RE: [SI-LIST] : Best System Grounding Scheme for ESD, and RF emission

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From: Doug (dmckean@gte.net)
Date: Mon Oct 30 2000 - 20:14:14 PST


Well, I'll give it a try. Can't say it's going
to help much.

You're asking some difficult questions based on just
the information given. In such a situation, I need
to be in a lab in front of the device with a current
probe or field probe in my hands to tell for sure.
And no, that's not an invitation.

I've worked with modules both grounded and not grounded
to the chassis. It is possible to make matters worse
by grounding to the chassis. I've seen this in the
case of connectors for external interconnect.

The point of connecting both ground planes together in
some way could be up for some serious debate. Especially
to the chassis of some module. Again, I've seen both.
Depends a lot on how well a connection is between the
chassis of the module and the chassis of the product
in which the module is used.

Generally, if you can guarantee a good solid connection
(that doesn't happen as often as you think), then *maybe*
you might consider it. You might even experiment with
this by using the famous copper tape found in EMC labs
as a connection.

Otherwise, if the ground connection is what's called
"incidental", then maybe that's not the thing to do.
You could force circulating currents originally not
present to be present on the faceplate and thus creating
an emissive surface. Obviously, making matters worse.

I've also worked with a terrible design which had very
little incidental contact between the body of the module
and the product chassis. Grounding to the body of the
module was achieved by connecting to a ground pin
on the main connector for the module. And obviously
in this case, ESD was a major problem.

As far as design guidelines for ESD. I've done some
of my own study of this by way of the school of hard
knocks and can say that separation should be a
primary concern. THEN, grounding.

I don't think you'll find many solid omniscient
"rules of thumb" to go by and I'm not sure I even
helped. But, you asked for "any input".

So, there it is ...

Good luck, Doug McKean

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