Requirements in power cycling for precise lifetime estimation

This paper discusses power cycling as a method to evaluate the reliability of interconnections in power electronic devices. While the approach proved a reliable tool for investigating the potential of improvement for alternative interconnect technologies and rejecting design flaws, precise estimations about lifetime in the field are still challenging. Many questions are still in discussion, such as ultra-high cycle fatigue, applicability of Miner's rule, or the influence of on-time and cross-effects with mechanical shocks or humidity. This leaves application engineers with a blurred safety margin. In the following basic considerations of power cycling are described. The introduction shows two applications with different load profiles. Section 2 explains methods of temperature measurement. In Section 3 theoretical requirements for measurement accuracy are given, the obstacle minimal measurement delay and possible workarounds are evaluated. Finally aging effects and their acceleration in different devices are discussed in Section 4. In the conclusion suggestions for power cycling methods and a revision of the end-of-life criteria are made. (C) 2015 Elsevier Ltd. All rights reserved.