Waveform Comparison and Difference Factors in Discharge Currents for Air Discharges from Different ESD Generators

Electrostatic discharge (ESD) generators must be calibrated for contact discharges with the current waveform specified in International Electro-technical Commission (IEC) 61000-4-2; however, there are no requirements in current waveforms due to their bad reproducibility for air discharges in the IEC standard. Nevertheless, the air discharge immunity testing is under obligation in the present standard. This implies that different ESD generators are likely to provide significantly different test results for air discharge testing. In this study, two types of different ESD generators were used to measure discharge currents both for contact and air discharges with respect to charge voltages from 2 kV to 8 kV under the same conditions of experimental environment. As a result, we confirmed that the measured waveforms were almost identical for contact discharges regardless of charge voltages, while we found that they are quite different for air discharges with the same approaching speed when the charge voltages are increased. The latter result is because the generator has different impedance characteristics deriving from its structure, and because the spark lengths from the generators with the same charge voltage are different. A formula for calculating the discharge current from an ESD generator through an ideal switch in lieu of a spark, which was previously derived by us, was also employed to obtain the current waveform peculiar to the generator, in order to reveal that the formula provides the different upper limit of air discharge current peaks according to the generator. (C) 2017 Wiley Periodicals, Inc.