In situ tensile testing of tin (Sn) whiskers in a focused ion beam (FIB)/scanning electron microscope (SEM)

Article history: Received 22 May 2017 Received in revised form 7 July 2017 Accepted 8 July 2017 Available online 19 July 2017 Tin and tin-alloyed electroplated films are known to be susceptible to whisker growth under a range of conditions,manyofwhich result in the generation of compressive stresses in thefilm. Compressive stress is considered to be one of the primary causes for whisker nucleation and growth. While extensive investigations have been performed on whisker growth, there have been few studies on the mechanical properties of tin whiskers themselves. We report on the tensile behavior of tin whiskers that were obtained by indentation and furnace aging of electroplated tinfilms on copper disks. Tensile tests of thewhiskerswere conducted in situ in a dual beam focused ion beam (FIB)-scanning electron microscope (SEM) system using a micro electro-mechanical systems (MEMS) based tensile testing stage. The strength of the whiskers was found to decrease with an increase in gage length and aged whiskers were found to be weaker than their indented counterparts. The observed gage length effect can be attributed to the probability of findingmore defects as the whisker length increases. The effect of processing on the observed strength variation was investigated by analyzing the oxygen content in the whiskers via energy dispersive spectroscopy and the microstructure through transmission electron microscopy (TEM). The deformationmechanisms of whiskers were also inferred using post-mortem TEM. It was observed that the whiskers grown by indentation were dislocation free both before and after deformation. In contrast, whiskers grown by aging showed notable dislocation content (arranged in low energy configurations) even before deformation. © 2017 Elsevier Ltd. All rights reserved.