Yes, paints are usually (but not always insulative). But when doing ESD
testing a guy at a lab once told me they dig the point in through the paint
because in the real world there will be scratches through the paint and that
is where ESD will get in.
My own practice for the past (too many to recall) years has always been dig in
the point on metal / conductive surfaces. We have also done contact discharge
to plastic surfaces such as control panels and displays because that is where
people will touch the product, though for that test we won't dig in the point.
Then we do air discharge on plastic surfaces, but tend to have the approach
start over plastic surfaces, then repeat with the approach over metal surfaces
heading toward the plastic. Found lots of leakage at the interfaces between
the two materials that way.
With regard to painted surfaces, I have used epoxy-based paints that are
virtually invulnerable to the ESD gun's point. Then I have used other paints
that scratch just by looking at them,
Scott
Philo Beddo wrote:
I've had customers state that painted surfaces are insluative.
I generally disagree. But, there is a point buried in there.
What is the dielectrict with-stand of the painted surface? AND how
does the
product's ESD immunity differ in either case?
ASH
----- Original Message ----
From: Derek Walton <[email protected]> <mailto:[email protected]>
To: "Grasso, Charles" <[email protected]>
<mailto:[email protected]>
Cc: John Woodgate <[email protected]>
<mailto:[email protected]> ;
[email protected]
Sent: Friday, May 22, 2009 12:08:53 PM
Subject: Re: [PSES] ESD testing
Hi Chas,
This is how I interpret the standard. Somewhere I recall if painted
surfaces
can be penetrated by the point, then Contact also applies.
Cheers,
Derek.
Grasso, Charles wrote:
The ESD standard is perfectly clear (at least to me) - The
product
is tested using contact discharge for conductive surfaces AND
air discharge
on insulating surfaces.
I don't perceive an interpretation issue.
If your product is a object constructed entirely of a
conductive material -
contact discharge only applies. Similarly if
the product is an object constructed entirely of an insulator
then only
air discharge applies. If your product has combinations of both
- then
both types of discharges apply.
Is this reasoning flawed??
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
John
Woodgate
Sent: Friday, May 22, 2009 7:50 AM
To: [email protected]
Subject: Re: [PSES] ESD testing
In message
<[email protected]>
<mailto:[email protected]> ,
dated Fri, 22 May 2009, Kate Savo <[email protected]>
<mailto:[email protected]> writes:
Safety/EMC Standards frequently omit the "and" in a
list of items such as
you excerpted here from 61000-4-2 - they only put an "or" in where they truly
mean it to be interpreted as such.
The "and" is implied and Contact ESD must be done on
all conductive
surfaces, and Air ESD on all insulating surfaces. If your product has both
surface types, you should not omit either test scenario. Your local EMC/ESD
lab should confirm this.
I do not support that interpretation. If the list just said:
- air discharge;
- contact discharge
to conductive surfaces, conducting planes and insulating
surfaces.
then 'and' might be inferred. But in fact, the inclusion of
further words,
defining the surfaces to which the two types of discharge shall be applied,
excludes such an inference:
a) contact discharge to the conductive surfaces and coupling
planes;
b) air discharge at insulating surfaces.
-
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