| Polymers are increasingly used for all levels of microelectronic devices and their packages because of their low cost, ease of processing, and excellent dielectric and mechanical properties. However, the performance and reliability of such multi-layer structures containing polymer layers are significantly influenced by interfacial adhesion and resistance to debonding of the resulting bimaterial interfaces. Subcritical debonding is of particular concern for packaging applications and is driven by residual stresses, thermomechanical cycling, mechanical or vibrational loading, and moisture uptake. Therefore, to produce reliable devices, it is critical to understand the fundamental mechanisms which determine the critical and subcritical debonding behavior of these interfaces, in terms of mechanical loading, moisture content, and temperature.; Accordingly, this study focuses on quantitatively characterizing and modeling the adhesion and subcritical debonding behavior of a representative polymer/metal interface (silica-filled epoxy polymer/Ni/Cu interface) typically found in the advanced microelectronic packaging applications. Using recently developed interface fracture mechanics techniques, debonding of a bimaterial interface can be quantified in terms of the strain energy release rate, G (J/m2), which represents the interface debond resistance or macroscopic energy required to separate the interface. Mechanisms of failure are identified and related to salient variables including intermediate metal layers (e.g., nickel plating), interface morphology, and plasticity in adjacent ductile polymer layers. The kinetics of environmentally-assisted subcritical debonding or stress-corrosion cracking are rationalized in terms of a stress-dependent chemical reaction occurring at the debond tip and mass transport of the environmental species to the debond tip, and the order of the chemical reaction with respect to water is found to be ∼5 in the reaction-controlled region. Unlike previous studies, plastic deformation of the ductile polymer layer adjacent to the debond is considered. Finally, by including the effect of cyclic fatigue loading, a thermomechanical model which can be used to evaluate the reliability of polymer interfaces is established. The activation energies for near-threshold and intermediate growth rates are found to be 1.51 and 0.57 eV, respectively. Implications for debonding in service and design considerations for promoting adhesion at engineering interfaces are discussed. |
