Chemical-Free Removal of Ag₂S Tarnish Layers Using Pulsed Laser Irradiation: Optical, Chemical, and Electrical Evaluation

Abstract Silver-coated electrical connectors are prone to the formation of silver sulfide (Ag₂S) tarnish layers, which impair both optical appearance and electrical performance. Conventional chemical cleaning can remove these layers effectively, although it may leave undesirable residues and introduces additional processing steps. This study investigates laser-based cleaning as a selective, chemical-free alternative by comparing nanosecond (long-pulse and Q-Switch) and picosecond laser irradiation. Optical microscopy, confocal laser scanning microscopy, scanning electron microscopy/ energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy were used to quantify the cleaning efficiency and assess potential surface damage. Long-pulse nanosecond irradiation produced largely homogeneous and mostly cleaned surfaces after several cycles, whereas Q-Switch operation enabled faster processing yet induced localized melting due to high peak powers. Picosecond laser treatment at 532 nm resulted in the most homogeneous appearance, minimal roughness and no detectable melting, with cleaning performance comparable to nanosecond irradiation from a chemical perspective. Electrical contact resistance measurements confirmed that the picosecond-cleaned samples, as well as the samples cleaned with the nanosecond laser operated in Q-switch mode, performed nearly as well as the chemically cleaned reference samples. The results highlight that laser cleaning offers a promising, selective and residue-free approach for integration into manufacturing processes involving silver-coated connectors.