William D. Greason

Electrostatic discharge: a charge driven phenomenon

Abstract The principal charge generation processes involved in ESD are reviewed. A quasi-static analysis of the ESD event for a two body system using a sphere model is presented. The method is applied to determine the probability and severity of a discharge and the amount of charge transfer.

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 Maxwells 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.

Electrostatic discharge characteristics for the human body and circuit packs

An experimental study of the electrostatic discharge (ESD) characteristics for the charged human body in close approach to various sizes and orientations of electronic circuit packs near and away from a horizontal ground plane was conducted. Calculations based on measured capacitance coefficients provide a comparison of the relative probabilities and severities of the ESD event.

ESD characteristics of a generalized two body system including a ground plane

Capacitance coefficients were measured for a system with two conductors of variable size, positioned at different elevations with respect to a horizontal ground plane. For a constant charge on the source, body potentials and energies were calculated and a comparison was made of the relative probability of a discharge and the severity of the discharge for the various source/sink geometries. Both a fixed-size source model and a fixed-size sink model were analyzed, for cases where the sink was floating or grounded. Positioning the bodies close to a horizontal ground plane decreases both the probability of a discharge and the severity of the discharge in all cases. Potential and energy sensitivity factors were calculated and used to show how the observed results can be interpreted using the changes in the capacitance coefficients of the system. The results provide a better understanding of the basic electrostatic discharge characteristics for simulations involving the human body model and the metallic cart model.<<ETX>>

Triboelectric charging between polytetrafluoroethylene and metals

Measurements were obtained on charge exchange processes occurring between small metal ballistic pellets and a polytetrafluoroethylene (PTFE) tube. Lead pellets of 5.5-mm diameter were propelled at a range of speeds through PTFE tubes of different lengths by compressed carbon dioxide. The charge incurred by the pellets and the tube was compared with the charge observed on copper and lead spheres rolled through the tube, driven by gravity. In all experiments, the charge on the moving pellet was measured with a Faraday cup. The experiments determined the effect of pellet speed on the magnitude of the charge accumulated on the pellet and on the PTFE tube. Sectioned shielding on the PTFE tube allowed the determination of surface charge distribution along its length by means of an electrometer. It was observed that the charge also depended on the work functions of the materials involved (lead, copper, PTFE). The charge on the pellets was found to range from +0.5/spl times/10/sup -8/ to +3.0/spl times/10/sup -8/ C, for pellet speeds from 10 to 80 m/spl middot/s/sup -1/. The reproducibility of results is discussed and comment provided on the degree of charge imbalance observed.

Analysis of the charge transfer of models for electrostatic discharge (ESD) and semiconductor devices

Various models are used to simulate the electrostatic discharge (ESD) event associated with semiconductor devices; these include the human body model (HBM), the charged device model (CDM), and the field induced charged device model (FCDM). Maxwells method is used to analyze these models to determine device potentials and the transfer of charge during typical discharges; existing test methods are also examined. A charge injection test method is introduced which provides control of the charge transferred to the device under test; it is proposed as a means to study charge related phenomena due to ESD.

Latent effects due to ESD in CMOS integrated circuits: review and experiments

A review of the current information published on the subject of EOS/ESD latent failures is presented. In order to gain a better understanding of the phenomena involved in the input protection networks of CMOS integrated circuits, measurements were performed on both commercially available integrated circuits and a set of custom designed and fabricated devices. The tests investigated the effects of electrical stress, thermal shock, exposure to ultraviolet light, and thermal annealing. The results demonstrate the presence of latent failures in CMOS integrated circuits following exposure to ESD. The cumulative effect of repeated discharge can be partially alleviated using thermal annealing or exposure to light. A charge injection model is proposed to interpret the results. >

Influence of a ground plane on the ESD event in electronic systems

Capacitance coefficients were measured for a basic two-conductor system, simulating the approach of a charged object (the human body) to a second object which can be floating or grounded (the equipment under test). Parameters studied include the size of the conductors, their separation, and position relative to vertical and horizontal ground planes. System equations, based on Maxwells technique, are solved to yield the body potentials and a relative probability of discharge for the various configurations. The presence of ground planes is shown to increase the ESD (electrostatic discharge) susceptibility of small floating bodies. The results provide a better understanding to the ESD event and demonstrate the importance of ground planes in electrostatic discharge test methods. >

Review of the Effect of Electrostatic Discharge and Protection Techniques for Electronic Systems

A review of the phenomena involved in the direct and indirect effects of electrostatic discharge for electronic systems is given. Quasi-static and dynamic analyses are developed for simple models of floating and grounded enclosures. An overview of related topics, including secondary discharge, EMI, and protection techniques, is also presented.

Experimental determination of ESD latent phenomena in CMOS integrated circuits

A series of measurements were performed on two types of commercially available and custom-made CMOS integrated circuits to investigate the latent mode of failure due to ESD. The current injection test method was used for both polarities of discharge. Test parameters studied included threshold failure, constant amplitude multiple stress, step stress, and the stress hardening effect. Statistical analysis of the results demonstrate the presence of latent failure in CMOS integrated circuits due to ESD. The work is used to further expand a charge injection model for latent failures. >