Full-Wave Simulation of System-Level Disruption During Secondary ESD Events in a Smartphone

To demonstrate the electromagnetic full-wave simulation of a secondary electrostatic discharge (ESD), an ESD generator is modeled in three dimensions (3D) and in contact mode discharging to a non-grounded, metallic ear-mesh of a smartphone. The nonlinear Rompe-Weizel SPICE model computes the arc resistance of the secondary discharge between ungrounded metal and a grounded enclosure. The SPICE model is solved using a circuit simulator, and the 3-D model is solved using the transmission-line matrix time-domain numerical method. Transient cosimulation is a new technique that is used to solve both circuit and 3-D models at the same time. The simulation predicts the coupling from ESD to a victim trace in the smartphone. Measurements performed at several stages validate the simulation results. Using this novel methodology, the user can simulate the secondary discharge in products to predict ESD damage and disruption on a system level.

I. Introduction

Disruption and damage from an electrostatic discharge (ESD) can be observed even if the discharge does not directly go into a sensitive trace. An ESD may also cause a secondary ESD event within a product. An example of a secondary ESD is sparking between decorative metal and the grounded housing of a system. Being a function of the capacitance between the decorative metal and the grounded enclosure, the secondary spark currents can reach as high as 600 A—five times higher than that of the primary ESD [1]– [3]; the rise time of this current can be on the order of only a few hundred picoseconds. Two factors contribute to the higher currents and faster rise times. The charged capacitance between the ungrounded metal and the grounded structures forms a low impedance source for the secondary spark. Second, the spark gap is usually a highly overvoltage effect, i.e., the fast charging of the gap by the primary ESD allows the voltage across the secondary gap to reach voltages higher than the static breakdown voltage. So, once the breakdown is initiated, the voltage collapse time will be much shorter than the voltage collapse time of the static breakdown case. Both effects lead to high peak currents associated with sub-nanosecond rise times.