Peter Onion wrote:
> For simple circuits will I need some think like this 
> http://www.rapidelectronics.co.uk/rkmain.asp?
> PAGEID=80010&CTL_CAT_CODE=30342&STK_PROD_CODE=M66161&XPAGENO=1
> or can normal OHP transparencies be used ?  I only want do make some
> small boards with 0.1" spaced DIP devices and for that using a whole
> sheet of that (expensive) sheet seems rather wasteful. 

I use normal transparencies fine. Make sure they're inkjet
transparencies though, else the ink won't stick (you probably knew
that already). I've printed 50mil PLCC packages and quite thin tracks
without error, although it takes some practice. Make sure the image on
the transparency is very black, with no tiny holes, etc (you might
have to mess around with the print settings. A black rectangle is OK
for a test pattern to see the uniformity of the print). Some films
work better than others, I've seen some really bad ones.

I have a UV exposure unit, although normal light works fine, just
needs more time. My PCB says recommended 3 minutes UV, I use 2m40s
which works fine for me. For developing, I just follow the directions
on the developer package. For etching I use HCl+H2O2 which is the
standard "fast etchant" kit from my electronics supplier. Others use
other methods, you might want to experiment.

Also, I found that wiping the board after developing helps a lot get
rid of the softened resist. No, the unexposed parts do not go away, it
is quite strong.

-- 
Hector Martin (hector@marcansoft.com)
Public Key: http://www.marcansoft.com/hector.asc

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