Benchmarking ESD best practice across industries

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.

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.

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.

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.

 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.

 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.

 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.

 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. 

 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.

Will 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.

Of course the overall risk of damage occurring is difficult to predict.

Why use an ESD seat?

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)
If they connected to ground via wrist strap, why should I connect them to ground via chair?

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!

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.

What ESD packaging should I use?

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.

There is no single recommended method or packaging type. However I reccommend the packaging used has the following characteristics:

1) no part of the packaging should be an exposed insulating materila which could charge up and cause ESD risk in an EPA.
2) the material in contact with the ESD sensitive parts should be dissipative
3) there should be a surrounding conductive material to form an electrostatic field shield
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.

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.

Why would a capacitor be ESD sensitive?

Why do some capacitors have a dependency on capacitor size vs ESD?

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.

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.


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.

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.

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.)

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.

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.

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.

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?

General guidelines for high voltage area?

What is general guide lines for EPA area, where live AC and DC equipment is used?


If personnel are handling ESD sensitive devices, the general guidelines are the same as for any other ESD Protected Area. See my ESD Guide.

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.

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.

ESD damage to motherboard?

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?

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.

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.

Is a foot strap adequate?

When my floor is dissipative do I need to utilize a foot strap and a wrist strap, or is a foot strap adequate?

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.

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.

ESD packaging

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?

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.

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.