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Electrostatic Discharge Overview

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ESD, or electrostatic discharge, is a major problem that impacts the reliability of electronics and can destroy components. ESD has caused problems in industry since the beginning of black powder manufacturing where a small ESD event or spark can cause significant safety issues. While ESD does not cause as many direct safety issues in the electronics industry, it is one of the main causes of early electronic device failure.

Overview

ESD is an extremely rapid, high voltage flow of electricity between two objects that can be easily created by common, everyday actions that cause damage to components in the path the discharge takes to ground. While ESD events are low power, their high voltage and very short (micro and nanosecond) durations generally push the current to very high levels as well. This causes significant damage to the microscopic traces and components within a microchip.

When ESD strikes a microchip the chip can be destroyed outright in a catastrophic failure event. When seen under a microscope, ESD strikes look like blue lightning running along a trace in the microchip, similar to the sparks seen when a CD is cooked in a microwave, with similar levels of damage. Even if the ESD event does not destroy the microchip, it will cause damage that may cause intermittent failures for days, weeks, or even months before failing completely, if at all. Any component can be damaged by ESD, even more rugged components like BJT transistors. Low voltage microchips are some of the most sensitive ICs, which can be damaged by as little as 3 volts!

The most noticeable form of ESD is when a static shock jumps from your hand to a metal surface. The voltage generated by ESD shocks that can be felt and seen exceed several thousand volts, deadly to most ICs. With voltages under several thousand volts, ESD events will not be felt or noticed by the average person. This makes it very easy to walk across a room and destroy a microchip by picking up a circuit board.

Causes

The most common cause of ESD events is a static electricity build up is due to the interactions of different materials in contact with each other. This method of generating static electricity is called triboelectric charging. Examples of triboelectric charging include scooting across a carpeted floor in socks, rolling across a carpet in a wheeled chair, rubbing a comb against dry hair, rubbing a ballon against a sweater and removing tape from a plastic surface. Simply removing tape from a plastic bag can generate thousands of volts of static electricity.

Electrostatic induction is another cause of ESD events. When an ungrounded conductive object is placed near an electrically charged object, the presence of the charged object induces an electric field on the ungrounded conductor by attracting or repelling the electrons in the conductor. The ungrounded conductor does not gain a charge, but the redistribution of the electrons can generate an electric field strong enough to cause an ESD event or spark if the conductor comes in contact with a conductive path that allows the electrons to flow. An example of this is a charged styrofoam cup inducing a charge on a nearby metal tool which could cause an ESD event when a component is touched.

Controlling ESD

ESD is controlled in a number of ways, with dedicated circuit protection chips, circuit design techniques, safe and controlled dissipation of ESD, and prevention of charge build up. The prevention of charge build up includes static safe practices, keeping materials that can generated ESD out of sensitive areas and away from sensitive components, the use of anti-static and static dissipative materials, ESD safe equipment, and the avoidance of devices that have moving parts that could generate a static charge. Grounding all conductive materials, people, and providing ESD safe work surfaces that prevent static build up also help prevent ESD.

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