Thursday, March 3, 2011
Weak current College】 【anti-static knowledge (8)】.
<br> <br> 1. why should enhance ESD protection awareness <br> 70 in this century, the former generation ago many static electricity problems are due to people not ESD consciousness, even now many people suspect that ESD will cause damage to electronic .products. This is because most ESD damage occurred in a person's feelings, because the human perception of electrostatic discharge voltage is approximately 3KV, and many electronic components in several hundred volts or even dozens of Volt is damaged, typically electronic devices are ESD damage without obvious .limits, the component installed on the PCB after testing, resulting in a lot of questions, the analysis is also very difficult. In particular, potential damage, namely the use of precision instruments is also difficult to measure its performance has obvious change, so too .are electronics engineers and designers who are suspected of ESD, but in recent experiments confirmed that the potential damage after a certain time, the reliability of electronic products decreased significantly. <br> 2. who should participate in ESD training? <br> Training who .? management training sector, management support, line management training, workers, technicians, etc. should be anti-static knowledge. The latest United States national standards and international standard electrostatic discharge Association (ANSI/ESDS20.20-1999) static training plans and .training requirements and certification for specialized lists section. ESD training focused on leadership, managers, line managers and engineering technology three people, but content and requirements vary. For leaders and managers, in addition to the requirement to understand static electricity safety management requirements, electrostatically .basics, anti-static work area requirements, electrostatically sensitive markers, etc. should also be aware of. For architects, engineers, maintenance technician, and so on will have comprehensive understanding. At present, China's various institutions apart from a few specialized graduate studies .with electrostatic, secondary school, college or University has opened a static course, only physical electricity describes some of the basic principles of electrostatics. But this basis, you will be able to learn the basics of electrostatic protection. <br> 3. electrostatic damage .to electronic products which forms? <br> The basic physical characteristics of static electricity to attract or exclusion, and the Earth has a potential difference, produces the discharge current. These three characteristics can influence of three components: <br> 1. electrostatic adsorption .dust, reducing component insulation resistance (shortened life expectancy). <br> 2. electrostatic discharge damage component damage cannot work (completely destroyed). <br> 3. electrostatic discharge electric or thermal currents, so that the components were injured (potential injury .). <br> 4. of electromagnetic fields generated by electrostatic discharge rate is very large (up to hundreds of volts / metres) spectrum is very wide (from dozens of megabytes to several gigabytes), for electronics production caused interference even damage (electromagnetic .interference) <br> If parts all damage, will be in production and quality control are aware but excluded, less damage if symbol minor, under the normal test see, in this case, the regular operation of processing multiple layers, even when in use ., only to find that not only checks are not easily destroyed, and their loss is difficult to predict. Consumes much human and financial to inventory all of the problems, but if you use is aware of the loss will fault may be huge. <br .> 4. electrostatic damage to electronic products which are the characteristics? <br> (1). the hidden <br> The human body cannot be directly perceived electrostatic unless electrostatic discharge electrostatic discharge occurred, but the human body does not necessarily have an electric .shock sensations, this is because the human perception of electrostatic discharge voltage 2-3KV, electrostatic has hidden. <br> (2). the potential <br> Some electronic components from electrostatic damage after the performance is not obvious, but many cumulative discharge .will give devices caused due to the risk. Therefore static damage to the device has the potential. <br> (3). the randomness <br> Electronic components what circumstances will suffer from electrostatic damage? so to speak, from one component to produce .onwards until it damaged before all the process are the threat of static electricity, static electricity generation has with the mobility aspect. Its damage also has with mobility. <br> (4). the complexity <br> Electrostatic discharge damage failure analysis work, .electronic products, fine, tiny structural characteristics and time consuming, laborious and expensive, requiring a higher technical and often require the use of scanning electron microscopy, high-precision instruments. Even so, some electrostatic damage phenomenon can and other causes of injury, the .distinction between mistake of electrostatic damage failure as other failure. This damage to the electrostatic discharge did not fully understand, often due to premature failure or failure of unknown circumstances, thereby unwittingly obscures the real cause of the failure. Therefore, static analysis on damage of .electronic components with complexity. <br> 5. how to control ESD? <br> From the preceding analysis that electrostatic separation due to contact with objects, or no contact with induction, etc, even the air around us is made of atoms, when .the air flow will also have static electricity, can say: at any time, anywhere, will generate static electricity. To completely eliminate anti-static almost impossible, but you can take a number of measures to control hazards not electrostatic in degree. <br .> 6. how to control the human body static electricity (human body static electricity protection)? <br> The human body is the most prevalent source of static electricity. For static electricity, the human body is a conductor, so you can take a .grounding on the human body. <br> (1). the use of anti-static floor / anti-static shoes / socks (static import from feet to the ground) <br> By anti-electrostatic of ground, mats, rugs, .personnel to wear an antistatic footwear, a combination of grounding. <br> (2). the wear an antistatic wrist strap and grounding (static import from hand to Earth) <br> By hand to discharge static electricity of the human body. It .consists of static elastic belt, campaign buttons, spring soft line. protection resistance and plugs or Chuck. Elastic belt for inner layer with antistatic yarns woven, knitted outer with ordinary yarn. <br> These two measures are practical and effective, depending on different .occasions, choose to use. <br> 7. anti-static shoes and wrist strap use human security issues <br> Only from the perspective of anti-static, humanTotal ground resistance as small as possible, but the minimum value subject to security restrictions ., the body must have a certain value of resistance, so that in case of a metal equipment or appliance and power frequency power shorted by the resistance to flow through the operation of the human body to limit the current. The minimum value should not be less .than 105 Ω, usually the current limiting resistor in wrist strap 1 M Ω, anti-static shoes minimum resistance should not be less than 105 Ω, maximum of 109 Ω. anti-static standards - in order to meet the anti-static equipment .industry in production, management, technical staff and the majority of users to learn and learn more about anti-static technical standards. We collect the more than 30 kinds of related anti-static standards, existing standard compilation of some of the information for your study .reference. <br> Anti-static standard compilation (a) electronic products anti-static discharge control manual <br> GJB/Z105-98 IC anti-static packaging tube <br> SJ/T10147-91 anti-static work area technical requirements .<br> GJB3007-97 electronics manufacturing anti-static system test method <br> SJ/T10694-1996 electronic products anti-static discharge control outline <br> GJB1649-93 electronic equipment manufacturing anti-static technical requirements <br> SJ/T10533 .-94 electronic components manufacturing anti-static technical requirements <br> SJ/T10630-1995 sealing flexible barrier materials and anti-static <br> GJB2605-1996 communication room electrostatic protection Handbook <br> YD/T754-95 electronic computer room construction and .acceptance <br> SJ/T30003-93 e design specifications for computer room <br> GB50174-93 electronic computer room design specification (provisions) <br> Anti-static standard compilation (2) anti-static floor general specifications <br> SJ ./ T10796-2001 anti-static General specification of the veneer. <br> SJ/T11236-2001 anti-static swing container specifications <br> SJ/T11277-2002 anti-static shoes, conductive shoes technical requirements <br> GB4385-1995 .anti-static overalls <br> GB12014-89 a helmet and experimental method <br> GB2811-2812-89 textile test methods for controlling static electricity <br> GB/T12703-91 rubber industry in the electrostatic safety procedures <br> GB4655- .84 ignition explosive safety regulation for manufacturing anti-static <br> WJ1912-90-antistatic accident general guidelines <br> GB12158-90 floor covering layer and assembled flooring electrostatic properties <br> SJ/T11159-98 computing station site security requirements <br .> GB9361-88 construction interior trim design fire protection standard <br> GB50222-95 aerospace system ground facilities grounding requirements <br> QJ1211-37 solid electrical insulation resistance, volume resistance coefficient and surface resistance coefficient test method <br> GB1410-89 shop .material critical flux of radiation heat source method <br> GB11785-89 anti-static floor construction and acceptance <br> SJ/T31469-2002 <br> Static electricity generation - static electricity is an objective of natural phenomena, resulting in many ways ., such as contacts, friction, streaming, and so on. the basic procedure can be summarized as: transfer charge → contact → → I layer forming ¡ .ú charge separation. <br> <br> Device or the human on the static up to tens of thousands of volts to hundreds of thousands of volts to normal operating conditions are often up to several hundreds to several kilovolt, human body because of its own .actions and contact with other objects - separation, friction or induction, and other factors, can take several kilovolt even tens of thousands of volts electrostatic. electrostatic be positive, negative charge in the local scope loses its balanced outcome. it is an electricity, retained .in the performance object, with high potential, low power, low-current and act only for short periods of features. <br> <br> Electrostatic control of the main measures are: static leakage and dissipation, electrostatic neutralization, electrostatic shielding and grounding ., humidity, etc. <br> <br> Electrostatic discharge damage caused by the breakdown of the components is the most common electronic industry, the most serious of static electricity, it is divided into hard breakdown and soft breakdown. hard breakdown is a one .-time causing components dielectric breakdown, burned or permanent failure; soft breakdown is the performance degradation caused by device or parameter index declined. <br> <br> Electrostatic sensitive components and printed circuit boards in the production process processes the delivery and storage, you .must use an antistatic material, component boxes, crates, pallets, etc. to prevent the harm caused by electrostatic accumulation as finished products for packaging-must be used against electrostatic shielding bags, bags, boxes, baskets, and so on, to avoid transport .process of electrostatic damage. <br> <br> Electronic products in the production process, its components, and component production often occurs with the device tools, and other contact, separation, friction generate static, you must use anti-static seat cushion, .trolley, maintenance kits, tools, work chairs and through appropriate grounding, so that the static rapid relief. <br> <br> Friction electrification and body static electricity is electronic, microelectronic industry's two major hazards, the harm is not static, harm in .electrostatic accumulation and resulting discharge electrostatic charge, live objects in the surrounding form electrostatic field, produces mechanical effects, effect and static induction effect, and therefore must be controlled. <br> <br> Due to the mechanical effects of static electricity, air flotation .of adsorption to particles will wait on the silicon wafer, seriously affecting the components of electronic products quality, therefore, to purify the space must take measures against static electricity-clean room walls, ceilings and floors should use anti-static not dust State materials, .the operator and job, utensils should also take a series of static electricity protection measures. <br> <br> To understand the production process static electrification, the discriminant in the production process to the effects of static electricity, as well as testing electrostatic protection .supplies, equipment, quality needs to measure static and related parameters. <br> <br> Measurement of static electricity, mainly on static electricityMaterial resistance, voltage, resistance, static gateway failure period, static electricity, static elimination eliminate electrical performance, cloth charge .surface density measuring. <br> <br> Electrostatic protection work produced a systematic project, any aspect of omissions or errors that will result in the failure of electrostatic protection work, you must always guard against everyone, everywhere. <br> <br> .<br> Static knowledge <br> <br> I. electrostatic phenomena and causes <br> <br> In the dry winter, before going to bed at night, turn off the lights in the dark and blended sweater (or wool pullover) ., will see a blinking light, also accompanied by a "brisk" sound. Sometimes when your finger touches the door handle, faucet, Chair and other metal objects or two when touched each had a shock; these are caused by what reason? <br .> <br> This phenomenon is due to frictional electrification caused by friction why electrification? original, substances with atom consists of positively charged nuclei and electrons in electronic form. Usually equal to the total number of positive and negative charges, so objects do not display .live abroad, in friction, part e ability from the shackles of the objects transferred to the binding capacity of objects, such as electronic objects lost due to lack of electronic and positive, the electronic objects because the extra e and negatively charged. So friction is .electrically and not since we created a charge, but electronic transfer, makes things happen on a number of positive and negative charges, etc. <br> <br> 2. electrostatic phenomena of hazards or prevent <br> <br> Concerned experts have .done testing: use the glass rod in the chemical fiber cloth, rub 20 on immediately with the instrument, the results show that the highest voltage can reach 1.5 million volts. Take a moment of pure polyester clothing produces 5 000-10 000 volt high voltage .. Static electricity can play a certain degree of damage, when the voltage to 2000 Volt, finger feel; more than 3000 volts is a spark, fingers and acupuncture-like pain; more than 70 Volt, people are shocked. <br> <br .> Walking on the carpet, and carpets with a lot of friction and, when he reached for the La metal door handles, the hand with metal handle (with induction charge) will produce a spark discharge between, lead to electric shock sensations. If in .factories and laboratories, the spark discharge may also be the resulting fire. Aircraft, and the air friction belt of electricity if the landing without Guide, local medical personnel closer to the fuselage, and the aircraft may be a strong spark discharge, serious people down .when possible. Designed to hold gasoline or diesel fuel, liquid fuel tank car in irrigation, transportation, oil and oil tank friction, impact and bring plenty of charge, if not timely Guide, accumulated to a certain extent, can produce sparks, burning liquid .fuel explosion. Surgical operation in hospitals, and also appeared on electrostatic sparks explosion the Aether. <br> <br> To prevent static damage to basic solution is the charge as soon as possible, avoid importing an accumulation of static electricity. The most simple .and reliable way is to take charge of the introduction of the Earth. Tank car is a drag on the ground by a chain to static import. The aircraft's wheel usually are equipped with a ground wire, and also useful conductive rubber wheel tire of doing, .landing them you can import the fuselage of static electricity. Inclusion in the carpet 0.05mm ~ 0.07mm of stainless steel wire conductive fibers, used to lead off electrostatic charge, etc. <br> <br> III. application of electrostatic phenomena <br .> <br> As with other physical phenomena, electrostatic phenomena can also be used. With the development of science and technology, the application of static electricity has a number. Mainly control live objects (particles). Such as electrostatic precipitator, try to keep .dust in the air, live in the power of dust is attracted to reach the electrode and collected; electrostatic copying both quickly and conveniently, books, information immediately copy on paper; electrostatic spray painting, including electrostatic flocking, electrostatic spraying, ink jet printing is .also an instance of using electrostatic; according to different particles in electrostatic field performance of different behavior, you can separate them, this is the electrostatic separation that can be used to seed selection, mineral processing and so on; in energy conversion, you can use .the static electric field as a medium for mechanical energy and power between the conversion. With the development of science and technology, electrostatic technology will have broader application. <br> <br> <br> <br> <br> <br>.