--- In
Homebrew_PCBs@yahoogroups.com, Len Warner <yahoo@...> wrote:
>
> No, nor new either: prior art in message 13667, Apr 21, 2006, 2:14 pm.
>
> Perhaps all mihai_hagianu needs to do is to bake the developed
> PVA image to make the colloid completely irreversible.
> Colour is a good indicator - dark straw should be about right.
>
> This definitely does work on a homebrew gelatin-dichromate
> photoresist in acidulated ferric chloride etchant.
>
>
> Regards, LenW
>
Hello again,
I have tryed to bake the PVA image as you sugested, at 3 temperatures,
and there is no perceptible impruvement.
You mentioned Gelatin-Dichromate homebrew resist. Do you have any
information about that?
Also, is there any reference of what was the PCB photoresist before
the canned aerosols like positive 20 came along ?
What I need to do is to get an emulsion which works on ungalvanised
steel sheets as etch resist (electroetch or chemical etch or better both).
I have done some more testing with ulano 995 water resistent emulsion,
but it is not good. On (Zn)galvaized steel it forms a good image but
it does not stand against electroetch nor FeCl3. On ungalvanised black
steel, something from the emulsion reacts with the iron, and the
emulsion becomes insoluble withouth the UV , so it cannot be developed
anymore.
any ideeas would be welcome. I'll keep you posted with my progres
(slow up to now)
thank's
mihai