Variations in Discharge Current Waveforms and its Power Spectra Injected from Contact Discharges of ESD-Gun with Different Arrangements

Abstract

The International Electrotechnical Commission (IEC) has prescribed an immunity test (IEC61000-4-2) of electronic equipment against electrostatic discharges (ESDs), in which a discharge current to be injected onto equipment under test is specified. As for the waveform, however, not the whole waveform but only the rise time, the first peak, and the current amplitudes at 30 ns and 60 ns are given in the time domain together with their uncertainties, which are required to check on the condition that an ESD generator (ESD-gun) shall be arranged vertically to an IEC recommended calibration target and its earth return wire is kept away as far as possible from a vertical ground plane (IEC standard arrangement). In this study, to clarify how arrangements of an ESD-gun and its earth return wire affect discharge currents, we measured discharge current waveforms for contact discharges of an ESD-gun onto an IEC calibration target with respect to various inclinations of the ESD-gun and arrangements of its earth return wire, and also calculated their current power spectra normalized to that of the discharge current for the IEC standard arrangement. As a result, we found that inclinations of the ESD gun affect the first peak current, which increases current power spectra by 14 dB at frequencies over 300 MHz, and that arrangements of the return wire influence the current waveforms between the first and second peaks, which provides variations in power spectra by ±12 dB in the frequency range from 10 MHz to 200 MHz. This finding suggests that arrangements of an ESD gun and its earth return wire are likely to cause different immunity test results. It was also found that in comparison with measured discharge currents for the standard arrangement, the calculated waveform of a discharge current from a formula, which has been included in the recent standard, has a more gentle falling waveform, and produces power spectra of +15dB in the frequency range from 10 MHz to 200 MHz and -12 dB at frequencies over 300 MHz.