Re: [SI-LIST] : stackup impedance.

Joachim Mueller (jmueller@ca.newbridge.com)
Thu, 18 Sep 1997 12:11:33 -0400 (EDT)

Hi,
I am a fan of numerical field solver too. I have no doubt that the
results are accurate. But the problem is that the PCB manufacturing
process is not as accurate as the field solver is. There are parasitic
parameters involved which are usually not considered in simulation models.

If the stackup has two or more adjacent signal layers, the coupling between
the traces on different layers is hard to model but will influence the
characteristic impedance. It is certainly not the case that you want a strong
coupling between all four signal layers (second stack up) by routing them on
top of each user.