Moisture diffusion in electronic packages. I. Transport within face coatings

Abstract

This paper reports the use of interdigitated aluminum electrodes to detect moisture ingress into molded electronic packages. Interdigitated aluminum metal lines deposited on polyimide-insulated silicon chips were used as capacitors. These structures have been used in the past to study moisture diffusion into polyimide. The study extends the usefulness of such devices to the evaluation of the effectiveness of an encapsulation. The following parameters are being investigated: physical characteristics of the encapsulation (filler size and shape, filler loading, and degree of cure of the resin), thickness of the coating, configuration of the package (molded vs face coating), relative humidity, and temperature of the surrounding medium. At a constant thickness of a silica filled coating, dual-mode sorption was observed with permeation decreasing with increasing volume fraction of fillers. It was also found that the saturation values of water absorbed were determined once the higher temperature of the test cycle was defined. Such differences with the hygro-thermal history of the samples could be explained in terms of microcavities formed by crazing of the matrix exposed to severe environmental conditions.