This paper presents a method of finite element analysis for calculating moisture concentration in non-isothermal and non-steady states of moisture for integrated circuit packages composed of dissimilar moisture-permeable materials. The method can address non-Fickian behavior of materials in moisture diffusivity. Specimens were put on a hot plate after pre-conditioning in a moist environment. Distribution of moisture concentration in the specimen used in adhesion strength measurement was calculated in the temperature-change process. Comparatively large change in moisture concentration occurs in the neighborhood of the dissimilar material interface during that process, demonstrating that adhesion strength between die-attach material and printed circuit board at high temperatures might have greater moisture-sensitivity than at low temperatures.

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