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CARBON – contacts (only for PcbOnDemand service)

1. Sometimes few copper elements or patterns of the pcb are used for keyboard contacts, LCD contacts, jumpers, etc...

to do this it is usable to print some conductive/resistive carbon ink over those copper part, which normaly are smd pads or fingers or other typical contact patterns. It is to be considered that the printing process is screen printing so tolerance in alignment and/or layer registration are not the same of the photoimageable process ( used for the soldermask).

2. It is mandatory to clearly indicate on which side of the PCB carbon is to be applied

This can be on one side or on both sides.

3. The carbon areas must be properly indicated on specific layers with proper file naming

indicating the position of the areas to be printed ( similar to legend rules)

4. A clear build up or layer sequence description must be present in the mechanical layer

and that's because it is useful to indicate this special particular characteristic of the pcb.

5. The board outline must be present in the carbon layer/layers

6. Some rules must be followed to get the correct result of this special material


- Minimum carbon gap ( carbon to carbon spacing) is 0.400mm (16mil)
- Minimum carbon line width is 0.300mm (12mil)
- Minimum carbon on copper overlap is 0.200mm (8mil)
- Minimum carbon on soldermask overlap is 0.125mm (5mil)

7. Following the drawing rules mean that a minimal isolation or spacing of 0.80mm (16mil) between the copper elements of a typical carbon finger contact is required

( if not respected the copper line could be reduced)

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