Sn-Cu based solders have been widely investigated due to their good mechanical properties, good fluidity, narrow melting range, environmental friendliness, and low price. In this paper, the effect of Ni content on the microstructure, mechanical properties, melting behavior, spreadability, and conductivity of Sn-0.7 Cu-xNi (0.5-2.0 mass%, mass fraction except when specified) lead-free solders was studied. The Sn-0.7Cu-xNi (x = 0.5, 1.0, 1.5, and 2.0) solder alloys consisted of a b-Sn solid solution, Ni 3 Sn 4 phase, and Cu 6 Sn 5 phase. The volume fraction of Ni 3 Sn 4 increased with increasing Ni content. The addition of Ni increased the solidus and liquidus temperatures of the Sn-0.7Cu-xNi solder alloys. However, the melting range of the Sn-0.7Cu-0.5Ni and Sn-0.7Cu-1.0Ni solder alloys is lower than that of the Sn-0.5Cu solder alloy. The spreading area of the Sn-0.7Cu-xNi solder alloy first increased and then decreased with increasing Ni content. Moreover, the ultimate tensile strength and hardness of the Sn-0.7Cu-xNi solder alloy increased gradually with increasing Ni content. The Sn-0.7Cu-2.0Ni alloy has maximum ultimate tensile strength and hardness values of 52.01 MPa and 16.45 Hv, respectively. However, the electrical conductivity of the Sn-0.7Cu-xNi solder alloy decreased with increasing Ni content. These changes in performance related to the formation of the intermetallic Ni 3 Sn 4 phase. The Sn-0.7Cu-1.0Ni solder alloy had the best comprehensive performance in the present experiment. For the Sn-0.7Cu-1.0Ni solder alloy, the expanded area was 1.28 times that of the Sn-0.7Cu alloy, and the liquidus temperature, melting range, strength, hardness, and resistivity of the alloy solder were at the intermediate level among the Sn-0.7Cu-xNi solder alloys. Therefore, the Sn-0.7Cu-1.0Ni alloy is a relatively ideal solder alloy with a good comprehensive performance among the Sn-0.7Cu-xNi solder alloys.
