Hi,

thank you all for you replies, in my board I have some more bga
components like a Blackfin DSP and some memories. I was thinking I'd
need at leat 6 layers, including a Vcc plane and a GND plane. Our pcb
manufacturer could go down to 4mils tracks and this should allow me to
route the board within those 6 layers, but, as long as this is my first
bga board, I decided to ask more experinced and skilled people like you
how to approach this project (how to start, routing startegies, how
many layers and so on).

Marco