A
Air Ionizer
- Ionizers produce large quantities of both positive and negative ions, usually air or
nitrogen molecules. These ions are directed in areas where electrostatically charged
objects require neutralization. The ion of the opposite polarity is attracted to the
charged object eventually will neutralize it. Ionizers are used where effective grounding
cannot be employed to bleed off static charges, such as a charged insulator. Ion
generation is usually accomplished using either a high-voltage emitter system or through
the alpha particle emission from a radioactive polonium source.
Antistat
- A material or agent that can be applied to materials to lower their surface resistivity
and/or increase lubricity to lower static charge voltage and reduce the time to dissipate
the voltage quickly. See Topical Antistat.
Antistatic Material
- An obsolete term that described materials with a surface resistivity
from 109 to 1014 Ohms per Square. This material only reduces the
amount of charge generated by tribocharging, but provides only
limited protection from an ESD event. The preferred replacement materials are Static
Dissipative. See Surface Resistivity.
Other Materials: Static Dissipative Conductive
Audit
- An evaluation of an area, activity, or process designed to identify potential sources of
ESD. An audit can be either formal or informal, but the goal is to reduce the possibility
of device damage by reducing or eliminating static charge buildup.
Avalanche breakdown
- Although the actual electrical power associated with an ESD pulse is very small, the
time interval is also very small and localized resistive heating can occur within the
affected device. If the heat buildup is sufficient, it can actually exceed the melt
temperature of the device and a short or open circuit can result within the device. This
is also called avalanche breakdown. Within a semiconductor device, this often occurs at
the emitter-base junction because this junction has the smallest physical dimensions of
any junction within the device. See Failure Mechanism.
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B
Bulk breakdown
- This is very similar to thermal secondary breakdown and results in changes to junction
parameters due to high temperatures. See Failure Mechanism.
Burn-in
- A process where a device or assembly is subjected to electrical or physical stress to
simulate actual or accelerated use. It is designed to verify the function of the device
under test and also to weed out any possible devices with latent defects.
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C
Capacitance
- Capacitance is the ability of an object to store an electrical charge. The capacitance
of the object can also change as it changes shape or location. As it relates to ESD, an
object can release its electrical energy via an ESD spark when its capacitance suddenly
drops. For example, a common poly bag sitting on a bench may hold only a few hundred volts
of ESD charge, but when picked up by an operator, the decrease in capacitance can increase
the voltage to several thousand volts - enough to produce a spark.
Catastrophic failure
- A device that completely ceases to function. It is usually the result of some type of
electrical, thermal, of mechanical overstress. This overstress is often caused by ESD such
as a discharge from a person or an object. See Failure Mechanism.
Caution Labels - ESD
- See Labels, ESD Caution.
Charged device model
- A failure model where the part in question holds an electrostatic charge and rapidly
discharges to another object when they are brought into contact. For example, a device
which becomes charged while sliding down a chute might then discharge suddenly when it
makes contact with a tote tray. The discharge could then cause a device failure.
(CDM Waveform) See Failure Model.
Classification testing
- Classification testing used to determine whether a device is ESD sensitive and how it
should be classified. ESDS Classifications
Conductive material
- An ESD protective material having a surface resistivity of 105
ohms/square maximum. (105=100,000) If configured correctly, provides static
event shielding, see Faraday Cage and Surface
Resistivity.
Other Materials: Antistatic Static Dissipative
Contact separation
- When two materials are brought into close contact and then separated, a transfer of
electrons occurs between them. One material will acquire a positive charge and the other
material will acquire a negative charge. If either of the materials is an insulator, the
charge imbalance will stay localized on the surface at the point of separation.
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D
Decay time
- The time for a static charge to be reduced to a given percent (usually 10%) of the
charge's peak voltage.
Dielectric breakdown
- The dielectric regions within a semiconductor have a unique breakdown voltage associated
with them. When an applied voltage, such as an ESD pulse, exceeds this voltage, a
dielectric puncture can occur. Depending upon the amount of pulse energy, the puncture may
fuse and the device may either exhibit a reduced breakdown voltage; an increased leakage
current (both possible parametric failures); or fail completely.
See Failure Mechanism.
Dissipative material:
- An ESD protective material having a surface resistivity greater than
106 but not greater than 1012 ohms/square. (106=1,000,000,000
and 1012=1,000,000,000,000). See Surface Resistivity.
Other Materials: Antistatic Conductive
DOD-HDBK-263
- A military handbook which provides guidance to develop, implement, and monitor elements
of an ESD control program.
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E
Electrical and electronic part
- A part such as a microcircuit, discrete semiconductor, resistor, capacitor, thick or
thin film device, or piezoelectric crystal.
-
Electrical Overstress (EOS)
- An event which results from applying a voltage or current that exceeds a device's
rating. It may originate from an electrical surge, or an electrostatic discharge (ESD).
ESD is only one type of overstress. EOS can cause either a catastrophic or parametric
device failure. It is also thought that latent damage could result from EOS that might
weaken the device (and shorten it's service life) without immediately destroying it.
Typically comes from a power source such as an IC or board tester, a circuit power supply
or hot swapping a board. See Failure Mechanism.
Electrostatic charge
- The type of electrical energy generated during tribocharging. The
amount of charge generated depends upon the amount of friction generated during contact
separation. Other factors include relative humidity, speed of separation, and properties
of the materials involved. Typical voltages generated at 50% relative humidity from common
in-plant activities are:
Walk across carpet--10,000 volts
Walk across tile-- 5,000 volts
Working at bench-- 1,500 volts
Removing ICs from tube-- 700 volts
Electrostatic detector
- When an electrostatic charge is present, it will usually establish an electrostatic
field radiating from the source of the charge. An electrostatic fieldmeter is a device
designed to measure the magnitude of this field. It is a very useful analysis tool to
evaluate how electrostatic charges accumulate that result from different types of
processes, activities, personnel, and materials.
Electrostatic discharge (ESD)
- The usually sudden transfer of an ESD voltage potential from one object to another with
a lower potential either by inductance or direct contact.
Electrostatic field
- A voltage gradient (difference) between an electrostatically charged surface and another
surface at a different voltage.
Electrostatic field-meter
- When an electrostatic charge is present, it will usually establish an electrostatic
field radiating from the source of the charge. An electrostatic field meter is a device
designed to measure the magnitude of this field. It is a very useful analysis tool to
evaluate how electrostatic charges accumulate that result from different types of
processes, activities, personnel, and materials.
EOS/ESD Association
- A non-profit industry association dedicated to promoting the exchange
of technical information and high standards of professionalism among its members. It's
primary field of interest is the advancement of the theory and practice of electrical
overstress avoidance, with emphasis on electrostatic discharge phenomena. Reach them at:
200 Liberty Plaza
Rome, NY 13440
(315) 339-6937
EOS/ESD Association
ESD (electrostatic discharge)
- The usually sudden transfer of an ESD voltage potential from one object to another with
a lower potential either by inductance or direct contact.
Is a rapid flow of electrons between two bodies of unequal charge or between one charged
body and ground with an electronic circuit being the path of least resistance between the two.
Ouch! But it happens when ESD handling precautions are lacking or overlooked.
See Failure Mechanism.
ESD protected area:
- Is an area where parts, assemblies, and equipment are handled in line
with the ESD sensitivity of the device. A protected area is constructed, equipped and
maintained with the necessary ESD protective materials and equipment to insure that
voltages are below the sensitivity level of the most ESD sensitive device handled in your
facility.
Ground Soft Ground
Hard Ground Apparel
Flooring Handling
Work Surface Table Mat
Floor Mat Wrist Strap
Foot Strap Tote Box
Air Ionizer Topical Antistat
ESD packaging material
- A material capable of one or more of the following:--Limiting the
generation of static electricity--Rapidly dissipating electrostatic charges over its
surface or volume--Providing shielding from ESD spark discharge or electrostatic fields.
ESD packaging materials are classified in accordance with their surface resistivity as
conductive, static dissipative and the less effective antistatic. See Surface
Resistivity.
Antistatic Static
Dissipative Conductive
ESD protective materials
- Are designed to provide a means to protect, or shield, a device from
this field. If the material is conductive enough it can form a "Faraday cage"
which can eliminate more than 99% of the effect of the local electrostatic field on the
contents of the shielding enclosure. The shielding effect is the reason that conductive
bags and tote boxes are in common use today.
Materials: Static Dissipative
Conductive
ESD protective packaging
- Packaging with ESD protective materials or properties to prevent
damage to ESD items.
Materials: Antistatic
Static Dissipative Conductive
ESD pulse
- The usually sudden transfer of an ESD voltage potential from one object to another with
a lower potential either by inductance or direct contact. The goal of ESD control programs
is to eliminate electrostatic charge buildup and to prevent ESD from occurring.
See Failure Mechanism.
ESD spark testing
- This is a special type of sensitivity testing where an ESD discharge in the form of a
spark is used to try to cause device failure or equipment upset.
ESD upset
- A loss of test data or incorrect test signals caused by ESD or the electromagnetic pulse
associated with an ESD spark. The device under test (DUT) may not be actually damaged, but
may only appear to be operating incorrectly. See Failure Mechanism.
EURONORM
Model
- Multi-conductor cables are another source of ESD primarily when connecting electronic
equipment. Bundled conductor sheaths within a cable can create excess charge through
triboelectric charging. This charge will migrate when the cable end is attached to the
equipment. The equipment may be turned on or turned off. The resulting discharge can
be in a range from 2kV to 20kV. The common values assigned to this model are:
Actual values of impedance on cables will vary but the above values are used for
standardized stressing in the laboratory. The current applicable testing standard is IEC 1000-4-2.
(EURONORM Waveform) See Failure Model.
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F
Failure analysis
- The process of evaluating an electronic part to determine the cause of its failure. This
information can often be used to determine the specific type of overstress so that some
way of preventing it may be found. See Failure Mechanism.
Failure mechanism (from ESD)
- ESD can cause device failure in one of several different ways. Listed below are the most
common failure modes. For a discussion of each mode, see the cross referenced definition.
1. Thermal secondary breakdown
2. Metallization meltdown
3. Dielectric breakdown
4. Gaseous arc discharge
5. Bulk breakdown
6. Metallization Meltdown or & "Fusing"
7. Parametric Failure
8. Surface Breakdown
9. Joule Heating
10.Latent Defects
11.Catastrophic Failure
12.ESD Upset
13.Electrical Overstress
Failure models
- ESD failure can occur from a variety of different methods. A series of different models
have been developed to identify the way an ESD event can damage or destroy a device. Each
model is listed below. An explanation of each model can be found by referring to the
definition of each in the glossary.
1. Charged device model
2. Human body model
3. Machine model
4. Field induced model
5. Floating Device model. Any of the models listed can result in
device failure from one or more ESD failure mechanisms.
Faraday cage
- A conductive, grounded enclosure which completely surrounds an object. It will shield
the contents within from the effects of an external electrostatic field. This concept is
of great practical use in protecting ESD sensitive items. For example, a metallized bag or
a conductive tote box can provide excellent Faraday cage shielding to protect its
contents. This shielding is also effective in most cases even when the conductive
enclosure is not grounded. See Ground, Soft
Ground &/or Hard Ground
Field induced model
- A failure model where the part in question becomes charged through the influence of a
nearby electrostatic field. If the device is grounded, a sufficient current flow can
result in device failure. If the device is not grounded, it will acquire an electrostatic
charge itself from the field. A charged device model discharge can then occur as the part
comes in contact with another object at a lower voltage potential. See Failure
Model.
Floating device model
- A specific type of field-induced model where the part in question is electrically
isolated from ground and acquires a static charge. See Failure Model.
Floor mat
- A floor covering material used to reduce or eliminate static charge buildup associated
with walking or standing. Floor mats are usually used as an alternative to a complete
conductive flooring system to provide local ESD protection. ESD floor mats are generally
soft or rigid pads and should be connected to ground with a proper current-limiting
resistor for personnel safety. See Ground, Soft
Ground &/or Hard Ground
Foot ground strap
- This device functions in the same manner as a wrist strap assembly except it relies on
electrical contact between the user's shoe and a conductive flooring system to limit
electrostatic buildup on the wearer. See Ground,
Soft Ground &/or Hard Ground
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G
Gaseous arc discharge
- This type of failure can occur in devices with closely spaced electrodes. An ESD energy
pulse can arc between electrodes and cause melting and fusing of the electrodes. A failure
can occur when the resultant fusing takes place along a path which then causes an open
circuit.
Ground
- A mass such as the earth, a ship or vehicle hull, capable of supplying or accepting a
large electrical charge. See Soft Ground &/or Hard Ground
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H
Handled or handling
- Actions in which items are manipulated by hand or machine during such steps as
inspection, assembling, manufacturing, processing, testing, repairing, reworking,
maintaining, installing, transporting, failure analysis, wrapping, packaging, labeling, or
marking.
Handling procedures:
- A detailed set of steps identifying proper methods for transport, storage, and handling
of ESD sensitive devices. (MIL-STD-1686)
Hard ground
- A connection to ground either directly or through a low impedance (resistance).
See Ground &/or Soft Ground
Human body model
- People are a primary source of ESD and are often responsible for part damage. Since the
human body has a charge-storage capacitance and a highly conductive sweat layer, the
discharge from a person's touch can be simulated using a resistor-capacitor (or RC)
circuit. Values for this circuit are typically:
R = 1,500 ohms
C = 100 Pf
Although actual values vary between individuals, these values are the
commonly used for standardizing the ESD sensitivity of parts. (HBM
Waveform) See Failure
Model.
Human body model discharge
- This is the type of failure model where an ESD pulse similar to that produced by a
charged individual causes part failure. This ESD failure model can produce any one of
several types of failures. See Failure Model.
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I
IC's
- Are ESDS (electro-static discharge sensitivity) classified as class 1 through class 3:
Class 1 = Sensitive to voltages of 1,000 volts or less
Class 2 = Sensitive to voltages greater than 1,000 volts and up to 4,000 volts
Class 3 = Sensitive to voltages greater then 4,000 volts up to 15,000 volts
Inductance
- An energy phenomenon that occurs as an electric field changes strength or polarity.
During this transition, changes in the field can cause an electrical current to flow in a
nearby object. As it relates to ESD, a charged object such as a plastic tray can induce a
current flow in an ESDS device without actually touching it. If the induced current is
high enough, it can cause an ESD failure.
Inductive charging
- A process in which an electrically floating (i.e. not grounded) object or surface is
subjected to an electrostatic field. The exposed object will then acquire an electrostatic
charge as a result of this exposure. Regardless of the means of charge generation, a
charged object or surface will still present the threat of static discharge.
Insulative material
- A material having a surface resistivity greater than 1012 ohms/square.
See Surface .
Insulator
- A material which will not conduct electricity. Insulators can often tribocharge to very
high levels since a charge will remain stationary, or static, on its surface for long
periods of time unless neutralized in some way, such as ionization.
Integrated circuit (IC)
- A semiconductor device where the function of a circuit composed of many components such
as transistors, resistors, capacitors, etc. are duplicated by a single chip of silicon.
Also known as an "IC".
Ion
- A charged particle, usually of air or nitrogen. The charge can be either positive (+) or
negative (-). A positive charge is the result of missing electron(s), a negative charge is
the result of extra electron(s).
Ionizers
- Ionizers produce large quantities of both positive and negative ions, usually air or
nitrogen molecules. These ions are directed in areas where electrostatically charged
objects require neutralization. The ion of the opposite polarity is attracted to the
charged object eventually will neutralize it. Ionizers are used where effective grounding
cannot be employed to bleed off static charges, such as a charged insulator. Ion
generation is usually accomplished using either a high-voltage emitter system or through
the alpha particle emission from a radioactive polonium source
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J
JEDEC Publication 108
- A specification describing minimum requirements for ESD control
methods and materials used to protect electronic devices that are susceptible to damage or
degradation from ESD. Published by
Electronic Industries Association
Engineering Department
2001 Pennsylvania, N.W.
Washington, D.C. 2006
(800) 854-7179
Electronics Industry Association
Joule Heating
- Usually refers to simple heating of materials due to power dissipation in the material.
The combination of current and voltage determines the power dissipated. The instantaneous
high voltage and current involved in ESD events combined with the microscopic dimensions
of materials can and often does result in extremely high temperatures. In many cases these
temperatures exceed 550 Degrees Centigrade (1022 Degrees Fahrenheit). Obviously, this
results in damage to most materials. See Failure Mechanism.
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K
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L
Labels - ESD Caution
- National uses one of two different ESD Caution labels. These industry standard ESD
symbols are printed on the packing materials to inform distributors and users that ESD
precautions and proper handling procedures must be utilized to insure the quality of the
IC's and electronic end products using the semiconductors inside. Both labels indicate to
the end user that these devices must be handled at ESD protected (safe) workstations,
using ESD safe handling practices.
Static Safe Work stations should also be easy to identify, they should be marked or
labeled with a label similar to this example:
See: Protected Area
Latent failure
- A device failure which does not occur immediately at the time of overstress. Latent
defects are very difficult to measure and are thought to shorten the life of the part.
Finding latent defects in parts or assemblies is part of the reason that product burn-in
is conducted. See Failure Mechanism.
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M
Machine Model
- An electrostatic discharge simulation test based on a discharge network consisting of a
charged 200 picofarad capacitor and (nominally) zero Ohms of series resistance. Actual
series resistance and inductance are specified in terms of the current waveform through a
shorting wire. The simulation test approximates the electrostatic discharge from a
machine. (MM Waveform)
See Failure Model.
Metallization meltdown
- Electronic devices often contain ultra-thin layers of metallization for circuit
function. As an ESD pulse travels through a device, internal device resistance can produce
localized resistive heating. If the magnitude of the ESD charge is sufficient, this local
heating can melt the metallization layer and produce a short or open circuit. This process
is very similar to thermal secondary breakdown except that it occurs at a different
location. See Failure Mechanism.
MIL-STD-1686
- A military standard which covers specific program requirements to establish and
implement an ESD control program for devices subject to damage up to 15,000 volts.
Mirror Effect
- Whenever a charged insulative material is in contact with a conductive surface, a
balanced opposite charge "appears" in the conductive surface. The electric field
normally "seen" by field meters is the sum of the charge on the insulator and
the mirror image in the conductor. This results in the meter reading zero (0) volts.
However, the charged insulative material can not discharge into the conductor. When the
insulator is removed from the conductive surface the charge "magically"
reappears. Actually, it never disappeared in the first place.
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N
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O
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P
Parametric failure
- An electrical or electronic part is designed to perform within a specified set of
limits, or parameters when used within a circuit. When ESD damage causes a change in the
part's operating parameters to exceed design values, it is said to be a parametric failure
even though it is still operational.
See Failure Mechanism.
Popcorn Effect
- May be electrically detected as an open or intermittent contact. Visual
defects may not be obvious, but may include cracked package, missing package
material, bulging or deformed package. Does not necessarily imply device
failure.
This problem generally occurs when an IC is mounted to a PC board via wave
or infrared soldering techniques. The rapid heating associated with these
procedures causes moisture in the package to vaporize. The resulting
pressure exceeds the yield strength of the epoxy mold compound (plastic) and
my cause the observed damage. The word "popcorn" is the term used
describing the IC forcefully detaching itself from the PC board..
Protected area
- An area where parts, assemblies, and equipment are handled in
accordance with their ESD sensitivity. A protected area is constructed and equipped with
the necessary ESD protective materials and equipment to limit ESD voltage below the
sensitivity level of the ESDS item handled therein.
Ground Soft Ground
Hard Ground Apparel
Flooring Handling
Work Surface Table Mat
Floor Mat Wrist Strap
Foot Strap Tote Box
Air Ionizer Topical Antistat
Caution Labels
Protective apparel
- Articles of clothing specifically designed to prevent the buildup of a static charge.
Included are things such as smocks, finger cots, and gloves.
Protective flooring
- A flooring type that will inhibit the buildup of a static charge or will provide a path
to ground for the effective bleed-off of a static charge. When used with some type of foot
grounding system, it can be an effective means of ESD protection.
See Ground,Soft Ground &/or
Hard Ground
Protective handling
- Handling of ESDS items in a manner to prevent damage from ESD.
Protective work surface
- The top surface of a workbench where work is performed. An ESD protective surface can be
either conductive, static dissipative, or antistatic depending upon how the work surface
is being used and what level of ESD protection is required. Protective materials for work
surfaces include soft mats, rigid mats, high-pressure laminates, coatings, and metal. They
should be connected to ground with a proper current-limiting resistor for personnel
safety. See Ground, Soft Ground &/or
Hard Ground
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Q
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R
Relative humidity
- Humid air contains moisture which helps to dissipate electrostatic charges and reduce
charge buildup by increasing surface conductivity. High relative humidity will reduce
charge formation, but will not prevent static charge buildup and discharge. Ionized air
can also be used to dissipate static charges, either with or instead of high relative
humidity.
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S
Shielding (electrostatic)
- An electrostatic field radiates in the area surrounding most charged objects. This field
can produce an ESD event or inductively charge other objects nearby and produce
undesirable results.
See Faraday Cage
Shorting bars
- Also called shunting bars, or shunts. These can either be rigid or foam shapes designed
to electrically short device leads and reduce the possibility of ESD damage.
Shunt
- Also called shorting bars or tie bars. These can either be rigid or foam shapes designed
to electrically short device leads and reduce the possibility of ESD damage.
Soft ground
- A connection to ground through an impedance sufficiently high to limit current flow to
safe levels for personnel (normally 5 milliamperes). Impedance needed for a soft ground is
dependent upon the voltage levels which could be contacted by personnel near the ground.
Spark
- The sudden transfer of electrical or electrostatic energy through the air from an object
with a higher voltage (potential) to an object at a lower voltage. Usually, several
thousand volts are necessary to overcome even a small air gap for a spark to occur. The
goal of an ESD control program is to eliminate the chances for sparks or any other type of
electrostatic discharge. See Failure Mechanism.
Static dissipative materials
- An ESD protective material having a surface resistivity greater than 105 but
not greater than 109 ohms/square. 105 =100,000 and 109
=1,000,000,000. See Surface Resistivity.
Surface breakdown
- This is a type of dielectric breakdown. It is a localized narrowing of the junction at
the surface of the device and usually results in a high leakage path which often causes
the junction to be bypassed. Like other ESD failure mechanisms, it is caused by an ESD
pulse of short duration and sufficient energy to cause a permanent change within the
device. See Failure Mechanism.
Surface resistivity
- Surface resistivity is a numerical measure of material or surface's ability to resist
the flow of electrical current. It is expressed in ohms per square because surface
resistivity is numerically equal to the resistance between two electrodes forming opposite
sides of a square. The size of the square is immaterial.
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T
Table mat
- The top surface of a workbench where work is performed. An ESD protective surface can be
either conductive, static dissipative, or antistatic depending upon how the work surface
is being used and what level of ESD protection is required. Protective materials for work
surfaces include soft mats, rigid mats, high-pressure laminates, coatings, and metal. They
should be connected to ground with a proper current-limiting resistor for personnel
safety. See Ground, Soft Ground &/or
Hard Ground
Thermal secondary breakdown
- Although the actual electrical power associated with an ESD pulse is very small, the
time interval is also very small and localized resistive heating can occur within the
affected device. If the heat buildup is sufficient, it can actually exceed the melt
temperature of the device and a short or open circuit can result within the device. This
is also called avalanche breakdown. Within a semiconductor device, this often occurs at
the emitter-base junction because this junction has the smallest physical dimensions of
any junction within the device. See Failure Mechanism.
Thin-film devices
- A device, such as a resistor or capacitor which relies on an extremely thin layer of
dielectric material for proper function. If an ESD pulse of sufficient strength is applied
to a thin-film device, the resulting overstress can rupture the dielectric layer and
produce either a parametric or catastrophic failure.
Tie bars
- Also called shunting bars, or shunts. These can either be rigid or foam shapes designed
to electrically short device leads and reduce the possibility of ESD damage.
Topical Antistat
- Chemical agents which are applied to the surface of insulative materials to make them
more conductive or to greatly reduce their tendency to generate static. They are effective
by increasing the lubricity and conductivity of the surface of the material. They often
have a limited service life so care should be taken during their use to maintain their
desirable antistatic properties. See Surface Resistivity.
Tote box
- A box or tray used for transporting and storing parts or assemblies. Material selection
for tote boxes should be made based upon whether simple antistatic properties or complete
shielding is required. See Surface Resistivity.
Tribocharging
- When two materials are brought into close contact and then separated, a transfer of
electrons occurs between them. One material will acquire a positive charge and the other
material will acquire a negative charge. If either of the materials is an insulator, the
charge imbalance will stay localized on the surface at the point of separation.
Triboelectric effect
- A phenomenon where an electrostatic charge imbalance is created due to contact
separation, or tribocharging of two materials. During this process, electrons will
"strip away" from one of the materials and accumulate on the other. A table
showing the relative tendency of materials to behave in this fashion is called a
triboelectric series. Tribo comes from the Latin word meaning "to rub".
Triboelectric series
- A list of materials in order of positive to negative charging when rubbed together. A
substance higher on the list will positively charge when rubbed against a substance lower
on the list. The lower substance will charge negatively due to an excess of free
electrons. There are also many other factors which affect the degree to which an
electrostatic charge will form when two objects rub together such as: speed of separation,
humidity, pressure, and cleanliness. Because of these other variables, the series should
only be used as a general guide because it does not absolutely predict charge polarity.
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V
Van de Graf Generator
- Often seen as science fair demonstration projects. This device utilizes the
triboelectric effect. A belt of a material at one end of the triboelectric series is
driven at high speed over a stationary and isolated bar of material from the other end of
the triboelectric series. This is very similar to rubbing your shoes on carpet. A high
voltage is generated up to the point that spectacular arcs (sparks) form to nearby
conductive objects. One common effect is to have a person with long hair stand on an
insulative surface and then touch the high voltage end of the generator, their hair then
stands straight out. Unfortunately, this same kind of device can be formed accidentally.
The most common form is to slide tote boxes, circuit boards, etc. across work surfaces.
Another common form is the common conveyor belt system. Extremely high voltages are formed
in these cases, with multiple ESD events occurring within seconds.
Voltage
- A measure of electrical potential. One volt is the amount of electrical energy required
to cause a current of 1 amp to flow through a resistor of 1 ohm. A voltage will flow from
a source of higher voltage (potential) to an object at a lower voltage
(potential). A
voltage charge becomes stationary, or static, on a surface when there is no way for it to
drain away because there is no path to ground or the charged material is an insulator.
Voltage suppression
- A charged object, such as a plastic poly bag, can be placed flat on a workbench. Using
an electrostatic field meter, it would seem that the charge on the bag disappears as it is
placed on the bench. However, the charge still remains, but the voltage is greatly reduced
because the apparent capacitance of the bag increases while it is in contact with the
bench. When the bag is lifted away from the bench, the charge seems to reappear. This
phenomenon of voltage suppression is described by Q=CV and simply represents the inverse
relationship between capacitance (C) and voltage (V) when the total charge (Q) stays the
same.
Volume resistivity
- Volume resistivity is the numerical measure of the resistance to electrical current flow
through a material. It is similar to surface resistivity except that the added variable of
material thickness produces a value expressed in ohms per centimeter of thickness.
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Warning Labels - ESD
- See Labels, ESD Caution.
Work bench
- This term is commonly used for the entire class of work surfaces where handling of ESD
sensitive parts is performed. The work bench surface should be connected to ground with an
appropriate current limiting resistor; and it should also have an ESD protective work
surface. See Ground, Soft Ground &/or
Hard Ground.
Work surface
- The top surface of a workbench where work is performed. An ESD protective surface can be
either conductive, static dissipative, or antistatic depending upon how the work surface
is being used and what level of ESD protection is required. Protective materials for work
surfaces include soft mats, rigid mats, high-pressure laminates, coatings, and metal. They
should be connected to ground with a proper current-limiting resistor for personnel
safety. See Surface Resistivity, Ground,
Soft Ground &/or Hard Ground
Wrist strap assembly
- A type of personnel grounding strap which forms an electrical connection between the
individual and a ground (usually a soft ground). It is designed to limit the buildup of
electrostatic voltage on the skin of the wearer. It usually consists of a conductive
bracelet and some type of tether wire with a built-in safety resistance.
See Ground, Soft Ground &/or
Hard Ground
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