My opinion:
When facing low humidity, the first priority should be the proper grounding
of all conductors in the ESD protected area, removal of insulators and/or
use of ionizers to remove charges. However, at less than 30% relative
humidity to require grounded ESD smocks (making sure that they are buttoned
up covering all clothing on torso and arms) makes sense to me.
Some info from ESD Association documents:
The Table 1 minimum recommended technical requirement of ANSI/ESD S20.20
for Humidity is greater than 30% Rh less than 70%.
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."
Although ESD Smocks are not a S20.20 requirement, it's a very effective
means to comply with paragraph 6.2.3.2's recommendation. Per ANSI/ESD
S20.20 Paragraph 6.2.1.1. Grounding / Bonding Systems Requirements,
"Grounding shall be used to ensure that ESDS items, personnel and any other
conductors (e.g. mobile equipment) are at the same electrical potential."
Smocks are a conductor and therefore, must be grounded. This is best
assured when they are designed to make intimate contact with the skin of a
grounded operator.
Per ESD Handbook TR 20.20 paragraph 5.3.15 Humidity "Humidity is
beneficial in all ESD Control Program Plans. Contact and separation of dry
materials generates greater electrostatic charges than moist materials
because moisture provides conductivity that helps to dissipate charge. For
this reason, ESD effects are most noticeable in the winter since heating
systems reduce building environment moisture. Geographic location (desert
vs. coastland) is also a major contributor to ambient conditions inside
buildings. Any circumstance that results in a low relative humidity will
permit a greater accumulation of electrostatic charges. Relative humidity
above 30 percent in ESD protective areas is desirable as long as other
adverse conditions are not created as a result of humidity levels.
Generally speaking an upper limit of 70 percent is desirable to prevent
corrosive effects on the metal portions of electronic devices and
assemblies.
Besides the increasing propensity to generate electrostatic charges on dry
materials in general, performance of many ESD protective materials degrade.
In fact, when exposed to low humidity conditions, some ESD protective
materials become totally ineffective or become sources of electrostatic
charges. Therefore, evaluation of ESD control materials should include
performance testing in controlled environments at the lowest expected
operating relative humidity level. Manufacturers of ESD protective
materials should be able to provide performance data in regards to relative
humidity. Like wise materials should be tested in moderate humidity
conditions as well to ensure they do not become "too conductive" and
present a potential safety hazard to personnel working with substantial
voltages. See the Personnel Safety section of this handbook for further
guidance in this area."
Gene Felder
[log in to unmask]
-----Original Message-----
From: Willie Duersch [SMTP:[log in to unmask]]
Sent: Wednesday, October 02, 2002 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] ESD ISSUE
<< File: ATT00023.html >> I agree. James, if you review VT-54
Electrostatic Discharge control for
operators (IPC video training) and the instruction/test there in, you can
not rely on Humidity to control ESD damage.
Regards,
Willie Duersch
Projects Manager, Technical Sales
Inovar, Inc.
1073 West 1700 North
Logan, UT 84321
Phone: 435-792-4949 x105
Fax: 435-792-4950
Cell: 435-881-2219 (best)
E-mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Dieselberg, Ron
Sent: Wednesday, October 02, 2002 8:35 AM
To: [log in to unmask]
Subject: Re: [TN] ESD ISSUE
James, I think it would be a bad practice not to use ESD smocks. ESD is a
surface phenomenon and although higher humidity lessens static generation
and build-up it does not reduce it enough to abandon other ESD safeguards.
my $0.02 worth.
Ron Dieselberg
CMC ELECTRONICS
CINCINNATI
[log in to unmask]
-----Original Message-----
From: Marsico, James [ mailto:[log in to unmask]]
Sent: Wednesday, October 02, 2002 8:00 AM
To: [log in to unmask]
Subject: [TN] ESD ISSUE
Good day Technetters:
I need some opinions (this may be asking for trouble!). Located in the
north east, temperature/humidity levels can change on a daily basis. It
has
been our policy that, during summer months when the humidity is high, the
operators do not have to wear ESD smocks in areas that are not air
conditioned. There is no hard fast rule as to what the conditions shall
be,
except that a decision is made (by yours truly) that smocks are optional
when conditions are uncomfortable. I'm trying to select a specific
humidity
level to use as a criteria for the mandatory wearing of smocks. I
understand that not wearing ESD smocks poses a risk, but the risk is
minimized during high humidity conditions. What do you think of this
policy? Any recommendations on a humidity level?
Thanks,
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] < mailto:[log in to unmask]>
631-595-5879
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