RE: Question on BGA pinout for 66MHz PCI

["Ingraham, Andrew" <Andrew.Ingraham@compaq.com>]

Many PGA or BGA packages have plating stubs on all pins.  This means that
even if you use an inner row or column pin, the package has a trace that
runs out fully to the edge of the package, in addition to the one running in
toward the die.

For very high frequencies the extra electrical load could be problematic.
It might not be an issue at 66MHz yet, but you might think about putting the
fastest or most important signals (i.e., CLK) on OUTER rows where the stub
is smallest.  Make the package trace an extension of the board trace.

Good grounding is always important.  Don't cluster all your ground pins in
the corners, or exclusively on inner rows.  For best results, the power and
ground pins should be mixed throughout the pinfield.  Every signal pin
should have ground and/or power pins nearby.

Trial layouts before pinning are indeed useful and can point out trouble
spots to avoid if you do them early enough.

Andy