Les,

The problem with TDR is that everyone has a good P/T but can't correlate to
anyone else.

My search for a non destructive method of checking dielectric spacing is to
find
a mechanical way to measure impedance.

I am only concerned with trace perimeter and dielectric thickness. Dk is
more
difficult to measure and I hoped I could make it a constant at the nominal
impedance value we fix and the construction we specify. I know we are not
the
PCB experts, but the tolerances are so tight that we need at least to create
a
consensus from the PCB manufacturers for construction.

Is there any hope here or am I just wasting my time?

Thanks for all the responses on this.

Steve

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