Experimental investigations 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 (ΔTj) 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 non-aged and aged modules, are designed to illustrate the failure mechanisms. IGBT modules in actual converters are usually operated in a ΔTj range up to 40degC, therefore tests are carried out to observe the effects of such narrow ΔTj 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. FEA modeling is utilized to verify the stress concentration effect. The experiment results show that the effects of the narrow ΔTj stress cycles are affected by the ageing status of the module and the stress level itself