Electrostatic Discharge Control Industry Standard Updated
In 2014, the Electrostatic Discharge Association (ESDA) updated its primary Electrostatic Discharge (ESD) control standard: American National Standards Institute/ESD S20.20. The changes affect how NASA defines the minimum requirements for ESD controls applied when the agency and its suppliers process and handle mission hardware that is sensitive to damaging ESD events.
When static charge finds a path to ground through a sensitive component, current flows and imparts an energy on that component that can overstress it beyond its maximum operating parameters. When this happens, the component is damaged catastrophically or weakened. Although ESD damage may not result in immediate failure, that doesn’t eliminate the risk of latent failure. If an ESD damaged part becomes a part of mission hardware, it puts the entire mission at risk for failure. It also can, and has, resulted in project delays.
The improvements to the standard reflect an improved understanding of how to measure performance for items that are used within an ESD protected area, such as garments and hand tools. They also reflect a general improvement in ionizer performance across the ionizer market — an improvement that the user community now can depend on. Finally, the changes emphasize that the user’s responsibility for item qualification is critical for ensuring that an S20.20-based ESD Control Plan is fully effective.
“In the update to S20.20, the ESDA emphasizes that individual test methods and specifications used to qualify items such as garments, wrist straps, ESD containers and ESD flooring in ESD protected areas are required to address important performance criteria,” said NASA Workmanship Standards Program Manager Jeanette Plante. “This revision clarifies that to implement a fully successful S20.20 ESD control program, these items must be qualified. In the absence of a third-party independent qualification authority, the ESDA delegates that responsibility to the user.”
The following are the highlights from the changes to ANSI/ESD S20.20 — ESD Association Standard for the Development of an Electrostatic Discharge Control Program for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices):
- The broadened scope defines the range of sensitivities addressed by the controls and protections required by the ESD control plan. Minimum safe charge thresholds were added: 200 volts for Charge Device Model-type sensitivity and 35 volts for Machine Model-type sensitivity. The Human Body Model value of 100 volts remains unchanged. These levels indicate the types of ESD sensitive items that will be protected from damage when the requirements are successfully implemented. Additional customized controls may be required to adequately control ESD events for hardware that is more sensitive.
- A new statement emphasizes that it cannot be assumed that ESD controls address electrical safety needs.
- Product qualification is now a required element of an organization’s ESD control plan. This amplifies the importance of ensuring all ESD control items such as wrist straps, garments, mats, chairs, bags, boxes and flooring meet the required performance limits prior to their use and also that not all manufacturers can meet these limits.
- Improved ESD garment test requirements include limits for cases where personal grounding is achieved through a grounded garment rather than use of a wrist strap.
- Ionization offset voltage is now set at plus or minus 35 volts, reduced from plus or minus 50 volts, which reflects widespread improvement in the quality of modern ionizers.
- There are new requirements applicable to mobile equipment and soldering and desoldering hand-tools.
- New insulator control requirements address insulators located within 1 inch of hardware presenting a field exceeding 125 volts per inch. As with the 2007 version of the standard, insulative items that present a measured field exceeding 2,000 volts per inch must be kept 30 centimeters (12 inches) away from ESD sensitive hardware and should be neutralized with ionization or another charge mitigation method such as shielding.
An additional note regarding procurements: It is critical that all procurements of ESD control items clearly state the performance limits and test method defined in ANSI/ESD S20.20 and its supporting requirements documents. Procurement language or source control document specifications should require the supplier to provide a manufacturer’s certificate of conformance and test data that is relevant for the product supplied. The language also needs to flow this requirement down to the manufacturer if the order is being placed with a distributer. The alternative to this approach transfers the task of performing the qualification tests from the product manufacturer to the user. If lot-based test data is not supplied by the manufacturer, incoming acceptance testing may be necessary to ensure product quality.
For more information about NASA’s ESD control requirements contact Gene Monroe.
Read “Space Addendum Adds Quality Requirements to Industry ESD Standards”