[SI-LIST] Re: VIA L and C values.
- From: "Dima Smolyansky" <dima@xxxxxxxxxxxxxx>
- To: <KKeskinen@xxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 7 Mar 2002 09:09:43 -0800
Hello, Kai:
I have done some measurements of the via using TDR, but one via is totally
different from another. If the opening in the ground plane around via is
larger, the via will be mostly inductive. If the opening is smaller, the via
will be mostly capacitive. I have measured via inductance anywhere between
400pH to 2nH and via capacitance anywhere in the 200fF to 1.5 pF range. It
is the old "is it capacitive or inductive" dilemma.
One thing about the Dave Dascher's paper you mentioned - one has to
carefully differentiate between "excess capacitance/inductance" and a "full"
capacitance or inductance. Excess inductance is more of an RF/microwave
term, meaning "if you decrease your inductance by that amount your T-line
will be matched." The excess inductance / capacitance value will vary
depending on the impedance of your T-line. For signal integrity, we mostly
use full capacitance, which is the value that can be used in SPICE/IBIS to
predict the effects of the via in the circuit simulation. We discuss
techniques for measuring full inductance and capacitance in our appnote
dealing with characterization of packages - the same techniques are
applicable for via and connector characterization.
Thanks,
===================
Dima Smolyansky
TDA Systems, Inc.
11140 SW Barbur Blvd., Suite 100
Portland, OR 97219
(503) 246-2272
(503) 246-2282 (fax)
www.tdasystems.com/download
----- Original Message -----
From: "Keskinen, Kai" <KKeskinen@xxxxxxxxxxxx>
To: <aumesh@xxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Thursday, March 07, 2002 8:02 AM
Subject: [SI-LIST] Re: VIA L and C values.
>
> Umesha:
>
> Both Tyco and Teradyne show some via capacitance values in the
presentations
> on their latest high speed connectors. Unfortunately they are provided
under
> NDA. I believe some of the teradyne values are in last year's DesignCon
> papers. The TDA software lets you extract the values from TDR plots. A
paper
> in the HP Journal, Article 11, April 1996, Measuring Parasitic Capacitance
> and Inductance Using TDR by David Dascher tells you how to do it without
the
> software. Perhaps someone who has made measurements could send some
measured
> values on similar thickness boards.
>
>
>
>
> Kai Keskinen
> C-MAC Engineering
> A Solectron Company
> 425 Legget Drive,
> Kanata, ON K2K 2W2
> kkeskinen@xxxxxxxxxxxx
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