Hi T'netters,
I'm curious regarding the documentation which
accompanies re-worked assemblies.  Naturally,
after all the effort involved in recovering
corroded assemblies, the client (or end user)
is informed of the special processing which
was provided on those assemblies.
Can someone direct me to the appropriate
IPC guidelines for the documentation and
disclosure that accompanies this type of re-work?
Regards,
Mike Simms
Trace Laboratories - Central
(ph.)  847-934-5300
(fax)  847-934-4600
1150 West Euclid Avenue
Palatine, IL  60067
www.tracelabs.com

Notice:  This message is confidential and intended for the private use
of the addressee only.


-----Original Message-----
From: Brian Ellis [mailto:[log in to unmask]]
Sent: Tuesday, March 19, 2002 2:26 AM
Subject: Re: Contamination


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

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