Electrostatic discharge

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Electrostatic discharge (ESD) is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. A buildup of static electricity can be caused by tribocharging or by electrostatic induction. The ESD occurs when differently-charged objects are brought close together or when the dielectric between them breaks down, often creating a visible spark.

Electricity physical phenomena associated with the presence and flow of electric charge

Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. In early days, electricity was considered as being not related to magnetism. Later on, many experimental results and the development of Maxwell's equations indicated that both electricity and magnetism are from a single phenomenon: electromagnetism. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others.

Short circuit electrical circuit, usually with very low or no impedance

A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a very low electrical impedance. This results in an excessive amount of current flowing into the circuit. The electrical opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes. It is common to misuse "short circuit" to describe any electrical malfunction, regardless of the actual problem.

Static electricity imbalance of electric charges within or on the surface of a material

Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors and transmits energy.

Contents

ESD can create spectacular electric sparks (lightning, with the accompanying sound of thunder, is a large-scale ESD event), but also less dramatic forms which may be neither seen nor heard, yet still be large enough to cause damage to sensitive electronic devices. Electric sparks require a field strength above approximately 40 kV/cm in air, as notably occurs in lightning strikes. Other forms of ESD include corona discharge from sharp electrodes and brush discharge from blunt electrodes.

Lightning atmospheric discharge of electricity

Lightning is a sudden electrostatic discharge that occurs usually during a thunderstorm. This discharge occurs between electrically charged regions of a cloud, between two clouds, or between a cloud and the ground.

Thunder sound caused by lightning

Thunder is the sound caused by lightning. Depending on the distance from and nature of the lightning, it can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave, similar to a sonic boom, often referred to as a "thunderclap" or "peal of thunder".

Corona discharge electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged

A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the electric field strength. A corona will occur when the strength of the electric field around a conductor is high enough to form a conductive region, but not high enough to cause electrical breakdown or arcing to nearby objects. It is often seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages, and emits light by the same property as a gas discharge lamp.

ESD can cause harmful effects of importance in industry, including explosions in gas, fuel vapor and coal dust, as well as failure of solid state electronics components such as integrated circuits. These can suffer permanent damage when subjected to high voltages. Electronics manufacturers therefore establish electrostatic protective areas free of static, using measures to prevent charging, such as avoiding highly charging materials and measures to remove static such as grounding human workers, providing antistatic devices, and controlling humidity.

Electronics physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter

Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. The identification of the electron in 1897, along with the invention of the vacuum tube, which could amplify and rectify small electrical signals, inaugurated the field of electronics and the electron age.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, cheaper, and faster than those constructed of discrete electronic components. The IC's mass production capability, reliability and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Antistatic device

An antistatic device is any device that reduces, dampens, or otherwise inhibits electrostatic discharge; the buildup or discharge of static electricity, which can damage electrical components such as computer hard drives, and even ignite flammable liquids and gases.

ESD simulators may be used to test electronic devices, for example with a human body model or a charged device model.

Causes

One of the causes of ESD events is static electricity. Static electricity is often generated through tribocharging, the separation of electric charges that occurs when two materials are brought into contact and then separated. Examples of tribocharging include walking on a rug, rubbing a plastic comb against dry hair, rubbing a balloon against a sweater, ascending from a fabric car seat, or removing some types of plastic packaging. In all these cases, the breaking of contact between two materials results in tribocharging, thus creating a difference of electrical potential that can lead to an ESD event.

Another cause of ESD damage is through electrostatic induction. This occurs when an electrically charged object is placed near a conductive object isolated from the ground. The presence of the charged object creates an electrostatic field that causes electrical charges on the surface of the other object to redistribute. Even though the net electrostatic charge of the object has not changed, it now has regions of excess positive and negative charges. An ESD event may occur when the object comes into contact with a conductive path. For example, charged regions on the surfaces of styrofoam cups or bags can induce potential on nearby ESD sensitive components via electrostatic induction and an ESD event may occur if the component is touched with a metallic tool.

Electrostatic induction

Electrostatic induction, also known as "electrostatic influence" or simply "influence" in Europe and Latin America, is a redistribution of electrical charge in an object, caused by the influence of nearby charges. In the presence of a charged body, an insulated conductor develops a positive charge on one end and a negative charge on the other end. Induction was discovered by British scientist John Canton in 1753 and Swedish professor Johan Carl Wilcke in 1762. Electrostatic generators, such as the Wimshurst machine, the Van de Graaff generator and the electrophorus, use this principle. Due to induction, the electrostatic potential (voltage) is constant at any point throughout a conductor. Electrostatic Induction is also responsible for the attraction of light nonconductive objects, such as balloons, paper or styrofoam scraps, to static electric charges. Electrostatic induction laws apply in dynamic situations as far as the quasistatic approximation is valid. Electrostatic induction should not be confused with Electromagnetic induction.

ESD can also be caused by energetic charged particles impinging on an object. This causes increasing surface and deep charging. This is a known hazard for most spacecraft. [1]

Particle small localized object in physical sciences

In the physical sciences, a particle is a small localized object to which can be ascribed several physical or chemical properties such as volume, density or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans moving in a crowd or celestial bodies in motion.

A possible source of danger is called hazard. A hazard is an agent which has the potential to cause harm to a vulnerable target. The terms "hazard" and "risk" are often used interchangeably. However, in terms of risk assessment, they are two very distinct terms. A hazard is any agent that can cause harm or damage to humans, property, or the environment. Risk is defined as the probability that exposure to a hazard will lead to a negative consequence, or more simply, a hazard poses no risk if there is no exposure to that hazard.

Spacecraft manned vehicle or unmanned machine designed to fly in outer space

A spacecraft is a vehicle or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle.

Types

The most spectacular form of ESD is the spark, which occurs when a heavy electric field creates an ionized conductive channel in air. This can cause minor discomfort to people, severe damage to electronic equipment, and fires and explosions if the air contains combustible gases or particles.

However, many ESD events occur without a visible or audible spark. A person carrying a relatively small electric charge may not feel a discharge that is sufficient to damage sensitive electronic components. Some devices may be damaged by discharges as small as 30 V. These invisible forms of ESD can cause outright device failures, or less obvious forms of degradation that may affect the long term reliability and performance of electronic devices. The degradation in some devices may not become evident until well into their service life.[ citation needed ]

Sparks

A spark is triggered when the electric field strength exceeds approximately 4–30 kV/cm [2] — the dielectric field strength of air. This may cause a very rapid increase in the number of free electrons and ions in the air, temporarily causing the air to abruptly become an electrical conductor in a process called dielectric breakdown.

Lightning over Ryman. Northern Poland. Thunder rym.png
Lightning over Rymań. Northern Poland.

Perhaps the best known example of a natural spark is lightning. In this case the electric potential between a cloud and ground, or between two clouds, is typically hundreds of millions of volts. The resulting current that cycles through the stroke channel causes an enormous transfer of energy. On a much smaller scale, sparks can form in air during electrostatic discharges from charged objects that are charged to as little as 380 V (Paschen's law).

Earth's atmosphere consists of 21% oxygen (O2) and 78% nitrogen (N2). During an electrostatic discharge, such as a lightning flash, the affected atmospheric molecules become electrically overstressed. The diatomic oxygen molecules are split, and then recombine to form ozone (O3), which is unstable, or reacts with metals and organic matter. If the electrical stress is high enough, nitrogen oxides (NOx) can form. Both products are toxic to animals, and nitrogen oxides are essential for nitrogen fixation. Ozone attacks all organic matter by ozonolysis and is used in water purification.

Sparks are an ignition source in combustible environments that may lead to catastrophic explosions in concentrated fuel environments. Most explosions can be traced back to a tiny electrostatic discharge, whether it was an unexpected combustible fuel leak invading a known open air sparking device, or an unexpected spark in a known fuel rich environment. The end result is the same if oxygen is present and the three criteria of the fire triangle have been combined.

Damage prevention in electronics

A portion of a static discharger on an aircraft. Note the two sharp 3/8" metal micropoints and the protective yellow plastic. Static discharger with plastic guards.jpg
A portion of a static discharger on an aircraft. Note the two sharp 3/8" metal micropoints and the protective yellow plastic.

Many electronic components, especially microchips, can be damaged by ESD. Sensitive components need to be protected during and after manufacture, during shipping and device assembly, and in the finished device. Grounding is especially important for effective ESD control. It should be clearly defined, and regularly evaluated. [3]

Protection during manufacturing

In manufacturing, prevention of ESD is based on an Electrostatic Discharge Protected Area (EPA). The EPA can be a small workstation or a large manufacturing area. The main principle of an EPA is that there are no highly-charging materials in the vicinity of ESD sensitive electronics, all conductive and dissipative materials are grounded, workers are grounded, and charge build-up on ESD sensitive electronics is prevented. International standards are used to define a typical EPA and can be found for example from International Electrotechnical Commission (IEC) or American National Standards Institute (ANSI).

ESD prevention within an EPA may include using appropriate ESD-safe packing material, the use of conductive filaments on garments worn by assembly workers, conducting wrist straps and foot-straps to prevent high voltages from accumulating on workers' bodies, anti-static mats or conductive flooring materials to conduct harmful electric charges away from the work area, and humidity control. Humid conditions prevent electrostatic charge generation because the thin layer of moisture that accumulates on most surfaces serves to dissipate electric charges.

Ionizers are used especially when insulative materials cannot be grounded. Ionization systems help to neutralize charged surface regions on insulative or dielectric materials. Insulating materials prone to triboelectric charging of more than 2,000 V should be kept away at least 12 inches from sensitive devices to prevent accidental charging of devices through field induction. On aircraft, static dischargers are used on the trailing edges of wings and other surfaces.

Manufacturers and users of integrated circuits must take precautions to avoid ESD. ESD prevention can be part of the device itself and include special design techniques for device input and output pins. External protection components can also be used with circuit layout.

Due to dielectric nature of electronics component and assemblies, electrostatic charging can not be completely prevented during handling of devices. Most of ESD sensitive electronic assemblies and components are also so small that manufacturing and handling is done with automated equipment. ESD prevention activities are therefore important with those processes where components come into direct contact with equipment surfaces. In addition, it is important to prevent ESD when an electrostatic discharge sensitive component is connected with other conductive parts of the product itself. An efficient way to prevent ESD is to use materials that are not too conductive but will slowly conduct static charges away. These materials are called static dissipative and have resistivity values below 1012 ohm-meters. Materials in automated manufacturing which will touch on conductive areas of ESD sensitive electronic should be made of dissipative material, and the dissipative material must be grounded. These special materials are able to conduct electricity, but do so very slowly. Any built-up static charges dissipate without the sudden discharge that can harm the internal structure of silicon circuits. [4]

Protection during transit

A network card inside an antistatic bag, a bag made of a partially conductive plastic that acts as a Faraday cage, shielding the card from ESD. Antistatic bag.jpg
A network card inside an antistatic bag, a bag made of a partially conductive plastic that acts as a Faraday cage, shielding the card from ESD.

Sensitive devices need to be protected during shipping, handling, and storage. The buildup and discharge of static can be minimized by controlling the surface resistance and volume resistivity of packaging materials. Packaging is also designed to minimize frictional or triboelectric charging of packs due to rubbing together during shipping, and it may be necessary to incorporate electrostatic or electromagnetic shielding in the packaging material. [5] A common example is that semiconductor devices and computer components are usually shipped in an antistatic bag made of a partially conductive plastic, which acts as a Faraday cage to protect the contents against ESD.

Simulation and testing for electronic devices

Electric discharge showing the ribbon-like plasma filaments from multiple discharges from a Tesla coil. Electrostatic-discharge.jpg
Electric discharge showing the ribbon-like plasma filaments from multiple discharges from a Tesla coil.

For testing the susceptibility of electronic devices to ESD from human contact, an ESD Simulator with a special output circuit, called the human body model (HBM) is often used. This consists of a capacitor in series with a resistor. The capacitor is charged to a specified high voltage from an external source, and then suddenly discharged through the resistor into an electrical terminal of the device under test. One of the most widely used models is defined in the JEDEC 22-A114-B standard, which specifies a 100 picofarad capacitor and a 1,500 ohm resistor. Other similar standards are MIL-STD-883 Method 3015, and the ESD Association's ESD STM5.1. For comportment to European Union standards for Information Technology Equipment, the IEC/EN 61000-4-2 test specification is used. [6] Another specification (Schaffner) C = 150 pF R = 330 Ω that gives high fidelity results. Mostly the theory is there, minimum of the companies measure the real ESD survival rate. Guidelines and requirements are given for test cell geometries, generator specifications, test levels, discharge rate and waveform, types and points of discharge on the "victim" product, and functional criteria for gauging product survivability.

A charged device model (CDM) test is used to define the ESD a device can withstand when the device itself has an electrostatic charge and discharges due to metal contact. This discharge type is the most common type of ESD in electronic devices and causes most of the ESD damages in their manufacturing. CDM discharge depends mainly on parasitic parameters of the discharge and strongly depends on size and type of component package. One of the most widely used CDM simulation test models is defined by the JEDEC.

Other standardized ESD test circuits include the machine model (MM) and transmission line pulse (TLP).

See also

Related Research Articles

Triboelectric effect

The triboelectric effect is a type of contact electrification on which certain materials become electrically charged after they are separated from a different material with which they were in contact. Rubbing the two materials each with the other increases the contact between their surfaces, and hence the triboelectric effect. Rubbing glass with fur for example, or a plastic comb through the hair, can build up triboelectricity. Most everyday static electricity is triboelectric. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.

Faraday cage

A Faraday cage or Faraday shield is an enclosure used to block electromagnetic fields. A Faraday shield may be formed by a continuous covering of conductive material or in the case of a Faraday cage, by a mesh of such materials. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.

Electrostatics branch of physics

Electrostatics is a branch of physics that studies electric charges at rest.

In electrical engineering, partial discharge (PD) is a localized dielectric breakdown (DB) of a small portion of a solid or fluid electrical insulation (EI) system under high voltage (HV) stress, which does not bridge the space between two conductors. While a corona discharge (CD) is usually revealed by a relatively steady glow or brush discharge (BD) in air, partial discharges within solid insulation system are not visible.

Lichtenberg figure

Lichtenberg figures, or "Lichtenberg dust figures", are branching electric discharges that sometimes appear on the surface or in the interior of insulating materials. Lichtenberg figures are often associated with the progressive deterioration of high voltage components and equipment. The study of planar Lichtenberg figures along insulating surfaces and 3D electrical trees within insulating materials often provides engineers with valuable insights for improving the long-term reliability of high voltage equipment. Lichtenberg figures are now known to occur on or within solids, liquids, and gases during electrical breakdown.

Electroscope scientific instrument

An electroscope is a scientific instrument used to detect the presence and magnitude of electric charge on a body. It was the first electrical measuring instrument. The first electroscope, a pivoted needle called the versorium, was invented by British physician William Gilbert around 1600. The pith-ball electroscope and the gold-leaf electroscope are two classical types of electroscope that are still used in physics education to demonstrate the principles of electrostatics. A type of electroscope is also used in the quartz fiber radiation dosimeter. Electroscopes were used by the Austrian scientist Victor Hess in the discovery of cosmic rays.

Electrical breakdown when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage

Electrical breakdown or dielectric breakdown is when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event, or may lead to a continuous arc if protective devices fail to interrupt the current in a power circuit.

Electric spark kind of electrical discharge

An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael Faraday described this phenomenon as "the beautiful flash of light attending the discharge of common electricity".

Body capacitance is the physical property of the human body that has it act as a capacitor. Like any other electrically-conductive object, a human body can store electric charge if insulated. The actual amount of capacitance varies with the surroundings; it would be low when standing on top of a pole with nothing nearby, but high when leaning against an insulated, but grounded large metal surface, such as a household refrigerator, or a metal wall in a factory.

Electrostatic-sensitive device

An electrostatic-sensitive device is any component which can be damaged by common static charges which build up on people, tools, and other non-conductors or semiconductors. ESD commonly also stands for electrostatic discharge.

Antistatic bag bag used for shipping (usually electronic) components

An antistatic bag is a bag used for storing electronic components, which are prone to damage caused by electrostatic discharge (ESD).

Applications of capacitors

Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose.

Failure of electronic components Ways electronic elements fail and prevention measures

Electronic components have a wide range of failure modes. These can be classified in various ways, such as by time or cause. Failures can be caused by excess temperature, excess current or voltage, ionizing radiation, mechanical shock, stress or impact, and many other causes. In semiconductor devices, problems in the device package may cause failures due to contamination, mechanical stress of the device, or open or short circuits.

Dielectric absorption is the name given to the effect by which a capacitor, that has been charged for a long time, discharges only incompletely when briefly discharged. Although an ideal capacitor would remain at zero volts after being discharged, real capacitors will develop a small voltage from time-delayed dipole discharging, a phenomenon that is also called dielectric relaxation, "soakage", or "battery action". For some dielectrics, such as many polymer films, the resulting voltage may be less than 1–2% of the original voltage, but it can be as much as 15% for electrolytic capacitors. The voltage at the terminals generated by the dielectric absorption may possibly cause problems in the function of an electronic circuit or can be a safety risk to personnel. In order to prevent shocks, most very large capacitors are shipped with shorting wires that need to be removed before they are used and/or permanently connected bleeder resistors. When disconnected at one or both ends, DC high-voltage cables can also "recharge themselves" to dangerous voltages.

An electrically conductive adhesive is a glue that is primarily used for electronics.

Electrostatic discharge materials

Electrostatic discharge materials are plastics that reduce static electricity to protect electrostatic-sensitive devices (ESD) or contain flammable liquids or gases.

References

  1. Henry B. Garrett and Albert C. Whittlesey: Spacecraft charging, an update; IEEE Trans. Plasma Science, 28(6), 2000.
  2. CRC Handbook of Chemistry and Physics
  3. "Fundamentals of Electrostatic Discharge". In Compliance Magazine. May 1, 2015. Retrieved 25 June 2015.
  4. "ESD Explained: What is Electrostatic Discharge?". Saline Lectronics. 2019-02-14. Retrieved 2019-02-26.
  5. GR-1421, Generic Requirements for ESD-[https://newtophome.info/best-power-strips/ Protective Circuit Pack Containers], Telcordia.
  6. "Baytems ESDzap - Lightweight ESD Simulator Product Overview" (PDF). Baytems. Aug 25, 2012. Retrieved 2012-08-25.