[SI-LIST] Re: ESD is a low frequency event -really??
From: "Knighten, Jim L" <JK100005@xxxxxxxxxxxxxxxx>
To: doug@xxxxxxxxxx, si-list@xxxxxxxxxxxxx
Date: Thu, 11 Mar 2004 17:53:04 -0500
Doug,
Quoted from your experimental results:
"One of the reasons cited for using a single board ground is to keep ESD
currents from flowing onto and off of the board. As can be seen, the board
coupling to the underlying metal plane is so strong the currents will flow
anyway and multiple connections can even reduce the board currents as shown
in Figure 4."
You have demonstrated benefit from the multiple grounding point design
approach to ESD mitigation.
Jim
_____________________
James L. Knighten, Ph.D.
Teradata, a division of NCR http://www.ncr.com
17095 Via del Campo
San Diego, CA 92127
tel: 858-485-2537
fax: 858-485-3788
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Doug Smith
Sent: Thursday, March 11, 2004 8:24 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: ESD is a low frequency event -really??
Hi All,
Quite separately from individual design techniques cited on this
subject, I would like to point out that there are so many parasitics
involved in ESD response of a circuit. Just because a design technique
worked a few times does not mean it worked for the reasons thought by
the person involved.
To have a really good understanding of what is happening, one needs to
set up a test case and measure induced EMI in a ciruit while changing
one variable at at time. I have lost count of clients that did not
have enough control over a set of troubleshooting experiments to be
able to draw a valid conclusion.
Tests are not difficult to perform, but one must be careful and
understand what the parasitics are. (2000 volts changing across 1 pF
in a nanosecond generates 2 Amps of current!)
As an example of a simple experiment, take a look at:
http://emcesd.com/tt2002/tt050102.htm
that describes an experiment I did on a circuit board mounted over
metal where the metal was subjected to ESD.
Can anyone report on experments like this in support of their
positions? It is not enough to say "I used this design technique and
it worked" unless you can explain carefully and in detail why it
worked. Only then can the design technique be generalized to other cases.
Doug
Tom Biggs wrote:
> "I presume you can give us some real example of systems with proper
> stackup failing ESD test and when BC is added it 'magically'(sic) passed
> ?" "This is a simple yes or no answer."
>
> -reply-
>
> "Designs within these companies were aided in the=20
> correction of susceptibilities by the use of BC."
>
> This sounds like a simple yes to me. Maybe you read it differently.=20
>
> If you don't think it would work tell us why. I bet most of the readers
> on this list would be interested in hearing this, rather than hearing
> you attacking another list poster no matter how poorly you think he
> presents his case.=20
>
--
-------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: doug@xxxxxxxxxx
\ _ / ] \ _ / Website: http://www.dsmith.org
-------------------------------------------------------
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