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

• Thermo-hygro-mechanical stress analysis in a potted electrolytic capacitor.
• Sequential and simultaneous multiphysics FEA analyses.
• Simultaneous FEA handles temperature dependent hygro-mechanical properties.
• Multiphysics FEA model explains reduced leakage rate due to potting compound.
• FEA results are qualitatively supported by combined temperature-humidity cycling experiments.

The focus of this paper is on comparing alternate methods for conducting a multi-physics analysis of the stresses generated in potted electronics by temperature and humidity excursions. This study is motivated by the fact that electronics in consumer electronics are often embedded in a polymeric potting compound, in part to protect the electronics from shock or mishandling damage, and in part to increase the moisture barrier to protect the embedded electronics from moisture assisted failure mechanisms such as corrosion, dendritic growth, and conductive filament formation. However, moisture-induced swelling (expansion) and thermal expansion generates mechanical stresses in the embedded electronics and this can have deleterious effects on the reliability of the electronics. The example considered in this paper is that of aluminum electrolytic capacitors commonly used in driver electronics for solid-state lighting products. Mechanical stresses in the seals are known to affect the electrolyte leakage rates and hence affect the reliability of the capacitors. This paper focuses on multi-physics methods to analyze these stresses. 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.