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

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 Cu6Sn5 formed after soldering transforms to a scalloped Cu5Zn8 after aging at 180 °C for 250 h. However, the Cu5Zn8 decomposes and the scalloped Cu6Sn5 reforms at the interface close to the solder alloy after aging for 400 h. The η′-Cu6Sn5 transforms to the η-Cu6Sn5 as aged at 180 °C. The interdiffusion coefficient of Cu and Sn in the Cu6Sn5 is determined as 2.58 × 10−13 cm2 s−1, and that of Cu and Zn in the Cu5Zn8 layers is determined as 3.36 × 10−14 cm2 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 cm2 s−1, respectively, from the microbeam EDS analysis.