The effect of current stressing and external loading on the growth of tin whiskers

Different current density and external loading were applied on pure Sn-plated surfaces to evaluate the effects of service conditions on the growth of tin(Sn) whiskers. The samples were aged at room temperature with an induced current density range of 0.1∼0.5×10⁴A/cm². Whiskers were found after 720 hrs aged at the room temperature and the maximum length was 2.0µm. While tin whiskers were much longer after current stress aged at the same conditions. With increased current density, intermetallic compounds (IMCs) grew at the interface between the Sn finish and Cu substrate. Accordingly, various lengths of columnar and bent whiskers were observed under all current stressing conditions for 240 hrs. At the same conditions, the higher current density induced longer whiskers. The current density effect on tin whisker growth at the anode is greater than cathode. The length of the whisker is 8.0µm on the surface of the sample with 0.5×10⁴A/cm² current density, which is about 4 times longer than the one aged at room temperature for 720 hrs without current stressing. In addition, these samples after current stressing were then applied alternating external force loading, the growth of tin whiskers can be significantly promoted.