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I'm designing a 8-layer PCB. Two layers have been reserved for GND and 2 for various digital supply voltages. Remaining 4 are meant for various signals( mostly serial data, video and USB).

How should the layers be arranged to make most sense considering noise immunity?

FYI: I decided on 8 layers because in 6 layers I couldn't imagine fitting all my signal traces.

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First, I would not waste whole layers for supplies, unless perhaps when they are unusually high current. With a good ground plane and good local bypassing, there is little purpose to power planes.

Second, I would use a single ground plane unless you are doing something unusual. If you want a capacitive shield, then you can dedicate the bottom layer to that, but it would be connected to ground at only one point near the middle of the board.

You can probably do your design with six layers. One of the two inner-most layers would be the ground plane, and then signals and power mixed everywhere else. I'd start with layer 3 being ground, layer 1 being the primary signal layer and layer 6 right behind it. I'd try to route as much of the power as possible in layer 4. Layers 2 and 5 are then left over for the router to use as it needs to make things work, although I'd set their costs higher so they only get used when needed.

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  • \$\begingroup\$ For 6-layer typically ground would be 2 and 5. Then for any impedance controlled signals (e.g. USB) you can then route them on any of 1 3 4 or 6 and have the plane as a reference. \$\endgroup\$ – Tom Carpenter Jul 22 '16 at 23:54
  • \$\begingroup\$ @OlinLathrop What if there are RF ICs on the PCB that need to have tight reference to GND plane? What to do with "local" polygons then? \$\endgroup\$ – Bip Jul 26 '16 at 23:24
  • \$\begingroup\$ @Bip: One possibility then is to put the via between the local ground and the main ground right at the ground pin of the part that needs tight coupling to the main ground. \$\endgroup\$ – Olin Lathrop Jul 27 '16 at 10:41
  • \$\begingroup\$ @OlinLathrop Where's the right place to connect antenna matching components ? They are pretty much away from the via that connects local and global ground nets. Tnx for help again! \$\endgroup\$ – Bip Jul 28 '16 at 19:06
  • \$\begingroup\$ @OlinLathrop Do you have answer to previous question maybe? Thanks for help! \$\endgroup\$ – Bip Aug 23 '16 at 9:30

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