Homebrew PCBs

Dennis, you were likely using Kodak KPR resist in college.

It's an excellent resist; capable of very fine lines.

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> )

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.

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>

There are aqueous-based liquid resists available also now,
of course.  You can find quite a bit of info on the web.

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.

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.

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>

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.

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.

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.

I'm not saying that all brands will last so long; but if you have

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.

R.
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