FreeLists / si-list / [SI-LIST] Stripline Characteristic Impedance

["Ched-Chang Chai" <ched_chang@xxxxxxxxxxx>]

Dear all,

I have a question regarding the stripline characteristic impedance Zo.
I have the following stack-up:

Reference plane -------------
a
Trace                ---

b

Reference plane -------------

where a<b.

When I used impedance calculator to get Zo, I have 2 ways to key in a and b 
values:
(1) Use the stack-up shown above.
(2) Reverse it upside down, as shown below:

Reference plane -------------

b

Trace                ---
a
Reference plane -------------

I got different values for Zo.
For example, a=0.2mm, b=0.4mm, trace width=0.15mm, trace thickness=0.035mm, 
and dielectric constant=4.5, approach (1) gives 51ohm while approach (2) 
gives 54ohm.

Can someone tell me which one is the correct value?
Thank you very much in advance.
--
Regards,
Chai






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