Trend Analysis of Dissipated Electrostatic Discharge Energy in Touchscreen Displays

Touchscreen displays can be susceptible to sparkless electrostatic discharge events. The energy observed by sensitive touchscreen circuitry can vary significantly with design parameters like the glass thickness, the capacitance between the sensor pad and the ground structure, and the resistance of the traces and sensor terminations connected to the pad. The energy dissipated in resistive structures within the display can lead to damage. Methods are presented to estimate the maximum energy dissipated in the touchscreen circuitry during a spark-less discharge to the display. The trends in the energy with variations in design parameters are analyzed using traditional curve-fitting techniques. The analysis was performed using measured data obtained for 20 touchscreen configurations when the ESD gun was charged to 9 kV and 15 kV. The analysis helps the designer to understand the trends and to predict how future design decisions may impact ESD susceptibility. Results suggest that immunity can be maximized by increasing the glass thickness, reducing the load resistance, and reducing the distance between the sensor pad and the PCB return plane.