Per ESD Association. Per ANSI/ESD S20.20 Paragraph 6.2.3.2. Protected Areas
Guidance
"All process essential insulators that have electrostatic fields that
exceed 2,000 volts should be kept at a minimum distance of 12 inches from
ESDS items."
Per ESD Handbook TR20.20 section 2.3 Nature of Static Electricity
"A charged nonconductor does possess and emanate an electric field.
ANSI/ESD S 20.20 allows nonconductors with a measured electric field of
less than 2000 volts per inch to reside in the electrostatic protective
area even if devices sensitive to 100 volts or greater (when tested
according to the Human Body Model) are present. If the measured field is
greater than 2,000 volts the materials must be kept at least 12 inches away
from the sensitive components. Other standards are far more restrictive in
this regard. Why the difference? It is misunderstood in the industry that
an electric field from a charged object, is not equal to the discharge
potential from contact with a charged conductor. In other words, it takes a
significant electric field to cause a level of induction to a device
grounded within the field that would be equivalent to the amount of charge
transferred in a conductive contact with a charged conductive object.
Empirical work during the development of ESD S 20.20 showed that a six-inch
diameter plate with a potential of up to 25,000 volts did not induce
sufficient charge to a 100 volt HBM field effect transistor (gate lead
grounded while in the field) to cause damage even at a distance of one
inch. Therefore, the 2000 volt at 12 inch specification has a significant
safety margin."
Per ANSI/ESD S20.20 Paragraph 6.2.3.1. Protected Areas Requirement
"All nonessential insulators, such as those made of plastics and paper
(e.g. coffee cups, food wrappers and personal items) must be removed from
the workstation. Ionization or other charge mitigating techniques shall be
used at the workstation to neutralize electrostatic fields on all process
essential insulators if the electrostatic field is considered a threat."
Gene Felder
[log in to unmask]
-----Original Message-----
From: Van Beveren Richard (RBAU/MFE4)
[SMTP:[log in to unmask]]
Sent: Sunday, May 08, 2005 10:47 PM
To: [log in to unmask]
Subject: Re: [TN] FW: Static and break over voltage spacing standards?
Lots of info in ESD on the internet, for example, http://www.esda.org is
not a bad place to start.
As suggested by others, it's easy to build up charges over 30,000 volts on
plastics and damage to ESD sensitive components can occur at a fraction of
this. There are also a few ways to inflict damage by ESD: discharge to the
device, discharge from the device and field induced charges that can then
lead to an dangerous discharge. Most component spec. sheets I've seen will
specify different maximum voltages for these ESD 'events' types typically
referred to as Human Body Model (HBM), Charged Device Model (CDM) and
Machine Model (MM).
If no specs exist, I'd be very, very careful about relying on a certain
charge not being able to jump a certain distance not only because
environment conditions influence this so much but because you could still
be damaging your parts without a 'zap' taking place, or inducing a charge
that leads to a 'zap' down the line somewhere. Of course, keeping in mind
that by the time you see or hear a zap you've got thousands of volts....
Richard van Beveren
Robert Bosch (Australia) Pty Ltd
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brooks,Bill
Sent: Saturday, 7 May 2005 1:07 AM
To: [log in to unmask]
Subject: [TN] FW: Static and break over voltage spacing standards?
I hope that someone on the forum may have a comment or two about this
subject... and can help John.
- Bill
-----Original Message-----
From: John Smith [mailto:[log in to unmask]]
Sent: Thursday, May 05, 2005 7:21 AM
To: 'Bill Brooks'
Subject: RE: Web site question
Thank you for your response Bill, I am trying find out at what voltage and
at what distance I need to be concerned about a static discharge from a
plastic surface. I have a silicon wafer processing tool and there is
concern
about static discharge from the exterior plastic panels. I want to be able
to determine, the voltage vs.. distance safe point, i.e. (at 500v of charge
an arc will not jump at a greater distance than .5") I understand that the
type of material, the humidity and other factors make a difference, but
there must be some test data some where that points to some generalities.
Thanks again for your time bill
John
-----Original Message-----
From: Bill Brooks [mailto:[log in to unmask]]
Sent: Wednesday, May 04, 2005 11:03 PM
To: 'John Smith'
Subject: RE: Web site question
http://sprott.physics.wisc.edu/demobook/chapter4.htm
see table 4.2
The issue with predicting electrical arcing is in defining the
environmental
conditions that contribute to the 'break over' voltage. The presence of dry
ionizing air, or ionic contamination on a surface can greatly increase the
distance at which break over will occur. Once the arc is established, it
ionizes an electrical path which is much lower in resistance that the
initial break over voltage required to jump across the electrodes and the
two points of potential can be moved much farther apart and they will still
conduct...
What are you trying to do?
Bill Brooks
-----Original Message-----
From: John Smith [mailto:[log in to unmask]]
Sent: Wednesday, May 04, 2005 2:09 PM
To: [log in to unmask]
Subject: Web site question
Is there a guideline that references how far a static charge will jump?
i.e. a 500v charge could be expected to jump or ark how far?
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