Using ESD gloves

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?

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.

Why 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.

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.

How does a vacuum cleaner cause static electricity?

How does using a vacuum cleaner cause static electricity?

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.

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.

What is high voltage for the purposes of ESD?

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?

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.

Can a supermarket shopping trolley really build up a static charge?

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.

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.

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.

You may be interested to read my on-line articles

Static shocks and how to avoid them
Why static builds up on people

How to prevent ESD damage

When you work with solid-state devices,what may help prevent ESD damage?

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 ESD guide

Can electrostatic discharges harm people?

Can static electricity cause any physical damage to people?

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.

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.

There are standards which may be helpful, PD 6519-2:1988 probably being the most relevant in this case:

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.

PD IEC/TR 60479-4:2004. Effects of current on human beings and livestock. Effects of lightning strokes on human beings and livestock.

DD IEC/TS 60479-1:2005. Effects of current on human beings and livestock. General aspects.

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)

Wanted - antistatic or conductive road surface material or coating

I have a number of client who's customers suffer shocks when they touch a car park ticket machine. In most cases this is due to the electrostatic characteristics of the road surface materials. The solution is far from easy.

I am looking for a conductive coating material that can be applied to, or instead of it, asphalt or epoxy coatings on car park approach road surfaces.

Another possibility might be to fit conductive speed bumps before the barrier - I am also looking for any manufacturer who may be interested in supplying such things.

If you can help, please get in touch via my web site.

Kelvin electrostatic generator generates static from water

I have been told of a simple apparatus that can generate an electrical potential out of drops of water. Can you give me any guidance as to where I can find details of the construction and the underlying science. I am told that it is called a storm in a teacup.

You may be thinking of the Kelvin electrostatic generator. This takes water from one container and drops it inoto two others. There is a system of loops and wires connected to the "output" cans which feeds back voltages to the input, resulting in the output cans charging to a high positive and negative voltages respectively

http://physicsnt.clemson.edu/physdemo/cat/elecstat/kelvinel.htm

http://www.physics.umd.edu/lecdem/services/demos/demosj2/j2-02.htm

If you search on google you will find other references.

Can rubbing the contacts damage a DIMM module?

A friend told me to clean the finger contacs of a DIMM memory module with an eraser :))).. I told him don't do it that way because you will get esd damage.... am I wrong????

To be honest, I don't know the answer to this. I think the main thing is that you should wear a wrist strap to ground your body while handling the module. If you are not doing this the risk is far greater that ESD from your body will damage the module.

If you are wearing a grounded wrist strap while handling the board, and working on a grounded work surface (if you are using a work surface), then I think the ESD risk from static generation as you rub the contacts is probably small.

There must be a better way to clean the contacts, but I don't know it.

Did I damage my RAM stick?

I'm recently going to upgrade my computer with a 200GB HD and 1GB RAM. I've been "messing" for months with the inside of my computer, but something happened yesterday. I opened it and took out both RAM sticks (256 + 128). Did some other stuff also, like cleaning and moving some cables, in order to make room for the HDD. When I closed my computer, opened it, it went directly from the POST screen to a black one. Then windows couldn\'t start because of a file missing. Then I couldn't start the Repair console or the Linux Live CD. It turned out to be the 128MB RAM stick. I took it out and it worked. I have some questions though.
1. Certainly it was damaged by static right?
2. Is there a chance that I ruined something else, including the RAM slot? I ran a 2h stress test and no errors came by.

We can rarely say for definite that ESD is the cause of damage unless expensive failure analysis confirms it to be so. However it certainly sounds as if it is possible, even likely. ESD can weaken semiconductor components and give later failures - so it's possible that another component could be damaged. You'll only know if it fails.


3. I\'m now buying a wrist strap from amazon now... to avoid more problems. Will this prevent any damage from ESD? I have to clip the wire to the metal chasis of the pc, unplugged?

Connect the wrist strap to the PC chassis and wear it in good contact with the skin of your wrist. For safety, the pc should not be plugged in. Don't touch and electronic parts until you are connected in this way.

I may have to work on a carpeted room... but if I absolutely have to, I'll work in some other room.

If you use the wrist strap it will remove most of the risk of damage, carpets or not. The biggest cause of ESD damage is from a charged person to a component at a different voltage. By connecting to the pc via the wrist strap you are "equipotential bonding" yourself to the pc and there will be no voltage difference between you and it - no voltage difference means no ESD.

Try to keep other sources of static such as polythene or foam packaging well away from the pc while the covers are off. Once the covers are back on, it is well protected.

Shocks in winter

As a baby i would give my mother shocks when she picked me up, and if i touched a car and someone was leaning against it they would receive a small shock too. I am now 40yrs old and have had many many static shock free years but at xmas it returned with a vengeance. The shocks i receive closing my car door cause a heavy sensation in the muscle of my arm, sometimes elbow down, sometimes into the upper arm and the pain can last for up to 8hrs... this now extends to receiving shocks from payment machines in car parks, from my allow wheels when checking tyre pressure, from light switches in my cottage, from my lamp. It sounds over dramatic and daft, i know, but it is really getting me down now and i have a certain amount of trepidation about touching some items that cannot be avoided - let alone the shocks i give from time to time to fellow colleagues. Brushing my hair is a theatrical act in itself.

Have you read my on-line article ? Most shocks of this type are due to the person becoming charged up with static electricity because of the materials of their shoes, floor material and furnishing materials. This often becomes worse in winter due to dry air conditions.

It's hard to say what can help in any particular case without investigation of the particular case. Sometimes choosing different types of shoes can help. Unfortunately the real cure may be in changing floor or furniture materials which is often not practical or expensive.

These problems often become less or disappear in spring when the weather becomes warmer and damper.

Why does static electricity increase in cold weather?

I'm hoping you could give me some information about why static electricity increases in the cold weather?

The reason static is more problematic in cold weather is because of low humidity of the air. "Relative humidity" is the percentage of moisture held in the air compared to the maximum it could hold at that temperature. So 50% rh means the air has only half the amount of moisture it could hold. It turns out that static is promoted if rh drops below about 30%.

Cold air can hold less moisture than warm air. So cold outside air at say 0oC and 100% rh is taken into a building and heated up to make it comfortable. The relative humidity drops by one half for every 10oC rise in temperature - so if no moisture is added, the air will be 50%rh at 10oC and 25%rh if heated to 20oC. 25% is certainly dry enough to promote static electricity!.

The main factors conributing to static electricity indoors are floor covering and shoe sole materials, and furniture covers materials, and dry air conditions.

Grounding through ESD footwear and flooring

We have a very peculiar problem while using the ESD ( Static Dissipative ) Shoes. The the pass band - lower limit on the tester is 0.75M Ohm and the upper limit is 35M Ohm) some shoes pass and some fail. Are the limits set on the footwear tester ok or should we increase the upper limit?

The limits on your tester are correct for measuring resistance from the person's body to ground via the footwear and flooring, for a person who is handling ESD susceptible parts. This is recommended by IEC 61340-5-1 to be between 750 k ohm and 35 M ohm.

However the limits might not be correct for testing footwear as worn, to a metal plate electrode. Under the IEC 61340-5-1 standard the range limit for this is between 100k ohm per shoe, or 50 k ohm testing both shoes together, and 10^8 ohms. Footwear can be within this range (and so compliant with the standard) and yet fail your test.

For primary grounding of personel (in other words, the main means of grounding people who are handling ESD susceptible parts) the resistance for shoes needs to be lower than the maximum required resistance for grounding through footwear and flooring. There must be some margin for the resistance of the floor. Also, the floor resistance needs to be low enough to achieve a resistance to ground less than 35 M ohm - this will require floor resistance considerably less than 10^9 ohm allowed by the standard. In this case the best procedure in my view is to measure the resistance from person's body to ground while they stand on the floor - this is recommended to be between 35 M ohm and 750 k ohm. This measurement, and compliance with this resistance range, is not specifically required by the standard.

In summary:
1) 61340-5-1 allows footwear and floors to have higher resistance than would be needed to achieve 35 M ohm resistance from a person's body to ground
2) In order to achieve 35 M ohm resistance from body to ground you would have to choose footwear and flooring types that would reliably give low enough resistance
3) It is recommended, but not required, by 61340-5-1 that the resistance from a persons body to ground should be between 750 k ohm and 35 M ohm when grounded by footwear and flooring - if they are relying on this as the primary means of grounding while they are handling ESD susceptible components.

What is the average static shock (in volts) that you get from touching a doorknob?

I cannot answer this question directly but I can say that body voltages can vary from zero up to 35000 V and above. In general you don't feel shocks unless your body voltage is above about 3000-4000 V. Getting out of a car, about 8000-10000 V is not uncommon. In general the likelihood of achieving a certain body voltage decreases as the voltage increases, so voltages of a few hundred volts are "normal", and a few thousand volts not uncommon, but tens of thousands of volts are more unusual.

How much of a charge can a human body build up from static electricity?

This question is a bit like "How long is a piece of string?" The answer depends on various factors and circumstances. We tend to think in terms of voltage rather than charge, because as the saying goes, "It's volts that jolts" - in other words voltage, rather than charge, causes us to feel a shock. About 3000-4000 Volts on the body will cause us to feel a shock when we touch some object. A shock felt when getting out of the car may be caused by a body voltage of about 10000 V. Body voltages up to 35000 V have been reported, but I see no reason that higher voltages might not be possible in exceptional circumstances. Body voltages up to 10 kV (10000 V) are commonly responsible for the shocks we feel in daily life, and are largely caused by insulating flooring, footwear and furnishings. For more information on this see my article on Static shocks and how to avoid them.

Recently I complained about a low charging bag. The manufacturer came to me and he wanted to prove that the bags are suitable. He used a charged plate monitor. He charged it to 1000V. He connectted his wist strap to EPA ground, than he touched the plate with the bag. He measured the time taken for the voltage to decay to 100V. I think it's not an adequate method.

Whether on not it is an adequate method it is not a standard test method used in 61340-5-1 for demonstrating compliance of packaging. Actually it works by electrical conductivity and so is not even a test of "low charging" but is a sort of "charge decay" test of conduction properties. In the case of "low charging" there is no test method in 61340-5-1, neither is there any pass/fail criteria. But I would not use "low charging" bags for protection of ESDS, I would only use them to package documents or non-ESDS components to prevent them causing electrostatic fields.

For use to protect ESDS within the EPA under the 61340-5-1 standard the bags must be low charging AND either dissipative or conductive. They should therefore pass the criteria using a surface resistance measurement. If the bag does not pass this then it is not compliant with 61340-5-1.

To protect ESDS outside the EPA the total packaging solution (which could have many packaging types e.g. conductive box and dissipative foam) should also have shielding properties.

Documents innside ESD packaging

As a producer of electronic printed board assemblies I work within manufacturing. I've recently been tasked with overseeing the effects of static during board production. As part of the storage of product I have found printed computer paper and photocopier paper placed directly on top of the boards in carriers without shielding. As far as I was aware with BS 61340-5-1:2001 this was found to create possible damage by static from the paper. However, I am locked into debate with the person concerned as I've always believed this to be unacceptable. Please could you advise.

I have not found any specific mention in 61340-5-1 or 61340-5-2 of inclusion of paper within ESD packaging. However I agree with you, I do not think that it is good practice. The characteristics of paper are extremely variable and this is introducing an unknown ESD risk into what is supposed to be a protected environment with controlled ESD risk. If you value your product, as I'm sure you do, why take the risk? A good way to put costs into perspective is to think about the potential cost of even one ESD failure in the customer's site. Usually this is sufficiently high to convince one that a small saving or doubtful practice in pursuit of convenience, is not worth while.

I have found computer paper in particular to often be at the insulating end of the paper spectrum and therefore possibly at higher risk of causing ESD problems. Usually in such cases it is much easier to remove the doubtful practice than it is to prove one way or another whether there is significant ESD risk.

If you can prove that the paper full fills the requirements for "intimate" packaging over the full range of environmental conditons (especially low humidity) then I concede you may have a technical argument for allowing the paper in with the boards. The requirements for "intimate" packaging are given in Table 2 of 61340-5-1 - the material should be low charging and at least static dissipative (< 10¹¹ ohm surface resistance measured at 100V with a concentric ring electrode. I recommend testng at 12 % rh). My guess is that you do not want to perform this characterisation test for the paper, including periodic verification of any paper you may use for the purpose in the future. Special ESD paper may be available if you really want to use this practice. Note that the resistivity of paper typically increases by several orders of magnitude with reducing humidity and so measurements at higher humidity will not give worst case results.

How to seal ESD shielding bags?

How important is it to fully close a static shielding bag that contains static-sensitive components? Is it good enough to fold and tape the bag (with what kind of tape?), should a double-fold be used, or are the zipper-style bags better?

A shielding bag gives best protection when closed and fully surrounding the components or board within. It has two functions - 1) to shield against electrostatic field, and 2) to protect against direct ESD to the ESD susceptible parts inside. A typical bag is a laminated material having some insulating layers to stop ESD curent flow through the material, and a metallisation layer to provide electrostatic field shielding. Inner and outer surfaces should be static dissipative (or in some cases may be conductive) to prevent charge build-up.

If you fold the bag do not crease it as this may break the metallisation layer and impair the protection. A loose single fold, held by a label or tape is fine. However, remember you don't want to be using ordinary high charging tapes within an ESD Protected Area. Avoid having component leads puncture the bag.

Never staple a bag as this gives a route for ESD to pass through and make contact with components inside.

A zipper style bag is fine.

A very useful article on ESD bags is given here

What level of ESD will damage parts?

>> I have currently been tasked with trying to improve the ESD standards
>> within our manufacturing facility.
>> One question which has arisen which I cannot find an answer to is this. Is
>> there a level of ESD at which it is generally accepted that on or above
>> this level, significant damage will occur to electronic parts?
>> We are shortly going to be going through the process in question, and
>> measuring the charges and voltages which are created whilst working. It
>> would help us greatly to know if there is a "safe" level of ESD which can
>> be allowed to occur.

The ESD susceptibility of devices depends on the particular component. Each has an "ESD withstand voltage" determined during QA tests. Virtually all semiconductor components have been tested using "Human Body Model" (HBM), some have also been tested using "Machine Model" (MM) or "Charged Device Model" (CDM). Unfortunately many manufacturers do not make this information readily available to users. As a result we end up relying on guesswork for the susceptibility of components. A rough guide is given in our ESD Guide

The ESD standards such as 61340-5-1 are designed to protect devices down to 100 V HBM. For many processes this will be adequate. Some types of components are more susceptible than this (< 100V HBM) and special measures and care are then required.

It is not easy to assess ESD risk in a process. The usual way is to measure electrostatic fields and potentials in the region of the ESD susceptible parts. The 61340-5-1 standard recommends that electrostatic fields should not exceed 10,000 V/m and potentials (voltages) should not exceed 100 V. Note that a 1,000 V/m field could be a 10,000 V source at 1m, or a 100 V source at 1 cm distance etc. In practice I regard the field criterion as the most useful.

The best approach is to remove all non-essential insulators and electrostatic field sources in the ESD Protected Area (EPA). Any essential insulators or other sources may then be assessed for ESD risk, and appropriate ameliorating action (e.g. use of ionisers) taken.