Temperature-Dependent Electrical Resistivity in Sn-Bi Alloys

Low temperature solders based on the Sn-Bi system have caught the attention of the electronics manufacturing industry as they make possible electronics assembly at lower temperatures, bringing technical, economic, and environmental benefits. However, the solid solubility of Bi in Sn ranges from around 3 wt% at room temperature to 21 wt% at the eutectic temperature of 139°C. This is expected to affect the electrical resistivity of the Sn-Bi alloys as temperature fluctuates during normal operations of electronic devices. This study investigates the change in electrical resistivity of a low temperature solder based on Sn-37wt ^% Bi with additions of Cu, Ni and Sb. The electrical resistivity of the alloy is found to increase non-linearly with temperature. Overall the resistance is slightly higher than that of the base Sn-37wt%Bi alloy and this is due to the presence of the (Cu,Ni) 6 Sn 5 intermetallic and dissolved Sb in the Sn phase, while being lower than that of the near-eutectic Sn-57wt%Bi alloy.