Revisited and Revised as of 2023
With the inventions of the transistor in 1947 and the integrated circuit in 1958, and the utilization of these major solid-state breakthroughs in the development of computers and other electronic devices, industry began to worry about designing components and end-products that could survive the impact of electrostatic discharges to chips, printed circuit boards, and final packaged-products. The 1960s and 1970s saw individual companies developing their own ESD test values and laboratory test techniques. The International Electrotechnical Commission (IEC), which is closely related to the International Standards Organization (ISO), got involved in the 1980s with the release of IEC 801-2 in 1984 on ESD limits and susceptibility test methods. Since the late 1980s, most electronic companies test their end-products for ESD immunity in accordance with the specifications found in IEC 801-2 and its follow-on standard, IEC 61000-4-2.
In the Beginning
The electrostatic discharge (ESD) phenomena have been known since the Greek civilization was dominant thousands of years ago. Experiments with glass rods and cloth material produced ESD sparks. And people in colder climates were very familiar with the ESD effect due to a low-relative humidity environment inside a building or house. They frequently experienced an ESD event as they walked across a carpet in the winter season.
As electronic components changed from electronic tubes to solid-state electronics in the 1950s, companies became concerned with the potential for physical damage to solid-state electronic components, interference to, and interruption of normal operation of electronic equipment. This article primarily addresses the latter of those two situations, that is, the interruption effects of ESD on packaged electronic equipment.
The 1960s and 1970s
Most electronic companies in the 1960s and 1970s were aware of and concerned about ESD. The companies tended to have proprietary standards and test methods on ESD and were not interested in exchanging information with their competitors on ESD.
The Human Body Discharge model was commonly used by companies to test products with an ESD tester. The capacitance of a human being was estimated to be in the 100 to 250 picofarad range depending on the size of the person and the length and shape of the human’s shoes. A common discharge value for early standards was 5000 volts. The discharge resistance was often taken as 500 ohms, the resistance of the human finger. The discharge was an air-gap discharge that closely simulated the actual ESD phenomena.
There were some companies that were using a contact discharge approach to ESD where the ESD tester was in physical (metal-to-metal) contact with the electronic equipment. The contact discharge was a more repeatable method than the air discharge method. Oftentimes, thousands of contact discharges were used to simulate the effects of one event, and statistical analysis was used to determine pass or fail criteria for the ESD test.
The common joke among EMC consultants in the 1970s was about the correct magnitude of the ESD discharge. In most cases, companies started at a recommended 5 kilovolts amplitude. Then, when all products could pass that level, consultants would increase their recommendation to 7500 volts amplitude so they could continue to consult with the customer and improve the design of the product.
Kangaroo Leather
A United States computer company in the 1970s began experimenting with ESD relative to its computers and computer peripherals. A Van de Graaf generator, some high-voltage sources, and a green nylon carpet were all tried as potential ESD generators. After experimenting with the three options, it was decided to go with the standard green nylon carpet concept. A number of volunteers were organized and asked to shuffle their feet on the carpet in a controlled humidity environment while holding onto a scientific electrostatic voltmeter. Again, in most cases, at relative humidity levels of 10% and greater, about 5 to 7.5 kilovolts was the maximum value measured on the human subjects.
One product made by the computer company had a wide distribution in Australia, and it had ESD problems while the same product shipped to other countries had no ESD problems. An engineer from the company who worked with the Australian customers visited the EMC lab and discussed the issue with the EMC lab engineers. The engineers took the Australian engineer into the controlled environment and asked him to shuffle his feet while connected to the electrostatic voltmeter. Much to the EMC lab engineers’ surprise, the voltmeter registered 18000 volts!
After some discussions with the Australian native, it was discerned that he had normal clothing on his body with the exception of his shoes which were made of kangaroo leather. Needless to say, the lab made that fact known while in parallel developing an engineering fix to its product to allow it to pass 18 kilovolts.
The 1980s
The 1980s saw the release of the IBM Personal Computer in 1981, which legitimized the PC market and led the computer industry to develop desk-supported computers (desktop, laptop, etc.) and similar desk-based electronic products for the manufacturers of medical equipment, laboratory equipment, etc.) based on international standards to help ensure satisfactory ESD product performance.
IEC 801-2 – 1984
The first edition of International Electrotechnical Commission (IEC) Publication 801-2 was released in 1984. It was titled “Electromagnetic Compatibility for Industrial-Process Measurement and Control Equipment – Part 2: Electrostatic Discharge Requirements.”
The standard carefully pointed out in a note that:
“From the technical point of view, the more precise term for this phenomenon would be ‘static electricity discharge.’ However, the term ‘electrostatic discharge’ (ESD) is widely used in the technical world and in technical literature. Therefore, it has been decided to retain the term ESD in the title.”
The characteristics of the ESD generator in the 1984 edition were: energy storage capacitor – 150 pF +/- 10%; discharge resistor – 150 ohms +/- 5%; and an output voltage of 2 kV to 16.5 kV (the output voltage was a positive voltage only!). The rise-time of the discharge current was 5 ns +/- 30% at 4 kV and the pulse width was approximately 30 ns +/- 30%. The test was an air-discharge test only.
The 1984 edition did have a requirement for discharging to the earth reference plane to simulate discharges to objects in the vicinity of the equipment under test (EUT).
Figure 5 of IEC 801-2 illustrated the “test set-up for table-top-mounted equipment, laboratory tests.” There was no “ground reference plane” on the floor; instead, the “earth reference plane” was on top of the table and grounded to a mains terminal (earth connection) via a cable. The insulating support between the EUT and the earth reference plane was 10 cm (4 inches) thick.
Second Edition of IEC 801-2 – 1991
The second edition of IEC 801-2 was released in 1991. One of the major changes in the standard was that the contact discharge was the preferred test method and not the air discharge method.
The energy storage capacitor remained at 150 pF but the discharge changed to 330 ohms plus or minus 10%. The output voltage was increased to 8 kilovolts for contact discharge and 15 kilovolts for air discharge (both positive and negative pulses were mandated!). The rise-time at 4 kilovolts had decreased to 0.7 to 1 nanosecond. The values of the parameters of the discharge current had to be verified with a 1 GHz oscilloscope. The grounding cables from the newly implemented vertical coupling plane (VCP) and its complement, the horizontal coupling plane (HCP) to the ground reference plane, had 470-kiloohm resistors located at each end of the cables.
Vertical Coupling Plane (VCP)
A VCP is called out in modern-day ESD standards. The basis for the VCP is a metal filing cabinet (usually four-drawer) that was commonplace in the offices of industry. The ESD charge simulated an employee walking across a floor, touching the handle of the metal filing cabinet, and discharging ESD energy to the cabinet, which would then re-radiate the field from the side of the cabinet.
Horizontal Coupling Plane (HCP)
The development of the HCP started with a well-known cash-register company in the 1970s. At that time, they had an air-discharge ESD gun which was used for their product development testing. The EMC engineers very cleverly developed an all-plastic cash register and the ESD gun would not discharge to the cash register. Therefore, by definition, the product passed the ESD test.
The all-plastic cash register went into production and out into the real world with real customers. One of the first buyers of the all-plastic cash register was a fast-food restaurant that used an all-metal countertop to separate the customers from the employee/kitchen area. When winter came, the customers would enter the restaurant and discharge an ESD event to the 3-meter-long metal countertop. The countertop would then re-radiate the ESD energy, affecting the all-plastic cash register’s electronics and immediately opening the cash drawer. The fast-food restaurant company was not pleased and returned the all-plastic cash registers to the manufacturer.
The EMC engineers went back to work. They placed a metal ground plane under the all-plastic cash register and discharged to the metal ground plane (now known as the HCP) to simulate the real-life experience. They eventually came up with design fixes that allowed the all-plastic register to pass the ESD test.
First Edition of IEC 1000-4-2
The follow-on standard to IEC 801-2-1991 was IEC 1000-4-2 – International Standard on EMC – Part 4: Testing and Measurement Techniques – Section 2: Electrostatic Discharge Immunity Test – Basic EMC Publication, which was released in 1995.
(Note: European regulators put a “6” in front of the “1000-4-2” and the International Community followed suit in the 1996 timeframe. So all the “IEC 1000” series standards became the “IEC 61000” series.)
The parameters of the ESD generator remained the same as those found in the 1991 IEC 801-2 standard; that is, the energy storage capacitor was 150 pF, the discharge resistance was 330 ohms, and the output voltage of 8 kV for contact discharge and 15 kV for air discharge. The polarity of the output voltages was both positive and negative.
Figure 5 (“Example of test set-up for table-top equipment, laboratory tests”) from the 1995 version of IEC 1000-4-2 showed a horizontal coupling plane on the tabletop that was larger than the earth reference plane on top of the table in the1984 standard, a vertical coupling plane (unmentioned in the 1984 standard), a ground reference plane on the floor, and grounding cables between the HCP and VCP and the ground reference plane (with 470 kiloohm resistors on both ends of the grounding cables.) Note that the insulating support between the EUT and the horizontal coupling plane was only 0.5 mm thick, reduced from 10 cm (100 mm) thick in the 1984 edition.
Released in 1998, Amendment 1 of IEC 61000-4-2 (1000-4-2) modified the language in Figure 5 to read “Example of test set-up for table-top equipment tests.”
Released in 2000, Amendment 2 of IEC 61000-4-2 (1000-4-2) added a new clause (7.1.3) – “Test Method for Ungrounded Equipment,” which included 7.1.3.1 – “Table-Top Equipment,” and 7.1.3.2 – “Floor-Standing Equipment.” It also replaced three paragraphs in 8.3.1 (“Direct Application of Discharges to the EUT”). Finally, it replaced Clause 9 with a new Clause 9, and it added Clause 10 – “Test Report.”
Second Edition of IEC 61000-4-2
The second edition of IEC 61000-4-2 was released in 2008 and it nullified and replaced the first edition published in 1995, as well as Amendment 1 (1998) and Amendment 2 (2000). The key parameters of the ESD generator remained constant at 150 pF for the energy storage capacitor and the discharge resistance was set at 330 ohms. The output voltage for contact discharge remained constant at the highest value of 8 kilovolts and the air discharge at 15 kilovolts. The amplitudes were quoted in both the negative and positive polarities.
American National Standards Committee (ANSC) C63 on EMC (C63 Committee)
The C63 Committee produced a guide to electrostatic discharge testing in 2016, American National Standards Institute (ANSI) – C63.16-2016 titled “American National Standard Guide for Electrostatic Discharge Test Methodologies and Acceptance Criteria for Electronic Equipment.”
The Introduction to the Guide states:
“This guide is intended to provide supplemental information for performing electrostatic discharge (ESD) testing to other established ESD standards by including information and test procedures that are not covered in those documents. It strives to improve product quality through proper operation in actual equipment installations. The suggestions provided herein should not be construed as mandatory and they should not be applied arbitrarily to all types of electronic equipment. Performance or acceptance test levels are not given in this guide. The specification of performance or acceptance levels for any particular type of electronic equipment remains the responsibility of the manufacturer and the users of the particular equipment.”
The Guide’s Scope is:
“This guide provides electrostatic discharge (ESD) test considerations that a manufacturer should use in assessing the expected ESD effects on products in a wide range of environments and customer use. The focus is well beyond that used to simply show that a product complies with a local, regional, or international standard or regulation. The following are included: charged peripheral testing, connector pin testing, and details on the use of ESD simulators. Finally, suggestions for assuring the safety of those who apply the ESD discharge are provided. The annexes include information on test method selection and more background on air and contact discharge for those who want to further understand the differences in these methods. This guide is not applicable to manufacturing, service, or maintenance of equipment. Personnel who perform these activities should be trained to avoid ESD effects or damage to the equipment. In summary, this guide has test techniques beyond those that are commonly used (e.g., IEC 61000-4-2), and hence it can be a significant tool for increasing the immunity of products to ESD events.”
Summary
Electrostatic discharge testing has evolved from a company-based reliability test in the 1960s and 1970s to a performance test on electronic products in the 2023 timeframe. The requirement is for electronic products to operate successfully when subjected to ESD phenomena representing the real-world environment as simulated in an electromagnetic compatibility testing laboratory. The emphasis has switched from the susceptibility of equipment to quoting how immune a product is to air-discharge and contact discharges from a portable ESD tester whose output is compliant with the latest international standard criteria.
The next version of IEC 61000-4-2 is currently under development by the IEC. The third edition of the standard is expected to be published around April 2025.
A valuable Guide was published in 2016 by the ANSC C63 Committee on EMC to aid engineers in understanding and using the universally recognized IEC standard on ESD (61000-4-2).
