M. Ciappa et P. Malberti, PLASTIC-STRAIN OF ALUMINUM INTERCONNECTIONS DURING PULSED OPERATION OF IGBT MULTICHIP MODULES, Quality and reliability engineering international, 12(4), 1996, pp. 297-303
Catastrophic burn-out occurring during power-cycling of insulated gate
bipolar transistor (IGBT) multichip modules has been observed to aris
e as a secondary failure mechanism caused by the lifting of the emitte
r aluminium bonding wires. In fact, the successive lift-off of the alu
minium wires turns in a current crowding through few IGBT cells with c
onsequent triggering of the internal parasitic thyristor-structure. Ba
sed on failure analysis data, this paper presents an exaustive descrip
tion of the symptoms and a simple qualitative model for the time-depen
dent lift-off of aluminium bond wires in IGBT modules. This power-cycl
ing induced failure mechanism (occurring in the field and during accel
erated tests) is described in terms of plastic deformation of the alum
inium interconnections (bond wires and chip-metallization) during puls
ed operation. Some practical conclusions are finally drawn for power c
ycle testing and for optimal thermal design.