Keith,
Without looking at the specifics. Disruption from a discharge can be caused
by direct high voltage gradients, localized breakdown which then applies
direct high voltage, and the often forgotten current injection where the
discharge makes enough current flow that the flow induces a voltage in
adjacent loops like turns on a transformer.
Probing with direct observation is very helpful. You'll be surprised where
all the energy ends up going. But it does help to try to characterize from
the source down to the recipient.
I highly recommend that you use only one board to gather information about
the mechanism that's occurring. Then "red label" the board as ESD damaged.
- Robert -
PS You did not state what the observed response to the offending ESD is.
It is important to characterize that, too. Find out what will make what you
see happen.
My experience with memory cards that lose their memory from ESD is that the
address lines, or any lines, get ripped around discombobulating the chips.
Much worse is if the lines get ripped below gnd potential, but maybe not
with enough energy this time to fry the components, just enough this time to
flood carriers out across the chip randomly changing memory in random
locations.
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
List-Post: [email protected]
Date: Sunday, March 05, 2000 11:48 PM
Subject: Debugging EN61000-4-2 Techniques
>
>I have a difficult ESD problem and I am looking for measurement methods
>to help isolate the error. Think of electronic logic card mounted to
>unshielded metal chassis. An ESD is discharged to the chassis causing a
logic
>error.
>
>Typically the symptoms of the failure are sufficient to determine
>mode and signal causing the problem. I have also used an oscilloscope to
>determine
>if there is a long term change to a signal after the coupling to the probe
has
>died down. This does not work for fast signals because the field pick is
>much bigger than the signal. A long time ago I used an optical transmitter
>that could be connected to the circuit and use a fiber to get the signal
into
>a shielded room with an optical receiver and oscilloscope to look at the
>resulting signal.
>One problem was the transmitter was big and hard to attach to the board.
You
>are also looking at a double buffered copy of the even as well.
>
>The question is what techniques are used to probe logic circuits during an
ESD
>event?
>
>Thanks in advance,
>Keith Hardin
>Lexmark International Inc.
>
>
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