Re: [SI-LIST] : resistance measurement

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From: Mike Degerstrom (degerstrom.michael@mayo.edu)
Date: Tue Nov 09 1999 - 09:12:20 PST


Jack,

I'm surprised that you could get capacitance and
inductance up to 6Ghz on a BGA. I will try to anwer your
question but I wouldn't think you can get results beyond
1 Ghz. At 1 Ghz, I would suspect that skin effect losses
are not your biggest worry when compared to L-C resonances.
However there have been postings many months ago which indicated
that skin-effect losses needed to be considered for leadframe packages
if I remember correctly. You may want to visit the archives
to review those postings.

You can fit a two-port network to a T-network or a pi-network
but the fit is valid only up to a certain frequency. The
technique to doing this is to covert measured S-parameters
to ABCD parameters then ABCD parameters to either T or pi-network.
The coversion formulas are given by a few good microwave textbooks
such as by Pozar. For example, let's say you did the fit to a pi-network
then the admittance of 'legs' to ground is your capacitance*jwf. The
reactance between the legs is your inductance*jwf. The real
part of your impedance between the legs of the pi-network
is your resistance vs frequency.

At some frequency your simple model does not work since your
physical structure is behaving like a distributed network. I will
plot magnitude and phases of the RLC values versus frequency
on log-frequency scale to help determine at what frequency
my results do not look correct.

Mike

On Nov 5, 11:38am, Jack wrote:
> Subject: [SI-LIST] : resistance measurement
> Hi All
> I have some problem on package resistance measurement. Take BGA for
> example,
> I used to make
> some "open" samples,and "short"samples to get the capacitance and
> inductance
> information
> within a certain frequency range(bellow 6GHz). But for resistance, skin
> effect let the resistance
> increase nonlinear. How can I get the "resistance vs. frequency"
> information from the VNA or TDR
> measurement method?Does someone can help me to solve this
> question?Thanks!
>
> Jack
>
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>-- End of excerpt from Jack

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