On Mon, Jan 25, 2010 at 7:35 PM, David Griffith <
dgriffi@...>wrote:
> I'm convinced now that I should give the photographic method a try and
> even try pre-sensitized boards. I'd like to do things the Right Way
> instead of going sloppo like I have been so far. That might explain my
> previous problems. Anyhow, I'll start with constructing a UV exposure
> box. The box and timer stuff seems straightforward enough, but what I'd
> really like is to make a gizmo that sandwiches the PCB and films between
> two sheets of glass or lexan. The idea is to put the things in this
> frame, adjust for registration, clamp it closed, and that's it. Insert
> into the UV box for exposure. I saw a page a couple years ago discussing
> something like this, but I can't find it anymore. Does anyone here smell
> what I'm cooking?
>
> I keep the boards small and one-sided, would a UV EPROM eraser work?
>
>
Get one or two "bug zapper" U-shaped lights and a ballast for T-40 lights
(and a AC plug and wire) and you're in business. I've been doing it that
way for years and I use kids "mega blox" stacked up 2 high on either side of
the board I've mounted the lights on (1/4-inch fiber board). I drilled
holes around the edges of the lights then gently zip-tied them to the board,
ballast and all, plus wire nuts for all the connections except for the
lights which I soldered onto the ballasts since the way I use them I'll die
before they do. It only takes about 3-4 minutes of exposure time with the
film people buy and I've also had success with the spray-on negative
photoresist that smells and looks the same when dry. It allows me to do
boards larger and thicker than my small laminator can handle and works well
once you get the trick of air-brushing on the resist and then drying in the
oven for a couple minutes.
Finally, I wouldn't worry too much about trying to get a setup that
sandwiches the board and artwork. Get a food vacuum sealer and put the
artwork with the printed side facing down onto the board and seal it up! It
works perfectly every time and there is zero gap between the board and
artwork, regardless of whether the board is a little warped from cutting or
whatever. You can usually get several exposures out of one bag before it
gets too small to keep your board out from under the logo and crap they
print on the bottom of the bag. Just make sure you seal using the clear
side of the bag up, not the matte side.
HTH,
Larry
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