界面反应及界面张力对Sn-Zn-Bi焊料润湿性的影响

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

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.

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. Asa 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.