Re: [SI-LIST] : Trace Capacitance

PETER_ARNOLD@hp-santaclara-om3.om.hp.com
Mon, 21 Jun 1999 10:09:24 -0700

Farrokh,

If you had a 5pF parasitic in your measurement setup then you might
see numbers like that. Tell us the dielectric material and stackup and
we can work out what the capacitance should be.

______________________________ Reply Separator _________________________________
Subject: [SI-LIST] : Trace Capacitance
Author: Non-HP-Farrokh.Mottahedin (Farrokh.Mottahedin@quantum.com) at
HP-Boise,mimegw18
Date: 6/21/99 8:59 AM

I hope someone can explain what is happening with the following capacitance
measurement. A friend asks if capacitance is directly proportional to
surface area, why doesn't his measurement scale linearly. On a pcb made
specifically for trace characteristics measurement, he measures
1) 10 pf for a 10 cm long trace that is 5 mils (.12 mm) wide
2) 25 pf for a 10 cm long trace that is 20 mils (.50 mm) wide
3) Both traces are far apart from each other and from other components.
4) Both traces are over a solid ground plane.
5) Equipment is HP 4285A Precision LCR meter set at 1 MHz

Thanks,

Farrokh Mottahedin
Quantum Corporation
(408) 324-7934
farrokh.mottahedin@quantum.com


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