Electric polarization and depolarization of solder, and their effects on electrical conduction

Abstract

This work provides the first report of the effect of the dielectric behavior on the conduction behavior of solder. The lead-free solder studied contains 96 wt% tin and 4 wt% silver. The electric polarization stems from the interaction of the valence electrons with the atoms. The fraction of valence electrons that participate in the initial polarization is of the order of 10–9. The injected electrons play a minor role compared to the valence electrons of the solder in the polarization. The efficiency of the injected electrons in promoting the polarization decreases with the increasing number of injected electrons. Due to the polarization under a constant applied DC current (30–100 mA), the apparent electrical resistivity increases beyond the true resistivity. The rate of apparent resistivity increase diminishes as the time of current application increases. The fractional increase is 0.10% at 130 s of 100-mA current application. The higher is the current, the greater are the degree and rate of polarization at a given time. The current effect saturates above ~ 90 mA. Upon reversal of the polarity of the applied current, depolarization (followed by reverse polarization) occurs. The rates of depolarization and reverse polarization, as indicated by the rate of apparent resistivity increase, increase with increasing current. These rates decrease with increasing time. At the same current and respective time, the rates of polarization and depolarization are essentially equal, but the rate of reverse polarization is much below that of the initial polarization. Furthermore, the nearly saturated degree of reverse polarization is much below that of the initial polarization. This indicates a partially irreversible effect of the initial polarization that hinders the reverse polarization.