Intermetallic compound layer formation between Au and In-48Sn solder

Recently, the harmful effects of Pb on the environment and human health have prompted widespread research on Pb-free solders for electronic packaging applications (1,2). Most of this research has been devoted to surface-mounting technology (SMT), with some also on flip chip attach (FCA), which gives smaller and lighter packages. In conventional FCA technology, Sn-Pb solder is generally used for chip bump and substrate bump materials (3), although Au has been used as a chip bump material for new applications (4), with indium based solders used as substrate bumps in order to release the thermal stress. It has been reported that In-48Sn (in wt%) solder has an excellent joint lifetime as regards thermal cycle stress (4). It shows promise as a Pb-free solder for FCA joints, although there are limited data available on the diffusion and growth of intermetallic compounds at the boundary between the Au and In-48Sn solder. The work described in this paper was performed to study the growth kinetics of the compounds formed on the boundary between the Au and In-48Sn solder in bulk diffusion couples.