微量Ga元素对低银系无铅钎料抗氧化性能的影响

Effect of Ga on Oxidation Resistance of Low-Silver Lead-Free Solder

电子封装波峰焊从有铅到无铅的转换过程中,由于无铅钎料中锡含量比传统Sn37Pb钎料高,导致波峰焊过程中氧化渣的产生量很大。其不仅造成生产中的浪费,还会影响焊接质量。控制钎料氧化渣的产生量是当前无铅波峰焊技术必须要解决的一个重要问题。研究了目前常用的Sn-0.3Ag-0.7Cu无铅钎料在模拟波峰炉中的抗氧化情况。主要研究了微量Ga元素的加入对该钎料抗氧化性的影响。通过钎料的润湿实验和氧化锡渣的产出量的比较可以发现微量Ga元素的加入可以提高钎料的抗氧化性能,Ga元素的最佳含量是0.02%(质量分数),Sn-0.3Ag-0.7Cu-0.020Ga的抗氧化有效温度范围是320℃以下,有效时间控制在120 min以下。利用俄歇能谱AES分析表明,微量元素Ga在焊料表面富集,O原子浓度的降低。热力学分析表明:Ga元素会在合金中优先氧化,阻碍钎料的进一步氧化;动力学分析表明:在保护膜内高价Ga离子使表面层离子排列空位增加并使电导率降低,是产生抗氧化性的原因。

Nowadays in electronic assembly process, wave soldering was changed from lead-contained to lead-free. While the more tin content in the Pb-free solder would lead to more dross during soldering process. Too much dross would not only waste the solder al- loy, but also affect the soldering quality. Therefore, a key problem for Pb-free wave soldering was to control the formation of the solder dross. The oxidation case of Sn-0. 3Ag-0.7Cu lead-free solder which was used widely now was researched. The effect of microelement Ga on the oxidation resistance of Sn-0. 3Ag-0.7Cu was studied. Add microelement Ga could improve the oxidation resistance of Sn- 0. 3Ag-0.7Cu by changing solder wettability and the dross formation. The optimal content of Ga was 0.02%. The anti-oxidation effect was available only when the temperature of solder was below 320℃and the time was below 120 min. The enrichment of Ga and the de- pressed concentration of O on the surface of the solder were investigated by Auger electron spectroscopy. In thermodynamic analysis, it was found that Ga could be oxidated first, consequently protected the solder from further oxidation. In kinetic analysis, it was found that the protective film the ion vacancy increased and the specific electric conductivity of film reduced by Ga ion, which was the reason of vieldiw, oxidation resistance.