Have you ever felt a tiny electric shock when you touch your car door or another metal doorknob?
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If so, you&#;re probably familiar with the release of static electricity, otherwise known as electrostatic discharge.
Electrostatic discharge (ESD) is the release of static electricity when two items touch. The jolt we get when we shuffle over our carpet and the static electricity we experience after drying clothes in a dryer are two common instances of ESD. Lightning is a more extreme example of ESD in action.
An electric charge that has accumulated on an object&#;s surface is known as static electricity. The loss or gain of electrons results in an imbalance between the negative and positive charges, which produces this type of electricity.
Surface separation and contact generate static electricity. This means that static charge can occur in powders, webs, sheets, rollers, and conveyors. The type of material, speed, and contact pressure all affect how intense the charge is.
While most ESD events are harmless, they can be an expensive problem in many industrial environments. We&#;ll learn more about static control in industrial environments in this article.
An electrostatic charge must initially accumulate for ESD to take place. When two unique materials brush against one another, the materials change their charges so that one is positively charged and the other is negatively charged. An electrostatic charge has formed on the positively charged substance.
The charge is transferred when that charge makes contact with the appropriate substance. The heat from this energy transfer is super hot &#; in some cases up to 50,000 °F!!! &#; but we do not feel the heat from the ESD event when we are shocked. The extreme heat from the charge can melt or evaporate the microscopic portions of expansion cards or other parts when the charge is released onto an electrical device. As a result, the device breaks.
A device may occasionally keep working even after a negative ESD event. Such damage is known as a latent flaw, which is hard to find and drastically reduces the device&#;s lifespan.
Many pieces of electronic equipment may experience low-voltage ESD incidents. Hard drive components, for instance, are sensitive to 10 volts. Due to this, producers of electronic products take precautions to stop ESD incidents during all stages of production, including testing, shipping, and handling.
We now know that ESD can affect electronic devices and lead to latent defects. So, how exactly does ESD play out in production?
In industrial environments, static electricity can cause:
Not surprisingly, these accidents are a costly waste of time.
To make matters worse, ESD accidents don&#;t just affect equipment &#; they can sometimes directly affect employees that work in manufacturing settings.
According to the United States Department of Labor, one 39-year-old employee received a static electric shock after she contacted a plastic film roll line on which static electricity had built up and was not dissipated prior to contact.
Another ESD event occurred at Barton Solvents during the filling of a steel tank with ethyl acetate (a flammable solvent), resulting in several minor injuries. According to CSB Chairman and CEO John Bresland, &#;These accidents show the need for companies to address the hazards associated with static electricity and flammable liquid transfer. They should apply good practice guidelines&#;to determine if facilities are properly designed and safely operated.&#;
Now that you have been properly warned, it&#;s time to learn more about the products that can prevent these kinds of ESD-induced mishaps.
In the making of electronics and other industrial processes, manufacturers use static control solutions to reduce electrostatic discharge. Some businesses utilize anti-static shoe straps, wrist straps or cords, gloves, and other personal grounding devices.
Others employ comprehensive static control systems or static electricity control equipment. Some examples of static control products include:
When working with devices, an employee may choose to wear a wrist strap, wear ESD control footwear, or work on an ESD floor mat, which causes the electrostatic charge to go into the ground rather than the object being handled. Rubber or vinyl anti-static mats are typically utilized on floors, countertops, or tabletops. Depending on the application, a static control mat may be either conductive or dissipative.
By generating both positively and negatively charged ions, a static control bar or ionizer bar can be used to eliminate static energy that has already built up.
Sensitive equipment can be packaged in materials that protect it from an electric charge. Because insulators like plastics prevent electrons from moving, grounding will not cause static electricity to dissipate.
Static electricity can be eliminated with a bi-polar ionization generator, which creates both positive and negative ions. The ions are drawn to the substrate&#;s static charge, which draws them and cancels them out. The ions are no longer drawn to the substance once the charge has been neutralized.
Static meters are a great tool for troubleshooting a potential static electricity problem because they measure static electricity on your material. They are also a useful tool to check how well ionizers work with your material.
Static bars must be inches from the target in order to work. The bar&#;s close proximity to the target allows for the neutralization of speedier targets due to more ions in the web.
How does this work? The charge of the static bar&#;s emitter pin has air ions that carry charge to the target. Opposite charges are attracted to one another.
Blowers operate on the same principle, but instead of only using the attraction of particles with opposite charges to drive ions, they use forced air. Because of this, blowers are effective at removing static from bigger areas, slower-moving webs, and three-dimensional objects.
Blowers work best in industrial situations in which the manufacturing setup does not leave room for bars. For instance, moving machinery parts can make a blower that controls static from a distance seem more practical. Over a nozzle or air assist bar, a blower has the advantage of not requiring pressurized air.
After outlining the foundations, let&#;s think about the best product option for the application. Since bars are most effective when they are a few inches or less from the web, they typically operate well when there is space around them. Bars can couple to the target&#;s charge because of how close they are to the web. They become more efficient on fast web sites as a result.
Discharging 3D parts is a perfect application for the blower because it can release ions that cover an object&#;s surface. Any neutralized trash is also displaced by the same air that is utilized to move ions. For procedures like preparing vehicle parts for paint, this is very effective.
Fixing problems brought on by static can seem like a difficult task. The good news is that Simco-Ion produces tools to assist you in finding the answers to these crucial concerns. Simco-Ion manufactures some of the most cutting-edge static electricity monitoring systems available today.
An FMX is one piece of equipment that practically all sales representatives have. This portable tool for on-the-go static monitoring is a terrific way for operators to check numerous locations or lines. However, if you want to keep an eye on a line for a while, there are other options.
Long-term line monitoring is done with the IQ Power Sensor Bar and its HL Bar brother, which is designed for hazardous areas. These two sensors can be placed over any line to give the operator useful data. This data is displayed on an IQ Power Control Station, which can also log data for review.
The IQ Easy Bar, IQ Power Nozzle, IQ Power Fantom Wide-Format Blower, and other neutralizing products are connected to sensors. This means that the Control Station is monitoring the condition of your web in real time and using that knowledge to modify the output of your static neutralizing goods. The outcome is the best static neutralization that is possible in an industrial setting.
Whether you&#;re new to static control or a seasoned pro searching for more knowledge about the systems you manage, Simco is for you! Contact your local sales representative right now if you&#;d like to find out more about static monitoring or if you want to buy any of the goods mentioned above.
https://www.globalspec.com/learnmore/manufacturing_process_equipment/electronics_microelectronics_manufacturing/static_control_products
https://www.techtarget.com/whatis/definition/electrostatic-discharge-ESD
https://www.csb.gov/csb-finds-static-spark-set-off-fire-and-explosions-at-barton-solvents-des-moines-facility-investigation-finds-equipment-not-intended-for-flammable-service-or-properly-bonded-and-grounded/
Still unsure which static control solution is best for your needs? Static control needs vary from application to application, it can be hard to determine what will work best. But you&#;re in luck! The staff at ISC Sales is very knowledgeable, able to answer any of your questions, and will ensure that you get the most efficient product for your business. Contact Us today and have the solution that&#;s perfect for you tomorrow.
Call ISC Sales today at 877.602. to get a free quote or to ask about our lineup of industrial equipment. You can also request a quote online, HERE.
Fundamentals of Electrostatic Discharge
Part One&#;An Introduction to ESD
© , EOS/ESD Association, Inc., Rome, NY
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.
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.
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.)
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):
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.
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
100V
Polybag picked up from the bench
20,000V
1,200V
Chair with urethane foam
18,000V
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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.
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.
+
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.
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.
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 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.
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.
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.
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.
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.
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.
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).
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.
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.
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.
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:
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.
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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