Re: [SI-LIST] : Comment on Johnson's article

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From: Keith Howard (howardk@modman.eng.sun.com)
Date: Fri Nov 05 1999 - 17:52:38 PST


Larry,

The low inductance capacitors from AVX have 8 or more leads, so require
multiple vias into the planes.
Unless you're talking about multiple vias in parallel with the required
vias.

Keith

> From owner-si-list@silab.Eng.Sun.COM Fri Nov 5 17:10:13 1999
> Date: Fri, 5 Nov 1999 16:59:50 -0800 (PST)
> From: Larry Smith <ldsmith@lisboa.Eng.Sun.COM>
> Subject: Re: [SI-LIST] : Comment on Johnson's article
> To: si-list@silab.Eng.Sun.COM
> MIME-Version: 1.0
> Content-MD5: A8S90goFyQs8Y3VUjvAQlQ==
>
>
> > Date: Fri, 05 Nov 1999 16:39:47 -0800
> > From: Howard Johnson <howiej@sigcon.com>
> >
> > If you want to achieve an even lower impedance, try smaller capacitors,
> > or go with some of the more advanced packages (for
> > example the new "IDT" package from AVX claims to
> > deliver an installed inductance of 0.1 nH per component.)
> >
> > Best regards,
> > Dr. Howard Johnson
>
> Most of the inductance is not in the capacitor but is in the pads
> and vias to the power planes. Our studies show that the inductance
> in the capacitor itself is between .2 and .4 nH for 0805 capacitors,
> depending on the height. The mounting inductance usually ranges
> from 0.3 to 2 nH depending on the depth of the vias to the power
> planes and the spacing between vias.
>
> The cost of low inductance capacitors is not worth it unless you
> are going to commit substantial board area for multiple vias to
> the power planes and can tolerate the loss of wiring channels.
>
> best regards,
> Larry Smith
> Sun Microsystems
>
>
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