Ted
I agree with St. Doug but ther may be some other steps you will find
useful. Corrosion products are usually a mixture of soluble salts, like
copper chloride, and insoluble ones, like carbonates, oxides and
hydroxides, as well as a gunge of the original contamination. The first
thing I would do is to immerse the products in a 2 - 3% solution of
hydrochloric acid at, say, 40deg C. This will dissolve away the soluble
and much of the insoluble corrosion products (a little brushing with a
nylon-bristles brush will aid the process). I would then suggest a
proprietary neutraliser (of the type used as a rinse-aid after soldering
with water-soluble fluxes) containing the disodium salt of EDTA. This
will help to chelate any remaining metal salts, especially the
relatively insoluble lead ones. Finally, I would give them a saponifier
wash, to make sure that all of the original flux residues are removed,
followed by a damned good rinse cycle, ending with DI water.
At this stage, you can be reasonably sure no corrosion-causing chemistry
remains on the assembly and it will be possible to evaluate the damage
and whether the assembly is usable/repairable/throw-awayable. Be
particularly cautious where there are noble metals: gold-plated kovar
leads, for example, are notorious for promoting stress corrosion on
bends and I've seen cases where the kovar has been completely eaten away
and the component is held on by the gold plating!
Oh, BTW, your solder joints will appear matt after this treatment, but
this does not matter: they will be perfectly OK from the chemical,
metallurgical and mechanical points of view. It is purely a cosmetic
dulling.
Just as an additional precaution, in view of their history, I think I'd
be inclined to give these assemblies a spray of an acrylic conformal
coating, but this won't be strictly necessary if they meet the testing
that Doug advocates.
Brian
Ted Tontis wrote:
>
> We have a number of PWB's that show signs of contamination,
> management wants to find out if there is a way to clean the boards. I have
> told them once the corrosion starts there is no way to clean the assemblies
> and make them dependable enough to cover our warranty. Some of the boards
> show slight contamination and some more aggressive, but these have been in a
> controlled environment for some time. I feel If we where to send them out in
> a industrial environment the corrosion would rapidly increases. These boards
> are FR-4 and not conformal coated. Am I correct on this?
>
> Thank you,
>
> Ted Tontis C.I.D.
> Engage Networks, Inc.
> 1320 N. Dr. Martin Luther King Jr. Drive
> River Level
> Milwaukee, WI 53212
> PH 414-918-4267
> FX 414-273-7601
>
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