Interfacial reactions in the Au/Sn-xZn/Cu sandwich couples

Abstract

Abstract The interfacial reactions in the Au/Sn-Zn/Cu sandwich couples were investigated. The Sn-xZn/Cu couples were reflowed at 270 °C for 1 h and then clamped together over an Au foil. These Au/Sn-Zn/Cu sandwich couples were aged at 160 °C for various periods of time. The AuSn, AuSn2, and AuSn4 phases were formed at the Sn-1Zn/Au interface when the Au/Sn-1 wt% Zn/Cu sandwich couple was aged for 20 h, the Cu6Sn5 phase was also observed between Au-Sn intermetallic compounds (IMCs) and solder. This result revealed that Cu atoms rapidly diffused through the Sn-1Zn solder to form Cu-Zn IMC on the Au side. The Au-Sn IMCs, Au-Zn IMCs, and an Au-Sn-Zn ternary metastable phase were formed at the interface in the Sn-5Zn/Au and Sn-9 wt% Zn/Au couple. When Zn contents were more than 20 wt%, only the Au-Zn IMCs, AuZn, Au3Zn7, and AuZn3 phase were formed at the Sn-xZn/Au interface. On the Cu side, when the Sn-Zn/Cu couple was reflowed at 270 °C for 1 h, the result indicated that the (Cu, Zn)6Sn5, (Cu, Sn)Zn phases were found at the Sn-1 wt.% Zn/Cu interface, the Cu5Zn8 phase was found at the Sn-5Zn/Cu interface and the (Cu, Sn)5Zn8, (Cu, Sn)Zn5 phases were found at the Sn-xZn/Cu interfaces (x = 9, 20 and 40 wt%). After 1000-h aging, the CuZn and Cu6Sn5 phases were formed at the Sn-1Zn/Cu interface, and only the Cu5Zn8 phase was observed at the Sn-(5 to 40) wt% Zn/Cu interfaces. The results indicated that no Au-Cu ordered phases were observed at both Au and Cu sides, and IMC formation in the Au/(Sn-xZn)/Cu sandwich couple strongly depended on the Zn concentration effect in the Sn-xZn alloys.