Interface reactions between 50In-50Pb solder and electroplated Au layers

Solid-state interface reactions were investigated when Cu-Fe alloy leads were attached to an electroplated Au layer using 50In-50Pb (wt.%) solder. Two Au layers of different plating process quality were studied. The annealing temperatures were 70, 100, 135, and 170 °C and the times were 1-2000 h. The dominant reaction layer was a composite of (Au, Cu)In2 IMC and Pb-rich phases. A Au9In4 layer remained <2 μm in most specimens. Linear rate kinetics (0.8 < n < 1.2) were observed, indicating an interface-controlled mechanism. The mean apparent activation energy, ΔH, was 56 < ΔH < 73 kJ/mol. The Au9In4, layer growth kinetics parameters were 0.5 < n < 0.9 and 45 < ΔH < 80 kJ/mol, respectively, suggesting a contribution by grain boundary diffusion. Annealing at 100 °C caused significant degradation to the interconnections through extensive void growth, more so for the poor plating process. Void development began with small Kirkendall voids at the In-Pb/Au interface caused by differing diffusion rates of Au and In through the IMC layer. That initial process was sensitive to the Au layer quality. Void enlargement was caused by a dissociation of the (Au, Cu)In2 IMC and Pb-rich phases in the absence of Au flux; this process was insensitive to Au layer quality.