Experimental investigation of time dependent degradation of coupling agent bonded interfaces

Moisture induced delamination between plastic encapsulant and substrate may lead to damage of interconnect and corrosion of metallic components. Coupling agents are widely used as additives in epoxy based encapsulants to improve the adhesive strength by introducing chemical bonding across the interface. The stability of the interfacial bonds is affected by the presence of active chemicals and stresses. Coupling agent chemistry, pH, temperature, and stresses have been observed to affect the rate of adhesion strength degradation and jeopardize the long-term reliability of packages. In this study, the subcritical interfacial debonding process under controlled chemical environment and stresses were quantified. Debonding rate of underfill adhesives with silane coupling agent, titanate coupling agent, and zirconate coupling agent were characterized by the shear fracture tests and the tapered double cantilever beams test under varied temperatures, pHs, and loadings. An analytical procedure was developed to delineate the kinetic parameters of gradual debonding. The implications of the results on subcritical failures of interfacial bonds were discussed with respect to material selection criteria and electronic package reliability.