Weak current College】 【anti-static knowledge (1)】.

<br> <br> 1. q: why some ESD grounding wire with impedance and some not? <br> A: the purpose of the ESD grounding wire is a conductive surface to connect to and the power and potential of local, "hard ."is used without additional resistance of the ground directly connected to the power to the ground; and the common point of contact resistance between the basic 0 Ω." Soft "is an internal series resistance of the ground, a typical value for this design 1M .aims to limit when the operator exposure in 110V and maximum 250V environment possible harm current. ESD Association ANEOS/ESDS6.1 - 1991 recommended the use of "hard" mode enables ESD floor or floor mat grounding. <br> <br> 2. .q: I often wear a anti-static shoes, but often told to put his feet, and why? <br> A: anti-static shoes only dressed correctly and with conductive floor or consumption and linked. Walking is the friction of a great .example. If you correctly use anti-static shoes, and in close connection with ESD floor, then you charge leak into the ground. Therefore, you and a network between the voltage is the same, but you have a lift to wear anti-static .shoes feet, and you will be charged again, either from your dress sense, either because the friction and lift foot friction electric. If you have two anti-static shoes, you will further significantly reduce more than few v much higher chance of net charge .(typical value is 2000-5000V) because you are in a prolonged ground state, it is recommended that you close to the moving body, be sure to wear a pair of anti-static shoes. <br> <br> 3. q: .will need a connection between the machine and to 1M resistance? <br> Answer: not necessary. Refer to the manufacturer in the machine or equipment grounding requirements, is used to protect 1M resistance of the human body, refer to the following questions. Margin .: will all the workstation near the ESD-sensitive isolated grounding conductors are good. You can make the unexpected field or charge accumulation. <br> <br> 4. q: 1M resistance in the semiconductor assembly process do? <br> A: .assuming 1: we are talking of ESD control issues; assuming 2: the human body and the semiconductor and semiconductor device with contact, anti-static wrist, anti-static shoes, zipper, ground, etc can be found 1M series resistance, its role .is limited to the human body of current, the protection of human security. 1M resistance of qualified requirements is: valid values in the 250V AC, the current is limited to 250 μA, happens to be the majority perception levels (nervous system occurs reflex threshold .). Current at break table and different physical perception depends on the body size, weight, water content, skin conditions, etc. <br> <br> 5. q: internal shipping boxes containing circuit boards are required to cover the lid? how .these shipping boxes work? <br> A: the General need to cover the lid, correctly installed in shipping boxes on the lid on the circuit board therein provided enough strong shielding, the shipping container can not only provide a general purpose mechanical integrity, but .also to provide for internal ESD security. To take off the lid, any stray electric field can cause numerous independent conductor on the Board's charge, these induced charge is ESD generation source. Stray electric potential source is a lot of people, clothing, not grounded .two-wheel vehicle, monitors, furniture, compartments, any non-grounding conductor, either an insulator, electromagnetic interference, etc. In the open ESD packing box of circuit boards, in Earth car transportation will pass (or exposure to) a few with .power (electric), also makes the internal devices. <br> <br> 6. q: If feet and anti-static wrist even together, they need to Earth? <br> A: no, just the handle of the device shall .pluck plugs and electrical connections to ESD, as long as conductive parts (superficial skin, ESD mat, equipment enclosures, operational part, etc.) is, potential, ESD (bleed charge) will not occur, the Earth is very suitable for voltage reference ., if you verify that all conductive parts are connected to the ground, then ensure these conductive parts are in the same potentials, once the two conductors of electric potential difference exists between the leads generated ESD charge relief. <br> <br> 7. .ask; ambient air temperature is relative to how it affects the ESD? <br> A: the relative humidity (RH) on surface accumulation of charge direct impact of the performance. The higher the relative humidity, parts storage charge time will be short, .surface charge decrease (because of the relative humidity increases) the transmission via composite or, when the relative humidity increases, the air conductivity. But even in 100% relative humidity, the charge-discharge rate of increase is not a substitute for proper ESD control .operation rules. <br> <br> 8. q: what percentage of relative temperature control requirements to a specific value? if so, how can you determine this value? <br> A: air gradually drying (relative percentage decrease of temperature) ., generate static abilities is to identify and clear. Relative humidity 10% (very dry air), walking on the carpet, it can produce 35kV charge, but when the relative humidity of 55% will be dropped to 7.5kV. The work environment the .best range of relative humidity in 25% -50%. Some clean areas generally require relative humidity at 50%, due to corrosion and humidity less sensitive devices, other environmental needs low relative humidity. In best humidity range testing equipment and ESD suppression products, .some ESD suppressor products is concerned with the humidity. <br> <br> 9. q: strong magnetic fields (such as magnet) causes ESD? magnetic field and there are some what ESD contact? <br> Answer: as long as the .magnetic field source and objects are static, it will not be due to the strong magnetic field produced ESD. Magnetic field fluctuation or object moves across the field, the induction currents (if the object is conducting). Fully exposed to the pulsating magnetic field of .isolated conductor, will accumulate enough charge ESD problems, caused by magnetic field may also be obtained from the electromagnetic noise (EMI), if not properly shielded, you will sense the orphaned on the conductorShould current (charge), some EMI source is a PC ., ESD, transformers, fluorescent lights, etc., in the General work environment, these are likely to be less important source of harassment. <br> <br> 10. q: our electronic assembly workshop with ESD conductive floor, use ESD dedicated .grounding shoelaces, requires that each operator must wear steel toe safety shoes. If you do not wear special shoes ESD grounding, not through grounding shoelaces detector. Our special ESD grounding shoelaces used # 2048 model of plastic, used a material made of shoes, a .106-108 of impedance, reduces static electricity, should I buy a new device or a new pair of shoes or something else? <br> A: first, make sure that your device has recently been calibrated, if not then you need to calibrate .. Test standard and grounding of shoe laces, standard ESDS9.1 - 1995, on the impedance of the 109 following 100V impedance instrument used, most grounded shoelaces Tester use 6-open-circuit voltage of 12V, substantially lower than on the shoes of 100V .voltage. If the shoe itself conductive material under high pressure, or buy a higher voltage tester or reconsider the electrostatic discharge control. Some foot ground (heel) Tester is being calibrated at the factory in 750k - 100M, others only 10M, some of the .new instrument, providing approximately 20-22V-circuit voltage, may also have some effect, in addition, there are some ESD shoes, used to detect the grounding tester, the foot because of their low voltage (on a consumption interval), you can .very easily. <br> <br> <br>.