Effect of solder layer thickness on thermo-mechanical reliability of a power electronic system

Abstract

In this work, we show that how solder thickness can affect the IGBTs’ useful lifetime. Hence, the thermo-mechanical response of joints in IGBT discrete with different solder thickness under thermal cycling were simulated and the results were merged to conditions of IGBTs in actual environment. The simulation results demonstrated that after thermal cycling, some creep strain is produced in the solder layer especially at the corners. This type of strain is accumulated in the volume of solder as stored energy. Accordingly, the decrease in solder thickness leads to the enhancement of stored energy per volume and as a result, the fatigue life of joint falls to shorter times. The SEM micrographs indicates that with the decrease of solder thickness, the number of voids and their concentration enhance across in the joint zone. The higher strain energy in thinner solder layers leads to the connection of voids and the formation of more concentrated defects. The EDS results also show that the diffusion of elements such as Si, Cu and Ag considerably increases across the joint zone after thermal cycling.