Silver is a common material used to connect resistor terminals to the resistive element within the resistor. This example shows some unknown crystals growing out of the termination area.
These crystals are shown in the BSE SEM image below.
EDS analysis showed that these are silver sulfide crystals.
These crystals most likely formed as a result of gaseous sulfur corrosion of the silver thick film conductor near the termination of the resistors. Corrosion such as the type seen here is typically due to atmospheric sources of sulfur such as diesel fuel fumes or out-gassing from cardboard.
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