Enhanced ductility and mechanical strength of Ni-doped Sn–3.0Ag–0.5Cu lead-free solders

In this paper, the tensile tests were conducted to investigate the effect of adding a small amount of Ni on the microstructure, thermal and mechanical properties of 3.0Ag–0.5Cu(SAC 305) solder. The results indicated that addition of Ni can effectively decrease both the undercooling and the onset melting temperature of SAC(305) solder alloy. The strength and ductility of the SAC(305) solder depend significantly on Ni content. In general, the SAC(305)–0.5%Ni solder reveals superior mechanical properties in terms of maximum strength and ductility when compared to the high Ni-content or plain solders. Microstructure analysis revealed that a new η-(Cu,Ni)6Sn5 intermetallic compound (IMC) phase containing large amount of Ni was generated, while the initial Cu6Sn5 phase was converted into (Cu,Ni)6Sn5 phase after 0.5%Ni addition. Besides, the fine fiber-like Ag3Sn and finer dot-shaped precipitates rather than needle-like morphology have occurred at the surface of β-Sn matrix easily, which could provide more obstacles for dislocation pile up in the adjacent grains and enhanced the mechanical property. With increasing Ni addition, the Ni-doped SAC(305) solder showed a corresponding deterioration in their mechanical property due to the coarsening of (Cu,Ni)6Sn5 IMCs and increasing the inter-particle spacing of Ag3Sn IMCs in the eutectic colony.