Monday, December 27, 2010
Weak current College】 【anti-static knowledge (2)】.
<br> <br> 11. q: testing anti-static wrist when there is no minimum requirements and minimum or more reasonable requirements? <br> A: in testing anti-static wrist without predetermined minimum requirements, but a very good experience is .: every time you wear an antistatic wrist or start another piece of work is to test it, test frequency depends on the full protection of ESD sensitive equipment, if the device is pretty expensive and a bit operator control, often monitor is necessary, but if .the device is not a particularly sensitive and relatively low-budget, regular testing is enough, in testing anti-static wrist when there are several things you should see: convinced anti-static wrist and the wrist close contact; conductive fiber or metal / conductive .material immediately skin; the metal tabs on the buttons are very suitable, coil-Mortice lock switch connector should properly tighten, banana plug Springs good elasticity, and banana plug plug hole in close contact with the other should view the thing is: the coils of .intermittent loss (usually at the end), dirt, oil and weld in the straps inside shell (which reduces belt conductivity), coil in the metal tabs on the press studs Shi 1 - 5 pounds of tension is secure. <br> <br .> 12. q: if taken all other ESD precautions to wear an antistatic wrist is still necessary? (that is, two ground (PIN), blouse, floor consumption materials, floor, etc.), and if so, why? <br .> A: If the operator in conductive floor wear two anti-static shoes without at the same time, lift the two heels, anti-static wrist would not, if the operator was wearing a blouse, but not with body or with electrical connections, .this blouse only a portion of the protection function, the accumulation of electric charges may not have the local release, common ground is: blouse with a wire rope system a press studs on the waist of a blouse, or use an antistatic wrist fastening to ESD .blouse internal cuffs. <br> <br> 13. q: our weekly to check ESD work surface to ensure it is properly grounded through 1M resistance. In ESD (hard) and earthing conductive face (soft) resistance reading instability in General? < .br> A: the power (ESD) and conducting work surface resistance readings between unstable due to electric current. If feet more grounded, you might have to current flow, which cause the ohmmeter reading errors. Other possible reasons include: instrument battery voltage is .too low, the instrument of AC power and is measured between the to loops, it is best to cut off the instrument power plugs in the ground, some digital instruments on their surrounding magnetic field or electric field is sensitive to the attention of the measurement power .distribution cables, EMI source, try to shield region repeated multiple times in order to ascertain whether the problem is excluded. <br> <br> 14. q: the answer to question 6: If the operator, ESD floorings received in the same potentials ., could not have happened ESD, my question is, what if the next floor "hard grounding" and operator to wear an antistatic wrist, and through 1M resistance grounding, so there are potentially dangerous, right? <br> Answer: not necessarily, .when the current through a resistance to it at both ends 1M has a potential difference, at this point you are correct. ESD control key is in charge of safety relief time eliminate surface or other conductors on the charge, if the relief is a few milliseconds ., then 0 - 0.01 seconds, 1M resistance ends there exists a potential difference, typical of body movements around 500ms, therefore, before you touch the sensitive devices, you have the time so potential 490ms attenuate to 0. <br> <br> 15 .. q: why ESD shielding bags can discharge electrostatic discharge procedure is?? anti-static bags and ESD shielding bags differ between? <br> ESD shielding bags: can discharge electrostatic surface, because the body bags (internal, external or both) of .the electrical conductivity and another conductor (ESD-floor) of the contact you want to make the shielding bags can bleed charge, you must have a electrical conductivity, and conductor (usually require grounding), anti static bag with antistatic properties, can not shielded ., conductive or MVB characteristics. All antistatic measures refers to the anti-static bag frictional charge will not exceed a certain voltage (typically 250V). Shielding bags in various parts of the bag should have a sheet of metal or conductive film, depending on the .devices you want to protect. Conductive, antistatic, shield and steam isolation material made of the bag to protect almost any sensitive devices, but may be protected. <br> <br> 16. q: we produce printed circuit board users need an anti .-static, some tire manufacturers provide conductive rubber or neoprene conductive made of tires, antistatic and conductive is one thing? <br> A: the meaning of the antistatic refers to when the wheels rolling on the ground, it does not produce higher voltage 250V .. Conductive and antistatic wheel can not, but as in ESD scroll will release on the floor. The ideal wheel is both conductive and antistatic properties, when exposed to a conductor, it will not produce excessive amounts of charge will not be stored charge. < .br> <br> 17. q: some people into their PC repair station purchase several "wireless" ESD anti-static wrist, it is said that it works and copier / laser printer of Corona. I think this may be part of a complex .system, but he said usage requirements did not mention the additional equipment, recently, when he opened the car door is electric shock (wearing a anti-static wrist) he convinced the anti-static wrist is useless, the elastic band with a small rectangular .block of plastic products, with a brass-coloured screws, screw cap exposed, I accidentally open a find 1M resistor connected to the second screw (and anti-static wrist connection) and a similar rubber soft "C" shaped Board (approximately 1mm thick ., formed after 2cm2, emptied), brass color screws up, it seems to be feasible? <br> Answer: not feasible, at ESD safe zone, this is not a viable ESD control device. These passive "wireless" anti-static wrist .has many limitations, if you as a result of frictional electrification up to 10kV and you wear an antistatic wrist, wireless needs in a few hours after theCan fall to 5kV (or even days, depending on the relative humidity of the environment), but never .less than 10V, most charge reduction is because your body's natural composite surface charge (this is your "wireless" anti-static wrist metal shell), as well as a certain relative humidity and conductivity of the air. (Report: hair cut to about .1 / 4 inch, you will get the same effect. In her hair brush on conductive adhesive, conductive hair once you end as in very high voltage at the tip of the corona discharge, make current flow of air or help to enhance the natural compound .. When your hair is very close to the ground - 0.1 1.5, regardless of any minimum 3kV voltage difference (because air dielectric strength) or the strengthening of the normal air conductivity, so that you are in the following few kV. <br> < .br> 18. q: what if a device placed in the box, the leader, so the leader have approximately several hundred ohms, end-to-end, end-to-shell of resistor and capacitor 10pF, if charging time up to several .minutes, the Office of the leader easily charge to 1kV (relatively). (Charging can be stored in the ground near the nozzle but incorrect drying of N2-Cabinet, or wearing nylon or shoes in a dry winter walking through a Daoist priest long carpeted .lobby) with grounding measures of user opens ESD bag, since charging to 1Kv leader through the other when it has been a leader of the discharge, causing damage to the discharge device. Increase in the potential of the oxide on device damage. All lead to .a short circuit or tying to ESD protection, right? <br> A: for your example, we assume that the device is in a box (the box is grounded and conductive) without ESD package, during transportation, box may charge separation, and .from external sensors. In it, the device can move anywhere, friction electric charge from a few volts to several kilovolt, depending on the material in contact with each other. When a grounding of the operator opens the box body, touch or close to the .vacant leader, may throw an ESD. If your device pins plug in conductive foam material or article with ESD bypass, device on the discharge of sensitivity and ESD damage is greatly reduced, when to use the bypass or conductive foam, depending on your question to .the protection of the device type, charge storage and shipping method. So be sure to consult the manufacturer of the correct precautions.? <br> <br> 19, asked; some with anti-static wrist of ESD Workbench can direct grounding, while .others need to be cited to ESD mat (diagonal), and then through a resistor to ground, which is correct? <br> Answer: both are not correct, since it depends directly grounded anti-static wrist and bench cushion of EMF, ESD .safe desk, grounding concept is that all conductors are in the same potential, allowing the potential difference between two conductors to a minimum. Because of the power and the Earth is always in control of the region, therefore is the most convenient connection points. If .an anti-static wrist and ESD cushions are connected to the same Earth point, they are the same, the potential is the correct installation. Anti-static ESD wrist first attached to the mat, and then through the desk pad, then from the desk .pad diagonal wear out, final grounding, this connection, the bed pad to have additional series resistance (resistance or capacitance), sometimes, the operator can and grounding of desktop device or on the desk pad on the ESD-sensitive equipment are at a different .electric potential. <br>.