[SI-LIST] Re: ESD is a low frequency event -really??
- From: Chris Padilla <cpad@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 04 Mar 2004 09:02:29 -0800
Doug,
What was the source of the fast-risetime ESD event you measured?
In my lab, I've measured fairly slow stuff in the 10s and sometimes 100s of
nanasecond risetimes. This was on a pretty slow scope so perhaps I was
missing something? Anyway, we reworked some of the design with the idea of
10-20 MHz in mind (1/2*risetime) and it fixed the problem.
However, one thing is for sure, ESD is a chaotic event and I am sure it
registers itself all over the spectrum in many guises. Thanks for the food
for thought on ESD.
----->Chris
At 06:05 PM 3/3/2004 -0800, Doug Smith wrote:
>Hi Charles and the "gang,"
>
>At the risk of a few dozen "out-of-office" messages, I think I can add
>to the discussion. As chance would have it, the Technical Tidbit I
>posted this month on my website ( http://emcesd.com ) talks about
>chassis coupling for a low frequency case, but at the bottom of the
>article are three links to other articles on my website bearing on
>this subject. One specifically addresses ESD coupling to a board over
>a metal plane and shows that "single point" grounding of the board
>sets up a nice parallel plate capacitor (board and metal plane) and
>inductor (the short connection) resonant circuit with bad results. In
>that case the ESD was applied to the metal not the board.
>
>Low voltage ESD events have the fastest risetimes. At the risk of
>oversimplication I like to think of it in this way: At high voltages
>(~10 kV) the arc length is long and the electrons collide with air
>molecules on the way across. The electrons are scattered by the
>collisions and are pulled in by the field over time resulting in a
>risetime of tens of nanoseconds. However, for a low voltge discharge
>(200-500V) the arc length is small, much less scattering occurs and
>the risetime is fast. As Charles said, I have observed risetimes of 80
>ps and that was the scope limit (about 10 years ago at Bell Labs in
>Murray Hill, NJ). It is a handy, if oversimplified, way of thinking
>about it. The di/dt is much greater for low voltage events than for
>high voltage events.
>
>I have been planning on simulating a circuit board over a ground plate
>for some time now. Maybe now is the time to perfect the models (I
>prefer to make up my own models so I know how they work) and get the
>simulation going (maby a paper in it). At least it will give all the
>computing power I mentioned in a posting a few days ago a workout. I
>expect the simulation to have the equivalent of more than 10000
>elements/components in it for the transient simulation.
>
>Doug
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