| What is ESD? | |
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"ESD" stands for ElectroStatic Discharge. You've encountered electrostatic energy in your everyday life and may not have known it. For example, when you get shocked by a doorknob after walking across a carpet on a dry day, you have experienced an ESD event. When your clothes cling to each other when you remove them from the dryer often called 'static cling', it is caused by an electrostatic charge. And in it's most dramatic form, the lightning in a thunderstorm is a massive electrostatic discharge. |
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| So ESD is a bad thing? | |
| No, not at all. Electrostatic charges are used for many positive things. Electrostatic charges are used to apply toner to paper in most modern copy machines and computer laser printers. It is also used in residential and commercial air cleaners to make dust stick to the filter. Like any other form of energy, when it is controlled it can be used in productive ways, but when it is uncontrolled, damage or destruction may result. | |
| What harm can ESD do? | |
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Around your house, not much. It is possible that if you get a shock
when touching your home computer, stereo,
or other electronic device that some damage may occur,
but the chances of this are remote. Most likely, your computer will reset
or your stereo will forget all the stations you've programmed into it. Most
companies design protection against ESD into their products.
Of course, if you have taken apart your computer or stereo, and have an ESD event when touching the internal components, you have a great risk of damaging or destroying the electronic circuitry. The protection designed into these products is no longer effective when you are in contact with the internal parts and components because the individual components usually have little or no ESD protection built into them. With this in mind, consider the factory where your computer or stereo was manufactured. The people and machines that work there are in constant contact with the internal workings and components of these products. ESD in such factories can be staggeringly expensive. Electrostatic discharges in manufacturing facilities can cause all kinds of defects and problems with the products assembled there. It can also damage sensitive equipment and machines used in the manufacturing process. ESD is a huge concern in factories that produce everything from computers and stereos, to electronic components. Even wheat flour and fertilizer. |
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| Wheat flour and fertilizer? | |
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Yes, for two reasons. One of the properties of an electrostatic charge is
its ability to attract dust and make it stick to things. In factories that
produce flour, fertilizer, and other powered products there is usually a
fair amount of dust flying around. An electrostatic charge on fixtures or
surfaces can easily cause them to be quickly coated with whatever powder or
dust is in the area.
The second reason is that the spark caused by an ESD event is incredibly hot, even though you can barely feel it when you touch that infamous doorknob. It is, after all, just a very tiny lightning bolt. Many powders, such as wheat flour, for example, are amazingly explosive when floating in the air as dust. Imagine a flour mill that is turning raw wheat into the flour used to make bread. The machinery is running and there is fine wheat dust floating through the air. A mill worker walks across the production floor and his polyester overalls generate an electrostatic charge. When he arrives at the machine, he reaches out to touch a control panel and there is an ESD event, a tiny spark jumps from his finger-tip to the control panel. This tiny spark ignites the dust in the air at his finger-tip, then this fire quickly travels through the dust suspended in the factory air, and within a fraction of a second a huge explosion leaves the factory on fire and in ruins. Disasters of this type are uncommon, but legendary. In this sort of environment, ESD controls do two things: First, they work to minimize the amount of dust suspended in the air and collected on surfaces, thus reducing the chance of an explosion. Second, they work to reduce or eliminate the possibility of the worker generating an electrostatic charge while going about his business. No spark, no boom. ESD is an issue in many other industries as well. Printing presses, factories that produce plastic wrap and other film products, hospital operating rooms, to name only a few, all have to deal with ESD and its potential to damage products, equipment, and possibly harm people. |
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| So, where does ESD come from? | |
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A complex physics lesson may be in order to explain how electrostatic
charges are generated, but for the purpose of this discussion, we'll use a
very simplified explanation.
The majority of electrostatic charges are caused by two different materials being rubbed together. When this happens, one of the materials tend to become positively charged, and the other tends to become negatively charged. You may think of these charges like the energy at the positive and negative connections of your car battery; as long as nothing lets the positive energy reach the negative energy, everything stays where it is, or "static." When you walk across the carpet, your shoes rub against the floor and generate a static charge which is stored in your body. The clothes tumbling around in your dryer rub against the drum and the other clothes, generating an electrostatic charge which is stored in the clothing itself. And when huge masses of air at different temperatures or pressures collide and rub against each other, massive charges are generated and stored in the clouds. Of course, different materials generate different amounts of charge. Without a doubt, the largest charges are generated when plastic is rubbed against some other material. Most clothing, carpeting, furniture, appliances, machines contain various types of plastic. Other materials that generate relatively large charges are hair, fur, rubber, and air. Charges can even be created from paper, cardboard, and water. One thing to remember is that an electrostatic charge can not be generated from materials which conduct electricity, such as sheet metal, aluminum foil, and copper, to name a few. |
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| How does this Electrostatic charge actually damage things? | |
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Though it's been explained how an electrostatic charge can cause a fire,
ESD- triggered fires and explosions are rare. Most often the damage is in
the form of destroyed or injured electronic components.
Picture a man welding a piece of metal. There are two cables that come from the welder; one is positive and one is negative. The workman attaches the negative cable to the metal he wants to weld, and the positive cable is attached to the welding rod in his handpiece. As he places the welding rod near the metal he wants to weld, the electrical charge leaps from the rod to the metal and creates an arc. This arc is hot enough to melt the metal, and the weld is made. Now imagine the inside of an electronic component, an integrated circuit, for example. There are all kinds of metal wires which allow the component to function. All the internal conductors of the component are near the same level of charge, so there can be no discharge or damage. However, when a human with a charge touches his finger to a lead of the component, his charge travels from his body into one of the wires leading to the inside of the component. When it gets near metal of a different charge, the electrostatic energy creates an arc, leaping from one component to the next. Now granted, this arc inside the integrated circuit is very small, but the metal parts in there are equally small. The arc in the component acts much as the one with the welder, melting or vaporizing some of the metal in the part. This can cause the metal parts in the component to 'short' together, or to be blown away completely. When an ESD-damaged component is dissected and the area of the ESD event photographed with an electron microscope, the damage to the inside of the component looks exactly like the effect of the welder on the metal that has been welded. However, not all ESD damage is this obvious. When an electronic component has been destroyed by an ESD event, it is fairly simple ( though expensive ) to isolate the bad part and replace it. A far greater problem occurs when a component has been damaged, but still functions. While the machine or product is still at the factory, it works perfectly. But, the ESD damage to the components inside may cause a failure days, weeks, or even months later. Many times a factory may not be aware that it has an ESD problem until they notice a high level of their products being returned when they originally worked fine. |
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| So how is ESD controlled? | |
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That depends on where the problem is. For your shocking doorknob, there are
materials that can be applied to the carpet that will stop the generation of
a charge. In a clothes dryer, you can add fabric softener sheets that will
apply a small amount of a chemical to your clothes to make them resist the
build-up of a charge.
Solving the ESD problem in a factory, however, is much more complicated. Factories are equipped with conductive floors that will not generate a charge. Employees wear special coats, and/or grounding straps on their shoes. When they are at a work bench, employees wear a grounding cord from their wrist to ground their bodies. Various types of ionizers are used to produce a gentle flow of ionized air to neutralize electrostatic charges on all kinds of materials. Millions of dollars are spent each year to battle ESD in manufacturing and other professional environments, but the potential for loss due to ESD caused damage is in the billions. |
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| Where can I learn more? | |
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To learn more about how to avoid, control, and deal with ESD in your
environment, the best source of information is the ESD Association. This
national nonprofit group, comprised of professionals and experts in this
field, was chartered to educate those with concerns regarding ESD. The
Association has a wide variety of documentation available, and holds
periodic educational meetings and symposia across the country.
There are local chapters of the association which can provide you access to experts in ESD who live and work in your own area. Most local chapters conduct regular educational meetings, and can allow you to network with people who have concerns just like yours. Another valuable source of information is the companies who manufacture equipment and materials to eliminate and control ESD. Though they will be obviously somewhat biased toward their own products, they can be good source of expertise for solving specific ESD issues in your facility. Talking to several vendors and as many experts as you can before making any purchase decisions is always wise. So this is ESD, in a nutshell. If you have further questions or concerns, contact the ESD Association by telephone at (315) 339-6937, or via E-mail at feedback@eosesd.org. (This ESD Primer written by John R. Schuch, Arizona Chapter) |
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