Conductive Anodic Filament (CAF) Testing

The Conductive Anodic Filament (CAF) test method provides a means to assess the tendency for conductive anodic filament (CAF) growth, a form of electrochemical migration, and similar conductive filament formation (CAF) laminate material failure modes within a printed wiring board (PWB). Conductive anodic filaments may be composed of conductive salts, rather than cationic metal ions, however insufficient dielectric for the applied voltage, component failures, and use exceeding the maximum operating temperature (MOT) of the laminate may also contribute to CAF failures. This test method can be used to assess PWB laminate materials, PWB design and application parameters, PWB manufacturing process changes and press-fit connector applications.

This CAF Failure can be exhibited in four ways:

  • hole-to-hole,
  • line-to-line
  • hole-to-line, and
  • layer-to-layer

CAF formation is a process involving the transport of conductive chemistries across a nonmetallic substrate under the influence of an applied electric field. CAF is influenced by electric field strength temperature, humidity, laminate material, and the presence of manufacturing defects. The occurrence of CAF failures has been primarily driven by the electronics industry pushing for higher density circuit boards and the use of electronics in harsher environments for high reliability applications.

CAF commonly occurs between adjacent circuits/PTH’s/Vias inside a Printed Circuit Board (PCB), as the copper migrates along the glass/resin interface from anode to cathode. CAF failures can exhibit as current leakage, intermittent electrical shorts, and even dielectric breakdown between conductors in PCBs. This often makes CAF very challenging to identify, particularly when it occurs as an intermittent issue.

REFERENCED DOCUMENT AND SPECIFICATIONS

IPC TM-650 Test Method 2.6.25

Conductive Anodic Filament (CAF) Resistance Test (X-Y Axis)

IPC-9691

User Guide for the IPC-TM-650, Method 2.6.25, Conductive Anodic Filament (CAF) Resistance Test (Electrochemical Migration Testing)

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