Project: DIY UV Exposure Unit Part 1
Making your own circuit boards is very rewarding, cost effective and fast, but actually getting the image of your circuit onto the board without missing or broken tracks and pads can be one of the most challenging parts.
Several methods exist for this:
- Toner transfer methods can have mixed results, with sections of toner failing to stick properly resulting in lost tracks.
- Milling involves a CNC milling machine, which is a major investment for anyone starting up, there are also limitations to track width.
- UV exposure produces a good quality image on coated circuit boards, but the UV exposure units are usually fairly expensive, unless you make your own, and that’s what we’re doing.
We’re using an old Genius scanner. The scanner still works, but is completely useless without new drivers for any software later than Windows XP. We seem to that same problem with most products from Genius, so avoid buying them now, but at least in this case, we’re able to upcycle our old hardware in some form.
So, here’s what’s involved:
First job is to strip out the innards. The case is made from 2 parts with are clipped together. Sliding a spudger or flat screwdriver into the ends frees up the clips and the cover comes away quite easily.
We now need to remove the stepper motor, belt drive mechanism, linear rod, scanner head, safety switch, circuit board and ribbon cable.
Most of this is screwed down with the odd clip. There’s nothing left but the plastic shell and the glass in the top half.
Now we have our UV exposure unit case, we’re ready to get to work on getting everything ready.
Placing the bulbs and ballast unit for a quick visual check of how the dimensions are working out shows that the plastic mouldings used for the scanner mechanism are going to leave us with an irregular base, so smoothing the base with some wooden boards roughly cut to size solves that problem.
Everything is screwed down, and a reflective plastic sheet has been added to help bounce more light up to the glass. The sheet we used was from the screen of an old monitor.
The tubes are mounted, and the ballast is fitted along the side of the cover. It’s a tight fit, but a good one. Now for wiring it all up, following the wiring diagram on the ballast. Everything is relatively straightforward, we've used 1.5mm single core twin and earth mains cable, stripped out to the individual black and red wires.
We added a mains switch at the back of the cover, along with a couple of inline fuses. A bullet connector makes for a quick and easy fuse holder also allowing quick separation of the cover from the base, but care should be taken to ensure that the cover is never opened with the power on, as live could be exposed.
The case is simply clipped back on, and we plug it in ready to go!
The result, the bulbs all light up properly, giving us a reasonably even spread of UV light. We put this to the test with a circuit board and found that we needed about 12 minutes exposure time for a pre-sensitised PCB. The unit got warm in that time, but not hot.
As it works for now, we’d consider this a finished project, but there are plenty more modifications to make. A couple of small cooling fans at the back, along with a timer would be great additions that we’ll cover in a future upgrade to this project.