Dependence of Electrical Resistivity on Temperature and Sn Content in Pb-Sn Solders

Pb(100-x)-Sn-x solders (x = 5 wt.%, 10 wt.%, 20 wt.%, 35 wt.%, 50 wt.%, 60 wt.%, 61.9 wt.%, and 95 wt.%) were directionally solidified upward with a constant growth rate (V = 37.4 mu m/s) in a temperature gradient (G = 4.8 K/mm) in a Bridgman-type growth apparatus. The variations of electrical resistivity (rho) with temperature in the range of 323 K to 423 K for the directionally solidified Pb-Sn solders were measured. The present measurements indicate that the electrical resistivity of the directionally solidified Pb-Sn solders increases with increasing temperature, whereas the resistivity of the Pb-Sn solders decreases with increasing Sn content. The dependency of the Lorenz number (L) on temperature and Sn content for the Pb-Sn solders was also investigated based on the Wiedemann-Franz law by using the measured values of the thermal (K) and electrical (sigma) conductivity for the same alloys.