Methodology for evaluating the relative probability and severity of an ESD event in electronic systems

Abstract

The susceptibility of an electronic system to electrostatic discharge (ESD) is determined by applying discharges, using an apparatus which simulates the discharge event, and determining the point at which either direct or indirect failures are observed. Another method, based on Maxwell's system equations, can be used to evaluate the relative probability of an ESD event in a system and is useful in determining body potentials and energies, both before and after a primary discharge. For a basic two-body problem, the body potentials are defined in terms of three capacitance coefficients and assumed body charges. The measurement method used to determine the capacitance coefficients is described and possible sources of error analyzed. The method is applied for a series of tests configured to investigate the influence of vertical and horizontal ground planes on the ESD characteristics of a two-body system. Body 1 was chosen to simulate a charged floating source (the human body), while body 2 was a computer chassis, which could be floating or grounded. The results show that external ground planes increase the probability of an ESD event and demonstrate the effect of body orientation with respect to these ground planes on both the probability and the severity of the discharge.