Sn-Cu钎料液态结构的研究

STUDY OF THE LIQUID STRUCTURE OF Sn-Cu SOLDERS

利用高温X射线衍射仪测试了Sn-0.7Cu和Sn-2Cu(质量分数,%)钎料在260,330和400℃的液态结构.在共晶Sn-0.7Cu钎料熔体中仅存在短程有序结构;Sn-2Cu在260℃下的结构因子曲线小角度区域出现预峰,表明熔体中除存在短程有序结构外还存在中程有序结构.中程有序结构与Cu_6Sn_5团簇的形成有关,团簇的数量随温度的升高而迅速减少,在400℃时消失,Cu-Sn间的交互作用不再存在.通过计算得到了两种钎料合金熔体的相关半径r_c和配位数N_(min),给出了它们随温度的变化趋势.对径向分布函数(RDF)的Gaussian分解显示,Sn-Cu钎料液态中Cu-Sn刚簇的尺寸随着Cu含量的增加而增大.

The liquid structures of two molten lead-flee solders, Sn-0.TCu and Sn-2Cu （mass fraction, %）, were studied at 260, 330 and 400 ℃ by using high temperature X-ray diffractometer. Only short range order （SRO） structure was detected in molten Sn-0.TCu solder under the above temperatures. A pre--peak was found in the low Q part of the structure factor S（Q） of Sn-2Cu tested at 260 ℃, implying that there exists not only SRO structure but also medium range order （MRO） structure in molten Sn-2Cu solder. The appearance of pre--peak is related to the existence of Cu6Sn5 type clusters in molten solder. But the amount of Cu-Sn clusters decreased sharply with increasing temperature, and the pre-peak disappeared finally at 400℃, indicating that the temperature of 400 is enough to destroy the bond between Cu and Sn. The correlation radius re and the coordination number Nmin of the two liquid solders were calculated, and their changing trends with temperature were given. The result of Gaussian decomposition of the radial distribution function （RDF） shows that the size of Cu-Sn correlations in molten Sn-Cu solders increases with increasing Cu content.