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, the study of the influences of Cu addition on wave soldering before is investigated. 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%