Interface microstructure evolution of lead-free solder on Ni-based under bump metallizations during reflow and high temperature storage

The interface microstructure evolution between SnCuAg lead-free solder and Ni-based alloys under bump metallization (UBM) systems are studied using transmission electron microscopy (TEM). Details on microstructure changes during reflow process and high temperature storage have help to understand some of the reliability concerns on using Pb-free solder in flip-chip packaging technology.