Characteristic Measurement of Discharge Current Injected by the Air Discharge of an ESD-gun onto a Ground

An immunity testing method for electrostatic discharge (ESD) is being specified in IEC 61000-4-2, in which the contact discharge of an ESD gun is being normally specified. Air discharge testing is known to be a severe immunity test compared to contact discharge testing, while the discharge current injected is not well reproduced. Grasping the behavior of the current injected by the air discharge would be helpful in establishing the worst-case ESD immunity testing. We previously measured the discharge currents for air discharge testing onto the IEC-recommended current transducer with a commercially available ESD gun, and showed that there exists a specific relationship of Ip·trξ/Vc=constant (ξ=0.75), between rise time tr and current peak Ip. The current transducer, however, has a frequency-dependent transfer impedance which should affect the measured current waveform. In this study, we investigated whether the above-mentioned specific relationship can be obtained for air discharge of an ESD gun onto a ground that assumes a metal enclosure of electronic equipment under test. A method was presented for estimating the discharge current from simultaneously measured magnetic fields with two magnetic field probes regardless of the distance between the gun discharge-point and the probe position. This method was validated for contact discharge of an ESD gun to an SMA connector. With this method, we estimated the discharge currents injected onto a ground for air discharge testing of an ESD gun with intentionally fast and slow approaches. As a result, we could confirm a specific relationship between rise time tr and current peak Ip of Ip·trξ/Vc=constant with ξ=0.57 independent of charge voltages and gun approaches. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 51– 59, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20454