[SI-LIST] Re: pwr-gnd loop inductance measurment
- From: Ray Anderson <Raymond.Anderson@xxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 23 Oct 2002 11:50:30 -0700 (PDT)
>
>I'm trying to correlate pwr-gnd loop Inductance of a bga package
>calculted from S11 and S21 measurement (VNA).
>
>FYI, For extracting the Inductance from S21 measurement ,
>1. I measure the capacitance of the vdd-gnd ,
>2. Short the BGA side (all vdd and gnd ball shorted together)
>3. measurement the s21 on vdd-gnd on the top side (C4 pad).
>4. Based on the first peak (resonance) I calculate the L .
>
>For S11, I think it is little more complicated, because we measure a
>package with a very low impedance versus the 50Ohms cable, and maybe the
>calibration is difficult ? Is someone have experience using S11 for the the
>pwr-gnd loop inductance of a bga paclkage?.. Also is someone try to find
>this very low loop inductance (a couple pH) with a TDR ?.. If yes, have you
>seen any chalenges.?
>
>Thanks
The S21 method you describe above is what we typically use in our lab
for measuring package inductance as well as mounting pad/via inductances.
We have achieved good correlation of our lab measurements with HFSS
simulations of the same geometry.
Your comments on the S11 measurements are correct. The calibration is
difficult because it is very difficult to account for the probe inductance.
Also, as you've pointed out, measuring small impedances with a 50
ohm instrument is error prone. S21 measurements have a much larger
dynamic range.
-Ray Anderson
Sun Microsystems
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