FreeLists / si-list / [SI-LIST] PCB layer stackup

["Kindt, Jan" <jan.kindt@xxxxxxxxx>]

Hi,
 
I need to specify a 8layer board. Fastest edges on the board are on the
600Mbit LVDS channels : about 500ps. I have two stackups in mind :
 
                  stackup 1              stackup 2
---------------------------------------------------------
L1                routing                routing
Substrate
L2                power plane            GND
Substrate
L3                power plane            routing
Substrate
L4                GND                    power plane
Substrate
L5                routing                power plane
Substrate
L6                routing                routing
Substrate
L7                GND                    GND
Substrate
L8                routing                routing
 
Stackup 1 has the advantage that all routing on L5, L6 and L8 is
referenced to GND. We need to push the LVDS channels over a board to
board connector. On the board to board connector, there are GND's
between separate pairs. So we keep the same reference to GND over the
connector.
 
Stackup 2 is the stackup I would normally use due to it's symmetry.
Signals on L3 and L6 are referenced to both GND and a power plane. But I
don't know why I would need to favour stackup 2 over stackup 1.
 
Can you comment om which stackup is most preferred ? Or what are the
drawbacks/advantages of one stackup to another.
 
best regards,
Jan

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