Conductive filament formation failure in a printed circuit board

A defective printed circuit board assembly that exhibited excessive current leakage was examined to determine the responsible failure mechanisms. Observation of the failure site (determined electrically) by optical and electron microscopy revealed an area in the circuit board where debonded fiber bundles bridged a plated‐through‐hole (PTH) to a copper plane. This phenomenon is highly suggestive of conductive filament formation.