pcb uv box
I spent quite some time making one. It took a while because I made a wooden case - I'm not good with wood!
Having finished it, I came across a perfect alternative case - an old scanner. If you can make do with a single-sided box, an old scanner case is absolutely ideal. The modern ones are a bit shallow. A nicely-fitting hinged lid is built in, as is a beautifully flat glass plate. Perfect size for 4 to 6 12-inch tubes and ballasts. I wish I had found it sooner... If you can get your hands on one (mine was free - faulty), use it.
Anyway, mine is a double-sided, 10mm MDF frame, hinged at the back and with all the ballasts and timer in tha bottom part. It weighs a bit, but is quite compact really. Exposure area is 28cm x 16cm with four tubes on each side. Exposure time is 10 minutes with microtrac presensitized board.
I chose 10mm MDF as it is easy to work and stiff enough not to bend and distort the glass plates. The whole case is made from this, screwed and glued together.
The best material for the 'glass' is 6mm acrylic (plexiglass, lexan); polycarbonate (perspex) is not as UV transparant. Some types of glass are better than others; standard window glass can be quite poor for UV use. Many people say it does not make much difference though. Glass might be easier to work with (if you get it cut to size) as it is stiffer than the acrylic and won't distort as much if the case is not perfect.
The most difficult and time-consuming part was making sure the two acrylic plates were perfectly flat and true to each other. The most vital part of making the PCB is getting the artwork perfectly flat to the board. Otherwise, the traces get blurred out and undercut. It took about 12 hours of gentle sanding of the MDF supports to get it just right. If you are making a single-sided unit, this is much easier as the foam-backed lid will take care of it.
The unit works perfectly; I can make boards for chips with 0.5mm pitch pins reliably. This is due to planning, attention to detail, patience and perseverence - not to my (lack of) woodworking skills! In other words, anyone can do it if I can.
The tubes are about 2cm from the 6mm acrylic plates. The inner is lined with tin foil. I have read about using a fine grill between the tubes and screen, with the effect of collimating the light so that undercutting of the tracks does not occure. I have not found this to be an issue though. Maybe when I need to make 0.25mm pitch traces(!)
I might make another when time permits, mainly for sake of even more compactness. I have in mind a vertical, cassette-loading unit. The board would be put into a simple, hinged, two-sided acrylic holder that is clamped shut. This is then inserted downwards into the UV unit, in simple guide rails, that has UV tubes either side. Should actually be easier to make, especially with regard to holding the artwork and board flat. I might even add rubber edges and a vacuum take-off to really get that artwork pressed onto the board.
Seriously, if you are making a single sided unit, find an old scanner. I you want more details about mine, ask and I might be able to draw you a sketch, although my drawing is worse than my woodwork.
I also built my own heated foam etching tank, interested???
Good luck with the build,
FoxyRick.