Corrosion behavior and underlying mechanisms of Sn-58Bi solder balls surfaces induced by EDTA, HEDP, DTPMPA, and DTPA via chelation reactions

Abstract

Sn58Bi solder balls are crucial interconnect materials for low-temperature electronic packaging; however, their susceptibility to oxidation and corrosion compromises their reliability. This research hypothesizes that complexing agents can form stable complexes with metal ions through hydroxyl, carboxyl, phosphonic acid, and nitrogen atoms, which would enhance the surface activity of Sn58Bi. This research systematically evaluated the chelating effects and mechanisms of four complexing agents—Ethylenediaminetetraacetic acid (EDTA), Diethylenetriamine pentaacetic acid (DTPA), Diethylenetriamine penta(methylene-phosphonic acid) (DTPMPA), and Etidronic acid (HEDP)—on Sn58Bi surfaces. Through comprehensive electrochemical testing, static weight loss experiments, and surface analyses (Scanning Electron Microscopy (SEM), Laser Scanning Confocal Microscopy (LSCM), X-ray Photoelectron Spectroscopy (XPS)) results indicate that these complexing agents significantly increase the corrosion current, reduce the corrosion potential, and accelerate corrosion-induced weight loss in HCl solution. These findings confirm their effective chelation and removal of surface metal ions. Surface morphology analysis further reveals variations in corrosion pit characteristics attributable to different complexing agents. All test results consistently rank the chelating ability of the agents as follows: DTPA > DTPMPA > EDTA > HEDP. Mechanistic analysis shows that DTPA, due to its molecular structure, forms multi-dentate ring-shaped complexes with metal ions through eight coordination bonds, exhibiting the highest chelating efficiency and structural stability, which is key to its superior chelating effects.