Electrostatic Discharge (ESD) is the sudden release of static electrical energy from an object to ground, between two objects, or between an object and a person. As long as different electrostatic potential exists between two conductive bodies, a discharge can occur. Before we go further, however, let’s quickly touch on some of the fundamentals of static electricity.

What is Static Electricity

Basic textbook discussion usually states that static electricity occurs as the result of an imbalance between positive and negative charges in objects or materials. This is typically caused by the contact and removal (or movement) of one material against another, resulting in the transfer of negative charges, or electrons between the materials. The material that loses electrons becomes positively charged, and the material that gains electrons becomes negatively charged. This imbalance produces a measurable electric field that can influence other objects.

While the displaced electrons can accumulate on the surface of the receiving object, they tend to remain stationary until they are released, or discharged. Thus, we have an electric charge that is at rest, or, in other words, “static” electricity.

This creation of a static electrical charge is known as triboelectric charging. Static electrical charge is measured in coulombs. A coulomb (C) is a unit of electrical charge in the International System of Units (SI) that is equal to the amount of electricity delivered by a one ampere current in one second. More commonly, however, static charge is expressed as the electric field strength, or surface voltage, of the material being measured.

Triboelectric charging can affect almost all materials to some extent, including water and soot particles in the atmosphere along with human bodies. Both you and your pet dog or cat can experience it together simply by touching after you walk across a carpet on a dry winter day.

The Problem With ESD

As we’ve said, static electricity charges can build-up on the surface of an object until conditions exist for them to be released, or suddenly discharged. ESD is the rapid transfer of electrostatic charge from one object to another. Basically, ESD occurs when any charged body suddenly becomes electrically neutral. The amount of this transferred charge is affected by the properties of the materials that makeup the objects, the area of contact between them, the relative humidity of the air, and the speed of object separation, along with other factors.

The transferred charge typically flows through a spark between the two conductive objects as they approach each other. This effect has been known for hundreds of years, and can lead to serious problems if not controlled. For example, militaries for centuries have used devices and materials, like brass powder flasks, to prevent ESD from accidentally igniting gunpowder in the field.

In addition to manufacturing munitions and explosives, static charge and ESD can also affect operations in pharmaceuticals, petrochemicals, textiles, painting, plastics, printing and many other areas. The development and continued miniaturization of modern electronic devices has also elevated the negative effects of ESD throughout all levels of the electronic supply chain. This can negatively impact product yield, cost, quality, reliability and, ultimately, profitability.

ESD Effect on Electronics

ESD can cause damage to many different electronic components, allowing them to fail to meet published specifications or even causing complete device failure. Susceptible components can range from simple diodes to expensive integrated circuits (ICs). ESD voltages can range from a few volts to kilovolts, but even discharges of 100V or less may cause problems. Consider that by simply picking-up a plastic bag from a workbench you can generate from 1,200 – 20,000 volts, you can see the problem.

In IC devices, ESD current flow can blow holes through chips, and cause contact and interface damage along with burnouts. Damage from ESD may also increase heat generation in ICs and cause thermal damage to nearby components on the board.

The build-up of a static charge on a device also means that an electrostatic field and lines of force are generated around it. Other conductive devices that approach this field can be polarized through induction. If another ESD-susceptible device enters the field while grounded, a charge transfer can occur.

ESD damage to sensitive components is typically caused by discharge from a material or person to a susceptible device, discharge from a susceptible device, or field-induced charges. Whether or not damage will occur is determined by the ability of the susceptible device to withstand the voltage involved or by its ability to dissipate the energy of the discharge. We discuss some of the current ESD prevention and mitigation solutions in a separate article.

Types of ESD-Induced Component Damage

The types of component damage that can be caused by an ESD event include:

• Parametric Failures – when an ESD event alters one or more of the stated performance parameters of the affected component, but does not make the component non-functional.
• Catastrophic Failure – occurs when an ESD event completely damages the susceptible component and renders it non-functional.
• Latent Damage – ESD component damage that is undetected by measurement or visual inspection but can eventually cause device degradation and failure due to operating stress on the component and reduced load life.

More Information

Our friends over at CircuitBread have lots of useful information on working with electronic components, including grounding and circuit protection. You can view their content at www.circuitbread.com. We also recommend checking out what CircuitBread has to say on the matter: What is Electrostatic Discharge?

You can also take your knowledge of ESD to the next level with our article on “How to Prevent Electrostatic Discharge”, which is available on this website.

Summary

Practically all materials, along with humans, can build-up a static charge that may be capable of damage to objects when suddenly released. The amount of this charge is determined by the make-up of the materials, the speed of their contact and separation, the humidity in the air, and other factors.

ESD can damage devices, including electronic components. This damage can occur at any point in the supply chain, from manufacturing to testing, handling, shipping and on to insertion in another system or service in the field. This damage can be expensive, not only in terms of the damaged components themselves, but also in the repair and rework of the board they are part of. Susceptibility to ESD can vary widely by type of component. ESD prevention and mitigation procedures and systems are useful and are covered in another article on this website.