Asymmetric stripline calculator confusion.

I went on web to find impedance calculator for asymmetric stripline. Basically I got two different answers.

I have asy stackup of H1=8mil, H2=25mil, all 1oz copper(1.4mil). I set width of trace of 8 mil with er=3.55. At least two calculators gave 67ohm, two gave 56ohm. What is the story?

Below are two links, first gave 67, the second gave 56. Which one should I trust?

http://www.eeweb.com/toolbox/asymmet...line-impedance

http://www.ideaconsulting.com/strip.htm


Do you have any calculator suggestion that I can trust?

Thanks

If you are able to verify these values with a EM simulator, check them ..
They give really different values ( there may be a computation method differences )

Rogers Corp also has a calculator that does asymmetric stripline. It appears to be reasonably accurate, "but" I'm with BigBoss on this one.

With the Sonnet EM solver, I get Z0=58.6 Ohm

Model detail: Thick metal model, line width 8mil, lossless conductor. Trace thickness 1.4mil, dielectric thickness above 8mil, dielectric thickness below 25mil, total thickness 1.4 + 8 + 25mil, er=3.55