ith 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.
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.
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.
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 standard carefully pointed out in a note that:
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.
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.
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.
(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.
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.”
The Introduction to the Guide states:
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).