[SI-LIST] Re: Self Inductance and TDR measurements


 
> a) Pat has confirmed the method I was using to calculate the self
> capacitance. However for inductance I have just been using 
> L11 as the self
> inductance. Is this correct?
> 

Yes.  The inductance matrix produced by most EM cross section
simulation tools is just that; inductance, and you can read the
values directly (both on- and off-diagonal).

> b) However I am still puzzled over which # to use to compare with TDR
> measurements. 
> The TDR measurements we do use a fixture from ALTAIR 
> microwave which has a
> Cu sheet on which the package balls sit and grounds all other 
> pins in the
> package except for the pin of interest.
> 

Capacitance is easier (at least for me) to visualize, because in
TEM mode, parallel plate capacitance can be directly calculated
based on the two elements you're trying to calculate the
capacitance between.

For inductance, it gets a bit more difficult, in that inductance is
for the "entire loop".  For example, inductance of a wire
is incomplete if you do not include the return inductance.

It is sometimes difficult (impossible?) to directly compare
the inductance produced by a simulation tool to something
you measure in the lab.

In the situation you describe (if I'm reading in between the
lines correctly), you are trying to measure the inductance of
a single trace with all other traces grounded.  The problem
is (typically in most BGA designs) that the grounded traces
have mutual coupling to the line of interest, so their presence
effects your measurement.

Also in your case, it might be that the referenced ground plane
in the simulation is not necessarily the return path
in your measurement, which will throw things off.

In addition, if the trace you're measuring exits the BGA 
at an appreciable distance from the ground-plane ball(s),
the separation can increase the effective inductance.

In short, I've have pretty good success in correlating
capacitance, but inductance is a real bugger of a parameter
to correlate without taking a few (sometimes many) extra
steps to make sure you are truly correlating the same
parameter.

>  I have not got a good answer yet as to which number in the simulation
> matrix I should compare the TDR meas. to. 
> 

Here are a few to keep you busy:

TITLE   Validity of Mutual Inductor Model for Electromagnetic Coupling
Between V
ias in Integrated-Circuit Packages and Printed Circuit Boards
AUTHOR  Jin Zhao and Jiayuan Fang
SOURCE  1998 ECTC Conference, Seattle, WA
DATE    May 25-28, 1998
PAGES   na

TITLE   Capacitance, Inductance, and Crosstalk Analysis
AUTHOR  Charles S. Walker
SOURCE  Artech House, Boston
ISBN    0-89006-392-3
DATE    1990

TITLE   Extraction of Coupled SPICE Models for Packages and Interconnects
AUTHOR  Scott Diamond and Bo Janko
SOURCE  Proceedings of IEEE International Test Conference
DATE    October 1993
PAGES   Paper 20.1

TITLE   Guideline for Measurement of Electronic Package Inductance and
Capacitan
ce Model Parameters
AUTHOR  na
SOURCE  EIA Standard JEP123
DATE    October 1995
PAGES   1-20

TITLE   Loop Areas - Close 'Em Tight
AUTHOR  D. Brooks
SOURCE  Printed Circuit Design Magazine
DATE    January 1999

TITLE   Measuring Package and Interconnect Model Parameters Using
Distributed Im
pedance
AUTHOR  Bo Janko (Tektronix) and Peter Decher (Analogy)
SOURCE  na
DATE    na
PAGES   1-6

TITLE   Return Path Inductance in Measurements of Package Inductance
Matrixes
AUTHOR  Brian Young
SOURCE  IEEE Trans CPMT, Part B, Vol 20, No 1
DATE    February 1997
PAGES   50-55

TITLE   TDR Tools in Modeling Interconnects and Packages
AUTHOR  na
SOURCE  Tektronix Appication Note
DATE    1993
PAGES   1-11

TITLE   The Inductance Matrix of a Multiconductor Transmission Line in
Multiple 
Magnetic Media
AUTHOR  Joseph R. Mautz, et. al.
SOURCE  IEEE Trans on MTT
VOLUME  36
NUMBER  8
DATE    August, 1988
PAGES   1293-1295
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