Influence Of Trace Elements On The Wettability And Oxidation Of Liquid Sn-0.7Cu Lead-free Solder

With the rapid development of the electronic information industries, lead solder of electronic packaging materials is transformed into lead-free solder. Increasing the amount of tin element in the lead-free solder and raising the soldering temperature will lead to the solder oxidation problem. Too many oxide slag will not only waste the solder and increase the cost of production, but also affect the soldering quality and reliability of electronic products. Therefore, how to control the formation of oxide slag in the production and application of solder products has been a very important research subject on lead-free solder field.Sn-0.7Cu lead-free solder which has been widely used in electronics industry was choosed in this paper. The main purpose is to improve the anti-oxidation performance of Sn-0.7Cu lead-free solder. Effects of P、Ge and Ni on oxidation resistance and wettability of Sn-0.7Cu lead-free solder were researched at first. Finally, the best solder alloy composition was investigated by orthogonal test.The oxidation rate of Sn-0.7Cu lead-free solder was slower at 250℃~265℃, then accelerated at 280℃~340℃ and increased rapidly over 355 ℃. The growth factor(k)of Sn-0.7Cu oxide layer were approximately equal to 1.59×10-6 at 250℃ and equal to 3.03×10-6 at 370℃, respectively. The spreading rate and the wetting force of molten solder were reduced and the wetting time were increased after adding trace P. The oxidation resistance of molten solder was significantly improved at high temperatures, but gradually lost antioxidant effect over 340℃ after adding P element. The growth factor of Sn-0.7Cu-0.009 P oxide layer were approximately equal to 0.5×10-6 at 250℃ and equal to 3.3×10-6 at 370℃, respectively. The performance of the molten solder spreading was significantly improved and the impact on the wetting time and wetting force is not significant after adding trace Ge. The molten solder oxidation resistance was significantly improved by Ge element. The growth factor of Sn-0.7Cu-0.012 Ge oxide layer were approximately equal to 0.56×10-6 at 250℃ and equal to 1.04×10-6 at 370℃, respectively. The wetting force and spreadability were significantly improved and the wetting time was reduced of molten Sn-0.7Cu solder after adding trace Ni. The influence of Ni on the high temperature oxidation resistance was weak. The growth factor of Sn-0.7Cu-0.1Ni oxide layer were approximately equal to 1.3×10-6 at 250℃ and equal to 2.6×10-6 at 370℃ respectively, which was similar to the matrix.Sn-0.7Cu-0.007P-0.018Ge-0.1Ni was investigated as the best performance composition by orthogonal test. Trace P, Ge elements were enriched at the solder surface, the spreadability and wetting force were significantly improved and the wetting time was reduced. The antioxidant properties of Sn-0.7Cu lead-free solder was significantly improved by adding complex trace elements. The growth factor of Sn-0.7Cu-0.007P-0.018Ge-0.1Ni oxide layer were approximately equal to 0.35×10-6 at 250℃ and equal to 1.22×10-6 at 370℃, which were about 27% and 40% to the substrate solder respectively.