New lead-free, Sn-Ag-Zn-Cu solder alloy with improved mechanical properties

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Abstract
A new, lead‐free solder alloy based on Sn‐3.5%Ag‐1%Zn‐0.5%Cu is described. The alloy exhibits mechanical properties superior to those in both the Sn‐3.5%Ag binary and Sn‐3.5%Ag‐1%Zn ternary eutectic solder alloys. The addition of small amounts of Cu, at less than 1% levels, is found to refine the effective grain size while retaining the uniform distribution of Ag3Sn precipitates in the solidification microstructure, thus significantly improving the ductility. The addition of excess amounts of Cu or Zn beyond about 1% levels is not desirable as it causes precipitation of additional intermetallic phases that depletes the finely dispersed precipitates in the surrounding matrix and induces nonuniformities in the microstructure that consequently deteriorate the mechanical properties.

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