by Ryne C. Allen and
Gene Felder, Desco Industries
ESD events are the cause of maddening,
difficult-to-duplicate, and intermittent product malfunctions. They consume a
great deal of time, annoy all involved, and are often never resolved.
Combating the invisible enemy with an
effective ESD control program can produce financial benefits. But the greatest
savings come from decreasing latent defects, which are extremely difficult to
detect after the component is assembled into a finished product.
Any relative contact and physical
separation of materials (or flow of solids, liquids, or particle-laden gases)
can generate electrostatic charges. Common sources include personnel, items
made from common polymeric materials, and processing equipment. ESD can damage
parts by direct contact with a charged source or by electric fields emanating
from charged objects that induce a charge on ungrounded sensitive items.
Although having a duration of less
than a nanosecond but with peak current reaching several amperes, a discharge
of static electricity literally is a miniature lightning bolt, producing heat
that can easily burn through microelectronic structures. A human being cannot
feel the ESD voltage until it reaches approximately 3,000 V, while the ESD
susceptibility or withstand-voltage rating of many components can even be lower
than 50 V.
As the drive for miniaturization has
reduced the width of electronic device structures to as small as 0.10 µm,
electronic components are being manufactured with increased susceptibility to
ESD. For product manufacturers using these electronic components, implementing
an ESD control program has become crucial. A program of this type must provide
continuous ESD protection through all manufacturing steps including inspection,
test, storage, shipment, installation, use, maintenance, replacement, and
Where to Begin
An effective ESD control program is
only as strong as its weakest link. Focusing on these fundamental ESD control
principles is a good place to start:
Clear identification of ESD
susceptible components and products.
Grounding of all conductors,
including personnel, in an ESD protected area.
Removal of nonessential insulators
from ESD protected areas and neutralization of charges on essential insulators
Enclosure of ESD-susceptible items in
static-shielding packaging while being transported or stored outside an ESD
An excellent foundation for an ESD
control program is ANSI/ESD S20.20-1999.1 According to the ESD
Association, “This standard covers the requirements necessary to design,
establish, implement, and maintain an ESD control program for activities that
manufacture, process, assemble, install, package, label, service, test,
inspect, or otherwise handle electrical or electronic parts, assemblies, and
equipment susceptible to damage by ESD greater than or equal to 100-V Human
Body Model (HBM). When handling devices susceptible to less than 100-V HBM,
more stringent ESD control program technical requirements may be required,
including adjustment of program Technical Element Recommended Ranges.”
In conjunction with the standard, the
ESD Association has begun an S20.20 certification program in which it appoints
ISO 9000 registrars to be approved to conduct audits according to S20.20. If a
company handles ESD-susceptible products, within some period of time, it is
likely that a prerequisite for doing business will be to become certified to
In addition to staying in business,
the benefits of optimizing an ESD control program can be huge. With improved
quality, productivity, and customer satisfaction, companies also can convert
ESD control from a prerequisite to a competitive advantage. For example, a
properly designed and successfully deployed ESD control program can prompt a
return on investment of up to 1,000% per year.2
An effective ESD control program
requires the support of top management and all other departments within a
company. ESD control knowledge and appreciation and a functioning ESD committee
with representation from all departments also are imperative.
An ESD control plan should be based on
the withstand voltage of the most susceptible components used in the facility
or work cell. Examples of ESD-susceptible parts are microcircuits, discrete
semiconductors, thick and thin film resistors, hybrid devices, and
piezoelectric crystals. Typically, the easiest way to establish the ESD
susceptibility of items in your facility is to refer to the Reliability
Analysis Center V-ZAP data book that contains ESD susceptibility data for
Writing the Program
Write an ESD control program plan per
S20.20 paragraph 6.0.1: “ESD Control Program Requirements—The Program shall
include both Administrative and Technical Requirements. The Organization shall
establish, document, implement, maintain, and verify the compliance of the
The plan must include guidelines for
personnel training, verification that the plan is being followed, and a list of
the technical requirements and ESD protective products approved for use in the
program. S20.20 paragraph 126.96.36.199 states:
“The Plan is the principal document
for implementing and verifying the Program. The goal is a fully implemented and
integrated Program that conforms to internal quality system
requirements….Efforts to identify and eliminate defects, and prevent their
introduction, shall be a component of the Plan to reduce the cost and risk
associated with ESD damage.”
Before we get to the key issues of ESD
control, it is important to note that personnel safety is paramount. In no way
should an ESD control program replace or supersede any requirements for
In the factory, grounding personnel
around the AC power line is a possible hazard. Personal grounding should not be
used when working around voltages greater than 250 VAC. Although personal
grounding items must include a 1-MW resistor to limit current to less than 0.25
mA, ground fault circuit interrupters should be used.
Typical Control Program
Written plans for an ESD control
program generally include the following:
Clearly identify ESD protected areas;
personnel should never enter an ESD protected area without taking the proper
Open or remove ESD-susceptible items
from protective containers only within an ESD protective workstation or area.
Personnel should be at ground
potential when handling ESD-susceptible items. When seated, they must wear a
wrist strap fitting snugly on the skin and have it plugged into a common-point
ground. If ESD-protected flooring is used as a primary grounding method, then
grounders must be worn on each foot in an ESD-protected area.
Remove unnecessary, high-charging
materials from ESD-protected worksurfaces, particularly common plastics or any
other electrostatic-generating items.
Clean ESD mats and
conductive/dissipative surfaces regularly and only with cleaners that do not
leave an insulative residue.
Cover work and storage surfaces in
ESD-protected areas with static-dissipative material, such as matting or
high-pressure laminate. Ground work and storage surfaces; daisy-chaining is not
Identify all ESD-susceptible items
with ESD susceptibility symbols and enclose them within ESD shielding bags or
other sealed conductive or shielding container during storage or transportation
outside an ESD protected area.
Neutralize insulative material or
other static-generating items necessary in the production process with an
ionizer. Test ionizers periodically to ensure balance and charge decay.
Test personnel and worksurface
grounding devices periodically and maintain records of test results.
Train and test personnel to verify
that they understand the principles of ESD control and how to effectively use
ESD protective equipment.
Conduct routine auditing and
inspection of ESD-protected work areas at regular intervals.
Specify test equipment.
Specify ESD protective products such
as wrist straps, mats, flooring, footwear, packaging, garments, and ionizers.
An ESD control program typically will
adopt the recommended range listed in Table 1 of S20.20:
ESD Protective Work Surface: <1.0
× 109 W tested per ESD S4.1, with the
lower limit of 1.0 × 106 as recommended in ESD-ADV 53.1.
ESD Protective Flooring or Floor
Mats: <1.0 × 109 W tested per ESD
S7.1. When the flooring/footwear system is the primary grounding method, an
S20.20 recommended range is <3.5 × 107 W
tested per ESD STM 97.1 where the resistance measurement is in combination with
the person or the charge generation is less than 100 V tested per ESD STM 97.2.
Wrist-Strap System: <3.5 ×107
W per ESD S1.1, which will provide a continuous
electrical path from the user directly to ground. Alternately, a continuous
monitoring system can be used.
ESD Protective Footwear: heel straps,
toe straps, or conductive shoes that provide a continuous electrical path from
the user directly to the ESD protective flooring or mat <1.0 × 109
W; shoes tested per ESD S9.1.
Electrostatic Generating Sources:
Nonessential and personal items shall not be placed on ESD protective
worksurfaces. Essential materials under normal use shall not cause or generate
static voltages of greater than ±2,000 V within 12 in. of unprotected
ESD Protective Garments: 1 × 105
to 1 × 1011 W tested per ESD STM 2.1. ESD
smocks may be used to shield ESD-susceptible items from charges on insulative
clothing. When worn, they should cover all personal garments above the wrist
except at the neck area and make intimate contact with the skin. The ESD smock
must be grounded, otherwise it becomes an isolated ungrounded conductor.
Ionizers: ±50 V voltage offset tested
per ESD S3.1.
A company’s written ESD control plan
should be cost-effective. S20.20 may not apply to all situations. Additional
precautions may be necessary if the withstand voltage of the components is less
than 100-V HBM. In addition to the HBM, the Charge Device Model (CDM) should be
considered when tailoring your plan.
Requirements can be relaxed when
appropriate. Per S20.20 paragraph 6.0.3, “Tailoring is accomplished by
evaluating the applicability of each requirement for the specific application.
Upon completion of the evaluation, requirements may be added, modified, or
deleted. Tailoring decisions, including rationale, shall be documented in the
ESD Control Program Plan.”1
To be effective, an ESD control
program must be comprehensive and documented into a protection plan that
encompasses the processes, personnel, and ESD-susceptible devices. This plan
must be adjusted to suit each company’s specific needs, but should follow basic
guidelines as set forth by S20.20. In addition, management support, personnel
training, and consequential follow-up audits are part of an effective ESD
control program.5 By following this advice, companies can turn ESD
control programs into a competitive advantage—a strategic tool focused on
quality, productivity, and customer satisfaction improvement.
ANSI/ESD S20.20-1999 Protection of
Electrical and Electronic Parts, Assemblies and Equipment (Excluding
Electrically Initiated Explosive Devices), ESD Association, 1999.
Allen, R., “ESD Control and ROI,” EE-Evaluation
Engineering, November 1999, pp. S2-5.
VZAP-95 Electrostatic Discharge
Susceptibility Data Book, Reliability Analysis Center.
Allen, R., “How to Set Up an ESD
Control Program,” EE-Evaluation Engineering, February 1999, pp. 112-123.
Allen, R., “Audits Essential to
Successful ESD Control Programs,” EE-Evaluation Engineering, December
1999, pp. 92-97.
About the Authors
Ryne C. Allen is the technical manager
at ESD Systems.com, a division of Desco Industries. Previously, he was chief
engineer and lab manager at the Plasma Science and Microelectronics Research
Laboratory at Northeastern University. The NARTE-certified ESD control engineer
is an active member of the ESD Association on several standards working groups
and secretary and webmaster of the local Northeast Chapter. He graduated from
Northeastern University with B.S.E.E, M.S.E.E., and M.B.A. degrees. ESD
Systems, 19 Brigham St., Unit 9, Marlboro, MA 01752-3170, 508-485-7390.
Gene Felder is the corporate product manager at Desco Industries. Before
joining Desco, he was general manager of BW/IP International SR Engineering.
Mr. Felder graduated from California State University with a B.A. in business
administration and earned an M.B.A. from the Anderson School of Management at
the University of California at Los Angeles. He is a member of the ESD
Association and APICS-certified in Integrated Resource Management. Desco
Industries, 3651 Walnut Ave., Chino, CA 91710, 909-627-8178, e-mail:
*Reproduced with Permission,