Influence of argon reflow on the microstructure and properties of lead-free solder joints

With human's increasing attention to the environment protection, the transition of electronic assembly technology from tin-lead to lead-free is a matter of necessity. Sn-Ag-Cu solder alloy systems have been considered as the most potential substitute for traditional Sn-Pb solder alloys. It has been accepted that, in protective atmosphere, the peak reflow temperature can be reduced and the wetting performance of lead-free solder joints can be improved. Ar is the most plentiful rare inert gas. To date, however, few researches on using Ar as reflow atmosphere have been reported. The focus of this study is to investigate the influence of Ar reflow atmosphere on the microstructure and properties of lead-free solder joints. Reflow process in Ar atmosphere was conducted for OSP-pad PCBs. Board level reflow in different atmospheres and microstructural characterization of the solder joints after both reflow process and environmental tests were carried out. The experimental results indicated that Ar atmosphere could obviously improve the wetting performance and reliability of solder joints in comparison with the solder joints fabricated in air atmosphere.