Many firms consider all components ESD sensitive. However, it is critical to be aware of the most sensitive item being handled.
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:
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.
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.
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.”
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 because it suggests a hazard to personnel.
Note: In Europe, for the same purpose the Earth Bonding Point symbol is used:
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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.
ESD damage is not always visible to the naked eye. ESD damage to electronic components can be:
• 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.
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.”
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.
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 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.
- 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.)
- 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
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.
All US operations will be closed for the holiday on: Thursday, November 24th and Friday, November 25th in observance of the Thanksgiving holiday.
Operations will resume on November 28, 2016.
Desco got its start as a two-man operation in small warehouse in Brea, CA in 1979. Since that time we have grown to include six USA based factories, 2 locations in the UK,1 location in Japan and to over 300 employees and their families. We are grateful for the those in the Desco family and all the veterans that have served in the armed forces. To see a Power Point of some of Desco family members that have served and their stories please click HERE.
Normal operations will continue at all Desco Industries locations on November 11, 2016. We thank all the veterans and their families.
Indicate surface voltage and polarity of objects.
Insulators must be identified at an ESD work area and must meet the guidelines in the ESDA’s ESD Control Program Handbook-ESD TR20.20.
Non-Process Essential Insulators
If items that can charge to 125 volts or more*, then one of the following will be used:
- Remove the item from the EPA
- Permanently secure, so that insulators that charge to > 125 volts are a minimum of 1″ from ESD susceptible items at all times (12″ from ESDS if can charge 2,000 volts or more)
Process Essential Insulators
If process essential non-conductors / insulators (i.e., circuit board materials, some device packages, and test fixtures) are used in the ESD Protected Area that can charge 125 volts* or more, then one of the following will be used:
- Replace insulators with an ESD protective version (binders, document holders, packaging, foam, chair covers, etc)
- Periodically coat with Reztore Topical Antistat
- Use ionization to neutralize the charge on the item
Use the field meter to verify that the the charge generation ESD protective version products (binders, shop travelers, packaging, foam, chair covers, etc) are < ±125 volts (<±2,000 volts) and ionization test kit to verify the offset voltage (balance) and charge decay of ionization equipment.
* Static field meters are used to measure the charge generation of insulators and isolated / un-grounded conductors. Surface resistance meters are used to measure the Resistance point-to-point (Rtt) and resistance point-to-ground (Rtg).
Click HERE to learn more about Desco Digital Static Field Meter and Ionization Test Kit.
In 1985 Apple produced a service video that explained the importance of ESD control when servicing an Apple II. Steve Wozniak, a co-founder of Apple computers, was featured in the 26 minute video explaining the handling of ESD susceptible devices. Other than the fact that ESD components are smaller and more sensitive than ever (see the ESDA Electrostatic Discharge (ESD) Technology Roadmap – Revised May 2016), the same principles laid out in the 1985 video hold true today. Take a step back in time:
All US based Desco Industries locations will be closed on Monday September 5, 2016 in observance of the Labor Day Holiday. Customer service, production, shipping, and all other departments will be closed. No orders will be processed for the day. Normal operations will resume on Tuesday September 6, 2014.
We thank you for being a valued customer of Desco Industries. Our staff would like to wish you a safe and happy Labor Day weekend.