I think if you plate it up afterwards it will widen again. Besides,
you need to contact all traces for plating so it is impractical for
real boards.
Thinner copper would definitely reduce the problems with underetching.
Professional board houses have a number of factors working in their
favour. They have high resolution imaging/plotting equipment so they
can actually draw fine lines. Their photoprocess supports transferring
those fine lines to resist using well collimated light and a number of
other factors i probably never even considered.
Then they have spray etchers which assure an even etch over the whole
area, so they don't have to over-etch so much. Also, spray etching
shows much greater directionality than immersion etching. The etching
process is carefully controlled (chemistry, temperature, etc..).
All in all, i think they can reduce the tolerances in just about every
step compared to our homebrew work.
I'm not saying fine lines are something to work towards. 8mil or
6.66mil is more than small enough, even for the boards i design for
production. I would not want to make any smaller traces simply for
electrical reasons. So i have no desire to push towards finer lines in
my homebrew setup, merely a curiosity about how it would be possible.
ST
On Sun, Mar 8, 2009 at 7:54 AM, Jim <jhutch17@...> wrote:
> If you start out with VERY thin copper (say 1/10 the thickness of 1 oz
> copper) ... lay down a 1.5 mil resist and etch it ... drill holes ...
> activate holes ... then plate the copper up to the thickness of 1 oz
> copper ... would this result in narrow traces? ... or is the limit in
> the photo/printer part of the process? ... some how the professional
> houses get very narrow traces and the edges look very good under
> magnification!
> Jim