> Dear Technetters,
>
> We've just finished our first few boards with Humiseal 1B31 conformal
> coating, applied with a selective spraycoating machine, and we asked the
> customer to inspect the products.
> He commented that some areas on top of the IC's were not covered
> completely, which is required (so he says) because these are plastic
> components which may absorb moisture if left uncovered.
>
> I'm not gonne argue about this with the customer, but still I'm
> interested to hear from you wether the fact that the IC's are plastic is
> indeed a reason to require them to be completely covered with coating.
> As far as my knowledge goes the problem with plastic IC's and moisture
> is limited to the soldering process only, but I may be wrong.....
> Anyone can comment ?
>
> Daan Terstegge
> Unclassified mail
> Personal Website: http://www.smtinfo.net

Daan,

I suspect that the reason for the lack of coverage to the IC covers is due
to dewetting. The dewetting will probably be caused by the presence of some
mould release residues. Is this a problem?

Not really, although it would be a good idea to try and obtain IC's that do
not exhibit this problem, as it may be that if you clean the assembly, and
the mould release is silicone, then you might be spreading the silicone over
the surface of the assembly.

Is this a problem? Yes. Inspect under UV and check for dewetting in other
areas.

As to the issue of component reliability due to moisture ingress, this is
highly unlikely with the IC. However the customer is right to require it for
the reason I just outlined. It should not happen...

Hope this helps

Regards, Graham Naisbitt
--
[log in to unmask]

Concoat - Engineering Reliability in Electronics
Concoat Systems - Measuring Electronics Reliability
Synergie - Electro-chemically compatible process chemistries

Concoat Limited
Alasan House, Albany Park
Camberley, GU16 7PH - UK

Phone: +44 (0)1276 691100
Fax: +44 (0)1276 691227
Mobile: +44 (0)79 6858 2121
Web: www.concoat.co.uk  &  www.concoatsystems.com

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/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
---------------------------------------------------------------------------------