Influence of reflow atmosphere on SAC305 solder joints

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 to present electronic assembly technologies. Inert nitrogen atmosphere can both widen the process window of reflow and improve the mechanical reliability of solder joints. The focus of this study is to investigate the effect of reflow atmosphere on the reflow process and solder joint reliability of lead-free solders (SAC305). Board level reflow in various kinds of atmospheres and microstructural characterization of the solder joint were carried out to demonstrate the influence of controllable atmosphere on the reflow quality of the lead-free solder joints. The SAC305 solder joint fabricated in 1000 ppm O₂ exhibited a good surface morphology and an interface with very small pores. Surface finish of the solder pad was found to have a great influence on the as-reflowed solder joints.