Preventing Electrostatic Discharge (ESD)

When we walk across a carpeted floor and touch a doorknob, we feel a startling shock. This is one of the simplest forms of electrostatic discharge (ESD). It  occurs during the transfer of electrical charge between two bodies at different electrical potentials, when electrons are rapidly moving between objects in an attempt to remain neutral. ESD can appear in forms so minor that humans do not even feel it, and it occurs in an extreme form through lightning.

ESD often involves the release of electricity from the human body, but it does not commonly harm humans. Instead, the primary concern that comes from an ESD is the effect it has on equipment, because the extreme voltages of static electric discharge allow ionization of the air and cause materials to break down, leading to damage throughout a system that is struck with an ESD. This is especially problematic because it usually takes several thousand volts for a person to even notice ESD in the form of a spark, and discharges in amounts much less than this can easily damage a semiconductor. When operating on the inside of a computer, several different precautions should be taken to prevent the risk of ESD.

One of the primary methods of reducing the possibility of ESD during operations with sensitive assemblies and devices is the use of wrist straps to ground the personnel. These wrists straps are connected to a ground cord, which completes the electrical circuit between the human body and the ground. ANSI/ESD S1.1-2013: Wrist Straps specifies guidelines for this system, focusing on the structure of the system to both eliminate static from the personnel and ensure that it does not add obstructions that will inhibit the individual’s work or put him or her in danger. It also details testing methods to guarantee a wrist strap that will successfully prevent ESD during operations. Users of the standard are also cautioned that the guidelines that it provides should not replace any other safety standards for the place of operations.

Working in an environment that reduces the static carried by different ESD generators requires the operator to stand on the floor while interacting with the sensitive material on a desk. Since a great deal of static can derive from the floor, such as with a carpet, it is essential that the floor be maintained in a manner that does not introduce a higher voltage into the operator. ANSI/ESD STM7.1-2013 - ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items - Floor Materials - Resistive Characterization of Materials - Floor Materials provides guidelines needed to evaluate the floor covering, coatings, paints, and floor finishes. In addition, it recommends a floor mat to attain static control. Just as the floor should not be a source of static, neither should the work surface. Guidelines to manage this are covered in ESD S4.1-2006: Worksurface - Resistance Measurements.

In addition to these specifications, ANSI/ESD S20.20-2014: Protection of Electrical and Electronic Parts, Assemblies and Equipment details processes for an ESD Control Program, which establishes the highest static levels that the sensitive materials can be exposed to and how exactly people should go about handling them. This designates electrostatic protected areas, which comprises the safe zone in which personnel can interact with the ESD-susceptible equipment.

The Electrostatic Discharge Association (ESDA), an ANSI-accredited standards developing organization, writes and publishes the standards intended to manage and prevent electrostatic discharge events that can damage sensitive materials.
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