 To counter the adverse effects of electrostatic discharge (ESD), the electronics industry spends nearly 10 billion dollars a year. The textile, medical, and material processing industries also spend billions annually to reduce the destructive results that static electricity can produce. The definition of static electricity states that it is the accumulation of an electrical charge on an insulated body. A different definition of this effect explains it this way: when two non-conductive materials are rubbed together to create friction, an imbalance occurs between the atoms of both materials (Figure 1, click to enlarge). This imbalance leaves one material lacking electrons (positively charged) and the other material with an excess of electrons (negatively charged). This resting potential can be low or relatively high depending on the number of atoms involved. Low potentials can cause such problems as IC damage, dust accumulation, and small shocks as they equalize. High potentials can cause high-magnitude sparking as their resting state becomes kinetic. This kind of ESD can be both dangerous and costly. In the electronics field, the lower magnitude potentials are more common and easier to deal with. Research for practical methods to neutralize or remove static electricity is a never-ending effort, however the range of products currently available to the technician to reduce ESD is surprising. Grounding wrist straps and anti-static work surfaces have been around awhile. Many new products have recently been developed that may give technicians some additional protection.
Some new products for ESD
A fairly new addition to the electrostatics market is an ionizing unit that clips to your belt to dissipate negative and positive charges. It generally runs on a 9V battery and is about the size of a standard pager, so it tends not to get in the way of your work. Static neutralization is its main working principle. Anti-static gloves that use corona discharge technology are another new product on the market. The ionizing fibers of the gloves act as sponges to absorb stray static electricity. These work well for assembly purposes and volume handling of PC boards. Another new area that many corporations are looking into is ESD-resistant furniture. Complete work tables, stools, and benches offer static protection by means of grounding, induction, and neutralization. Many of these products simply use materials that do not attract static electricity. Some of the materials that offer anti-static qualities are: ABS, Acetyl, Acrylics, Polycarbonates, Polyethylenes, and Polypropylenes.
Electronic static bags used to ship and store sensitive components utilize some of these materials in their construction (Figure 2, click to enlarge). The polyester outer layer and polyethylene inner layer offer a resistance of about 1012Ω/in2. The metal sandwich layer is less than 2Ω/in2. This aluminum layer also guards against EMI (electromagnetic interference). Metals in themselves can offer anti-static qualities. Conductive materials, by their nature, are not subject to static build-up or discharges.
Electrostatic charges on the body
In electronics repair, the main issue of electrostatics seems to be the potential that the person themselves pick up or carry with them. Although you may not be generating a static charge, any object you handle may have a potential that will be transferred to you. A simple piece of plastic may have hundreds of volts of static charge that will transfer to you the second you pick it up. You probably will not feel the transfer, especially if you're wearing rubber soled shoes. This type of situation only isolates the charge until you come in contact with an adequate discharge source; possibly a sensitive PC board. Many technicians say they have never taken any static precautions and have never had a problem. It really depends on many variables why this is true for some. If the relative humidity in the work place is high, this will decrease static activity. Tool coverings, material handling, grounding sources, clothing, and numerous other factors contribute to either high or low static potentials in the work place. Since static electricity has three different states: generation, accumulation, and finally, discharge, it makes sense that control devices are made for each of these situations. Preventive devices deal with anti-generation and accumulation and active devices deal mainly with dissipation of the charge.
Static-prevention products
An explanation of some preventive devices will illustrate some of their positive characteristics. An aerosol static guard that is sprayed on a circuit board is a good example of a preventive device. Generally, this spray may also be used on work surfaces and can be an effective deterrent for weeks after treatment. A humidifier in the work area may reduce static charges, so this is also a good preventive measure. Anti-static floor mats fit into this category, but they can also be considered active devices because of their dissipating qualities. Cleaning supplies, such as copper gauze, anti-static chemicals, and ionizing vacuum cleaners, are some others that fit into both the preventive and active product categories. Anything that stops the generation and accumulation of static electricity is classified as a preventive device. Active anti-static devices include products such as; compressed air ionizers (which include both blowers and air gun types), conductive heel straps, ionizing air filters, and clip-on belt ionizers. Anytime a constant activity is needed to dissipate a charge; the device will be an active one. Grounding is a major factor in all anti-static systems. A potential cannot accumulate if it already has a low-resistance path to the earth. Workbenches, test equipment, and even the repair material itself should have proper grounding. It not only helps prevent circuit damage due to ESD; it also leads dangerous high-voltage faults safely to ground. A static detector is another device that provides an added level of safety. Charged material can be located by waving a detection wand about an inch away from suspected areas. There are meters on the market that read voltages up to and beyond a 30,000V potential charge.
Each solution to the problem is unique
Different working environments require different protection. If electrostatic discharges are a problem in your work area, it may be a simple task to find out why they are happening and what you might be able to do to solve them. If discharges occur after moving about the room, maybe anti-static mats and heel straps will solve this problem. If your equipment seems to be collecting too many static charges, possibly your grounding system needs checking. Many ESD companies will work with you to find a solution that is both affordable and effective.
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