Air ion
Groups of about 10 molecules (water, impurities, etc.), bound by polarisation forces into individually charged oxygen or nitrogen molecules.
 
Air Ionizer
Electrically charged source of air molecules (ions).
 
Antistat, agent
A substance applied partially or partially to a material so that the surface is dissipative to static electricity or less sensitive to frictional initiation.
 
Antistatic
Usually refers to the property of a material to inhibit the initiation of electricity by friction. Note: The antistatic characteristics of a material are unnecessarily linked to its impedance or resistance.
 
Auxiliary ground
Separate supplementary earthing conductor, unlike conventionally used earthing devices.
 
Charge decay
Reduction and/or neutralisation of the net residual electrostatic charge.
 
Charge induction
The transfer of charge when an insulated conductor is placed within an electric field (e.g. from a charged body). Note: The momentary grounding of the conductor at this point causes it to acquire a net residual charge.
 
Charged device model
A defined circuit that displays the characteristics of the electrostatic discharge generated when a device insulated from ground is first charged and then grounded.
 
Charged plate monitor(CPM)
A tool for measuring the charge neutralisation properties of ionisation equipment.
 
Cold workstation
A working area with products, components, black boxes or systems that do not use energy.
 
Common point ground
(1) An earthing device for connecting two or more conductors.
(2) A system or method for connecting two or more earthing conductors to the same potential.
 
Component
A finished product, such as resistors, two transistors, crystals, integrated circuits and hybrid circuits.
 
Component failure
A component under test does not comply with one or more of the specified static or dynamic parameter data.
Static parameters about the component are necessary in a non-functional state (spare parts). These parameters may include, but are not limited to: input leakage currents, input breakdown voltages, high and low output voltages, output drive currents, and supply currents.
Dynamic parameters regarding the components are necessary to achieve a functional state (operation). These parameters may include, but are not limited to: full functionality, rise and fall times of the output under specified loads, and the depiction of dynamic currents.
 
Conductive Material
The material has a surface resistivity of less than 1 x 105 ohm/square or a volume resistivity of less than 1 x 104 ohm-cm.
 
Conductivity
(1) The ratio of current per unit area of a material in an electric field (current density). The unit of electrical conductivity is expressed in “Siemens/m”.
(2) In non-technical terms, it is customarily referred to as the ability to conduct current.
 
Contact-mode Discharge
An ESD phenomenon is transferred to the internal part of the component. This transfer is generated by a probe connected to a component pin and this component is not in a socket.
 
Contact-mode, non-socketed discharge
An ESD phenomenon occurs by transferring to the inside of a component. This transfer is generated by a probe connected to a component pin and this component is not in a socket.
 
Decay rate
The amount of reduction in charge or voltage per unit of time.
 
Decay time
The time required to reduce the electrostatic potential to a set percentage of its initial value (usually 10%). (See Static Decay Test.)
 
Dissipative Materials
Materials with a surface resistance greater than or equal to 1 x 1104 ohms but less than 1 x1011 ohms, or a volume resistance greater than or equal to 1 x 104 ohms but less than 1 x1011 ohms.
 
Discharge time
The time necessary to allow the voltage (due to electrostatic discharge) to decay from an initial value to an arbitrarily chosen final value.
 
Electric charge
Lack or excess of electrons.
 
ElectricField Shielding Materials
Materials with a surface resistance or volume resistance of less than 1 x 103.
 
Electrical ionizer
A device for generating ions in a gas using high voltage electrodes.
 
Electrical Overstress(EOS)
The phenomenon of exposure when the current or voltage of an object exceeds its maximum rating. This phenomenon may or may not cause a serious fault.
 
Electrostatic discharge (ESD)
The rapid and spontaneous transfer of electrostatic charges due to a high electrostatic field. Note: Usually when two objects with different electrostatic levels are in close proximity to each other, charge flows through the sparks between them. Details of this process, such as the rate of charge transfer, are described in the specific electrostatic discharge model.
 
Electrostatic discharge ground
A point, electrode, bus, metal strip, or other conductor system that forms a path from a person or object carrying static electricity to ground.
 
Electrostatic discharge protected area (EPA)
Having a specific environment for limiting electrostatic potential materials and equipment.
 
Electrostatic discharge protective
Properties of a material with one or more of the following capabilities: reduction of electrostatic generation, elimination of electrostatic charges, shielding against electrostatic discharge or shielding against electrostatic fields.
 
Electrostatic discharge protective station
An area constructed and equipped with the necessary protective materials and equipment to limit damage to electro-statically discharged sensitive products within it.
 
Electrostatic discharge protective symbol
Graphic for identifying special designs where ESD protection products need to be provided.
 
Electrostatic discharge protective workstation
An area constructed and equipped with the necessary protective materials and equipment to limit damage to electro-statically discharged sensitive products within it.
 
Electrostatic discharge protective worksurface
A working surface where the electrostatic charge is removed by the material placed on the surface or by the surface itself.
 
Electrostatic discharge sensitivity(ESDS)
The ESD level that causes the component to fail. (Note: See Electrostatic discharge susceptibility.)
 
Electrostatic discharge susceptibility
The tendency to be damaged by electrostatic discharge. (See Electro-staticdischarge sensitivity.)
 
Electrostatic discharge susceptibility classification
The products are arranged according to a classification of electrostatic discharge sensitivity voltage values. Note: Various classification methods are available.
 
Electrostatic discharge susceptibility symbol
Graphics placed on hardware, components and documents in order to identify electrostatic discharge sensitive products.
 
Electrostatic discharge susceptible item
Electrical or electronic parts, devices, assemblies, components or equipment having an electrostatic discharge sensitivity level.
 
Electrostatic discharge withstand voltage
The maximum level of electrostatic discharge that does not cause component failure.
 
Electrostatic field
The amount of attraction or push-repulsion generated in space due to the presence of an electric charge.
 
Electrostatic potential
The voltage difference between a point and a reference.
 
Electrostatic shield
A barrier or encapsulant is used to limit the penetration of electrostatic fields.
 
Emitter
A sharp, electrically conductive object, usually a needle or wire, will cause a corona discharge when held at a high potential.
 
Equipment ground
(1) The grounding point of the equipment earth at any part of the end of the equipment conductor.
(2) The terminal of a 3-wire receptacle (green).
(3) The entire low impedance path from a part of the electrical equipment to a hard earth electrode.
 
ESD ground
A system of points, electrodes, buses, metal strips, or other conductors that form a pathway from a static charged body or object to ground.
 
ESD protective
A material property that has one or more of the following capabilities: prevents the generation of static electricity, dissipates static charges on its surface or volume, or provides shielding against ESD or electrostatic fields.
 
ESD protective station
An area that must be constructed and equipped with protective materials and equipment to limit damage to ESD sensitive products by touch within it.
 
ESD sensitivity
Electrostaticdischarge sensitivity and Electrostatic discharge susceptibility.
 
ESD withstand voltage
The highest voltage level that does not cause component failure.
 
ESDS
See ElectrostaticDischarge Susceptible and Electrostatic Discharge Sensitivity.
 
Faraday cage
An electrically conductive housing which attenuates a static electrostatic field.
 
Field induced charging
A charging method that uses electrostatic induction.
 
Flooring/Foot GrounderSystem Resistance
Total resistance when the foot grounder is worn by a person and the person is standing on the static control floor.
 
Foot Grounder System
A foot earthing device worn by the body with an electrical pathway that includes the body and the foot earthing device.
 
Foot Grounder System Resistance
Measurements of the total resistance of the foot earthed should be taken by a person wearing and standing on a stainless steel plate.
 
Ground
(1) A conducted connection between a circuit or device, whether intentional or accidental, and the earth or some conducting object in place of the earth.
(2) This location or part is of zero potential to the earth.
(3) A conducting object used as a return path for electric current like the earth, such as the shell of a steel ship, and an arbitrary zero reference point.
 
Ground cord
Part of the wrist strap with removable winding, completing the electrical connection between the wrist sleeve and the ground and ensuring flexibility of movement.
 
Ground fault circuit interrupter
A device for the protection of persons whose function is to delay the switching of a circuit or part of a circuit for a defined period of time. It is activated when the difference in current between the centre line and the fire line exceeds a number of predetermined values and this overcurrent, which protects the power circuit equipment. This difference in current is usually caused by the earth current.
 
Ground lead
A part of the wrist strap that provides flexibility of movement when a circuit is connected between the wrist sleeve and the earthing system.
 
Ground Pin
The plug or group of plugs that return current to the mains supply is called an earth plug.
 
Ground reference point
A grounding reference point is a fork on the equipment earth wire that can be hand soldered to a workstation grounding point. Examples include: (a) a grounding plug on an AC power cord; (b) a banana plug on a grounding wire; (c) a ring or spade lug on a grounding jumper.
 
Ground strap
(1) A conductor used to provide an electrical earthing path.
(2) A component used to provide an earth path with a specified resistance for personnel.
 
Groundable point
A specific connection location or combination used to provide a suitable electrical ground for ESD protective materials or equipment.
 
Groundable point ESD protective floor material
A point on the flooring material used to provide a suitable ground point for the electrical connection of the flooring material.
 
Groundable point, seating
Conductive castors or grounded drag chains to provide an electrical path between the seat cover and the static control floor or mat.
 
Grounded
Already connected to the ground or some other conducting object as ground.
 
Grounded conductor
A system or circuit conductor that has been deliberately earthed.
 
Grounding conductor
A conductor used to connect the earth circuit of a device or a wiring system to an earth electrode or group of earth electrodes.
 
Grounding resistance
The sum of the resistances from any point on a conducting path to the earth electrode.
 
Hard ground
Connected to ground by wire or other conductor with little or almost no resistance to ground (impedance).
 
Hot work station
A working area with an object, component, black box, or system, with power supply for testing or repair.
 
Human body model
An electrostatic discharge circuit with simulated data conforming to the waveform conditions of standard ESD-S5.1, showing the characteristics of a typical human discharge from a fingertip.
 
Impedance
The total resistance (i.e. resistance or reactance) offered by a circuit to the flow of AC current. It is measured in ohms, with lower ohmic values and better quality conductors.
 
Impedancen. Symbol z
The measurement of the total resistance to the flow of current in an AC circuit consists of two components, ohmic resistance and reactance, usually denoted by the symbol Z = R + iX, where R is the ohmic resistance and X is the reactance. Impedance is measured in ohms.
 
Inductive charging
The transfer of charge from an object when it is momentarily grounded within an electric field.
 
Insulative Materials
Materials with a surface resistance of at least 1 x 1012 ohm/square or a volume resistance of 1 x 1011 ohm-cm.
 
Ionization
The process of acquiring a positive or negative charge from a neutral atom or molecule.
 
Ionizer
Device for generating positive and/or negative air ions.
 
Isolated conductor
There is no grounded conductor.
 
Isolated ground receptacle
A type of earthing for containers where, due to the method of installation of the container, the container is in contact with the earthing conductor of the equipment, and the terminals are electrically insulated.
 
Machine model
The simulation test for electrostatic discharge is based on a discharge network consisting of a 200 microfarad charging capacitor, and a zero ohm series resistor (nominally). The actual series resistance and inductance series is determined by the current waveform of the test item through a short metal wire. This simulated test approximates the electrostatic discharge of a machine.
Main bonding jumper
Provides a connection between the earth circuit conductor and the equipment earth conductor.
 
Monitor, charge(d) plate
An instrument for measuring the charge neutralisation properties of ionic devices.
 
Neutralize
The elimination of an electrostatic field by recombining positive and negative charges, or by conducting either charge to ground, or by introducing an equal and opposite charge.
 
Non-contact mode, non-socketed discharge
An ESD phenomenon caused by the proximity of the probe tip to the device pin, which is not placed in the socket.
 
Nuclear ionizer
An ion-generating device that usually consists of alpha rays stripping electrons from gas molecules until an equal number of positive and negative ions are formed in the gas.
 
Offset voltage
The voltage observed from the insulated conductive plate of a charging plate monitor placed in an ionised environment.
 
Output protection
At the output of the object, components, devices or networks are connected to prevent damage from electrostatic discharge.
 
Oxide punch-through
Insulator breakdown of an oxide layer, e.g. in a semiconductor device.
 
Passive ionizer
A device, usually a sharply grounded spike, close to the discharge surface that forms a conduction pathway for air ions.
 
Peak offset voltage
For pulsed ion generators with a maximum residual voltage for each polarity, this value cycles between positive and negative ion outputs according to the ion generator’s period.
 
Periodic verification
Upon completion of the tests it was noted that the performance of the air ioniser remained unchanged from the initial data to beyond the selected limits.
 
Personnel grounding device
An electrostatic discharge protection device that discharges any electrostatic charge accumulated on the human body to earth.
Note: The impedance to earth of the personnel earthing device must be sufficiently high to avoid causing electrical accidents.
 
Planar material
An object with a surface large enough and flat enough to fit over the surface of an electrode to be used to measure the electrical properties of a material.
 
Point-to-point resistance
The ohmic resistance measured from two electrodes placed on any surface.
 
Garments
The ohmic resistance measured from one point to another on the surface of the same piece of cloth, or on two different pieces of cloth of a garment.
 
Resistance range
The user specified high and low end resistance values define the user acceptable resistance values for the wristband or wristband system.
 
Resistance to ground
The resulting ohmic resistance value measured between an electrode placed on the surface and ground.
 
Resistance to groundable point
The ohmic resistance value measured between an electrode and a ground point placed on a surface.
 
Room ionization
Ionisation system providing ionisation of large areas of air.
 
Service equipment
Required equipment, usually consisting of line breakers or switches and fuses and their accessories, located near the entrance to the power lines of a building or other structure, or of a separately defined area intended to form the main control and disconnection of power.
 
Sleeve-to-Sleeve Resistance
The ohmic resistance value obtained by measuring from the cuff of a garment to the other cuff of the same garment.
 
Socketed Device Model) (SDM
An approximate model of the discharge phenomenon, reproduced in the test system, includes the total charge storage of the ICs, sockets and RLC add-ons of the test simulator, which are discharged to an additional object of lower electrostatic potential (ground) via the relay matrix of the test system.
 
SocketedDevice Model (SDM) Tester
A device that simulates the component socket device model electrostatic discharge (SDM ESD) phenomenon level on a socket
 
Socketed Discharge
A removable isolated material is placed on the current floor and is dissipated by grounded personnel, equipment, or other grounded objects, or related materials that can control the generation and build-up of static charges.
 
Static control (or, electrostatic discharge control)
1. protective measures against electrostatic discharges.
2. General term for measures to reduce the effects of electrostatic discharges.
 
Static control floor
Permanently installed flooring materials, such as tile, carpet, polymer, epoxy, or sheet flooring, dissipate static charges by connecting people, equipment, or other objects on the floor, or control the generation and build-up of static charges associated with the flooring material.
 
Static control floor finish
A non-permanent coating applied periodically to common floor surfaces to dissipate static charges by connecting people, equipment, or other objects on the floor, or to control the generation and build-up of static charges associated with flooring materials.
 
Static control floor mat
A removable island of material is placed on the current floor and is connected to this floor by people, equipment, or other grounded objects to dissipate static charges or to control the generation and build-up of static charges associated with the floor material.
 
Static control floor material
Permanently installed flooring materials, such as tile, carpet, polymer, epoxy, or sheet flooring, dissipate static charges by connecting people, equipment, or other objects on the floor, or control the generation and build-up of static charges associated with the flooring material.
 
Static control footwear (footwear)
A covering for human feet which, when connected to a static control floor or ground, has the property of dissipating static charges, as defined in the standard.
 
Static control footwear (other devices)
Equipment (other than shoes) such as foot straps attached to the human foot, grounded toes, boots, or other electrical connectors that enable the control of static charge build-up when it is connected to a static control floor or ground coating, or floor mat.
 
Static control footwear (shoes)
A covering for human feet which, when attached to a static control floor or ground coating, or mat, has the property of controlling the build-up of static charges.
 
Static control garments
Personnel clothing designed for the control of electrostatic charges.
 
Static control seating
A seat cover designed for use with static control floors or static control mats for chairs that wish to control the generation, build-up and dissipation of static charges.
 
Static decay test
The process of measuring the duration of discharge of an item during which it is first charged to a specified voltage and then drained to a specified voltage.
 
Static dissipative
A property of a material having a surface resistivity of at least 1×105 ohm/square or a volume resistivity of 1×104 ohm-cm, but less than 1×1012ohm/square surface resistivity or 1×101 ohm-cm volume resistivity.
 
Surface resistance
The ratio of the flowing current to the DC voltage between two electrodes on the same side of the contacting material in the specified configuration. The unit of measurement is expressed in ohms.
 
Surface resistivity
Because current flows across the entire surface, this ratio is the ratio of the DC voltage drop per unit length to the surface current per unit width. In essence, the surface resistivity is the resistance between two opposite sides of a square and does not depend on the size of the square or its spatial units. Surface resistivity is expressed in ‘ohms/square’.
 
Triboelectric charging
When two materials come into contact or rub against each other and then separate, an electrostatic charge is generated. (See Triboelectric series)
 
Triboelectric series
A sequence of material arrangements. A material can carry a positive charge when separated from another material further down the sequence, or a negative charge when separated from another material further up the sequence. Note: The sequence is mainly used to indicate the polarity of the charge that may arise after friction. However, the sequence is derived from the special preparation and cleaning of the material and is tested under strictly controlled conditions. In a normal environment, materials properly placed close to another in the sequence are expected to produce charges of opposite polarity to each other. This sequence is only a guide.
 
Voltage suppression
According to the equation V = Q/C, it is better to reduce the voltage (V) of a charged object by increasing its capacitance (C) than by reducing its charge (Q). Note: Voltage suppression is typically reproduced when a charged object is close to ground.
 
Volume resistance of static dissipative materials
The ratio of a specified DC voltage to the current flowing between two electrodes, or in the lower part with a specified structure, touching opposite sides of a material or object. The volume resistance of a static dissipative material is expressed in ohms.
 
Volume resistivity
Ratio of DC voltage per unit thickness of material to the amount of current per unit area passed. The volumetric resistivity is set to ohm-cm.
 
Worksurfaces groundable point
A point on the working face prepared to provide an electrical connection between the working face and a suitable electrical ground.
 
Wrist strap
A combination apparatus comprising a wrist sleeve and an electrically connected grounding cord providing a human skin to ground.
 
Wrist strap system
When a wrist strap is properly worn by a person, its electrical path consists of the person, the wrist sleeve and the grounded flexible wire.

The Class 100 workshop is called Class 100 because of its cleanliness, the number of particles with a particle size greater than or equal to 0.1 microns cannot be greater than 100. The concept that there can be no more than 100 dusts of 0.1 microns in the workshop is what it is all about. So in the protection requirements above strict, do not think that the choice of dust-free clean gloves will not care, this idea is wrong.

Each industry has different requirements for clean rooms, which are graded as 10w, 10,000, 1,000, 100 and 10 (the smaller the number, the higher the clean room grade). Generally speaking the clean room for the food processing industry is class 10w, the electronic industry has relatively high requirements for clean rooms, but a class 10,000 clean room is sufficient for its use, and most clean products are of a higher class than the clean room.

The details of clean gloves are also particularly important, which clean gloves are used in class 100 areas. The following is a list of the details you need to pay attention to when choosing clean gloves for class 100 workshops:

Each industry has different requirements for clean rooms, which are classified as 10w, 10,000, 1,000, 100 and 10 (the smaller the number, the higher the clean room level). Generally speaking, clean rooms in the food processing industry are class 10w and in the electronics industry the requirements for clean rooms are relatively high, but a class 10,000 clean room is sufficient for its use and most clean products are of a higher class than clean rooms.

To sum up, a class 100 clean room should wear class 100 dust-free clean gloves!

WootC nitrile gloves do not contain latex proteins and will not cause allergic reactions. They are also anti-static, ageing and oil resistant and are shaped according to the shape of the human hand, with great sensitivity, excellent stretching and puncture resistance, high tensile strength and excellent abrasion resistance and cleanliness.

Nitrile gloves are mainly processed from nitrile rubber and are used in opto-electronic factories, medical, pharmaceutical, hygiene, food processing and other operating industries to prevent the hand from touching and holding products in the process of production to prevent falling and sweaty hands causing poor product protection.

The main properties are puncture resistance, oil and solvent resistance, fingertip linen treatment to avoid slipping of the apparatus when using, high tensile strength to avoid tearing when wearing, effective to avoid skin allergy caused by powder and cause poor products.

What is Class 100 Nitrile Glove

 

Only ESDP hand tools should be used in the EPA. Manufacturer recommendations for usage and cleaning shall be followed. Component holding trays, microscopes, and other devices or fixtures commonly found in an EPA shall be constructed of metal or permanent static dissipative plastic and shall be maintained at ground potential by placing them on a grounded tabletop while in service at the workstation.

A good practice is to have the technician always touch the metal portion of a tool when picking it up. This practice will assure that any charged metal in the tool will discharge through the technician’s wrist strap to ground.

Soldering Equipment

Soldering iron and desoldering/rework system tips shall be grounded. The resistance between the tool’s tip and its ground shall not exceed 10 ohms. All soldering iron tip grounds in an EPA shall be periodically verified. The test methodology is found in ESD DS13.1 “ESD Association Standard Test Method for Measuring Electrical Potential from Soldering/Desoldering Hand Tools”.

Desoldering Equipment

Only ESD-protective desoldering equipment shall be used when working on ESD sensitive hardware. Only antistatic solder suckers made from metal or having at least a metallized plastic barrel and dissipative tip shall be used in an EPA.

Common Ground at the Workstation

All tools, equipment, or fixtures (such as lead forming tools, test fixtures, lights and solder pots, etc.) that are too large to be placed on the protective work surface shall be connected to the common ground point.

 

Relative Humidity Control

Humidity control is important for an effective ESD program for two primary reasons;

At lower humidity levels (< 30% RH), the dissipation of commonly generated static charges does not take place, thus adding to the probability of ESD events.

Materials (such as pink poly) rely on the moisture in the air to combine with the material’s antistatic agent to form a microscopic conductive layer over the entire surface of the material. At lower humidity, (typically below 15% RH) these antistatic materials can become charged, creating an ESD hazard.

The optimum relative humidity in an EPA is 50% (plus or minus 10%).

When humidity falls below 30% RH, ESDS devices and assemblies shall be processed using special controls and procedures such as air ionization and increased awareness of the greater potential for triboelectric charging. The Facility ESD Monitor must verify the humidity prior to each shift or operation if work is not shift based unless an automatic low humidity alarm system is monitoring the work area. It is highly recommended that facility air handlers include automatic humidifiers to maintain humidity control. EPAs shall control relative humidity within a range of 30 to 70 percent relative humidity.

Air Ionizers

Air ionizers can neutralize the static charge on insulators or isolated objects by charging the molecules of the surrounding area that causes the accumulated charge to be neutralized. Air ionizers are generally used when it is not possible to properly ground everything at the workstation using previously described methods and equipment or as a back up to those methods.

As an example, most adhesive tapes are nonconductors and would require an ionizer to neutralize the charge on the tape if used in close proximity to ESDS devices. An ionizer shall be used at all, times when work is being performed in a Class 1 facility and must be available for use when needed in a Class 2 facility. Ionizers are specifically required for use in some manufacturing operations that generate static charges such as vapor degreasing, vacuum packing, spraying conformal coating, wave soldering, and the use of pressurized air guns. In addition, ionizers are a recognized static charge deterrent when humidity falls below 30 % RH. Any part sensitive to damage below 250 volts requires that an ionizer be used any time the part is removed from its ESDS packaging. Calibration of the air ionizer to verify balance and performance is required.

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

 Dispersion Leakage Elimination Electrostatic Method

For synthetic fiber fabrics, the conductivity of the fabrics can be increased by reducing the resistance. The main method of reducing resistance is to use surfactants to hydrophilicize the fibers or fabrics, so as to improve the hygroscopicity of the fibers, thereby reducing the resistance of textiles, speeding up the charge dissipation, dispersing the charge and eliminating static electricity through propagating, leaking. The antistatic effect of this method is difficult to preserve for a long time, the washing resistance is poor, and the antistatic performance is not shown under low humidity conditions. In addition, in order to reduce the production of electrostatic charge, antistatic oils coated on the interface of textile materials make the friction and contact between materials insufficient and direct, thus reducing the charge transfer. 。 Another mechanism is that the hydrophobic end of surfactant molecule is adsorbed on the surface of the fiber, and hydrophilic groups point to the space, forming a polar interface, adsorbing water molecules in the air, reducing the surface specific resistance of the fiber or fabric, and accelerating the charge dissipation. This is the main way most antistatic agents work. Another way that antistatic agent works is ionization. Ionized antistatic agent itself has good conductivity. Under the action of surface water molecule, this kind of oil agent molecule ionizes, which significantly improves the conductivity of the fiber surface. At the same time, it can eliminate charges by neutralizing the surface charge.

 Dispersion Leakage Elimination Electrostatic Method

Chemical Modification Methods

Antistatic fibers were prepared by blending, copolymerization, grafting modification of fibre-forming polymers, introducing hydrophilic polar groups, or adding antistatic agents inside the fibers. Its common characteristic is to improve the hygroscopicity of fibers and accelerate the charge dissipation. Textiles made from antistatic fibers or blended with high proportion of synthetic fibers can eliminate electrostatic problems in processing and use, but the high humidity environment is still a necessary condition for charge dissipation.

Chemical Modification Methods

Corona discharge method for eliminating static electricity

Fabrics are made of uniformly mixed textile fibers and conductive fibers. Conductive homogeneous conductive fibers such as metal fibers, carbon fibers and conductive polymers or conductive materials such as carbon black coated on the outer layer of synthetic fibers are used to coat conductive fibers, and conductive materials such as carbon black or metal compound polymers are used to prepare conductive composite conductive fibers by composite spinning. The application of conductive fibers makes textiles have remarkable antistatic effect, durability and not affected by environmental humidity, and can be applied to special functional textiles such as antistatic work clothes. Using different electrostatic sequences, different fibers are blended or interwoven to reduce electrostatic.

corona-discharge-method-for-eliminating-static-electricity

The application and development of conductive fibers in the above three methods are the direction of antistatic product development. At present, more and more attention has been paid to them. However, there are many problems that need to be further discussed in the application. For example, the anti-static mechanism of conductive fiber inlay and the evaluation method of anti-static property of fabric containing conductive fiber need to be further studied and discussed.

Cleanroom testing is a very necessary process before the cleanroom is used by the owner after construction. Whether the cleanroom testing meets the standards will directly lead to whether the cleanroom meets the production requirements.

According to the standard of IES-RP-CC006.2 cleanroom test, the working state of cleanroom may fall into three states: empty, static and dynamic. The testing mode depends on the type of cleanroom design and the working state of cleanroom.

Working state of cleanroom

In the construction contract of cleanroom, only the most basic air test is usually specified, while the static and dynamic test is often omitted because of the tight schedule. However, we still recommend that both contractors and owners test the cleanroom under static and dynamic conditions. This will ensure that the construction of the cleanroom meets the design requirements. The comparison of test results under two different conditions, static and dynamic, will provide a very effective help for the analysis of the problems existing in the cleanroom.

For example, under static conditions, the cleanliness reaches the standard, while under dynamic conditions, it doesn’t meet the standard. This may be due to poor cleanroom management: non-standard cleaning when installing machines, inappropriate cleaning procedures, inadequate discipline management, incorrect machine placement (blocking the vent or blocking the air supply of filters), etc.

Therefore, we recommend that the cleanroom be tested in both static and dynamic conditions.

Cleanroom Performance Testing and Reference to Relevant Certification Standard

Cleanroom testing standards and practices

All cleanroom tests are basically based on internationally recognized standards (e.g. ISO14644-1; IEST-RP-CC006.2; NEBB manual and terminated FS-209E). These standards and practices provide the most basic guidance for cleanroom testing and certification. In fact, owners and builders of cleanrooms have different agreements on technical indicators, testing methods and acceptance standards of cleanrooms due to product and process requirements.

Therefore, most acceptance criteria are agreed upon by the owner and builder of the cleanroom through consultation and referring to the recommendations of the professional cleanroom testing and certification company. Since independent third-party testing and certification companies can usually propose suitable solutions for cleanroom testing, we recommend that owners and builders invite testing and certification companies to participate in the discussion of cleanroom technical parameters, testing methods and acceptance criteria. In case of disagreement on relevant parameters or standards, the testing and certification company will act as a mediator between the owner and the builder with their own expertise.

Selection of test items

The recommended cleanroom test items include the uniformity of the air velocity of the filter, leak detection of the filter installation, differential pressure, airflow parallelism, cleanliness, noise, illumination, humidity/temperature and so on. These are the basic test items, which include the main and auxiliary test items. These items should be consistent with the original design criteria and parameters of the clea room, and the test certification should be completed before the cleanroom is transferred to the owner.

Four main items (filter wind speed and uniformity, filter installation leak detection, differential pressure and cleanliness) are the most important and basic in all test items. It must be completed before the equipment enters the cleanroom. Other auxiliary test items such as airflow parallelism (only applicable to one-way flow clean room), temperature, humidity, illumination, noise also need to be completed, because they are related to the movement and environmental parameters of air in clean room. We believe that these auxiliary tests need to be done at least under dynamic conditions.

The performance test of cleanroom is a means to check whether the cleanroom project meets the standards, which will directly affect whether the cleanroom meets the production requirements. Therefore, enterprises should pay attention to the performance test of clean rooms.