Influence of nonuniform initial porosity distribution on adhesive failure in electronic packages

Abstract

Adhesives in electronic packages contain numerous pores and cavities of various size-scales. Moisture diffuses into these voids. During reflow soldering, the simultaneous action of thermal stresses and moisture-induced internal pressure drives both pre-existing and newly nucleated voids to grow and coalesce, causing adhesive failure. In this work, a nonuniform initial porosity distribution in the adhesive is assumed. The entire adhesive is modeled by void-containing cells that incorporate vapor pressure effects on void growth and coalescence through an extended Gurson porous material model. Our computations show that increasing nonuniformity in the adhesive's initial porosity f0 drives the formation of multiple damage zones. Under the influence of vapor pressure or residual stresses, interface delamination becomes the likely failure mode in low mean porosity adhesives with nonuniform f0. For high mean porosity adhesives, the combination of vapor pressure and nonuniform f0 distribution induces large-scale voiding throughout the adhesive. Residual stresses further accelerate voiding activity and growth of the damage zones, resulting in brittle-like adhesive rupture. © 2007 IEEE.