Investigations into Methods to Stabilize the Spark in Air Discharge ESD

In the interest of improving the reproducibility of air discharge during IEC 61000-4-2 ESD testing, different methods are investigated that reduce the variation of the spark current during air discharge. As the variation is caused by the interplay of the statistical time lag and the approach speed, methods are investigated that provide initial charge carriers for the avalanche initiation at the beginning of sparking. These methods include ionizers, cold plasma, humidity, exposure of the electrodes to UV light, different electrode materials, and surface shapes. Most of these methods reduce the variations of the spark currents. However, only some can be implemented during testing. The strongest effect was achieved by using cold plasma and by one surface material found in a gasket.

I. Introduction

The IEC 61000-4-2 ESD standard requires both air discharge and contact mode testing. Contact mode does not reflect ESD outside the test lab, but its reproducibility is better. Further, the IEC 61000-4-2 standard does not contain a calibration method for air discharge. This, and the low reproducibility of air discharge, led to suggestions to remove air discharge from the standard’s mandatory requirements. However, if this step would be taken, many DUTs would not be tested for air discharge. As most critical test points are non-conducting (knobs, switches, displays, gaps in plastic enclosures, wires), the ESD test would lose its ability to hold ESD induced field failures to a low level.