Investigation for Highly Reliable Free Air Ball Formation for Silver Bonding Wire

Application of Ag bonding wire is expected to grow as a low cost alternative to Au bonding wire. Ag wire is a relatively new material for bonding wire, and its optimum condition for Free Air Ball (FAB) formation process is not well known. In this paper, effects on discharge parameters, especially discharge patterns, on the FAB formability of Ag wire are studied. The results show that the two-step discharge mode and slope discharge mode are both effective for the suppression of off-center FAB, which is often observed in Ag wire. The high speed camera analysis also reveals the process of off-center ball correction during two-step discharge mode and slope discharge mode. The results of this study are useful for robust and reliable formation of high sphericity FAB in Ag wire.