A Model for Corona Streamer Propagation on Glass During an Air Discharge

Corona discharge to a glass surface is challenging to model due to a poorly understood air and surface ionization process. A modeling methodology based on the transmission line modeling (TLM) approach is proposed to simulate the streamer propagation process. The time-changing corona streamer resistance is estimated using the Rompe and Weizel spark model. The streamer is represented using small segments consisting of the arc resistance, per unit length (PUL) capacitance of the streamer, PUL inductance, a switch representing streamer formation, and a surface discharge gap voltage representing the voltage drop caused by ions within the streamer length. The propagation of the corona streamer depends on the tangential electric field strength at the streamer tip being higher or lower than the breakdown threshold for streamer formation. This preliminary 1D model shows plausible results for the current waveform shape, Lichtenburg dust figure diameter and streamer propagation velocity for a positive surface discharge to the glass. Although the model requires further improvement to predict propagation of multiple corona streamers, it provides a basis for simulation of a corona discharge on a glass surface which is related to the behavior of the underlying physics.

I. Introduction

Electrostatic discharge (ESD) to a touchscreen can cause hard and soft failures of the device. IEC 61000-4-2 [1] defines air discharge as the main concern for ESD events to insulators. In an air discharge, the air breaks down before the ESD gun tip reaches the glass surface. This discharge is not visible to the human and is more of a corona type discharge rather than a spark or arc discharge. A corona streamer propagates from the gun to the glass and then multiple streamers propagate across the glass surface due to a high tangential electric-field strength caused by space charging [2]. The corona streamer generated by a corona discharge propagates until the tangential electric-field at the end of the streamer drops below a threshold. An example corona discharge to glass, visualized using the Lichtenberg dust figure method is shown in Fig. 1, where one can see how individual streamers radiate outward from a central discharge location. The characteristics of a corona discharge to glass is dependent on the discharge voltage and polarity, the clean or dirty condition of the glass, glass thickness, and glass type [3], [4], [5]. Modeling of corona streamer propagation without prior experimental results is important but hard to achieve, as there are many unknown factors, or factors known but hard to strictly control, such as temperature, humidity and air molecule distribution around the discharge location.