Techies, I know this to be a late posting but, according to the gospel of St Brian of Cyprus - be careful with your bristles! Regards Graham Naisbitt [log in to unmask] <mailto:[log in to unmask]> Concoat Limited Alasan House, Albany Park Camberley GU16 7PH - UK www.concoat.co.uk <http://www.concoat.co.uk> Phone: +44 1276 691100 Fax: +44 1276 691227 Mobile: +44 79 6858 2121 > -----Original Message----- > From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis > Sent: 19 March 2002 08:26 > To: [log in to unmask] > Subject: Re: [TN] 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 > > 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 > > > > > ------------------------------------------------------------------ > --------------- > > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > > To unsubscribe, send a message to [log in to unmask] with > following text in > > the BODY (NOT the subject field): SIGNOFF Technet > > To temporarily halt delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL > > To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest > > Search previous postings at: www.ipc.org > On-Line Resources & > Databases > E-mail Archives > > Please visit IPC web site http://www.ipc.org/html/forum.htm for > additional > > information, or contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > > > ------------------------------------------------------------------ > --------------- > > ------------------------------------------------------------------ > --------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt delivery of Technet send e-mail to > [log in to unmask]: SET Technet NOMAIL > To receive ONE mailing per day of all the posts: send e-mail to > [log in to unmask]: SET Technet Digest > Search previous postings at: www.ipc.org > On-Line Resources & > Databases > E-mail Archives > Please visit IPC web site http://www.ipc.org/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > ------------------------------------------------------------------ > --------------- > --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------