[SI-LIST] : Another trace-Z question

Peterson, James F (jfpeterson@space.honeywell.com)
Thu, 28 May 1998 16:30:43 -0400

hey all,
This question is IRT trace impedance calculations.
Most of the pcb-trace-Z utilities I've used seem to come up with the
same numbers. I'm thinking of 2 specifically - the one at
http://www.automata.com/engtools/impednce/imphome.htm and the one from
http://www.ultracad.com/calc.htm.
Recently a colleague of mine showed me a utility that took into account
adjacent traces. If you specified everything the same as in the above
two utilities but added neighbors to the trace at a 6 mil distance the Z
was reduced approximately 10%.
So my question is (finally) does this make sense? Will normal signal
traces effect the impedance of an adjacent net? If so, this really makes
the accuracy of some of the Z-calculators out there questionable.

By the way, the case I tested was a dual stripline (planes are 1 oz. sig
layers are 1/2 oz.):
gnd plane
8 mil
signal layer
5 mil
trace of interest (5 mil width)
8 mil
gnd plane

I appreciate the feedback,
Jim
Jim Peterson
jfpeterson@space.honeywell.com
Honeywell, Space Systems Division, M/S 934-5
13350 US 19 N., Clearwater, FL, 34624
813-539-2719
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