Glossary of ESD Terms
Antistatic: an obsolete term often used generically to describe the full range of static control materials and products. This term has been misused and misapplied, resulting in a great deal of confusion between suppliers and end users. A new term, "low charging," has replaced the word antistatic.
Catastrophic failure: a device that completely ceases to function. It is usually the result of some type of electrical, thermal or mechanical overstress.
Charge device model (CDM): a failure model where the part in question holds an electrostatic charge and rapidly discharges to another object when they are brought into contact. The discharge could cause a device failure.
Conductive material: an ESD protective material having a surface resistivity of 105 ohms per square centimeter (ohms/cm2). If configured correctly, conductive material provides static event shielding.
Degradation: a type of static electricity damage that weaken an electronic device but still allows it to continue to operate within normal parameters. However, a degraded device may later fail catastrophically.
Dissipative material: An ESD protective material having a surface resistivity greater than 105 ohms/cm2, but less than 1012 ohms/cm2.
Electrostatic charge: the type of electrical energy generated during tribocharging. The amount of charge created depends upon the amount of friction generated during contact separation. Other factors include relative humidity, speed of separation and properties of the materials involved.
Electrostatic discharge (ESD): the usually sudden transfer of voltage between bodies at different voltage potentials.
Failure model: several different models have been developed to identify the way an ESD event can damage or destroy a device. The three most common failure models are the charge device model (CDM), the human body model (HBM) and the machine model (MM).
Foot strap: a special device that relies on electrical contact between the user’s shoe and a conductive flooring system to limit electrostatic buildup on the wearer.
Ground: 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 mass is capable of supplying or accepting a large electrical charge.
Grounding: the process of establishing a connection between an electrical circuit or equipment and an earth ground or electrical ground.
Human body model (HBM): people are a primary source of ESD and are often responsible for part damage. Because 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 circuit.
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.
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.
Insulative material: a material having a surface resistivity greater than 1012 ohms/cm2.
Ion: a charged particle, usually of air or nitrogen. The charge can either be positive (+) or negative (-). A positive charge is the result of missing electrons. A negative charge is the result of extra electrons.
Ionization: a device that is used where effective grounding cannot be employed to bleed off static charges, such as a charged insulator. Ion generation is usually accomplished using a high-voltage emitter system.
Latent failure: a device failure that does not occur immediately at the time of overstress. Latent defects are very difficult to measure and usually shorten the life span of a part.
Low charging: refers to the low static charge generation between surfaces that contact and separate. This term has replaced the word "antistatic."
Machine model (MM): an ESD test that simulates automatic handling operations. It is based on a discharge network consisting of a charged 200 picofarad capacitor and (nominally) 0 ohms of series resistance.
Neutralization: the process of eliminating potentially harmful static charges by exposing a charged object to ionized air. The static charges on the surface attract opposite charged ions from the air so that the ions recombine to reform neutral molecules.
Relative humidity: humid air contains moisture that helps 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 or discharge.
Shielding: 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. A conductive, grounded enclosure, such as a Faraday cage, that completely surrounds an object will shield the contents within from the effects of an external electrostatic field. A metallized bag or a conductive tote box are examples of shielding.
Static dissipative material: a material that allows electrons to flow across its surface or through its mass. It is more resistive than conductive material and less resistive than insulative or nonconductive material.
Static electricity: an electrical charge caused by an imbalance of electrons on the surface of a material.
Triboelectric charging: the generation of static electricity that results from two materials coming into contact and then separating. When this phenomenon occurs, one of the materials typically comes away with a positive charge; the other receives a negative charge. Tribo comes from the Latin word meaning "to rub."
Wrist strap: a special device that forms an electrical connection between the user and a ground. It is designed to limit the buildup of electrostatic voltage on the wearer’s skin. Wrist straps usually consist of a conductive bracelet and some type of tether wire with a built-in safety resistance.
Zap: the mild electrical shock a person may feel when he has built up a charge of at least 3,000 volts on his body and then discharges by touching a grounded object at a different electrical potential, causing electrons to transfer suddenly.