Effects of antimony on the microstructure, thermal properties, mechanical performance, and interfacial behavior of Sn–0.7Cu–0.05Ni–xSb/Cu solder joints

We investigated a new, lead-free solder alloy to replace traditional lead-based solder alloys. A Sn–0.7Cu–0.05Ni solder alloy was formulated and 1.0 and 2.0 wt%Sb were added to improve the microstructure, thermal properties, and mechanical properties of the alloy. The microstructure of the solder alloy was refined by the addition of Sb. The Cu6Sn5 and (Cu, Ni)6Sn5 IMC phases were smaller when 2.0 wt%Sb was added. SnSb solid solution phases formed in the solder matrix. The melting point and melting range of the solder alloy slightly increased with the addition of Sb. The addition of 2.0 wt%Sb reduced undercooling from 38.8 to 27.1 °C. The addition of Sb increased the ultimate tensile strength and hardness of the Sn–0.7Cu–0.05Ni solder alloy but the solid solution strengthening effect reduced ductility. The microstructure and shear strength of solder joints at the interface of Cu substrates were investigated. The interfacial layers of all solder joints comprised (Cu, Ni)6Sn5 and Cu3Sn IMC layers. The presence of Sb in the solder alloy reduced the thickness of the IMC layers and the shear strength of solder joints increased. Thus, the addition of Sb refined the microstructure, reduced undercooling, and improved the mechanical performance of solder joints. The results of this research work can be applied to produce solder wire for use on electronic circuit boards.