Weak current College】 【anti-static knowledge (3)】.

<br> <br> 21: when wearing anti-static shoes, shoe covers and foot skin close contact is important for you, there are also shoes can shoes and socks in between? <br> A: when wearing anti-static shoes operations .electronic instrument, not necessarily make the shoes direct contact with skin. Anti-static shoes, conductive connectors indirectly conductive floor () the receipt of the human body (skin). Typically, the conductive connectors are rooted in the insoles and socks. Skin after .socks electrical connections to the connector. Foot moisture makes socks conductive and feet (skin) and connectors provide a conductive path between. When first sandals, you can put 10 to 60 minutes to ensure there is enough moisture, thus allowing the socks with good electrical .conductivity, which makes the skin can be effectively and electrically conductive connectors are connected. <br> <br> 22: at present, my company has been used cardboard template checks the PCBA (manifold and table with chip) missing components. Cardboard in PCBA .top, produces static charge. According to the size of the component in the cardboard openings to check to see if any components are missing. My question is, can replace the Board of the proper materials? and how we can freely say? <br> .Answer: you can replace with dissipation, cardboard template as long as it can be suitable to receive your work surface to the same power. FRP is machinable, easily bored, maybe will meet your requirements. You should avoid using conductive properties of ultra strong materials ., as they can between components and conductive template results in ESD. <br> <br> 23: in accordance with the standard test film MIL-B-81705-B, I need surface resistance Tester and static decay time test table, how to .choose? <br> A: MIL-B-81705C, for I class shielding materials, electrostatic decay test procedures in FTM4046 (attenuation rate "in 2s =; on the surface resistance" X "test is carried out in accordance with ASTMD257, the .applicable scope is: inner surface impedance: 1 × 105 ≤ X ≤ 1 × 1012/square, outer surface impedance: 1 x 1012 X "/ sq. According to the standards for the measurement device available in instrument store to buy, including high- .speed oscilloscope, the Ann meter, the volt meter, high-precision megohm meter, high-voltage power supply, etc. For surface resistance: model 41262 and 41272 ASTMD257 requirements are met; 41272 also meet standard EIA-541 and ESDS11.11 requirements .. For electrostatic decay: we do not have to match with MIL-B-81705C. Model 42630 coincided with the requirements, ESDS3.1 can do to film some preliminary attenuation test, but based on standard test method. <br> <br> .24: "zero static" gun works? <br> Answer: the "zero static" gun work through mechanical compression (stretch) Crystal substances causing charge separation and connections in the Crystal at either end of the two conductors (apart from each other about .2mm) induction out very high potential (2kV-5kV) to work. Crystal with resilient (memory), it can compress to provide several times over and piezoelectric energy or electrostatic discharge, but its performance is very small. <br> <br> .25: antistatic packing material surface coating on the surface of what material the Activator? how does it work? <br> A: surface activator is a material surface activation of the medium, used to increase or reduce the surface tension so that the surface material .becomes wet or spreading on the surface. <br> <br> 26: we try to use less expensive ESD flooring tiles together to improve the combined work is not easy to use a wrist grounding of a place. Is there a paint can be used .in epoxy paint spraying of cement mats on the floor? trolleys are not easy, not easy to clean, and the price is quite high. We will change the layout of the workspace, so that the shape and size of the mat is not appropriate. .<br> A: Yes, some economic approach to solving your problems of protection of cement floor. Conductive paint is a single component floor coating, electrostatic charge managed to wear off. On electronic manufacturer, electronics assembly workshop and warehouse, static control flooring antistatic .conductive coating is very effective. A gallon of coatings can be sprayed 225 square feet, thickness 1-1.5 mils (1 mil = 1 / 1000 inch). Recommend spraying two layer, electrical grounding protection coatings for at least 60 square feet. <br .> <br> 27. q: use anti-static wrist set Tester testing anti-static Bowl set, instead of like megohm-Fluke85 ohmmeter, what are the benefits? <br> Answer: do not use an ohmmeter measured the following reasons: .first, the typical test voltage ohmmeter for 3V, this will get and set the typical anti-static wrist Tester (open-circuit voltage 9-30 v (depending on the manufacturer)) completely different readings. Lower test (open-circuit condition) .voltage will get higher resistance readings. Second, when the readings above or below the set value, the ohmmeter are not automatically prompted. Finally, and anti-static wrist tester for the electrical test on board and banana socket combination and structure of the leader contact .an ohmmeter are often different. To avoid this problem you can make a dedicated an ohmmeter fixture, but does not want to use as the dedicated fixture. <br> <br> 28: L type three layers of rubber mat what material is made of .? why to consider its lifespan if cushions in metal mesh is cut off, it still is? if you continue to have effect, why? <br> <br> A. the L type of material is a three-layer of white or blue .rubber gasket materials. In the area of welding and Assembly, has played a soft wear layer is very good, its top and bottom of the long service life and durability. This kind of rubber material for high wear resistance, corrosion resistance, easy cleaning and .maintenance. L type material is heat-resistant, even put it in the high temperature environment, it also will not produce toxic gases. Welding and welding flux will not damage its surface. L types of materials are also suitable for cleaning. Conductive layer is .not a metal mesh, if you cut each piece cushions, as long as the earth good, soIts performance is not the same. <br> <br> 29: I received some scene returns components (installed in the chip on the Board, when .the power-on test fails), the laboratory analysis was identified as ESD / EOS. This potential failure probability of? what are the symptoms before they occur? <br> Answer: EOS and ESD in some different physical processes, further stresses that ESD .damage can be decomposed into one-time and longer potential damage, depending on the energy of the ESD and the role of the material. On bipolar devices study: 80% of poor-quality amplifier as EOS or high energy ESD damage, another 20% .of the operational amplifier also showed a small reduction in performance (due to potential ESD damage). <br> 30: in the PC is used in the site, I noticed that when using the machine wear an antistatic wrist, even if the machine is .placed in carton, and plug in a outlet plug can also let the electrostatic discharge. This is true? <br> A: Yes, will you and large pieces of metal plates or other large conductor, will keep you connected to the surface of electrostatic .charge distribution, so that you and conductor at the same potential. In some occasions, you can do to make the power away from the workspace. It is recommended that you use a separate ground wire to the machine to Earth point of grounding to ensure that .the machines and the human body with proper electrical connections to be able to contact the outside world into workspace objects all parts maintain zero Volt EMF. <br> <br> <br>.