Homebrew PCBs

Hi Baxter,

 

I read a message from a few months ago on the UV Pen discussion that you
were experimenting with a UV LED and a microscope objective to focus the LED
down for resist developing.  How are your experiments going?  Any findings
yet?

 

Jeff

 

  _____  

From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
On Behalf Of bebx2000
Sent: Tuesday, December 27, 2011 4:24 PM
To: Homebrew_PCBs@yahoogroups.com
Subject: [Homebrew_PCBs] Re: Photoresist

 

  



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
<mailto:Homebrew_PCBs%40yahoogroups.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? 
> 
> 
> 





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