Primary solidification phases of the Sn-rich Sn-Ag-Cu-Ni quaternary system

The eutectic and near-eutectic Sn-Ag-Cu solders are the most promising lead-free solders, and nickel is frequently used as the barrier layer material. Nickel dissolves into the molten Sn-Ag-Ni alloy during the soldering process, and the ternary solder becomes a Sn-Ag-Cu-Ni quaternary melt near the nickel substrate. Liquidus projection is the projection of the liquidus trough and it delineates the boundaries of various primary solidification phases. Information of liquidus projection is helpful for understanding the alloys’ solidification behavior. This study prepared the Sn-Ag-Cu-Ni alloys of various compositions at the Sn-rich corner. The alloys were melted at higher temperatures and solidified in air. The solidified alloys were metallographically examined to determine the phases formed, especially the primary solidification phases. No ternary or quaternary compounds were found. The knowledge of the primary solidification phases, phase formation sequences, and reaction temperatures determined in this study were put together with all of the available liquidus projections of the constituent ternary systems to determine the primary solidification phases of the quaternary Sn-Ag-Cu-Ni system at the Sn-rich corner.