Determination of the thermal and electrical contact resistance in press-pack IGBTs

Press-pack IGBTs are manufactured with a multi-layered structure composed of internal layers with different geometrical shape and physical properties. The device is clamped and an external pressure is applied on the housing in order to establish a sufficient electrical and thermal contact between these layers. The modeling of interlayer contact resistances is necessary to characterize the behaviour of the device in Finite Element Methods (FEM) simulations. However, this modeling task can be difficult since they are pressure sensitive and cannot be easily determined by a direct measurement. This paper presents a method to identify these contact resistances combining FEM analyses with experimental measurements only on the external surfaces of the chip assembly. Indeed, the method procedes with an iterative process where contact resistances are changed according to a genetic search algorithm in order to match the results of the FEM simulations with the experimental measurements.