Abstract
We investigated the effect of Ge additions (0.1-0.5 at.%) on properties of Sn 84 Zn 13 Bi 3 solder-alloys, specifically the anti-oxidation capability, electrical resistance, thermal expansion behavior, and mechanical strength. The Sn-Zn-Bi-Ge alloys have a melting point around 197 °C, and are not noticeably oxidized after soaking at 250 °C for 180 min under ambient air flow 100 ml/min. Coefficient of thermal expansion, tunable between 10 and 17 ppm/°C by the Ge addition, matches those of various metals such as Cu, Ni or lead-frames, leading to low thermal stress. Electrical resistivity of Sn-Zn-Bi-Ge solder-alloys, 10-15 μΩ cm, is much lower than that of Sn-37Pb solder. The micro-Vickers hardness, up to 400 MPa with 0.5 at.% Ge addition, is 150% that of Ge-free Sn 84 Zn 13 Bi 3 , or 300% that of Sn-37Pb solder. Moreover, it possesses better tensile strength, being 127% that of Ge-free Sn 84 Zn 13 Bi 3 , and 190% that of Sn-37Pb solder. © 2010 Elsevier B.V. All rights reserved.