Wallisch,

It all depends on how much rework you do for BGA's.  Generally it
is a required practice to leave a gap of 2 to 4mm for tall smt
components for inspection and rework.  It could be that a 3mm
clearance is a compromised solution if your rework tool can be
fitted to remove/install a BGA and if there are no tall smt/th
components adjacent to the device.

Maybe you should initiate a rework program for your design
groups where a few of them come down and do a real practical
work of fiddling with BGA's for a couple of weeks.   That will make
them rethink about board real estate.  They should not ignore
completely the manufacturability of board.

Just my opt.

regards
Matthew Park
NII-Norsat International Inc
Surrey,  BC.

>>> "Wallisch, Ernst" <[log in to unmask]>
June 11, 1998  8:05 am >>>
Fellow Technetters,

        I have been debating with my design groups about the
usefulness of
leaving 0.150" to 0.200" of clearance around BGAs to facilitate
rework, if
required.  The design groups wish to use this real estate for
other devices,
ignoring rework requirements.

        My question is this:  Is it better to have a  "keep-out" area
around
BGAs for rework, or use up all available space around the BGA
for a
preferred design?

Thanks in advance,

Ernst Wallisch
Manufacturing Engineering
Computing Devices Canada
[log in to unmask]

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