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Parts, Packaging, and Assembly Technologies Office
Code 562
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Electrical Engineering Division
Code 560, NASA GSFC Greenbelt, Maryland

ESD Terms

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

Where:

Q = Charge in coulombs

C = Capacitance in farads

 V = Voltage in volts

(Note: This is where a sidebar on the mathematics of ESD could be included.)

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 ionizers.

Dielectric - A non-conductor that can sustain an electric field.

Dielectric Breakdown Voltage - The voltage at which an electrically conductive path is created through a dielectric.

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 potentials.

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 failure.

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 objects.

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 waves.

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)

Ground -

  1. 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.
  2. The position or portion of an electrical circuit at zero potential with respect to the earth.
  3. 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

Where:                        

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 (I/V) characteristics.

Latent Failure - A malfunction, attributable to earlier exposure to ESD, that occurs following a period of normal operation.

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 surface.

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 used.

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 volume resistivity.

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) ] R

Where:

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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