The process of reclaiming function of a corroded assembly as described would
be classified as repair. Repair methods are described in IPC-7721. I doubt
that the procedure outlined by Doug is in the document.
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Simms, Michael
> Sent: Wednesday, March 20, 2002 8:55 AM
> To: [log in to unmask]
> Subject: Re: [TN] Contamination
>
>
> 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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