Waveform Quality and Quantitative Evaluation of Discharge Current from ESD Generator with Reference to IEC Specified Waveform

In 2008 the International Electrotechnical Committee (IEC) offered an ideal contact current waveform as the IEC specified waveform, while there have never been new requirements based on it for the calibration waveform. In this paper, a calculation method is proposed to quantitatively evaluate to what extent the contact discharge waveform from an ESD generator deviates from the IEC specified waveform. The energy ratio of the difference waveform between the contact discharge waveform and the IEC specified waveform to the IEC specified waveform energy is used as an index of waveform quality, and the relationship is shown between the waveform quality and waveform parameters of the standard requirement adding "60% time width of first peak" and "falling depth", not in the requirement but newly introduced. The energy ratios are calculated for the measured contact discharge currents from different eight models of ESD generators and the measured air discharge currents from an ESD generator in a hot and humid environment, which were conducted in our previous studies. The results show that even if the contact discharge waveforms from the ESD generators meet all the IEC requirements, the energy ratio increases according to the generated ringing after the first peak and the resulting waveform quality degrades, but the ringing tends to be reduced and the waveform quality is improved when the ESD generators provide the time width of 60%t peak and falling depth closer to those of the IEC specified waveform. For the air-discharge waveforms that are not subject to the calibration standard, the energy ratios of the waveforms that meet all the IEC requirements are smaller than those of the contact discharge waveforms from the same type of the ESD generator, and the energy ratios of the waveforms that do not meet the first peak requirement are comparable to those of the contact discharge waveforms from the ESD generators. In the air discharge waveform, as with the contact discharges, it is confirmed that the wider the 60% time width of the first peak and the shallower the falling depth, the lower the energy ratio and the better the waveform quality. Future work is to clarify the mechanism how come the time width of 60% peak and falling depth improve the waveform quality of contact discharge and air discharge currents from the ESD generators.