New Lifetime Model for Advanced Power Semiconductor Interconnects

Within the scope of this work a new lifetime model for IGBT power modules with advanced assembly and interconnection technology for operation under harsh conditions is developed. The lifetime of the tested specimens is investigated for temperature cycles of usual acceleration and also for conditions significantly beyond specified limits. In addition, the influences of the mean temperature (Arrhenius relationship) and the load pulse duration are determined and modelled. From the failure analyses, a new failure mechanism was found, that appears apart from the already widely studied lift-off of the bond wires and fatigue of the soldered die attachment. Failures appear in the form of cracks propagating in the top-side metallisation of the semiconductors. Evidence for the new failure mechanism was demonstrated over the entire range of experimental parameters. This justifies the investigated highly accelerated test conditions. Consequently, the time-to-failure of these specific reliable interconnects can be reduced from several months under conventional test conditions to one day with highly accelerated test conditions.