Grounding and Packaging for ESD Control

Proper grounding and packaging practices are essential for effective ESD control.

Q. Can ESD-protective lab coats be used without heel straps in an ESD-protected area?

A. If the garment is an electrically groundable one, it should be electrically bonded to the wearer's grounding system so that it will not act as a floating ground. Typically, the garment would be grounded to the body with a direct connection to a wrist strap, a conductive wrist cuff in direct contact with the skin of a grounded wearer, or a separate ground cord attached to an identified groundable point on the garment.

If the garment is in direct contact with the skin of the wearer, that person also needs to be grounded, either through a wrist strap or through static control footwear (foot straps or shoes) to a grounded static control floor. If heel straps or static control shoes are not worn and there is no static control floor, then the person is not grounded. Both the proper footwear and the proper floor are needed to complete the connection from garment to body to ground.

If the garment is not electrically groundable (for example, a topically treated garment), then heel straps are not necessary.

Q. Our supplier wraps a paper lot sheet around extremely ESD-sensitive printed-circuit-board assemblies with a rubber band, and the boards are not in a barrier bag. Does this provide enough protection?

A. This type of packaging, if it can be called that, does not protect the board from potential ESD damage. ESD protective packaging should accomplish two major goals in controlling electrostatic discharge: eliminating or reducing charge generation and accumulation, and preventing discharges from reaching susceptible parts and assemblies.

Several factors influence the selection of the proper package. First is determining whether the item being packaged is to be protected from triboelectric charge generation, direct electrostatic discharge, electrostatic fields, or a combination of those. Packaging decisions and designs should consider the ESD sensitivity of the item. Most companies use packaging materials that provide several levels of protection. For example, conductive or shielding materials may be required to prevent direct discharges from reaching the product, and these materials may need to be combined with dissipative material to reduce the possibility of a charged-device-model discharge from the product.

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.com/esdhelp.html. Information on the ESD Association may be found at http://www.esda.org.

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