FATIGUE-CRACK PROPAGATION ALONG POLYMER-METAL INTERFACES IN MICROELECTRONIC PACKAGES

In this study, a fracture mechanics-based technique was used for chara cterizing fatigue crack propagation (FCP) at polymer-metal interfaces, Sandwich double-cantilever beam (DCB) specimens were fabricated using nickel and copper-coated copper substrates banded with a thin layer o f silica-filled polymer encapsulant, Under cyclic loading, crack propa gation was found to occur at the polymer-metal interface, The interfac ial failure made was verified by scanning electron microscopy (SEM) an alysis of the fatigue fracture surfaces, The crack growth rate was fou nd to have a power-law dependence on the strain energy release rate ra nge, and exhibited a crack growth threshold, much like the fatigue cra ck growth threshold stress intensity factor range for monolithic bulk metals, polymers, and ceramics, interfacial FCP data for three candida te encapsulants predicted cracking resistances that were well correlat ed with package-level reliability tests, By varying the surface roughn ess of the copper anal nickel plating, it was shown that interfacial F CP resistance increased with increasing roughness, The observed increa ses in FCP resistance were attributed to a reduction in the effective driving force for fatigue fracture along the rougher interfaces, and c ould be accounted for by a crack-deflection model.