Anti-tarnishing evaluations of silver solid solution phase with indium

Pure silver or sterling silver can be tarnished under ordinary atmospheric conditions after a long period of time, or can be easily tarnished under severe environment with high concentration of hydrogen sulfide, sulfur gas, or sulfur dioxide. In electronic packaging, the epoxy molding compounds are gas permeable so that those corrosive gases could penetrate into plastic encapsulation. Therefore, silver-based interconnections will not be widely accepted if the issue of silver tarnishing cannot be addressed properly. In this paper, the authors present an alternative method to reduce the chemical reaction rate between silver and sulfur element containing gases by introducing silver solid solution phase with indium. A brief summary of preparation of the homogeneous silver solid solution phase with indium will be illustrated. The X-ray diffraction (XRD) patterns and scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDX) results are shown in the paper to verify the chemical composition of silver solid solution phase with indium samples. In the following sections, both qualitative and quantitative experimental results of the chemical reactions between silver solid solution phase with indium samples and corrosive gases will be demonstrated and discussed with pure silver samples in comparison. According to experimental results of the anti-tarnishing evaluations, the reaction rate between silver and corrosive gases can be largely reduced without changing the appearance and color of the surface of silver samples. Finally, the impacts and implications of this research result to electronic packaging industry will be illuminated.