Investigations Into Unintended ESD Generator Artifacts: Prepulse and Postpulse

An electrostatic discharge (ESD) generator may create pre- and postpulses in addition to the main pulse. These artifacts can cause additional device under test (DUT) failures. The origin and magnitude of these pulses were investigated in four commercial generators using measurements and simulation. Two types of unwanted pulses were identified. One is caused by the reignition of the spark, and the other relates to the relay contacting for charging the main capacitor. These pulses cause strong high-frequency signals, partially surpassing the radio frequency content of the main pulse. The spectrum of the pre- and postpulses varies greatly between different generators. These differences and the fact that some DUTs may react to the pre- or postpulse instead of the main pulse lead to repeatability problems between test sites. The other artifact that has been investigated is the leakage current in contact discharge mode. The charge accumulated on the gun tip by the leakage current can contribute to a short (few nanoseconds) fast-rising pulse (<500 ps) that occurs the moment the tip is contacted, thus, before the main pulse in contact mode.