SnAgCu钎料焊点电化学迁移的原位观察和研究

In situ observation and research on electrochemical migration of SnAgCu solder joints

通过恒定电压条件下的水滴实验,对Sn-4Ag-0.5Cu钎料焊点的电化学迁移(ECM)行为进行了原位观察和研究。结果表明,树枝状的金属沉积物总是在阴极上生成,并向着阳极方向生长,在接触阳极的瞬间,发生短路失效。外加电压不超过2 V时,形成的沉积物数目往往比较少并且粗大。焊点间距的减少和外加电压的增加都会使得ECM造成的短路失效时间显著缩短。当钎料不能完全包裹焊盘或者焊盘局部位置上钎料的厚度很薄时,发生ECM的金属除了来自钎料焊点,还来自Cu焊盘;钎料中的Ag不发生迁移。

Electrochemical migration （ECM） tests on SnAgCu solder joints were conducted by applying constant voltage with a DC power supply. Water was used as the test environment. A period of incubation was necessary for the formation of dendrites on the cathode solder joints, then the dendrite grew fast towards the anode solder joint, resulting in a short circuit. Lower applied voltage （less than 2 V） always led to not too many but bigger dendrites. Time of short circuit decreases rapidly with the increase of applied voltage and the decrease of the distance between the two solder joint specimens. The solder joint was not the only source for migrating metal elements, the Cu pad is another Cu source when the solder could not cover all the surface of the pad or cover is thin. Ag is immune to ECM.