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

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From: Rick Brooks (ribrooks@nortelnetworks.com)
Date: Fri Nov 05 1999 - 18:48:15 PST


Has anybody ever tried 0508 caps (not 0805) with multiple trace/vias to the planes?
It seems like a better idea for low inductance, but I don't know about the cost or availability.

- Rick Brooks

At 04:59 PM 11/05/1999 -0800, you wrote:
>
>> 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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>

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