Electrostatic discharge is a serious issue in solid state
electronicsElectronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
, such as
integrated circuitAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s. Integrated circuits are made from
semiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
materials such as
siliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
and insulating materials such as
silicon dioxideThe chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
. Either of these materials can suffer permanent damage when subjected to high voltages; as a result, there are now a number of
antistatic deviceAn antistatic device is any item which has the effect of reducing static electricity charges on a person's 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...
s that help prevent static build up.
Causes of ESD
One of the causes of ESD events is
static electricityStatic electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
. 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
frictionFriction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
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 inductionElectrostatic induction is a redistribution of electrical charge in an object, caused by the influence of nearby charges. 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...
. 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
styrofoamStyrofoam is a trademark of The Dow Chemical Company for closed-cell currently made for thermal insulation and craft applications. In 1941, researchers in Dow's Chemical Physics Lab found a way to make foamed polystyrene...
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.
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 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 10 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.
Sparks
A spark is triggered when the
electric fieldIn physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
strength exceeds approximately 4–30 kV/cm — the
dielectric field strengthIn 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, i.e., without experiencing failure of its insulating properties....
of air. This may cause a very rapid increase in the number of free electrons and
ionAn ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s in the air, temporarily causing the air to abruptly become an electrical conductor in a process called dielectric breakdown.
Perhaps the best known example of a natural spark is a
lightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
strike. In this case the potential difference between a cloud and ground, or between two clouds, is typically hundreds of millions of
voltThe volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s. The resulting current that flows through the ionized air causes an explosive release of
energyIn physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
. 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 lawPaschen's Law, named after Friedrich Paschen, was first stated in 1889. He studied the breakdown voltage of gas between parallel plates as a function of pressure and gap distance. The voltage necessary to arc across the gap decreased up to a point as the pressure was reduced. It then increased,...
).
Earth's atmosphereThe atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
consists of 21%
oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(O
2) and 78%
nitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
(N
2). During an electrostatic discharge, the intervening atmosphere become electrically overstressed. The
diatomicDiatomic molecules are molecules composed only of two atoms, of either the same or different chemical elements. The prefix di- means two in Greek. Common diatomic molecules are hydrogen , nitrogen , oxygen , and carbon monoxide . Seven elements exist in the diatomic state in the liquid and solid...
oxygen molecules are split, and then recombine to form
ozoneOzone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
(O
3), which is unstable, or reacts with metals and organic matter. If the electrical stress is high enough,
nitrogen oxideNitrogen oxide can refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:* Nitric oxide, also known as nitrogen monoxide, , nitrogen oxide* Nitrogen dioxide , nitrogen oxide...
s (
NOxNOx is a generic term for the mono-nitrogen oxides NO and NO2 . They are produced from the reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures...
) can form. Both products are toxic to animals, and nitrogen oxides are essential for
nitrogen fixationNitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
. Ozone attacks all organic matter by
ozonolysisOzonolysis is the cleavage of an alkene or alkyne with ozone to form organic compounds in which the multiple carbon–carbon bond has been replaced by a double bond to oxygen...
and is used in
water purificationWater purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
.
Sparks can cause serious explosions because of the high temperatures reached in a spark.
MethaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and
coal dustCoal dust is a fine powdered form of coal, which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal.-Explosions:...
explosions have been caused by electrostatic discharges. The
Hindenburg disasterThe Hindenburg disaster took place on Thursday, May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed during its attempt to dock with its mooring mast at the Lakehurst Naval Air Station, which is located adjacent to the borough of Lakehurst, New Jersey...
has been attributed to spark discharge igniting flammable panels tainted with
thermiteThermite is a pyrotechnic composition of a metal powder and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction...
, which burned vigorously, violently, and extremely swiftly, which ultimately led to the ignition of
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas held in or leaking from the
airshipAn airship or dirigible is a type of aerostat or "lighter-than-air aircraft" that can be steered and propelled through the air using rudders and propellers or other thrust mechanisms...
at the time. The ship had just passed through a
thunderstormA thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
and therefore may have acquired a large charge. Discharge supposedly occurred when mooring ropes were dropped as it came in to land in
New JerseyNew Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
in 1937.
Corona discharge
A corona discharge occurs between a highly curved electrode, for example the tip of a needle or a small diameter wire, and an electrode of low curvature such as a flat plate. The high curvature produces a high potential gradient around one electrode.
Brush discharge
A brush discharge occurs between an electrode with a curvature between 5 mm and 50 mm and a voltage of about 500 kV/m. The resulting discharge paths have the shape of a brush.
Damage prevention in electronics
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 CommissionThe International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
(IEC) or
American National Standards InstituteThe American National Standards Institute is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international...
(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 matsAn antistatic floor mat or ground mat is one of a number of antistatic devices designed to help eliminate static electricity. It does this by having a conductive material embedded within the mat that collects the static. The mat would need to be grounded . This is usually accomplished by plugging...
or conductive flooring materials to conduct harmful electric charges away from the work area, and
humidityHumidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...
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
dielectricA dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing 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 dischargerStatic dischargers are commonly known as static wicks or static discharge wicks. They are used on aircraft to allow the continuous satisfactory operation of onboard navigation and radio communication systems. During adverse charging conditions , they limit the potential static buildup on the...
s are used on the
trailing edgeThe trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...
s 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 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 10
5 to 10
11 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 electronic devices
For testing the susceptibility of electronic devices to ESD from human contact, an
ESD SimulatorESD Simulators, also known as ESD Guns are used to test the immunity of a device to electrostatic discharge. These devices are used in special electromagnetic compatibility laboratories...
with a special output circuit, called the
human body modelThe human-body model is the most commonly used model for characterizing the susceptibility of an electronic device to damage from electrostatic discharge...
(HBM) is often used. This consists of a
capacitorA capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
in series with a
resistorA linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
. 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 testDevice under test , also known as unit under test , is a term commonly used to refer to a manufactured product undergoing testing.-In semiconductor testing:...
. One of the most widely used models is defined in the
JEDECThe JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
22-A114-B standard, which specifies a 100
picofaradThe farad is the SI unit of capacitance. The unit is named after the English physicist Michael Faraday.- Definition :A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second...
capacitor and a 1500 ohm resistor. Other similar standards are
MIL-STD-883The MIL-STD-883 standard establishes uniform methods, controls, and procedures for testing microelectronic devices suitable for use within Military and Aerospace electronic systems including basic environmental tests to determine resistance to deleterious effects of natural elements and conditions...
Method 3015, and the ESD Association's ESD STM5.1. For comportment to
European UnionThe European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
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.
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 is strongly depending on size and type of component package. One of the most widely used CDM simulation test models is defined by the
JEDECThe JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
.
Other standardized ESD test circuits include the following:
- Machine model (MM)
- Transmission line pulse (TLP)
See also
- Antistatic device
An antistatic device is any item which has the effect of reducing static electricity charges on a person's 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...
- Automotive Electronics Council
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.- See also :* Body electronics* Car audio* Carputer* Chassis electronics...
, which defines in some of its standards, ESD test qualification requirements for electronic components used in vehicles
- Dielectric wireless receiver
Dielectric wireless receiver is a type of radiofrequency receiver front-end featuring a complete absence of electronic circuitry and metal interconnects. It offers immunity against damage from intense electromagnetic radiation, produced by EMP and HPM sources...
- Electric arc
An electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on...
- Electromagnetic pulse
An electromagnetic pulse is a burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation usually results from certain types of high energy explosions, especially a nuclear explosion, or from a suddenly fluctuating magnetic field...
- Electrostatic voltmeter
Electrostatic Voltmeter can refer to an electrostatic charge meter, known also as Surface DC Voltmeter, or to an electrical potential measuring voltmeter, traditionally called Electrostatic Voltmeter.-Surface DC Voltmeter:...
- Hindenburg disaster
The Hindenburg disaster took place on Thursday, May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed during its attempt to dock with its mooring mast at the Lakehurst Naval Air Station, which is located adjacent to the borough of Lakehurst, New Jersey...
- Latchup
Latchup is a term used in the realm of integrated circuits to describe a particular type of short circuit which can occur in an improperly designed circuit...
, for qualification testing of semiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
devices, ESD and latchup are commonly considered together
- Spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
- Spark plug
A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...
- Static electricity
Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...
- Wimshurst machine
The Wimshurst influence machine is an electrostatic generator, a machine for generating high voltages developed between 1880 and 1883 by British inventor James Wimshurst ....
External links