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Multiple layer boards.....does prepreg come precoated with copper, like FR4 cards?

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I am doing a 4 layer PCB.....(central FR4 core and outer prepreg layers).

How do they put the copper on the top and bottom layers.....i mean does the prepreg "card" come precoated with copper , and then they dissolve the unwanted copper off it?......or do they have to somehow coat the prepreg with the copper traces and pads etc?

....i am asking because if the latter, then that would mean that having copper pours on the prepreg copper would be expensive.....because the copper would all need to be actively coated on opposed to with FR4 cards, where they come pre-coated with copper and so having a copper pour is actually cheaper because it means less etchant is needed to dissolve away the unwanted copper.

More confusion about PCB technical terms. :-(

Prepreg is just precured FR4. In the standard process, it gets laminated with copper foil at the top and bottom side. I think to have already sketched the basic processing in your previous thread. More copper is selectively deposited, finally the foil is etched back to create the isolation.

Galvanical copper deposition is primarly "expensive" in terms of processing time rather than area. PCB manufacturers don't charge you for area because it's a minor aspect. Technically it's important to an achieve halfway uniform density of copper features over a board. This should be considered when planning copper pours.
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