Homebrew PCBs

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