Hi,
I have a 6-layers PCB with several high speed controlled impedance signals including LVDS, Ethernet, USB etc.
The previous version of the board had EMI emissions very close to the limit. So in this version I am thinking of shielding all high speed signals by sandwiching them between GND plane (layer 3) and GND copper pour (on layer 1). The stackup is:
- Layer 1 = copper flood/pour in red
- Layer 2 = high speed differential (and single ended) signals in yellow
- Layer 3 = GND plane in green
I am wondering which via fence configuration is most efficient in reducing EMI emissions? Adding via fences on the edge of the copper pour as well as between the differential pairs (i.e. the top sketch in the attached picture) or via fences only on the two outer edges of the copper pour along the outer traces (i.e. bottom sketch in the attached picture)?
Thank you