The formation and evolution of intermetallic compounds formed between Sn–Ag–Zn–In lead-free solder and Ni/Cu substrate

The formation and evolution of intermetallic compounds (IMCs) layer between the Sn–3.7Ag–1.0–In–0.9Zn lead-free solder and Ni/Cu substrate were investigated for different reflow time. The morphology and thickness of the IMCs layer formed at the interface varies apparently with increasing the reflow time. At the early reflow stage, a thin continuous Ni₃Sn₄ dissolved with small amount of Cu is observed. As the reflow time going on, a thick Sn–Ni–Cu ternary intermediate compound layer is formed at the interface after the plated Ni layer is consumed totally. When the reflow time is long enough, a final Cu₆Sn₅ IMC layer dissolved with minor Ni will be formed. The IMCs layer grows very slowly until the plated Ni layer was completely consumed. Once the plated Ni layer disappears, the corresponding growth rate of the IMC layer increases apparently.