Abstract
Power devices nowadays possess low switching and conduction loss characteristics owing to the improvement in semiconductor device manufacturing. Insulated gate bipolar transistors are widely utilized in power modules because of such characteristics. When a power module is subjected to cyclic temperature load, the thermal stress resulting from the mismatch among the coefficients of thermal expansion of materials causes fatigue to the interface of the materials. Different operating requirements cause the module to have different temperature profiles. Different dwell times and ramp rates produce different stress relaxation, which eventually affect the reliability of the power module. A 2D finite element model has been established based on an actual sample. The model was subjected to thermal cycling between -40°C and 125°C to determine the effect of dwell time and ramp rate on the creep behavior of the solder. The results indicate that dwell time produces accumulative creep strain because of stress relaxation. Furthermore, dwell time at a high temperature leads to evident stress relaxation. Ramp section produces more accumulative creep strain than dwell phase in one thermal cycle. Decreasing the ramp rate increases creep strain and diminishes reliability.