Influence of non-uniform initial porosity distribution on adhesive failure in electronic packages

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 non-uniform 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 non-uniformity in the adhesive's initial porosity shifts the damage zone from the crack plane to sporadic sites between the crack plane and the film-substrate interfaces. For low porosity adhesives with non-uniform initial porosity distribution, internal pressure promotes extensive damage along the film-substrate interfaces. For high porosity adhesives, the combination of vapor pressure and non-uniform initial porosity distribution induces large-scale voiding throughout the adhesive, causing catastrophic failure.