September 5th, 2011 by Espen

I am a very DIY kind of guy, and lately I’ve been wanting to have my own custom PCB. After researching the processes of making one I realized I wanted one, but what to make? I figured it had to be simple, and with large traces – to be sure it would be working even if the etching went semi-bad. Then when reading about exposing photoresist to sunlight for development I figured I needed to make myself an artificial sun (well, something radiating UV light (20nm – 400nm)).

The process is as follows:
First get a hold of some sensitized copper board (can be done with positive photoresist spray)
Then expose the parts of the board you want to etch to UV light, this is where you have to figure out what your circuit will look like on the board. There are several ways to only expose the things you want to etch, but it usually boils down to two methods: Toner transfer or transparent paper.

For toner transfer you use a laser printer to print on some glossy paper, then apply this on the board and apply a heat source to make the toner melt a circuit down on your board.

I choose to use the transparent paper method, you print your circuit on a piece of transparent paper and keep it tight on your board.

The second step is to expose this board to UV light, then you need to use some kind of developer to get this developed. I used just plain water and NaOH – I don’t have a good way of telling how much NaOH I used for how much water, but I used about 1L of water and sprinkled a little bit of NaOH on top of it. (DON’T pour water on the NaOH).

Here is one of my first results for a developed board:

When the board is developed, it’s gonna have to be etched. I first bought some “professional” etching solution, but after contemplating for a long while about using it (due to safety hazards and such) I ended up using another method: Hydrogen Peroxide, White Vinegar and Salt. (Yes, table salt). The hydrogen peroxide is food grade, 3%. I used 50% of the hydrogen peroxide and 50% of the white vinegar and sprinkled salt on top of it. Put the board in and let it sit for about an hour with some occasional stirring of the solution.

Here is what it looked like during etching (should have used a tray, but didn’t have one available and was too eager to get going):

Here is the board I etched:

And here it is with the components mounted and powered up:

I have plans to mount this and another identical board inside a box and use an ATmega168 to control an LCD and to switch a MOSFET, thus making this into an exposure box. (Then I won’t need the sun again!)

Well, that was a short writeup.