Copyright (c) 1999, Desco
Reproduced with Permission, EE-Evaluation Engineering,
An ESD audit is an essential part of
a good ESD control program. This checks all ESD control practices
and products, provides a constant reminder to personnel of their
responsibilities, and gives management the necessary feedback for
any corrective action.
An audit is based on an ESD control
program plan that has been defined, approved by management, and
implemented at all operating levels. Generally such a program is
based on some industry-generated standards. The new parent document
for an Electrostatic Control Discharge Program developed and controlled
by the ESD Association is the ANSI/ESD S20.20-1999, an excellent
choice for a guiding standard.
In the audit, all facets of the program
must be checked to see that they are in accordance with defined
company procedures. Any discrepancies must be recorded and reported
to the work area supervisor and to company management. Graphic summaries
are helpful tools for presenting audit results, and will enable
managers to commend personnel in areas that have improved and to
detect and analyze problems in areas that are having difficulties.
Each company’s audit procedures
are unique to the local control program or plan, but certain aspects
will be part of every program. The major areas to be examined are
work area integrity, operator conformance to proper procedures,
condition of the workbench and floor, and general aspects of the
It is highly recommended to on
occasion include external auditors in the audit process to ensure
a non-biased audit. External Auditors can include personnel from
other work areas, location or even hired consultants.
The audit must verify that the
boundary that separates an ESD-Protected (ESDP) area from non-ESDP
areas is clearly defined. Signs, directional arrows, aisle marking
tape, and other methods may be used. This is a reminder to the workers
in that area, of course, but also reminds visitors that they are
entering or exiting a sensitive control environment.
When entering an ESDP area, it
should be easily identified by the use of signs, posters or other
designations to enforce the proper use of ESD controls.
Any supply carts in the sensitive
area used to store or transport ESD sensitive devices should have
the uprights and shelves electrically connected and grounded to
the ESD ground via a drag chain to minimize tribocharging. A permanently
attached ground snap to the cart is highly recommended for hard
grounding the cart when docked in an ESDP area.
Cleaning crews, contractor personnel,
and maintenance workers must come into sensitive areas from time
to time. These visiting personnel should be quizzed or trained for
ESD safe practices before entering ESDP areas and asked to not touch
ESD-Sensitive (ESDS) devices. If ESDS devices are stored in ESDP
packaging, then this problem is minimized. Depending on their involvement
with ESD sensitive devices or proximity to, their training does
not need to be extensive.
Any visitor who will be in the area
for an extended period should be required to wear a smock of a different
color from regular workers, or should be given a different-colored
badge for control purposes. This makes it easy to identify and monitor
them for ESD Safe practices.
Generally, assembly workers clean their
own workbenches, and outsiders are forbidden to touch anything on
the benches unless they are properly trained and protected. This
should be verified by the audit.
Every operator, supervisor,
material handler, or other employee that comes near ESDS equipment
or parts should go through an orientation to be certified or trained
in ESD Safe practices according to the internal ESD control plan.
A yearly refresher ESD control training program is recommended for
Certification records should be readily
available to the auditor and to area supervisors. In reality, the
operators are the full-time ESD monitors, and this role should be
There should be a prominently-posted
self-checking procedure in the area, and the auditor must verify
that each operator is aware of the procedure and follows it every
day. One such procedure requires each employee to:
check the work area for charge generators,
don and test personal grounding devices,
check for insulators and clear them from the
verify that sensitive devices are in ESDP
packaging with proper labels,
make sure that there are no static generators
inside ESDP packaging with ESDS items,
determine that the approved cleaners are on
verify that wiring of discharge devices is
see that if an ionizer is used, it is positioned
and working properly, and
make sure that non-grounded personnel stay
a least a foot away from your static-safe area.
Some companies require that every person
entering the sensitive area pass a grounding test, and that certification
be verified. The audit must verify that such a system, if implemented,
is operating properly.
Each operator must wear the prescribed
grounding devices at all times. A useful device is the continuous
monitor, which tests the wrist strap and static mat connections
continuously, and sounds an alarm when there is a problem. If each
operator uses such a monitor, the auditor must verify proper operation.
If the continuous monitor is not used, the audit must determine
that wrist straps are checked daily. The same goes for heel straps,
if they are used. Part of the audit is getting assurance that such
daily checks are part of the workstation routine.
If smocks or other ESDP
outer clothing are required by the ESD control plan, the auditor
must verify that that they are worn properly and checked regularly.
Smocks help to minimize problems with street clothing and possibly
hair. Proper donning of a smock includes securing the smock at the
opening and covering of the sleeves. A further precaution is to
ground the smock either connecting it to a grounded wrist strap
or ground cord at the hip connection to ground when in a stationary
position. Smocks also look neat, clean and increase the perception
of professionalism and uniformity. Garments should be bar-coded,
laundered and tested (sleeve-to-sleeve) according to ESDA Standard
on Garments, ESD STM2.1.
The floors in an ESDP area must
be checked for surface resistance, especially in the high-traffic
areas. A common high-end limit for this is 1 GW per ANSI/ESD-S7.1.
The audit will check this by using a megohmeter that meets both
ESD S4.1 and ANSI/ESD-S7.1. Especially check for high traffic areas.
ANSI/ESD S20.20 states that footwear and flooring are individual
elements and for each element should be less than 1x10^9 ohms, but
the total system resistance should be less than 35 Megohms. The
best electrical check for a floor is surface resistance to ground
(RTG) as this insures a connection to ground as well.
Each workbench must be evaluated
for ESD prevention, which involves removal of non-essential insulators,
such as coffee cups, radios, food wrappers, etc. or the control
of essential insulators via ionization such as some tools and jigs.
The workbench should have a dissipative-grounded
work surface, a common point ground or continuous monitor with banana
jacks for grounding wrist straps and a ground cord to power ground
(connected to the common point ground or continuous monitor).
A good practice is to use a conformity
sticker (always located in the same spot for each workstation) indicating
that the bench meets all ESD control requirements. If a sticker
is missing, it denotes that an infraction had occurred and not to
use the bench. If the bench is ever moved then the sticker should
be removed until re-inspected.
The positioning of equipment that
generates static must be monitored carefully in relation to ESD-sensitive
devices. Some companies have a one-foot rule, and others require
a three-foot separation. The PC monitor, a well-known static generator,
is necessary on many production benches. The static generation from
this device can be made acceptable by use of a well-grounded protective
screen or a topical antistatic-dissipative treatment.
If ionizers are used on or above
workbenches, then the audit must include a verification that each
ionizer is working properly. The checking procedure should be defined
in the ESD Control Program, and the audit should verify that each
operator can and does follow that procedure.
An auditor should check trash holders
to verify that they are ESDP containers.
Documents stored at the bench should
be in dissipative holders and or binders.
Packaging or general purpose tapes
found at the ESDP bench should be verified that they are ESD safe
(antistatic and or dissipative) with a field meter.
The auditor must evaluate the types
of cleaning materials and the cleaning practices for the work area.
Cleaners should not contain insulators such as silicon, soap, lanolin,
free-salts, mineral oil, etc.
All sensitive components must be
protected both as they arrive and as they leave the ESD Sensitive
area. The audit must verify that proper care is taken. Equipment
to be shipped is especially vulnerable, because the manufacturer
cannot control the environment in transit. Therefore those goods
must be packed for the worst possible ESD environment.
Report to Management and Others
If there are any discrepancies, then
the archived test records should be consulted to verify that the
control devices in question have been historically tested and comply
to internal specs. Also, whether the discrepancy is corrected or
not on the spot, it needs to be recorded on the audit form as an
As each audit is completed, the
auditor must go over it with the supervisor in charge of the area,
and must present it to plant management. Corrective recommendations
will be a part of the report, and the net result will be an improved
or well-run ESD Control program. This is the reason for and the
discipline of an ESD Audit.
Test Schedule for ESD Control Products
An ESD coordinator, chairman or another
person responsible for your static control program should regularly
test the ESD Control products to ensure that they are functioning
See below for a "laundry list" of how
often your ESD control products should be tested, according to the
Electronics Industry Association, Standard ANSI/EIA-625 , and
general practices of major corporations. Each test referenced also
explains the methodology used to perform the test.
ESD Protective Item Checks
Wrist straps, Footwear, Smocks (properly worn)
Workstations, Floor mats, ESD ground connections
Static surveys of ESDP areas and workstations,
Smocks (electrical tests)
RTG of work surface, RTG of floor, Wrist strap
monitor check, ESD ground continuity
Ionizer balance and charge decay
ESD system compliance to the ESD control program
The MIL-HDBK-263, section K, has a suggested checklist
to use in performing an ESD audit which encompasses over 500 specific
questions in several subjects: Management; Training; Engineering;
Procurement; Receiving area; Storage area; Work areas; Shipping
area; Intra-plan and inter-plant movement; ESDS protected work
stations; and Quality functions. The checklist should be tailored
to reflect the requirements of the ESD control program as well
as complement the program plan.
With the introduction of ANSI/ESD S20.20-1999,
we now have a collective source for ESDA recommended constraints
on product performance. Designing your ESD Control program around
your ESDS devices and complying with ANSI/ESD S20.20 makes it easy
to audit your ESD control program.
The ANSI/ESD S20.20 will be used extensively
for ESD auditing by most companies and organizations.
The ESD audit is the feedback channel to assure
company management and the customer that the ESD Control Program
is working. Dangelmayer  notes, "The auditing process
is the binding force behind the entire ESD control program".
Auditing is easy. The hard
part is making the results bear fruit through improved ESD control.
An ESD auditor must persevere until all the right things have been
recognized and rewarded, and all the wrong things have been corrected.
About the Author
Ryne C. Allen is the technical manager
at ESD Systems, a division of Desco Industries. Previously he was
chief engineer and laboratory manager at the Plasma Science and
Microelectronics Research Laboratory at Northeastern University.
Mr. Allen is a NARTE-certified ESD control engineer and the author
of 29 published papers and articles. He is a member of the ESD Association,
involved with several standards working groups as well as the Northeast
Chapter of the ESD Association. 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.
1. ESD Program Management, 2nd
Edition, T. Dangelmayer, Kluwer Academic Publishers, 1999.
2. ANSI/ESD S20.20-1999, Electrostatic
Discharge Control Program, The ESD Association, 7900 Turin Road,
Bldg. 3, Suite 2, Rome, NY 13440-2069.
3. ANSI/EIA-625, Requirements for Handling
Electrostatic-Discharge-Sensitive (ESDS) Devices, Electronics Industries
Association, Global Engineering Documents, Washington D.C., 1994
4. MIL-HDBK-263B, ESD Control Handbook
for Protection of Electrical and Electronic Parts, Assemblies, and
Equipment, Appendix K, ESD Damage Prevention Checklist. DoD, Defense
Printing Service Detachment Office, Philadelphia, PA, 31 December