While the underfilling thread is still hot, and following right along from
my "reworking a single BGA ball", I need now to draw on the benefit of your
collective experience with replacing underfilled BGA's. This is my first
time of doing this, so be gentle with me.

The board in question has two of these Xilinx XCV600E beasties on one side
and 12 White Electronics SRAM BGA's next door, but on the other side of the
board, The SRAMs are arranged in 4 rows of three devices, separated
horizontally by 0.15" and vertically by 0.3". The SRAMs at the Xilinx-end
of the rows overlap the Xilinx footprint by about 0.1" and all BGA's are
underfilled.

I want to remove one Xilinx without damaging the underfill of the other
BGA's. The underfill is Dexter Hysol FP6100 "Flow" type (reworkable) epoxy,
which degrades at about 220 deg C (approx solder reflow temp) to permit
component removal. Its curing temp is 165 deg C. Can anyone share their
experiences of replacing BGA's under similar circumstances to the above?

I'm hoping to use our new IR rework station for this job (angling for a
response from Steve G), as I can then use a low back heat around the
underfill curing temp, and hopefully get the top side component temperature
up to escape velocity without transmitting enough of it through the board
to damage the underfill of the underlying components.

If I ever have to replace any of the bank of 12 SRAM's underneath, I hope I
can adopt the same method, but shield surrounding components from the IR.
We have a hot air rework station as well, but I'm reluctant to use it for
this particular job.

Have a good weekend, all,
TVMIA
Peter

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