Influences of Impurities on wave soldering properties for Sn-9Zn solders

Environmental and health concerns with Pb have led to development of lead-free solders to replace commercial Sn-Pb solders in electronic packaging applications. Sn-3Ag-0.5Cu solder is one of the solders applied to both the reflow soldering process and the wave soldering process. However, its melting temperature is about 30 K higher than that of Sn-Pb eutectic, so the temperature on the soldering process becomes higher. With regards to protecting electronic components from heat, the soldering process in low temperature is desirable. Therefore, Sn-Zn system solders are expected as the candidate solders able to produce PWBs in lower temperature soldering process. Sn-8Zn-3Bi solder is practically used for the reflow soldering process. However, the wave soldering process using Sn-Zn solders has scarcely been investigated. So, we investigated the study of the influences of Cu addition on wave soldering [1] before. In this study, the influence of several kinds of impurity on the properties of wave soldering for Sn-Zn system solder is discussed by using small sized wave soldering equipment. As a result, it was found that the solderabilities of Sn-Zn solder became worse by the addition of Cu, especially in solder bridging. It is thought that this is because of the rise of liquidus line on Sn-9Zn alloy to the addition of Cu. Therefore, the impurity level of Cu on Sn-9Zn solder should control under the content of 0.1%.