• Keep the static generators as far away from your ESDS products as possible, preferably at a distance of 1–3 ft.
• 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.
• Ionize the material.
• Treat the surface of the static generator with a topical antistat to reduce the charge generated on the material.
• 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 x 10⁹ 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: eosesd@aol.com.

 

To 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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