Sudden flow of electric current between two electrically charged objects by contact

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Electrostatic discharge (ESD) is a sudden and momentary flow of electric current between two differently-charged objects when brought close together or when the dielectric between them breaks down, often creating a visible spark associated with the static electricity between the objects.

ESD can create spectacular electric sparks (lightning, with the accompanying sound of thunder, is an example of 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 4 × 106 V/m in air, as notably occurs in lightning strikes. Other forms of ESD include corona discharge from sharp electrodes, brush discharge from blunt electrodes, etc.

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.

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

Causes

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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.

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]

Types

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Electrostatic discharge (ESD) phenomena vary in complexity and magnitude, with the electric spark being the most visible and dramatic example. This occurs when a strong electric field ionizes the air, creating a conductive channel that can convey an electric current. People may experience this as a small jolt of discomfort, but ESD can inflict severe damage on electronic components, potentially leading to malfunctions and failures. In hazardous environments where flammable gases or dust particles are present, ESD can trigger fires or explosions.

Not all ESD events, however, are accompanied by a visible spark or noise. It is possible for a person to carry a charge that, while undetectable to the human senses, can still be potent enough to harm delicate electronics. Some components can be compromised by discharges as faint as 30 V, with such damage sometimes not becoming apparent until significant usage has occurred, thus affecting the lifespan and performance of the devices.[citation needed]

Cable discharge events (CDEs) are discharges occurring when connecting electrical cables to a device.

Sparks

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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 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 result is the same if oxygen is present and the three criteria of the fire triangle have been combined.

Damage prevention in electronics

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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 integrated circuits and 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

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ESD Jacket

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 cannot 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 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.

Protection during transit

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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.[4] 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

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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 , and the ESD Association's ESD STM5.1. For compliance to European Union standards for Information Technology Equipment, the IEC/EN -4-2 test specification is used.[5] Another specification referenced by equipment maker Schaffner calls for C = 150 pF and R = 330 Ω which provides high fidelity results. While the theory is mostly there, very few 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

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References

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Fundamentals of Electrostatic Discharge

Part One&#;An Introduction to ESD

© , EOS/ESD Association, Inc., Rome, NY

 

HISTORY & BACKGROUND

Greek scientist, Thales of Miletus mentioned the earliest report of electricity. He found that after amber was rubbed, dust and leaves were attracted to it. The word "triboelectric", covered later, comes from the Greek words, tribo &#; meaning "to rub" and elektros &#; meaning "amber" (fossilized resin from prehistoric trees). When flowing electricity properties were discovered in the s, static electricity became the term for the old form of electricity, which distinguished it from the new forms of electricity.

 

Many people have experienced static electricity and "shocks", or electrostatic discharge (ESD) when touching a metal doorknob after walking across a carpeted floor or after sliding across a car seat. However, static electricity and ESD have created serious industrial problems for centuries. As early as the s, European and Caribbean military forts were using static control procedures and grounding devices trying to prevent inadvertent ESD ignition of gunpowder stores. By the s, paper mills throughout the

U.S. employed basic grounding, flame ionization techniques, and steam drums to dissipate static electricity from the paper web as it traveled through the drying process. Every imaginable business and industrial process has issues with an electrostatic charge and discharge at one time or another. Munitions and explosives, petrochemical, pharmaceutical, agriculture, printing and graphic arts, textiles, painting, and plastics are just some of the industries where control of static electricity has significant importance.

 

The age of electronics brought with it new problems associated with static electricity and ESD. And, as electronic devices become faster and the circuitry gets smaller, sensitivity to ESD in general increases. This trend may be accelerating. The EOS/ESD Association, Inc.'s Electrostatic Discharge (ESD) Technology Roadmap is revised every few years and states, "with devices becoming more sensitive, it is imperative that companies begin to scrutinize the ESD capabilities of their handling processes". Today, ESD impacts productivity and product reliability in virtually every aspect of the global electronics environment.

 

Despite a great deal of effort during the past decades, ESD still affects production yields, manufacturing cost, product quality, product reliability, and profitability. The cost of damaged devices ranges from only a few cents for a simple diode to thousands of dollars for complex integrated circuits. When associated costs of repair and rework, shipping, labor, and overhead are included, the opportunities exist for significant improvements. Nearly all of the thousands of companies involved in electronics manufacturing today pay attention to the basic industry-accepted elements of static control. EOS/ESD Association, Inc. industry standards are available today to guide manufacturers in establishing the fundamental static charge mitigation and control techniques (see Part Six &#; ESD

 

Standards). It is unlikely that any company which ignores static control will be able to manufacture and deliver undamaged electronic parts successfully.

 

STATIC ELECTRICITY: CREATING CHARGE

Definitions for  ESD terminology  can be  found  in  ESD ADV1.0  -  Glossary,  which   is available as a complimentary download at w ww.esda.org. Electrostatic charge is defined as "electric charge at rest". Static electricity is an imbalance of electrical charges within or on the surface of a material. This imbalance of electrons produces an electric field that can be measured and that can influence other objects. Electrostatic discharge (ESD) is defined as "the rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. Note: Usually, the charge flows through a spark between two conductive bodies at different electrostatic potentials as they approach one another".

 

ESD can change the electrical characteristics of a semiconductor device, degrading or destroying it. ESD may also upset the normal operation of an electronic system, causing equipment malfunction or failure. Charged surfaces can attract and hold contaminants, making removal of the particles difficult. When attracted to the surface of a silicon wafer or a device's electrical circuitry, air-borne particulates can cause random wafer defects and reduce product yields.

 

Controlling electrostatic discharge begins with understanding how electrostatic charge occurs in the first place. Electrostatic charge is most commonly created by the contact and separation of two materials. The materials may be similar or dissimilar, although dissimilar materials tend to liberate higher levels of static charge. For example, a person walking across the floor generates static electricity as shoe soles contact and then separate from the floor surface. An electronic device sliding into or out of a bag, magazine, or tube generates an electrostatic charge as the device's housing and metal leads make multiple contacts and separations with the surface of the container. While the magnitude of electrostatic charge may be different in these examples, static electricity is indeed formed in each case.

 

Creating electrostatic charge by contact and separation of materials is known as triboelectric charging. It involves the transfer of electrons between materials. The atoms of a material with no static charge have an equal number of positive (+) protons in the nucleus and negative (-) electrons orbiting the nucleus. In Figure 1, Material "A" consists of atoms with equal numbers of protons and electrons. Material B also consists of atoms with equal (though perhaps different) numbers of protons and electrons. Both materials are electrically neutral.

 

 

Figure 1: The Triboelectric Charge. Materials Make Intimate Contact

 

When the two materials are placed in contact and then separated, negatively charged electrons are transferred from the surface of one material to the surface of the other material. Which material loses electrons and which gains electrons will depend on the nature of the two materials. The material that loses electrons becomes positively charged, while the material that gains electrons is negatively charged. (Shown in Figure 2.)

 

 

Figure 2: The Triboelectric Charge - Separation

 

Static electricity is measured in coulombs. The charge (q) on an object is determined by the product of the capacitance of the object (C) and the voltage potential on the object (V):

q = CV

However, commonly we speak of the electrostatic potential on an object, which is expressed as voltage.

 

The process of material contact, electron transfer, and separation is a much more complex mechanism than described here. The amount of charge created by triboelectric generation is affected by the area of contact, the speed of separation, relative humidity, the chemistry of the materials, surface work function, and other factors. Once the charge is created on a material, it becomes an electrostatic charged material or object (if the charge remains on the material or object). This charge may be transferred from the material, creating an electrostatic discharge or ESD event. Additional factors, such as the resistance of the actual discharge circuit and the contact resistance at the interface between contacting surfaces, also affect the actual charge that is released. Typical charge generation scenarios and the resulting voltage levels are shown in Table 1. Also, the contribution of humidity to reducing charge accumulation is shown. However, it should be noted that static charge generation still occurs even at high relative humidity.

 

 

Table 1. Examples of Typical Static Generation Voltage Levels

 

Means of Generation

Walking across carpet Walking across vinyl tile

10-25% RH

35,000V

12,000V

65-90% RH

1,500V

250V

Worker at bench

6,000V

For more information, please visit electro static discharge film.

100V

Polybag picked up from the bench

20,000V

1,200V

Chair with urethane foam

18,000V

1,500V

 

An electrostatic charge may also be created on the material in other ways, such as by induction, ion bombardment, or contact with another charged object. However, triboelectric charging is the most common.

 

HOW MATERIAL CHARACTERISTICS AFFECT STATIC CHARGE

Triboelectric Series

When two materials contact and separate, the polarity and magnitude of the charge are indicated by the materials' positions in a triboelectric series. The triboelectric series tables show how charges are generated on various materials. When two materials contact and separate, the one nearer the top of the series takes on a positive charge, the other a negative charge. Materials further apart on the table typically generate a higher charge than ones closer together. These tables, however, should only be used as a general guide because there are many variables involved that cannot be controlled well enough to ensure repeatability. A typical triboelectric series is shown in Table 2.

 

Table 2. Typical Triboelectric Series

+

Positive

 

 

 

 

 

 

Negative

-

Rabbit fur
Glass
Mica
Human Hair
Nylon
Wool
Fur
Lead
Silk
Aluminum
Paper
Cotton
Steel
Wood
Amber
Sealing Wax
Nickel, copper, Brass, silver
Gold, platinum
Sulfur
Acetate rayon
Polyester
Celluloid
Silicon
Teflon

 

Virtually all materials, including water and dirt particles in the air, can be triboelectrically charged. How much charge is generated, where that charge goes, and how quickly, are functions of the material's physical, chemical, and electrical characteristics.

 

Insulative Materials

A material that prevents or limits the flow of electrons across its surface or through its volume, due to having an extremely high electrical resistance, is called an insulative material. ESD ADV1.0 defines insulative materials are defined as "materials with a surface resistance or a volume resistance equal to or greater than 1.0 × ohms". A considerable amount of charge can be generated on the surface of an insulator. Since an insulative material does not readily allow the flow of electrons, both positive and negative charges can reside on an insulative surface at the same time, although at different locations. The excess electrons at the negatively charged spot might be sufficient to

 

satisfy the absence of electrons at the positively charged spot. However, electrons cannot easily flow across the insulative material's surface, and both charges may remain in place for a very long time.

 

Conductive Materials

A material that allows electrons to flow easily across its surface or through its volume is called a conductive material. ESD ADV1.0 defines conductive materials as "a material that has a surface resistance of less than 1.0 × 104 ohms or volume resistance of less than 1.0 × 104 ohms". When a conductive material becomes charged, the charge (the deficiency or excess of electrons) will be uniformly distributed across the surface of the material. If the charged conductive material makes contact with another conductive material, the electrons will be shared between the materials quite easily. If the second conductor is attached to AC equipment ground or any other grounding point, the electrons will flow to ground, and the excess charge on the conductor will be neutralized.

 

Electrostatic charge can be created triboelectrically on conductors the same way it is created on insulators. As long as the conductor is isolated from other conductors or ground, the static charge will remain on the conductor. If the conductor is grounded, the charge will easily go to ground. Or, if the charged conductor contacts another conductor of different electrical potential, the charge will flow between the two conductors.

 

Dissipative Materials

Dissipative materials have an electrical resistance between insulative and conductive materials. ESD ADV1.0 defines dissipative materials as "a material that has a surface resistance greater than or equal to 1.0 × 104 ohms but less than 1.0 × ohms or a volume resistance greater than or equal to 1.0 × 104 ohms but less than 1.0 × ohms. There can be electron flow across or through the dissipative material, but it is controlled by the surface resistance or volume resistance of the material.

 

As with the other two types of materials, a charge can be generated triboelectrically on static dissipative material. However, like the conductive material, the static dissipative material will allow the transfer of charge to ground or other conductive objects. The transfer of charge from a static dissipative material will generally take longer than from a conductive material of equivalent size. Charge transfers from static dissipative materials are significantly faster than from insulators and slower than from conductive material.

 

Figure 3: Resistance Classifications (from ANSI/ESD S541)

 

Electrostatic Fields

Charged materials also have an electrostatic field and lines of force associated with them. Conductive objects brought into the vicinity of this electric field will be polarized by a process known as induction. (See Figure 4.) A negative electric field will repel electrons on the surface of the conducting item that is exposed to the field. A positive electric field will attract electrons near the surface, thus leaving other areas positively charged. No change in the actual charge on the item will occur in polarization. However, if the item is conductive or dissipative, and is connected to ground while polarized, the charge will flow from or to ground due to the charge imbalance. If the ground contact is disconnected and then the electrostatic field is removed, the charge will remain on the item. If a nonconductive object is brought into the electric field, the electrical dipoles will tend to align with the field creating apparent surface charges. A nonconductor (insulative material) cannot be charged by induction.

 

 

 

Figure 4: Induction

 

ESD DAMAGE&#;HOW DEVICES FAIL

Per ESD ADV1.0, electrostatic damage is defined as "change to an item caused by an electrostatic discharge that makes it fail to meet one or more specified parameters". It can occur at any point, from manufacture to field service. Typically, damage results from handling the devices in uncontrolled surroundings or when poor ESD control practices are used. Generally, the damage is classified as either a catastrophic failure or a latent defect.

 

Catastrophic Failure

When an electronic device is exposed to an ESD event, it may no longer function. The ESD event may have caused a metal melt, junction breakdown, or oxide failure. The device's circuitry is permanently damaged, causing the device to stop functioning totally or at least partially. Such failures usually can be detected when the device is tested before shipment. If a damaging level ESD event occurs after testing, the part may go into production, and the damage will go undetected until the device fails in final testing.

 

Latent Failure

Per ESD ADV1.0, latent failure is "a malfunction that occurs following a period of normal operation. Note: The failure may be attributable to an earlier electrostatic discharge event. The concept of latent failure is controversial and not fully accepted by all in the technical

 

community". A device that is exposed to an ESD event may be partially degraded, yet continue to perform its intended function. Therefore a latent defect is difficult to identify. Still, the operating life of the device may be reduced. A product or system incorporating devices with latent defects may experience premature failure after the user places them in service. Such failures are usually costly to repair and, in some applications, may create personnel hazards.

 

With the proper equipment, it is relatively easy to confirm that a device has experienced a catastrophic failure as basic performance tests will substantiate device damage. However, latent defects are challenging to prove or detect using current technology, especially after the device is assembled into a finished product.

 

BASIC ESD EVENTS&#;WHAT CAUSES ELECTRONIC DEVICES TO FAIL?

ESD damage is usually caused by one of three events: direct ESD to the device, ESD from the device, or field-induced discharges. Whether or not damage occurs to an ESD susceptible item (ESDS) by an ESD event is determined by the device's ability to dissipate the energy of the discharge or withstand the voltage levels involved. The level at which a device fails is known as the device's ESD sensitivity or ESD susceptibility.

 

Discharge to the Device

An ESD event can occur when any charged conductor (including the human body) discharges to an item. A cause of electrostatic damage could be the direct transfer of electrostatic charge from the human body or a charged material to the ESDS. When a person walks across a floor, an electrostatic charge accumulates on their body. Simple contact (or proximity) of a finger to the leads of an ESDS or assembly, which is typically at a different electrical potential, can allow the body to discharge and possibly cause ESD damage to the ESDS. The model used to simulate this event is the human body model (HBM). A similar discharge can occur from a charged conductive object, such as a metallic tool or fixture. From the nature of the discharge, the model used to describe this event is known as the machine model (MM).

 

Discharge from the Device

The transfer of charge from an ESDS to a conductor is also an ESD event. Static charge may accumulate on the ESDS itself through handling or contact and separation with packaging materials, worksurfaces, or machine surfaces. This frequently occurs when a device moves across a surface or vibrates in a package. The model used to simulate the transfer of charge from an ESDS is referred to as the charged device model (CDM). The capacitances, energies, and current waveforms involved are different from those of a

discharge to the ESDS, likely resulting in different failure modes.

 

The trend towards automated assembly would seem to solve the problems of HBM ESD events. However, it has been shown that components may be more sensitive to damage when assembled by automated equipment. For example, a device may become charged

 

by sliding down the feeder. When it contacts the insertion head or any other conductive surface, a rapid discharge occurs from the device to the metal object.

Field-Induced Discharges

Another electrostatic charging process that can directly or indirectly damage devices is termed field induction. As noted earlier, whenever any object becomes electrostatically charged, there is an electrostatic field associated with that charge. If an ESDS is placed in the electrostatic field and grounded while located within the electrostatic field, a transfer of charge from the device occurs as a CDM event. If the item is removed from the region of the electrostatic field and grounded again, a second CDM event will occur as the charge (of opposite polarity from the first event) is transferred from the device.

 

HOW MUCH ESD CONTROL PROTECTION IS NEEDED?

Damage to an ESDS by an ESD event is determined by the device's ability to dissipate the energy of the discharge or withstand the voltage levels involved in the discharge. As explained previously, these factors determine the ESD sensitivity of the device. Test procedures based on the models of ESD events help define the sensitivity of components to ESD. Although it is known that there is very rarely a direct correlation between the discharges in the test procedures and real-world ESD events, defining the ESD sensitivity of electronic components gives some guidance in determining the degree of ESD control protection required. These procedures and more are covered in Part Five of this series.

 

Per ESD ADV1.0, the ESD withstand voltage is "the highest voltage level that does not cause device failure; the device passes all tested lower voltages". Many electronic components are susceptible to ESD damage at relatively low voltage levels. Many are susceptible at less than 100 volts, and many disk drive components withstand voltages even below 10 volts. Current trends in product design and development pack more circuitry onto these miniature devices, further increasing the sensitivity to ESD and making the potential problem even more acute. Table 3 indicates the ESD sensitivity of various types of components.

 

Table 3. ESD Sensitivity of Representative Electronic Devices or Parts with Sensitivity Associated with HBM and CDM*

 

Device or Part Type

Microwave devices (Schottky barrier diodes, point contact diodes and other detector diodes >1 GHz)

Discrete MOSFET devices

Surface acoustic wave (SAW) devices

Junction field-effect transistors (JFETs)

Charged coupled devices (CCDs)

Precision voltage regulator diodes (line of load voltage regulation, <0.5%)

Operational amplifiers (OP AMPs)

Thin-film resistors

Integrated circuits

GMR and new technology Disk Drive Recording Heads

Laser Diodes

Hybrids

Very high-speed integrated circuits (VHSIC)

Silicon controlled rectifiers (SCRs) with Io <0.175 amp at 10 °C ambient

*Specific Sensitivity Levels are available from supplier data sheets

 

SUMMARY

Part 1 of the ESD Fundamentals has discussed electrostatic charge and discharge, the mechanisms of creating a charge, materials, types of ESD damage, ESD events, and ESD sensitivity. We can summarize this discussion as follows:

1. Virtually all materials, including conductors, can be triboelectrically
2. The amount of charge is affected by material type, speed of contact and separation, humidity, and several other factors.
3. Charged objects have electrostatic
4. ESD can damage devices, so a parameter fails immediately, or ESD damage may be a latent defect that may escape immediate detection but may cause the device to fail prematurely.
5. ESD can occur throughout the manufacturing, test, shipping, handling, or operational processes, and during field service
6. ESD damage can occur as the result of a discharge to the device, from the device, or from charge transfers resulting from electrostatic fields. Devices vary significantly in their susceptibility to

 

Protecting products from the effects of ESD damage begins by understanding these fundamental concepts of electrostatic charges and discharges. An effective ESD control program requires an effective training program where all personnel involved understand the key concepts. See Part Two for the basic concepts of ESD control.

 

REFERENCES

ESD ADV 1.0, Glossary, EOS/ESD Association, Inc., Rome, NY.

ESD TR20.20, ESD Handbook, EOS/ESD Association, Inc., NY.

ESD ADV11.2, Triboelectric Charge Accumulation Testing, EOS/ESD Association, Inc., Rome, NY.

ANSI/ESD S20.20&#;Standard for the Development of Electrostatic Discharge Control Program, EOS/ESD Association, Inc., Rome, NY.

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