We have used following 10-layer stack up (full digital design):
L1 : signal
L2: signal
L3 : gnd
L4: power 1
L5: signal (strip line)
L6: signal (strip line)
L7: gnd
L8: power 2
L9: signal
L10: signal
I have named the 5V en 2.5V power and the ground gnd. The power planes 5V and
2.5V could be switched, depending on the circuit.
The setup as three advantages:
(1) There is a set of 3 pairs of signal layers, each pair is
uncoupled from the other pairs and in each pair one can route x and y.
Crosstalk is only a concern in the same layer!
(2) The power-gnd planes are well coupled, in our specific buildup the spacing is a low
160microns.
(3) The setup is symmetric!
A disadvantage is possibly the difference in impedance between the three pairs, however
this can be controlled with the track width. Also, critical signals, clocks, control ...
could be x-y routed in the strip line layers L5 and L6.
regards,
jan vercammen
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