Effect of Sb and Ag additions on the melting and solidification of Sn-Bi solder alloys

Low temperature solders based on tin-bismuth (Sn-Bi) are used as substitutes for tin-silver-copper (Sn-Ag-Cu, SAC) alloys, reducing warpage-induced defects and reflow temperature. Understanding the effects of microalloying elements on the solder mechanical, microstructural, and thermodynamic properties constitute an essential part of alloy design. This study focuses on the changes in melting and solidification behavior of near-eutectic Sn-Bi alloys with antimony (Sb, 0.5–2 wt%) and silver (Ag, 0–1 wt%) additions. Our differential scanning calorimetry studies show that addition of Sb increases the melting temperature of the alloy and reduces the amount of undercooling, while the addition of Ag has a minimal effect on the melting and solidification behavior. Of note is the melting temperature between the initial melting of as-solidified solders and subsequent cycles in Sb-containing alloys decreases. Microstructural and thermodynamic analysis reveals that the distribution of solute Sb atoms in as-received, more rapidly solidified alloys compared with reflowed alloys is likely the cause of the difference in melting behavior. Graphical abstract