Q&A on Electrostatic Discharge
Provided by the ESD Association
A: Ideally, you should try to keep static-generating materials
to a minimum in such environments. But since this is not always
possible, there are several steps you can take to minimize
the potential impact on ESD-sensitive (ESDS) products.
Keep the static generators as far away from your ESDS
products as possible, preferably at a distance of 13
Be sure to keep ESDS products from entering any
field that may be produced by the static-generating item.
If a given static generator is a conductor, ground
it if possible.
Treat the surface of the static generator with
a topical antistat to reduce the charge generated on the
Use static-protective garments to help suppress
any fields given off by employee clothing.
You may need to implement several of these
steps for adequate protection.
Q: Static-shielding packaging materials are
often defined as those with surface resistance equal
to or less than 1.0 x 103
when tested according to EOS/ ESD-S11.11. Yet some
materials with a higher surface resistance of 1.0
are said to have shielding properties. Can you explain?
A: This definition classifies materials by their
electrical rather than their functional characteristics.
A functional definition of an ESD shield is a barrier
or enclosure that protects the packaged contents from
a direct discharge to the exterior of the package.
A common method of providing shielding functionality in packaging
materials is the incorporation of a layer of electrical conductive
material within the package to create a Faraday cage structure.
Resistance measurements or capacitive probe testing could
be used to describe the package's shielding capabilities.
Research conducted at Bell Laboratories in the early
1980s indicates that an air gap between a sensitive device and
the inner surface of its protective packaging also provides
a shielding effect. The packaging materials involved might have
a surface resistance as high as 1.0 x 109
With this methodology, resistance measurements could not be
used to define the material's shielding capability, but capacitive
probe testing could indicate shielding.
Additional information may be obtained by
contacting the ESD Association, 7900 Turin Rd., Bldg. 3, Ste.
2, Rome, NY 13440; phone: 315/339-6937; fax: 315/339-6793; e-mail:
submit your questions to the ESD Help Desk or to browse the archives
of past questions and answers, go on-line at http://www.ce-mag/esdhelp.htm.
Information on the ESD Association may be found at http://www.eosesd.org.
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