Hi Mark

Here is a paper for you.

www.polarinstruments.com/support/cits/AP148.html

Often etch taper more of an issue on tightly coupled
differential pairs.  Also when the copper is thick relative
to the trace width.

Kind regards
Martyn Gaudion
www.polarinstruments.com




At 05:05 PM 03/05/04, you wrote:
>Hi,
>
>when doing an impedance calculation of a trace more accurate results come
>from using the trapizoidal shape of the trace cross section rather than a
>square one, is there a rule of thumb people use for what the top width of
>the trace is in relation to the base? obviously this will be based on the
>copper thickness. Since it is such a small variable, is there ever a
>situation where it is really important?
>
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