PLASTIC-STRAIN OF ALUMINIUM INTERCONNECTIONS DURING PULSED OPERATION OF IGBT MULTICHIP MODULES

摘要

Catastrophic burn-out occurring during power-cycling of insulated gate bipolar transistor (IGBT) multichip modules has been observed to arise as a secondary failure mechanism caused by the lifting of the emitter aluminium bonding wires. In fact, the successive lift-off of the aluminium wires turns in a current crowding through few IGBT cells with consequent triggering of the internal parasitic thyristor-structure. Based on failure analysis data, this paper presents an exaustive description of the symptoms and a simple qualitative model for the time-dependent lift-off of aluminium bond wires in IGBT modules. This power-cycling induced failure mechanism (occurring in the field and during accelerated tests) is described in terms of plastic deformation of the aluminium interconnections (bond wires and chip-metallization) during pulsed operation. Some practical conclusions are finally drawn for power cycle testing and for optimal thermal design.