Waveform Comparison of Discharge Currents for Contact Discharges from Different Eight Models of Electrostatic Discharge Generators

Abstract

Immunity testing of electronic equipment for electrostatic discharge (ESD) is prescribed as IEC 61000-4-2 by the International Electrotechnical Committee (IEC), in which contact discharge current testing from an ESD generator is specified with only the following four parameters: the rise time of the first peak current, the current value of the first peak, the current values at 30 ns and at 60 ns. To reduce the variations in test results by different ESD generators, the Japanese national committee of IEC SC77B once proposed a time width of 60% of the first peak current as an additional specified parameter in the IEC standard, while the proposal was not adopted since a round robin test was unable to confirm the effectiveness. In the 2008 revised version, a theoretical calibration current waveform based on the Heidler’s formula was shown as the typical contact discharge current waveform from an ESD generator. In this paper, using different eight models of commercially available ESD generators manufactured by six manufacturers from the market, we compare the waveforms of discharge currents measured for contact discharges with the calculated waveform from the Heidler's formula. In addition to the IEC specified parameters, the previously proposed time width (1.5 ns to 3.5 ns) of 60% of the first peak current is also examined. Results show that almost all the ESD generators except for one generator meet the specifications, and that there are only four generators whose time widths of 60% of the first peak currents satisfy the suggested time width. Furthermore, all the frequency current spectra at frequencies lower than 30 MHz approximately agree with the current spectrum calculated from the Heidler’s formula, whereas they vary depending on the ESD generators at frequencies higher than 30 MHz, even though ESD generators meet both the IEC specified requirements and the assumed time width of 60% of the first peak.