The Impact Of Trace Elements On Sn-0.3ag-0.7cu Lead-free Solder Antioxidant Capacity

Nowadays in electronic assembly Process, wave soldering is changed from lead-contained to lead-free. While, the more tin content in the Pb-free solder will lead to more dross during soldering Process. Too many dross will not only waste the solder alloy, but also affect the soldering quality. Therefore, a key Problem for Pb-free wave soldering is to control the formation of the solder dross.In this work, the most popular Pb-free solder, Sn-0.3Ag-0.7Cu alloy, is selected as the base alloy. In order to improve the anti-oxidation effect of lead-free solder, Several elements, such as P, Ge, Ga, In and Ce, have been added into the base alloy. By comparing the anti-oxidation effect and influence on the wetting ability, it is found Ge is the most practical element for the improvement of anti-oxidation ability. The solder owns the best cost-effective when Ge content is 0.017%.During the simulated wave soldering, the dross mass of Sn-0.3Ag-0.7Cu-0.017Ge solder alloy is 40% less than the normal basealloy. Ge element content decreases during the wave soldering. The anti-oxidation ability of solder will dismiss when Ge content is less than 0.002%.Through decreasing the surface tensile force, depressing the growth of Cu₆Sn₅ and boosting up liquidity, Ge greatly improve the wetting ability of Sn-0.3Ag-0.7Cu solder.By means of the AES and XRD analysis, it is found that SnO is the major oxides of Sn-0.3Ag-0.7Cu. Ge is highly enriched in the surface of lead-free solder and oxygen atom content decreases greatly. Since Ge has a higher reactivity with oxygen than Sn or Cu, GeO₂ will generate priorly. A new kind of oxide film will generate since adding Ge element, which protects lead-free soder from further oxidation. New protective oxide film will yield the oxidation rate since the number of ion and electron decrease.