Electrostatic discharge (ESD) has been problematic for centu- ries. According to the ESD Association, “As early as the 1400s, European and Caribbean military forts were using static ontrol procedures and devices trying to prevent inadvertent
electrostatic discharge ignition of gunpowder stores. By the 1860s,
paper mills throughout the U.S. employed basic grounding.” Various
motion and activity can create static charge.
Preventing static damage is possible by selecting the proper
ESD protective totes and packaging. ESD protective materials
are categorized as conductive, static dissipative, or antistatic, and
are measured by surface resistivity units of ohms per square.
Conductive surface resistivity
When conductive totes are grounded they bleed off their charge
to the surface upon which they make contact, preventing electrostatic discharges. When conductive totes are enclosed with
covers they also provide a Faraday cage —an electrically continuous conductive enclosure that provides electrostatic protection.
Conductive plastic material is usually made by compounding carbon particle material into plastic resin.
This process permanently changes surface resistivity, essentially changing an electrical insulator to electrical conductor.
Static dissipative mate-
rial should make direct
contact with the electro-
advocate for static dissi-
pative material because
the rate of discharge is
slower than conductive
material. Static dissipa-
tive surface resistivity
can also be achieved by
compounding carbon particles material into plastic resin.
Antistatic surface resistivity
Antistatic material resists high amounts of charge accumulation
thereby preventing triboelectric charging when two dissimilar
objects are separated. Antistatic materials do not need to be
grounded. Some antistatic additives are dependent on the relative
humidity of the environment to attract moisture to the material’s
surface. However, the antistatic property may not be permanent.
The additive may migrate to the surface and evaporate in the air.
Corrugated paper and
ESD protective corrugated paper
and paperboard provide lower
cost and protection. Typically,
this is achieved by coating the
surface of the corrugated paper
or paperboard with carbon black.
Some manufacturers also laminate
the surface with foils and other
materials to achieve ESD protection.
However, paper packaging often
emits small fibers, dust, and corrosive
sulfur contaminates which can damage electronic components. Standard sizes are readily available
from many manufacturers and industrial supply companies.
ESD protective injection and thermo formed molded plastic totes
are available in conductive, static dissipative, and antistatic material.
These totes have a level of durability and can be reused many times.
However, if the optimal molded tote design and size is not standard
from a supplier, customizing molded totes can be cost prohibitive.
For example, tooling costs can be in the five to six figure range for
injection molded totes. Many times manufacturers require minimum order quantities that may exceed the need for the project.
Profile extruded plastic corrugated is also available in ESD
protective conductive and antistatic material in thicknesses
ranging from 2 to 6mm. Conductive corrugated material is
recommended for long term use since antistatic material will
not give permanent static protection.
Corrugated plastic costs more than corrugated paper but
it is more durable. Plastic corrugated containers are available
in stock sizes from some manufacturers and industrial supply
companies. Plastic corrugated is fully customizable for a wide
variety of in-plant uses such as material handling totes with
partitions, storage bins, and shipping containers. Prototypes
and small production runs readily available.
Determine the use
The checklist below contains some design considerations and
questions to be asked. As always, it is useful to obtain input from
all parties involved in using the ESD protective material.
• Will the tote be used as an in-process, shipping, or storage container?
TYPICAL ELECTROSTATIC VOLTAGES VOLTS1
Event Relative Humidity
10% 40% 55%
Walking across a carpet 35,000 15,000 7,500
Walking across a vinyl floor 12,000 5,000 3,000
Motions of bench employee 6,000 800 400
Removing dual in-line packages (DIPs)
From plastic tubes
2,000 700 400
Removing DIPs from vinyl trays 11,500 4,000 2,000
Removing DIPS from polystyrene foam 14,500 5,000 3,500
Removing bubble pack from PWBs 26,000 20,000 7,000
Packing PWBs in foam-lined box 21,000 11,000 5,500
Reprinted from ESD