Corrosion of ImAg-Finished PCBs Subjected to Elemental Sulfur Environments

This paper discusses the corrosion process of immersion silver (ImAg) board finish on printed circuit boards subjected to elemental sulfur environments in the presence of high-sulfur content clay and moisture. The tests induced various types of metal migration processes and corrosion products. Migration phenomena ranged from short dendrites of Ag₂S, Cu₂S, and CuS, which grew from ImAg surface edges without solder masks, to long dendrites of Cu₂S growing from ImAg surface edges with solder masks that had copper traces beneath them.