Electrostatic Discharge

Electrostatic discharge (ESD) refers to the sudden and brief flow of electric current between two objects with differing electrical potentials. This occurs when the objects are brought close enough for a discharge to take place or when the insulating material between them breaks down. The process is often associated with visible sparks, although many discharges are too small to be noticed by human senses. Despite their subtlety, low-energy ESD events can still harm sensitive electronic components and create hazards in industrial environments.

Nature and Causes of Electrostatic Discharge

ESD originates from the accumulation and sudden release of static electricity. One of the most common mechanisms for charge build-up is triboelectricity, which occurs when two different materials come into contact and are then separated. Everyday activities such as walking across a carpet, combing dry hair, rubbing a balloon on clothing, or removing plastic packaging can generate significant electrostatic charges. When two tribocharged objects approach each other, the potential difference may be high enough to cause a discharge.
Another important cause of ESD is electrostatic induction. When a charged object is placed near a conductive object that is electrically isolated, the electric field causes charge redistribution on the surface of the uncharged object. Although its overall charge remains unchanged, distinct positive and negative regions form. If a conductive path is introduced, a discharge may occur. For example, expanded polystyrene packaging can induce charges on nearby electronic components, and touching them with a metal tool may trigger an ESD event.
A further source of ESD involves energetic charged particles striking an object. This type of charging is especially significant in spacecraft, where interactions with solar wind and charged plasma particles can produce deep dielectric charging, potentially leading to damaging discharges.

Types and Characteristics of ESD Events

ESD phenomena vary in intensity, complexity and impact, with the electric spark being the most dramatic form. A spark occurs when the electric field is strong enough to ionise the surrounding air and form a temporary conductive channel. This process, known as dielectric breakdown, allows a rapid flow of current. The dielectric strength of air is typically around 4 × 10⁶ V/m, and sparks can occur at potentials as low as a few hundred volts. A familiar large-scale natural example is lightning, where charge separation within clouds or between clouds and the ground results in potentials of hundreds of millions of volts.
During a lightning stroke, intense electrical stress splits atmospheric molecules such as oxygen and nitrogen, forming reactive species including ozone (O₃) and nitrogen oxides (NOₓ). These play roles in environmental chemistry but are also hazardous in high concentrations and corrosive to materials.
Not all ESD events involve visible or audible effects. Humans can carry electrostatic potentials below their perceptible threshold—often under 3,000 V—that can nonetheless damage delicate integrated circuits. Components may be harmed by discharges as low as 30 V. Some damage may not immediately disable the device, instead reducing its long-term reliability. Cable discharge events (CDEs), arising when electrical cables are connected to equipment, represent another form of ESD that is particularly problematic for modern electronics.

Electric Sparks and Their Effects

Electric sparks arise when local electric field strengths exceed the dielectric strength of air. This induces a rapid increase in free electrons and ions, forming a conductive plasma channel. On a large scale, lightning releases immense energy, while smaller sparks can occur from everyday electrostatic charging.
Sparks are significant hazards in environments containing flammable materials. In industrial settings, a single spark can ignite gas vapours, fuel residues or dust clouds, potentially leading to dangerous explosions. Many industrial accidents have been traced to small, unexpected electrostatic discharges that occurred in the presence of combustible substances. Since oxygen, fuel and an ignition source comprise the fundamental fire triangle, an ESD event can readily trigger combustion when these conditions are met.

Protection and Damage Prevention in Electronics

Electronic components—particularly integrated circuits—are vulnerable to ESD. Manufacturers therefore implement stringent protective measures throughout the production, assembly, transportation and operation of devices. A fundamental principle of ESD control is grounding, which provides a safe path for charge dissipation and minimises voltage differentials that may cause discharges.

ESD Protection in Manufacturing Environments

To mitigate ESD risks during manufacturing, companies establish Electrostatic Discharge Protected Areas (EPAs). These controlled zones can vary from single workstations to entire production facilities. EPAs are designed according to international standards, such as those issued by the International Electrotechnical Commission (IEC) and the American National Standards Institute (ANSI). Key principles include:

• eliminating highly charging materials near sensitive components
• grounding all conductive and static-dissipative materials
• grounding workers through wrist straps, footstraps or conductive flooring
• using antistatic packaging and protective clothing

Humidity control within an EPA is essential, as moisture can help dissipate charges on surfaces. Ionisers are used when insulating materials cannot be removed or grounded. These devices generate ions that neutralise charged areas on dielectric materials, preventing unwanted field induction.
Materials likely to generate more than 2,000 V through tribocharging should be kept at least 12 inches away from sensitive components. In aviation, aircraft employ static dischargers along wing and tail edges to help dissipate charges safely during flight.

Device-Level Protection

Modern electronic design often incorporates ESD protection within the device itself. Techniques include:

• protective circuitry at input and output pins
• external components designed to divert or limit surges
• careful circuit layout to minimise discharge paths

Because electronic components are small and often handled by automated equipment, preventing ESD at points of contact is vital. Surfaces that come into physical contact with sensitive parts must be made from static-dissipative materials, which conduct electricity slowly enough to prevent sudden discharges. These materials generally have resistivity values below 10¹² ohm-metres. When grounded, they allow controlled dissipation of any accumulated charge.