I am not a chemist by background either, and did not
read the rest of this post, but I on occasion clean Si
wafers (already processed into devices) and x-ray
optics.
flux, if not evaporable (at room temp) by itself,
won't generally evaporate, no matter what solvent
absorbs it.
Cleaning means basically dissolving whatever
contaminants are on the part to be cleaned by some
chemical, and then getting the chemical/dissolved junk
off the part. The nature of the contaminant is an
issue. If it's oils, fingerprints, etc.. then use a
detergent. I use alconox (powder detergent mixed with
DI water), and have never tried but suspect on pcbs
standard dishwasher detergent would work ok. Then I
use acetone and then methanol.
Getting off the solvent/dissolved junk is another
issue: For the detergent, the detergent will dry
fast, but does remove most organics. Blowing off the
detergent mix directly doesn't work so well(it also
evaporates fast), so after I've soaked something in
detergent, while the sample is still wet I dilute with
a bunch of DI water, then rinse several times more
with water. After each water rinse, I blow off with
dry nitrogen. For PCBs air is probably fine. For
alcohols, it is important to blow off after every soak
so that the still wet alcohol is blown off the sample
with the contaminants it has absorbed before it has
much chance to evaporate, otherwise it leaves behind
whatever it was sucked up in the first place.
Another thing that would help a lot is an ultrasonic
cleaner - www.harborfreight.com sells them cheap, but
I don't know the quality.
--- dl5012 <
dl5012@...> wrote:
> --- In Homebrew_PCBs@yahoogroups.com, "Stefan
> Trethan"
> <stefan_trethan@...> wrote:
> > I don't think flux will ever evaporate, no matter
> in what it is
> dissolved.
>
> Well, I'm not a chemist (didn't pay much attention
> to chemistry - I
> was an EE major). But I can tell you what I'm
> seeing. If I clean
> flux from an area with 70% IPA and compare it to an
> area cleaned
> with 98% IPA, the 98% IPA area is cleaner; has less
> residue. This
> is without allowing it to run off the edge of the
> board or blowing
> off the residue with compressed air. I'm pretty
> sure some amount of
> flux will be carried off when a volatile solvent
> evaporates.
>
> Did you ever think about what's going on when you
> smell some dog
> crap? You're actually breathing molecules of dog
> crap...
>
> > Maybe the water is doing something bad, i sure
> don't understand
> it. Flux
> > will not solve in water, maybe that's causing the
> dusturbance.
>
> It's the water that's cauing the problem. I talked
> to several
> Pharmacists when I was searching for a source of
> anhydrous IPA.
> They all said that rubbing alcohol was 70% IPA and
> 30% water.
>
> > What does the good IPA cost in comparision?
>
> 98% IPA is costing me $4/pint vs. $1 for drug store
> variety rubbing
> alcohol.
>
> > In general i noticed IPA seems to leave more
> residue than
> denatured
> > alcohol.
>
> The more volatile the solvent, the less residue it
> will leave. I
> attribute that to how quickly it evaporates. But
> I'm not a chemist.
>
> > I do know what you mean by the snagging wires
> problem, that's why
> i rarely
> > clean the flux off.
>
> I'm somewhat of a Perfectionist. I started working
> as a technician
> before I became an engineer. I prided myself on
> quality of
> workmanship. When I was an R&D Tech at HP Labs, I
> used to gold
> plate my prototypes and black annodize my heatsinks.
> I got a lot of
> compliments on my work. Back then, I used an
> endmill to layout my
> boards (a manual CNC if you will). Even though I
> could have sent
> them out to have boards made. Since I never did
> more than one of
> each design, I did it manually. It was less work in
> the end. I did
> more than a few calculations to determine the proper
> width for 50
> ohm transmission lines.
>
> Once flux has done it's job of preparing materials
> for good solder
> joints, it needs to be removed or deactivated so it
> doesn't cause
> problems. I was always taught to remove the flux.
> Every single
> person who worked on the line where I built
> computers removed flux.
> But, I've seen commercial equipment that was hand
> soldered and no
> attempt was made to remove the flux. Whenever I
> open up a piece of
> equipment and see that, I remove it; at least from
> the area where I
> make repairs. Even if it didn't have the potential
> to cause
> problems, it still looks better without it.
>
> If I were buying two similar products and one looked
> like there was
> more quality in workmanship, I'd probably buy the
> one that had
> better workmanship; even if it cost more. Maybe
> that's just me.
>
> Regards,
> Dennis
>
>
>
>
>
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