Q. Can you define electric field induction?
8.3.1 Insulators
All nonessential insulators such as coffee cups, food wrappers and personal items shall be removed from the EPA. The ESD program shall include a plan for handling process-required insulators in order to mitigate field-induced CDM damage. Can you define field-induced? Since this only addresses CDM damage, are process required insulators such as in process documentation, product packaging, and other things that are just a part of how we work acceptable to be present in the EPA?
A. Electric field induction occurs when a conductive item is brought into an electric field and then grounded while in the electric field. A charge will be transferred from ground to compensate for the intensity of the electric field at the exact location. The transfer of charge to and from ground represents a discharge to or from the conductor. If the conductor Q&A is then isolated from ground again, as often occurs in automated processes, the conductor will trap a charge. When the conductor is grounded again, a second discharge occurs. This type of event is discussed in numerous tutorials that are offered by the ESDA.
Any insulator that you consider process essential needs to be evaluated while in the process to ensure that the electric field from the insulator is within the established limits and within what you have established as the risk, at the location where sensitive items are present. The values and distances are stated in ANSI/ ESD S20.20.
The measurement of the electric field is most often done with electric field meters but it is important to understand the limitations of the measurements and how to interpret them. These considerations are also discussed in numerous tutorials. It is possible to measure the induced charge on isolated conductors using a contact electrostatic voltmeter which is a new class of instrument. This is now one of the best ways to determine what is actually happening in regards to induction in the actual process.
You may want to have a more in-depth discussion with some of the consultants listed in our Buyer’s Guide as many of them have considerable experience in this area.
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