New Solder Based on the Sn-Zn Eutectic with Addition of Ag, Al, and Li

Abstract

New solder, based on Sn-Zn, with the addition of 1 at.% Ag, 1 at.% Al, and 0.5 at.% Li (SZAAL) was prepared. The influence of alloying elements on mechanical and electrical properties, microstructure, and melting point was investigated. The tensile test showed enhanced mechanical properties of SZAAL alloy compared to Sn-Zn eutectic and Sn-Zn-Ag. Investigated Al and Li additions improve the mechanical properties of the alloy, tensile strength and solder plasticity. Another positive effect is that those elements caused a decrease in the melting point, compared to Sn-Zn with 1 at.% Ag. Microstructural investigation revealed a fine Sn-Zn eutectic structure with the present epsilon phase (AgZn3). The addition of lithium and silver decreased the coefficient of linear expansion of the tested alloys. Li addition reduced significantly both the surface and interfacial tension, which translates into improved solder wettability. The surface tension of all solders decreased with temperature, but the interfacial tension increased with temperature. That is due to the weakening effect of the flux. Thus, the soldering temperature in the presence of the ALU33® flux should not exceed 250 °C.