Development of a lead‐free solder: Sn‐4.0Bi‐3.7Ag‐0.9Zn

Abstract

Purpose

The purpose of this paper is to study the relationship between microstructure and mechanical properties of Sn‐4.0Bi‐3.7Ag‐0.9Zn (in wt%) solder, and the structural evolution of the soldered interfaces.

Design/methodology/approach

The solder was prepared by a vacuum arc furnace. Scanning electron microscopy (SEM) and X‐ray diffraction were used to identify the microstructure and composition. The melting temperature, microhardness and tensile strength were measured. Solder joints were prepared by reflowing at 250°C for 1 min in a vacuum oven and the soldered interfaces were observed by using SEM.

Findings

The microstructure of the slowly cooled Sn‐4.0Bi‐3.7Ag‐0.9Zn specimen is composed of bulk Ag₃Sn, AgZn intermetallic compounds (IMCs), Bi precipitates and a β‐Sn phase. The developed solder exhibits good comprehensive properties, such as low‐melting temperature, high microhardness and ultimate tensile strength. A complicated IMC layer forms at the interface with Cu pads and it turns into a thinner Ni₃Sn₄ layer with Ni/Cu substrates.

Originality/value

The paper shows how a high performance, lead‐free solder was developed.

Citation

Wang, X., Liu, Y., Yu, L., Dong, Z. and Gao, Z. (2011), "Development of a lead‐free solder: Sn‐4.0Bi‐3.7Ag‐0.9Zn", Soldering & Surface Mount Technology, Vol. 23 No. 1, pp. 15-21. https://doi.org/10.1108/09540911111099668