|Provided by the ESD Association
Grounding and Packaging for ESD Control
Proper grounding and packaging practices are essential for effective
Q. Can ESD-protective lab coats be used without heel straps in an
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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