An Introduction to Static Electricity
People have dealt with and managed the problems of static electricity for hundreds of years. For example, in the early 1400s, military forts, implemented static control procedures when dealing with black powder to prevent ignition from Electro Static Discharge (ESD). As early as the 1860s, paper mills throughout the US utilized basic grounding and flame ionization techniques to dissipate static electricity from steel drums and paper webs during the drying process. When the U.S. Navy sent the first nuclear submarine below the north pole in the 1950s, typical antistats were used to reduce static electrical influences on the navigational equipment. Through the years, electrical devices became smaller and faster, thus, more susceptible to the damaging effects of static. In order to assure continued proper functioning of electrical devices, the navy required some form of electrostatic control. As a result of the navy’s mandates, static control awareness increased throughout the world. Subsequently, the static control industry developed products and devices in order to control static electricity and electrostatic discharge.
According to Grolier’s encyclopedia, Static Electricity is electricity at rest or the accumulation of electric charge, as opposed to an electric current which is the movement of electricity. The flow or movement of people and/or materials in and through the environment causes separation and therefore static electricity. A familiar example is when a person walks across a carpeted floor. Static Electricity is generated simply by the contact and separation of the soles of shoes from the carpeted floor. ESD occurs when the electrostatic charge is transferred from a material that carries the charge to an electrostatic sensitive device. In the example above this ESD is the shock felt after walking across the carpeted floor and then touching a door knob. It is this ESD, which comes in varying degrees, that can be most damaging to electrical devices and other industrial, commercial and consumer products.
Static Electricity, a natural phenomenon, and consequently ESD are the primary causes of multiple number of problems affecting industry, business and personal life. These problems can be as simple as the shock resulting from walking across a carpet; as costly as the destruction of sensitive electronic components or jamming of machinery; and as dangerous as the ignition of combustible vapors, powders or dust. Typical problems caused by static;
Attraction of dust, dirt and bacteria to all environmental surfaces, as well as to products and product packages Damage or destruction of sensitive electronic components and sub-assemblies during manufacture, testing, packaging, shipping or receiving.
Computer and electronic office equipment data errors memory loss, system failures and other glitches.
Charge generation on surfaces of tote boxes and carriers used to process and store electronic components can create a potential for discharge. Jamming or slipping of paper, plastics or other material during printing, packaging or converting. Ignition of combustible vapors, dust or solvents causing fire or explosion. Irregularities caused by static in high quality printing, heat sealing, silk screening, lamination and other applications.
Work benches and production surfaces in electronic manufacturing and repair facilities will triboelectric charge components, assemblies, or their handling containers in contact and separation with a surface thereby creating a discharge
1. Almost any material can generate static electricity. The ability to store or dissipate the charge depends on the type of material
2. Static can cause damage to sensitive devices resulting in instant failure. In contrast, static damage can also go undetected for a period of times resulting in product failure once the product is in service.
3. Electrostatic fields are associated with charged objects
4. The degree of severity of ESD events is contingent upon the type of discharge which occurs.
Electrical Characteristics of Materials
In order to understand how to control the generation of static electricity and the prevention of ESD, one must know the different electrical characteristics of materials that can generate static electricity. There are four varying degrees of electrical resistance.
Insulative An insulative material does not allow for the flow of electrons across or through its bulk. In this case, the material has a high electrical resistance. Surface resistivity is greater than 1013 ohms/sq
Antistatic Static Electricity caused due to friction gets dissipated from this type of a material within 2 seconds. The surface resistivity is lower than of insulative material, which enables dilution of charges due to electron movement and redistribution. Surface Resistivity > 109 and < 1013 ohms/sq
Static Dissipative Although static electricity can be generated on this type of material, the material allows the transfer of electrons to ground or other conductive objects. This material has a lower electrical resistance than an insulative material. Surface resistivity >106 ohms/sq < 109 ohms/sq
Conductive Conductive material allows a charge to flow across or through its volume easily. Surface Resistivity < 106 ohms/sq