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)Sn₄ phase in joints made with Ni or Au/Ni substrates. We considered joints created with Au_0.1Sn_99.9 or Au_0.1Pb₂₆Sn_73.9 solders reflowed on Ni substrates, and Sn_94.35Ag_3.8Cu_1.85 solder reflowed on Au/Ni metallization. The Au_0.1Pb₂₆Sn_73.9 solder alloy reflowed on a Ni substrate at 185°C for 30 s above liquidus and subsequently annealed at 150°C gave rise to two layers of intermetallic compounds at the solder/substrate interface, Ni₃Sn₄ and (Au, Ni)Sn₄. However, when this solder alloy was reflowed at 235°C for 30 s above liquidus, only one interface layer was observed, Ni₃Sn₄, while the (Au,Ni)Sn₄ 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°C. (Au,Ni)Sn₄ 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°C up to 261 hours. For the Au_0.1Sn_99.9/Ni system, only one layer, the Ni₃Sn₄ phase, was found to grow at the solder/substrate interface, both after reflow (at 260°C for 46 s above liquidus) and for an annealing schedule at 150°C of up to 49 hours.