Tin whisker growth driven by electrical currents

Abstract

Tin whisker growth was investigated in pure Sn using Blech structure. Blech structure was used to investigate the electromigration behavior in pure tin, in which 5000 Å tin strips were on 700 Å titanium films. Tin whiskers grew on the anode side, and voids were observed on the cathode side after stressing at the current densities of 7.5×104 and 1.5×105 A/cm2 at room temperature. To investigate temperature effect, samples are stressed at room temperature and 50 °C. The whisker growth rates were estimated to be 3 and 7.7 Å/s at room temperature and at 50 °C, respectively, in the current density of 1.5×105 A/cm2. The whisker growth rate reduced to 0.4 Å/s at the current density of 7.5×104 A/cm2, which is still faster than that driven by mechanical stress. Transmission electron microscopy results showed that the whiskers are single crystalline and a thin Sn oxide formed on their surfaces. The mechanism of tin whisker growth driven by electrical force is proposed in this article.