[volt-nuts] Best cleaning procedure for precision cirquits

[Chuck Harris]

In my experience IPA does dissolve all rosin flux residues.  It is not
as aggressive as Trichlor was.  You have to provide a little mechanical
help in the form of a brush.  I use the tin handled glue/flux brushes
for any scrubbing on the component side, and old tooth brushes for any
scrubbing on the solder side.

The boards I clean with fresh IPA are easily as clean as I used to get
using trichlor in vapor degreasers.

Also, IPA will not touch the citrus based fluxes that are intended to be
water washed.  I use solder with that awful flux for some customers that
are particularly concerned about their hydrocarbon emissions.  I have
to use a flux hood, and a smoke straw then soldering.  The water washed
fluxes are strictly murder on your eyes and nose.

Trichlor is so dangerous that it is no longer available in containers
larger than about 1L.  I don't think it is actually being manufactured
any more, and any that you can buy (at high price) is left over stock
from the 1970's.  One 55 gallon barrel would fill a whole lot of pint
bottles.

Pentachlor is sold by CRC as a brake cleaner product.  It smells just
like trichlor, but is about 16lbs per gallon... very heavy!  Any that
hits the environment sinks immediately through the soil and down to
the water table.  And it is not a very aggressive cleaner.  I am certain
in a few years hence it too will be banned.  It should be avoided.

Water based cleaning is what the industry does these days.  Virtually
all parts are made to withstand short exposure to water and detergent.

You might also notice that surface mount boards are not cleaned at all!
They just leave the flux where it lay.  I have fixed many irratic
behaviors by scrubbing the boards with IPA and really removing the flux.
It is slightly hygroscopic, and forms leakage paths.

Regardless of how I clean, I bake the boards for a few hours at 50C in
an environmental chamber (aka convection oven).

-Chuck Harris

Alan Scrimgeour wrote:
> In my experience IPA doesn't dissolve all flux residue, leaving an off
> white powdery material not due to IPA impurities. Acetone dissolves the
> lot, but can damage some plastics.
> I've been looking into Vapour Degreasing for the first time in many
> years and am surprised to find it is virtually a thing of the past. 3M
> sell some 'green' fluorinated solvents, but I'd imagine they're
> horrendously expensive. Flammable solvent degreasing would be just too
> dangerous indoors! Methylene Chloride is still readily available for
> some reason, but it's a potent paint stripper/plastic destroyer, so
> that's out for electronics. I was hoping at least there might be some
> small vapour degreasing tanks at scrap prices, but no sign of those either.
> I'd be concerned about using water based cleaning on very sensitive
> circuits, as described in a recent post. Although I wouldn't expect it
> to cause any problems with PTFE, it may affect the component package.
> A long bake after cleaning might be a good idea however you clean..
>
> Alan