Hi Peter! You have me confused (which is a normal state for me if I don't
have a Coke in my hand). Collins has been using BGAs in avionics use
environments, not underfilled, with acrylic conformal coating very
successfully for a couple of years. What was the reason/rationale for using
BGAs with underfill? Was is an issue with solder joint thermal cycle
fatigue for a given use environment? Corrosion? Customer requirements?
Residual flux issues? Sheer terror of the unknown?
Dave Hillman
Rockwell Collins
[log in to unmask]
[log in to unmask]@ipc.org> on 03/26/2002 07:48:52 PM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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Subject: Re: [TN] Conformal Coating BGA's
Hi, Bruce,
We apply Humiseal acrylic coating to boards that fit your description and
application precisely, except that we do underfill the BGA's with a
reworkable epoxy, applied after assembly. The only exception was for the
case of two boards destined for temperature cycling measurement, for which
we couldn't get a supply of underfill material at the time. We substituted
thinned Humiseal as the boards would not be flying, as we were concerned
about entrapped air and also no suuport for the BGA joints. Humiseal is not
a proper substitute for the specialised proper epoxy, but was sufficient
for our particular purpose.
The main issue as I see it would be moisture and other contaminants in the
entrapped air, but I have no first hand data to help you decide if that
causes problems or not.
Good luck
Peter
"Misner,
Bruce" To: [log in to unmask]
<Bruce_Misner cc: (bcc: DUNCAN Peter/Asst
Prin Engr/ST
@ATK.COM> Aero/ST Group)
Sent by: Subject: [TN] Conformal
Coating BGA's
TechNet
<[log in to unmask]
ORG>
03/20/02
03:48 AM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
"Misner,
Bruce"
My question of the day: Is anyone conformal coating (not parylene) plastic
BGA's on FR-4 in Hi-Rel applications (aircraft; -20 to +71C ambient
operating temperature requirement) without benefit of an underfil? If yes,
has entrapped air been a major issue? Anyone care to comment on this
approach?
Regards,
Bruce Misner
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