# Impedance formula for an edge coupled differential stripline in an asymmetrical stackup?

I've been searching and have not been able to find a formula for calculating the impedance of differential lines on inner layers where the dielectric above and below it is not symmetrical. I've seen plenty of examples of symmetrical stackups, but that would not help in my case. Does anyone know what the formula would be for this? Thanks!

Edited for more information: For those that don't know, a stackup consists of all the different layers of a PCB (Printed Circuit BOard). You can have, for example, a 4 layber PCB which has individual copper material & glass epoxy stacked on top of each other. This allows the board to have more layers for routing the nets of the circuits.

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For those of us who don't know, could you tell us what a stackup is? –  Greg P Jan 14 '11 at 16:27
(I am one of those people by the way) –  Greg P Jan 14 '11 at 16:28
A stackup consists of all the different layers of a PCB (Printed Circuit BOard). You can have, for example, a 4 layber PCB which has individual copper material & glass epoxy stacked on top of each other. This allows the board to have more layers for routing the nets of the circuits. –  Dan Jan 14 '11 at 17:09
that would be good information to edit into the question itself. Also, (to anyone) would this question also fall under the [condensed-matter] tag or something like that? –  David Z Jan 14 '11 at 21:01
This is a problem of theoretical electronics, often solved by physicists :=( –  Georg Jan 25 '11 at 15:58