Silver and Sulfur: Case Studies, Physics, and Possible Solutions

The reaction of silver platings to atmospheric sulfur has been documented for several decades, but the fundamentals as to its initiation are still poorly understood. This is aggravated by the general inconsistency observed when exposing silver platings to accelerated test conditions and the relatively long incubation period before issues are observed (12 to 48 months). Speculation has also been presented as to the influence of various potting materials and their ability to 'absorb' sulfur-containing gases. This talk will provide an overview of known silver sulfide corrosion failures, with examples for component (resistor), substrate, and printed board. The fundamentals of these case studies will provide a path for a discussion on the physics of this phenomenon, including how sulfur reacts with silver, how this reaction is influenced by humidity, temperature and other reactive gases, how classic corrosion behavior may accelerate this reaction, and how sulfur-containing gases may migrate through and be retained by polymeric materials. Only after an understanding of the observed field failure behavior and a comparison to the known science can possible corrective actions be reasonably identified and implemented.