Good Luck,

The impedance numbers are easy.  Its meeting the tolerancing that is
challenging.
Personally I am a Polar Bear.  I also do sanity checks with 2-4 other
calculators, including home made ones from spread sheet software.
"Standard" thickness is always a curve ball, as is additive copper (external
and buried sub external layers), diff pair spacing to each other and distance
to ref plane is wicked important,  adjacent "look thru" plane clearance, and
more "stuff" like correct terminals for verification, dedicated coupons, etc.
 If new to impedance I would read "Electronic Packaging of High Speed
Circuitry"  by Konsowski and Helland (McGraw Hill '97). It does a very nice
job with diffs, cabling and lengths.
Remember the output of any calculator reflects the quality of the input.  And
one last biggy for impedance; sameness is good.

Boston Brad
781 858 0783

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