Multi-physics simulations for combined temperature/humidity cycling of potted electronic assemblies

The focus of this research is to conduct a multi-physics analysis of the effect of cyclic temperature and humidity on embedded electronics. The motivation of this study is from the potted electronics often seen in consumer electronics to protect the electronics from shock or mishandling damages. In some cases another reason of potting the driver electronics is to create a resistance in the path of moisture to protect metal components of the driver electronics from corrosion. One application where these potted electronics are currently being used is in the driver electronics of solid state lighting products. Although the potting compound is used to increase the reliability of the driver electronics, on the downside the existence of the potting compound will have a direct effect on the stress distribution of the driver electronics. Therefore, it is important to understand the effects of the potting compound on critical failure modes in the driver electronic system. Examples of relevant failure modes are: degradation of electrolytic capacitors due to stress-induced changes in the electrolyte escape rate; stress-induced failures in surface mount components and their interconnects; delamination from the PWB resulting in moisture traps adjacent to the PWB metallization. The first step in this understanding is a better characterization of the stress fields caused by potting compounds due to the manufacturing process and expansion and contraction caused by thermo-mechanical and hygro-mechanical effect under temperature and humidity cycling environments. In this paper we investigate the resulting cyclic stress and strain history in an embedded electrolytic capacitor, to verify whether the potting compound can play a significant role in capacitor degradation. The results show that the stress exerted by the potting compound is not a significant concern and accelerated stress test results are found to qualitatively support this finding.