Good Morning Colin,

I found this presentation from CALCE that talks about conformal coatings
mitigating tin whiskers. It's one of the few free things from CALCE that
I've found. It's big (23MB) because of all the photos, but it's pretty
good:

http://www.calce.umd.edu/lead-free/tin-whiskers/WoodrowConfCoatPres.pdf

I agree with Gordon about the lack of information about potting, and
also agree that whiskers WILL penetrate coatings as this presentation
shows.

One of the interesting points brough up in the presentation is that most
sprayed coatings will not effectively coat component leads. The only
coating that can accomplish that is parylene since it is a vapor
deposition under vacuum.

Steve Gregory

-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Davy, Gordon
Sent: Monday, July 23, 2007 7:26 AM
To: [log in to unmask]
Subject: Re: [LF] Potted Assemblies

Colin,

Potting will almost certainly prevent short circuits due to whiskers,
but only if there are no voids that span the space between a tin-plated
surface and a metal at a different electrical potential. The reason I
say "almost" is that we know that whiskers can penetrate several mils of
conformal coating (i.e., with nothing on the other side). I don't think
much is known about whiskers penetrating a few mils of potting material
between two metal surfaces. The gaps between metals in your design are
probably many mils, so provided you have a material and process that
make voids highly unlikely I think your risk is negligible.

 

Gordon Davy 


------------------------------------------------------------------------
-------Leadfee Mail List provided as a 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 Leadfree To
temporarily stop/(start) delivery of Leadree for vacation breaks send:
SET Leadfree NOMAIL/(MAIL) Search previous postings at:
http://listserv.ipc.org/archives Please visit IPC web site
http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100
ext.2815
------------------------------------------------------------------------
-------

-------------------------------------------------------------------------------Leadfee Mail List provided as a 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 Leadfree
To temporarily stop/(start) delivery of Leadree for vacation breaks send: SET Leadfree NOMAIL/(MAIL)
Search previous postings at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-------------------------------------------------------------------------------