Fatigue crack propagation in a copper/epoxy molding compound interface as impacted by mode-mixity

Abstract

Microelectronic packages contain numerous bimaterial interfaces which influence both device design and reliability. The failure of these bimaterial interfaces have been observed to be a function of both the relative shear and tensile loads, otherwise referred to as “mode-mixity.” While the failure of such bimaterial interfaces has been the focus of much study, their performance under fatigue, in particular with respect to mode-mixity, is underexplored. Double cantilever beam tests for a copper /epoxy molding compound interface have been performed for several different mode-mixity conditions, both monotonically and cyclically. The resulting Paris’ laws are reported. In particular, the impact of mode-mixity on fatigue crack propagation is explored. The Paris’ law coefficients and exponents have been seen to be dependent on mode-mixity. The dependency of fatigue behavior on mode-mixity means that some of the properties of fatigue crack propagation can be determined from a bimaterial interfaces monotonic fracture behavior. Finally both numerical analysis in ANSYS and SEM surface characterization are performed to further the understanding of the mechanisms behind the observed trends in fatigue interfacial delamination propagation behavior as a function of mode-mixity.