So, you were just using tacky flux to mount the BGA, and you got a
bridge on the outside corner. With X-ray, are the "good" connections
uniformly larger at the corners than in the center of the package? It
really does not matter how warped the board or package is after it has
cooled what really matters is what is going on as you enter and exit
reflow.

BGA 169 or 225? These should not present a problem. Though it is
possible to warp the package, the board or both.
How many layers is the board? What is the board material? What nozzle
are you using? What are the heater settings?

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee
> 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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