Effects of Trace Amounts of Rare Earth Additions on Microstructure and Properties of Sn-Bi-Based Solder Alloy

Abstract

The effect of trace amounts of rare earth additions on the microstructure and properties were studied for the Sn-58Bi and Sn-58Bi-Ag solder alloys. At the same time, the intermetallic compounds (IMCs) in the solder alloys and intermetallic layer (IML) thickness at the solder/Cu substrate interface were investigated, both as-reflowed and after high-temperature aging. The results indicate that adding trace amounts of rare earth (RE) elements has little influence on the melting temperature and microhardness of the solders investigated, but adding RE elements improves the wettability and shear strength of the Sn-58Bi and Sn-58Bi-Ag solder alloys. In addition, it was found that the addition of RE elements not only refines the microstructure and size of the IMC particles, but also decreases the IML thickness and shear strength of the Sn-58Bi solder joint after high-temperature aging. Adding trace amounts of RE elements is superior to adding trace amounts of Ag for improving the properties of the Sn-58Bi solder. The reason may be related to the modification of the microstructure of the solder alloys due to the addition of trace amounts of RE elements.

Effect of Zn Addition on Interfacial Reactions Between Sn-Bi Solder and Cu Substrate

“…In addition, the average approximate concentration of Sn, Cu, and Zn in the IMC layer adjacent to the Cu is also obtained which are 24, 56, and 20, respectively. These results which are consistent with the elemental-mapping analysis suggest that the IMC layer adjacent to the solder is a Cu 5 (Zn,Sn) 8 IMC layer while the IMC layer adjacent to the Cu substrate a Cu 6 (Sn,Zn) 5 IMC layer. The formation of Cu 6 (Sn,Zn) 5 IMC between Cu 5 (Zn,Sn) 8 IMC layer and the Cu substrate may be attributed to the penetration of Sn atoms through the Cu 5 (Zn,Sn) 8 IMC layer during the long solid-state reaction to form Cu 6 (Sn,Zn) 5 IMC.…”

“…The elemental analysis of the thermally aged solder joints revealed that a layer of Cu 6 (Sn,Zn) 5 IMC was also formed between Cu 5 (Zn,Sn) 8 and the Cu substrate after thermal aging for 1008 h.…”

“…Eutectic Sn-Bi solder has been recognized as a promising low-temperature lead-free solder [1][2][3] , due to its low melting point (138 C 4) ) and higher tensile strength when compared to that of eutectic Pb-Sn solder 5) . Low-temperature soldering allows the fabrication of inexpensive printed circuit boards without high-temperature resistance.…”

“…In the study by Li et al 18) , it was found that upon the addition of 1 mass% Zn 19) reported the effect of addition of 0.7 mass% Zn to the Sn-Bi solder during liquid-state aging. In this study, the CuZn IMC was formed on top of a Cu 6 (Sn, Zn) 5 IMC layer that acted as a barrier layer and suppressed the growth of the Cu 6 (Sn, Zn) 5 IMC layer during liquid-state aging.…”

Liquid-Phase Reaction Sintering Behavior at below 200 °C and Electrical Sheet Resistance of Sn-58Bi/Cu Composite Pastes

“…Sn-Pb solders [12,13]. In previous reports, Sn-58Bi solder alloys undergoing tensile tests have shown relatively high intensity values compared to other solder alloys; this indicates that brittleness is high, and fracturing has been observed during plastic deformation or elastic deformation [14,15]. The plastic deformation of Sn-58Bi solder can be improved by reducing the deformation rate.…”