Effect of Zn addition in Sn-rich alloys on interfacial reaction with Au foils

To restrain the formation of AuSn x intermetallic components (IMCs) in solder joints, Zn was added into Sn-rich solders. The solder joints were fabricated by a laser reflow soldering method, and then they were aged at 125 °C. The results show that the total thickness of AuSn x IMCs at the interface of pure Sn solder and Au foils reaches about 54 μm under the condition of 600 h aging. In Sn-1.5Zn solder joints, however, formation of AuSn 4 IMCs is restrained greatly. As the content of Zn in the solder is increased to 3.5%(mass fraction), no AuSn 4 IMC is observed at the interface. Au-Zn phases form beside AuSn 2 and AuSn IMCs layers. As for Sn-9.0Zn solder joints, Au-Zn and Au-Zn-Sn phases and few AuSn x IMCs form at the interface. Moreover, total thickness of the phases and IMCs is far less than that of AuSn x IMCs in the pure Sn solder joints.