Evolution of thermal property and creep resistance of Ni and Zn-doped Sn–2.0Ag–0.5Cu lead-free solders

• Small amount of Ni and Zn have been added into SAC (205) solder.
• Ni and Zn enhanced the formation of new (Cu,Ni)6Sn5 and Cu5Zn8 IMCs.
• Correlations between the microstructure and creep parameters were analyzed.
• Ni and Zn can effectively reduce the undercooling and solidus temperatures.
• Ni and Zn provide about 190–450% higher creep resistance than in SAC (205) solder.

The effect of small amount of Ni and Zn additions on thermal behavior and creep properties of Sn–2Ag–0.5Cu (SAC 205) lead free solder alloy was investigated. Additions of Ni and Zn, respectively, into SAC (205) solder caused its undercooling temperature to decrease significantly from 26.1 °C to 18.0 and 1.4 °C. The results show that the formation of new (Cu,Ni)6Sn5 and Cu5Zn8 hard particles in the β-Sn matrix are drastically strengthen the SAC (205) solder. The lead-free SAC (205) – 0.5Zn solder joints showed superior creep resistance in terms of much lower creep rate and elongated creep fracture lifetime over the traditional SAC (205) and SAC (205) – 0.05Ni solders. However, the ductility of SAC (205) – 0.5Zn alloy is lower than that of the other two alloys. This difference was attributed to the lower precipitate coarsening and higher precipitate density of Cu5Zn8 and Ag3Sn IMCs in Zn-doped SAC (205) cast alloy, which could provide more obstacles for dislocation pile up in the adjacent β-Sn grains. Nevertheless, the strengthening effect depends on the undercooling of the solder.