Tuesday, January 11, 2011
【 Weak current College 】 prevent electrostatic method 】
In order to effectively combat and prevent electrostatic discharge (ESD, electrostatic discharge), you must use the correct way to use the correct device. As a result of a series of powerful closed loop ESD prevention, monitoring and ion device, now you can put the ESD as a process control issues. Electrostatic discharge (ESD) is in the electronic Assembly and component damage in circuit board of a familiar and underestimated origins. It affects every manufacturer, no allowed size. Although many people think they are in ESD-safe environment, the production of the product, but in fact, ESD-related damage to continue to the world of electronics manufacturing industry billions of dollars each year. ESD? electrostatic discharge (ESD) is defined as, to or from the original already have static (fixed) charge (e or surplus) discharge (electron flow). Electric charge in two condition is stable: 1. When it "in" electrical insulation; electrical conductivity; but, such as objects, there is a metal with plastic handle with a screwdriver.
2. when it stay in insulated surface (e.g. plastic), cannot flow above. However, if the charge with a sufficiently high electrical insulation conductor (screwdriver), close to the contrary potential of integrated circuit (IC), charge "crossover", caused by electrostatic discharge (ESD). ESD to extremely high strength occurs very quickly, usually will generate enough heat to melt the internal circuit semiconductor chips, in electron micrograph outer appearance to blow out of small bullet holes, causing instant and irreversible damage. More seriously, this kind of harm only one tenth of the bad to cause in the final testing of the entire component failure. The other 90%, ESD damage caused only part of the demotion-means that the damaged components can be silently through the last test, but is shipped to the customer after the premature failure of the site. The result is the loss of reputation, for a manufacturer to correct any manufacturing defect where most pay. However, the main difficulties in ESD control is that it is not visible, but you can achieve the damage electronic components. Audible "ticking" a sound of discharge requires the accumulation of approximately 2000 volts rather larger charge and 3000 volts can feel small electric shock, 5000-Volt can see sparks. For example, such as complementary metal oxide semiconductor (CMOS, complementary metal oxide semiconductor) or electrical programmable read only memory (EPROM electricall read-only, programmable memory) these common elements, were only 250 v and 100 v ESD electric potential difference is destroyed, but more and more sensitive of modern components, including the Pentium processor, as long as 5 volt can be destroyed. The problem is caused by damage in a day of activities combined together. For example, from vinyl factory floor walk the floor surface and rubbing between shoes. The result is pure charge of objects, cumulative reach 3 to 2000 Volt charge, depending on local air humidity of equivalent. Even workers in the stage of the natural movement of the friction can produce 400 ~ 6000 volts. If the voiding or packing foam cartridge or bubble bag of PCB, the worker has processed insulator, the workers body surface accumulated net charge up to around 26000 volts. Therefore, as the main source of ESD damage, all entered the ESD protection zone (EPA, electrostatic protected area) of staff must be grounded to prevent any charge accumulation, and all the surface should be ground to keep everything the same electric potential, prevent ESD occurs. To prevent ESD's main product is a bowl of belt (wristband), kinky corduroy and dissipative surface or bedding-both of which must be properly grounded. Additional AIDS such as dissipative footwear or heel belt and suitable clothing, are designed to prevent personnel in ESD protection zone (EPA) cumulative and maintain when you move the net charge. During and after the Assembly, PCB should prevent from internal and surface transport in ESD. There are a number of circuit board packaging products can be used for this connection, including shielding bags, shipping boxes and removable trolley. Although the correct use of these devices will prevent 90 percent of ESD-related issues, but for the last 10% takes another kind of protection: ionization. And those who can produce the electrostatic charge of Assembly equipment and surfaces the most effective method is to use the ion generator (ionizer)-a device blowing out ionization air flow in the work area, and accumulated in the insulation of any charge. A common fallacy is that because the workstation with the bowl with the insulator in the region, such as polystyrene Cup or cardboard boxes, the charge will be safely dissipated. By definition, an insulator is not electrically conductive, except through ionization cannot discharge. If a charge of insulators remain in EPA, it will radiate an electrostatic field, raises net charge to any nearby object, thereby increasing the damage to the product of ESD. Although many manufacturers attempt to ban from the EPA, but the insulating material is very difficult to implement. Insulating material is daily life too much part-from the operator is located and comfortable foam pad, that some of the plastic cover. As a result of the use of ion generator, manufacturers can accept some insulation material in the EPA in fact. Because ion system continuously and may occur in any charge above insulator, so for any of the ESD programme, they are a reasonable investment. Standard electronic assembly equipment, ion occurs in two basic forms: * desktop (a single fan) * over the top of the device (in a single over the top of the unit, there is a series of fan) also have indoor ion generator, but it is mainly used for clean room environment. Select the required size of the protected area. Desktop ion generator will coverCover a single work surface, and over thetop-ion generator will cover two or three. Another advantage is the ion generator also prevent dust and electrostatic attached to product may give rise to an appearance of degraded. However, without the validity of the ESD equipment and monitoring of normal testing, then none of the protection scheme is perfect. First-class ESD control and ionization expert reports on the use of (and therefore useless) ESD equipment and do not know the manufacturer of its failure. In order to prevent this situation, in addition to the standard equipment of ESD, ESD vendors also provide constant monitor, if a performance is out of the automatic alarm. Monitor can be used as a stand-alone unit or in network connections. Also has automatic data acquisition of network software, real-time display of the relevant operator and workstation system performance. The Profiler can eliminate many daily tasks to simplify the ESD programme, such as ensuring proper measurements per day with a bowl, ion generator of balance and the correct maintenance, no damage to Earth point of table. Prevent ESD of the first step is to evaluate if neglected, how small details may result in irreparable damage. An effective scheme requires not only use effective ESD protection devices, and rigorous operational procedures to ensure that all factory ground personnel are ESD safe. Although many manufacturers use automatic bowls with tester, but often you can see the operator because the bowl with a too loose, or by testing or failure. Many operator tries to use the other hand simple hold Tester close to their wrists to the test. Nevertheless, the good news is that ESD is avoidable. Investment in the correct equipment and to improve safety procedures in time and money through the corresponding rate increases be reciprocated.