Combined Reliability Testing: An approach to assure reliability under complex loading conditions

Reliability tests, which combine different loading types, come into the focus of research activities. One reason can be given by their ability to enable test acceleration. Based on an understanding of failure mechanisms, tests can be developed, which indicate robustness of power devices with respect to loads like mechanical loads (vibration, bending), moisture, temperature and temperature cycling. On the other hand the real life use conditions of modern electronic modules are characterized by a combination of different loading types, which occur in a sequential and parallel manner. Hence robustness validation methods which consider combined loads are needed. Our results on solder interconnect and polymer-silicon interface reliability are assembled in this publication. They show that competing and interacting failure mechanisms occur. Depending on the ratio of loading types different mechanisms dominate the degradation process. Therefore it is concluded that a combined load test is not in general relevant for qualification of complete modules or systems. To cover for the observed effects, a development and application of lifetime models of the potential failure mechanisms and their interaction is needed. The approach is exemplified on solder interconnects under vibration and thermal cycling loads, but can be transferred to other coupled failure mechanisms.