Influence of chemistry and applied stress on reliability of polymer and substrate interfaces

Epoxy-based underfills in flip-chip assembly have been widely employed to enhance electronic package reliability. Addition of coupling agent in the underfill encapsulant can increase the adhesive bonding by introducing chemical bonding across the interface. The stability of this interfacial bonding is depended on the active chemicals and residual stress from curing and thermal mismatch present at the interface. The effects of chemicals and stresses have been independently observed to accelerate debonding. A model of the combined influence of stress and chemistry on the debonding rate has been proposed, but data on the combined influence of chemical and stress are not available. In this study, the stress-assisted interfacial debonding of epoxy adhesives is quantified. Underfill adhesives with silane coupling agent, titanate coupling agent, and zirconate coupling agent were characterized. Basic material properties including the curing behavior, coefficient of thermal expansion, glass transition temperature, elastic modulus and moisture absorption profile were measured by differential scanning calorimetry, thermal mechanical analysis, 3-point bending test and dynamic mechanical analysis. Debonding rates of adhesives under varied applied stress conditions were characterized using tapered double cantilever beam specimens. The implications of the data and the kinetic parameters on material choices are discussed with respect to electronic packaging reliability