Measurement of spark length for air discharges of electrostatic discharge generators

Electrostatic discharges (ESDs) due to the collision of charged metals cause serious malfunctions in high-tech information devices. In particular, the fast collision provides severe ESD events, while the mechanism has not fully been elucidated, though the approach speed is known to affect a spark length. In this study, to investigate this mechanism experimentally, we developed a setup for electronically measuring a spark length in air discharges of ESD generators (ESD guns), and measured spark lengths at charge voltages from + 1kV to + 8 kV with two constant approach speeds of 20 mm/s and 100 mm/s. Measurement of the spark length was conducted using a commercially available velocity meter based on the laser Doppler effects, which was validated by comparing the calculated values from three different types of empirical formulae based on the Paschen´s law. As a result, we found that regardless of the approach speed, the measured spark lengths at charge voltages above + 4 kV agree well with those calculated from one type of the empirical formula, while the spark lengths at voltages less than + 4 kV for the fast approach are in agreement with other type of the formula. It should be noted that the approach speed did not almost affect spark lengths and the fast approach at charge voltages below + 3 kV would rather cause slightly longer spark length than the slow approach.