Here’s a simple ultraviolet exposure box I made with some UV LEDs that have been hanging around for a while.
The box is just some pine cut to size and nailed together. I tested various exposure times and wrote down the ones that work best on the underside of the lid.
I’m using an old 12v 1000mA supply from an HP printer. The box is intentionally deep for two reasons. These LEDs have a fairly narrow viewing angle so the distance means less “hot spots”. Also, the further away the glass is, the more perpendicular the light beams are when they hit the mask (a laser printed transparency or two) and so there is less undercutting. (It’s been very forgiving of space between my mask and exposure area.)
I built this as cheaply as possible, which meant making my own hinges. They work better than normal hinges, however because they allow the lid to get totally out of the way. This is a necessity because the screenprinting screens I use are larger than the top.
I cut the glass down from a piece I got from an old picture frame. It apparently wasn’t a very good picture frame as the glass doesn’t seem to block much UV. (good!)
The total area of exposure is about 9″x11.5″, just over the size of a standard piece of paper (or in this case, transparency that comes out of my laser printer). This wasn’t by accident. 😉
The LEDs are in a serial-parallel configuration with a resistor regulating the current of every row. There is no switch, I just use my wristwatch as a timer and pull the plug to end the exposure. It’s simple and works really well for burning screens for screenprinting, and exposing pre-sensitized PCBs.