Analysis of long term reliability of plated-through holes in multilayer interconnection boards Part B: Fatigue results and fracture mechanisms

Abstract

Strain-controlled fatigue experiments were conducted using a specimen designed specifically for modeling the stress distribution in a plated-through-hole (PTH) structure. These tests were conducted to allow critical evaluation of the influence of significant design and material parameters on the long term cyclic life of the PTH. Acoustic emission analysis was performed during each test to elucidate the mechanisms contributing to the copper barrel failure. The results indicate that the most significant improvement in fatigue life is obtained by reducing the substrate-copper barrel interface surface roughness which serves to increase interfacial strength and reduce stress concentrations. The most detrimental effect on fatigue life resulted when the ductility of the copper was reduced. Fatigue test results revealed that delamination along the copper/epoxy-glass interface invariably reduced cyclic lifetime. Fatigue test results were used to derive an expression relating the strain range to the number of strain cycles to failure. This relationship along with the stress analysis results [1] may be used to predict conservative lifetimes of a PTH.