Homebrew PCBs

Hi Jeff,
I got your email. I have pretty much put my experiments with DIY photoresists on the backburner. The patent that I originally cited has very precise instructions for making your own. The application was for solder mask. I assembled all of the ingredients, but discovered that that I need a mixing mill to make a decent emulsion. Elmer's School Glue is basically the same formula, PVA and PVac  plus surfactants  and flow aids. I made up a batch using diazo as a sensitizer in the same proportion as the patent, coated a blank PCB with a soft hair brush (it levels very nicely because of the surfactants) and pre-baked it. I then took a transparency with some pads and traces and exposed it with a 150 watt metal halide UV source. The time was calculated from the mJ of the patent based upon the UV intensity as measured at the surface of the PCB with a UV radiometer.

After exposure, I washed the board in water with a little gentle rubbing and the areas under the black part of the transparency washed away, but not perfectly. I didn't bother with the post-bake so perhaps this was part of the problem. I also tried just dipping a pre-baked board in a 1% solution of ammonium dichromate (as in the second patent), but the exposure time seemed to be off. All-in-all I think this is a viable concept, but one needs to have patience and setup a systematic sequence of experiments to establish the exposure time relative to the amount of sensitizer. 
Baxter
N.B. I caution you in the use of ammonium dichromate. It really likes to cross-link collagen.

--- In Homebrew_PCBs@yahoogroups.com, "Jeff Heiss" <jeff.heiss@...> wrote:
>
> I have been researching and have found that making your own resist looks
> possible.  The ingredients are polyvinyl alcohol (PVA) and ammonium
> dichromate.  An alternative is Elmers glue and ammonium dichromate.  Baxter,
> a member on here was performing experiments in this area.  Maybe he can
> chime in if he is reading?  
> 
>  
>