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What Is Electrostatic Discharge (E.S.D)?

Electrostatic discharge (E.S.D) is an uncontrolled surge of “static” between objects with different voltage potentials.

Have you ever felt a random zap when touching a doorknob or a screen? This zap you have experienced is known as static electricity.

What Is Static Electricity?

Static electricity is a fixed electric charge, typically produced by friction, which causes sparks, crackling or the attraction of dust or hair.

All items are made of tiny atoms. These atoms are made up of even smaller particles – protons, neutrons and electrons. The protons have a positive charge, the neutrons have no charge, and the electrons have a negative charge.

In normal conditions, there are the same amount of protons and electrons, giving atoms no control. However, these electrons can move. When separating or rubbing together, electrons can move from atom to atom or from one material to another (triboelectric charges). This can mean that atoms can hold a positive or negative charge. (Dependent on movement and direction of electrons). If the material in question is an insulator, this charge can be held and not moved – this is called static electricity.

What Is Electrostatic Discharge (ESD)?

Electrostatic discharge can occur when two surfaces come into contact and create friction with each other. Examples include: walking over synthetic floors, rubbing of synthetic garments, shifting of plastic boxes, unrolling of PVC adhesive tape and the movement of a conveyor belt. When two surfaces come into contact with each other, this can build up an electrostatic charge. One surface becomes positively charged and the other surface becomes negatively charged causing an imbalance.

The amount of static electricity generated depends on the materials subjected to contact or separation, friction, the area of contact or break, and the relative humidity of the environment. At lower relative humidity, as the climate is drier, charge generation will increase significantly. If the electrostatic charge comes into contact with the suitable material, it transfers and causes an ESD event. ESD can also occur when a high electric field develops between two objects nearby.

In a typical environment like your home, numerous ESD events can occur, most of which you do not see or feel. It takes a discharge of about 2,000 volts for a person to feel an electric “zap”. Although, with events like lightning, it requires a much larger ESD event to arc and be seen.

While a discharge may be a nuisance in the home, ESD is a significant problem in a high tech manufacturing environment and should be avoided at all costs. The modern electronic circuitry we see on components such as printed circuit boards, can be burnt or melted from these miniature lightning bolts of ‘ESD’ and cause irreversible damage to them. ESD has cost the electronics manufacturing industry millions, if not, billions of pounds worth of damage and replacements. ESD control is, therefore, necessary to reduce and limit these ESD events.

ESD can result in:

  • Higher costs
  • Lower quality
  • Reduced customer satisfaction

Types of ESD Damage

Electrostatic damage to electronic devices can occur from manufacture to field service. Damage results from handing the devices in uncontrolled surroundings or when poor ESD control practices are used. Generally, the damage is classified as either a catastrophic failure or a latent defect.

Catastrophic:

When an electronic device is exposed to an ESD event, it may have caused a metal melt, junction failure or oxide breakdown, permanently damaging its circuitry and resulting in a loss. Such negligence is usually detected when the device is tested before shipping. If the ESD event occurs after the test, the damage will go undetected until the device fails in operation. It is the most accessible type of ESD damage typically detected during testing and incurs a lower cost.

Summary:

  • A device is exposed to ESD and no longer works
  • The device circuitry is permanently damaged
  • Such failures are usually caught when tested and before shipping

Latent:

A latent defect is much more challenging to identify. A device may be partially degraded yet continue to perform its intended function. However, the operating life of the device may be reduced dramatically. This could cause premature systems failure, which can prove extremely hazardous and very costly.

Summary:

  • A device is exposed to ESD and is partially damaged, yet it continues to perform its intended function
  • Latent defects are much harder to identify since they occur over a long period
  • This may pass testing and be shipped to a customer and fail whilst in service
  • It can significantly shorten the operating life of the device, and it can be very costly

A latent failure is a higher cost due to:

  • Servicing facility
  • Replacement equipment
  • Customer complaints
  • Loss of reputation

It is important to note that ESD damage can occur at any time!  The most common times for ESD damage are during:

  • Goods input
  • Acceptance
  • Production
  • Assembly
  • Testing
  • Storing
  • Packing
  • Shipping
  • Maintenance

ESD Is A Huge Problem For Many Industries

Did you know people are the primary source of electrostatic charges?

Static electricity has been an industrial problem for centuries, as early as the 1400s. European forts used static control procedures and devices to prevent electrostatic discharge igniting gun powders and other explosives.

The electrostatic discharge (ESD) phenomena has been known since the Greek civilisation was dominant thousands of years ago. People in cold climates were very familiar with the ESD effect in a low-relative humidity environment, as was frequently experienced in indoor environments in the wintertime.

As electronic components changed from electronic tubes to solid-state electronics in the 1950s, companies became concerned with damage to electronic components and interruption of the regular operation of electronic equipment.

Within today’s electronics industry, it is widely accepted that electrostatic discharge (ESD) events are a significant cause of device failure and that implementing static control measures is not only desirable but essential. Damage to this industry has been estimated at billions of dollars annually. However, while the costs of static control measures can be high, the return on investment certainly does justify implementing such measures.

ESD problems have magnified during the past three decades because of 2 reasons:

  • The increased use of insulating manufactured fibres and plastics for clothing, furnishing, flooring, etc.
  • The ever-increasing sensitivity of integrated circuits due to smaller conductors and components within the circuitry.

ESD can change the characteristics of a semiconductor device, degrading or destroying it. Controlling ESD begins with understanding how electrostatic discharge occurs in the first place. Electrostatic charge is most commonly created by the contact or separation of two materials. This is known as “triboelectric charging”, which involves the transfer of electrons between materials.

Static discharge can fire flammable concoctions or vapours in laboratories or even destroy sensitive and costly electronic components in factories. It can also draw contaminants in cleanroom settings or even lead products to stick together and interfere with the overall manufacturing process. Common plastics generally create the most significant static charges.

Why Is Managing ESD Important?

Static discharge is destructive to sensitive electronic components. Even 1 volt of electricity is enough to cause damage, but most devices need around 100 volts to cause damage that is beyond repair.

Humans cannot feel a static discharge unless it is 2,000 volts or higher. So, if you don’t feel a zap, it doesn’t mean a static discharge did not happen or damage your electronic components.

Many industries depend on electronic components and their reliability to work in harsh conditions, so the need for reliable ESD-safe equipment is significant.

Electronic component producers are often unaware that static discharge has damaged their products during the assembly process unless they test all components one by one or see their final product fail after assembly. If these products were used in aerospace, one minor problem on a small component could lead to an enormous failure, which is why ESD is a significant challenge for many industries.

Typical Electrostatic Voltages

  • Walking across a carpet: 1,500 – 35,000 volts.
  • Operator at a bench: 100 – 6,000 volts.
  • Walking over an untreated vinyl floor: 250 – 12,000 volts.
  • Picking up a standard plastic bag from a bench: 1,200 – 20,000 volts.
  • Chair with urethane foam: 1,500 – 18,000 volts.

What Voltage Can Damage Components?

The voltage can be as little as 10 volts depending on the size, sensitivity and type of component. To comply with the British standard, 100V is the maximum threshold that can be produced within an EPA.

Potential Difference

The potential difference causes ESD when there is a difference in charge between two objects. These can include work surfaces, articles of clothing, people, flooring and shelving/conveyors.

ESD Symbols

If you’ve been handling static sensitive devices for a while, you’ve most likely come across the various ESD symbols already. But do you know the difference(s) and when to use them? If you are new to ESD protection or have just taken over responsibility for an existing ESD program, keep reading below!

The ESD Standard ANSI/ESD S20.20 requires that “ESDS items, system or packaging marking shall be in accordance with customer contracts, purchase orders, drawing or other documentation.” [ANSI/ESD S20.20 clause 8.5 Marking]. If ESD sensitive items are not covered in any of these documents, each company has to decide whether marking is required. If it is deemed necessary, the ESD Control Program Plan needs to define the details.

ESD Protective symbol

Just like the ESD Susceptibility Symbol, the ESD Protective Symbol has a reaching hand in a triangle. However, note the arc and missing slash through the triangle! Because of these differences it has a very different meaning.

This symbol should be on ESD protective products identifying a specialty product that has at least one ESD control property.

The ESD Protective Symbol is also called the ESD Packaging Symbol.

Used to designate all ESD protective products such as bags, boxes, garments. A letter is added under the symbol to indicate the primary function:

  • C – conductive (For use in ESD Protected Areas)
  • D – dissipative
  • S – shielding
  • L – low charging

Colour of the ESD Protective Symbol

The color is optional except “the color red shall not be used because it suggests a hazard to personnel.” [ANSI/ESD S8.1 clause 5.2.1 color].

Normally, a hand symbol is used on a black triangle on a yellow background.

ESD Susceptibility Symbol

ESD Susceptible Symbol

The ESD Susceptibility Symbol is the most commonly known symbol which consists of a yellow hand in the act of reaching, deleted by a bar; all within a black triangle. It is intended to identify devices and assemblies that are susceptible to ESD.

The ESD Susceptibility Symbol is correctly used as follows:

  • On individual components and related documents to state: ‘this device is static sensitive; do not touch without appropriate precautions’.
  • On assemblies and related documents to state: ‘includes static sensitive components; take appropriate precautions’.
  • As part of a sign identifying an area where sensitive devices are handled; to warn all who approach it that precautions are required.

Colour of the ESD Susceptibility Symbol

The color is optional except “the color red shall not be used because it suggests a hazard to personnel.” [ANSI/ESD S8.1 clause 4.2.1 color].

Normally, the hand and slash symbol is used on a black triangle on a yellow or orange background.

How Can You Prevent ESD?

Nowadays, investing in ESD protection is an essential element of all electronics-based industries as it’s applied in every manufacturing, production, repair, and testing stage.

Many industries want to avoid the occurrence of an ESD event and reduce static discharge in the workplace. By ensuring you have the essential EPA equipment, you would prevent the risk of static discharge from damaging components and entering your EPA.

Essential EPA Equipment You Should Use:

  • ESD mats and flooring ESD mats dissipate charge through the mat’s top (dissipative) layer, travelling through the conductive layer, and then the stud to Earth.
  • Wrist-straps and cords Carry the charge away from the person and discharge the static safely to the ground. The cables are always fitted with a 10^(6) Ω resistor next to the skin. The wires are usually connected to the Earth through a stud on a mat or straight to an Earth bonding point.
  • Heel grounders and ESD shoes Heel grounders and ESD shoes work similarly. They only pass the charge into an ESD Floor where the charge will be grounded.
  • ESD garments The primary purpose for wearing conductive smocks is to suppress static fields on employee clothing. The conductive fibres woven into the material provide a ‘Faraday Cage’ effect that prevents dangerous areas from extending to and damaging sensitive products. There shall be electrical conductivity between all parts of the garment.
  • ESD gloves ESD sensitive devices can experience a damaging discharge if touched by a person, even if that person is adequately grounded. Increasing the electrical path’s contact resistance is one way to control the speed of the discharge. An excellent way to accomplish this is by wearing static dissipative gloves.

Remember these four golden rules:

1) Assume that all active components are sensitive to ESD.

2) Handle electronic components only in the ESD protected area (EPA) and only when you are correctly grounded.

3) Store and transport the ESD-sensitive items in ESD protective containers.

4) Check regularly the ESD protection system, internal and external (suppliers).

Creating an Electrostatic Protected Area (EPA)

An EPA (ESD Protected Area) is a defined space where no items or activities can cause damage to a sensitive device. In the simplest case, a workstation may consist of a dissipative mat, a wrist strap and a standard grounding facility for both. The maximum allowed electrostatic field in an EPA is 100V/cm.

The best way to create an Electrostatic Protected Area (EPA) is by doing the following:

  • Define a boundary with suitable signage and physical barriers.
  • Provide effective methods for grounding personnel – wrist straps, static dissipative floor with suitable footwear.
  • Install static dissipative worksurfaces grounded to a typical Earth facility.
  • Ensure that all containers and bins are non-insulative – i.e. conductive or static dissipative.
  • Provide adequate packaging for transit outside EPAs. The function of this packaging is to shield or separate sensitive electronics from ESD events.
  • Ensure that all trolleys used within the EPA are grounded.
  • Install test equipment for daily checking of personal grounding items – wrist straps and footwear, with a system for recording checks.
  • Exclude all non-essential insulators. Consider the use of ionisers for neutralising charges on process-essential insulators.
  • Identify and provide ESD training for all staff involved in handling ESD sensitive items or who may be required to operate within the EPA.
  • Implement checking and auditing procedures for the ESD Protection Programme.

Once you have established an Electrostatic Protected Area (EPA), you then have a designated space where you can handle static-sensitive components safely.

ESD Training

Do your employees require ESD training? Improve your employee’s knowledge of electrostatic discharge with Bondline’s ESD training course. Our program is excellent for those who are complete beginners to ESD, and even those who would like to refresh their knowledge. The course is ideal for production personnel, engineers, support staff, managers and even purchasing staff who require some basic knowledge on ESD.

Why invest in ESD training for your employees? By taking our course, your employees will not only learn about the causes of static generation, the effects of static discharge, and the materials and methods necessary for prevention and protection, but also help them to avoid common ESD control mistakes.

Our ESD training course can be tailored to your requirements at your own premises, so your employees can be learning at the comforts of their own workplace. The course content will reflect the facilities and current practice.

Understanding the phenomenon is enhanced through practical demonstrations and audience participation. Courses can also be presented on a ‘one-to-one’, ‘train-the-trainer’ basis.

Costs will depend on the amount of information/ training required. All training is designed to meet the requirements of IEC-61340-5. Please contact us below if you would like more information about our ESD training course.

Contact Us

Our company’s objective is to prevent ESD with our diverse range of anti-static products. Using our anti-static products can prevent further damage to electrical components and devices whilst also promoting a static-safe working environment.

If you would like further advice on how to control ESD or are interested in our ESD training programme, please contact our sales team on sales@bondline.co.uk or 01793 511000, where we will be happy to help you find a solution to answer any queries.

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