Standards continuously evolve, and EOS/ESD Association, Inc. standards are no different. Besides the routine five-year and ten-year review of standards (S), standard test methods (STM), and standard practices (SP), documents on new topics in the field of electrostatic control, electrostatic discharge (ESD) testing and characterization, electrical overstress (EOS), and ESD design and modeling are developed and published by more than thirty working groups (WGs). From 2021 to the beginning of 2024, approximately 30 documents have been reaffirmed, revised, or newly released. Slightly more than half of these documents address ESD control topics, some of which are covered in this short overview article. A second article will cover the new developments in ESD and EOS test and characterization and ESD design and modeling documents.
The central document on ESD control is 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. This standard defines the limits of ESD control items and ESD control measures. ANSI/ESD S20.20 refers to several standards and STMs defining the test methods for ESD control items, such as ESD-control flooring, seating, packaging, etc., and ESD control measures, such as personnel grounding (see Figure 1). Furthermore, it references the technical report (TR) ESD TR53 – ESD Association Technical Report for the Protection of Electrostatic Discharge Susceptible Items – Compliance Verification of ESD Control Items for all requirements on compliance verification. The new version of ANSI/ESD S20.20 was released at the end of 2021, and, consequently, ESD TR53 as a “companion document” was updated slightly later in May 2022 to align with the new version of ANSI/ESD S20.20. The second companion document of ANSI/ESD S20.20, ESD TR20.20 – ESD Association Handbook for the Development of an Electrostatic Discharge Control Program for the Protection of Electronic Parts, Assemblies, and Equipment, is currently being updated to address the comments received during the review processes of ANSI/ESD S20.20.
The major technical changes in ANSI/ESD S20.20 include requirements on product qualification, the assessment of the risk by process-essential insulators, which now adds the measurement of the electrostatic field at the location where the ESD-sensitive (ESDS) item is handled as an alternative test method. Additionally, a new section was added to the United States Department of Defense (DoD) packaging requirements per a request from the DoD to support the withdrawal of Mil-STD 1686. ANSI/ESD STM4.2 – ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items – ESD Protective Worksurfaces – Charge Dissipation Characteristics was removed as a qualification method for worksurfaces as this test method was withdrawn due to a lack of commercially available test equipment. A separate article will discuss all relevant changes in ANSI/ESD S20.20 and the compliance verification document ESD TR53.
In Annex A, ANSI/ESD S20.20 provides guidance and outlines documents available to help the users evaluate additional control products and equipment, such as ANSI/ESD SP17.1 – ESD Association Standard Practice for the Protection of Electrostatic Discharge Susceptible Items – Process Assessment Techniques. This newly developed standard practice describes a set of methodologies, techniques, and tools that can be used to characterize a process where ESDS items are handled. This document aims to identify whether potentially damaging ESD events are occurring or if significant electrostatic charges are generated on personnel, equipment, materials, or devices – even though there is a static control process in place (for example, ANSI/ESD S20.20). It can be used to assess whether devices of a given ESD robustness can be handled safely in the process, improve ESD capabilities if required or desired, or save money by reducing ESD control measures. ANSI/ESD SP17.1 addresses some challenges of current ESD control programs, such as the assessment of automated handling equipment (AHE), the use of ESD-sensitive items with an ESD robustness lower than defined in ANSI/ESD S20.20, that is 100 V against Human Body Model (HBM), 200 V against Charged Device Model (CDM), and 35 V against isolated conductors. Obviously, increasing I/O bandwidth and new packaging techniques such as die-to-die or wafer-to-wafer can lead to significantly reduced ESD robustness; process assessment is a crucial tool to ensure safe handling of ESD-sensitive items. The flows and measurement methodologies of ANSI/ESD SP17.1 can also be used for “troubleshooting.”
The document suggests ESD risk assessment flows in processes for ESD risks due to charged personnel, conductors, charged ESDS items, and insulators. Additionally, a simple assessment flow is described using ESD event detection methods. The document’s annex describes ESD measurement techniques typically used for ESD risk assessment. The overall approach for an ESD risk assessment with the framework of ANSI/ESD SP17.1 is shown in Figure 2. A sine qua non condition for a successful ESD risk assessment is a detailed understanding of the process and the potential ESD risks. Questions to be answered in preparation for the ESD risk assessment are, for example, whether there is a “critical” contact to the ESD-sensitive item in the process, that is, a metal-to-metal contact to the ESD-sensitive item. If potentially critical contacts are identified, the first step is to clarify the ESD robustness of the ESDS item in the process. The relevant parameter for the ESD robustness is the ESD withstand current; guidance is given in the document on how to come to the ESD withstand current even if “only” ESD qualification data with a withstand voltage are known. As the withstand current can rarely be measured in the process, limits for other ESD-relevant parameters such as the charging (voltage) in the process, the contact resistance of the object enabling the ESD-sensitive item to discharge or electrostatic fields have to be derived from the ESD withstand current. Finally, those parameters must be measured in the process and compared with the limits.
Without question, ANSI/ESD SP17.1 is already a very important document today, and its importance will continue to grow in the future with lower ESD robustness. However, the procedures in this document are not simple and are for use by personnel possessing advanced knowledge and experience with electrostatic measurements. Also, interpreting the results from the measurements described in this document requires significant experience and knowledge of the physics of ESD and the process. ESDA WG17 is working on documents and training materials with examples of applying the methodology and the measurement methods to processes in different applications.
Another ESDA document that addresses a new topic is ESD TR19.0-01 – ESDA Technical Report for the Development of an Electrostatic Discharge Control Program for Protection of High-Reliability Electrical and Electronic Parts, Assemblies, and Equipment. This document discusses best practices for defining, establishing, implementing, and maintaining an ESD control program for electronic items in high-reliability applications. High-reliability electronic items are defined in this document as items that serve functions where failures can have catastrophic effects, such as flight-critical, space, critical communication, weapons, and medical device/life science systems. This TR is intended to be used with ANSI/ESD S20.20 and to provide supplemental information and guidance on reducing risk when handling high-reliability electronic parts, assemblies, and equipment. ESDA WG19 has started developing an SP for an ESD control program for high-reliability electronic parts.
The oldest ESDA document, ANSI/ESD S1.1 – ESD Association Standard for the Protection of Electrostatic Discharge Susceptible Items – Wrist Straps, received minor updates in the 2021 release. There are no major developments in wrist straps; therefore, the changes are more editorial, such as aligning the units to the metric or SI system (for example, giving the break-away force now in N (Newton) instead of kg). Some figures have been added for clarity, and an alternative test method for the wrist strap continuity and resistance test is now included.
ANSI/ESD STM7.1 – ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items – Flooring Systems – Resistive Characterization changed its title from “Flooring Material” to “Flooring System” to highlight that the test is applied to a system of materials combined to make the flooring system and that those materials’ interactions can affect the overall resistance measured. The definition of conductive flooring is now changed from previously “less than or equal to 1.0 × 106 ohms” to now “less than 1.0 × 106 ohms”, and consequently, the definition of dissipative flooring from previously “greater than 1.0 × 106 ohms” to now “greater than or equal to 1.0 × 106 ohms and less than 1.0 x 109 ohms” – which has no practical implication. This is explained in a new Annex. As in all document revisions, boilerplate statements such as the definition of the meter have been updated.
ANSI/ESD STM9.1-2022 – ESD Association Standard Test Method for the Protection of Electrostatic Discharge Susceptible Items – Footwear and Foot Grounders – Resistive Characterization is now a consolidated document of ANSI/ESD/ESD STM9.1-2014 which addressed footwear and ANSI/ESD SP9.2-2019 which defined resistance test methods for foot grounders. Technically, the test methods for both footwear and foot grounders have not been changed.
The ESDA is always striving to achieve the highest quality standards. One important aspect is the alignment of verbiage and requirements amongst the different ESD standards. The ESDA’s Manufacturing Ad-hoc Task team is working continuously to harmonize the ESD control standards. A minimum set of reporting requirements is defined and will be included in all revised standard documents. Recommendations on equipment calibration and verification, together with simple verification methods, will be added to new documents. All compliance verification tests have now been removed from standards and standard test methods and moved to ESD TR53 as a single source of compliance verification tests. There is no longer a requirement to qualify ESD control items at moderate humidity; it is sufficient to perform qualification tests under the most critical low-humidity condition at 12% ± 3% relative humidity and 23 °C ± 3 °C. The only exception is ANSI/ESD STM11.31 – ESD Association Standard Test Method for Evaluating the Performance of Electrostatic Discharge Shielding Materials – Bags (“shielding bag test”), for which a higher relative humidity is critical. You will see those changes in the next revisions of the documents.
Founded in 1982, EOS/ESD Association, Inc. is a not-for-profit, professional organization dedicated to education and furthering the technology of Electrostatic Discharge (ESD) control and prevention. EOS/ESD Association, Inc. sponsors educational programs, develops ESD control and measurement standards, holds international technical symposiums, workshops, and tutorials, and fosters the exchange of technical information among its members and others.
