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
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                    "TechNet
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                    Please
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                    "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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