A New Method for Immunity Testing Less Dependent on Arrangements of Equipment-Under-Test and Contact Discharges of ESD-Gun onto Vertical Coupling Plane

The International Electro-technical Commission (IEC) prescribes immunity test methods (IEC 61000-4-2) of electronic equipment against electrostatic discharges (ESDs), which also specifies contact discharges of an ESD-gun onto a vertically placed metal plate named vertical coupling plane (VCP) in the vicinity of equipment under test (EUT) to simulate personnel ESDs onto metal objects being close to the EUT. According to IEC 61000-4-2, EUT shall be placed at a distance of 0.1m from the VCP, and the contact discharge of an ESD-gun should be conducted to the centre of a vertical edge of the VCP, while inclinations of an ESD-gun and reference locations of EUT are not specifically determined, which can provide different test results even for the same EUT. In this study, using a simple printed circuit board (PCB) with a trace in lieu of EUT, we measured induced voltages on the trace for contact discharges from an ESD-gun onto a VCP in conformity to IEC 61000-4-2. As a result, we found that peaks of the induced voltages on the PCB arranged at a fixed position change with variability of ±20% for contact discharges of the ESD-gun with different inclinations, while an additional VCP placed at a right angle to the VCP edge reduces the peak variability by 7% or less. It was also found that although different locations of the PCB provide variability from+18% to -14% in the peak voltages for contact discharges of the ESD-gun with a fixed inclination, the additional VCP gives the peak variability from +37% to -11%. The above findings suggest that an additional VCP provides an immunity test method that could be less affected by arrangements of EUT and contact discharges of an ESD-gun, when EUT to be tested is placed away from the additional VCP.