[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: Wed, 10 Mar 2004 09:01:30 -0800

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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