ANSI/ESD S20.20-1999 included Humidity in Table 1 with the "recommended
range" be ">30% Rh <70%". If used, that is still the recommendation, see
ESD Handbook..
Note: In ANSI/ESD S20.20-2007 the table column heading was changed from
"Recommended Range" to "Required Limit(s)"
Here's what it says in the ESD Handbook ESD TR20.20 just updated in 2008.
"5.3.16 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% 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% 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.
Likewise, 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.
Humidity control in factories or physically large areas or buildings can be
difficult and expensive. In smaller rooms or areas, it may be possible to
use portable humidifiers to raise the immediate area humidity. However, in
large facilities and factories the environmental systems many need to
include steam generation and monitoring equipment to control humidity. This
type of equipment is expensive to install and purchase especially in
pre-existing facilities. To reduce the total cost impact, companies should
consider the need for humidification equipment when planning new facility
construction."
Gene Felder
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: 2010 - 05 - 10 9:07 AM
To: [log in to unmask]
Subject: Re: [TN] ESD QUESTION ABOUT ANSI/ESD S202.20-2007 AND HUMIDITY
MIL-HDBK-263 is still active.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon (SA-1)
Sent: Monday, May 10, 2010 11:42 AM
To: [log in to unmask]
Subject: [TN] ESD QUESTION ABOUT ANSI/ESD S202.20-2007 AND HUMIDITY
In updated our ESD training, I noticed that the latest 20.20 drop
humidity as a subject or requirement, which was under Paragraph 6.2.3.2
of ANSI/ESD S20.20 1999.
Do any of you know why? Another spec used maybe? Thanks, Jon
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