[SI-LIST] Re: Sanmina patent on dielectric thicknesses under 4 mi ls
- From: Chris Padilla <cpad@xxxxxxxxx>
- To: chris.cheng@xxxxxxxxxxxx
- Date: Tue, 27 Nov 2001 15:41:22 -0800
I use plenty of sub nf caps to help curb emission problems in a lot of my
systems and they do work just fine and are necessary.
However, you point specifically to core noise (presumabley on some large
ASIC or processor or something) and while that is not an area I
specifically deal with, it certainly comes into play. EMI is a system
level phenomenon and the size of your PCB most certainly can resonate at
frequencies well above 100 MHz.
I fear I am missing your point here....
----->Chris
EMC Engineer
Cisco Systems
>Ron,
>May I ask what is the intend use for the sub nf caps ?
>
>By no means I claim there is absolutely no need for sub-nf caps,
>however, I always question the need for sub-nf caps for EMI or
>noise decoupling in a digital system. I believe the place for
>such decoupling is either on die or package not on the PCB.
>In fear of sounding like a broken record again, I claimed :
>a) High frequency core noise cannot propagation through the
>package back to the PCB. Same reason you have sso limitation
>on a package, its just as bad to go out of than go into a
>package. Core noise above 100MHz can not be decoupled
>outside the package.
>b) I/O switching noise is related to the image current
>return path which exist between the power plane sandwiching
>the signal layers and dictated by the impedance control
>of the stackup.
>
>I've used Zycon before thinking they can lower EMI or
>power noise but the reality is they don't and the reasons
>are stated above.
>
>If you have other reasons to use distributed sub nf
>decoupling caps, I will keep by mouth shut. And I practice
>what I preach. I never use decoupling below 1nf in any of
>my systems and they pass class B just fine.
>
>
>
>-----Original Message-----
>From: Ron Miller [mailto:rmiller@xxxxxxxxxxx]
>Sent: Tuesday, November 27, 2001 10:36 AM
>To: si-list@xxxxxxxxxxxxx; rfmeas@xxxxxxxxxxxxxxxxxxxxxxx
>Subject: [SI-LIST] Sanmina patent on dielectric thicknesses under 4 mils
>
>
>Hi Guys
>
>I am up against the problem of using thinner dielectric in order to
>eliminate the need for sub-1000 pf bypass capacitors.
>
>While this technique was used for many years some idiot at the patent
>office actually gave them a patent for it. No novelty at all but
>standard practice.
>
>Is anyone else having trouble with this?
>
>Does anyone have published articles or books that document this use prior
>to 1989?
>
>If so, please let me know. Perhaps a consortium of industry professionals
>can help to remove this travesty of the patent system.
>
>Ron Miller
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