1. ElectroStatic Discharge (ESD)
ESD BASICS
Basic Concepts in
ElectroStatic Discharge (ESD)
©Copyright 2005 DESCO INDUSTRIES INC.
9/05

2. Introduction ESD Control Training
Per ANSI/ESD S20.20 Training Plan Requirement, "Initial and recurrent ESD awareness and prevention training shall be provided to all personnel”
Per ANSI/ESD S20.20 Training Plan Requirement, "Initial and recurrent ESD awareness and prevention training shall be provided to all personnel who handle or otherwise come into contact with any ESDS (ESD sensitive) items. The type and frequency of ESD training for personnel shall be defined in the Training Plan. The Training Plan shall document the procedures for recording this training in personnel training records. Training methods and the use of specific techniques are of the Organization's option. The option that is selected shall include an objective evaluation technique to ensure trainee comprehension and training adequacy."
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3. Safety Safety First - Concern WHEN Working Around High Voltage
As important as ESD control is, it is of secondary importance compared to employee safety
When working with voltages over 250 VAC, ESD personnel grounding should not be used including Wrist Straps, ESD Footwear & Garments
Ground fault circuit interrupters (GFCI) and other safety protection should be considered wherever personnel might come into contact with electrical sources.
Safety First - Concern WHEN Working Around High Voltage
As important as ESD control is, it is of secondary importance compared to employee safety
When working with voltages over 250 VAC, ESD personnel grounding should not be used, rather ionization may be required to neutralize electrostatic charges. ESD Handbook TR 20.20
ANSI/ESD S20.20 states: "Paragraph 5. PERSONNEL SAFETY
“Ground fault circuit interrupters (GFCI) and other safety protection should be considered wherever personnel might come into contact with electrical sources. Electrical hazard reduction practices should be exercised and proper grounding instructions for equipment must be followed."
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4. Introduction
The written ESD Control Plan should be in accordance with ANSI/ESD S20.20
100 volt Human Body Model limit as a large majority of the ESD products greater than 100 volt sensitivity
ESD Association wrote commercial version of MIL-STD for US Department of Defense which has adopted it
ESD training should be repeated as specified in the company’s written ESD Control Plan
Quizzes in Awareness Guide could be “objective evaluation technique to ensure trainee comprehension and training adequacy.”
The written ESD Control Plan should be in accordance with ANSI/ESD S20.20
Per ESD Handbook TR20.20 section 1.1 Overview “The 100 volt Human Body Model limit was selected for ANSI ESD S20.20 as the baseline susceptibility threshold since a large majority of the ESD products on the market have a sensitivity of greater than 100 volts.”
Per ESD Handbook TR20.20 section 1.1 Overview “ANSI ESD S20.20 is the culmination of the ESD Association’s response to the request of the US Department of Defense to write a commercial version of MIL-STD-1686, Electrostatic Discharge Control Program for Protection of Electrical and Electronic parts, assemblies and equipment (excluding electrically initiated explosive devices).”
ESD training should be repeated as specified in the company’s written ESD Control Plan. The quizzes included in this booklet may be determined as possible “objective evaluation technique to ensure trainee comprehension and training adequacy.” [S20.20]
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5. Static Electricity OR Electrostatic Charge
Defined as Electric charge at rest
All Materials Tribocharge
ElectroStatic Charge Generation or Tribocharging
When 2 Surfaces in Contact then Separate
Some Atom Electrons Move Causing Imbalance
STATIC ELECTRICITY OR ELECTROSTATIC CHARGE
ALL MATERIALS TRIBOCHARGE.
ElectroStatic Charge Generation:
o When 2 surfaces in contact then separate
o Some atom electrons transfer, causing imbalance
One surface has positive charge polarity and one surface has negative charge polarity.
Both polarity charges need to be controlled in your ESD control program. Both positive and negative charges can discharge and damage electronic components. A static field meter can measure the charge of a field, and after contact and separation, show that one item will be negatively charged (having an excess of electrons). The other item will be positively charged (having lost some electrons).
Definition per ESD ADV1.0: Electrostatic charge: Electric charge at rest.
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6. All Materials Tribocharge
ElectroStatic Charge Generation:
One Surface Has Positive Charge & One Surface Has Negative Charge
Radio static
Build up charge walking on carpet, sliding across car seat
When weather is cold and dry
Problem when moves
Per ESD Handbook TR20.20 section 2.1 Introduction "For most people, static electricity is represented by the noise or crackle heard on a radio that interferes with good reception or the shock experienced when touching a metal object after walking across a carpeted room or sliding across a car seat. Static electricity is also observed as static cling when clothes are stuck together after coming out of a clothes dryer. Most of the time, people observe static electricity when the weather is cold and dry. While many people tend to think of static electricity as being at rest or not moving, static electricity causes the most concern when it ceases to be stationary."
Per ESD Handbook TR20.20 section 2.3 Nature of Static Electricity "Electrostatic charge is most commonly formed by the contact and separation of two materials. The materials may be similar or dissimilar although dissimilar materials tend to liberate higher levels of static charge. An example is a person walking across the floor. Static electricity is produced when the person's shoe soles make contact, then separate from the floor surface. Another example is an electronic device sliding into or out of a bag, magazine or tube."
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7. Charge Generation or Tribocharging
When two materials make contact and are then separated, a transfer of electrons from one material to the other may take place.
The amount of static electricity generated depends upon the materials subjected to contact or separation, friction, the area of contact or separation, and the relative humidity of the environment.
At lower relative humidity, as the environment is drier, charge generation will increase significantly. Common plastics generally will create the greatest static charges.
As electrons transfer, the deficiency or surplus of electrons creates an electrical field known as static electricity. The simple separation of two materials, as when tape is pulled off a roll, can create the transfer of electrons between surfaces, generating electrostatic fields.
The amount of static electricity generated depends upon the materials subjected to contact or separation, friction, the area of contact or separation, and the relative humidity of the environment.
At lower relative humidity, as the environment is drier, charge generation will increase significantly. Common plastics generally will create the greatest static charges.
Per ESD Handbook TR20.20 section 2.2 "The phenomenon of forming an electrostatic charge by contact and separation of materials is known as "triboelectric charging", from the Greek -"tribos" meaning "to rub" and "elektros" meaning "amber". It involves the transfer of electrons between materials. The atoms of a material with no static charge will have an equal number of positive (+) protons in their nucleus and negative (-) electrons orbiting the nucleus and is electrically neutral. When the two materials are placed in contact, negatively charged electrons will transfer from the surface of one material to the other material. Electrons are carried off upon separation of the two materials. The material that loses electrons becomes positively charged, while the material that gains electrons is negatively charged. An electrostatic field sensing instrument would now indicate an electrical field emanating from the surface of each charged material. The amount of charge created by triboelectric charging is affected by the area of contact, the speed of separation, relative humidity, and other factors. Once the charge is formed on a material, it becomes an "electrostatic" charge (if it remains on the material.) This charge may be transferred from the material, creating an electrostatic discharge, or ESD, event."
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8. ESD or ElectroStatic Discharge
Charges Seek Balance
Discharge is Rapid
Creating Heat
If two items are at different electrostatic charge levels, as they approach one another, a spark or Electrostatic Discharge (ESD) can occur. This rapid, spontaneous transfer of electrostatic charge can generate heat and melt circuitry in electronic components.
Definition per ESD ADV1.0
"Electrostatic discharge (ESD): "The rapid, spontaneous transfer of electrostatic charge induced by a high electrostatic field. Note: Usually, the charge flows through a spark between two bodies at different electrostatic potentials as they approach one another."
If two items are at different electrostatic charge levels, as they approach one another, a spark or Electrostatic Discharge (ESD) can occur. This rapid, spontaneous transfer of electrostatic charge can generate heat and melt circuitry in electronic components.
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9. Examples Of Electrostatic Discharge or ESD
Lightning
Zap from a door
In a normal environment, like your home, there are innumerable ESD events occurring, most, of which you do not see or feel. It takes a discharge greater than 2,000 volts for a person to feel the discharge. ESD is the hidden enemy in a high tech manufacturing environment. Just because you cannot see or feel an ESD event, it does not mean that ESD events are not occurring. Human beings are insensitive unless the ESD is several thousand volts.
Many electronic components can be damaged by much smaller discharges. There is no exact voltage number where a person starts to feel a discharge. ESD control is necessary to prevent innumerable little lightning bolts or ESD events from occurring. 25% of unidentified electronic failures are typically a result of ESD.
There are innumerable ESD events occurring which you do not see or feel. ESD is the hidden enemy in a high tech manufacturing environment.
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10. Photo of ESD arcing from finger to component
This is not a computer simulation. Technician was connected to a small magneto.
Photos courtesy of Hi-Rel Laboratories, Inc., Spokane, WA
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11. Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
Scanning electron micrograph (SEM) image of the ESD damage after removal of the capacitor metallization. Note the characteristic eruption thru the oxide. Magnification is 10,500 times.
Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
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12. Two Types of Materials Conductors
Electrical Current Flows Easily
So Can be Grounded Examples: metals, carbon and people (due to impurities the human body's sweat layer)
Materials that are called dissipative are conductors, able to remove electrostatic charges to ground. The resistance of dissipative materials is the higher portion of the conductive range.
TYPES OF MATERIALS
CONDUCTORS
o Electrical current flows easily
o Can be grounded
Materials that easily transfer electrons (or charge) between atoms are called conductors and are said to have "free" electrons. Some examples of conductors are metals, carbon, and due to impurities, the human body's sweat layer.
Materials that are called dissipative are conductors, able to remove electrostatic charges to ground. However, the resistance of dissipative materials is the higher portion of the conductive range.
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13. Two Types of Materials Insulators
Insulators or Non-Conductors
Electrical Current Does Not Flow Easily
So Cannot be Grounded Example: Plastics, glass, and dry air
Insulators like this plastic cup will hold the charge and cannot be grounded and "conduct" the charge away.
INSULATORS
o Electrical current does not flow easily
o Cannot be grounded
Non-conductors are called insulators, which are materials that do not easily transfer electrons. Some well known insulators are common plastics, glass, and dry air.
Both conductors and insulators may become "charged" with static electricity.
When a conductor is charged, the ability to transfer electrons gives it the ability to be grounded.
Insulators like this plastic cup will hold the charge and cannot be grounded and "conduct" the charge away.
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14. Typical ElectroStatic Voltages
Walking across a carpet: , ,000 volts
Walking over untreated vinyl floor: ,000 volts
Vinyl envelope used for work instructions: ,000 volts
Worker at a bench: ,000 volts
Many of the common activities you perform daily may generate charges on your body that are potentially harmful to electronic components. (Higher number is the charge generated at low humidity, dry environment.)
Some of these activities include:
Walking across a carpet, 1,500 to 35,000 volts
Walking over untreated vinyl floor, 250 to 12,000 volts
Worker at a bench, 700 to 6,000 volts
Picking up a common plastic bag from a bench, 1,200 to 20,000 volts
Per ESD Handbook TR20.20 section 2.2 "Moisture levels or relative humidity in the environment is an important consideration in static electricity. It is well known that static electricity, in the form of static cling and static shocks are more prevalent when the air is dry. Heating interior air in the winter months dries out the already dry air in the higher latitudes. Static charge accumulation is easier on dry materials since moisture on surfaces tends to allow charges to slowly dissipate or recombine. It is impractical to use humidity control alone to provide static control since static charges are developed even at relative humidity levels of 90% and greater."
Unwinding regular tape: , ,000 volts
Higher number is generated at low humidity
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15. But to Feel a Discharge it must be about 2,000 volts
Costly Effects Of ESD
People Discharge Frequently
But to Feel a Discharge it must be about ,000 volts
When you feel the discharge of electricity, that ESD event is about 2,000 volts of electricity or more.
This "shock," known as Electrostatic Discharge or ESD, is likely responsible for damaging many of the rejected electronic components in your company.
While you can feel electrostatic discharge of 2,000 volts, smaller charges are below the threshold of human sensation.
Unfortunately, smaller ESD events can, and do, damage electronic components. Many of the CMOS technology components used in your facility can be damaged by discharges of less than 1,000 volts. Some of the very sophisticated components can be damaged by charges as low as 10 volts.
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16. ESD That a Person Can’t Feel Can Easily Damage Electronic Components
Even less than100 volts might damage a component!
Many of the Discrete MOSFET (Metal Oxide Semiconductor Field Effect Transistor) devices used in your facility can be damaged by ESD events of less than 1,000 volts.
Some sophisticated components such as used in GMR (Giant Magnetoresistive) disk drive recording heads face challenges from even 10 volt discharges.
EVEN LESS THAN 100 VOLTS MIGHT DAMAGE A COMPONENT
Per ESD Handbook TR20.20 section2.2 "Electronic items continued to become smaller, faster and their susceptibility to static damage increased…all electronic devices required some form of electrostatic control to assure continued operation and product reliability."
Per ESD Handbook TR20.20 section "Static electricity is a natural phenomenon that occurs in all climates and at all levels of relative humidity year round. Most people cannot feel an electrostatic discharge unless the static voltage is greater than 2000 volts.
However, some electronic circuitry can be damaged by ESD that is less than 2000 volts. The damage can be done without people having any sensation of the ESD event.
When a wrist strap is worn properly and connected to ground, the person wearing it will stay near ground potential."
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17. ESD is The Hidden Enemy
Consider all electronic components ESD sensitive
Program may identify classification of sensitivity to ESD damage
Newer electronic components can have reduced width of circuits and microscopic spacing of insulators within them, increasing their sensitivity to ESD
ESD damage cannot be seen by the naked eye
Many firms consider all electronic components ESD sensitive. Otherwise, it is critical to be aware of the relative sensitivity to ESD damage of the devices you may be
working with.
Classifications from the ESD Association help do this. As electronic technology advances, electronic components tend to become smaller and smaller. As the size of these components is reduced, so is the width of circuits and microscopic spacing of insulators within them, increasing their sensitivity to ESD. As you can predict, the need for proper ESD control increases every day.
ESD is the hidden enemy in electronics manufacturing. ESD damage cannot be seen
by the naked eye. Only very sophisticated high magnification photography with the aid of a scanning electron microscope, can show the damage.
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18. Optical photo of a large Integrated Circuit which has experienced ESD damage to the pin noted by the arrow.
Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
Per ESD Handbook TR20.20 section ESD Effects "In the electronics industry, smaller device geometries have resulted in higher density devices. ESD events can cause device damage such as metal vaporization, punch-through of thin oxide layers, or other failure modes. As mentioned earlier ESD events may or may not weaken devices so that they still pass production testing, but fail when installed in a customer's equipment. In extreme cases, such as military or aerospace applications, these failures may even result in loss of life."
Per ESD Handbook TR20.20 section Determining Part ESD Sensitivity "The first step in developing an ESD Control Program plan is to determine the part, assembly or equipment sensitivity level under which the plan is to be developed.
The organization can use one of several methods to determine the ESD sensitivity of the products that are to be handled. Some of the various methods are: 1) Assumption that all ESD products have an HBM sensitivity of 100 volts; 2) Actual testing of products using accepted test methods".
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19. Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
Higher magnification photo of pin noted by the arrow in the prior slide This taken at 400 times magnification on a 4" X 5" photo. The damage is noted as the "fuzz" at the end of the arrow.
Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
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20. Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
Now you see it!! Overlying glassivation has been removed and the surface decorated to show the ESD damage at 5,000 times magnification in this scanning electron micrograph.
Photos courtesy of of Hi-Rel Laboratories, Inc., Spokane, WA
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21. Types Of ESD Device Damage
Catastrophic Failures Inspection is able to detect failure
Latent Defect Component wounded but Inspection passes as good
Catastrophic failures occur when a component is damaged to the point where it is DEAD NOW and it will never again function. This is the easiest type of ESD damage to find since it can be detected during testing.
Latent defects occur when ESD weakens or wounds the component to the point where it will still function properly during testing, but over time the wounded component may cause poor system performance. Later, after final inspection, perhaps in the hands of your customer, a latent defect may become a catastrophic failure.
Not only is this type of damage hard to find, but it also severely affects the reputation of your company's product. Latent defects can cause upset or intermittent failures and be very frustrating, including the customer returning a product with a problem which then again passes all inspections. The cost for repair increases as detection of the failure moves through the system.
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22. Latent Defects More Costly
Sub Assembly passes inspection
Assembly passes inspection
Product passes inspection
Works a while for customer
Then Upsets & Mysterious Problems
More Returns
More Warranty Costs
Lower Customer Satisfaction
Per ESD Handbook TR20.20 section 2.7 Device Damage - Types and Causes "Electrostatic damage to electronic devices can occur at any point, from the manufacture of the device to field service of systems. Damage results from handling the devices in uncontrolled surroundings or when poor ESD control practices are used. Generally damage can manifest itself as a catastrophic failure, parametric change or undetected parametric change (latent defect)."
2.7.1 Catastrophic Failures "When an electronic device is exposed to an ESD event it may no longer function. The ESD event may have caused a metal melt, junction breakdown, or oxide failure. The device's circuitry is permanently damaged, resulting in a catastrophic failure."
2.7.2 Latent Defects "A device that is exposed to an ESD event may be partially degraded, yet continue to perform its intended function. However, the operating life of the device may be reduced dramatically. A product or system incorporating devices with latent defects may experience a premature failure after the user places them in service. Such failures are usually costly to repair and in some applications may create personnel hazards. It is easy with the proper equipment to confirm that a device has experienced catastrophic failure or that a part is degraded or fails test parameters. Basic performance tests will substantiate device damage.
However, latent defects are virtually impossible to prove or detect using current technology, especially after the device is assembled into a finished product. Some studies claim that the number of devices shipped to users with latent defects exceeds the number that fail catastrophically due to ESD in manufacturing."
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23. Repair Costs Increase if Failure Detected Later
One study indicated the repair cost to be:
$10 Device
$10 Device in board - $100
$10 Device in board and in system - $1,000
$10 Device and system fails - $10,000
Catastrophic failures are detected during inspection but components with latent defects pass as good
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24. Latent Defects Most Frustrating
Pass inspection as good
May fail later
Cause equipment down time
Costly field repair work
Adversely impacting customer satisfaction
Hidden Enemy ESD damage may occur
Cannot be felt
Cannot be seen
Not detected through normal inspection procedures
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25. Like Germs, ESD Is The Hidden Enemy
Sterilization in medicine
Control ESD
Control Germs
Damage caused by invisible and undetectable events can be understood by comparing ESD damage to medical contamination of the human body by viruses or bacteria. Although viruses and bacteria are invisible to the naked eye, they can cause severe damage even before you can detect their presence. In hospitals, the defense against this invisible threat is extensive contamination control procedures including sterilization. We are aware of the benefits of sterilization and isolation in medicine. You should develop the same attitude about ESD and "sterilize" against its contamination.
As an employee, the hidden threat of electrostatic discharge or ESD should be of great concern to you. ESD damage can significantly reduce your company's profitability. This may affect your profit sharing, your company's ability to compete in the market place, and even your employment. Everyone likes to take pride in their work, but without proper ESD controls, your best efforts may be destroyed by electrostatic discharges that you can neither feel nor see. .
You would never consider having surgery in a contaminated operating room, you should never handle electronic assemblies without taking adequate protective measures against ESD
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26. The Prerequisites of ESD Control
Identify ESD Protected Area
Identify ESD sensitive items
Provide ESD control training
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27. The Basics Of ESD Control
Ground Conductors
Remove or Neutralize Insulators with Ionizers
Shield ESDS when Stored or Transported outside EPA
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28. Personnel Grounding Devices
Ground Conductors Including People
Personnel Grounding Devices
Wrist Straps
Snug on skin
Clean
Cord connected to ground
GROUNDING
Grounding is very important for the removal of static charges that are generated on conductors. Human beings are conductors and major generators of static electricity, therefore we must remove electrostatic charges from any person who will come in contact with ESD sensitive components or assemblies. Removing static charges from the human body is best accomplished by grounding personnel by means of personnel grounding devices such as wrist straps or ESD footwear. Personnel grounding devices directly connect an operator to ground, removing static charges from the operator's body.
TYPES OF PERSONNEL GROUNDING DEVICES
A basic principle of ESD control is to ground conductors including people at ESD protected workstations. Wrist straps are the most common grounding device used in the industry, to ground people who are the most significant cause of ESD damage. The wrist strap will safely and effectively remove static charges from your body. A wrist strap must be properly grounded to a wrist strap ground.
Foot Grounders
Grounding tab under foot
Worn on both feet
Contact to ESD floor
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29. Daily Test Personnel Grounding Devices
Wrist Straps
Must work, so test wrist strap daily (or use continuous monitors)
Foot Grounders
ESD S1.1 requires that wrist straps be tested on the person, at least daily, or monitored continuously, to determine that no break in the path-to-ground has occured. When seated an an ESD protective workstation, a person must be grounded via a wrist strap.
In some locations, such as the wave solder or test areas, wrist straps may be too confining or unsafe to use. ESD protected footwear or foot grounders may be used on an ESD floor to remove charges from the person to ground.
It is critical that foot grounding devices maintain constant contact with a properly grounded conductive or dissipative floor. Foot grounder grounding tab should be placed in the shoe, underneath one's foot. Foot grounders should be worn on both feet to ensure constant contact to grounded ESD floor or floor mat.
Foot grounders will not function properly if used on surfaces which are insulative, improperly grounded, or highly soiled. It is also advisable that footwear be tested daily to determine if it is functioning properly with a path-to-ground from moisture on the person's skin through the grounding tab and via the conductive/dissipative ESD footwear.
Per OSHA 3075 "Pure water is a poor conductor. But small amounts of impurities in water like salt, acid, solvents, or other materials can turn water itself and substances that generally act as insulators into conductors or better conductors. Dry wood, for example, generally slows or stops the flow of electricity. But when saturated with water, wood turns into a conductor. The same is true of human skin. Dry skin has a fairly high resistance to electric current. But when skin is moist or wet, it acts as a conductor."
Must work, so test foot grounder daily
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30. Workstation Grounding Devices
Dissipative Worksurfaces
Ground ESD worksurface via ground cord to common point ground to equipment ground
Conductive Floor Mats
Dissipative work surfaces are an integral part of the ESD protective workstation, particularly in areas where hand assembly occurs. It is necessary for the work surface to be properly grounded to a common point or equipment ground. It is also recommended to have a dissipative work surface that is clean. This will ensure that the work surface will properly dissipate or remove static charges, and therefore provide proper ESD protection.
ESD protective work surfaces are manufactured in a variety of materials, such as specially modified vinyl, rubber, and high pressure laminates. Conductive and dissipative flooring materials are used in conjunction with ESD footwear. Flooring materials are also available in various forms, most commonly vinyl and rubber matting, floor tiles and dissipative floor finishes. Conductive and dissipative material may generate static charges, but when properly grounded static charges will be removed.
Ground ESD floor mats via ground cord to equipment ground
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31. Clean Using Only ESD Cleaners Dissipative WorkSurfaces
You should be aware of the type of work surfaces and flooring materials used by your company
Be sure to keep your work surface clean, and follow the maintenance procedures recommended by the manufacturer
Regular cleaners contain silicone, an insulator
Per ANSI/EOS/ESD S6.1, Grounding paragraph 4.1.1, "Every element to be grounded at an ESD protected station shall be connected to the same common point ground."
Per ANSI/ESD S20.20 paragraph Grounding / Bonding Systems Guidance, "In most cases, the third wire (green) AC equipment ground is the preferred choice for ground."
Per ESD Handbook TR20.20 paragraph Electrical Considerations "[RTG is] The most important functional consideration for worksurfaces. This establishes the resistance of the primary path to ground for items, placed on the surface. When worksurface materials are being selected, consideration should be given to possible Charged Device Model (CDM) damage to ESD sensitive products. If CDM damage is a concern then setting a lower resistance limit for the worksurface should be considered. Typically, the lower limit for these types of worksurfaces is 1 X10^6 ohms."
ESD Handbook TR20.20 section Maintenance "Periodic cleaning, following the manufacturer's recommendations, is required to maintain proper electrical function of all worksurfaces. Ensure that cleaners that are used do not leave an electrically insulative residue common with some household cleaners that contain silicone."
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32. Neutralize Insulators Via Ionization
Insulators Cannot be grounded
Ionizer air flow floods area with Ions - Neutralizing Charge
The second basic principle of ESD control is to neutralize essential insulators with ionization. Non-essential insulators should be removed from the ESD protected workstation.
Insulators, by definition, are non-conductors. Neutralization may be a necessary part of an ESD program because grounding will not remove charges from insulators such as common plastics. The elimination of charges on insulators does occur naturally by a process called neutralization. Ions are charged particles that are present in the air, and as opposites attract, charges will be neutralized over time.
A common example is a balloon rubbed against clothing and "stuck" on a wall by static charge. After a day or so the natural ions in the air will be attracted to the balloon and will eventually neutralize the charge, and the balloon will drop to the floor.
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33. Direct Ionizer Air Flow to ESD Sensitive Items
Ionizers produce positively and negatively charged ions
Fans airflow to cover the work area
Ionization can reduce static charges on an insulator or isolated conductors
To speed up this process, an ionizer creates billions of ions. Ionizers employ high voltage to produce a balanced mix of positively and negatively charged ions, usually with fans to direct the ions flow over the work area. Ionization can reduce static charges on an insulator or isolated conductors in a matter of seconds (discharge time), thereby reducing their potential to cause ESD damage.
Per ANSI/ESD S20.20 Paragraph Protected Areas Requirement "All nonessential insulators, such as those made of plastics and paper (e.g. coffee cups, food wrappers and personal items) must be removed from the workstation. Ionization or other charge mitigating techniques shall be used at the workstation to neutralize electrostatic fields on all process essential insulators if the electrostatic field is considered a threat."
Per ESD Handbook TR Ionization, Paragraph Introduction and Purpose / General Information "The primary method of static charge control is direct connection to ground for conductors, static dissipative materials, and personnel. A complete static control program must also deal with isolated conductors that cannot be grounded, insulating materials (e.g., most common plastics), and moving personnel who cannot use wrist or heel straps or ESD control flooring and footwear.
Air ionization is not a replacement for grounding methods. It is one component of a complete static control program. Ionizers are used when it is not possible to properly ground everything and as backup to other static control methods."
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34. Types of Ionizers Bench Top Ionizers
Neutralizing Air Nozzles / Hand Gun
Overhead Ionizers
Neutralize charges on insulators and isolated conductors
Ionizers require periodic cleaning of emitter pins
If out of balance (or voltage offset) they can charge items
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35. Shield ESD Sensitive Items Outside Protected Area
Faraday Cage effect charges to be conducted on surface of the conductor.
Since like charges repel, charges will rest on the exterior. Charges Kept on Outside of Package:
Closed Metallized Shielding Bag
Covered In-plant Handler
SHIELDING
The third basic principle of ESD control is shielding ESD sensitive components and assemblies during storage or transportation when not in an ESD protected area. The Faraday Cage is a conductive enclosure which will provide protection to contents as charges will be restricted to the exterior surface of the enclosure. Since like charges repel, a charge on the inside will move and rest on the outside surface of the conductor. There are standard tests measuring the energy penetration of electrostatic fields or discharges to the interior. ESD protective products that provide a Faraday Cage or shielding include ESD Metal-In and Metal-Out Shielding Bags, Impregnated Corrugated Conductive Boxes with buried conductive layer, and other material handling containers.
An impressive demonstration of the Faraday cage effect is that of an aircraft being struck by lightning. This happens frequently, but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, a car may be a safe place to be in a thunderstorm.
Make sure that any container used during the storage and transport of ESDS components or loaded printed circuit boards outside the ESD protected area has appropriate shielding properties to protect them from possible ESD damage.
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36. ESD Packaging
Electrostatic discharge shield "A barrier or enclosure that limits the passage of current and attenuates an electromagnetic field resulting from an electrostatic discharge."
ESD bags should be closed and containers have lids in place
ESD packaging only be opened at an ESD protective workstation by properly grounded personnel.
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37. ESD Protected Workstations
An ESD protective workstation is an area that has been established to effectively control electrostatic charges.
Grounding all conductors (including people)
Removing all insulators
Or neutralizing process essential insulators with an ionizer
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38. ESD Protected Products
Best Practice Remove Insulator or Change to ESD Version
ESD Garments and Gloves
Conductive Foam & Shunt Bars
Dissipative Binders & Document Protectors
Conductive & Dissipative Flooring
ESD Packaging, bags, boxes, etc.
Antistatic or Low Charging Tape
ESD Carpeting, Tiles, etc.
Dissipative Floor Finishes
Material Handling Containers
Per ESD Handbook TR paragraph 2.4 "It should be understood that any object, item, material or person could be a source of static electricity in the work environment. Removal of unnecessary nonconductors, replacing nonconductive materials with dissipative or conductive materials and grounding all conductors are the principle methods of controlling static electricity in the workplace, regardless of the activity."
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39. You Are On The Front Lines Fighting The Hidden Enemy
Only allow trained or escorted people in EPA
Ground all conductors including people at ESD workstation
Test wrist straps at least daily, or use continuous monitors
Test ESD footwear at least daily, if used
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40. You Are On The Front Lines Fighting The Hidden Enemy
Visually check all grounding cords to make sure they are connected
Handle unpacked ESDS items only when grounded
Keep wristband snug, foot grounder grounding tab in shoe, and ESD smocks buttoned up
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41. You Are On The Front Lines Fighting The Hidden Enemy
Make sure Ionizers are maintained and air flow directed at ESDS items
Use shielded packaging for shipping or storing ESD sensitive items outside the ESD Protected Area
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