Innovative metal system for IGBT press pack modules

Two important design aspects encountered in IGBT press pack modules used for HVDC applications are short circuit failure mode (SCFM) and intermittent operating life (IOL) capabilities. The requirement that press-pack IGBT (PPI) fail safely into a short causes a design conflict with the module's desired capability to survive a high number of power cycles in normal operation. An innovative materials design to optimize this trade-off is described. The failure mechanism that leads to an open circuit after the PPI has operated extensively in SCFM was found to be liquid metal corrosion of the baseplate followed by the formation of intermetallics with poor conductivity and silicone gel degradation. The beneficial effects of dry interface plating materials to avoid thermomechanical fatigue under IOL conditions are described.