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?
Jeff
_____
From:
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com]
On Behalf Of Harvey White
Sent: Monday, December 26, 2011 8:00 PM
To:
Homebrew_PCBs@yahoogroups.comSubject: Re: [Homebrew_PCBs] Photoresist
On Mon, 26 Dec 2011 20:32:02 -0000, you wrote:
>Hi,
>
>it's been years since I made my first circuit boards the old fashioned way,
carefully tracing over the artwork with a sheet of carbon paper underneath
onto the bare copper board and retracing again over the pattern left from
the carbon paper using an etch resist pen and then using a #11 xacto to
gently scribe any excess ink from the edges of the traces, touch up with
pen, scribe, etc. until perect and then etch.
I never got that to work.
>
>ok that was 30 years ago and I want to make some new boards now so looking
at products ranging from DIY hobby to industrial production, youtube videos
and websites I am in a better position to understand the processes now.
basically from what I gather the first step is the one with the most
variation, applying the etch resist to the board. etching is still pretty
much the same all around.
>
DIY is one thing, professional gets nasty.
>there are 2 ways to go, either positive or negative photoresist,
also toner transfer, which can be surprisingly decent.
>
>the former seems more straight forward considering the artwork is
unchanged, but the chemicals to apply positive resist are expensive and not
as readily available I am discovering.
>
Take your word, presensitized boards are expensive, say 6 to 8 USD for
a 4 x 6 board.
>There is a discontinued positive resist spray that was made by MG Chemical,
and various liquid positive like Kodak KPR, and POSITIV 20 photoresist
lacquer spray available by mail order from UK distributors. These all need
to be applied in dark room conditions and fully cured before developing,
possibly with heat from an oven.
>the nice thing I think is that no laminating machine is needed, since
looking into that I find that "hot roller" is the way to go and that can get
expensive.
>
Avoid KPR like the plague. Works really well, but nasty chemicals,
really.....
Problem with these is that unless you manage to get the coating even,
the exposure can vary a bit.
>
>next is the dry film negative that must be applied with a laminator, I see
many videos showing DIYers running boards through the laminators several
times in an attempt to compensate for low or uneven heat, something a more
expensive 4 Hot Roller laminator (Tamerica / Tashin TCC6000) would be needed
for even light production.
I hear good results if you are careful.
>
>when comparing the 2 methods it's possible to see pros and cons in both,
positive must have a dedicated darkroom to work and negative is an
investment into equpiment, namely a reasonable quality laminator that new
might run over $400
negative may need that same darkroom. However, a bathroom with some
towels across the door bottom can be just fine. I wouldn't worry
about the cost of the darkroom that much.
>
>both need uv exposure but the latter need less power so maybe the cost is
offset somewhat not having to absolutly have UV.
Generally, three or four Blacklight tubes will do well enough, unless
you use something that needs shortwave UV (which gets nasty, really).
Longwave is not all that bad, tubes are easy enough. The MG chemicals
uses pretty much 6500 degrees K daylight fluorescents. Slightly
difficult to find, but not expensive.
>
>then it comes to what brand of dry negative resist?
no ideas here.
>
>there are several including:
>
>MG Chemical
>
>Dupont Riston
>
>Kolon
>
>eBay nameless brands, etc.
>
>and then there are different types, thichnesses intended for different
processes, electroplating, sandblasting, etc.
>
>I'm skipping the part where the transparency is made, guessing that would
be fine just bringing the pcb file to Kinko's or an Office Box store on a
flash drive, or buying at least a 600dpi, maybe even 1200dpi laser black and
white printer, ok for cad art, a scanner also for magazine or other art.
either pos or neg transparency for either spray on/chemical or dry film,
that I get.
Not really, the more opaque the negative, the better you get.
Sometimes you need red ink from an inkjet, laser may not be
sufficient. Some experimentation is needed. Not opaque enough, you
start to expose the wrong regions.
Ideal would be a photolith film, which is pretty much opaque black and
transparent. Sadly, Kodak Photolith is not made (IIRC) and it still
requires a good photoplotter (ideally), otherwise it's negative on
transparency.
>
>so my questions then are,
>
>anyone with any experience either with the positive resist chemicals and/or
the various brands of negative dry resist films?
Only the MG boards and KPR.
>
>I'm looking for information beyond manufacturers claims and DIY videos or
websites to help in comparison of these 2 photoresist methods and the
various processes and products required.
>
>Many thanks and happy holidays to all,
And to you.
Harvey
>
>Robert
>
>
>
>
>
>------------------------------------
>
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>
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