| Because the threat of Pb to the body health and environment attracted increasing attention of public, the large scale of use of solders containing Pb in the electronic industry is seriously challenged, and desire of restriction of usage of Pb-bearing solders arised, therefore, the trend of research on Pb-free solder was heatedly raised. Among the Pb-free solder systems which had been set up, there were many problems to solve. This paper just was based on solving the poor wettability of S n-Zn solder system to exploit a new type of Pb-free solder whose every property could meet the practical needs to a certain extent. Pointing to the such problems of Sn-Zn binary alloy as easy to oxide and poor wettability, on the base that guaranteeing no increase of the melting point, we chose the CuP14 alloy which contains rich P element as the alloying component, and anticipated that P covering layer could constrain the oxidation , and so to result in the wettability improvement. The decision of the composition of the alloy was performed by the trial experiments, and proceeded the multi-alloy design and properties improvement based on the current Sn-Zn binary near eutectic composition. The method of flux smelting was introduced in alloys preparation, and through many experiments, we decided ideal composition of the flux. At the same time, we tried using the air smelting method in the preparation of Pb-free solders, and compared the quantities of oxidation and over-heat losing performed by the two smelting methods, and attained the relation between the losing quantities of the elements and the contents of the elements. This paper focused on the effects of the CuP14 alloy to every property of Sn-Zn alloy system, and made a analysis on the wettability, melting point, mechanical properties, over-potential and the interfacial reaction in the soldering joint respectively. Wettability and melting point are the most important standards to access solders, this paper had used the method of spreading area to test the wettability of solders, and assure the wettability of solders in the practical soldering systems through testing under 232℃and 252℃. It was found that the wettabilities of Sn-Zn binary near eutectic solder alloy containing trace CuP14 alloy were all better than Sn-9Zn eutectic alloy, but worse than Sn-37Pb eutectic alloy. The contents of Zn and CuP14 should control in 5-8wt.% and 0.2-0.5wt.% respectively. the wettabilities of this alloy system in high temperature soldering systems could meet the practical needs, and were as good as the present prevailing Sn-Ag-Cu alloy system. Small amounts of Ag had little effect on wettability, but could improve the mechanical properties of solders, however, the existence of CuP14 alloy resulted in the worsening of mechanical properties of the solder system. UTS and elongation reduced with the increase of CuP14 contents.CuP14 alloy could benefit the constraining of the interfacial reaction of solders, and promote forming thin and continual interfacial layers, improving the reliabilities of soldering joints. Through testing resistance and polarization curves, we assessed the electrical conductive reliability of Sn-Zn-Ag-CuP14 solder alloy system. It was found that the resistances of Sn-Zn-Ag-CuP14 increase with CuP14 and Zn contents increase, but still much smaller than conventional Sn-Pb solder, so, the probabilities which resulted in short circuit due to alloy re-melting decreased. Whereas the over-potential of this alloy system was relatively low compared with Sn-Pb solder, so it was easy to produce electrochemical reaction, Ag and CuP14 have little effects on the over-potential of solders.
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