Microstructure and mechanical properties of Sn–1.0Ag–0.5Cu solder with minor Zn additions

Low silver (Ag) solder alloys e.g., SAC 105 (Sn–1.0Ag–0.5Cu) have attracted a great deal of attention recently due to economic concerns and improved in impact resistance as compared to other SAC solder with higher silver content. This work studies the influence of addition of minor zinc (0.1–0.5 wt%) to SAC105 on the interfacial structure between solder and copper substrate during reflow and after aging. Zn has shown significant solubility in Cu–Sn intermetallic compound (IMC) and formed Cu₆(Sn,Zn)₅ which resided in the bulk microstructure and at the solder/Cu interface. Results reveal that minor Zn addition decreased the thickness of interfacial Cu₆Sn₅ IMC after reflow and significantly suppressed the growth of interfacial Cu₃Sn after thermal aging without changing the IMC’s morphology. It is suggested that Zn exerts its influence by stabilizing Cu₆(Sn,Zn)₅ and hindering the flow of Sn and Cu atoms at the solder/IMC and IMC/Cu interface. Nanoindentation results showed that Cu₆(Sn,Zn)₅ exhibited a higher hardness in comparison to Cu₆Sn₅ and creep performance of SAC + Zn has improved in comparison to that of SAC105.