[SI-LIST] Stack up for EMI reduction

Hi,
I'm looking at re-layout of a 10 layer board because of EMI problems.  The
board contains 4 differential serial signals a ~700Mhz, and about 20 single
ended signals at 70 MHz.  The main problem frequencies are around 350 Mhz.
There are 4 large BGA components on the board.

I would ideally like to move into a 12 layer board, however there is quite a
bit of (non technical) resistance to doing that.

I like to eliminate 2 signal layers, by making my other 2 signal layer
denser.  Then I'll use the eliminated signal layers as ground/power layers,
but I will need to use these new gnd/power layers to assist with breakout of
4 high density (500pins) BGA.   

My question is can any one comment on whether I should in theory get an EMI
improvement?  What should I look out for?


My current stack up is:

1 Mainly GND with some breakout
2 Signal
3 Gnd
4 Signal
5 Power
6 Gnd
7 Signal
8 GND/Power (mixed)
9 Signal
10 mainly GND with some breakout



New proposed stack up

1 GND with some breakout
2 power with some breakout
3 Gnd
4 Signal
5 Power
6 Gnd
7 Signal
8 GND/Power (mixed)
9 Power with some breakout
10 mainly GND with some breakout


Thanks,
Nima



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