Good point, we have reworked boards made from exotic materials that did try
to bulge locally under the BGA during rework. But our solution was to reflow
the entire assembly. Even temperatures on accross the board eliminated the
localized swelling.

 Guy Ramsey
American Competitiveness Institute
Senior Lab Technician / Instructor
610 362-1200 ext 107


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Trevor Goddard
Sent: Wednesday, February 28, 2001 8:35 AM
To: [log in to unmask]
Subject: Re: [TN] Heat-sinked BGA Bridging...


Hi guys

 I don't have a whole lot of experience with trouble shooting BGA problems,
but I have been following this conversation and would like to bounce a few
things off you experts.
 First of all in Steve's case where the interior balls are bridging in both
reflow and rework, the possibility of component warpage was mentioned. My
question on this is, if the component had enough center warpage to bridge
the interior balls, would it not pull up on the perimeter balls to create
opens? Is there a possibility that the balls are collapsing at different
rates? Like in this case more so in the center than the perimeter. If this
is the case, could you put an adhesive dot in the center of the component to
hold it up?
 When talking about component warpage. Are you able to determine, for sure
that it is defiantly the component warping and not the PCB? Would it not be
easier to warp the PCB, being that the PCB is usually much larger than the
component and loaded with many different forces? Minimum deflection in a
large plane would have a much greater effect on a smaller plane, would it
not?

Just a couple of thoughts

Trevor

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