Adhesive strength and tensile fracture of Ni particle enhanced Sn–Ag composite solder joints

This study forms composite solders by adding 0.5–3 wt% of Ni particles in situ to Sn–3.5 wt%Ag lead-free solder. Cu/solder/Cu specimens are prepared by dipping two Cu rods into a solder bath to produce a solder joint. Some of the joint specimens are retained in the as-soldered condition, while the others are aged at 150 °C for 100, 200, 400, or 500 h, respectively. The experimental results reveal that the addition of Ni to the molten Sn–Ag solder leads to the formation of in situ Ni3Sn4 dispersoids. The adhesive strength of the joint is found to increase with increasing Ni content in the as-soldered specimens. In general, the strength of the thermally processed specimens reduces as the thermal storage time increases. The Sn–Ag–0.5 wt%Ni joints show a mixture of ductile and brittle fracture, whereas the joints containing more than 1 wt% of Ni show mainly brittle fracture with solder residue at the exposed (Cu,Ni)6Sn5 IMC layer.