Air Ionizer - A source of ionized
air. Air naturally contains ions. However, they are not sufficiently
abundant in most cases to neutralize static charges rapidly enough
to protect static sensitive devices. Further, air ions are completely
removed by HEPA and ULPA filters in clean rooms. For this reason,
ESD problems in clean rooms require air ionization to be used.
Antistatic- This is a term that has
fallen in disfavor. A traditional definition was a material that
inhibits or resists triboelectric charging. The term implies that
no static charge will be generated, which is not true.
Antistat, Topical - A chemical compound
applied to the surface or impregnated within a material to render
an insulative material static dissipative. Plastics made static
dissipative through impregnation of topical antistatic agents become
can become depleted by water and alcohol cleaning, rendering them
ineffective. Most topical antistatic agents have significant vapor
pressure. For this reason topical antistatic agents are not to
be used in clean rooms.
Charged Device Model - A model in
which the ESD sensitive device is charged and then discharged.
The fine structures of a MR head are so sensitive to damage, that
heads must not become tribocharged at any time in their processing.
In addition, disks to which heads are merged must not become charged,
or head damage will result during merge.
Conductive Material - Material with
volume resistivity less than 10 5 ohm cm and surface
resistivity less than 10 6 ohm/square.
Conductivity - The ability of a material
to conduct electricity.
Cold Healing - A phenomenon whereby
device characteristics, changed by ESD stress, return to normal
at room temperature.
Conductive Material - A material
with surface resistivity less than 106 ohms per square
or volume resistivity less than 105 ohms.
Coulomb - The unit of electrical
charge, equivalent to 6.24 x 1018 electrons.
Q = CV
Q = Charge in coulombs
C = Capacitance in farads
V = Voltage in volts
(Note: This is where a sidebar on the mathematics of ESD could
Decay Time - Time required for voltage
to reduce to a specified percentage of its initial value. One of
the two principal criteria for evaluating acceptability of air
ionizers and materials used in work stations provided with air
Dielectric - A non-conductor that
can sustain an electric field.
Dielectric Breakdown Voltage - The
voltage at which an electrically conductive path is created through
Dielectric Strength - The rated voltage
(or electric field) above which the creation of an electrically
conductive path through the dielectric is possible.
Electrostatic Discharge (ESD) - The
transfer of electrostatic charge between bodies at different electrostatic
Electrostatic Discharge Sensitive (ESDS) -
The property of a component or assembly that it can be damaged
by electrostatic discharge. Generally reported as voltage using
one of the three test models, human body, machine or charged device.
Electrostatic Field - The lines of
force surrounding an electrically charged object.
Electrostatic Overstress (EOS) -
Exposure of an electronic component or assembly to current or voltage
greater than its maximum rating. EOS may or may not result in catastrophic
Electrostatic Potential - The voltage
difference between a point and an agreed-upon reference.
Electrostatic Shield - A barrier
or enclosure that limits the penetration of an electrostatic field.
ESD Ground - The plug in point, bus
bar, conductive braid, bare wire or metal strip designated as a
connection point to eliminate electrostatic charge on connected
ESD Protected Area - A work environment
with materials and equipment to limit electrostatic voltage, also
called a static safe wo rk area.
ESD Protective - A property of materials
capable of one or more of the following: limiting the generation
of static electricity, dissipating electrostatic charges, or providing
shielding from ESD or electrostatic fields.
ESD Protective Work Station - A work
position with materials and equipment to limit electrostatic voltages.
ESD Protective Work Surface - A work
surface that is intended to discharge electrostatic charges from
materials placed on the surface or from the surface itself.
ESD Susceptibility (Sensitivity) (ESDS) - A
measure of the susceptibility (sensitivity) of an item to ESD damage.
Susceptibility or sensitivity is defined as that level of ESD that
produces changes in characteristics, such that the item fails to
meet its specified parameters.
Faraday Cage - An enclosure that
provides an electrostatic shield. Note: May or may not affect electromagnetic
Field Induced Model - A charged device
model event where the charging method is by electrostatic induction.
Floating Device Model - A model of
an isolated device subjected to an electric field producing a voltage
across the device.
Float Potential - The second measure
of performance of an air ionizer. The highest positive and negative
potential measured using an uncharged, ungrounded charged plate
monitor or ionizer verifier. (See discharge time)
- A conducting connection, whether intentional or accidental
between an electrical circuit or equipment and the earth, or
to some conducting body that serves in place of earth.
- The position or portion of an electrical circuit at zero potential
with respect to the earth.
- A conducting body, such as the earth or the hull of a steel
ship used as a return path for electric currents and as an arbitrary
zero reference point.
Ground Straps - An item intended
to provide a conductive path to ground.
Groundable Point - A designated connection,
location or assembly used on an ESD protective material or device
that is intended to accommodate electrical connection from the
device to an appropriate electrical ground.
Human Body Model - A model representing
the ESD from a human being.
Input Protection - Structures, devices
or networks connected at the terminals of an item to prevent damage
due to ESD.
Insulative Material - A material
that has a surface resistivity greater than 1 x 1012 ohms/square
and volume resistivity greater than 1 x 1011 ohm-cm.
Ionization - The process by which
a neutral atom or molecule acquires a positive or negative charge.
Joule - A unit of energy. One joule
is equal to one volt times one coulomb. One joule is equal to 0.2391
calorie. One calorie is defined as the amount of energy required
to raise the temperature of one gram of water one degree Celsius
at 20 °C. The quantity of energy in a spark necessary to ignite
the optimum mixture of methane (the principal gas in natural gas)
in air is about 0.25 millijoules. The quantity to ignite an optimum
mixture of hydrogen in air is about 0.017 millijoules (about 17
microjoules). [NFPA 77, Recommended Practice on Static Electricity,
1993] By comparison, the quantity of energy to damage to damage
most electronic devices is in the range of 2 to 1,000 nanojoules.
H = ½ C V2
H = Energy in watt sec or joules
C = Capacitance in farads, and
V = Voltage in volts
(Note: A sidebar on units could be included here, tera, giga,
mega, kilo, milli, micro, nano, pico, femto, etc.)
Junction Damage - A power dependent
mechanism resulting in a change in the semiconductor current/voltage
Latent Failure - A malfunction, attributable
to earlier exposure to ESD, that occurs following a period of normal
Oxide Punch-Through - Dielectric
breakdown of an oxide layer, as in a semiconductor device.
Sensitive Electronic Device Symbols - The
symbols placed on hardware assemblies and documentation for identification
of ESDS items.
Shunting Bar - A device that shortens
together the terminals of an ESDS item forming an equipotential
Spark - An electrical discharge of
very short duration, normally between two conductors separated
by a gas (such as air).
Static Decay Test - A procedure that
specifies contact-charging a material and measuring the decay time
to a specific voltage. Decay to 10% of the initial voltage is frequently
Static Dissipative - A material having
a surface resistivity greater then 1 x 106 ohms/square
or 1 x 105 ohm-cm volume resistivity but less than 1
x 1012 ohms/square surface resistivity or 1 x 1011 ohm-cm
Static Electricity - Electrical charge
at rest. The electrical charge is due to the transfer of electrons
within a body (polarization) or from one body to another.
Static Eliminator, Electrical - Electrical
static eliminators generally consist of one or more electrodes
and a high voltage power supply. Ion generation from electrical
static eliminators occurs in the air space surrounding the high
voltage electrodes. (See Air Ionizer, Ionization.)
Static Eliminator, Induction - A
passive device having an electric field of sufficient intensity
to supply ions for static elimination.
Static Eliminator, Nuclear - Nuclear
static eliminators create ions by the irradiation of air molecules.
Most models use an alpha particle emitting isotope to create ion
pairs to neutralize static charges. (See also Ionization, Air Ionizer).
Static Safe Workplace - A workplace
that has been designed to protect ESD sensitive devices from damage
by electrostatic charge. Also called an ESD protected wo rk area.
Step Stress Testing - A test consisting
of increasing stress levels applied sequentially to a sample for
periods of equal duration.
Surface Resistivity (rs) - The
ratio of d.c. voltage drop per unit length to the current per unit
width that passes across the surface of the system. In this case,
the surface consists of a square unit of area. In effect, the surface
resistivity is the resistance between two opposite sides of a square
and is independent of the size of the square or its dimensional
units. Surface resistivity is expressed in ohms/square. When using
a concentric ring fixture, resistivity is expressed in ohms/square.
When using a concentric ring fixture, resistivity is calculated
by using the following expression:
Surface Resistivity = rs = [ 2 p / ln (D2/D1)
D2 = Inside diameter of outer electrode,
D1 = Outside diameter of inner electrode
R = Measured resistance in ohms
Note: This particular term is in review by EOS/ESD Standards Subcommittee
11.0 because the unit, ohm per square (W/sq.), is so confusing.)
Triboelectric Charging - The generation
of electrostatic charges when two pieces of material in intimate
contact are separated. Substantial generation of static electricity
can be caused by contact and separation of two materials or by
rubbing two substances together. (See also Triboelectric Series.)
Triboelectric Series - A list of
substances arranged so that one can become positively charged when
separated from one farther down the list, or negatively charged
when separated from one farther up the list. The series’ main utility
is to indicate likely resultant charge polarities after triboelectric
generation. However, this series is derived from specially prepared
and cleaned materials tested in very controlled conditions. In
everyday circumstances, materials reasonably close to one another
in the series can produce charge polarities opposite to that expected.
This series in only a guide.
Unprotected ESDS Device - An ESD
sensitive device that is not protected by static shielding enclosures
(bag, box or cabinet) and/or having exposed electrical connectors.
Voltage Suppression - A phenomenon
were increasing the capacitance of the object rather than decreasing
the charge on the object reduces the voltage from a charged object.
Volume Resistivity (rv) - The
ratio of the dc voltage per unit thickness to the current per unit
area passing through a material. Volume resistivity is generally
reported in ohm centimeters.
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