For Humidity, the minimum recommended technical requirement of Table 1 of
ANSI/ESD S20.20 is > 30% Rh < 70%.

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.

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:   Morse, Carrie [SMTP:[log in to unmask]]
Sent:   Thursday, February 05, 2004 5:26 AM
To:     [log in to unmask]
Subject:        Re: [TN] Facility Humidity control

J-STD-001C Paragraph 3.6.2 outlines the specifications.  In summary, if the
humidity falls below 30%, then proper ESD control needs to be in place.  It
also specifies a max of 70%.  We are in the east and find our humidity
ranges from as low as 10% in the winter up to 50% or so in the summer.
 Even with humidity controls in place we have difficulty maintaining the
30% min in the winter.

Although the spec states a range, other considerations need to be kept in
mind.  These include the affect of humidity of MSD's, paste processes,
assembly processes, and even reflow.  If paste dries out or absorbs
moisture, variation in these processes will be evident.

-Carrie

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Peter L.
Sent: Wednesday, February 04, 2004 5:46 PM
To: [log in to unmask]
Subject: [TN] Facility Humidity control


Technet,

What is the typical humidity/ temperture (nominal and +/-) for a CEM
production environment?

Is there an industry "acceptable" range?

We are located here in the west coast and have seen relative humidity level
varied from low 30s% (winter) to high 60s in the summer. Under what
conditions should a HVAC control system be introduced and without that,
what would be the potential impact on the overall manufacturing process?


Rgds,
Peter

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