Abstract
In electrostatic discharge (ESD) immunity tests specified by the international electrotechnical commission (IEC), it has been learned empirically that a contact discharge test sometimes provides a severe test result even under the same test level. This is said to be due to the existence of small air gaps between an ESD generator and equipment under test. To clarify the phenomena, we previously measured discharge currents through small air gaps from 30 µm to 1000 µm in contact discharges of an ESD generator to an IEC current calibration target, which revealed that multiple current peaks appear depending on the gap length and test voltage as well. It was also demonstrated that the contact discharge current with a small gap provides a faster rise time and larger current peak in comparison with normal contact discharge tests even at the same test voltage. In this study, to explain these findings quantitatively, we proposed a simplified circuit model combined with a spark-resistance formula which allows one to analyze the discharge currents through the above-mentioned air gaps in 8 kV contact discharge tests. As a result, we found that the calculated waveforms in contact discharges with/without a gap fairly agree with the measured results. It was also found that the proposed circuit provides roughly the same dependence of current peaks on a gap length as the measured results.
