POSITIV 20 negative photo resist doesn't work anymore. I believe the formula
was changed a few years ago and now the method they recommend, the same has
before, produces no results. Haven't found a cheap alternative that I can
try yet. Having the board made TT method is my temporary solution for now.
Nuno T.
> -----Original Message-----
> From: Homebrew_PCBs@yahoogroups.com
> [mailto:Homebrew_PCBs@yahoogroups.com] On Behalf Of Robert
> Sent: segunda-feira, 26 de Dezembro de 2011 20:32
> To: Homebrew_PCBs@yahoogroups.com
> Subject: [Homebrew_PCBs] Photoresist
>
> 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.
>
> 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.
>
> there are 2 ways to go, either positive or negative photoresist,
>
> 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.
>
> 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.
>
>
> 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.
>
> 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
>
> both need uv exposure but the latter need less power so maybe
> the cost is offset somewhat not having to absolutly have UV.
>
> then it comes to what brand of dry negative resist?
>
> 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.
>
> 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?
>
> 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,
>
> Robert