108 INTERIORS & SOURCES MAY 2015
according to the Electrostatic Discharge Association’s (ESDA) 2010 report,
“Electrostatic Discharge Technology Roadmap,” ESD impacts productivity and
product reliability “in virtually every aspect of the global electronics market. It
is imperative that companies begin to scrutinize the ESD capabilities of their
handling processes.” The report concludes that “It is unlikely that any company
which ignores static control will be able to successfully manufacture and
deliver undamaged electronic parts.”
Further, the effects and annual losses attributed to ESD are estimated to
run into the billions of dollars in the electronics industry alone. Despite a great
deal of effort during the past 30 years to minimize the impact of ESD, it still
interrupts production yields, manufacturing costs, product quality, product
reliability, and profitability across the board3. The cost of damaged devices
themselves ranges from only a few cents for a simple diode to thousands of
dollars for complex integrated circuits. When associated costs of repair and
rework, shipping, labor, and overhead are factored into the equation, the
need for dissipative flooring solutions takes on new significance4.
As a result, many flooring manufacturers have developed products that can
help effectively address ESD problems in a variety of applications. In order to
fully appreciate the solutions that the flooring industry offers, it’s imperative to first
understand the nature of ESD, what causes it, and the risks associated with it.
Effectively managing ESD starts with the knowledge of how electrostatic
charges occur in nature. Let’s take a closer look at the science behind
electrostatic charges and why it’s important for designers and specifiers to
establish a thorough understanding of it.
An electrostatic charge is simply defined as an “electric charge at rest,”
which is most commonly created by the contact and separation of two
materials. Depending on the type of materials in question, the charge can be
relatively high if they are dissimilar (similar materials can produce a charge,
but at lower thresholds). Table 1 below illustrates a number of common
materials that may carry an electrostatic charge.
As a person walks across a carpeted floor, the soles of the shoe come into
and out of contact with the surface, creating an imbalance of electrical charges
within or on the surface of the floor. The imbalance of electrons produces an
electric field that can then be measured. The amount of charge generated in
each case depends upon factors such as the area of contact, the speed of
separation, relative humidity, and chemistry of the materials, among others5.
The process of creating electrostatic charge by contact and separation of
materials described in the example above is known as “triboelectric charging.”
The word “triboelectric” comes from the Greek words, tribo—meaning “to
rub”—and elektros—meaning “amber” (fossilized resin from prehistoric trees).
It involves the transfer of electrons between materials during which the atoms
of a material with no static charge have an equal number of positive (+)
protons in their nucleus and negative (-) electrons orbiting the nucleus6.
Once a charge has been established, a material becomes electrostatically
charged if it is not grounded or dissipated naturally over time. This charge
can then be transferred from the material, creating an electrostatic discharge
or ESD event. Electrostatic discharge, then, is defined as “a swift discharge
of electric current between two objects with different charges and different
numbers of electrons. This exchange of electrons creates a large electromagnetic
field buildup, resulting in ESD.”
ESD has the potential to disrupt the normal operation of an electronic
system and cause equipment malfunction or failure, or degrading or even
destroying it in some cases. The level of the charge that is released depends
upon factors such as the resistance of the actual discharge circuit and the
contact resistance at the interface between contacting surfaces8. Typical voltage
levels of static generation are illustrated in Table 2 below, as well as the role
that relative humidity plays in the accumulation of static charges.
Common Material Sources of Static Electricity
OBJECT OR PROCESS MATERIAL OR ACTIVITY
Work surfaces Waxed, painted, or plastic surfaces
Floors Waxed, common vinyl tiles, sealed concrete
Clothes Common smocks, non-conductive shoes,
Chairs Vinyl, fiber-glass, finished wood
Packaging Common plastic bags, foam, trays, tote boxes
Assembly area Spray cleaners, heat guns, blowers, plastic
tools (e.g. solder suckers, brushes) cathode
SOURCE: MINICIRCUITS.COM Examples of Static Generation: Typical Voltage Levels
MEANS OF GENERATION 10-25% RELATIVE HUMIDITY 65-90% RELATIVE HUMIDITY
Walking across carpet 35,000V 1,500V
Walking across vinyl tile 12,000V 250V
Worker at bench 6,000V 100V
Poly bag picked up from bench 20,000V 1,200V
Chair with urethane foam 18,000V 1,500V
SOURCE: ELECTROSTATIC DISCHARGE ASSOCIATION, 2013.
TOP Any floor with a level of conductivity that minimizes static charge
generation and drains charges to the ground from personnel wearing
conductive footwear falls under the category of ESD flooring.
BOTTOM ESD tiles may be “heat welded” producing a seamless
installation for a precision fit.