SparkFun Forums

[treez]

Hello,

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 there...............as 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.

[Ross Robotics]

That's a question for your fab company.

[treez]

Thanks, though i believe some things are general to all fab companies? ....eg consider FR4 cards....these are made with full double sided copper as a rule.....whatever the fab company.............................i wondered if the same situation exists for prepreg?

FR4 cards (almost always) come with full double sided copper, then fab companies etch away what is not wanted to make the printed circuit............


is it the same with the prepreg?

[MichaelN]

I understand the prepreg comes pre-coated in copper. This shouldn't be something to worry about (I've never heard of a fab place charging different amounts depending on the etchant they use) - just design your board as you normally would, taking good EMC practices into account etc..

[treez]

Thanks, but i can't see how prepreg layers could come pre-coated with copper....as they are often only 0.6mm thick.

Sometimes a single prepreg layer is made up of several prepreg layers, and as such, they couldnt each be pre-coated with copper.

If pre-preg does not come pre-coated with copper, and needs the circuit pattern to be "infused" onto it......then a circuit pattern with big copper pours on it, would obviously be expensive to make?

.....this is not the case with FR4 cards, which come double sided pre-coated with copper, and as such , big copper pours are fine, and just means less etchant will be used.

[leon_heller]

Copper foil is added, as required:

http://www.multi-circuit-boards.eu/en/p ... -foil.html