Inhibiting the growth of Sn whisker in Sn-9Zn lead-free solder by Nd and Ga

Abstract

The effect of Nd and Ga additions on Sn whisker growth inhibition in Sn–9Zn solder is newly reported in this work. After ageing treatment at room temperature and 125 °C for over 4 months, no Sn whisker growth was observed in the joints soldered with Sn–9Zn–0.5 Ga–0.08Nd and Sn–9Zn–0.5 Ga–1Nd solders. XRD analysis shows that the formation of GaNd and GaNd3 compounds instead of SnNd compound is the key factor. Because the Gibbs formation free energies of GaNd and GaNd3 are more negative than that of SnNd, the GaNd and GaNd3 compounds are relatively more stable, no free Sn atoms released during exposure and oxidizing reaction to feed the Sn whisker growth. EDX analysis was also identified that the formation of Ga–Nd compounds substituted for the Sn–Nd IMC is the main factor that inhibited the spontaneous growth of Sn whisker.