PCB success!

[jorgen.bergfors at idg.se]

Hi DIYers!

Yesterday evening I managed to etch almost perfect circuit boards of my own 
design, at home in the kitchen.
I have found a method that seems to give almost professional results every time.

I design the boards in Corel Draw. The traces are in one layer, the component 
symbols in another. All traces are magenta, because it looks good together with 
the components when I print it on a colour printer.

I print the board using color separation on transparencies. I tried both a 
Lexmark Optra Rx laser printer and a HP Deskjet 720C inkjet, with film material 
suitable for each. It turned out the inkjet gives better, more opaque traces, 
so that's what I used. It is important that the inkjet uses dye-based black 
ink. HP 720, 8xx and up, Lexmark 5700 and up are fine, but forget Epsons.

I buy the boards pre-coated with positive photo resist (www.elfa.se). 
The film is put on top of the board, with the printed side down. 
A glass pane from a picture frame is put on top.  
Two lead weghts are placed on the glass (outside the board) to press it down.
The boards are exposed to UV-light, using a tanning lamp that I bought at a 
flea market last weekend for SEK 15 ($2). A distance of 40 cm and 4 minutes 
exposure is ideal.

The board is developed in NaOH (I think) for one minute.

The etching is done in a ceramic heatproof container on the stove (normally 
used for baking food in the oven). That way the temperature can be kept around 
50 degrees C, by turning the heat on now and then. Etching takes 20 - 30 
minutes. I don't remember the formula for the etching powder, but it is what is 
sold for PCB etching. 

The result is almost perfect. I didn't do too thin traces because I wasn't sure 
about the results, but traces between IC legs should be no problem at all. 
Seven point text looked perfectly clear on the board.
This is the way to do one-off or a small series of boards I think. It's so 
quick and easy. An it uses no hard to get or expensive materials. Nothing seems 
to be particularly critical. There is no touching up or grinding to do to get 
functional boards.

/Jorgen