Contents I. Introduction
ESD discharge between metal parts can produce discharge currents up to hundreds of ampere at sub nanosecond rise times. The current levels and rise times depend on the voltage and the local source impedance which drives the current, but also on the time dependent arc resistance which is a strong function of the arc length. The fields associated with such currents will couple into flex cables, PCBs and other metallic structures. To simulate such currents one needs to combine an electromagnetic description of the geometry with a non-linear description of the arc resistance [1]. A variety of approaches has been published such as [2], [3], and [4] which prove the concept of noncontact ESD numerical modeling and simultaneous time-stepping with SPICE, but these are only suitable for simple geometries with numerical methods that are rarely used for consumer electronics design. In this paper, we explain and compare multiple methodologies to solve for air discharge current and fields within the widely used CST Studio Suite [11]. For methodology, the fullwave simulation is either combined with the arc resistance law of Rompe-Weizel (RW) directly by exchanging voltage and current information in every time step or the combination is achieved by a two-step process which first simulates impedances which are then combined with the arc model in a circuit simulation. Using a simple model of a discharging rod, it is shown that the methodology can match measured current and current derivative results. As for the significance to system level ESD, simulation of contact mode ESD is already widely used in industry to predict results such as soft failures [12], and we will analyze how this new methodology can improve the existing simulation workflows with a simple real world example with an ESD gun.
