Homebrew PCBs

Chris Maness wrote:
> On Fri, Apr 2, 2010 at 5:57 PM, Russell Shaw <rjshaw@...> wrote:
> 
>> Chris Maness wrote:
>>> I made up a board on a CAD transfer program, and printed it off on a 
>>> transparency.  I exposed it to my homebrew UV LED array for 1'30" and 
>>> transferred it to a store baught developer.  I agitated it in the
>>> developer at the recommended 10:1 concentration for well over 5 minutes
>>> and the light sensitive coating showed no sign of coming off.  I exposed
>>> it again for a solid 5 minutes, and again put it in the developer with no
>>> sign of any action.  I have left in the back yard now to see if it will
>>> finally come off.  It does look like some milky looking material is
>>> slowly coming off, but this is MUCH longer than I expected.  I am asuming
>>> all the positive boards require the same NaOH solution, so I don't think
>>> that's the problem, but I am not sure.
>> Positive resist or negative?
>> 
> 
> I'm an idiot.  I did not realize that there is a sticker covering the 
> sensitive side.  However, after developing, my traces look a little on the 
> thin side.  Maybe my masque was not dark enough, or I over exposed.  I ran 
> 1m30s, using 15 LEDs on a 4x5 perf board.

With the film still on, the traces get thinner due to light-undercutting
travelling through the film under the track.