I've used some of the Kepro pcb materials in the past. I still have one of their hobbyist kits, but I expect it's exceeded it's shelf life. I wouldn't mind having some more of their presensitized PCB stock if it's available and reasonable.
Concerning the dry film processing, you mentioned stripping the material after etching. Isn't dry film also used for "solder mask" , in which case it remains on the PCB?
I'd expect that the etching of copper is completed, rinsed, then dry-film for solder mask is laminated on, then some type of light (UV?) exposure is performed through artwork for the solder mask, then the exposed portions of the mask are washed off. Perhaps this last "wash off" is actually called stripping?
I'd like to learn how to do solder mask and silk screens via dry film at home. Especially if it can be done little to no chemical solvents.
Paul
----- Original Message ----
From: twb8899 <
twb8899@...>
To:
Homebrew_PCBs@yahoogroups.comSent: Thursday, January 25, 2007 11:24:22 AM
Subject: [Homebrew_PCBs] Re: someone with dry film processing experience?
--- In Homebrew_PCBs@ yahoogroups. com, "jcarlosmor" <jcarlosmor@ ...> wrote:
>
> Hi to everybody. I would like to start this thread to know/share
> different experiencies about dry-film processing (home-made lamination,
> imaging, developing, etc.)
> Right now I am planning to build a laminator, uv-exposure unit,
> developing tanks, etc. (all of them DIY of course). After almost 15
> years using all other methods of PCB fabrication, including silk-
> screening for whole big quantities of PCBs, I am tired of doing that
> kind of stuff again and I am planning to use the dry-film method (the
> only one that I should learned many years ago).
> What about the ThinkTink supplies (resist and soldermask)?
>
I may be able to help with dry film if anyone is interested. I ran a
commercial multilayer board shop for over twenty five years. Dry film
was the only resist we ever used. The earliest dry films were
processed with solvents and bad news to work with. We got into the
business right as solvent based films were being phased out.
We started out with semi-aqueous dry film which required a small
amount of butyl carbitol solvent to be added to the water based
developer. Butyl carbitol is a water soluble solvent and it helps to
remove the adhesion promoters left on the copper surface. When the
total aqueous films came on the market the solvents were no longer
needed. Now days all dry films are processed with weak sodium
carbonate (soda ash) solutions.
I use a DuPont HRL-24 laminator to apply the dry film. Developing is
done in a batch type spray tank similar to a spray etcher. After
etching the dry film is stripped in a weak sodium hydroxide(lye) solution.
When Kepro shut down their facility I purchased most of the larger
equipment they had for my own use. This included their CNC drilling
equipment and the entire silk screening department. Jim Keil who owned
Kepro is a personal friend of mine and he said I should offer the
photo resist coated materials for the small shops and hobby guy's that
use it. Thought about doing that many times but I don't know if there
is enough interest these days. Kepro couldn't do it any longer but
then again they had a large operation and the overhead that comes with
it.
Using photoplotted or camera shot films and dry film photo resist will
produce the finest quality printed wiring with a minimal reject rate.
The boards I use for my products are not very large and working alone
I can produce as many as one hundred pieces in an afternoon using
these methods with almost a 100% yield everytime.
If there was enough interest I would offer these materials for sale.
Any comments or suggestions on this topic would be appreciated.
Tom
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