--- In
Homebrew_PCBs@yahoogroups.com, Richard <metal@...> wrote:
>
> Dennis, you were likely using Kodak KPR resist in college.
I remember that KPR photoresist from back in the mid-1970s. It
did a reasonably good job, if used with care. I seem to remember
that it disappeared from the market shortly thereafter, although
I don't remember why. Didn't Kodak spin off it's chemicals
division? Or, was it due to environmental problems?
> It's an excellent resist; capable of very fine lines.
Yes, I was very pleased with it.
> In fact, it was used for IC processing in the early days
> (60's).
>
> I used it in past years, via a dirt-simple dip-coating method
> from a VERY thin staintless tank I tig-welded up (it was
> 70 bucks a -quart- at that time...so I made a THIN tank... <g> )
Well, it was expensive, but you didn't use very much per board.
> It -is- a solvent-based chemistry tho; so for those frightened
> of anything potentially dangerous in life, it's probably not a
> good one to choose.
If I remember correctly, the developer was based on Xylene, which
was a suspected carcinogen.
> Otherwise, it's an excellent resist for our purposes; because
> it coats nicely, has a wide process latitude, develops cleanly,
> and washes off cleanly. All using solvents of course. <g>
Is it still available?!?
> There are aqueous-based liquid resists available also now,
> of course. You can find quite a bit of info on the web.
Pointers, please. I did a bit of research 8-10 years ago when
I was thinking about starting up my wet-lab again, and it looked
like the technology had changed completely. Or, was I just not
looking in the correct place?
> Dry-film resists are virtually all aqueous-based processing;
> and with quite benign chemicals. Well, I say that as one
> who isn't scared of things like that. The developer is simple
> washing-soda (sodium carbonate) and the stripper is simple
> "lye" (sodium hydroxide). Technically 'lye' is actually
> potassium hydroxide, but everyone calls the sodium version 'lye'
> as well.
My grandmother used to make soap with it (Well, ok, so a bad batch
would take your skin off.).
> In any case, lye is a strong caustic, and will burn the eye if
> splashed into it. However, it is in no way what I consider
> a "toxic". I.e., it will -damage- you if you drink it, but it's
> not a lethal 'poison' as such.
Common sense isn't common anymore.
> In a can of crystal "Drano", the white crystals are lye; the
> metal chips aluminum. Lye eats aluminum vigorously; which
> gives off heat and gas, which helps unclog the drain. And
> lye tends to eat organic materials, like hair, skin, etc..also
> loosening up the clog. And also a good reason to keep lye
> off your skin... <g>
And to stay away from poorly made lye soap. :-)
There are other drain openers which don't have the Aluminum chips
in it, so you don't have to experience the joy of picking out the
chips.
> In any case, I was going to suggest lye here for loosening
> the paper from the board after ironing; but saw so much
> chem-fright when I first joined, that I didn't say anything.
That might work. The problem is that paper is based on celluose
fibers, and those are pretty tough to chew up, at least without
the right chemicals. I'm not sure if lye would do it or not.
Obviously, termites have solved the problem of digesting celluose
fibers, but I don't think that turning a bunch of termites loose
on your thermal toner transfer boards would be a good (or quick)
idea.
> A 10% solution might turn out to be effective at softening the
> fibers and the bonding agents. I've never tried it....just a
> guess,
> based on paper being organic...might work better than soap.
Well, unless you're using some of that poorly made lye-soap. :∗)
An enzyme based approach might be useful, too, if we could come
up with a cheap, readily available enzyme. Maybe.
> Someone mentioned the shelf-life of dry-film being 6 months.
>
> That may be what the spec says, but I've made boards from
> a roll of Dupont Riston (4712 I think) which was 5 YEARS
> old when -I- got it, and I used it for another 5-7 years after
> that, until it was gone. Never had a lick of trouble with it;
> never even had the exposure or development process shift.
>
> Kept it in a 50F basement, sealed in a giant ziploc with the air
> sucked out. No special treatment other than that. I would
> generally pull it out 2-3 times a year, laminate a bunch of
> 12x12" panels, and put the roll away. Then use up the panels
> over the next 3-6 mos.
A lot depends on the storage method. And, of course, it's good
to test old material out in a small sample before starting a major
production run.
> I'm not saying that all brands will last so long; but if you have
And, different batches may have different storage characteristics,
even for the same brand.
> a chance to pick up some surplus dry-film dirt cheap; it's
> well worth taking a small risk on it. It may turn out to be
> perfectly usable still, regardless of date-code.
Just test it out first.
> R.
Dave