Spark-less electrostatic discharge (ESD) on display screens

Abstract

An electrostatic discharge (ESD) to a display screen may lead to sparking into the phone's structure, e.g., via the glue that connects the different glass layers of the touching panel/LCD, or it may just cause surface charging. The latter is the most likely case for a well-designed display, as the insulation design usually prevents any sparking to the electronics. Even if no spark is visible, strong surface charging occurs. These charges couple via displacement current and via their magnetic field into the display electronics. Most phone and tablet manufacturers currently suffer from damages or upsets caused by this type of spark-less ESD. As far as we know, no data has been published showing the magnitude, rise time and total charge parameters of these surface discharges for displays. In this paper, discharges to different displays have been measured at ±4, ±8, ±10 and ±14 kV. The discharge currents are measured using an F65 current clamp. Five different types of display screens have been tested and the results of transient current discharges are compared in this paper. During the experiments, repeatability of results is investigated. Moreover, the effects of touch position as well as dirty screens (i.e., presence of finger prints, etc) are investigated.