Properties of low melting point Sn-Zn-Bi solders

Because of low melting point, it is possible to substitute Sn-Zn base alloys as a lead-free solder for toxic Sn-Pb solder. In the present paper, Sn-Zn-Bi alloys were investigated by, respectively, changing Bi or Zn concentration, to display their melting points, wettabilities, mechanical properties and reliabilities of joints with Cu. The results show that addition of Bi could obviously improve wettability of Sn-Zn base alloys with decrease melting point. Tensile strength of solders and shear strength of joint with Cu could be enhanced by small Bi dissolving in the matrix of the alloys, but mass addition of Bi would cause decrease of tensile strength. Reducing Zn concentration can amend mechanical properties of the solders without obviously changing the melting points and paste ranges of them.