Characterization of dual-stage moisture diffusion, residual moisture content and hygroscopic swelling of epoxy molding compounds

Experimental and FEM studies have been undertaken in order to characterize the non-Fickian behavior of moisture absorption, temperature-dependent residual moisture content and hygroscopic swelling of epoxy molding compounds exposed to moist environments. Moisture absorption and desorption tests of two molding compounds and two IC packages using these materials have been carried out by gravimetric methods. Finite element analysis has been performed to simulate the anomalous dual-stage moisture absorption. To consider the residual moisture remaining in the package after the desorption process, a simple method has been developed, which allows for consideration of bake-out conditions and provides much more flexibility, enabling calculation of the non-Fickian moisture desorption with a specific residual moisture content. The coefficient of moisture expansion (CME) has been also measured by coupling the results of thermal mechanical analyzer (TMA) and Thermal Gravitational Analyzer (TGA) at different temperatures. It has been shown that the moisture desorption model of this study can be used as an alternative for TGA.