FreeLists / si-list / [SI-LIST] add new power island in a 8 layer stack

["calaf_calaf_calaf" <calaf_calaf_calaf@xxxxxxxx>]

Hi again,
I do not get how adding and 2.5V power island in a signal plane. The 
fact is that I need four layers for power and gnd, and four layers 
for signal routing. Can I use any of the signal layers for such 
island? should I add a gnd island for that 2.5V island? Can I share 
gnd layer between 2.5V island and 1.2V layer? 
Can I separate one power plane in two layer or I should leave 3.3V 
plane in one layer and 1.2V plane in just another?
Thank you for any help you can tell me 
Regards

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