tag:blogger.com,1999:blog-100531222024-03-13T17:20:29.338+00:00Static Consultants NotebookThoughts on static electricity and ESD related issues from a leading consultantStatic Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.comBlogger51125tag:blogger.com,1999:blog-10053122.post-52757430000965770172012-09-21T10:16:00.001+01:002012-09-21T10:22:50.703+01:00When components in non-ESD packaging are assembled with ESDS in an EPA used in the <i> Users of electrononic components do not want static-generating materials in their EPAs, but suppliers of non-ESDS often use non-ESD packaging. Is there</i><i> any packaging guidance for non-ESDS?</i><br />
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Users of ESD susceptible components will not want to bring ordinary packaging materials into an EPA workstation where ESDS are handled. There are no requirements in the standards for suppliers of non-ESDS components to supply their product in non static generating packaging. So, many will use ordinary plastics in their packaging which could compromise ESD safety and compliance if brought onto an EPA workstation. It is for the user to decide how to handle this, e.g. by removing non-compliant packaging before bringing the component into the EPA workstation. <br />
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This is one reason why the modern standards say that non-essential insulators must not be present on a workstation where ESDS are handled, rather than in the EPA in general. Some people write their ESD control program to allow items in non-ESD packaging to a bench conveniently placed near the one where they handle ESDS, but not near enough to cause ESD risk from the plastic packaging. The packaging can then be removed from the component on a workstation where ESDS are NOT handled and the component transferred to the workstation where they are assembled with ESDS. This approach relies on a high level of understanding by operators to prevent stray packaging arriving on the workstation where ESDS are handled and other ESD risks. <br />
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Others write their ESD program to prohibit non-essential insulators from the EPA, and repackage the non-ESDS into ESD packaging before they are brought into the EPA. <br />
<br />Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-90334532419739904432012-08-21T11:00:00.001+01:002012-08-21T11:00:12.838+01:00Is my core conductive garment suitable for use in electronics manufacture?<i>We are looking for a new ESD garment/jacket. The recent garment we tested reduces in Rp-p with washing, but passed the charge decay test. The supplier stated that this fabric is woven with a core conductive fibre, so therefore the charge decay is the valid test (referring to BS EN 1149-3). BS EN 61340-5-1:2007 only specifies that the garment should pass Rp-p < 1x10<sup>12</sup> ohms. So if the garment passes the charge decay test but fails the resistance test where do we stand?</i><br />
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EN1149-3 is a standard for evaluating garments for use in flammable atmosphere areas, not electronics manufacture. The evaluation criteria are quite different. <br />
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The only test currently recognised by 61340-5-1 is the point to point resistance test for which it gives requirements. If it fails the test, it fails the test. <br />
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If you want to accept garments on a different basis than this test, and still comply with 61340-5-1, then you would need to devise some sort of technical evaluation of the garment performance to convince yourself it does the job you intend it to do. You should then document your technical evaluation, including your qualification test methods and results, as a tailoring exercise in the ESD Program Plan. You should of course also instigate a program of suitable compliance verification tests in your Compliance Verification Plan. <br />
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Core conductive fabrics often fail the resistance test by the nature of their construction. Whilst that does not necessarily mean they are unsuitable for use in electronics manufacture, it does mean we have no agreed method of demonstrating whether they are suitable or not. Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-45212241608144134672011-06-03T12:30:00.000+01:002011-06-03T12:30:29.915+01:00Benchmarking ESD best practice across industries<div>I work across a range of industries and topics covering ESD in electronics manufacture, electrostatic ignition hazards in industrial processes and occasionally explosives handling. I think that static control has developed further in the electronics industry than in the other areas, partly because the sensitivity of components to ESD is often much greater than the sensitivity of (for example) flammable gases or dusts to ignition by ESD. The 100pF capacitor in a 100V HBM test contains only 0.5 uJ of energy, and most of that energy is not delivered to the device under test. In contrast 20uJ is required to ignite hydrogen-air mixture (which is quite sensitive) and 200uJ to ignite most hydrocarbon-air mixtures. So, for handling modern electronic components we have to control static electricity in some ways more carefully than in industrial processes. </div><div>One similarity that runs between the 3 areas is that human body ESD (from charged personnel) is very important in manual processes. So, grounding of personnel is a key ESD prevention measure. </div><div>One big difference is in the degree of standardisation of ESD control. In the electronics industry we have the option of compliance with one of the ESD control standards such as ESD S20:20 or IEC 61340-5-1. Standards like this do not exist for static control in industrial flammable atmosphere areas. This is deliberate on the part of the experts who write standards as industrial processes can be very different and what is a high risk in one process can be acceptable in another depending on the exact circumstances. It would be very difficult to write standards that do not burdon industry with inappropriate control measures. In contrast, in explosives handling there are well defined key control measures that are enshrined in documents such as the UK Manufacturing and storage of explosives regulations. These requirements depend on the sensitivity of the explosives handled. </div><div>In the electronics industry, we have highly automated manufacture of systems in which charged device ESD is a significant source of ESD damage. This occurs when a device itself charges to a high voltage and is the source of ESD. This type of risk is absent from industrial flammable atmosphere areas and explosives handling. However isolated conductors such as metal parts can become charged and be a significant risk in all three fields. </div><div> The basis of static control is similar in all three fields. In manual operations, the voltage built up on personnel is controlled by grounding them. In all 3 industry areas footwear and flooring are used extensively for this. Wrist straps are used especially for grounding seated personnel in the electronics industry. </div><div> The use of insulating materials is carefully controlled in all three industry areas. In electronics this is mainly due to their ability to build up charge and give high electrostatic fields which can induce high voltages on nearby conductors. In the flammable atmosphere areas, and in explosives handling, it is also because brush discharges from insulators can ignite sensitive materials. </div><div> In all three industry areas it is very important to avoid having isolated conductors which can charge to high voltages and provide a source of damaging or incendive ESD. So, all conductors (especially metal items) are normally grounded where possible unless risk evaluation shows this to be unnecessary.</div><div> Modern electronics ESD standards have a requirement that the user write an ESD Control Program Plan, and ESD Training Plan and a Compliance Verification Plan documenting what the organisation is doing for ESD control. This documentation imposes a rigour on the ESD Control Program which is very beneficial. Sadly this approach is often lacking in the other industry areas, although less so in explosives handling. </div><div> So in conclusion, I believe the electronics industry leads the way in ESD control compared to other industries. This is partly through necessity due to the particular sensitivity of the devices handled, and partly because the industry lends itself to standardised ESD control measures and approaches.</div>Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-31620556490269853692011-06-03T12:16:00.000+01:002011-06-03T12:16:51.847+01:00Will conformal coating help prevent ESD?Yes and no. It will help prevent direct ESD to the components which are protected by the coating. However the coating itself can become charged and can induce high voltages on the pcb. This can give ESD when a connector pin or other exposed conductive part makes contact with another conductor. The energy in this type of ESD is quite high and is a risk to any component through which the ESD current may flow on the pcb. Modules in plastic enclosures can also suffer this risk. Also, the conformal coating gives no protection against external electrostatic fields which can have the same effect as charge on the coating. <br />
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Of course the overall risk of damage occurring is difficult to predict.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com3tag:blogger.com,1999:blog-10053122.post-4809734123676795962010-09-28T11:54:00.000+01:002010-09-28T11:54:23.856+01:00Why use an ESD seat?<i>I have read the IEC 61340-5-1/2 and we are building a new production area. If everyone who works with ESDS, uses wrist straps while seated, do they need to sit on an ESD chair? (The floor, the tables, the garments are ESD protected)<br />
If they connected to ground via wrist strap, why should I connect them to ground via chair?</i> <br />
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Firstly, the ESD chair is not for grounding personnel. The seat may have quite high resistance to ground, up to 10^10 ohms. For grounding personnel, we need a much lower resistance <35 Mohms and this cannot be achieved by contact with many seats. Contact between the seat and body is unreliable because there are layers of clothing in between!<br />
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The purpose of having an ESD seat is so that the material of the seat does not become charged and cause an electrostatic field and ESD risk.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com6tag:blogger.com,1999:blog-10053122.post-36363787640729767742010-06-15T12:32:00.000+01:002010-06-15T12:32:29.734+01:00What ESD packaging should I use?<i>We need to move pcbs with ESD sensitive components on from an EPA to another EPA passing through a non-EPA area. What is the recommend method for tranporting these devices to minimise ESD damage? We don't want to use individual shielding bags. </i><br />
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There is no single recommended method or packaging type. However I reccommend the packaging used has the following characteristics:<br />
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1) no part of the packaging should be an exposed insulating materila which could charge up and cause ESD risk in an EPA.<br />
2) the material in contact with the ESD sensitive parts should be dissipative<br />
3) there should be a surrounding conductive material to form an electrostatic field shield<br />
4) an air gap, dissipative material or other barrier should prevent ESD currents being conducted from the outside of the packaging to the ESD sensitive parts. <br />
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A shielding bag has all these characteristics, but it is quite possible to design a larger packaging system to contain many items that achieves the same using different packaging materials.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-73291130545559245172009-10-08T15:31:00.002+01:002009-12-08T18:15:54.957+00:00Why would a capacitor be ESD sensitive?<span style="font-style:italic;">Why do some capacitors have a dependency on capacitor size vs ESD?</span><br />
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There is good reason for a capacitor to be ESD sensitive. If you push enough charge into it, you will eventually exceed the dielectric strength and breakdown voltage, and the insulation will break down. So the ESD susceptibility is dependent on the capacitance and breakdown voltage. A high capacitance high breakdown voltage device will have low ESD susceptibility, but a low capacitance low voltage capacitor could be easily damaged by ESD.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com3tag:blogger.com,1999:blog-10053122.post-13770639796994823652009-03-09T16:57:00.000+00:002009-03-09T17:02:33.530+00:00<span style="font-style:italic;">If I was within 2 inches of a printed circuit board with no ESD protection would I discharge any voltage to the pcb causing any partial damage? The reason I ask is our design engineer tells us 2 inches is a safe distance, but according to an ESD Trainer on a course I have recently done damage can occur from as far as 12 inches away.</span><br /><br /><br />This is a tricky question and the answer depends on various factors, but I will try to answer simply. I will only consider the risks due to your body being possibly at high voltage because it is not grounded. These are usually the most important and damaging ESD risks in manual handling of PCBs, and are completely removed if your body is grounded via wrist strap or ESD footwear and flooring. So,it is most important for all personnel handling PCBs to be grounded at all times. There are other ESD risks which I will not go into, if the PCB itself is at high voltage. <br /><br />There are two types of ESD risk in this situation. Firstly, there could be a direct ESD from your body to the PCB if you get sufficiently close so that a spark jumps from your body to the PCB. At normal body voltages this can only happen if you get within a few mm of the PCB, as it takes a few thousand volts to jump each mm of air gap. If you are not getting closer than 50 mm (2 inches) then this is unlikely to happen. <br /><br />The second risk happens because if your body is at high voltage it is surrounded by an invisible electrostatic field. Any isolated (non-grounded) conductor, including PCB tracks or components, which come within this field have a voltage induced on them. If the conductor becomes grounded at this point, ESD will occur and could if great enough, be quite damaging. (There is also another damage mechanism which could happen which would not require the grounding of the PCB, but it is unusual and I won't go into it here.) <br /><br />The voltage that is induced on the conductor increases as the conductor gets closer to the high voltage source. Above a certain level, it gets to a point where any ESD arising could be damaging to the PCB. However it is very difficult to predict at what level the damage threshold would be passed. This would depend on the voltage on your body and other factors, as well as the closeness of your body to the PCB and the sensitivity of the components you handle. <br /><br />So, we could say that the "safe distance" is a matter of guesswork and also influenced by your level of concern over possible damage and tolerance of the risk of ESD damage. If your component ESD susceptibility is low and you aren't too worried by the consequences of a possible ESD, you might judge that a closer distance is safe. If the component susceptibility is high and you have an expensive high reliability product you might judge that a greater separation is necessary for safety. In either case it is just based on guesswork unless backed by a considerable research program involving subjecting your PCBs to field induced ESD.<br /><br />So, you could consider that both your Engineer or your ESD course Trainer could be right, we just don't know. The Trainer is being more careful and risk averse than the Engineer. But neither of them know for sure, and I can't advise you either without a considerable research program involving subjecting your PCBs to field induced ESD. <br /><br />One thing I can say is that the risk is easily removed completely if you ground your body through a wrist strap or ESD footwear and flooring. So why not just ground yourself and remove the concern?Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com2tag:blogger.com,1999:blog-10053122.post-89967164952300052522009-01-19T14:49:00.000+00:002009-01-19T14:52:29.938+00:00General guidelines for high voltage area?<span style="font-style:italic;">What is general guide lines for EPA area, where live AC and DC equipment is used?</span><br /><br /><br />If personnel are handling ESD sensitive devices, the general guidelines are the same as for any other ESD Protected Area. See my <a href="http://www.electrostatics.net/ESD_Guide/welcome.htm">ESD Guide</a>.<br /><br />However where high voltages are present there may be a safety concern about earthing the body either through a wrist strap or through conductive footwear and flooring. In this case the risks must be evaluated and if necessary, the ESD precautions modified to reduce safety risks to an acceptable level. <br /><br />Usually, wrist straps and footwear for ESD use have a minimum of 750k ohm resistance, which is designed to give some protction for up to 250Vac systems. For higher voltages higher resistance (pro rata) can be used if desired. If the risk of shock is unnacceptabe it may be necessary to avoid grounding personnel and use other ESD protection methods. There is no general advice on this as far as I am aware.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com3tag:blogger.com,1999:blog-10053122.post-22421734970669762532009-01-19T12:22:00.000+00:002009-01-19T12:24:53.811+00:00ESD damage to motherboard?<span style="font-style:italic;">I have a computer motherboard and I plugged it in a week ago and plugged it back in 2 days ago and now I got power but no video, no keyboard/ mouse, or hard drive activity and I'm told it is do to static build up how do I get rid of it?</span><br /><br />If you have already damaged a board through electrostatic discharge (ESD) the damage can be permanent. This is why it is important to prevent static building up on your body while you are hndling the components in the first place. <br /><br />The usual method is to wear an ESD wrist strap. When replacing a board, disconnect the computer from the mains and connect your wrist strap cord to the computer chassis. Don't take the board out of its packaging until you are ready to plug it in, and don't place it on any ordinary surface. Whilst attached to the computer via the wrist band, take the board out of its packaging and plug it in. Do not touch any of the ESD sensitive parts of the computer unless you are "grounded" to it via the wrist strap.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-81239336134419462572008-04-02T11:59:00.000+01:002008-04-02T12:01:51.469+01:00Is a foot strap adequate?<span style="font-style:italic;">When my floor is dissipative do I need to utilize a foot strap and a wrist strap, or is a foot strap adequate?</span><br /><br />If you are handling ESD sensitive electronic components within an ESD Protected Area , then you body needs to be grounded with a resistance to ground less than 35 M ohms. If seated, this must be achieved using a wrist strap because you may take your feet off the floor, and grounding contact would then be broken. <br /><br />If handling ESD sensitive components while standing, grounding can be achieved through footwear and flooring if the floor and footwear resistance is low enough. To achieve this, you may need a floor which has resistance-to-ground less than 35 Mohm as well as footwear which is less than 35 M ohm. You should wear two foot straps - one on each foot. If the resistance from body to ground when grounded by footwear/flooring is not < 35 Mohm, it may be advisable to wear a wrist strap to achieve < 35 Mohm.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com2tag:blogger.com,1999:blog-10053122.post-24619525619322487262008-04-02T09:36:00.000+01:002008-04-02T09:41:30.178+01:00ESD packaging<span style="font-style:italic;">We are receiving Diodes, Resistors, etc. from our warehouse in non-ESD bags. I was taught that these should be in ESD packaging. Can you send me information on this?</span><br /><br />Diodes are semiconductor devices and are normally packaged in ESD protective packaging. Some diodes are quite robust and others may be very ESD sensitive, and so the ESD risk depends on the type of diode.<br /><br />Usually the main problem with putting resistors and other non-ESD sensitive components in non-ESD packaging is that the non-ESD packaging is then taken into an ESD Protected Area. The non-ESD packaging is an ESD generator and can become an ESD risk to any ESD sensitive components that are present. So, if packaging is required for any components taken into the EPA, it should normally be ESD packaging.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-68024578053946409262007-12-20T11:21:00.000+00:002007-12-20T11:24:13.031+00:00ESD susceptibility of PCB (PWB)<span style="font-style:italic;">Does ESD effect components on PCBs (PWBs)? If so, what is the sensitivity of the PCB?</span><br /><br />The first part is easy - yes, ESD sensitive components on a PWB can be damaged by ESD. <br /><br />The second part is not easy. The answer can depend on the ESD sensitivity of the devices on the board, and the board design. The components on the board may be less susceptible or even more susceptible to ESD damage, and it is impossible to predict. Many experts say we should consider the ESD susceptibility of the board is the same as the most sensitive component on the board.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-75962321748499085822007-11-09T15:07:00.000+00:002007-11-09T15:14:15.292+00:00Is it necessary to wear ESD foot straps on both feet?<span style="font-style:italic;">Is it necessary to wear ESD foot straps on both feet? Where is this defined in the standards?</span><br /><br />Most standards do not explicitly tell you to wear foot straps on both feet. However in order to control the body voltage reliably and prevent ESD risk, the body must be continuously grounded and the resistance from the body to ground must not be greater than 35 Mohm. <br /><br />If you wear only one footstrap, your body is not grounded when that strap loses contact with the floor and the body voltage can quickly rise to hundreds of volts, giving ESD risk. So, it is not good practice to wear only one footstrap.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com2tag:blogger.com,1999:blog-10053122.post-84497646158929628882007-10-26T14:27:00.000+01:002007-10-26T14:41:54.755+01:00Why is a high resistance of Megohms suitable for grounding static electricity?<span style="font-style:italic;">Why is a high resistance of Megohms suitable for grounding static electricity?</span><br /><br />Engineers are often surprised by the high levels of resistance that give an adequate ground in static electricity work. The reason is simple - static electricity charge generation is effectively a small current generator in the microamp or nanoamp range. We are usually happy to achieve limitation of voltages to a few volts. Simple consideration of Ohms law shows that for, say, 1 microA current generated (which is average level) a 1 M ohm resistance will only show 1V buildup. Increase that to 10<sup>9</sup> ohms and it might start to get more problematic, showing 1kV!<br /><br />You can now start to easily see why with modern insulating materials static charge build-up is common - with a 10<sup>12</sup>ohm material (which are quite common) only 10nA charge generation rate would give 10kV. Modern polymers can be well over 10<sup>13</sup> ohm. <br /><br />Of course life is not so simple in reality but it gives a good first approximation. The second important parameter is charge storage (capacitance) which with resistance forms a characteristic RC charge decay time. If this gets above about a second or so, static voltages stay around long enough for use to notice them. <br /><br />So for a static dissipative floor in an ESD Protected area, 10<sup>9</sup> ohms resistance or below is all that is needed to keep static voltages on chairs, trolleys and other items to a low level. Humans are more problematic as they move around and generate a higher current - someone found that 35 Mohms resistance from body to ground would keep body voltage below 100V in most cases with some margin of safety. <br /><br />People start feeling shocks if their body voltage goes above about 3-4 kV. This can start to happen if the floor resistance goes much above about 10<sup>10</sup> ohms. An average body capacitance might be of the order 100pF, so the time constant is around 1 sec. (People like me who have big feet have higher capacitance). Many modern laminates, glass, plastics, synthetic stone etc have resistance well over 10<sup>12</sup> ohms. So the decay time can be hundreds of seconds, and voltage reach tens of kilovolts. Any high voltages generated sty on the body for several minutes under these conditions. <br /><br />There's some more information on this in my on-line article on <a href="http://www.electrostatics.net/articles/static_build_up_on_people.htm">Why static charge builds up on people </a>Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-59251408302885141052007-10-11T14:47:00.000+01:002007-10-11T14:48:56.099+01:00Is cardboard a problem in my EPA?<span style="font-style:italic;">We have various types of cardboards (dissipative & insulating types) in our ESD protected manufacturing area. Is the cardboard static-generating material? Is it ok to have them in the EPA?</span><br /><br />Any insulating material is likely to be static-generating. One problem with cardboard and paper is that they are very variable materials and their electrical properties vary with air humidity by several orders of magnitude. Under humid air conditions they could be dissipative but under dry air conditions they could be insulating and cause a problem. So, unless you have specific ESD grades, it is better to keep them out of the ESD Protected Area.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-4484555136462955342007-10-01T09:06:00.000+01:002007-10-01T09:10:09.193+01:00<span style="font-style:italic;">While vaccuuming sand with a 6m long and 5cm dia. pvc pipe connected to a flexible pvc hose attached to the vaccuum truck, a considerable amount of static is produced, shocking the worker holding the apparatus. How can I reduce the shocks?</span><br /><br />It's difficult to say for sure without examining the situation, But there are two main possibilities. The main one is that the operator is getting charged up and eventually discharges to some nearby object, feeling a shock. If the operator is standing on a concrete floor, or other conductive material, and they wear "antistatic", static dissipative or conductive shoes, then their body should not charge up and the shocks can often be avoided. <br /><br />However the root cause of the charging is the dust in the pipe. Dust particles impact the pipe walls and create static electricity on the pipe walls. If there are any isolated (not earthed) metal parts these will charge up and can be the source of shocks. The best way to get rid of these risks may be to replace the pipe with conductive or static dissipative pipe, and earth it. Any metal parts in the pipe system should also be earthed (grounded).Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-26594175843108280522007-09-06T09:11:00.000+01:002007-09-06T09:15:20.825+01:00Can we use ESD chairs instead of wrist straps?<span style="font-style:italic;">In one area in our factory they want to buy ESD chairs so that they can eliminate their wrist straps.</span> <br /><br />Using ESD chairs is not a substitute for personal grounding through wrist straps. Personal grounding requires a reliable electrical connection between the body and ground, achieving a resistance less than 35 M ohm. Generally this cannot be achieved by a person sitting on a chair for two reasons. Firstly the resistance of the chair is usually too high, and secondly the contact between the body and chair cannot be guaranteed due to the clothing worn.<br /><br />In my view the use of an ESD chair is to prevent the chair itself becoming a source of electrostatic fields which could cause ESD risks, and could increase the charging on personnel sitting on the chair. If you have chairs in your EPA they should be ESD chairs in any case.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com2tag:blogger.com,1999:blog-10053122.post-70985228545103795792007-08-09T09:25:00.000+01:002007-08-09T09:27:48.679+01:00Using ESD gloves<span style="font-style:italic;">Why should I have to use ESD gloves if we are using wrist bands? How can the ESD gloves help us? How can I explain to the people the importance of using esd gloves?</span><br /><br />There may be various reasons for wearing ESD gloves. The wrist band grounds your body and prevents it acting as an ESD source. If you are not wearing gloves, anything you hold (e.g.tools or boards) are grounded through your body. If you wear non-ESD gloves this grounding is prevented - the tool or other item held in the hand could become charged and be an ESD source. So if you need to wear gloves when handling ESD sensitive components in an EPA, the gloves should be ESD gloves.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com4tag:blogger.com,1999:blog-10053122.post-84117078944886498352007-04-20T12:31:00.000+01:002007-04-20T12:33:50.909+01:00Why don´t I get static shock when I touch somethings like a wall or a tree or door?Shocks are only felt if your body is charged to over about 4000V, and you touch something conductive. <br /><br />If the wall or door is made of wood, concrete or some other material that has low or intermediate conductivity, any static charge on your body escapes slowly and does not cause a shock. In contrast if you touch metal, water, or another person when your body is highly charged, the charge is discharged quickly as the material is highly conductive. In this case you may feel a shock.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com4tag:blogger.com,1999:blog-10053122.post-87897311350020570932007-04-03T17:24:00.000+01:002007-04-03T17:26:53.536+01:00How does a vacuum cleaner cause static electricity?<span style="font-style:italic;">How does using a vacuum cleaner cause static electricity?</span><br /><br />When dust travels in the air sucked through a vacuum cleaner it impacts on the pipe walls and other internal parts. These impacts generate static charges on the particles and on the pipe walls. If these parts are made from plastics or other insulating materials they can charge up and give static shocks. Rotating parts such as carpet beaters can also charge up through rubbing action. If the suction pipe has a metal coil and is not earthed, this can charge up and give quite an energetic spark.<br /><br />If there are flammable vapours (for example solvent fumes) present, these sparks could cause a fire or explosion risk. In larger vacuum cleaners (above about 1 m3) if the dust can give a flammable atmosphere, there may be a risk of fire or explosion in the dust collector.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com5tag:blogger.com,1999:blog-10053122.post-29387364032388424342007-03-14T15:19:00.000+00:002007-03-14T15:23:29.223+00:00What is high voltage for the purposes of ESD?<span style="font-style:italic;">I have read that personnel should not be grounded when working on or around high voltages. Can you tell me what is considered high voltages for the purposes of ESD?</span><br /><br />That may depend on your local Health and Safety regulations. However the IEC 61340-5-1 ESD prevention standard regard over 250 V.a.c. and 500 V.d.c. as high voltage. Conventional wrist straps and footwear usually have some level of protection up to those voltages afforded by the resistance built into the wrist band cord or footwear. 61340-5-1 recommends that above these voltages the minimum resistance-to-ground from the person's body should be increased, with a minimum of 750 kohm per 250 V.a.c. (500 V.d.c.). Whether you are happy to do that may depend on your safety analysis and regulations. The manufacturers of your ESD equipment may give some further information on their partcular products.Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com1tag:blogger.com,1999:blog-10053122.post-15315745160853225772007-01-26T10:58:00.000+00:002007-01-26T11:03:59.955+00:00Can a supermarket shopping trolley really build up a static charge?<span style="font-style:italic;">Can a supermarket shopping trolley really build up a static charge? I can see the insulated wheels having chance, but would have thought the very large surface area of metal would discharge this to the atmophere quickly enough so that a shock from the trolley would be very unlikely. I would have thought any shock from a trolley would have been a discharge of static built up on the person.</span><br /><br />Yes, a trolley can charge up. Air is a very good insulator and does not allow charge on the trolley to escape easily unless quite high voltages (thousands of volts) are reached. The main paths that charge can leak away are through the tyres and floor, both of which can often be highly insulating, or through the person touching the trolley, through their shoes and the floor. <br /><br />There are at least 3 ways in which a person could get a shock when they touch a trolley - either the person is charged, or the trolley is charged, or both are charged. <br /><br />You may be interested to read my on-line articles <br /><br /><a href="http://www.electrostatics.net/articles/static_shocks.htm">Static shocks and how to avoid them</a><br /><a href="http://www.electrostatics.net/articles/static_build_up_on_people.htm">Why static builds up on people</a>Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com2tag:blogger.com,1999:blog-10053122.post-34733862658727826132007-01-25T12:14:00.000+00:002007-01-25T12:19:22.229+00:00How to prevent ESD damage<span style="font-style:italic;">When you work with solid-state devices,what may help prevent ESD damage?</span><br /><br />A device outside and ESD Protected Area (EPA) must be protected by ESD shielding packaging. Devices should only be taken out of their ESD protective packaging when inside an ESD Protected Area in which electrostatic risks are controlled to an insignificant level. In manual handling and assembly, it is most important to ground the body of the person who is working with the ESD susceptible devices. There are many other precautions that might be needed. Please look at our <a href="http://www.electrostatics.net/ESD_Guide/welcome.htm">ESD guide</a>Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0tag:blogger.com,1999:blog-10053122.post-10780025060616745012007-01-25T11:56:00.000+00:002007-01-25T12:20:12.365+00:00Can electrostatic discharges harm people?<span style="font-style: italic;">Can static electricity cause any physical damage to people?</span><br /><br />Static electricity discharges do have significant current flow, which can be several amps or tens of amps for a few hundred nanoseconds. The stored energy which is released in a discharge is also important.<br /><br />Small static discharges do not do damage to a person and may not even be felt. At the other extreme lightning is a static electricity discharge and can certainly kill. So between the two extremes we can expect there to be a range over which a person could be injured in some ways. Where that range lies, and what the effects are, is not well documented as far as I know.<br /><br />There are standards which may be helpful, PD 6519-2:1988 probably being the most relevant in this case:<br /><br />PD 6519-3:1999 (IEC 60479-3:1998).Guide to effects of current on human beings and livestock. Effects of currents passing through the body of livestock.<br /><br />PD IEC/TR 60479-4:2004. Effects of current on human beings and livestock. Effects of lightning strokes on human beings and livestock.<br /><br />DD IEC/TS 60479-1:2005. Effects of current on human beings and livestock. General aspects.<br /><br />PD 6519-2:1988, (IEC 60479-2:1987). Guide to effects of current on human beings and livestock. Special aspects relating to human beings. (Under review)Static Doctorhttp://www.blogger.com/profile/13413070539308266308noreply@blogger.com0