This is what’s needed to create a circuit board using your brand new UV exposure box:
Rubber gloves (for use with chemicals)
Copper clad board
2 boxes for the development and etching
Let’s do Some Etching!
The pictures and text below describes the first try-out in which the ideal exposure time was to be found. The process is the same regardless so you can use it as an instruction for creating whatever circuit board you want to create.
Print your pattern on a plastic sheet for overhead projectors. In this case a test pattern has been used just to find a reasonable exposure time. Cut them out with some margin but make one of the pieces bigger than the other. Put them on top of each other, align the pattern and tape them together. Using two layers will reduce any irregularities in the print during the exposure to the UV light.
This pattern is for a positive photoresist where the areas exposed to the light will be dissolved in the development process. Even though they don’t seem as common there are negative ones as well, keep that in mind when you’re buying the boards and creating the patterns.
Yes, that’s a cool Atmel cup by the way…
Follow the instructions on the package for the development powder (Sodium hydroxide, NaOH) on how to mix it. Use water that is around 30°C. This is where you use the protective goggles and rubber gloves! Put the liquid and the board in a plastic box and keep it in motion until the pattern appears, this should take about 5 to 10 minutes. A good way to do this is to put it in one of the boxes and wiggle it back and forth.
Mix the etching powder (Sodium persulfate, Na2S2O8) according to the instructions on the package. It will dissolve any copper that has been exposed to the UV light and turn the liquid blue. If you’re not still wearing the protective goggles and the rubber gloves; put them on again! The liquid should be warm, around 30-40°C, and it should be kept in motion just as during the development solution. The process can take up to 20 minutes but take a look after the first ten to see how things are going
Wash the copper thoroughly with acetone. Make sure to get rid of all the excess photoresist if there is any. This can be done mechanically with a needle for instance. Just be careful not to damage the pattern that should be on the board.
A number of different exposure times were evaluated in this try-out in a divide and conquer manner. It was obvious that using double layers of the plastic film was needed in order to make the pattern more regular by preventing light from going through the mask.
Using two plastic sheets and exposing for 2 minutes seems to do it. The circuit was in the development liquid for about 5 minutes (at 30+ °C) and in the etching liquid for about 10 minutes (at 40+ °C). The time needed is pretty obvious once it’s done though, keep it in the former until the pattern is clearly visible and the latter until the excess copper is dissolved.