In this study, 0.1~1.0 wt.% of pure Ce was added into a Sn3Ag0.5Cu solder alloy, resulting in the formation of precipitated CeSn3 clusters of a size greater than 20 1m in the reflowed solder matrix. After natural aging at room temperature for more than 3 days, oxidation on the surface of the CeSn3 clusters was much heavier than in the undoped Sn3Ag0.5Cu solder matrix. In addition, many tin whiskers with a diameter of about 0.1 to 0.3 μm had been squeezed out of the oxide layer of the CeSn3 precipitates. The increase in aging time at room temperature causes the tin whiskers to grow rapidly. The whiskers can grow even to a length of over 300 μm after 21 days of storage. The whisker growth rate in one particular case reached 8.6Å/s after room temperature storage for only one day. The whiskers formed during storage at a higher temperature (1500C have a coarse diameter of 1 to 3 μm. In some cases, high temperature storage results in the formation of short whiskers in a hillock shape with a diameter of about 5 to 10 μm.