Ex-situ observation of microstructure evolution and electrical resistance transition in micro joints under electron current stressing

Abstract

Micro joint fabrication is a prevalent technology for microelectronic industry and the joint electrical and mechanical integrities significantly impact the electronic package reliability. In this study, the transitions in electrical resistance and crystallographic characteristics (grain orientation and size) of micro joints upon electron current stressing was characterized using an ohmmeter and an electron backscatter diffraction analysis system equipped in a field-emission scanning electron microscope. A significant decrease (approximately 7 %) in the joint electrical resistance accompanied with β-Sn grain reorientation and grain boundary elimination was induced in a few hours of the current stressing test. Mayadas-Shatzkes (M-S) model was employed to evaluate the contribution of grain boundary characteristics to the resistance drop, and revealed that approximately 85 % resistance drop was caused by the Sn grain reorientation and the remaining part (approximately 15 %) was by the grain boundary elimination. This quantitative analysis advanced the fundamental understanding of micro-joint characteristics in electrical transition induced by electromigration. Finally, a mitigation strategy of electromigration-induced β-Sn crystallographic and electrical transitions was proposed in this study.