CROSS SECTION CHANGING GROWTH PHENOMENON OF Sn WHISKER IN Sn-3.8Ag-0.7Cu-1.0Er LEAD-FREE SOLDER

Large sized ErSn_3 particles precipitated in the Sn-3.8Ag-0.7Cu-1.0Er solder alloy are oxidized when exposed in air,and it was found that Sn whiskers can rapidly grow on the oxidized ErSn_3.During aging at room temperature,a few rod-like Sn whiskers were observed and their diameter could be gradually changed.During aging at 150℃,a great number of needle-like Sn whiskers were observed and their diameter could be also changed step by step.A model,in which the volume strain energy is not a constant during oxidation of ErSn_3,was suggested to explain the observed results.