From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: Problems with using Aerosol Photoresist
Date: Sun, 01 Dec 2002 04:20:30 GMT
NNTP-Posting-Date: Sat, 30 Nov 2002 20:20:30 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
Viacheslav Slavinsky wrote:
> Ross wrote:
> > Has anyone out there had any success in using the Electrolube PRP positive
> > photoresist for making PCB's. I understand this product has changed
> > recently from an easy to use blue chemical, to the current green
> > formulation. Can any one explain to me the steps involved in getting this
> > newer product to work, the type of UV lamp used, developer etc.
> From the description, it seems to be the same, or very similar to,
> photoresist that I have here. It's still purple and can be developed in
> caustic soda. I guess the only way to get the right exposure is
> experimental, I heard that properly exposured areas should look a little
> brighter than unexposed in side light. On my first try I went with a
> seriously underexposed board and it was a real pain to develop it, but
> somehow it made out well and with help of a marker I could finish the
> board. I don't know characteristics of my UV lamp so no real advice
> here, sorry.
> What I'd like to hear is how people use their wits to make a THIN and
> UNIFORM layer of this fabulous fluid on their boards. Here it seems to
> ignore all cleaning and degreasing and forms annoying spots on the
> surface, unless the layer becomes really thick, which is not good.
The easy and "nasty" way to make a thin and relatively uniform
coating, is to use a suitable solvent/thinner - a chemical that is the
solvent listed on the can, or chemically related.
I used benzene for KPR.
Use 1 to 3 parts thinner to 1 part "glop" - just enough to make it
close to water consistency.
Pour a little of the mixture on the middle of the board and carefully
tilt the board slightly each way; use the thick "wave" of the liquid to
wet all parts of the board, set it down on a level surface and let it
dry (keep the dust bunnies away, tho).
Surface tension will keep the thickness uniform; just do not put too
much liquid on - to prevent wetting beyond edges or the corners.
Another way is to mount the PCB on a spinner, and slowly pour the
"glop" in the center - until it is all coated (excess will be thrown off
and get you all wet unless there is a circular guard).
This second method was the way Kodak Photo Resist aka KPR (or KMER)
was put on wafers in the 70s to 80s.
If the liquid now seems to be avoiding areas, they are prolly greasy
or otherwise contaminated, meaning etching will also go poorly.
Ya gots ta have a clean board....