Peter,
The small amount of warparge may actually be enough to cause the bridge.
I would also look at how much spacing you have between BGA and the nozzle.
If the nozzle touches or is too close, OR, if it is too close to the board
the air flow may cause excessive heating at that one corner and cause the
BGA to warp/dip even further resulting in the bridge.

-Carrie


-----Original Message-----
From: Peter Lee [mailto:[log in to unmask]]
Sent: Monday, September 09, 2002 4:16 PM
To: [log in to unmask]
Subject: [TN] BGA rework - excessive collapsing


Technet,

We are having problems replacing 35mm BGA, 1.27mm pitch on a OK industry
BGA rework station. The resulting X-ray revealed a solder bridge at one
corner.

There was some warpage on the BGA but not significant. PCB was
reasonably flat. Thermal profiling was done to ensure all temp. were
optimum. I did notice the BGA balls collapsing quite a bit (at least
half of the ball height) after rework.

Anyone has suggestion on how to minimize the chance of bridging? Is it
common for BGA of this size? We don't have the capability to paste the
board for BGA rework.

Rgds,
Peter

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