Estimating the Engineering Properties of Electronic Packaging Materials

Silica-filled epoxy composites represent an important class of electronic packaging materials. In this paper, a series of semi-empirical equations are proposed for estimating the density, temperature-dependant modulus, expansion coefficient and Poisson´s ratio of silica-filled epoxy composites as a function of the silica content and glass transition temperature. The density and expansion coefficients are calculated using the rule of mixtures, while the composite moduli in the glassy and rubbery plateaus are derived using the Halpin-Tsai equation, the theory of rubber visco-elasticity, and elementary considerations of the polymer cross-link density. A four-parameter sigmoidal function is shown to account well for the composite stiffness in the transition region between the glassy and rubbery states, while a three-parameter single rise to maximum equation expresses the change in the composite´s Poisson ratio with silica content. The models are corroborated against a large data library of actual packaging materials. Their usefulness in calculating e.g., the warpage in a plastic ball-grid array package is demonstrated in a worked example.