25 Apr
2017
25 Apr
'17
3:06 a.m.
On 25/04/2017 10:08, jim stephens via cctalk wrote:
On 4/25/2017 1:39 AM, Pete Turnbull via cctalk wrote:
>
> "Little residue" would be more accurate, and some of that residue
> will be water (look up "azeotrope") - plus you need a lot of
> alcohol for something the size of a PDP-8 backplane. Blow dry,
> even after an alcohol rinse.
I should perhaps have mentioned that the idea is to flush the remaining
water or alcohol out by blowing, not evaporate it like your hairdresser
would :-) And you ought to use dry air, ideally - most compressors have
water in their air.
In the process of cleaning optics indeed you need air
and other
means to do that, you are right. But in this case I'm suggesting
the alcohol as a way to displace water out of internal parts. The
spotting or such is not much to worry about in the cleaning job on a
computer part.
Except those spotty residues are usually hygroscopic, which can lead to
corrosion later.
But in optics the process is much longer and
elaborate, but still
needs the ventilation to be sure you don't have a problem with
fumes.
Sure. Outside of electronics, my experience is in a chemistry lab
needing clean dry glassware. The process would go something like this:
- preliminary clean with whatever is best, often water and a little
detergent/surfactant, then drain most off
- rinse with distilled water
- rinse with ethanol to flush out remaining water, then drain
- rinse with acetone to remove the alcohol/water residue
- air dry
In photography, on the other hand, the final rinse would just be water -
tap water if not too hard - with a tiny amount of a wetting agent (eg
detergent) in it.
For a backplane or some PCBs I'd compromise, but closer to the
photographic example than the chem lab. In fact I've done that with my
PDP-8s, rinsing the backplanes then blowing out most of the residue.
We had a booboo in assembly that required cleaning and
we no longer
had freon cleaner we wanted to use in that quantity, so we went with
the water / alcohol process. A switch had defective sticky seals on
it and they had all gotten waterlogged. Vendor claimed they would
survive water process wash and they were wrong. Paid us quite a bit
in credit for messing up a couple hundred boards before we caught
the problem.
Ouch!
--
Pete
Pete Turnbull