Evolution of intermetallic compounds layers in the soldered Sn–3.7Ag–1.0In–0.9Zn/Cu interface

The formation and evolution of intermetallic compounds (IMCs) layer between the Sn–3.7Ag–1.0In–0.9Zn lead-free solder and Cu substrate were investigated for different soldering periods. The structure of the IMCs layer in the soldered interface varies apparently with increasing the soldering time. The interface soldered for 1 min is composed of a thick Cu5Zn8 layer and a thin Cu6Sn5 IMCs layer, which are separated by an intermediate solder layer. When the soldering time reaches 3 min, both the Cu5Zn8 and Cu6Sn5 layers grow thicker towards the middle solder layer, with the Cu5Zn8 layer much thicker than the Cu6Sn5 one. Later the Cu5Zn8 layer will decomposed completely and the Cu6Sn5 layer will grow prominently when the soldering time reaches 4 min. The evolution of the soldered interfacial structure was discussed in view of the governing factor for the atomic diffusion through the intermediate solder layer.