All permanent and semi-permanent metallic structures and test equipment utilized during handling or manufacturing of ESDS components or hardware shall be grounded using a common point ground. A major goal of this document is to ensure that all conductive materials are tied together at the same potential. An equal potential workstation is the secret to preventing damage to ESDS components.

The practice of having a separate ESD ground from the third wire (green) alternating current (AC) ground is wide spread but has the potential for damaging components because it places the operator and the work surface at a different ground potential with respect to any soldering irons and/or test equipment. The recommended practice is to use the third wire AC line ground for grounding all items at the ESDP workstation. When a separate grounding line is present or used in addition to the equipment ground, it must be bonded to the equipment ground at each ESDP station to minimize the difference in potential. ANSI EOS/ESD S6.1 “ESD Association Standard for the Protection of ESDS Items – Grounding-Recommended Practice” contains detailed hookup diagrams for ESDP workstations and support equipment.

The resistance of the conductor from the groundable point of the work surface, wrist strap, walking surface or other items to the common point ground should not be greater than 1.0 ohm. If a series resistor is used in the circuit, the total resistance shall be the value of the resistor.

The resistance of the conductor from the common point ground to the equipment ground should not be greater than 1.0 ohm.

The impedance (AC resistance) of the equipment-grounding conductor from the common point ground to the neutral bond at the main service equipment should not be greater than 1.0 ohm.

Each ESDP workstation should have a grounding block that provides sufficient wrist strap connections for all potential users. These grounding points shall not utilize portions of the protective work surface as a series element to complete the ground circuit. Receptacle grounds in an EPA shall be verified at least semiannually.

A good example of ESDP workstation setup is shown in Figure 6.5.1 Typical ESD Protective Station Grounding Systems and in ESD TR20.20-2008, Figure 13.

Stools and Chairs

Personnel performing ESDS tasks while seated should use ESDP stools and chairs. Only chairs of metallic frame construction shall be used in an EPA. Class 1 facilities shall provide ESDP chairs or stools at the workstation if seating is required. Test methods are found in ESD STM 12.1 “ESD Association Standard Test Method for the Protection of ESDS Items – Seating – Resistive Characterization”

Personnel grounding devices are the primary means of ESD control. For static charges generated during ordinary body movements, personnel-grounding devices provide a permanent path to ground. Such devices may take various forms such as:

  • Wrist Straps
  • Leg Straps
  • Heel Straps
  • Conductive Shoes

Wrist Straps

Wrist straps are considered to be the first line of defense against ESD and shall be required in the majority of ESDS work environments. Metallic contacts are preferred over conductive plastics. The wrist strap cuff shall always be in direct contact with the operator’s bare skin. It must never be worn over clothing. Bead-type chain wrist straps are prohibited.

Wrist straps shall always be worn snugly against the skin and shall not dangle freely. The electrical integrity of each wrist strap shall be checked during initial certification and verified by the operator at the beginning of every shift during which it is used. A wrist strap checker specifically designed for that purpose shall be used to verify the wrist-strap is functional. The wrist straps shall be connected to ground using one common ground point for each workstation. ESD S6.1 “Grounding Recommended Practice” outlines the recommended grounding practices.

Continuous, in-line continuity checkers are highly recommended. (Reference ESD TR20.20-2008, Section 5.3.9 – Continuous Monitors). The electrical resistance of the wrist strap measured between the opposite hand and the (ungrounded) grounding end of the wrist strap assembly shall not exceed 9M ohms above the value of the incorporated current-limiting resistance. The static dissipative work surface material shall never be used as part of the series path to ground for a wrist strap.

More information on wrist strap testing and set up is available on ESDS1.1 “ESD Standard Test Method for the Protection of ESDS Items – Wrist Straps”.

Leg Straps, Heel Straps, and Conductive Shoes

A conductive/dissipative floor and/or conductive floor mats are required when using leg straps, heel straps, and conductive shoes as acceptable alternatives to a wrist strap in those instances where the use of a wrist strap is impractical or unsafe. Examples of such instances would include working near moving conveyor belts or wave soldering machines and when working on large systems. The foot strap should have a built-in resistance of 1X106 +/- 20 percent. If the resistance does not meet this recommendation, the value should be approved by the ET&V Officer.

The ET&V Officer shall measure the conductivity of leg straps, heel straps, and conductive shoes during the initial certification. The operator shall verify this conductivity for each work shift. Test methodology is found in ESD S9.1 “ESD Association Standard Test Method for the Protection of ESDS Susceptible Items – Footwear – Resistive Characterization”.


Conductive floors or grounded conductive floor mats are mandatory in any EPA where personnel handling ESDS items are not wearing wrist straps. Under these circumstances, personnel shall use leg straps, heel straps, or conductive shoes.

ESDP flooring or floor mats shall be used in all Class 1 facilities.

The proper cleaning and maintenance of a conductive floor is of extreme importance since the use of normal floor wax on conductive floors or floor mats can defeat their effectiveness. Personnel cleaning these items shall use the manufacturer approved cleaning agents and cleaning recommendations as minimum requirements. With guidance from the ET&V Officer, the Facility ESD Monitor will determine the cleaning regimen for the flooring and mats if the manufacturer’s recommendations are not acceptable.

Conductive/dissipative floors or grounded conductive/dissipative floor mats shall have a maximum resistance to ground of 1×109 ohms and a minimum resistance of 1×105 ohms. The test methodology for flooring is found in ESD S7.1 “ESD Association Standard Test Method for the Protection of ESDS Items – Resistive Characteristics of Materials – Floor Materials”.

Standard carpeting shall not be used in an EPA. Even the use of ESDP carpet woven with conductive fibers, which have previously been approved for use at JSC, can still be very problematic. If the conductive fibers are not dense enough, the resistance to ground will increase as the carpet wears. The selection of carpet in an EPA environment shall require pre-installation approval of the ET&V Officer.

The ESDP work surface (Reference ESD TR20.20-2008, section 5.3.1 – Work surfaces) will provide a safe path to ground for static charges within the operator’s general working area. Either the ESDP work surface may be fabricated as a part of the workbench or it may be a separate addon item. In either case, the ESDP work surface shall be grounded and static dissipative with a resistance to ground measurement between 1×106 to 1×109 ohms. Applications where hard grounding of the LRU is required are excluded. ESD S4.1 “ESD Association Standard Method for the Protection of ESDS Items – Workstation – Resistive Characterization” describes the test methods for work surfaces. Grounding of the work surface may be accomplished with the use of a current limiting resistor that is generally a ¼ watt, 250V part. The maximum voltage rating of the resistor defines the maximum working voltage of the surface. The use of a series resistor is recommended for personnel safety if the currents from accessible voltages at the workstation could exceed 5mA through the static-dissipative protective work surface. For personnel safety, the use of a ground fault circuit interrupter (GFCI) is recommended in situations where personnel may come in contact with hazardous current levels.

The ET&V Officer shall check the work surface ground continuity during initial certification. Thereafter this check can be done by lab personnel on a weekly basis. It is strongly recommended that electronic monitors be used to monitor continuously the integrity of the work surface ground.

The manufacturer’s recommended chemicals and methods that will not damage the work surface shall be used to clean the work surface as required.

Exposed metalwork surfaces are not acceptable for ESD workstations. If a special situation requires a conductive work surfaces, it must be hard grounded. If a painted metal bench is used, the metal must be covered with a static dissipative material. See Figure 6.5.1 and Figure 6.5.2 for examples of how a workstation should be connected to meet ESD requirements.

Typical ESD Protective Station Grounding Systems

Figure 6.5.1 Typical ESD Protective Station Grounding Systems

Typical Barrier Strip Common Ground Point

Figure 6.5.2 Typical Barrier Strip Common Ground Point

Static electricity is a natural phenomenon, which can be generated from different ways, such as contact, friction, stripping and so on. Electrostatic protection technologies, adopted by electronics, semiconductors, petroleum, ordnance, textile, rubber, aviation and military fields, resort to reduce the loss caused by static electricity.
  • Precautionary Measures
  • Grounding
  • Shield
  • Neutralization
  • Protective Equipment
  • Daily Life Common Sense
  • Explanation on Electrostatic
  • Main ESD Prevention Products
  • Electrostatic system

Precautionary Measures

There are three main anti-static measures: antistatic clothing, antistatic shoes and anti-static wrist bands.

Anti static shoes and anti-static wrist bands are used to conduct static electricity so as to avoid accumulation on the human body.

Antistatic garments & shoes

Common clothes produce a large static voltage (> 1000V) while the wearer moving around. This wouldn’t occur to antistatic clothes, and that’s the main reason for wearing antistatic clothes.

Long strip material anti-static clothing can not shield the static electricity generated by clothing (still >1000V after wearing). While he grid material antistatic clothing can do its job (<200V).

The static electricity is introduced into the outer ground line of the factory through conductive floor boards and the ground wires .

The prevention includes preventing static electricity generation and preventing its damage.

Electrostatic protection is a long-term system engineering, any fault or carelessness will lead to the failure of electrostatic protection.

Mainly the measures for electrostatic protection in the production process are electrostatic leakage, dissipation, neutralization, humidification, shielding and grounding.

Human body electrostatic protection system usually consists of anti-static wristband, anklet, work clothes, shoes & socks, caps, gloves or fingerstalls etc., with electrostatic leakage, neutralization and shielding functions.

The ground anti-static treatments are anti-static ceramic steel-based composite movable floor, anti-static steel movable floor, anti-static ceramic floor tiles and so on.
Grounding is very important to reduce the electrostatic charge on the conductor, the human body is a conductor, also a main source of electrostatic generation. Therefore, we must reduce the static charge generated by contact with the sensitive electrostatic components. Prevention of static electricity on the human body is best through grounding.

Some grounding devices:

In industry, wristband is the most commonly used grounding device. The wristband will safely and effectively drain the static charge from your body. Reasonable use of a wristband requires reasonable contact with the skin. A dirty or loose wrist strap may retain the static charge, which makes the antistatic control will fail. Conductive footwear or foot grounding can be used to overcome shortcomings of wrist bands.

Work Station Grounding Device

Conductive or electrostatic dissipative working surfaces are an indispensable part of an electrostatic safety workstation, especially where manual assembly occurs. While using wristbands, it is necessary for a clean working surface to be grounded properly at a joint. Conductive or electrostatic dissipative materials can produce electrostatic charges, however., when they are properly grounded, they can effectively drain static charges.


The next concept is to isolate parts and components during storage or transportation. It is isolated from a charged object or a charged electrostatic field. Insulator is the best way to prevent electrostatic discharge during storage or transportation. Since grounding cannot remove static charges or insulators, it is necessary to isolate sensitive parts and components from them. Reducing conventional plastics and other types of insulators in stationary working, shipping and handling areas is the best way to isolate products from insulators. Isolation can also be done by limiting access to the entire work area or workstation. Finally, we take advantage of the fact that electrostatic charges cannot enter containers made of conductive materials or layers. This effect is called the Faraday cup effect. When storing and transporting electronic components or loading circuit boards, ensure that containers with similar Faraday cup characteristics are used, and these containers will be isolated from electrostatic injuries.


Utilizing electrostatic elimination equipment, its main component is ion generator.

Neutralization is important because earthing and isolation will not release charge from insulators such as synthetic fabrics or conventional plastics. Neutralizing or removing the charge generated in insulator is called ionization. Ions are simply charged substances existing in the air. Ions are produced by natural energy materials. Including sunlight, lighting, open-air flame and radiation. We can get trillions of ions through ion generators, which use high voltages to produce a balanced mixture of charged ions, and fans to help ions drift to objects or regions to neutralize. Ionization can neutralize static charges on insulators in eight seconds, thus reducing their potential damage. Ionization is not a substitute for grounding or isolation. It only reduces the possibility or risk of electrostatic discharge accidents.

Protective Equipment

Personal static eliminator mainly refers to contact static eliminator and auto-sensor static eliminator.

Contact static eliminator

Contact hand-held personal electrostatic eliminator is a device that eliminates static electricity on human body or metal objects by touching metal objects with hand-held devices. But this is only temporary. In daily life, static electricity is produced all the time. After using contact static eliminator for a period of time, our body will feel electric shock when it contacts the electrostatic object/metal conductor again. So when we use the product, we need finish to the work as soon as possible.

Auto-sensor static eliminator

Automatic personal static eliminator is a device that automatically detects the static electricity in the surroundings and then automatically eliminates the static electricity. We don’t need any operation. The most outstanding feature of this automatic key chain is its exquisite workmanship, anti-static load up to 40,000 volts, and the ability to eliminate static electricity continuously.

Daily Life Common Sense

In daily life, people often accumulate static electricity due to clothing, climate, friction and other reasons. When they bump into metal, people will suffer from electric shock pain. Psychological pressure may be caused in some cases. If you avoid touching iron for a while, you may accumulate more electric charges on your body, sooner or later you will suffer from stronger electric shocks.

1. In the house, the rubbing of carpet and sole may produce static electricity, and outside, you may also be electrified by wind. Be careful when you enter or exit metal gate, your hands may experience shock. If this happens repeatedly, the following measures can be taken to avoid electric shock:

1.Don’t touch an iron door directly with your hands. Instead, hold the keys before that(usually you can avoid electric shock), touch the metal with the tip of a key, the electricity on your body will be released and you won’t get shocked.

Principle: Pain caused by hand discharge is due to high voltage discharge, because a sudden contact of your hand and metal door leaves a small area for discharging, resulting in instantaneous high voltage. If you take out the key in your pocket and hold it in a large area (a bunch of keys can’t transfer much electric charge by themselves, so there won’t be an electric shock at this time), then use the tip of a key to contact the large conductor. At this time, the contact point of discharge is not a point on the skin of the hand, but the tip of the key, so the hand will not feel it. (Maybe the key! If it feels pain.)

2. Frequent electric shocks occur when getting off the taxi. The main reason is that static electricity accumulates when the body rubs against the seat when getting off, and when the door closes, the hand will be shocked when it suddenly touches the iron door.

If this often happens, it’s better to take notice when you get off the car, that is, when your body rubs against your seat, you can hold the metal door frame in advance. When static electricity is generated by friction, you can remove static electricity from your body at any time, instead of discharging when you suddenly touch the iron door while getting off.

Explanation on Electrostatic

In order to effectively combat and prevent ESD (electrostatic discharge), the right equipment must be used in the correct way. Because of a series of powerful closed-loop ESD prevention, monitoring and ionizers, ESD can be regarded as a process control problem.

Electrostatic discharge (ESD) is a familiar and underestimated source of circuit board and component damage in electronic assembly. It affects every manufacturer, regardless of its size. Although many people believe they produce products in an ESD-safe environment, in fact, ESD-related damage continues to cost the world’s electronics manufacturing industry billions of dollars a year.

What is ESD?

Electrostatic discharge (ESD) is the sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown. A buildup of static electricity can be caused by tribocharging or by electrostatic induction. The ESD occurs when differently-charged objects are brought close together or when the dielectric between them breaks down, often creating a visible spark. The charge is stable under two conditions.

1. When it “falls” into a conductive but electrically insulated object, such as a metal screwdriver with a plastic handle.

2. When it resides on an insulating surface (e.g. plastic), it can not conduct on it.

However, if an electrically insulated conductor (screwdriver) with sufficient high charge is close to an integrated circuit (IC) with opposite potential, the charge “crossover” causes electrostatic discharge (ESD).

ESD occurs very quickly at very high intensity, usually producing enough heat to melt the internal circuit of semiconductor chips, which seemingly blows out small bullet holes under an electron microscope, causing immediate and irreversible damage. What’s more, a tenth of the cases are so bad that the whole component fails in the final test. In the other 90% cases , ESD damage only causes partial degradation – meaning that the damaged components can pass the final test without detection, and premature on-site failure occurs only after shipment to the customer. It will dishonor a manufacturer to have to correct any manufacturing defects.

However, the main difficulty in controlling ESD is that it is invisible but can damage electronic components. To produce a discharging that can hear a beep, a considerable charge of about 2,000 volts needs to be accumulated, while with 3,000 volts you can sense slight shock and with 5,000 volts you may see sparks.

For example, common components such as complementary metal oxide semiconductor (CMOS) or electrically programmable read-only memory (EPROM) can be destroyed by ESD potential differences of only 250 volts and 100 volts, while more and more sensitive modern components are out there. Including the Pentium processor, it can be destroyed by only 5 volts.

The problem is compounded by activities that cause damage every day. For example, in the vinyl factory floor, there is friction between the floor surface and the shoes. As a result, pure charges accumulate between 3 and 2,000 volts, depending on the relative humidity of the local air.

Even the friction generated by the natural movement of workers on the platform can produce 400~6000 volts. If the worker has treated the insulator during the PCB dismantled or packed in foam box or bubble bag, the net charge accumulated on the workers can reach about 26000 volts.

Therefore, as the main source of ESD hazards, all staff entering the electrostatic protected area (EPA) must be grounded to prevent any charge accumulation, and all surfaces should touch ground to maintain the same potential of everything and prevent ESD from occurring.

Main ESD Prevention Products

The main products used to prevent ESD are wristbands, with curly corduroy and dissipative surfaces or pads – both must be properly grounded. Supplements, such as dissipative footwear or heel straps and suitable clothing, are designed to prevent people from accumulating and maintaining net charges while moving in an electrostatic protection area (EPA).

PCB should also prevent ESD from internal and external transportation during and after assembly. There are many PCB packaging products that can be used in this area, including shielding bags, shipping boxes and mobile trolleys. Although the correct use of these devices will prevent 90% of ESD-related problems, in order to reach the final 10%, another protection is needed: ionization.

The most effective way to neutralize assembly equipment and surfaces that generate electrostatic charges is to use an ionizer, a device that blows ionized air out of the working area to neutralize any charges accumulated on insulating materials.

Antistatic Gloves

Antistatic Gloves

A common fallacy is that because a bowl belt is attached to the workstation, the charges of insulators in the area, such as polystyrene cups or cardboard boxes, will dissipate safely. By definition, insulators do not conduct electricity, and it is impossible to discharge them in addition to ionization.

If a charged insulator is retained in EPA, it will radiate an electrostatic field, causing a net charge to any nearby object, thus increasing the risk of ESD damage to the product. Although many manufacturers try to prevent insulation materials from their EPA, this method is difficult to implement. Insulating materials are too much part of everyday life – from operators’ comfortable foam mats to plastic covers.

Because of the use of ion generators, manufacturers can accept the fact that some insulating materials appear in their EPA. Since ion generation systems continuously neutralize any charge accumulation that may occur on insulators, they are a reasonable investment for any ESD program.

There are two forms of ion generating equipment in standard electronic assembly:

* Desktop type (single fan)

* Overhead equipment (with a series of fans in a single over top unit).

There are also indoor ion generators, but they are mainly used for cleaning rooms.

To use which one depends on the size of the protected area. Desktop ion generators will cover a single working surface, while overhead ion generators will cover two or three. Another advantage is that the ion generator can also prevent dust from sticking to the product and may degrade the appearance.

However, without proper testing and monitoring of the effectiveness of ESD devices, no protection plan is perfect. First-class ESD control and ionization experts report examples of manufacturers using failed (and therefore useless) ESD devices without knowing their failure.

To prevent this, in addition to standard ESD equipment, ESD vendors also provide a variety of constant monitors, which automatically alarm if a performance exceeds the requirements. The monitor can be used as an independent unit or linked together in the network. It also has an automatic data acquisition network software that displays the performance of operators and workstations in real time.

The monitor can simplify ESD plans by eliminating many routine tasks, such as ensuring proper measurements of bowl belts every day, balancing and correct maintenance of ion generators, and no damage to the worktable grounding points.


The first step in preventing ESD is to correctly evaluate how small details can cause irreparable damage if ignored. An effective plan requires not only the use of effective ESD protection equipment, but also rigorous operating procedures to ensure that all plant personnel are ESD safe.

Although many manufacturers use automatic bowl belt testers, it is common to see operators passing tests or failing because the bowl belt is too loose. Many operators attempt to pass the test by holding the tester close to the wrist with the other hand.

Nonetheless, the good news is that ESD is avoidable. The time and money invested in proper equipment and improved safety procedures will be rewarded by increasing the corresponding eligibility rate.

Electrostatic system

As an effective system for electrostatic protection, it is mainly composed of two parts: hardware and software.

The hardware part includes:

* Body electrostatic protection products

* Anti-static logistics transfer products

* Anti-static floor

* Anti-static operation system

* Anti-static earthing

Anti static grounding must be installed in the anti-static work area.

* Environmental control system

Temperature and humidity control equipment should be installed in the anti-static working area, and environmental cleanliness control system should be installed in the assembly of electrostatic sensitive devices with special requirements, so that the production environment can reach the corresponding cleanliness level.

* Special production assembly equipment

Production equipment such as mounter, Bonding, plug and pull, welding and so on should be adopted.

* Special antistatic products.

* Electrostatic measurement (monitoring) system

The software part includes:

* Training

* Antistatic technology and design documents.

* Professional standards for anti static electricity

* Operation procedures and rules and regulations

* Complete quality assurance system

* Anti-static signs

* Storage and transportation requirements

Anti-static shoes are special protective shoes in special environment. They can prevent static electricity and dust. They are suitable for shoes worn in clean rooms such as biopharmaceuticals, electronics factories, aerospace, petrochemical and food factories. Sometimes they do not prevent static electricity long after they are worn. People may think they are broken. In fact,  the problem was that they don’t wear them in the right way. We need to pay attention when we use it.

Why Antistatic Shoes Don't Prevent Electrostatic Discharge

Some people like to wear socks when they wear work shoes, especially when it is cold in winter, cotton thick socks will lead to anti-static performance failure. Socks should wear thin nylon socks or conductive fiber socks, not wool or chemical fiber socks!

Cleaning is another important factor for ESD shoes. Employees need to clean and maintain after wearing them for a period of time. Cleaning is not just for employees to take home for cleaning, but for professional cleaning companies, so as to ensure its special function. Here we need to pay attention to check whether the anti-static effect is up to the standard before cleaning. If the anti-static effect is not up to the standard, it needs to be replaced immediately. Otherwise, it is a waste of money to wash out the non-wearable.