Bond wire lift-off in IGBT modules due to thermomechanical induced stress

In this paper the bond wire lift-off failure mechanism experienced in insulated gate bipolar transistor modules, under realistic operation conditions, is investigated theoretically. This failure type is generally believed to be due to thermally induced stress arising from a mismatch in the coefficients of thermal expansion of the materials constituting the module. The theoretical evaluation is based on a finite element approach combined with empirical equations. Here the thermomechanical stress around the bond wire/substrate interface is evaluated. Based on the computations a new approach for characterizing degradation of bond wire junctions is proposed. From this function the lifetime as well as module performance may be evaluated for varying parameters: load, geometry etc.

I. Introduction

Insulated gate bipolar transistors (IGBT) combines the current densities of the bipolar junction transistor with the gate handling capabilities of the ordinary MOSFET. Based on this the IGBT module is today widely used in power electronic systems in e.g. the automotive industry or in energy production. Accordingly, to increase the sustainability of a power electronic system the IGBT modules must be as reliable as possible [1].