| In this article, the properties of Sn-Ag and Sn-Zn system lead-free solder alloys were improved by adding some trace elements. Sn-Ag lead-free solder alloys including In, Bi, Cu, Sb and RE elements and Sn-Zn lead-free solder alloys including P, Al and Mg elements have been studied. The influence tendency of adding contents of these elements to solidification temperature, solidification range, conductance rate, solder joints tensile and shear strength has been tested and discussed. On the base of these tests, Sn-3Ag-l.5Cu-0.4Sb and Sn-7.3Zn-0.2P-0.5Al lead-free solder alloys have been selected from the improved Sn-Ag and Sn-Zn system alloys as the best alloys. The results were shown as follows:(1) In Sn-Ag lead-free solder alloys, under the interaction of multi-composition, the addition of the element In and Bi can decreases the solidification temperature obviously. Sb can increase the solder joints tensile and shear strength but RE on the contrary. The conductance rate increases with the increase of Cu content The conductance rate and the joints tensile and shear strength of the solders both decrease when the content of Ag is up to 1.5% or more.(2) In Sn-Zn lead-free solder alloys, under the interaction of multi-composition, the solidification temperature can decreases obviously with the increase of Mg contents from zero from 2 percent. Adding Al element into Sn-Zn lead-free solders can decrease the solidification temperature of the alloy systems too. The tensile and shear strength can be improved by adding Mg and Al into Sn-Zn solder alloys. The conductance rate of this alloy can increase by adding P and Al, but it decreases when the content of P and Al is up to certain value.(3)The wettability of Sn-Ag system lead-free can be enhanced by adding element Bi into this system. However the wettability of the solders decreases as the content of Cu and Sb become high. The adding of trace elements Mg and Al into Sn-Zn lead free solder alloys also decreases its wettability.
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