Growth and morphology of the intermetallic compounds formed at the Sn–9Zn–2.5Ag/Cu interface

Abstract

The growth and morphology of the intermetallic compounds formed at the solder joint between the Sn–9Zn–2.5Ag lead-free solder and the Cu substrate have been investigated in this study. The planar Cu 6Sn 5 formed after soldering transforms to a scalloped Cu 5Zn 8 after aging at 180 °C for 250 h. However, the Cu 5Zn 8 decomposes and the scalloped Cu 6Sn 5 reforms at the interface close to the solder alloy after aging for 400 h. The η′-Cu 6Sn 5 transforms to the η-Cu 6Sn 5 as aged at 180 °C. The interdiffusion coefficient of Cu and Sn in the Cu 6Sn 5 is determined as 2.58 × 10 −13 cm 2 s −1, and that of Cu and Zn in the Cu 5Zn 8 layers is determined as 3.36 × 10 −14 cm 2 s −1 at 180 °C, from the estimated thickness of the intermetallic compound (IMC). On the other hand, they are determined as 3.43 × 10 −13 and 2.36 × 10 −14 cm 2 s −1, respectively, from the microbeam EDS analysis.