Microstructures and Properties of SnZn Lead-Free Solder Joints Bearing La for Electronic Packaging

In this paper, the effect of rare earth (RE) La on the properties of
$ \hbox{Sn}\hbox{9}\hbox{Zn}$
solder was carried out. The results indicate that RE La plays an important role not only in the wettability and the structure of the solder but also in the mechanical property of the solder joint. The results show that adding trace amount of RE La can remarkably improve the wettability and oxidation resistance of SnZn solder and can enhance the mechanical properties of solder joints. When RE La content is 0.06%, the SnZn-based solder has the best properties. In addition, it is found that
$\hbox{Sn}\hbox{Zn}\hbox{0.06}\hbox{La}$
shows a finer and more uniform microstructure than SnZn, and the sizes of Zn-rich phases are obviously reduced.