I was sick of soldering on strip boards and getting circuits, that look like they would instantly catch fire, if any kind of electrical power is applied to them. So I decided to build an UV LED exposing unit, to be able to etch my own PCB´s.
After browsing the web for similar DIY projects, I ordered 100 5mm UV LED´s (96 of them landed on the board) + resistors and went to my local hardware store, coming back with the following items:
My hands do already hurt, just from looking at this :D
Now I soldered the LED´s and resistors onto two 10X16cm strip boards (for better reflection, I covered the PCB´s with adhesive chrome film).
To power this, I used a specialized 20W LED power supply and to control everything, I chose an ATMEGA 328 and a relay. For setting the time and starting the process, three buttons and a 2X16 character LCD were added. To make sure that you notice, when the process is finished, I also connected a little piezo speaker, to give an alarm sound.
The next Step was, to put together the wooden cube, that was chosen to work as a housing, because it was cheaper than anything else (for sure it could have been smaller, but I had no idea how the distance between the LED´s and the PCB had to be, so this gave me some tolerance). After that, the control electronics were assembled within a plastic case and this was mounted at the front of the cube. To get a removable (for customizing reasons), reflective inner Structure for the cube, I cut some plywood boards, glued them together with triangular cleats. The four inner sides were fully covered with chrome film. On top of this lays a Plexiglas board, in order to hold the PCB (I used normal Plexiglas, but this actually is not the best choice, because it absorbs much of the UV radiation. Specialized acrylic glass for growing applications or normal glass from picture frames does a better job I think).
To finish the project, I got a thick and heavy (to have enough pressure on top of PCB and the print) board of white 8mm plastics and mounted two handles, to make this a nice looking cover plate. For me, the result of this project works just fine (I had no idea what I was doing or what I had to pay attention to) and since UV LED´s are not that expensive anymore, a DIY exposing unit based on these is a good alternative to commercial solutions.