Influence of Ni concentration and Ni₃Sn₄ nanoparticles on morphology of Sn-Ag-Ni solders by mechanical alloying

Abstract

The mechanical alloying (MA) process was employed as an alternative method to produce the lead-free solder pastes of Sn-3.5Ag-xNi (x=0.1, 0.5, 1.0, 1.5, and 2.0) in this study. When the Ni concentration was low (x=0.1, 0.5), MA particles agglomerated to a flat ingot with particle sizes >100 µm. For higher Ni concentration (x=1.0, 1.5, and 2.0), MA particles turned into fragments with particle sizes <100 µm. The particle size of the solders appeared to be dependent on the Ni concentration. To reduce the particle size of SnAgNi alloys with low Ni concentration, Ni₃Sn₄ nanoparticles were doped into Sn and Ag powders to derive a Ni₃Sn₄-doped solder. For the Ni₃Sn₄-doped solder, the particle size was smaller than that doped by the pure Ni. The distinction of milling mechanism between Ni₃Sn₄-doped solder and the pure Ni-doped solder by MA process was probed and discussed. In addition, differential scanning calorimetry (DSC) results ensured its feasibility in applying the solder material in the reflow process. Wettability tests between solders and Cu substrate also revealed that the wetting angles for Ni₃Sn₄-doped solder with low Ni concentration (0.1 and 0.5 wt.%) were smaller than those for pure Ni-doped solder. The wetting angles on both Cu substrate and electroplated Ni metallization for SnAgNi solders were also comparable with commercial Sn-3.5Ag and Sn-3.0Ag-0.5Cu solders. Favorable wettability of the as-derived solder in this study was clearly demonstrated.