I was in the PWB business for many years. Most jobs started with half ounce copper (.0007"). After drilling and electroless processing the panel was laminated with dry film photoresist, exposed, and then developed. At this point the only copper showing was the trace pattern which was then copper plated at 25 to 30 amps per square foot.
After copper plating the panels were solder plated. The solder plating was also used as the etch resist. After stripping the dry film the panel had solder plated traces with a copper background that was only .0007" thick so the etching time was only a couple of minutes. That's the basic method of how it was done. Of course there was more processing after etching depending on the job requirements such as soldermask over bare copper etc.
--- In Homebrew_PCBs@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
>
> I know that "real" circuit board houses don't etch away all the copper they don't want, I believe they plate up where the copper is desired over a very thin layer, then etch just a little copper away from everywhere. Does anyone know how long it takes to lay down the 1oz (0.0014in) of copper on a "real" circuit board in the panel plating part of the process?
>
> Thanks,
> Donald.
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