Mike
Following on from Doug's response, I have customers in 2 camps:
#1 : "We require the coating to be under low stand-off devices but with no
filleting. So we apply a thinned dip coat first, and then top-off with a
proper spray coat"
#2 : "We want no coating under the components so we only dip with high
viscosity material"
I guess the issue they have concern about is TCE mis-match, however the
coating SHOULD be forgiving in this sense. Silicones, as I learnt from Brian
Ellis, are not suitable for such requirements/applications.
If you want to ensure that all the solder joints are protected under a BGA,
my suggestion is to dip coat. This may well cause you major problems with
component masking, but is the only easy way to get the coating penetration
under such devices.
Regards, Graham Naisbitt
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Mike Manwell
Sent: Friday, November 16, 2001 12:15
To: [log in to unmask]
Subject: [TN] Conformal Coating to IPC Class 3
When I read IPC Standards regarding conformal coating requirements for the
different classes, all I can find is coating thickness on a board.
I'm trying to work to class 3 standards for conformal coating and am
meeting those thickness requirements, however, I have to wonder how it
works on a BGA for example, where the coating thickness is sufficient but
doesn't completely cover and encapsulate the component. In other words,
there is a gap between the top of the BGA and the PCB.
Any thoughts on this would be appreciated.
Thanks,
Mike Manwell
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