Sn-3.8Ag-0.7Cu-1.0Er无铅钎料中Sn晶须变截面生长现象

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

在Sn-3.8Ag-0.7Cu无铅钎料中添加质量分数为1%的稀土Er会在其内部形成尺寸较大的稀土相ErSn_3.暴露于空气中ErSn_3将发生氧化,同时在其表面会出现Sn晶须的快速生长现象.室温时效条件下,在氧化的ErSn_3表面会生长出少量的杆状Sn晶须,Sn晶须的截面尺寸会发生连续变化;高温时效条件下,在氧化的ErSn_3表面会生长出大量的针状Sn晶须,Sn晶须的截面尺寸会发生阶梯式变化.提出了ErSn_3氧化过程中体积应变能是一个变量的模型,可以解释观察到的现象.

Large sized ErSn3 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 ErSn3. During aging at room temperature, a few rodlike 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 ErSn3, was suggested to explain the observed results.