Severity evaluation of immunity test for air and contact discharges of ESD generators

An immunity test method for electrostatic discharges (ESDs) is being specified in the IEC 61000-4-2, in which two types of discharges, contact and air discharges of ESD generators (ESD-guns), are given. To achieve an immunity test of higher quality, severity evaluation of discharge currents for both the current injection methods is essential. In this study, to evaluate the severity of air and contact discharges of ESD-guns for immunity testing, using a 12-GHz digital oscilloscope, we measured discharge current waveforms for both the discharges of an ESDgun onto an IEC calibration target. In consideration of low voltage ESDs below several hundred volts, the charge voltages were set from 200 V to 15 kV despite the IEC test levels from 2 kV to 15 kV. For a severity evaluation index, we used maximum rising slopes (peak current divided by rise time) of the discharge currents, and obtained them with respect to charge voltages. As a result, we found that at charge voltages below 5 kV, air discharges give current rising slopes higher than contact discharges do, and particularly at charge voltages below 1 kV, the rising slopes double and also have smaller variation. This finding suggests that air discharges at charge voltages below 1 kV can provide a severe and reproducible immunity test.