Experimental Investigation on the Effects of Narrow Junction Temperature Cycles on Die-Attach Solder Layer in an IGBT Module

This paper presents a series of experiment results on the ageing effects of cyclic junction temperature variations ( $\Delta T_{j}$ ) of low amplitudes in power modules, to help the capturing of module reliability characteristics and the derivation of lifetime models in the future. Power cycling tests, for nonaged and aged modules, are designed to illustrate the failure mechanisms. Insulated gate bipolar transistor (IGBT) modules in actual converters are usually operated in a $\Delta T_{j}$ range up to 40 °C; therefore, tests are carried out to observe the effects of such narrow $\Delta T_{j}$ stress cycles on the module lifetime. It is found that the relatively minor stress cycles may not be able to directly initiate a crack but can contribute to the development of damage in the die attach solder layer due to stress concentration. Finite element analysis modeling is utilized to verify the stress concentration effect. The experiment results show that the effects of the narrow $\Delta T_{j}$ stress cycles are affected by the ageing status of the module and the stress level itself.