I recently embarked on a project to build a pcb with a maxim temperature sensor, a power supply and a monitor signalling pass through for a psone screen. In doing so I tried out an idea that I had. i have not seen this exact technique used before, but it worked.... so I thought I would share. Tried out the photoresist technique for making PCBs. I can recomend this technique for noobs to PCB manufacture.. Its so much easier to get a good print on the board than the toner method. Here is the setup I used. I have an OHP which uses a 650w halogen lamp. This was going to be my method of exposure. First of all I inkjeted two copies of the circuit. I also added a test bar to the top of it. This had two functions. One to let me try a test strip, to determine my exposure time. Secondly it was to ensure that the two sheets of acetate were lined up correctly. I should mention that I removed the Fresnell lens before begining. The Fresnell would leave dark rings on the image. I have looked round the intermwebby, but noone else seems to use OHP's for this... I may have hit onto something here, it seemed obvious to me. This photo is me getting ready to make a test exposure. The card under was supposed to be for cutting out the light. I intended to move it every 30 seconds to expose more of the board. When I turned the OHP on however light shone throught the card. I used some very thin alu sheet instead. The rest is pretty boring, I just followed the instructions on the beginners kit I got from Maplins. At the end I had a nice PCB The camera is rubbish for the closeups. There is a little pitting on 4 of the 0.5' tracks. This was cause i smudged the negative. in this photo you can see the less shiny area where the pitting is worst. There is a hole in fact, but by good fortune it occured on the ground plane where I had widened the track. Tested everything first by holding it against the lamp, then by multimeter. All is well. Now for an admission... This was my second attempt. My first had scratches on it which cut several of the tracks. The mistake I made was when I was agitiating the developer with the plastic tweezers from the kit. I thought I would hurry it along. What I learned was that the photoresist layer is very fragile. Just brushing it with the tweezers is enough to damage it... I didn't expect to get it right the first time so hey ho
