The kinetics of formation of ternary intermetallic alloys in Pb-Sn and Cu-Ag-Sn Pb-free electronic joints

A simple model of the formation of Au/sub 0.1/Ni/sub 0.1/Sn/sub 0.8/ in Pb-Sn solder/Ni interconnects is examined by numerical simulation. Previous experimental observation has shown that after reflow the interface consists of the Ni/sub 3/Sn/sub 4/ alloy between Pb-Sn solder and Ni, with Au distributed through the PbSn solder ball. Au/sub 0.1/Ni/sub 0.1/Sn/sub 0.8/ was observed to form at the Pb-Sn solder/Ni/sub 3/Sn/sub 4/ interface during annealing at 150/spl deg/C in a number of studies. The numerical simulation was used to calculate the maximum flux of Au to the interface, and with the assumption that this Au was immediately incorporated in to Au/sub 0.1/Ni/sub 0.1/Sn/sub 0.8/ a maximum rate of formation of Au/sub 0.1/Ni/sub 0.1/Sn/sub 0.8/ was calculated. This rate was found to be similar to measured rates of formation of Au/sub 0.1/Ni/sub 0.1/Sn/sub 0.8/ from two different studies. The formation of(CuNi)6SnS in Sn-Ag-Cu/Ni solder interconnects was discussed within the context of these observations.