On the operation of a press pack IGBT module under short circuit conditions

Press pack insulated gate bipolar transistor (IGBT) modules connected in series for high-voltage direct current (HVDC) converter applications are designed such that when a failure occurs, it occurs in a safe manner by the formation of a stable short circuit, while redundant modules take up the voltage blocking function of the failed module. One such design using individual pressure contacts is described and the events occurring from the initiation of the short circuit to its final failure due to open circuit are reported from an electronics packaging materials design point of view. Experiments to hasten the failure under accelerated test conditions on modules were performed and interrupted at various stages of operation under a short circuit condition. The formation and subsequent aging of the metallurgical alloy under short circuit conditions was investigated by analyzing cross sections of the alloy forming the short circuit. Liquid metal corrosion along with the formation of intermetallics with poor conductivities lead to the final failure by open circuit