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.