[SI-LIST] Re: 0306 Capacitors
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Steve Weir" <weirsp@xxxxxxxxxx>, Farah.Haddadin@xxxxxxxxx,"Ken Patterson" <pattken@xxxxxxxxxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Thu, 11 Mar 2004 08:51:57 -0800
Steve,
Looked at the data from X2Y. Most of the tests use two different values of
capacitor, the value used for the X2Y making it look better. (IDC 470 nF,
X2Y 56 nF) (0612 100 nF, X2Y 56 nF) I could get the same results with the
same skewed tests. Sadly, this is a common problem with vendor furnished
data. Remember Getek?
I was really interested in tests you have personally made that demonstrate
true A-B comparisons on a PCB that is representative of a real power
subsystem, as we have done. What I mean by that is examine impedance vs.
frequency for a PCB with enough plane capacitance to support the switching
transients seen when driving data buses, etc. When you do that, you are
going to come to the same conclusions that we did- not worth the extra
resources and not worth forcing your manufacturer to use a single sourced
part.
Remember, what counts is the frequency at which the capacitor is series
resonant and that is a combination of the value of C and total ESL. For
all of the examples shown it is less than 30 MHz. Switching harmonics
usually start abouve 100 MHz.
Final comment on the data is the vertical scale is in db. It would be of
far greater value if it were in milliohms. Then we could tell more about
what these capacitors do for us in the power subsystem.
Lee
> [Original Message]
> From: steve weir <weirsp@xxxxxxxxxx>
> To: <leeritchey@xxxxxxxxxxxxx>; <Farah.Haddadin@xxxxxxxxx>; Ken Patterson
<pattken@xxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 3/10/2004 3:17:18 PM
> Subject: Re: [SI-LIST] Re: 0306 Capacitors
>
> Lee, the file is available on X2Y's web site, but I have attached it here
> as well. I spoke with Dave Anthony, dave@xxxxxxx and he will be happy to
> supply you with one of the test boards if you like.
>
>
> Regards,
>
>
> Steve.
> At 01:50 PM 3/10/2004 -0800, Lee Ritchey wrote:
> >Steve,
> >
> >How about sharing the actual test results with us?
> >
> >Lee
> >
> >
> > > [Original Message]
> > > From: steve weir <weirsp@xxxxxxxxxx>
> > > To: <leeritchey@xxxxxxxxxxxxx>; <Farah.Haddadin@xxxxxxxxx>; Ken
Patterson
> ><pattken@xxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > > Date: 3/10/2004 10:44:23 AM
> > > Subject: [SI-LIST] Re: 0306 Capacitors
> > >
> > > Lee, It is all in the coefficients. There is no magic here. I have
the
> > > data carefully taken at the planes themselves and it does show
dramatic,
> >as
> > > in 3:1 improvement at the planes using X2Y versus 0603. All the data
I
> > > have, does in fact correlate well to what you have published. While
that
> > > may seem a contradiction, it is not.
> > >
> > > What we are dealing with is a simple 1/( M + N ) equation for
admittance
> > > where M is the ESL of the discrete device and N is the partial
inductance
> > > of the mounting structure and the planes themselves. As I suggested a
> > > month or two ago, if we take a graphical view of this to gain
intuition,
> >we
> > > can simply hold M or N constant and plot against the other. It is
easy
> >to
> > > confirm that if M >> N, then reductions to N offer little help and
> > > vice-versa. When dealing with ordinary capacitors with ESLs of
> >450-500pH,
> > > that means that reducing the attachment inductance from values much
below
> > > 1nH show rapidly diminishing returns. A good two via mount on a four
> > > layer 0.062 board yields total inductance of just about 1200pH. Here
the
> > > attachment inductance is not too much bigger than the ESL of the
device,
> > > and as you have experience with, dropping the attachment inductance
by a
> > > factor of two only improves the total inductance by less than 1/3 to
> >about
> > > 850pH, while doubling the number of holes that we have to drill. So,
we
> > > are only able to exchange primarily parts placement costs against
drill
> >holes.
> > >
> > > However, when we take an ESL on the order of 120pH, that picture
changes
> > > completely. Now, the mounting inductance of 700-750pH is very
dominant,
> > > and there are substantial gains to be had by reducing same. So, for
> > > example by using a properly designed six via mount for the X2Y, the
total
> > > mounted inductance drops to 300-400pH depending on just how aggressive
> >you
> > > want to get with the vias. I have test boards you can measure in your
> >own
> > > facilities with repeatable values under 300pH. That is a 75%
reduction
> >in
> > > parts count, and a 25% reduction in total vias to achieve the same
high
> > > frequency impedance AS SEEN AT THE PLANES.
> > >
> > > Regards,
> > >
> > >
> > > Steve.
> > >
> > >
> > >
> > > At 09:01 AM 3/10/2004 -0800, Lee Ritchey wrote:
> > > >Steve,
> > > >
> > > >I have similar tests that show the inductance reduction and I agree.
> >What
> > > >counts is the effect the mounted capacitor has on the impedance of
the
> > > >power system. When this test is done, the lowering of the overall
> > > >inductance is visible as a shift to a higher frequency of the series
> > > >resonance as well as the parallel resonance between the capacitor
> >parasitic
> > > >inductance and the plane capacitance.. However, in almost all cases
this
> > > >shift is not large enough to warrant the extra cost of the vias or
the
> >more
> > > >expensive capacitors.
> > > >
> > > >I hate to mention books, but we have published this data. I'll post
it
> >on
> > > >my web site. UMR has done similar tests and published the results
in the
> > > >IEEE proceedings on EMC.
> > > >
> > > >Lee
> > > >
> > > >
> > > > > [Original Message]
> > > > > From: steve weir <weirsp@xxxxxxxxxx>
> > > > > To: <leeritchey@xxxxxxxxxxxxx>; <Farah.Haddadin@xxxxxxxxx>; Ken
> >Patterson
> > > ><pattken@xxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > > > > Date: 3/9/2004 10:00:18 AM
> > > > > Subject: RE: [SI-LIST] Re: 0306 Capacitors
> > > > >
> > > > > Lee, I have a whole lot of test data that shows big differences
> >between
> > > > > normal 0603's, with 2 and four via patterns as well as reverse
> >geometry
> > > > > caps versus X2Y's.
> > > > >
> > > > > On a four layer board where the differences will be the least due
to
> >the
> > > > > dominance of via inductance, we go from about 1200pH for an 0603
with
> > > > > 0.050 spaced side mount via's, one per pad, to 850pH with four
vias
> > > >total,
> > > > > to under 300pH with X2Y 0603 and a optimized via pattern. A 4:1
> > > >reduction
> > > > > in parts count saves a lot of money.
> > > > >
> > > > > Nothing is free, the via pattern isn't as friendly as that
convenient
> > > > > 0.050" spacing, but the total number of vias needed in the board
to
> >yield
> > > > > an impedance at say 100MHz also comes down considerably versus
normal
> >or
> > > > > reverse geometry 0603s.
> > > > >
> > > > > Steve.
> > > > >
> > > > > At 09:29 AM 3/9/2004 -0800, Lee Ritchey wrote:
> > > > > >Farah,
> > > > > >
> > > > > >By the time you add in the inductance of the mounting inductance
for
> >your
> > > > > >PCB, the lower inductance you get with this uncommon shaped
> >capacitor is
> > > > > >not worth it. Stick with 0603 and use via mounting pads on the
> >sides of
> > > > > >the capacitor rather than the end and you get the best compromise
> >between
> > > > > >cost, PCB space and performance. Using multiple vias does
reduce the
> > > > > >mounting inductance some, but is not worth the cost in terms of
PCB
> >space
> > > > > >and drilling costs. We've made many controlled tests to
establish
> >this.
> > > > > >
> > > > > >Lee
> > > > > >
> > > > > >
> > > > > > > [Original Message]
> > > > > > > From: steve weir <weirsp@xxxxxxxxxx>
> > > > > > > To: <Farah.Haddadin@xxxxxxxxx>; Ken Patterson
> > > > > ><pattken@xxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > > > > > > Date: 3/9/2004 6:27:44 AM
> > > > > > > Subject: [SI-LIST] Re: 0306 Capacitors
> > > > > > >
> > > > > > > Farah,
> > > > > > >
> > > > > > > I believe Murata does make 0306's, but you will get lower
> >inductance
> > > >at a
> > > > > > > much lower price from an 0603 X2Y. The only caveat is that
you
> >are
> > > > > > > presently limited to 200nF in the X2Y, whereas an 0306 in X5R
can
> > > >support
> > > > > > > larger values. Unmounted an 0306 is about 190-200pH, whereas
an
> >0603
> > > >X2Y
> > > > > > > is about 120pH.
> > > > > > >
> > > > > > > Regards,
> > > > > > >
> > > > > > >
> > > > > > > Steve.
> > > > > > > At 08:16 AM 3/9/2004 -0600, Haddadin, Farah wrote:
> > > > > > >
> > > > > > > >I tried AVX... They don't make 0306 caps, although their data
> >sheets
> > > > > > > >indicate that they do.
> > > > > > > >
> > > > > > > >Thanks,
> > > > > > > >Farah
> > > > > > > >
> > > > > > > >-----Original Message-----
> > > > > > > >From: Ken Patterson [mailto:pattken@xxxxxxxxxxxxxxxxxx]=20
> > > > > > > >Sent: Tuesday, March 09, 2004 8:16 AM
> > > > > > > >To: Haddadin, Farah; si-list@xxxxxxxxxxxxx
> > > > > > > >Subject: RE: [SI-LIST] 0306 Capacitors
> > > > > > > >
> > > > > > > >
> > > > > > > >Try AVX. They make a line of reverse aspect caps.
> > > > > > > >
> > > > > > > >Regards,
> > > > > > > >
> > > > > > > >Ken
> > > > > > > >
> > > > > > > >-----Original Message-----
> > > > > > > >From: Haddadin, Farah [mailto:Farah.Haddadin@xxxxxxxxx]
> > > > > > > >Sent: Tuesday, March 09, 2004 9:11 AM
> > > > > > > >To: si-list@xxxxxxxxxxxxx
> > > > > > > >Subject: [SI-LIST] 0306 Capacitors
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > >Experts,
> > > > > > > >
> > > > > > > >Does anybody know vendors that can produce 0306 ceramic
> >capacitors?
> > > > > > > >
> > > > > > > >Thanks,
> > > > > > > >Farah
> > > > > > >
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