[Elecraft] Cleaning Solder Flux, Redux

[Alan Bloom]

Kester specifically says that rosin residue removal is for cosmetic 
considerations.    Here's the exact quote:

"Rosin flux residues are non-conductive and non-corrosive. Under normal 
circumstances they do not have to be removed from a printed circuit 
assembly. Rosin residue removal would be for cosmetic considerations. In 
an environment where the working temperature of the assembly will exceed 
200°F the rosin residues will melt and become conductive, in these 
situations flux removal is required."

https://www.kester.com/knowledge-base/faq#46137-rosin-flux-removal-the-question-that-frequently-comes-up-is-do-rosin-flux-residues-need-to-be-removed

Again I recommend that you not attempt to remove the flux residue unless 
you have the technical means to ensure that all traces of it are 
completely removed.

Alan N1AL


On 1/1/2022 2:01 PM, Eric Garner wrote:
> >The only reason for removing flux is purely cosmetic
>
> That isn't accurate. Even modern no-clean fluxes can cause corrosion 
> and current leakage if left in place under certain conditions If 
> leakage is a concern, you can specify a surface resistivity level and 
> the boards can be ultrasonic washed or double DI washed to meet that 
> criteria.
>
> Eric KI7LTT
>
> On Sat, Jan 1, 2022, 11:16 AM Alan Bloom <n1al at sonic.net> wrote:
>
>     Another problem with cleaning flux is ionic contamination.  The
>     activator in the flux, which is necessary to get the solder to
>     stick, is
>     acidic.  As long as the flux is left alone, the ionic
>     contamination is
>     trapped in the rosin where it can do no harm.  But when you
>     dissolve it
>     with alcohol or another solvent is is spread over the surface of the
>     board, unless you do a VERY thorough job of cleaning it off.  That
>     can
>     cause electrical leakage between circuit nodes and potentially
>     corrosion.
>
>     The only reason for removing flux is purely cosmetic. When I was at
>     HP/Agilent the rule in production and service was that any flux
>     remaining on the board due to re-work or repair was just left in
>     place.
>
>     Alan N1AL
>
>
>     On 1/1/2022 3:25 AM, CUTTER DAVID via Elecraft wrote:
>     > Ted
>     > If the residue is clear, don't bother, you might create more
>     damage than you realise (ESD).  If the residue is brown, you've
>     been using the wrong solder.  If you really feel the desire for
>     aesthetics then you can can brush it with IPA, but beware ESD if
>     there are sensitive components on board.  Also beware some
>     components can dissolve in some cleaners, eg old style polystyrene
>     capacitors.
>     >
>     > 73 and HNY
>     > David G3UNA
>     >
>     >> On 31 December 2021 at 20:52 edauer at aya.yale.edu wrote:
>     >>
>     >>
>     >>
>     >>
>     >> Is there a consensus among builders of the traditional kits
>     (K1, K2, etc)
>     >> about the best way to remove solder flux from a completed
>     circuit board?
>     >> Some Internet sites recommend acetone, others say isopropyl
>     alcohol. A few
>     >> tout their own product without saying exactly what it is.  I
>     remember
>     >> reading someplace that one or the other of those will clean the
>     flux but
>     >> could also cause damage by being absorbed into components. 
>     Yes, I know this
>     >> is all purely cosmetic but if it can be done safely I'd like to
>     try it on
>     >> the next kit.  Suggestions?
>     >>
>     >>
>     >>
>     >> Thanks,
>     >>
>     >>
>     >>
>     >> Ted, KN1CBR
>     >>
>     >>
>     >>
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