Effect of rapid solidification on microstructure, creep resistance and thermal properties of Sn-10 wt.% Sb- 3 wt.% X (X= In, Ag, Bi and Zn) lead-free solder alloys

The harmful effects of lead on the environment and human health, coupled with the threat of legislation, have prompted a serious search for lead-free solders for electronic packaging applications. The melt-spinning processes of ternary Sn-10 wt.%Sb-3 wt.%X (X=In, Ag, Bi and Zn) were analyzed using x-ray diffractometer (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Vickers hardness tester (HV). The investigation showed that, the addition of a small amount of the third element enhances the ductility of the Sn?10 wt.% Sb lead-free solder due to the formation of a fine, homogeneous ternary microstructure.. It is concluded that, the addition of 3.0 wt% Ag improves the grain size of the ternary microstructure. Moreover, SnSb intermetallic compound, precipitated finely from the solid tin solution near the grain boundaries with antimony. This fine precipitated intermetallic compound suppresses the coarsening of the ternary structure and thus enhances solder ductility. Structural and microstructural analysis revealed that the origin of change in mechanical behaviors was due to refined beta-Sn grains and formation of intermetallic compounds (IMCs) SnSb, InSn19, β-In3Sn and Ag3Sn. The results indicated that the melting point of Sn-10Sb-3 wt.% Ag and Sn-10 wt.%Sb- 3 wt.% Zn alloys reduced to 230 and 240 ˚C respectively. In particular, the zinc addition at 3 wt.% is the most effective in improving solder ductility. The good creep resistance of Sn-10 wt.% Sb-3 wt.% Zn lead-free solder correlated to a large β-Sn grain size and complete soluble of SnSb IMC particles in the β-Sn matrix.