FEDEVEL
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Clarice Starling , 08-27-2024, 08:17 PM

There is a stackcup -> (L1 SIG+PWR) - (L2 GND) - (L3 GND) - (L4 SIG+PWR). When switching between layers, would it be a problem to go from L1 to L4 and then go back to L1? Or is it better to go from L1 to L1GND and go back to L1? This does not make sense since it will break the ground.

QDrives , 08-27-2024, 08:53 PM

In your stack-up, if you go from L1 to L4 that is not a problem. However, do have a Gnd return via close by the signal via too.
This would always be needed when the signal changes "reference planes" -- as in the nearest Gnd layer.
If you change the stack-up to Sig-Gnd-Sig-Gnd it is a bit less of an issue as the signal can keep L2 as the reference (L1->L3). However, there too, the nearest Gnd plane would be L4, so you would still need to couple L2 and L4 together regularly.

Clarice Starling , 08-27-2024, 09:22 PM

So, can I make this layer change for diff pair lines? (ETH/USB etc)

Robert Feranec , 08-28-2024, 06:14 AM

you can, just keep in mind GND vias (stitching vias) that need to connect the two grounds together close to the places where your signals are changing layers from L1 to L4 or L4 to L1.