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June 1998

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Subject:
From:
David D Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 24 Jun 1998 07:08:40 -0500
Content-Type:
text/plain
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text/plain (86 lines)
Hi Jerry - processing a double sided BGA PWA design is no different than
processing a double sided 0.4mm (16 mil pitch for the metrically impaired)
QFP PWA design. You need to calculate your surface tension to component
weight ratio to make sure that physics are in your favor. I have done some
soldering trials with reasonable success without taking any special steps
(pad design, footprint location, etc. ) other than conducting the normal
assembly reflow profiling steps. I would be more concern with having the
BGA's located to facilitate rework if necessary. Having the BGAs mirror
each other on opposing assembly sides or having high profile components
adjacent to a BGA (i.e. a high skyline) would be a problem for our rework
scheme. Spending time on getting the reflow profile tuned has been the key
for me. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]





Jerry Cupples <[log in to unmask]> on 06/23/98 05:15:22 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to Jerry Cupples <[log in to unmask]>

To:   [log in to unmask]
cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
Subject:  [TN] ASSY: BGA sanity check




Hello, TechNet....

Soldering (inline convection furnace) BGA's on both sides of a board is
beyond my own experience, but it seems to violate a principle (at least an
imaginary one) related to the controlled collapse, or perhaps liquids under
tension.

For a board design using 3 commercial BGA packages (PBGA 256, eutectic
balls on 1.27 mm pitch), am I obstinately blocking the path of progress by
requesting that this package style be confined to only one surface of a new
board design?

If you are doing this today and it is a piece of cake, go ahead and brag;
but I would prefer to hear that caution is well advised, i.e. tales of
misery, shame and corporate disaster resulting from such mistakes. ;-)


cheers,




Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

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