Defect of the Month - Conductive Anodic Filament (CAF)
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Conductive Anodic Filament (CAF) is a failure found in printed circuit boards. This can occur under high humility and high voltage gradients found on ever smaller and more closely spaced through hole terminations demanded by design engineers. CAF was highlighted as an issue in the late 70s and has been researched by many engineers including the National Physical Laboratory NPL in England.
CAF is a conductive path that forms between two through holes or vias that are closely spaced, the formation follows the glass strand bundles present in the laminate. It is an electrochemical reaction that forms over time between an anode and cathode junction in the epoxy/glass that is used to produce printed circuit boards. It can grow from the anode on one circuit layer to a cathode on another. Although not a dendrite that may be associated with poor cleaning on the surface of the board, the results are the same, a short leading to failure.