Handbook for the Development of an Electrostatic Discharge Control Program for the Protection of Electronic Parts, Assemblies and Equipment
|Publication Date:||1 January 2008|
The Electrostatic Discharge (ESD) Association Standards Committee produced this ESD Handbook for individuals and organizations that are faced with controlling ESD. It provides guidance that can be used for developing, implementing and monitoring an electrostatic discharge control program in accordance with ANSI/ESD S20.20. This Handbook applies to activities that: manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts human body model (HBM).
The 100 volt HBM limit was selected for ANSI/ESD S20.20 as the baseline susceptibility threshold since a large majority of the ESD susceptible products on the market have a sensitivity of greater than 100 volts. The 100 volt value is predicated on maximum voltage levels attainable on an individual when they are grounded via techniques accepted throughout the electronics industry as outlined in ANSI/ESD S20.20. Further, the required technical elements outlined in ANSI/ESD S20.20 are assumed to be equally effective in protecting devices in situations where charged device model (CDM) discharges are a concern. Proper grounding techniques, reduction of electrical fields from process essential insulators, and removal of all other insulators from the process area are requirements of ANSI/ESD S20.20 that aid in reducing CDM risk.
ANSI/ESD S20.20 is the culmination of the ESD Association's response to the request of the US Department of Defense to write a commercial version of MIL-STD-1686, Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices). The Handbook is a living document that will be periodically updated as new ESD control technology emerges.
The fundamental ESD control principles that form the basis of ANSI/ESD S20.20 follow:
All conductors in the environment, including personnel, must be bonded or electrically connected and attached to a known ground or contrived ground (as on shipboard or on aircraft). This attachment creates an equipotential balance between all items and personnel. Electrostatic protection can be maintained at a potential above a "zero" voltage ground potential as long as all items in the system are at the same potential.
Necessary nonconductors in the environment that have been triboelectrically charged cannot lose their electrostatic charge by attachment to ground. Ionization systems reduce the residual charge on these necessary nonconductive items over time (circuit board materials and some device packages are examples of necessary nonconductors). Assessment of the ESD hazard created by electrostatic charges on the necessary nonconductors in the work place is required to ensure that appropriate actions are implemented, commensurate with risk.
Transportation of electrostatic discharge sensitive (ESDS) items outside an ESD Protected Area (hereafter referred to as "EPA") requires enclosure in static protective materials, although the type of material depends on the situation and destination. Inside an EPA, low charging and static dissipative materials may provide adequate protection. Outside an EPA, low charging and static discharge shielding materials are recommended. While these materials are not discussed in detail in ANSI/ESD S20.20, the reader is encouraged to understand the differences in their application as outlined within this handbook.