In-situ EIS study on the initial corrosion evolution behavior of SAC305 solder alloy covered with NaCl solution

The corrosion performance of SAC305 solder joints is closely related to the working efficiency and life-span of electronic devices. Available studies on corrosion of SAC305 solder have seldom concentrated on its initial corrosion evolution behavior, which is critical in understanding its corrosion behavior in the long run. In this work, comb-like electrodes have been designed for in-situ EIS measurements to investigate the initial corrosion evolution process of SAC305 solder covered with 3.5 wt.% NaCl solution, and Raman, XRD, SEM and EPMA have also been employed to characterize the formed corrosion product layer. The results indicate that the initial corrosion evolution behavior of SAC305 solder mainly involves four stages, i.e. the corrosion degradation of the pre-existing SnO2 protective film in a short duration in contact with NaCl solution, the anodically dissolved Sn2+ undergoes hydrolysis under the effect of Cl− in electrolyte to form stannous hydroxychloride intermediates of various structures, the formation of Sn3O2(OH)2 from stannous hydroxychloride intermediates after Cl− releasing, and finally the formation of nano-SnO2 particles from Sn3O2(OH)2 after steps of dehydration and oxidation. Meanwhile, the acidified NaCl electrolyte can make the formed SnO2 slightly dissolved and favors the formation of SnCl4·4H2O crystals. These findings clearly demonstrate the initial corrosion evolution behavior and corrosion product formation mechanism of SAC305 solder, and are expected to provide potential guidelines on maintenance of microelectronic devices in marine atmosphere.