While browsing some fora about PCB etching, I ran into some comments about UV photo exposure with CFL (compact fluoriscent lamp / Energy Saving Lights).
I was surprised by the fact that there's so much UV exposure from such lights. But it made me also eager to build a "CFL UV exposure box" just to see whether I was able to create some DIY PCBs
First thing that I needed was a list of goodies in order to make it a successfull project.
So here's my shopping list:
- 2 x 15W CFLs
- two bulb fittings
- a box to hold the lights. I found a cheap one at a local DIY store
- some aluminium foil for better results.
- photo sensitive board
- a photo frame for pressing the printed design to the photo sensitive board
- photo development powder
- 3-wire cable
- power plug
Additionally you need a printed design. I created a design for a "variable voltage supply". How can one live without one?
So, if the project does succeed (utter coincidence) then I'll have one of my own.
Building the box
Depending on the type of fitting you either:
- cut/drill/saw two holes in which the fittings fit tight and mount it by two rings.
- or use screws to mount your fittings to the box.
Drill 3 small holes for the 3-wire cable. Two for connecting the fittings and one for connecting the power plug.
After the wiring the cable, use the aluminum foil and glue it to the inside of the box.
The picture below shows the CFL box (withoud the foil).
There's an improvement using aluminium foil inside the box, at least for the visible light. But it's likely that the UV light is reflected by the foil as well. And yes, I waited a while before taking both pictures, to assure that the lights were warmed up.
For creating the printed design, I used gEDA
, but there are many many other programs fit for the job.
Before exposing the board, prepare the photo development 'bath'. You only need a small amount of powder and you can use it several times.
The necessary exposure time is about 8 minutes, but it depends on the CFLs, and photo sensitive board and the distance between lights and board.
Both under and over exposure result in bad PCBs because the contrast will be too low. The first will take you a lot of time to etch everything away (including the parts you wanted to keep). The latter will etch everything away before you know it.
The pictures below show results of under exposure. When you take a good look at the zoomed picture, you can see the pattern, but the contrast is low.
After 4 times I found the right exposure time and the right etching procedure.
The next step is to develop your board. Put the board in the development bath. This is less time critical then the exposure.
Within a few minutes you should see the design on your board. When the development process is done, clean the board with water.
The next step is the etching part which I will describe in a different post. The pictures below show my first etching success and my variable power supply.