thermal cycling (TC) and power cycling (PC) tests are conducted and simulated by FEM. Secondly, the thermal grease pump-out phenomenon is explicitly simulated via a combined FEM and smoothed particle hydrodynamic (SPH) method for the first time. SPH method shows great potential for the thermal grease material selection and engineering, base plate optimization, and thermomechanical reliability optimization of power devices in general. The simulated contact opening results at the interface between copper base plate and heat sink indicates different pumping modes associated with different loading conditions. All modeling approaches presented in this work offer insight into our understanding of deformation, stress status, and thermal grease related failure mechanisms of high power devices.