Growth mechanism and mitigation of tin whisker after temperature cycling and temperature humidity tests were mainly studied in this paper. The difference between matte Sn finish and SnBi lead finish(Bi: 1 ～ 4%), which had been already developed, was investigated in terms of whisker results and related phenomena. Whiskers were measured after three whisker tests. Three whisker tests were TC500 cycles whose temperature range was between -55 ～ 85°C, storage at 60°C/93%RH chamber for 1000hr, and storage at room temperature for 6 months. Maximum whisker lengths of pure Sn plated alloy42 lead frames after TC500 cycles were measured at various heat treatment conditions. The types of Sn plating solutions, species of underlayer, reflow and annealing all affected the maximum whisker length. The maximum whisker length of the matte Sn finish annealed at 150°C and 175°C for 1hr was 29.0um, and that of the matte Sn finish not annealed was 37.2um. In contrast, the maximum whisker length of the matte Sn finish reflowed at the peak temperature of 250°C was 0um. The considerable effect of reflow on whisker mitigation was explained by a proposed model. The mechanism of tin whisker growth attributed to the corrosion under higher humidity environment was studied for standard matte pure tin and tin-bismuth plated lead frame packages. In 6-month storage at 60°C/93%RH, surfaces on the lead shoulder and the lead toe corroded severely, forming the black tin oxide of SnO and SnO_2. The inspections of the base of whiskers formed on the corroded layer revealed that the corrosion spread from the outermost surface of the plating layer up to the interface with base material. Corrosion of the tin deposit formed the hard and large volume tin oxide on top of the tin grains and at the grain boundaries, which exerted high compressive stress in the deposit, result in forming long filament whiskers.
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