A combined physicochemical-microstructural approach to predict the crack path at the topside interconnections in IGBT power devices

The thermal fatigue of the bond-wire contacts at the topside interconnections of power electronic devices is one of the main reliability issues. This paper presents a new methodological approach to characterize and model the damages during aging by a combination of fracture mechanics and physicochemical approaches. The approach relies first on correlating the change of the microstructure with aging at the bond-wire contact, then on looking for possible links between the microstructure and the parameters of damage models. After reviewing the effect of the microstructure on the whole cycling process, the correlation is made by relating the driving force of the device failure which is the crack propagation to some physicochemical properties and microstructural parameters such as surface energy (gamma(s)), grain boundary energy (gamma(gb)), misorientation angle between neighbor grains (delta theta), plane of orientation of each singular grain, grain size and hardness values (H). This requires EBSD analysis and some post treatments. Those relationships were then used to configure the effect of the microstructure on cracks passage at the interconnection interfaces using cohesive zone models (CZM).