What’s New in Standards?
In the past six months, EOS/ESD Association, Inc., the only organization accredited by ANSI to write and produce standards on electrostatics, released eight new or revised documents on electrical overstress (EOS), grounding, packaging materials, seating (chairs), footwear, hand tools, gloves, and human metal model.
EOS is an area that has long been overlooked by the industry, not because of any limited importance, but rather because of its complex definition and multiple root causes. Indeed, it has proven difficult to find complete agreement among experts on even the fundamental definitions. Thus, the language of EOS, EOS threats, and responsibility remains open for discussion. ESDA’s newest technical report, ESD TR23.0-01-20 – ESD Association Technical Report for the Protection of EOS/ESD Susceptible Items – Electrical Overstress in Manufacturing and Test, is the first in a series of documents intended to provide information that promotes the reduction of EOS damage in manufacturing and test, and provide the knowledge base for on-going mitigation and monitoring for possibly damaging electrical stresses. The document will be revised and expanded as others in the industry come forward with additional best practices used in their facilities. The content in this version represents best practices that have been shared and reviewed up to the time of publication.
The most critical concept in the field of static control is grounding. Attaching all electrically conductive and dissipative items in the workplace to ground allows built-up electrostatic charges to equalize with ground potential. A grounded conductor (includes dissipative items) cannot hold a static charge. Electrically interconnecting all electrically conductive and dissipative items (bonding) allows charge to equalize across these items without actual contact to ground. This provides static control in areas where an actual connection to ground may not be accessible, such as in a field service environment. Electrically bonded conductors and dissipative items share stored electrical charge and therefore have no difference in electrical potential between them. Many types of ESD susceptible parts can be handled within a bonded system without causing damage. Users of ESDA’s grounding document, ANSI/ESD S6.1 – ESD Association Standard for the Protection of Electrostatic Discharge Susceptible Items – Grounding, need to consider the National Electric Code or other applicable laws and electrical system designs and specifications in the country where an ESD control program plan is being implemented. During the recent five-year review of ANSI/ESD S6.1, clarification language was added for use in countries outside of North America. User’s were directed to reference their country’s local electric code, if available, and common international terms were included for AC equipment ground (protective earth) and auxiliary ground (functional ground).
Packaging is necessary to protect electronic items from physical and environmental damage during manufacturing, transportation, and storage. While most packaging (not for static sensitive items) provides physical and environmental protection, some forms of packaging also may harm static sensitive electronic items by allowing the accumulation or the discharge of static electricity. Packaging for ESD susceptible (ESDS) items are commonly derived by modifying existing packaging to prevent the packaging itself from causing static damage. The packaging generally retains its physical and environmental protective qualities. Some forms of ESD protective packaging have been modified further to prevent other sources of static electricity from damaging a packaged item. ANSI/ESD S541 – ESD Association Standard for the Protection of Electrostatic Discharge Susceptible Items – Packaging Materials describes the packaging material properties needed to protect ESDS electronic items and references the testing methods for evaluating ESD protective packaging and packaging materials for those properties. Where possible, required limits are provided. Guidance for selecting ESD protective packaging with protective properties appropriate for specific applications is also provided. In a recent revision, the marking requirement was changed from a shall to a should because not all packaging can be marked due to material and design.
One source of electrostatic charge generation in a work environment is the separation of personnel from chairs, stools or other types of seating along with the movement of seating across the floor. This results in the generation of electrostatic charge that can accumulate on the seating and on personnel. The effect of this generation and accumulation of electrostatic charge can be minimized with the appropriate selection of seating. To effectively control electrostatic discharge, seating must be used in combination with an ESD controlled floor or mat. Seating is not a primary means of controlling electrostatic charge buildup on personnel in an ESD protective work area. Wrist straps or other means of personnel grounding should be used for this purpose. In the current revision of ANSI/ESD STM12.1 – ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items – Seating – Resistance Measurement, an alternative test methodology has been introduced that allows a significant reduction of the qualification measurements. Instead of measuring the resistance of all test points against all groundable points, if the groundable points are electrically connected, one groundable point can be selected as representative for all measurements.
An update was recently released for ANSI/ESD SP9.2 – ESD Association Standard Practice for the Protection of Electrostatic Discharge Susceptible Items – Foot Grounders – Resistive Characterization. The document describes the electrical resistance test methods for qualification of foot grounders (for example, heel straps, toe grounders, sole grounders, and booties). ANSI/ESD SP9.2 is intended for testing foot grounders used for grounding personnel engaged in working with ESD sensitive items. It does not address static control footwear (shoes) as those are covered in ANSI/ESD STM9.1 – ESD Association Work in Progress for the Protection of Electrostatic Discharge Susceptible Items – Footwear – Resistive Characterization. The recent updates include removing the foot grounder system section, Figure 3, Annex A – Tester Voltage Influence on High/Accept/Low Indications, Annex C – Parallel Ground Paths, and Annex E – Foot Grounder Classification. Round robin testing to verify repeatability and reproducibility of the test method was successfully completed in the last 12 months. ANSI/ESD STM9.1 and ANSI/ESD SP9.2 will be merged into one document within the next two years.
EOS and ESD can damage or degrade certain electronic components and assemblies in repair, debug, and rework stations. The intent of ANSI/ESD S13.1 – ESD Association Standard for the Protection of Electrostatic Discharge Susceptible Items – Electrical Soldering/Desoldering Hand Tools is to provide test requirements for soldering/desoldering hand tools used in ESD safe work areas or on materials that are deemed to be ESD sensitive. The methods described can be used during procurement, qualification, and verification of soldering/desoldering hand tools to verify that electrical integrity has not been compromised which could result in EOS/ESD damage. There is no attempt to define how the soldering irons are to be used. The current version is a reaffirmation of the 2015 version with only minor editorial changes.
After the successful completion of round robin lab testing to verify repeatability within single labs and reproducibility between labs, the ESDA’s gloves and finger cots document was re-designated from a standard practice to a standard test method. ANSI/ESD STM15.1 – ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items – Methods for Resistance Measurement of Gloves and Finger Cots provides test procedures for measuring the electrical resistance of gloves or finger cots and personnel together as a system. In addition, a procedure for measuring the intrinsic electrical resistance of gloves and finger cots is included. ANSI/ESD STM15.1 applies to all gloves and finger cots used in an electrostatic discharge (ESD) control program. The procedures described in this document provide data that are relevant in a specific environment and application. The system test uses a constant area and force electrode (CAFE) specifically designed for resistance measurements at the thumb and finger-tips. A further advantage of the CAFE is that it can be used to test finger cots as well as gloves using an identical procedure. A normative annex was added on the intrinsic testing of gloves and finger cots using ANSI/ESD STM11.11; ANSI/ESD STM11.12 and ANSI/ESD STM11.13, as well as an informative annex describing the differences between in-use and intrinsic resistance measurements.
The name human metal model (HMM) is derived from the anticipated ESD stress that could be generated from a person holding a metal tool. The current pulse delivered to the component in this test is intentionally the same pulse as defined in the IEC 61000-4-2 testing method. Customers of IC manufacturers have begun requesting that ICs be evaluated for their ability to withstand the IEC 61000-4-2 stress pulses. However, because this IEC specification only describes testing a complete system, that specification cannot be directly applied to devices such as ICs and discrete components. This document provides IC manufacturers and IC customers with testing methods applicable to devices that utilize the current waveform of IEC 61000-4-2. The technique described in this document is termed human metal model testing to differentiate it from the system level IEC 61000-4-2 and from human body model testing of integrated circuits, ANSI/ESDA/JEDEC JS-001. Many companies have developed their own testing techniques using IEC 61000-4-2 pulses from hand-held gun generators for device and circuit design evaluation. This technique or practice is being utilized on products in packaged configurations. Development of ESD SP5.6 – ESD Association Work in Progress for Electrostatic Discharge Sensitivity Testing – Human Metal Model (HMM) – Component Level is in response to the need of the industry for consistent testing methods. Significant changes during the recent update include extensive editing to account for the default stress being pin to ground rather than pin to pin, language added for stressing pin to pin with an HMM pulse source, adding test procedures to be followed when using an ESD gun during HMM testing, adding information on the use of an HMM pulse source with a wafer prober, and removing references to qualification.
If you have specific questions about these documents or any of ESDA’s other currently published documents, please send an email to info@esda.org.
