[SI-LIST] : What is effect of adjacent signal layer on PCB on Zo?

Chris Bobek (cbobek@cadence.com)
Tue, 15 Jun 1999 08:18:16 -0700

When you have a PCB stackup that has a signal plane sandwiched between two
ground planes, you have stripline. Zo at this point is fairly easy to
characterize.

Now, if you add a second signal layer in between the two ground planes, one
in the X direction and the other in the Y, you still have stripline
(asymetric), but now you have a bunch of traces crossing the path above (or
below) your signal layer. I understand this introduces crosstalk, but what
does it do to the characteristic impedance of your traces? Is the impedance
still controlled? Does it vary widely, or not have much effect at all?

I see a lot of stackups with this arrangement, and I wonder how Zo is
maintained.

Thanks,

Chris

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