Reliability of 1206 capacitor/SAC305 solder joint reflowed in protective atmosphere

Electronic assembly technology is in the transition from traditional tin-lead to lead-free. In comparison with Sn-Pb solders, high melting point and poor wettability of the lead-free solders lead to great challenge in many aspects. It has been accepted that inert N₂ atmosphere can improve the wettability and reliablity of solder joints. The focus of this study is to investigate the reliability of 1206 capacitor/SAC305 solder joint reflowed in N₂ atmosphere with dilute oxygen. Reflow process in N₂ atmospheres with dilute oxygen was conducted for OSP-pad PCBs. The wetting behavior during reflow was in-situ observed with SMT microscope. Visual inspection through optical microscope and microstructural characterization of the solder joints after both reflow process and environmental tests were carried out. The experimental results indicated that N₂ atmosphere could obviously improve the wetting performance and reliability of solder joints in comparison with the solder joint fabricated in air atmosphere.