Influence of Vapor Pressure on Rate-Dependent Void Growth in IC Packages

IC packages exposed to humid environment are susceptible to thin film adhesive failures during reflow soldering. Under reflow temperatures, moisture trapped in the micropores of the polymeric adhesives vaporizes and induces vapor pressure within these voids, accelerating failure via void growth. In this work, a computational discrete void approach is adopted to study the rate-dependent void growth in the adhesive layer under the influence of vapor pressure. The model problem consists of a ductile adhesive layer with a centerline crack, sandwiched between two elastic substrates. The adhesive thin film is modeled by a non-linear viscoelastic material model. Damage in the adhesive is confined to a single row of discrete voids placed ahead of the crack tip. Void growth and the damage mechanism of the viscoelastic thin film adhesive is observed to be different from that of adhesives modeled as elastic-plastic; non-uniform void growths are observed for the initial porosity levels considered, and that the voids prolate during loading. Large-scale adhesive damage is predicted under vapor pressure assisted voiding. Our study also offers findings of initial void´s aspect ratio and spacing between neighboring voids playing significant roles in aggravating adhesive damage and failure.