界面反应及界面张力对Sn-Zn-Bi焊料润湿性的影响

通过合金化的方式得到了Sn-Zn-Bi三元及Sn-Zn-Bi-Nd四元无铅焊料,采用润湿平衡法测量了其润湿力和润湿时间,并对润湿后的焊料/Cu界面组织进行了分析.结果表明:Bi元素不参与焊料/Cu界面的扩散反应,但能够通过吸附作用降低界面张力,从而提高焊料在Cu基底上的润湿力;Zn元素优先向焊料/Cu界面进行扩散形成Cu5Zn8金属间化合物,且扩散层随焊料中Zn含量的提高而增长,此时固-液界面张力方向发生改变,润湿力提高,但润湿时间延长;Nd元素的作用类似于Bi,既能提高焊料的润湿力,也能够缩短润湿时间,是一种改善Sn-Zn基焊料润湿性的有效元素.

Effect of interface reaction and interface tension on wettability of Sn-Zn-Bi solders

Wetting balance method was used to measure the wetting force and wetting time of Sn-Zn-Bi ternary solders and Sn-Zn-Bi-Nd quaternary solders on Cu substrate and the microstructure of solder/Cu joint after reactive wetting was investigated.The results show that Bi rarely diffuses into Cu substrate,but it is inclined to be adsorbed in Sn-Zn-Bi solder/Cu interface,which results in decrease of solder/Cu interface tension.Zn individually reacts with Cu in the progress of wetting and forms intermetallic compound Cu5Zn8.With addition of Zn into the Sn-Zn-Bi solders,orientation of solid-liquid interface tension changes with the increase of thickness of reactive layer.As a result,the wetting force increases,but wetting time obviously extends.Like the role of Bi,addition of Nd into Sn-Zn-Bi solders can enhance wetting force and shorten wetting time, therefore effectively improves wettability of the solders.