Conductive Anodic Filament (CAF) is an important phenomenon to understand in printed circuit board (PCB) manufacturing because it can cause serious reliability issues if not adequately addressed. CAF can result in a short circuit between two or more copper traces on the board, which can cause the circuit to fail.
Conductive Anodic Filament (CAF) is a phenomenon that occurs in printed circuit boards (PCBs) when an electrically conductive path forms between two or more copper traces on the board due to the presence of a conductive material, such as moisture or ionic contaminants.
CAF can occur in through-hole and surface-mount PCBs, leading to serious reliability issues. CAF formation can be accelerated by high humidity or elevated temperatures, so it is crucial to ensure that PCBs are correctly stored and handled to prevent moisture ingress.
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What PCB Design Practices Can Help Prevent CAF?
To prevent CAF, PCB designers, and manufacturers must consider potential sources of ionic contaminants that can cause the formation of conductive filaments on the board. They must also ensure that the board’s materials and design suit the intended application.
- Increase the distance between adjacent PTHs.
- Use phenolic-cured resin
- Use CAF-resistant grade laminate
- Increasing the glass transition temperature (Tg) of a laminate material can help prevent the occurrence of Conductive Anodic Filament (CAF) by improving the board’s resistance to heat and moisture.
- Select a laminate material with a higher Td to improve its thermal degradation resistance
- Select materials with a higher T288 to improve the thermal performance of the board
- Decrease non-plated through-holes (NPTHs), reducing the potential pathways for metal ion migration. Blind, buried vias, can be considered alternatives to NPTHs
- Increase the spacing between PTH and power and ground planes – reduces the potential for metal ions to migrate between the two layers and cause CAF
- Use intermediate layers between the PTHs and power/ground planes to provide additional insulation and reduce the risk of metal ion migration