Here is my 6 layer ARM board with a couple of bga's (CPU and SDRAM Memory)
http://dl.softplc.com/ds_Smartboard.pdf
as an example.
To do some of the fan out under the BGAs I added some through hole pins
as part of the footprint. These through hole pins would share the same
pin number as the ball pad, and then by adding the solder mask to the
padstack for the through hole pins, they end up being "pre-placed" vias
on the layout.
A board like this cannot be done without bridging to freerouter
however. Without the push and shove manual routing it is impossible.
I did not use the autorouting in freerouter, just manual routing.
Dick
