Graham,
I too have drawings which specify where not to coat and everything else must
be coated. This has spawned much debate over what to do with BGAs during
coat. How are you handling BGAs?
Your comments are appreciated,
Linda Woody
Process Engineer
Lockheed Martin
-----Original Message-----
From: Graham Collins [mailto:[log in to unmask]]
Sent: Wednesday, August 14, 2002 10:22 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal coating on top of plastic IC's
Hi Daan!
Well - given that the coating will slowly allow moisture to pass through,
his concern is based on misinformation. We spray 1B31, but it is to protect
the boards against things like condensation due to temperature fluctuations,
as well as dust and other contamination. Eventually the plastic parts will
absorb moisture, and that should not cause any problems. Ask him what
happens to the underside of the part - it is not coated. Or maybe you
should not bring that up, he will want the underside of the parts coated...
Given that you are not worried about contamination or dendrites growing on
the top of an IC, I would say your not coating the tops of the ICs is
technically not a problem. However it is a problem on two counts:
1) as you say, the customer does not like it - and is it worth arguing with
the customer about it? Sounds like you have decided it isn't.
2) if your customer's drawings are like my customer's drawings, they define
where they don't want coating, and everything else must be coated. For me
to not coat the tops of ICs they would have to be mentioned in the drawing
somehow.
regards
Graham Collins
Process Engineer,
Northrop Grumman
Atlantic Facility of Litton Systems Canada
(902) 873-2000 ext 6215
>>> [log in to unmask] 08/14/02 09:28AM >>>
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
----------------------------------------------------------------------------
-----
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
----------------------------------------------------------------------------
-----
----------------------------------------------------------------------------
-----
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
----------------------------------------------------------------------------
-----
---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------
|
