Separation of failure modes in short cycle time power cycling experiments

Performing active power cycling tests is a commonly used method in the power electronics industry to detect different failure mechanisms in a power device, or to get information on their expected life time. The two major failure mechanisms triggered this way includes bond wire degradation or cracks and die attach problems. During the power cycling test process it is very valuable to detect these failures while they are forming. This way beside the time-to-failure data one can also understand the cause of the failure without any offline inspection. In both cases the assessment can be done based on voltage measurements. In case of bond wire degradation the collector-emitter voltage of the devices will increase, however in case of degradation of the thermal path, a similar elevation in the same voltage parameter can be expected. In this article we will present a combination of two evaluation methods - simple voltage reading and structure function based evaluation, which enables distinguishing between the two effects.