There are two CI-CGAs on two different assemblies.  I mapped the direction
of the shift on six different assemblies (we are low volume) and the
directions were both left, one left/one right, both up, one twist/one right,
etc.  None matched.  So a thermal pattern is not observed.

-----Original Message-----
From: Ofer Cohen [mailto:[log in to unmask]]
Sent: Tuesday, February 18, 2003 9:17 AM
To: 'TechNet E-Mail Forum.'; 'Shoda, Steve'
Subject: RE: [TN] Ceramic Interposer - Column Grid Array Shifting


Steve,
Did you check the fan out of the components (the connections from the pads
to the nearby via holes) to ensure it is thermally balanced - that is, same
count of traces to all the directions?

Ofer Cohen
Quality Assurance Manager
Seabridge Ltd.

-----Original Message-----
From: Shoda, Steve [mailto:[log in to unmask]]
Sent: Tuesday, February 18, 2003 16:12
To: [log in to unmask]
Subject: [TN] Ceramic Interposer - Column Grid Array Shifting


We have a 255 grid CI-CGA device which exhibits shifting during reflow. We
confirmed the shifting was random so the problem is not related to handling
or the SMT processes.  We've analyzed all of the process factors and arrived
at paste volume (via pad size & stencil thickness) and column tip as the two
factors to examine through experiment.  The paste volume we used was
slightly more than was recommended.  My question for Technet is in regards
to the column tip.

The CI-CGA we have has a round tip. The shift always moves to the point
where the column tip reaches the pad edge.  Our research into other company
practices resulted in learning their devices had columns which were
flattened.  So, I took a file and made a flat tip instead of a round tip
and, whala', the shift was only slight and solder wetting completely
surrounded the column.  We since learned this is referred to "coining." Some
here are concerned the flat tip results in a weaker solder connection.  Does
anyone have any information / experience regarding the difference between
the round and flat tips?

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