Homebrew PCBs

On Sat, May 19, 2012 at 1:31 AM, Jeff Heiss <jeff.heiss@...> wrote:

> **
>
>
> Someone mentioned recently they were going to perform experiments using
> screen printing emulsion as photoresist. Are there any updates on the
> discussion? Are the experiments still pending?
>
> Jeff
>
>
That may have been me.  I have tried it and the results were not
encouraging or usable.  I used a premixed diazo-type emulsion and coated a
few boards with it.  It's very difficult to get an even, thin coating with
it because it is very thick, somewhat like old latex paint.  After drying I
found that it required a specific amount of scrubbing to remove the
unexposed areas and it was easy to exceed this.  What made it worse was
that there was no developer per se besides water used to dissolve it, so
there was no way of adjusting the strength of the "developer".  Finally,
the emulsion is rubbery after exposure and does not tend to stick very well
to a plain copper board that lacks the texture of fabric to bind with.
Fine details were out of the question because it didn't adhere well enough
and the stretchy, flexible nature of the emulsion made it impossible to
preserve anything but the largest of features.  It tended to peel off as it
softened under the flow of water.

The thing that makes the Riston-type photoresists so great is that they
stick extremely well to copper, are robust to start with, and become very
rigid where exposed and rinse off quickly where they are not.

Regards,
Larry


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