ESD CORNER
ESD Systems’ ESD Technical Newsletter
Issue 12, December 1999: Volume 2
Reference: http://www.esdsystems.com/newsletters/v2issue12.htm
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Sender : ESD Systems, 19 Brigham
Street, # 9, Marlboro, MA 01752-3170
Phone
: 508-485-7390
Fax : 508-480-0257
E-mail : editor@esdsystems.com
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This is a free monthly newsletter, which specializes on issues in static
control in the semiconductor/electronics workplace.
Need your own copy? Want to subscribe to this Newsletter? All you, or your
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IN THIS ISSUE:
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·
HOT TIP of the MONTH (Be Prepared!)
·
ESDA NE
Chapter's General Meeting (ANSI/ESD S20.20)
·
NEPCON
WEST (VISIT US)
·
ESD Q&A CORNER (ESD Audits)
·
PRODUCT UPDATES (ESD Tapes)
·
Dr. ZAP (ESD Audits)
HOT TIP of the MONTH (Be Prepared)
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Be Prepared
as ESD
increases during the winter [colder] months. As the colder months approach, the amount of
water the air can hold is reduced inside building because the cold air is
heated and expands, netting less water content per volume. This translates into dryer air which because
there is less water content, allows for greater charging during triboelectrification.
To combat this problem, we suggest that you tighten
up on your ESD Control Program. Make
sure your floors are antistatic (non tribocharging), mobile personnel wear ESD
foot wear, all ESD Sensitive products are kept in sealed ESD Safe containers
like ESD Shielding Bags and only opened in a fully compliant ESD Safe
area. Increasing the relative humidity
of the air to a minimum of 30% helps too, refer to our white paper on humidity
for more info: http://www.esdsystems.com/whitepapers/wp_humidity.asp
ESDA NE
Chapter's General Meeting
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January 12th, 2000
Date: Wednesday, January 12th
Time:
Registration 4:30, Seminar 5:00 - 6:30 PM
Location:
Hawthorn Room, HP, 29 Mall Road (across from the Lahey Clinic), Burlington, MA
01803, PH:781-221-5200
Topic:
ANSI/ESD S20.20-1999
Speaker:
David Swenson, President of the ESD Association
The
ANSI/ESD S20.20 is the parent document for all ESDA standards and will be the
main reference for Auditing an ESD Control program. As the parent document, all
the constraints for various control devices, systems and procedures are housed
in this standard for easy reference. This will become a key auditing tool for
ESD Control. The ANSI/ESD S20.20 may replace both the MIL-STD-1686 and the
ANSI/EIA-625 ESD Control Standards.
For more information on this General Meeting, contact the Northeast Chapter of the
ESD Association, P.O. Box 394, Wilmington, MA 01887. Phone:
508-485-7390; Fax: 508-480-0257; e-mail: noreast@eosesd.org Web Site: http://www.nechapteresda.org/
Visit ESD Systems.com at this years NEPCON West at
the Anaheim Convention Center in California this February 29th –
March 2nd at Booth 5708 which is right at the front door in Hall C.
NEPCON West, Opens the door to a world of
innovative solutions and makes it easy to find the products, services and
information you need. The world's most important electronic manufacturing event
has leading suppliers from around the globe, a world-class conference, exciting
special events and more. If you want to be a leader in today's highly competitive
global electronics market; you have to be there.
For general questions or
comments on about any NEPCON event, please contact Customer Service via e-mail, telephone (800-467-5656),
or FAX (203-840-9656). For technical questions or comments on the web site,
please send e-mail to the NEPCON Webmaster at webmaster@nepcon.reedexpo.com.
ESD Q&A CORNER
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The following questions and answers were selected from our FAQ WEB Page: http://www.esdsystems.com/?PageNo=QANDAINDEX
concerning Questions about ESD Audits.
Q1: We are planning to
conduct ESD audit in our organization. We are manufacturing electronic
products. Kindly send us various formats for conducting ESD audit. Kindly
indicate min. & max. in respect of each parameters. - Anonymous, Bangalore,
India.
A1: To conduct an ESD Audit, you need to know what constraints your
ESD Control program is running at. That is, you need to define the ESD
sensitive parts that you are protecting by voltage thresholds and how they are
handled. Once this is known, you can easily define the ESD Control program and
audit it.
There are guidelines to help you with ESD Audits written in various standards.
The EIA-625 lists the frequency, items and suggested acceptance limits when
performing an audit. Note that this is a 5 year old document and the ESD
Association has been charted to update it. The ESD DS20.20-1998 is another
standard that can help guide you in the constraints of a program. Another good
reference source is the MIL-HDBK-263 standard, Appendix K, ESD Damage
Prevention Checklist, for performing ESD Audits.
All of these documents are items in ESD Systems’ catalog for your convenience.
For an audit kit I would recommend the following items, also available from ESD
Systems:
++++++++++++++++++++++++++++++++++++++++++
Q2: Is there a
source of info that will describe the ESD sensitivity of various common IC's,
etc? - Chris Hampton, Scottsdale, AZ
A2: The RAC (Reliability Analysis
Center) in Rome, NY has a "V-ZAP"
data book that may help (http://rac.iitri.org/DATA/RMST/esd_succept.html).
The IC suppliers also have data for their own components. There is also an
industry resource for device qualification data "ASPEC" that may have what you
are looking for. .
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PRODUCT UPDATES (NEW!)
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ESD TAPES – Item #s 16120 - 16154
Wescorp ESD Anti-Static Tapes for packaging, general purpose,
masking, shielding, etc.
Acetate
Tape for general purpose and packaging, clear, w/symbols, red & blue (Items
# 16120-16139)
Conductive Grid Shielding Grid Tape for applications requiring EMI shielding
(Items # 16140-116143)
Masking Tape used for masking PCB gold features for some wave solderers (Items
# 16144-16149)
Hi-Temp Polyimide Tape used for masking PCB gold features for all wave
solderers (Item # 16150-16154)
Dr. ZAP
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Topic:
ESD
Audits
topic
gleaned from paper: http://www.esdsystems.com/whitepapers/wp_esdaudit.asp
ESD Audits
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[2], 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 program.
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.
Operators
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 all personnel.
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 emphasized.
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 work area,
· · 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 hand,
· · verify that wiring of discharge devices is grounded,
· · 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[1][1] 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.
Workbenches and Floors
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.
Other Audit Concerns
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.
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 infraction.
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.
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 properly.
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 [3], and general practices of major corporations. Each test referenced also explains the methodology used to perform the test.
ESD Protective Item Checks [3] |
|
|
Frequency |
Items |
|
Daily |
Wrist straps, Footwear, Smocks
(properly worn) |
|
Weekly |
Workstations, Floor mats, ESD
ground connections |
|
Monthly |
Static surveys of ESDP areas and
workstations, Smocks (electrical tests) |
|
Quarterly |
RTG of work surface, RTG of
floor, Wrist strap monitor check, ESD ground continuity |
|
Semi-annually |
Ionizer balance and charge decay |
|
Annually |
ESD system compliance to the ESD
control program plan |
Checklists
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.
Standards
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.
Conclusion
The ESD audit is the feedback
channel to assure company management and the customer that the ESD Control
Program is working. Dangelmayer [1] 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.
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This is a
free monthly newsletter, which specializes on issues in static control in the semiconductor/electronics workplace.
Need your own copy? Want to subscribe to this Newsletter? All you or your
colleague(s) need to do is simply fill out the subscription form at http://www.esdsystems.com/?PageNo=SENDEMAIL
This
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Let us know what you think. Tell us what you would like to see in future
issues. Want to contribute articles or other related information to our
Newsletter? Send your comments to the editor@esdsystems.com
Copyright © Desco Industries, Inc. 1999
END V2I12