>Alright, call me crazy, but an idea just occurred to me, and I can't see why
>it can't work. To me, the most difficult (expensive, complicated,
>unreliable, etc) part of creating a PCB is getting the pattern laid out on
>the board so it can be exposed, etc. The rest is science ... standard
>procedure, standards times, standard results. Yes, laying out the pattern
>can be science, but at a higher price, and still takes time to line up the
>image transparencies, etc.
>
>So this idea just randomly came to me ... why not use a projector to project
>the image on the board. Use a positive-coated board and an XGA LCD
>projector, with a UV bulb instead of the usual bulb. I get quite good
>results at 300dpi, so if we go with a projector resolution of 1024x768 for
>now, that's about 3.4" x 2.5". There may need to be some optical
>manipulation done to get it to focus clearly at that distance, and a bunch of
>other little things sorted out (such as calibration for
>non-linear/inconsistent pixel spread), but I can't see why it can't work.
>No, it's not cheap, but I believe it would be really fast, going from
>computer straight to PCB.
>
>Maybe this has been thought of or done already? Or maybe I'm going off the
>deep end?
There was a thread about this in a german usenet group not so long
ago. Anyways, while this might be possible, let me tell you that I do
not agree with you on getting the pattern laid out on the board being
difficult. Actually this is a very straight foreward process which can
also be standard procedure, standards times, standard results.
I simply print the artwork using the CAD software onto cheap
transparency paper. I do agree that aligning - with no experience -
can be difficult. However let me tell you how I do it and you will see
that it can be very simple in fact.
I align the top and bottom layers by puting the two transparencies
directly ontop of each other. Since they are transparent, aligning is
very simple by moving them around until the vias and holes macht
perfectly. I cut the top layer transparency so as it's a bit smaller
than the other one Once I have them aligned, I simply tape some tesa
film on one side to fix them. I then take two cut off's of FR4
material that I aling along the OPOSITE side of the just added tesa
film and one in the right angle of it. If you do it once this way, you
quickly see that it's actualy a lot simpler than it may sounds. With
this angle, you can slide the FR4 material into this "pocket" and
hence have it propperly aligned no matter if you have to move it
around or turn it over. Exposing this unit of PCB and transperncies
then becomes really simple. Building an exposing box (or buing a ready
made one) is also much easier and cheaper then using your sugested
prjector setup.
Again, I do agree that you may can do it the way you proposed, but the
described method is magnitudes cheaper and simpler.
Markus