What
is static electricity / electrostatic
discharge?
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History
People have dealt with and managed the problems of static electricity for hundreds of
years. For example, early military forts, dating back to the 1400's, implemented static
control procedures when dealing with black powder to prevent ignition from electrostatic
discharge (ESD). As early as the 1860's, paper mills throughout the U.S. utilized basic
grounding and flame ionization techniques to dissipate static electricity from steam drums
and paper webs during the drying process. When the U.S. Navy sent the first nuclear
submarine below the North Pole in the 1950's, topical 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/electrostatic
discharge.
Definitions
According to Grolier's Electronic 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 of
static electricity is when a person walks across a carpeted floor. Static
electricity/electrostatic charge is generated simply by the contact and separation of the
soles of that individual's shoes from the carpeted floor.
ELECTROSTATIC DISCHARGE
(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
electrostatic discharge is the "shock" felt after walking across the carpeted
floor and then touching a door knob. It is this electrostatic discharge, which comes in
varying degrees, that can be most damaging to electrical devices and other industrial,
commercial, and consumer products.
Examples of Static Electricity & ESD
Static electricity, a natural phenomenon, and consequently electrostatic discharge are the
primary causes of a myriad 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.....
The attraction of dirt, dust and bacteria to
all environmental surfaces, as well as to products and product packages.
Damage or destruction of sensitive electronic
components and subassemblies 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.
Facts About Static Electricity
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 damage devices, which can result in immediate
product failure to operate. In contrast, static damage can go undetected for a period of
time and the results are 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. The three most common ESD charge transfers are:
- from an external object to the device
- from a device to another object
- resulting from electrostatic fields
Electrical Characteristics of Materials
In order to understand how to control the generation of
static electricity and the prevention of electrostatic discharge, one must know the
different electrical characteristics of materials that can generate static electricity.
There are three 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. (Examples include mica
and rubber.)
STATIC DISSIPATIVE
Although static electricity can be generated on this type of material, this material
allows the transfer of electrons to ground or other conductive objects. This material has
a lower electrical resistance than an Insulative material. (Examples include medium
conductive resin loads and topical anti-stats.)
CONDUCTIVE
Conductive material allows a charge to flow across the surface or through its volume
easily. Thus, conductive materials have a low electrical resistance.(Examples include
shielded bags, foils, metal.)
Five Basic Rules For ESD Control
(As defined by the ESD Association.)
1. Define the boundaries of the
environment in which unprotected electrostatic sensitive devices will be present. This is
the ESD protective area.
2. Define the sensitivity of devices to be handled in the ESD
protective area.
3. Do not contaminate the area with unnecessary non-static
controlled materials.
4. Establish a suitable static control program that both
limits static generation to less than the damage threshold of the most sensitive device in
the environment, and provides a safe, defined path for the dissipation of static charges.
5. Audit the ESD protective area regularly to ensure that
static control is maintained. Document the findings for future reference.
Conclusion
The natural occurrence of static electricity and
electrostatic discharge is the invisible enemy. Static and electrostatic discharge attacks
any business from plastics fabrication to electronics manufacturing and other high tech
industries. Even computer users are not safe from damaging effects of static. It is
estimated that billions of dollars are lost from the daily system or manufacturing
interruptions caused by static. An effective static control program not only requires you
to guard your business or computer against static before it strikes, but also after static
related problems have occurred. ACL Staticide Incorporated has a variety of anti-static
products that will eliminate static discharge thereby saving companies considerable sums
of money.
This information was provided by the ESD Association located
in Rome, New York.
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