I. Introduction
Conventional soldering is increasingly replaced by silver sintering as die attachment due to its outstanding reliability [1], [2]. With the substitution of the die attachment, however, the reliability problem has entirely shifted to the top-side electrical contacts, which are usually made of thick aluminium wire bonds [3]. The latest developments have therefore led to new material systems on top of the dies, e.g. sintered metal buffer layers with heavy copper wire bonds. This development improved the lifetime of the electrical contacts and thus of the entire system [4]. These introductions to the thermal layer stack also led to a change in the failure mechanisms and also induce changes to the thermomechanical behaviour of the systems [3]. One of the main root causes of failures of power electronic devices are the thermal strains and stresses caused by temperature variations. In order to contribute to a better understanding of the new failure mechanisms, the thermo-mechanical behaviour in active operation is therefore investigated. The investigations in this work were carried out with respect to the total operating time of the test module.