[SI-LIST] Re: ESD is a low frequency event -really??
- From: "hansm" <hans.mellberg@xxxxxxxxxxxx>
- To: <cpad@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 4 Mar 2004 10:21:03 -0800
The extremely fast risetime is from the displacement current between the EUT
and the human hand or discharge instrument due to the immediate local
charges between them. There is a small but significant equivalent
capacitance between the hand an EUT in addition to the capacitiance between
the rest of the human and the EUT which is in addition to the capacitiance
of the EUT to ground and the human to ground. Modeling is dificult because
it is a geometry coupled with distance coupled with time to reach the
discharge point through a resistive medium with varying impedance over
frequency. There are many research papers on this subject both at IEEE and
EOS/ESD (IITRI) symposia. This is not a disputed event, high voltage
discharge phenomenae has been studied to death and resultant current wisdom
does not dispute the sub-nanosecond risetimes. You will not find ESD
exxperts disputing subnanosecond risetimes of the lower voltages (less than
6-8 kV) Doug Smith is among the world experts on ESD phenomenae.
Hans Mellberg
Engineering Manager
BACL, a TCB and an EU CAB
230 Commercial Street
Sunnyvale CA 94085 USA
408-732-9162 x38
408-732-9164 fax
----- Original Message -----
From: "Chris Padilla" <cpad@xxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Thursday, March 04, 2004 9:02 AM
Subject: [SI-LIST] Re: ESD is a low frequency event -really??
> 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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