Effects of reflow conditions on the formation of Au-Ni-Sn compounds at the interface of Au-Pb-Sn and Au-Sn solder joints with Ni substrate

We investigated the effect of reflow conditions (temperature and time above the liquidus temperature) on the growth, morphology and location of the ternary (Au,Ni)Sn/sub 4/ phase in joints made with Ni or Au/Ni substrates. We considered joints created with Au/sub 0.1/Sn/sub 99.9/ or Au/sub 0.1/Pb/sub 26/Sn/sub 73.9/ solders reflowed on Ni substrates, and Sn/sub 94.35/Ag/sub 3.8/Cu/sub 1.85/ solder reflowed on Au/Ni metallization. The Au/sub 0.1/Pb/sub 26/Sn/sub 73.9/ solder alloy reflowed on a Ni substrate at 185/spl deg/C for 30 s above liquidus and subsequently annealed at 150/spl deg/C gave rise to two layers of intermetallic compounds at the solder/substrate interface, Ni/sub 3/Sn/sub 4/ and (Au, Ni)Sn/sub 4/. However, when this solder alloy was reflowed at 235/spl deg/C for 30 s above liquidus, only one interface layer was observed, Ni/sub 3/Sn/sub 4/, while the (Au,Ni)Sn/sub 4/ ternary phase was found to grow in the bulk of the solder. The SnAgCu/Au/Ni joints were reflowed for 74 s above liquidus and the peak temperature attained was 244/spl deg/C. (Au,Ni)Sn/sub 4/ phase was observed to form in the bulk of these joints upon reflow, with a Cu content less than 1 atomic percent. This intermetallic compound remained in the bulk of the joint as the samples were annealed at 150/spl deg/C up to 261 hours. For the Au/sub 0.1/Sn/sub 99.9//Ni system, only one layer, the Ni/sub 3/Sn/sub 4/ phase, was found to grow at the solder/substrate interface, both after reflow (at 260/spl deg/C for 46 s above liquidus) and for an annealing schedule at 150/spl deg/C of up to 49 hours.