Properties enhancement of low Ag-content Sn–Ag–Cu lead-free solders containing small amount of Zn

• Small amounts of Zn have been added into Sn–1Ag–0.3Cu solder.
• Zn addition refined the microstructure and developed the formation of (Cu, Ag)5Zn8.
• This effect enhanced significantly both the mechanical property and ductility.
• Zn can also reduce the undercooling and pasty range.

This study examines the effect of Zn addition on the microstructure, melt properties and tensile behavior of low Ag-content Sn–1.0Ag–0.3Cu (SAC103) lead-free solder. The results show that addition of 2.0 wt.% Zn to SAC(103) solder resulted in an excessive tensile strength and low ductility, which may be attributed to the dual effect of grain refinement and formation of course (Cu, Ag)5Zn8 intermetallic compound (IMC) particles. Meanwhile, the alloy with 3.0 wt.% Zn exhibited both the highest strength and large ductility, which may be due to the high volume percentage of fine (Cu, Ag)5Zn8 particles and fiber-like Ag3Sn precipitates. These eutectic micro-constituents contributed more significantly to the obstacles for dislocation pile-up along the slip systems in Zn-containing SAC(103) solders, as it shows better deformation resistance than the plain SAC(103) solder. Besides, the addition of Zn not only reduced the liquidus and melting temperatures, but also decreased the undercooling and pasty range of SAC(103) solder.