Thermal Stress Simulation for HV Inverter Module

The thermal stress occurred in the solder joint of HV (Hybrid vehicle) inverter module is the key factor for the achievement of high reliable modules. Therefore, thermal stress simulation technique with high accuracy is proposed which is useful in developing the HV inverter module. It has the feature of modeling the inelastic behavior of the lead-free solder based on the novel inelastic constitutive equation proposed by Ohno. The validation of this simulation is demonstrated by using the novel high temperature diffused-type Si strain gauge as reference in the thermal cycling test of the inverter module. This simulation is also expected to be able to predict the fatigue lifetime of the solder joint accurately, because it can calculate the inelastic strain in the solder joint.

I. Introduction

Recently HV (Hybrid Vehicle) is expected to be promising as a mild vehicle for environment at present and in the future because HV can achieve high fuel efficiency and low emission maintaining driving performance compared to be a conventional gasoline vehicle. HV can lead to the superior performance mentioned above by switching the driving force from the engine to that from motor or reversely according to the running state of the the vehicle dynamically.