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Encyclopedia > Electrostatic discharge

Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment. Electric current is the flow (movement) of electric charge. ... Electrical potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential or the electric potential, typically measured in volts. ... This article is about the engineering discipline. ...

Contents

Causes of ESD

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, descending from a car, or removing some types of plastic packaging. In all these cases, the friction between two materials results in tribocharging, thus creating a difference of electrical potential that can lead to an ESD event. Static electricity is a class of phenomena involving the net charge present on an object; typically referring to charged object with voltages of sufficient magnitude to produce visible attraction, repulsion, and sparks. ... The triboelectric effect is an electrical phenomenon where certain materials become electrically charged after coming into contact with another, different, material. ... For other uses, see Friction (disambiguation). ...


Another cause of ESD damage is through electrostatic induction. This occurs when an electrically charged object is placed near a conductive object isolated from 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 plastic 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 is a method by which an electrically charged object can be used to create an electrical charge in a second object, without contact between the two objects. ... Styrofoam is a trademark name for polystyrene thermal insulation material, manufactured by Dow Chemical Company. ...


Types of ESD

The most spectacular form of ESD is the spark, which occurs when a strong 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 combustable gases or particles. 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 12 volts. These invisible forms of ESD can cause device outright 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 the service life of some devices. Look up Spark in Wiktionary, the free dictionary. ...


Sparks

A spark is triggered when the electric field strength exceeds approximately 30 kV/cm (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. In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ... In physics, the term dielectric strength has the following meanings: Of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down, , without experiencing failure of its insulating properties. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... This article is about the electrically charged particle. ... In science and engineering, conductors are materials that contain movable charges of electricity. ... The term electrical breakdown has several similar but distinctly different meanings. ...


Perhaps the best known example of a natural spark is a lightning strike. In this case the potential difference between a cloud and ground, or between two clouds, is typically hundreds of millions of volts. The resulting current that flows through the ionized air causes an explosive release 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 volts (Paschen's law). Not to be confused with lighting. ... Josephson junction array chip developed by NIST as a standard volt. ... Paschens Law, named after Friedrich Paschen, was first stated in 1889. ...


Earth's atmosphere consists of 21% oxygen (O2) and 78% nitrogen (N2). During an electrostatic discharge, the intervening atmosphere can become electrically overstressed. The diatomic oxygen molecules can be split, and then recombine by probability into ozone (O3), which is unstable, or react with metals and organic matter. If the electrical stress is high enough, nitrogen oxides (NOx) can form. Both products are toxic to animals, but ozone is essential for the ozone layer, and nitrogen oxides are essential for nitrogen fixation. Air redirects here. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... A computer rendering of the Nitrogen Molecule, which is a diatomic molecule. ... For other uses, see Ozone (disambiguation). ... The term nitrogen oxide is a general term and can be used to refer to any of these oxides (oxygen compounds) of nitrogen, or to a mixture of them: Nitric oxide (NO), nitrogen(II) oxide Nitrogen dioxide (NO2) Dinitrogen monoxide (N2O) (Nitrous oxide) Dinitrogen trioxide (N2O3) Dinitrogen tetroxide (N2O4) Dinitrogen... Look up nox, Nox in Wiktionary, the free dictionary. ... The ozone layer is a layer in Earths atmosphere which contains relatively high concentrations of ozone (O3). ... Nitrogen fixation is the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds (such as, notably, ammonia, nitrate and nitrogen dioxide)[1] useful for other chemical processes. ...


Prevention

A portion of a static discharger on an aircraft.
A portion of a static discharger on an aircraft.

ESD is a serious issue in solid state electronics. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide. Either of these materials can suffer permanent damage when subjected to high voltages. Image File history File linksMetadata Download high-resolution version (2816x2112, 1480 KB) Static discharge. ... Image File history File linksMetadata Download high-resolution version (2816x2112, 1480 KB) Static discharge. ... A portion of a static discharger showing a metal portion exposed. ... This article is about the engineering discipline. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... Not to be confused with Silicone. ...


Prevention of ESD bases on Electrostatic Protective Area (EPA). EPA can be a small working station 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 materials are grounded, workers are grounded, and charge build-up on ESD sensitive electronics is prevented. International standards are used to define typical EPA and can be found for example from International Electrotechnical Commission (IEC) or American National Standards Institute (ANSI). The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ... The American National Standards Institute or ANSI (pronounced an-see) is a nonprofit organization that oversees the development of standards for products, services, processes and systems in the United States. ...


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. Ion generators are sometimes used to inject ions into the ambient airstream. Ionization systems help to neutralize charged surface regions on insulative or dielectric materials. Insulating materials prone to triboelectric charging should be kept away from sensitive devices to prevent accidental charging of devices through induction. On aircraft, static dischargers are used on the trailing edges of wings and other surfaces. An Anti-static wrist strap or ESD wrist strap is a device used to prevent electrostatic discharge (ESD) by safely grounding a person working on electronic equipment. ... Humidity is the amount of water vapor in air. ... A dielectric is a physical model commonly used to describe how an electric field behaves inside a material. ... A portion of a static discharger showing a metal portion exposed. ...


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 made with automated equipment. ESD prevention activities are therefore important with those processes where component is touching on equipment surfaces. In addition, it is important to prevent ESD when 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 in the range of 105 to 1011 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.


Simulation and testing

For testing the susceptibility of electronic devices to ESD from human contact, a simple test 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 1500 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-61000-4-2 test specification is used. 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. The human body model (HBM) of electrostatic discharge is the most common mechanism for characterizing an ESD event. ... See Capacitor (component) for a discussion of specific types. ... Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ... Device under test (DUT) is a term commonly used to refer to a manufactured product undergoing testing. ... JEDEC stands for Joint Electron Device Engineering Council and is the semiconductor engineering standardization body of the Electronic Industries Alliance (EIA), a trade association that represents all areas of the electronics industry. ... Examples of various types of capacitors. ... The ohm (symbol: Ω) is the SI unit of electric resistance. ... MIL-STD (Military-Standard) or MIL-SPEC (Military-Specifications) is an abbreviation used to describe an item that can meet standards determined by the United States Department of Defense. ...


Charged Device Model (CDM) test is used to define device ESD 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 and causes most of the ESD damages in electronics manufacturing. CDM discharge depends mainly on parasitic parameters of the discharge and is strongly depending on size and type of component package. One of the most widely used CDM simulation test models is defined by the JEDEC. JEDEC stands for Joint Electron Device Engineering Council and is the semiconductor engineering standardization body of the Electronic Industries Alliance (EIA), a trade association that represents all areas of the electronics industry. ...


Other standardized ESD test circuits include the following:

  • Machine model (MM)
  • Transmission line pulse (TLP)

All these ESD testing standards define the testing method and procedure as well as the test circuit.


References

  • Danglemayer, G. Theodore, ESD Program Management: A Realistic Approach to Continuous Measurable Improvement in Static Control [1] ISBN 0-412-13671-6

See also

A 3000 volt electricity arc between two nails Electricity arcs between the power rail and electrical pickup shoe on a London Underground train An electric arc can melt calcium oxide An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current... A latchup is the inadvertent creation of a low-impedance path between the power supply rails of an electronic component, triggering a parasitic structure, which then acts as a short circuit, disrupting proper functioning of the part and possibly even leading to its destruction due to overcurrent. ... The team qualification may refer to: Certification A process of deciding the running order in many auto racing events This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ... The Automotive Electronics Council is an organisation based in the USA that sets qualification standards for the supply of components in the automotive electronics industry. ... An antistatic device is any item which has the effect of reducing static electricity charges on a persons body or equipment, either to prevent fires and explosions when working with flammable liquids and gases, or to prevent damage to static-sensitive objects such as electronic components or devices. ...

External links


  Results from FactBites:
 
Electrostatic discharge device of surface mount type and fabricating method thereof - Patent 6721157 (4760 words)
The electrostatic discharge device according to claim 2, wherein said discharge opening of said middle insulating plate is predetermined in its size so as to have desired ionization voltage characteristics in consideration of both a gap between said first and second discharge terminals and a composition of the discharge gas filling said discharge opening.
The electrostatic discharge device according to claim 3, wherein each of said first and second discharge terminals of said middle insulating plate includes at least one triangular projection tip formed at each of said opposite edges of said discharge opening, and is integrally formed on said middle insulating plate.
In addition, the general discharge characteristics of the ESD device of this invention, such as the discharge start voltage and discharge time, are predetermined in accordance with the ionization characteristics of the plasma discharge gas filling the discharge opening of this ESD device and the size of the discharge opening.
Electrostatic Discharge Association: Fundamentals of ESD (2747 words)
Electrostatic discharge is defined as the transfer of charge between bodies at different electrical potentials.
The most common cause of electrostatic damage is the direct transfer of electrostatic charge from the human body or a charged material to the electrostatic discharge sensitive (ESDS) device.
Electrostatic discharge can damage devices so they fail immediately, or ESD may result in latent damage that may escape immediate attention, but cause the device to fail prematurely once in service.
  More results at FactBites »

 
 

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