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The New Footwear/Flooring Systems Requirements of ANSI/ESD S20.20-2014

ANSI/ESD S20.20 now requires the Operator Walking Test (ANSI/ESD STM97.1) and conformance to Operator Resistance Measurements (ANSI/ESD STM97.2) for product qualification of flooring / footwear systems for grounding personnel.

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Walking Test

What is the importance of the Walking Test?

  • It is necessary to qualify the Footwear / Flooring personnel grounding system for certification to ANSI/ESD S20.20.
  • It can provide records to prove that Footwear / Flooring personnel grounding system used as a static control method is actually providing the performance expected.
  • It is used when testing samples for qualification of a Footwear / Flooring personnel grounding system or on an existing installed floor when evaluating a change in footwear or flooring maintenance.

For Product Qualification, what Operator Resistance Measurements does ANSI/ESD S20.20-2014 state product should test to?

  • < 100 volt peak voltage per ANSI/ESD STM97.2 Voltage in Combination with a Person.
  • < 1 x 109 ohms Resistance per ANSI/ESD STM97.1 Resistance in Combination with a Person.

These are both to be performed in a walk-in environment chamber, including 12% RH.

For more information on the Walking Test and ANSI/ESD STM97.2, click HERE for the ESD Association’s PowerPoint.

Want more information? Sign up for a Free Flooring / Footwear Assessment. The Assessment will only take about 30 minutes of your time. We will demonstrate the Walking Test and provide more information on how you can be sure your Flooring / Footwear personnel grounding system meets the current S20.20 guidelines.

Desco 81705 Series Bags Qualified to MIL-PRF-81705E Type III, Class 2

19210DESCO now manufactures a series of bags which are qualified to MIL-PRF-81705E Type III, Class 2. These products are on the Qualified Product Listing under the Defense Standardization Program. Check our listing HERE.

Standard stock bags are converted per MIL-DTL-117H. For standard sizes and further see the product pages HERE.

The DESCO 81705 bags are made and stocked in our Sanford, NC facility.

Please contact Service@Desco.com for more information.

Fundamentals ESD Control Principles – Personnel Grounding

usewriststraps

Wrist strap connected to continuous monitor.

A fundamental principle of ESD control is to ground conductors including people at ESD protected workstations. Wrist straps are the first line of defense against ESD, the most common personnel grounding device used, and are required to be used if the operator is sitting. The wristband should be worn snug to the skin with its coil cord connected to a common point ground which is connected to ground, preferably equipment ground.

 

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Test wrist straps daily if continuous monitors are not used.

 

 

If continuous monitors are not used, a wrist strap should be tested while being worn at least daily. Part of the path-to-ground is the perspiration layer on the person; an operator with dry skin may inhibit the removal of static charges and may cause a test failure. Specially formulated ESD lotion can solve this problem. Failures may also be caused by dirty or loose wristbands which should be cleaned or tightened. When a wrist strap fails a test, the supervisor should be contacted, and the failure effectively addressed or the wrist strap replaced.

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ESD Footwear are required with an ESD floor for standing and mobile workers.

 

 

 

A Footwear / Flooring system is an alternative for personnel grounding for standing or mobile workers. Foot grounders or other types of ESD footwear are worn while standing or walking on an ESD floor. Both ESD footwear and ESD flooring are required. Wearing ESD footwear on a regular, insulative floor is a waste of time and money.

 

 

 

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Test each foot grounder separately if not using a split footplate.

 

 

ESD footwear is to be worn on both feet and should be tested independently at least daily while being worn. Unless the tester has a split footplate, each foot should be tested independently, typically with the other foot raised in the air.

If an operator leaves the ESD Protected Area and walks outside wearing ESD footwear, care should be taken not to get the ESD footwear soiled. Dirt is typically insulative, and the best practice is to re-test the ESD footwear while being worn each time when re-entering the ESD Protected Area.

 

 

 

Contact Desco for more information on Personnel Grounding.

To shop personnel grounding products, click HERE.

How to Measure Resistance Point-to-Point (Rtt) or Surface-to-Ground (Rtg) in Accordance with ESD Association Documents

The Desco Digital Surface Resistance Meter Kit measures resistance point-to-point (Rtt) or surface-to-ground  (Rtg) of worksurfaces, flooring systems, garments, and other materials in accordance with ESD Association documents: ESD TR53, ANSI/ESD S4.1, ANSI/ESD S7.1, ANSI/ESD STM97.1 and other documents.

Learn more about Desco’s Digital Surface Resistance Meter Kit Here

Operator’s Part in ESD Control

Think Of Static Electricity as Germs and Contamination!

A medical team performing an operationDaily life has other examples of hidden enemies where careful procedures must be followed to regularly obtain positive results. One example is sterilization, which combats germs and contamination in hospitals.

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 invisible, they can cause severe damage. In hospitals, the defense against this invisible threat is extensive contamination control procedures including sterilization.

motherboard doctorsWe are aware of the benefits of sterilization in medicine. We must develop the same attitude towards ESD control and “sterilize” against its contamination. Just as you would never consider having surgery in a contaminated operating room, you should never handle, assemble, or repair electronic assemblies without taking adequate measures against ESD. For the hospital to sterilize most of the instruments is not acceptable; actually it may waste money. Each and every instrument needs to be sterilized. Likewise, it is not acceptable to protect the ESD sensitive items most of the time. Effective ESD control must occur at each and every step where ESDS items are manufactured, processed, assembled, installed, packaged, labeled, serviced, tested, inspected, transported, or otherwise handled.

 The Operator’s Role in Controlling ESD 

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ESD operator need proper training.

In order for the ESD control program to be effective, operators must be aware of the threat of ESD, and understand and adhere to the rules of controlling static electricity, and how to properly use ESD Protected Area (EPA) ESD control items.

ESD control items are ESD protective products that have been specially formulated to possess at least one of the following ESD control properties:

1) low charging (antistatic) – refers to the property of a material that inhibits triboelectric charging.

2) resistance (conductive or dissipative) – able to be grounded

3) shielding – based on a the Faraday Cage concept  and creates an enclosure that attenuates a stationary electrostatic field.

These products should be identified by the ESD Protective Symbol. Note: the ESD Protective Symbol has an arc while the ESD Susceptibility Symbol does not.

The ESD Protective Symbol identifies products designed to provide ESD control protection.handarc

For more information on ESD Control and ESD Control products, visit Desco.com

This is the fifth in a series of blogs concerning the Basics of ESD. Be sure to sign up for our blog to follow the series.

What is OHM’s Law?

Voltage
At this point in our blog series concerning ESD Awareness, we should  consider some basic physics:

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Ohm’s law is an extremely useful equation in the field of electrical/electronic engineering because it describes how voltage, current, and resistance are interrelated.

Ohm’s law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (.i.e. voltage drop or voltage) across two points, and inversely proportional to the resistance between them.

Resistance determines how much current will flow through a component. A very high resistance allows a small
amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in jardinier5ohms.

An analogy to help understand these terms better is a water hose. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the hose size.  For example, you can spray the water further away by increasing the water pressure and consequently the flow rate of the water.  There is a direct relationship between pressure, flow and the hose diameter.

In a similar way, voltage, current and resistance are related to each other by the electrical engineering formula Ohm’s law.

Resistance to ground (Rtg) is a measurement that indicates the capability of an item to conduct an electrical charge (current flow) to an attached ground connection. For ESD control purposes, devices with a Rtg of less 1.0 x 106 are known as conductors (foam, floor mats) and must be connected to ground. ESD Control devices with an Rtg of 1.0 x 106 to < 1.0 x 109 are a special class of conductor, called dissipative (worksurface mats, gloves, smocks) and must also be grounded. The dissipative range of conductors is especially important for ESD control because it “slows down” a static discharge event. Devices with an Rtg of 1.0 x 1011 or greater are known as insulators.  Insulators cannot be grounded and must be removed from the ESD Protected Area or neutralized with ionization.

The measurement may be shown in various ways. Most commonly:

  • 1 kilohm
  • 1kΩ
  • 1 x 103 ohm
  • 10^3 ohm

ohm-chart

For more information on ESD Control and ESD Control products, visit Desco.com

This is the fourth in a series of blogs concerning the Basics of ESD. Be sure to sign up for our blog to follow the series.

ESD Awareness Symbols Explained

Electronic component

Many firms consider all components ESD sensitive. However, it is critical to be aware of the most sensitive item being handled.

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Identify ESD sensitive items with ESD Susceptibility Symbol.

Any ESD sensitive item should be identified with the ESD susceptibility symbol, either on itself or its container. The ESD Susceptibility Symbol (also called Sensitivity or Warning Symbol) identifies items that can be damaged by ESD and must be un-packaged and handled by a properly grounded operator at an ESD protected workstation.

Most firms use the ANSI/ESD S20.20 document to construct their ESD control plan which is based on handling ESD sensitive items having a Human Body Model withstand voltage of 100 volts or greater. The Human Body Model simulates discharges from a person and increasingly tests an electronic device at higher and higher discharges until it fails, thus establishing the device’s withstand voltage.

There are three ESD Awareness Symbols defined in ANSI/ESD S8.1:

ESD Susceptibility Symbol
ESD Protective Symbol
ESD Common Point Ground
To view information about each symbol please click the link or image above.

ESD Susceptibility Symbol

The ESD susceptibility symbol incorporates a reaching hand in a triangle with a slash through it and is used to indicate that an electrical or electronic device or assembly is susceptible to damage from an ESD event. Used to identify ESDS [ESD sensitive items] and that personnel should be grounding when unpackaging or handling that item. It is also referred to as the ESD sensitivity symbol or ESD warning symbol.

ESD Susceptibility Symbol

Application: The ESD susceptibility symbol should be used on assemblies and devices that have a sensitivity to ESD events. The symbol may be incorporated on a sticker used to close or seal ESD protective packaging to indicate that materials inside the package are ESD susceptible.

Format: The symbol is a reaching hand with defined fingers and fingernail, in a contrasting triangle with a slash in front of the hand.

Color: The choice of color for this symbol is arbitrary. The color red shall not be used because it suggests a hazard to personnel. The preferred color is a yellow hand and slash on a black background.

Note: Three Arrows In A Circle Symbol, per ESD Handbook ESD TR20.20 “Military organizations sometimes use MIL-STD-1285 for hardware marking and that document once required the use of the “three arrows in a circle” symbol. That symbol has been changed for consistency with industry marking to the “hand in triangle” ESD Susceptibility symbol”


ESD Protective Symbol

The ESD protective symbol differs from the ESD susceptibility symbol, by the addition of an arc around the outside of the triangle and the omission of the slash across the hand and the triangle.

ESD Protective Symbol

Application: The ESD protective symbol should be used to identify items that are specifically designed to provide ESD protection for ESDS items. Examples of these are packaging, ESD protective clothing and personnel grounding equipment. The ESD protective symbol should also be used on items designed to replace static generative materials. Examples of these items are ESD protective work station equipment, trash can liners, and chairs. The item is to be ESD protective or non-static generative by design.

Color: The choice of color for this symbol is arbitrary. The color red shall not be used because it suggests a hazard to personnel. The preferred color is a yellow hand on a black background.

Note: In Europe per Packaging standard EN 61340-5-3 there is a requirement to place a letter under the triangle denoting the product’s primary ESD control function:

S electrostatic discharge shielding

F electrostatic field shielding

C electrostatic conductive

D electrostatic dissipative

If the letter is “L” the primary ESD control property is low charging (antistatic); if “EPA” is meant to indicate the product is designed to be used in an ESD protected area.


ESD Common Point Ground

This symbol is established to indicate an ESD common point ground, which is defined by ANSI/ESD-S6.1 as “a grounded device where two or more conductors are bonded.”

ESD Common Point Ground
ESD Common Point Ground

Application: The ESD common point ground symbol should be used to indicate the location of an acceptable common point ground as defined by ANSI/ESD-S6.1.

Format: This symbol consists of a bold outer circle inside of which are the words, ESD COMMON POINT GROUND, in bold type. Inside that are two thick contrasting circles and one thick circle that may fill the center or extend to the center where a snap, plug or other fastener may be connected.

Color: The choice of color for this symbol is arbitrary but black or white on green is suggested. The color red shall not be used Earth Bonding Point symbolbecause it suggests a hazard to personnel.

Note: In Europe, for the same purpose the Earth Bonding Point symbol is used:

For more information on ESD Control and ESD Control products, visit Desco.com

This is the third in a series of blogs concerning the Basics of ESD. Be sure to sign up for our blog to follow the series.

Types  Of  ESD Device Damage

ESD damage is not always visible to the naked eye. ESD damage to electronic components can be:

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Catastrophic Failures are immediate and can be least costly.

• Catastrophic Failures

• Latent Defects

Catastrophic failure causes a failure in an ESD sensitive item that is permanent. The ESD event may have caused a metal melt, junction breakdown or oxide failure. Normal inspection is able to detect a catastrophic failure. A latent defect can occur when an ESD sensitive item is exposed to an ESD event and is partially degraded. It may continue to perform its intended function, so may not be detected by normal inspection. However, intermittent or permanent failures may occur at a later time.

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Latent Defects may continue to perform and can be more costly.

COSTLY EFFECTS OF ESD

A catastrophic failure of an electronic component can be the least costly type of ESD damage as it may be detected and repaired at an early manufacturing stage.

 Per ESD Handbook ESD 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.”

 

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Even less than 100 volts might damage a component.

 

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.”

 Latent damage caused by ESD is potentially more costly since damage occurs that cannot be felt, seen, or detected through normal inspection procedures. Latent defects can be very expensive as the product passes all inspection steps, and the product is completed and shipped. Latent defects can severely impact the reputation of a company’s product. Intermittent failures after shipping a product can be frustrating, particularly when the customer returns a product, reporting a problem which the factory again fails to detect. It consequently passes inspection and the product is returned to the customer with the problem unresolved.

The worst event is when the product is installed in a customer’s system, and performs for a while and then performs erratically. It can be very expensive to troubleshoot and provide repairs in this situation.

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Catastrophic failures are detected during inspection but components with latent defects pass as good.

 

 One study indicated the 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

 Industry experts have estimated average electronics product losses due to static discharge to range from 8 to 33%. Others estimate the actual cost of ESD damage to the electronics industry as running into the billions of dollars annually.

The best practice is to ensure proper ESD Control measures are in place to reduce the risk of both Catastrophic Failures and Latent Defects.

For more information on ESD Control and ESD Control products, visit Desco.com

This is the second in a series of blogs concerning the Basics of ESD. Be sure to sign up for our blog to follow the series.

 

 

 

 

ElectroStatic Charges vs Electrostatic Discharges (ESD)

Business man holding electricity light bolt in his hands

Beryllium atom on a white background

Balanced atom with no charge

ElectroStatic charges and ElectroStatic discharges are different. All material can tribocharge (generate ElectroStatic charges). This is static electricity which is an electrical charge at rest. When an electrical charge is not at rest, but discharges (i.e. ESD), problems can occur. All matter is constructed from atoms which have negatively charged electrons circling the atom’s nucleus which includes positively charged protons. The atom having an equal number of electrons and protons balances out having no charge.

 

Electrostatic charges are most commonly created by contact and separation; when two surfaces contact then separate, some atom electrons move from one surface to the other, causing an imbalance. One surface has a positive charge and one surface has a negative charge.

Charge Generation, or Tribocharging Examples

The simple separation of two surfaces, as when tape is pulled off a roll, can cause the transfer of electrons between surfaces, generating an ElectroStatic charge.

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  • Unwinding a roll of tape
  • Gas or liquid moving through a hose or pipe
  • A person walking across a floor with heels and soles contacting and separating from the floor

The amount of static electricity generated varies and is affected by materials, friction, area of contact, and the relative humidity of the environment. At lower relative humidity, charge generation will increase as the environment is drier. Common plastics generally create the greatest static charges.

Typical Electrostatic Voltages

Many common activities may generate charges on a person’s body that are potentially harmful to electronic components. (A higher charge is generated at low humidity, in a dry environment.)esd7new

  • Walking across carpet: 1,500 to 35,000 volts
  • Walking over untreated vinyl floor: 250 to 12,500 volts
  • Vinyl envelop used for work instructions: 600 to 7,000 volts
  • Worker at bench: 700 to 6,000 volts
  • Picking up a common plastic bag from a bench: 1,200 to 20,000 volts

Electrostatic Discharge (ESD)

If two items are at the same electrostatic charge or at equipotential, no discharge will occur. However, if two items are at different levels of ElectroStatic charge, they will want to come into balance. If they are in close enough proximity, there can be a rapid, spontaneous transfer of electrostatic charge. This is called discharge, or ElectroStatic Discharge (ESD).

 Examples in daily life:

  • Lightning, creating lots of heat and light
  • The occasional zap felt when reaching for a door knob
  • The occasional zap felt when sliding out of an automobile and touching the door handle
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Less than 100 volts might damage a component

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 of about 2,000 volts for a person to feel the “zap”. It requires a much larger ESD event to arc and be seen. While a discharge may be a nuisance in the home, ESD is the hidden enemy in a high-tech manufacturing environment. Modern electronic circuitry can be literally burned or melted from these miniature lightning bolts. Even less than 100 volts might damage a sensitive Class 0A component! ESD control is necessary to reduce and limit these ESD events.

 

For more information on ESD Control and ESD Control products, visit Desco.com.

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