One other thing that made a big difference to me
was the quality of the transparency.  Photo-copied
transparancies are never as dark as laser-printed
ones and always seem to cause problems.

Cheers,
-Neil.



> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Tony Harris
> Sent: Sunday, January 05, 2003 6:20 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: PCB exposure/developing timing?
>
>
> Good news!!
>
> I've had more success!!!!  Albiet after wasting a few more cuts
> of material
> ;)
>
> I exposed a board for 8 minutes under my light.
>
> Developed in my weaker mix of developer (known strength level)
>
> Etched it.
>
> Best board yet.
>
> Flaws:
>
> 1) Seems I didn't let it sit *quite* long enough in the developer - there
> are some small streaky areas of copper, really small - mostly right around
> the traces or pads, but nothing affecting continuity of the rest of the
> board
>
> 2) One of my traces is near open - it is still connected enough
> to generate
> tone with my tester, but I will probably have to do a wash over
> of solder to
> make sure of a solid trace.
>
> Thanks again to all that helped me out here - I really appreciate it.  I
> think I am beginning to get the hang of it - I have found that I hate my
> laser printer when it comes to printing on transparencies, and am going to
> have to get transparency film for my Pictrography to print out my stuff
> normally.
>
> -Tony
> KG4WFX
> ----- Original Message -----
> From: "Brian Aase" <res0qrqr@VERIZON.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Sunday, January 05, 2003 4:22 PM
> Subject: Re: PCB exposure/developing timing?
>
>
> > > I've seen my trace appear, but then "develops" itself right off the
> > board -
> > > either I've left it in too long, I haven't exposed it long
> enough, or my
> > > developer mixture is too strong.
> >
> > If you're using positive-acting photoresist, remember that the
> > UN-exposed resist lacquer is supposed to stay on the PCB without
> > developing away.  Only the part that "sees" light should dissolve.
> > So, you either:
> > 1) are developing way too long or the solution's too strong, or
> > 2) the material was exposed to too much ambient light beforehand.
> >
> > I'm sure others will offer lots of suggestions for optimizing your
> exposure
> > time.  But here are a couple hints that might not otherwise appear:
> > 1) Try developing a small, completely unexposed piece of material that
> > you are sure has been kept in total darkness.  If the lacquer still
> > dissolves, ease up on the developing process.
> > 2) If Experiment 1 works (i.e. the lacquer doesn't dissolve), then move
> > ahead
> > and expose/develop a small piece of material that is half exposed and
> > half covered with solid black film.
> > 3) Now, in the event that Experiment 1 succeeded, but
> everything dissolved
> > away during Experiment 2, you might have a problem that your film is not
> > opaque enough to UV light.  Or, as alluded to above, the raw material
> > might have been exposed to too much ambient light.  Or finally -- as you
> > first suspected -- your exposure time is too long.
> >
> > Let us know how the experiments progress!
> >
> > Brian Aase
> >
> > --
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