Shen Hao, Zhu Wenxin, Li Yao, Tamura Nobumichi, Chen Kai
Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 China.
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Sci Rep. 2016 Apr 18;6:24418. doi: 10.1038/srep24418.
Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction. With this technique, crystal orientation evolution is monitored at intragranular levels with high spatial and angular resolution. During the entire experiment, no crystal growth is detected, and rigid grain rotation is observed only in the two grains within the current crowding region, where high density and divergence of electric current occur. Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains. A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.
在此，我们通过同步辐射多色X射线微衍射报告了一项关于无铅β-Sn基焊点中电迁移诱导的微观结构早期演化的原位研究。利用该技术，在晶粒内水平以高空间和角分辨率监测晶体取向演化。在整个实验过程中，未检测到晶体生长，仅在电流拥挤区域内的两个晶粒中观察到刚性晶粒旋转，该区域出现了高密度和发散的电流。理论计算表明，在当前条件下，高电阻率晶粒中的电阻下降趋势仍然成立，而另一个低电阻率晶粒重新取向，使其a轴与其相邻晶粒的a轴更平行。对位错密度和亚晶界的详细研究表明，与经历位移变形的高熔点金属中的晶粒旋转不同，β-Sn中的晶粒旋转主要通过扩散过程完成，这是由于高同源温度所致。
