Reaction Between Thin Gold Wires and Pb-Sn-In Solder (37.5%, 37.5%, 25%), Part B. The Axial Reaction Of Gold Wires Soldered To PbSnIn Solder Mounds, Its effect On Electrical Resistance And Physical Structure.

Abstract

Here we describe the gold-indium reaction along gold wires soldered at both ends. It begins with the combined radial/axial reaction in the vicinity of the solder mound as seen in metallurgical sections along the axis of the wire. We show that this combined radial/axial reaction has no effect on the resistance of the system, even though it shortens the length of the gold wire while converting it to gold indide. After this radial/axial reaction is complete, a purely axial reaction begins. For thin gold wires (i.e. 38.1 {micro}m diameter) the onset of that reaction is strongly correlated with the time at which the linear reaction model predicts the complete consumption of the gold wire inside the solder mounds. This purely axial reaction converts the whole wire rapidly to gold indide, and leads to substantial resistance changes and complete distortion of the wire between the solder mounds. The reaction product is AuIn{sub 2} everywhere, but both Sn and Pb also are identified everywhere on the surface by Electron Dispersive Spectroscopy.