Microstructure and properties of Sn-3.8Ag-0.7Cu-xCe lead-free solders with liquid-liquid structure transition and Ce addition

Our previous work suggested that the Sn-3.8Ag-0.7Cu-xCe (x takes 0%, 0.2%, 0.5% and 1.0wt%) solder melt experienced a temperature-induced liquid-liquid structure transition (L-LST) which was reversible during two heating and cooling cycles far above the liquidus. In this work, the effects of liquid state manipulations and rare earth element Ce addition on solidified Sn-3.8Ag-0.7Cu-xCe structures and properties were investigated. The results revealed that the microstructure was remarkably refined, the spread ability and the shear strength were enhanced when the melt experienced L-LST and Ce addition. Meanwhile, 0.2 wt% Ce addition showed the most homogenous microstructure, leading to better properties. This work elicited that melt manipulations and Ce addition could be an effective way to optimize microstructure and properties of Sn-3.8Ag-0.7Cu-xCe soldered joints.