Rare earth elements are recognized as the “vitamin” of metals, and trace amount of rare earth Ce can effectively improve the comprehensive properties of the solder alloy. However, rapid tin whisker growth has been found when excessive amount of rare earth were doped in the solder alloys. The results indicated that the rare earth-phase will be oxidized and induce volume expansion when Sn 3.8Ag0.7Cu1.0Ce solder was exposed in air, and the constraint action of the solder matrix on the volume expansion of the oxidized rare earth-phase will result in a compressive stress that will accelerate the growth of tin whiskers