低熔点Sn-Zn-Bi无铅钎料的组织和性能

研究了Sn—Zn—Bi钎料的组织、相变及润湿性．在Sn-9Zn二元共晶的基础上加入质量分数为(2～10)％的Bi，合金结晶过程中形成富Zn的初生相．这导致合金的结晶温度降低，也标志着熔点的降低，但熔程扩大．在加Bi基础上，适当降低Zn的含量则可以缩小熔程，且熔点无明显变化．Bi的加入明显改善了Si—Zn系钎料的润湿性，提高了钎料在Cu基底上的铺展面积，缩短了润湿时间．钎料中Zn原子向Cu基底的扩散而形成扩散反应层，导致钎料熔体／Cu界面能的下降．因此，钎料中Zn含量提高，其在Gu基底上的铺展面积增大，润湿力提高．而由于扩散过程需要一定时间，导致润湿时间延长．因此，必须合理控制Zn的含量以获得铺展性与润湿时间的良好匹配．

Microstructures and Properties of Sn-Zn-Bi Solder Alloys

The microstructures, phase transformations and wetting behaviors of the Sn-Zn-Bi solders were investigated. The results show that adding 2%-10% Bi(mass fraction) to Sn-9Zn binary alloy, the primary Zn rich phase appears from the melts firstly on cooling, which results an increase of the pasty ranges. The crystallizing points decrease with addition of Bi, indicating a decrease of the melting points. Fixing Bi concentration, reduction of Zn decreases the pasty ranges, and the melting points keep stable. Addition of Bi improves the wettabilities, because the wetting areas on Cu substrates of the alloys are increased, and the wetting times are shorten. The diffusion of Zn into Cu at the solder/Cu interface is accelerated by increaseing Zn concentration, which decreases the solder/Cu interfacial energy. With addition of Zn, the wetting areas on Cu substrates of the Sn-Zn-Bi solders increase and the wetting forces enhance. But the diffusion needs a period of time, which means a prolonged wetting time. Therefore, Zn concentration must be controlled in order to obtain a good matching between the spreading area and the wetting time.