Effect of the soldering time on the formation of interfacial structure between Sn–Ag–Zn lead-free solder and Cu substrate

Abstract

The evolution of interfacial structure between the Sn–3.7%Ag–0.9%Zn lead-free solder and Cu substrate were systematically explored for different soldering times (1, 5, and 10 min). According to microstructural observations, it is found that the longer the soldering time is, the thicker the soldered interface becomes. The interface soldered for 1 min is composed of the Cu5Zn8 intermetallic compounds (IMCs) layer locating above the Cu6Sn5 IMCs layer. The interfaces soldered for 5 and 10 min are mainly made up of the Cu6Sn5 IMCs with some bulk Ag3Sn IMCs randomly distributing within it. The evolution of the IMCs layer in the soldered interface can be divided into three stages: the Cu5Zn8 IMCs firstly forms, then Cu6Sn5 IMCs separated out from the bottom (controlled by diffusion of Sn in the Cu5Zn8), finally, subsequent growth of the Cu6Sn5 IMCs layer is controlled by diffusion of Sn in Cu6Sn5 IMCs.