With the lead-free trend and development in electronic packaging, the lead bearing finishes have already been replaced by lead-free finishes. However, the lead-free finishes such as pure tin and tin-rich alloy finishes have the propensity to grow tin whisker spontaneously. The formation of electrically conductive whiskers may bridge adjacent conductors, leading to electrical shorts, and resulting in failures of electrical hardware. This phenomenon has enhanced a reliability issue in electronic components, for example, the security of satellite, missile and nuclear weapon system will suffer potential risk. Due to the reasons above, to clarify the mechanism of tin whisker growth and develop a practical mitigation strategy has become a focus for the scientists at present. Therefore, the objective of this study is to investigate the behaviors and mechanism of tin whisker growth on lead-free finish. Three traditional electrolytes（sulfate-based, alkaline stannate-based and stannous chloride-based） were used to prepare tin platings on phosphor bronze metal coupons. The plated coupons were subjected to room temperature and high temperature（55℃/100RH%）exposures, and the growth behaviors of tin whiskers were observed. Furthermore, the rare earth elements were added into pure tin to investigate the effects on the growth of tin whisker. Finally, a pulse current circuit was designed to check the influences of current pulse on tin whisker growth. The experimental results show that: the electrodeposits produced by alkaline stannate-based bath have the most propensities to grow tin whisker; with in-situ observation of marked tin whisker, the discontinuous growth behavior by a start-stop way was observed; after adding rare earth elements into pure tin, tin whiskers were observed on the tin-rare earth alloys’ surfaces, and the tin whiskers formed in the IMC zones, the growth propensity of tin was increased with the increasing of rare earth addition; the pulse current applied on the samples influenced the growth propensity of tin whisker, and the tin whisker growth was not observed after high current density （1.0 ×105 A/dm2）was applied for 15days.
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