[SI-LIST] Re: Importance of Package Height
- From: "Tony Anthony" <tony@xxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Mon, 18 Mar 2002 13:35:58 -0500
Earlier, Larry Smith talked about the need measure capacitors in low inductance
fixtures and to look
at capacitors from the standpoint of transmission line models. I am sure both
points will help
explain the effects we are seeing in X2Y capacitors and so we look forward to
the publication of his
upcoming paper at ECTC in May.
As far as capacitor height vs. inductance is concerned, it may be dependent on
the structure being
measured. The X2Y capacitors have four terminals, vs. most standard capacitors,
which are two
terminal devices. Our licensees have been making measurements (all series thru
so far) in a low
inductance ICM test fixture and the results seem to fly in the face of standard
capacitor behavior
as height increases. We continue to only see the expected effect of the
capacitance change. We have
posted the impedance/freq data of the following different X2Y package
size/height, data at this
link:
http://www.x2y.com/cube/x2y.nsf/(files)/ImpedanceComparisons.pdf/$FILE/ImpedanceComparisons.pdf
Slide #1)X2Y Comparisons
Size Max Height(mm) Cap Value
0805 1.02 47nF (x 2Ycaps = 94nF)
1206 1.27 100nf (x 2Ycaps = 200nF)
1410 1.78 400nF (x 2Ycaps = 800nF)
1812 2.29 470nF (x 2Ycaps = 940nF)
Slide #2) Standard cap impedance comparisons from an MLCC library. We tried to
find comparable
devices here.
Slide #3) We have also began measuring standard capacitors to correlate with
published data sheet
results, starting with feed thru capacitors. We have found the results in the
low inductance ICM
test fixture to be very close to the data sheets. We will soon begin measuring
standard capacitors
to check those results as well.
Slide #4&5) X2Y vs. standard feed thru cap impedance comparisons, although used
differently in the
circuit, both are four terminal capacitors.
For inductance of vias: If a capacitor design has benefits that can reduce the
B field stored in the
vias through cancellation, lower mounted inductance can result. You don't need
an interdigitated
design to accomplish this. We have accomplished B field reduction inside a
capacitor with minor
changes to electrode arrangement and circuit attachment. SI designers do the
same with their board
layouts every day.
thanks, Tony
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zabinski, Patrick J.
> Sent: Monday, March 18, 2002 7:34 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Importance of Package Height
>
>
>
> If you read Kemet's statement about ESL, they state they use
> a copper-slug of the same dimensions as the cap to "zero" out
> a "short". They the calculate the inductance of the slug and
> add it back in. The end result is that their values will
> be about 600 pH higher than that reported by others (which
> matches closely to the values Abe points out).
>
> Another difference I've seen between the inductance
> values provided by the two companies is that it looks like
> AVX provides one ESL value per package type, irregardless
> of capacitance value. In contrast, Kemet reports different
> inductance values for the various capacitance values. Considering
> the internal physical geometries (layer count, layer thickness, ...)
> change to obtain different capacitance values, I tend to
> rely more on Kemet's data (and manually remove the 600 pH).
>
> Pat
>
>
> > Larry Smith Wrote:
> >
> > > >
> > > I'm not sure what assumptions Kemet is making for
> > > inductance in their calculator. Their inductance seems way high to
> > > me. We have measured a lot of caps from a half dozen vendors and
> > > Kemet is no different than any of the others. When mounted
> > on a low
> > > inductance structure, the Kemet cap will behave as if it is
> > > significantly less than 1 nH.
> > >
> >
> > The AVX SpiCap program may output considerably
> > smaller ESL for similar capacitor than the kemet Spice
> > Simulator. As an example, for the ceramic capacitor we
> > recently discussed the AVX answer is 1.0 nH compared to
> > kemet's 1.94 nH. Sometimes, use of Kemet software is
> > preferable because it can show variations of ESL with
> > capacitance values (for fixed package
> > size) while the AVX calculator can not.
> >
> > I think (please correct me if I am wrong) the 1.0 nH by AVX
> > and the Kemet's 1.94 nH (and all other ESL results by these two
> > programs) apply to un-mounted capacitors. Therefore, based
> > on your expected 600 pH for that 100 nF 0805 X7R cap
> > both of these manufacturer calculators are providing ESL
> > values which are too large/inaccurate in this case.
> >
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