Here at SCI we have designed 4 layer boards using BGA up to 530 balls.
The design of the board required will depend on the layout of  your BGA
as to whether more layers will be required to interconnet that device.
The BGAs  we have done are 50 mil pitch and 5 or 6 rows of balls so that it
is possible to route it out on 2 signal layers .
If you have a solid array of balls or smaller pitch you may need more layers.

For the 4 layer designs ( 2 signal , 2 planes) there has been no additional
cost to manufacture the boards above previous technology.

Tim Easterling
SCI
(205) 882 4426

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