Influence of protective atmosphere on the solderability and reliability of OSP-based solder joints

Abstract

Electronic assembly technology is in the transition from traditional tin–lead to lead-free age. 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 is accepted that inert nitrogen atmosphere can improve the wettability and reliability of solder joints. But few systemic investigations have been performed on confirming the specific atmosphere requirement and optimizing the oxygen concentration in nitrogen. The focus of this study is to investigate the effect of reflow atmosphere on solder joint solderability and reliability for SAC305 lead-free solder. By in situ observations of the wetting behavior during reflow with SMT microscope, we developed a novel method to evaluate the wettability of solder joints. The spreading area and the tin climbing height of 0805 type capacitor were measured for different reflow atmospheres. Experimental results showed that nitrogen atmosphere could obviously improve the solder joint quality and the solder joint fabricated in 100 ppm O2/N2 exhibited the best wetting performance. Visual inspection through optical microscope and microstructural characterization of the solder joints after both reflow process and environmental tests were also carried out. It indicated that thermal cycle tests had serious degradation effect on the reliability of components fabricated in all of the atmospheres.