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ESD Control Program Periodic Verification

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					                     Feature Article
                     Fred Tenzer and Gene Felder, Desco Industries, Inc.




                     ESD Control Program Periodic
                     Verification
                     Some practical advice for implementing ESD control
                     periodic checks

                                                                                                             ESD Handbook TR 20.20

                     W
                              ant to accomplish something           properties of the technical
                              important? A familiar formula         requirements that are incorporated       S20.20 has an accompanying ESD
                              is write a plan, select the           into the ESD program plan.”              Handbook, TR 20.20, which offers a
                     specifications, and then periodically                                                    comprehensive list of questions (Ref:
                     test to verify that the plan is being        S20.20, paragraph 6.1.3.2., Compliance     paragraph 4.3.3, Checklists). However,
                     implemented according to the test            Verification Plan Guidance, states:         only general periodic testing frequency
                     results. This is basically the                 “In addition to internal audits,         advice is offered, as follows:
                     requirements of an ESD control                 external audits (organization and          Worksurface: “Periodic testing of
                     program, per the ESD Association               supplier of ESDS items) should be          worksurfaces is necessary to
                     standard, ANSI/ESD S20.20. This                performed to ensure compliance             evaluate functionality. While not
                     important standard, entitled                                                              covered specifically in ESD STM-
                                                                    with planned requirements.
                     Development of an Electrostatic                                                           4.1, resistance to ground
                                                                    Verifications should include routine
                     Discharge Control Program, covers the                                                     measurements verify that the path to
                     requirements necessary to design,              checks of the Technical
                                                                    Requirements in the Plan. The              the equipment grounding conductor
                     establish, implement, and maintain an                                                     is intact. Surface to groundable
                     ESD control program to protect                 frequency of verification checks
                                                                    should be based on the control item        point [RTG] or point to point
                     electrical or electronic parts, assemblies                                                resistance [RTT] measurements
                     and equipment susceptible to ESD               usage, its durability and associated
                                                                    risk of failure”                           across the surface are recommended
                     damage.                                                                                   periodically to ensure that excessive
                                                                                                               wear, dirt, or coatings do not
                     S20.20 is a process document, and            The purpose of this article is to add
                                                                                                               interfere with worksurface function.
                     provides ESD control plan guidance;          practical advice on dealing with             The frequency of periodic testing is
                     one of its requirements is having a          verification checks, otherwise referred       normally specified in corporate
                     “compliance verification plan” as a           to as periodic testing. Technical            operating procedures. However, a
                     component of the ESD control plan.           requirements and frequency of periodic       common guide would be to conduct
                     Per S20.20, paragraph 6.1.3.,                testing will depend upon the value of        these measurements at least
                     Compliance Verification Plan:                 the ESD sensitive product, probability       quarterly.”
                        “A Compliance Verification Plan            of failure, and the potential cost of an
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                        shall be established to ensure the        ESD induced failure. We will assume          Wrist Strap: “Wrist straps should be
                        organization’s compliance with the        adoption of Table 1 in S20.20, listing       tested periodically. The frequency of
                        requirements of the Plan. Formal          the minimum recommended technical            testing, however, is driven by the
                        audits or certifications shall be          requirements of ANSI/ESD S20.20,             amount of risk exposure that can
                        conducted in accordance with a            and note typical periodic test               occur between tests. Because wrist
                        Compliance Verification Plan that          frequencies that are currently being         straps have a finite life, it is
                        identifies the requirements to be          practiced in the field. Our advice uses       important to develop a test frequency
                        verified, and the frequency at which       system tests that will provide overall       that will guarantee integrity of the
                        those verifications must occur. Test       information making periodic testing          system. Typical test programs
                        equipment shall be selected to make       more effective and productive.               recommend that wrist straps that are
                        measurements of appropriate                                                            used daily should be tested daily.”

                     20     CONFORMITY ® MARCH 2004
                     Feature Article

                        Footwear: “Once products are                               case of shoes, when the wearer is                              The types of monitoring and type of
                        found to meet the existing standards,                      fitted, the shoe should be tested as                            equipment are considerations. In
                        a system test of the footwear in                           worn at the point of acceptance. This                          some cases, a simple electrical
                        combination with the existing or                           is typically done by a resistance                              resistance test with a megohmmeter
                        proposed floor materials in the plant                       test.”                                                         may suffice. In others, a static
                        should be made to ensure that the                                                                                         charge generation test may be
                        criteria for the facility are met.                         Floor: “Another consideration is the                           required.”
                        Incoming inspection on a lot                               monitoring requirement to assure
                        sampling basis should be performed                         that the floor material is still                                Seating: “The recommended
                        for all static control footwear. In the                    functioning within specifications.                              electrical resistance range for

                     Frequency           ESD Protective Item                           Tests*                                 Specification                            Tool/Reference*

                     Daily               EPA access controlled      Verify that control procedures are being     “Access limited to trained or escorted    Visual
                                                                    followed                                     personnel”                                ANSI/ESD S20.20

                     Weekly              ESD protective versions of Check areas for presence of non-essential “All nonessential insulators ..must be       Visual
                                         Insulators                 items, particularly insulators            removed”                                     Static Field Meter
                                                                    Measure charge or RTG of ESD protective                                                ANSI/ESD S20.20
                                                                    product versions

                     Quarterly           Signs                      EPA has sufficient identification signage     “Posted and clearly visible to            Visual
                                                                    EPA boundary marked with aisle tape          personnel prior to entry”                 ANSI/ESD S20.20
                                                                    Workstations have identification signage

                     Quarterly           -                          For personnel safety, verify that GFCI are   “Ground fault circuit interrupters        Visual
                                                                    installed & personal grounding items not     should be considered wherever             ANSI/ESD S20.20
                                                                    used if exposure to over 250 VAC is          personnel might come into contact
                                                                    possible                                     with electrical sources.”

                     Quarterly           Electrical Ground          Verify correct wiring of 3-wire electrical   “Receptacle wiring should be checked AC Outlet Analyzer
                                                                    outlet                                       to verify correct wiring configuration” TR 20.20

                     Quarterly           Worksurface                Measure RTG to equipment ground              10E6 to 10E8 ohms                         Megohmmeter Test Kit
                                                                                                                                                           ESD S4.1 (Work Surfaces)

                     Quarterly           Seating                    Measure RTG to equipment ground              Less than 1 x 10E9 ohms                   Megohmmeter Test Kit ESD-STM12.1
                                                                                                                                                           (Seating)

                     Quarterly           Shelves                    Measure RTG to equipment ground              Less than 1 x 10E9 ohms                   Megohmmeter Test Kit
                                         (Mobile or Stationary)                                                                                            ANSI/ESD S20.20 (Table 1)

                     Quarterly           Flooring-Footwear System Measure RTG through ESD footwear &             Less than 3.5E7 ohms                      Megohmmeter Test Kit ESD STM 97.1
                                                                  person to equipment ground                                                               (Resistance Measurement in
                                                                                                                                                           Combination with a Person)

                     Quarterly           Flooring-Footwear System Approximate voltage on person wearing          Less than 100 volts                       Charged Plate Analyzer
                                                                  ESD footwear walking on ESD floor                                                         ESD STM 97.1 (Floor Materials and
                                                                                                                                                           Footwear-Voltage Measurement in
                                                                                                                                                           Combination with a Person)

                     Quarterly           Garment                    Check for ESD Protective Symbol              10E5 to 10E10 ohms                        Visual
                                                                    Measure Sleeve to Sleeve RTT                                                           Megohmmeter Test Kit ESD STM2.1
                                                                                                                                                           (Garments)

                     Quarterly           Ionizers                   Measure Offset Voltage (Balance)             Less than +/- 50 volts                    Ionization Test Kit
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                                                                    Measure Charge Decay Time                    1,000 to 100 volts (< 6 seconds is        ESD SP3.3 (Periodic Verification
                                                                                                                 typically used)                           of Air Ionizers)

                     Semi-Annual         Wrist Strap                Measure Breakaway Force (Para. 5.4)          >1<5 pounds                               Force Gage & Fixtures
                                                                    Measure Resistance Interior Cuff to plug     0.8E6 to 1.2E6 ohms                       ESD S1.1 (Wrist Straps)
                                                                    Run Cord Bending Life Test (Para. 5.7)       >16,000 cycles

                     Semi-Annual         Continuous Monitor         Follow manufacturer’s instructions           “Constant monitoring devices should       Manufacturer Calibration or Verification
                                                                                                                 be functionally checked periodically to   Unit
                                                                                                                 ensure that they are operating as         ANSI/ESD S20.20
                                                                                                                 designed.”

                     * Using modified test methods in accordance with concepts outlined in ESD Association standards
                     Table 1: Typical ESD control plan document
                     22          CONFORMITY ® MARCH 2004
  seating is less than 1 x 10E9 ohms as    audit, and the consequences of failing
  tested in accordance with ESD STM        such an audit can be drastic.
  12.1. This value should be during
  acceptance testing, installation and     Typical Periodic Testing Practice
  periodically thereafter.”                Depending upon the situation, one might
                                           test each item or conduct nonrandom
  Garments: “To maintain process           sampling looking for worst case
  control, it is imperative that the       conditions. Where a variety of ESD
  garment be tested per ESD STM 2.1.       protective products are being used, the
  The point to point and sleeve to         user should measure at least one product
  sleeve resistance test should be         representative of each type.
  made.”
                                           Many companies claim that the major
Goals                                      benefit to an ESD control program is
Verification checks or periodic testing     improving discipline on the shop floor.
should be done with the goal that the      See our Daily Check Form (Table 2),
ESD control system is functioning          which can be used to remind workers to
properly, so as to provide the company     control their area and check access,
with improved productivity, quality, and   ground at their ESD protected
customer satisfaction. Keenly important    workstation, removal of non-essential
to the ESD coordinator is that these       items particularly insulators, ESD
daily, weekly, monthly, quarterly, and     protective worksurface, ionizers,
semi-annual checks will ensure that the    handling of ESD sensitive part handling
annual ESD audit will be passed with       , packaging, and that products are used
flying colors. This is particularly         products properly. These checks are in
important if a major customer’s contract   addition to at least daily testing of wrist
is dependent upon passing the annual       straps and ESD footwear while worn.




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Table 2: Daily ESD check form                                                            Go to www.conformity.com/INFODIRECT
                                                                                                      Input #13
                                     MARCH 2004 CONFORMITY ®                     23
                     Feature Article

                     Testing is typically performed using a        Protected Area.” This is often              grounding system is dependent upon
                     wrist strap/ ESD footwear combo tester        accomplished by equipping the               the electrical outlets being wired
                     located at the entrance to the ESD            entrance to an ESD Protected Area           properly. This can be easily checked
                     Protected Area, and results should be         with a wrist strap / ESD footwear           with an AC outlet analyzer. A typical
                     logged.                                       combo tester, where test results are        company would verify their electrical
                                                                   logged (Ref: S20.20, paragraph              receptacles quarterly.
                     ESD Control Prerequisites                     6.2.2.2). This daily visual verification
                     The prerequisites of ESD control are:         check should verify that controlled
                     1) identifying the ESD Protected Area;        access procedures are being followed.
                     2) identifying all ESD sensitive items;
                     and 3) providing ESD control training.        ESD Control Basics
                                                                   The basics of ESD control are:
                     Signs                                         ● Ground all conductors
                     A typical periodic                            ● Remove all non-essential insulators,
                     testing program                                 or convert to ESD protective versions,
                     would include a                                 & neutralize essential insulators with
                     quarterly check that                            ionizers if the electrostatic charge is
                     the ESD Protected                               considered a threat
                     Area is clearly                               ● Use low charging and dissipative
                     identified using signs                           packaging including static discharge      Figure 4: ESD workstation
                     (see Figure 1) & aisle   Figure 1: ESD          shielding property to store or
                     tape. (Ref: S20.20,      protected area         transport ESD susceptible items
                     Paragraph 6.2.3.1)       warning sign
                                                                     outside the ESD protected area            Worksurface / Floors / Seating /
                                                                                                               Shelves
                     ESD Susceptible Items Clearly Identified       Grounding                                   The ESD Association standards,
                     ESD Susceptible Items should be
                                                                   Equipment Ground                            primarily used for test lab qualification
                     clearly identified and handled only in
                                                                   The most important element of ESD           testing, details RTT and RTG tests
                     an ESD Protected
                                                                   control is to ground all conductors,        where the RTG test is to the mat’s
                     Area. The ESD
                                                                   including people. Personal grounding        groundable snap. Steve Halperin of
                     susceptibility symbol
                                                                   devices used to ground human beings         Stephen Halperin & Associates advises
                     (see Figure 2) exists to
                                                                   should be checked daily while being         using a three-wire extension cord and
                     do this (Ref: S20.20,
                                                                   worn. In addition, there are ESD            measuring RTG to equipment ground.
                     Paragraphs 6.2.3.1 &
                                                                   protective product dissipative or           The electrical outlet and the extension
                     6.2.5.1). However,        Figure 2: The ESD
                                                                   conductive versions of common               cord should be checked to ensure that
                     many companies find susceptibility
                                                                   production supplies such as mats,           they are properly wired. Using a
                     that it is more cost      symbol
                                                                   flooring, garments, gloves, chairs,          surface resistance megohmmeter with
                     effective to consider
                                                                   packaging, etc. For example,                one 5# electrode, the sensing lead can
                     all electronic components and
                                                                   dissipative loose-leaf binders or           be plugged into the extension cord
                     sub-assemblies containing electronic
                                                                   document holders can have charges           (equipment ground), and then one can
                     components as ESD sensitive, requiring
                                                                   removed from them when handled by           move the 5# electrode on many
                     that ESD precautions be followed when
                                                                   grounded personnel or when in contact       surfaces and quickly take many
                     handling. In addition, employees are to
                                                                   with a properly grounded ESD                measurements. We refer to this test as
                     be grounded and follow all ESD
                                                                   worksurface. Since “the third wire          using modified test methods in
                     control procedures while working at an
                                                                   (green) AC equipment ground is the          accordance with concepts outlined in
                     ESD-protected workstation, regardless
                                                                   preferred choice for ground,” the           ESD S4.1.
                     of what they are working on (even nuts
                     & bolts!). If running different systems
                     dependent upon identifying ESD sus-
                     ceptible items, then periodic verification
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                     of this should occur at least quarterly.

                     Controlled Access to An ESD Protected
                     Area
                     Access to an ESD Protected Area is to
                     be controlled. Per S20.20, Paragraph
                     6.2.3.1, “access to the Protected Area
                     shall be limited to personnel who have
                     completed appropriate ESD training.
                     Trained personnel shall escort                                                                Figure 5: Surface resistance meter
                     untrained individuals while in a                Figure 3: Data logger

                     24     CONFORMITY ® MARCH 2004
                                                                                                           Feature Article

Periodic testing would typically not be    If the measurement is high,                  cleaner and letting the surface dry
performed on every item. Non-random        troubleshooting would include                completely. Ground snaps, common
sampling should be used, for example,      measuring each component separately          point grounds, and ground cords can be
particularly with worn or dirty            to determine which item is out of spec.      checked for less than 1 ohm resistance
worksurfaces, and at least one each of     The first troubleshooting measurement         using a multimeter. If the ground cord
different types should be tested. If the   would typically be RTT of the surface,       includes a 1 Megohm resistor, the
following elements are part of the ESD     which can measure high if dirty (as dirt     measurement should be 1E6 ohms.
control program, measuring RTG to          is typically insulative), or coated with
equipment ground would include:            silicone from non-ESD cleaners. If           Flooring-Footwear System Resistance
● Worksurfaces 1 x 10E6 –                  surface RTT measures high, it should         in Combination with a Person
  less than 1 x 10E9 ohms                  be re-tested after cleaning with an ESD      The above noted RTG to equipment
● Floors – less than 1 x 10E9 ohms
● Chairs – less than 1 x 10E9 ohms
● Shelves – less than 1 x 10E9 ohms
● Carts – less than 1 x 10E9 ohms

Ideally, particularly if unpackaged ESD
sensitive items are placed upon the
surface, it should be dissipative with
RTG of 1 x 10E6 to less than 1 x 10E9
ohms. Per ESD S4.1, paragraph 8,
Resistance Guidelines, “Resistance-to-
groundable point 1 x 10E6 to 1 x 10E9
ohms. These guidelines represent a
range of resistance that has generally
been proven to provide protection in
the manufacturing environment.”

ESD Handbook, TR20.20, paragraph
5.3.1.7, Electrical Considerations,
states:
   “[RTG is] the most important
   functional consideration for
   worksurfaces. This establishes the
   resistance of the primary path to
   ground for items, placed on the
   surface. When worksurface materials
   are being selected, consideration
   should be given to possible Charged
   Device Model (CDM) damage to
   ESD sensitive products. If CDM
   damage is a concern then setting a
   lower resistance limit for the
   worksurface should be considered.
   Typically, the lower limit for these
   types of worksurfaces is 1 X10E6
   ohms.”

Resistance Troubleshooting
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If the overall resistance RTG to
equipment ground measurement is
good, this system method provides the
information that all the components are
good:
● RTT of the surface material
● Snap or other conductor connections
  to surface material
● Ground cord or other path-to-ground
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                                                                                 MARCH 2004 CONFORMITY ®                   25
                     Feature Article

                     ground systems test provides overall information, making           walking pattern is suggested Figure 1 in the standard.
                     periodic testing more effective and productive. Instead of         However, per Appendix A, “the user of this test method
                     testing program components, it verifies that they are working       should choose a step pattern typical of the majority of the
                     together properly. Another such systems test is in accordance      workers.” This test can be approximated using a charged plate
                     with ESD STM 97.1, Floor Materials and Footwear -                  analyzer where the electrostatic charge on the person is
                     Resistance Measurement in Combination with a Person,               transferred to the conductive plate clipping worn wrist strap
                     which measured the path-to-ground of the ESD floor and              cord to the plate. The charged plate analyzer will measure the
                     ESD footwear and the person together not separately.               charge on a person wearing ESD footwear walking upon ESD
                                                                                        Floor taking a few normal steps.
                     Per S20.20, paragraph 6.2.2.2, Personnel Grounding
                     Guidance, “ESD protective flooring, used with approved              ESD Protective Product Version of Insulators
                     footwear, may be used as an alternative to the wrist strap         ESD workstations should be checked to verify that all non-
                     system for standing operations.” That is, both ESD floor and        essential insulators are removed. Ideally, all ESD protective
                     ESD footwear need to be used together. Personnel will likely       items are marked or identified. A grounded static field meter
                     be testing their ESD footwear daily, but doing so standing on      should be used to measure the ability of questionable items to
                     a metal plate. As part of a quarterly periodic verification plan,   generate a charge. Per S20.20, “all nonessential insulators,
                     we suggest using a Megohmmeter with one lead attached to           such as those made of plastics and paper (e.g. coffee cups,
                     equipment ground and electrode held by person wearing ESD          food wrappers and personal items) must be removed from the
                     footwear standing on factory’s ESD protective floor measured        workstation.” Instead of removing them altogether, many
                     at 10 volts. RTG should be less than 3.5E7 ohms.                   insulative items are replaced with ESD protective versions
                                                                                        which will be low charging, conductive/dissipative, or both.
                     Flooring-Footwear System Voltage Measurement in                    These include ESD protective packaging, material handling
                     Combination with a Person                                          containers, tape, document holders, loose leaf binders, etc.
                     Alternatively, the proper functioning of the flooring-footwear      The worksurface RTG test can be repeated with the 5#
                     system can be verified by measuring less than 100 Volts on          electrode placed upon the dissipative ESD protective item,
                     the person in accordance with ESD STM 97.2, where voltage          verifying a path-to-ground.
                     on the person is measured using a charged plate analyzer. A
                                                                                        Per ESD Handbook, TR 20.20, paragraph 2.4:
                                                                                          “It should be understood that any object, item, material or
                                                                                          person could be a source of static electricity in the work
                                                                                          environment. Removal of unnecessary nonconductors,
                                                                                          replacing nonconductive materials with dissipative or
                                                                                          conductive materials and grounding all conductors are the
                                                                                          principle methods of controlling static electricity in the
                                                                                          workplace, regardless of the activity.”

                                                                                        Garments
                                                                                        ESD garments are not required by S20.20, but can be an
                                                                                        effective means of complying with Paragraph 6.2.3.2,
                                                                                        Protected Areas Guidance. “All process essential insulators
                                                                                        that have electrostatic fields that exceed 2,000 volts should be
                                                                                        kept at a minimum distance of 12 inches from ESDS items,”
                                                                                        since worker clothing may charge to that level and beyond.

                                                                                        An ESD garment is manufactured from a number of panels,
                                                                                        which must have electrical continuity. Garments whose
                                                                                        electrical continuity wears out over time can do more harm
                                                                                        than good. Per ESD Handbook, TR 20.20, paragraph
                                                                                        5.3.13.2.6, Proper Use, “the garment should be electrically
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                                                                                        bonded to the grounding system of the wearer so as not to act
                                                                                        as a floating [conductor].” If not grounded or if a conductive
                                                                                        panel is electrically isolated, the garment can become an
                                                                                        isolated charged conductor that can discharge to ESD
                                                                                        sensitive items.

                                                                                        To verify point-to-point RTT of 10E5 to 10E10 ohms, the
                                                                                        garment should be placed on an insulative test surface. Place
                                                                                        a 5# electrode on each sleeve, and measure resistance using a
                                                                                        Megohmmeter. The sleeve to sleeve resistance test can be
                                                                                        made using a “banker’s clip” on each sleeve and isolating the
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                     26     CONFORMITY MARCH 2004
                                                ®
                                                                                                               Feature Article

garment by hanging it in air (a wooden        airflow to measure the balance (offset           should be performed periodically,
hanger can also be used). Connect             voltage). Just place a 1,000 volt charge        perhaps semi-annually; the “breakaway
Megohmmeter leads to banker’s clip via        on its isolated plate and place the             force” test and the “bending life” test.
alligator clip or bulldog clip. This          ionization test kit on a worksurface.
verification should be done quarterly.         Count or use a stopwatch to measure             For ESD control, to prevent accidental
                                              charge decay time until the charge is           disconnects, a strain gage or torque
Ionizers                                      reduced to 100 volts. This should be            meter can be used to verify the ESD S.1
Ionizers are pieces of equipment that         done with both a positive and a negative        breakaway force requirement of greater
can also do more harm than good if not        1,000 charge on the isolated plate. A six       than one pound. The less than five
properly maintained. Insulators cannot        second charge decay time requirement            pound requirement can be an important
be grounded (non-conductors by                is not unusual, and the S20.20-                 safety issue.
definition). Ionizers neutralize               recommended technical requirement
electrostatic charges with fans that blow     range is < +/- 50 volts voltage offset.         Per ESD Handbook, TR 20.20,
large quantities of negatively and            Many users perform this periodic test           paragraph 5.3.2.2.1.1, Cuffs:
positively charged ions. The quantity of      quarterly and/or whenever the ionizer             “Wrist strap cuffs may have a quick
negative and positive ions cannot be          emitter pins are cleaned.                         parting electrical-mechanical
exactly the same. Measured in volts, the                                                        connector that mates with a
difference is referred to as balance or       Wrist Straps                                      corresponding connector on the head
offset voltage. If significantly out-of-       Most companies will have workers test             of the ground cord. This connector
balance, the ionizer can place a              their wrist straps while being worn               serves two purposes. First, it is a
significant charge on items instead of         daily. Per ESD-S1.1, paragraph 6.1.3,             physical connection for attaching the
neutralizing charges.                         Frequency of Functional Testing, “the             ground cord. Second, it is the
                                              wrist strap system should be tested               groundable point on the cuff. Quick
Per ANSI/ESD S20.20, Paragraph                daily to ensure proper electrical value.”         release is an important feature of the
6.2.3.1, Protected Areas Requirement,         However, two important wrist strap test           connector. The breakaway force
“ionization or other charge mitigating                                                          should be low enough to allow easy
techniques shall be used at the                                                                 release, but high enough to prevent
workstation to neutralize electrostatic                                                         unintentional disconnection. If the
fields on all process essential                                                                  breakaway force is too light, the
insulators if the electrostatic field is                                                         ground connection could be lost
considered a threat.”                                                                           without the knowledge of the
                                                                                                wearer.”
An ionization test kit, in accordance
with ESD SP3.3, Periodic Verification                                                          Per ESD Handbook, TR20.20,
of Air Ionizers, can very quickly verify                                                      paragraph 5.3.2.2.2, Wrist Strap
the proper functioning of an ionizer.                                                         Ground Cord:
The ionization test kit should be                                                               “At first glance, the ground cord
grounded and placed in the ionizer             Figure 6: ESD mat with test kit                  appears to be a relatively simple




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                                            Go to www.conformity.com/INFODIRECT   Input #16

                                                                                     MARCH 2004 CONFORMITY ®                        27
                     Feature Article

                       assembly. However, the design requirements are                  Most companies will check their continuous monitors semi-
                       considerable, given the wide range of user applications         annually. Following manufacturer’s instructions, this can be
                       and the durability requirements of constant tugging,            accomplished within a minute without removing the monitor
                       flexing, and dragging over the edge of workstation tops          from the workbench.
                       and equipment chassis.”
                                                                                       Conclusion
                     To ensure reliable circuit connections, the bending life test
                     found in paragraph 5.7 applies, using the apparatus described     An ESD control program should be treated as an on-going
                     in ESD S1.1. Many companies consider the 16,000 cycles            process, like any good quality control system. As such, it
                     figure found in ESD S.1 totally inadequate as most good            should never be treated as an event. The ESD control plan
                     quality wrist strap cords will operate a million cycles or many   compliance verification plan must include ongoing and
                     times that. Instead of part of their periodic testing, some       effective periodic or verification checks. Issues will be
                     companies require the breakaway force and bending life test       identified which can be corrected, greatly improving the
                     wrist strap test information to be provided by their suppliers.   probability of passing annual audits.

                     Continuous Monitors                                               ESD control programs must be comprehensive and ESD
                     If used, continuous monitor functions can be quickly verified      protective products must be checked periodically to verify
                     at the workstation as leading manufacturers have calibration      that they are working properly. If used effectively, companies
                     or verification units available. Frequency of the periodic test    can turn ESD control programs into a competitive advantage -
                     might be done semi-annually. Continuous monitors are              a strategic tool focused on quality, productivity, and customer
                     becoming increasing important as a cost effective means to        satisfaction improvement.
                     verify on an ongoing basis that operator and worksurface
                     ESD controls are functioning properly. Per the ESD                About The Authors
                     Handbook, “if the products that are being produced are of         Gene Felder is the corporate product manager at
                     such value that knowledge of a continuous, reliable ground is     Desco Industries, and can be reached by e-mail at
                     needed, and then continuous monitoring should be considered       gene.felder@desco.com.
                     or even required.” (Ref: TR 20.20, paragraph 5.3.2.4.4.)
                                                                                       Fred Tenzer is the Midwest Regional Sales Manager for
                                                                                       Desco and can be reached by e-mail at
                                                                                       fred.tenzer@desco.com

                                                                                       References
                                                                                       1. ANSI/ESD S20.20, Protection of Electrical and Electronic
                                                                                          Parts, Assemblies and Equipment (Excluding Electrically
                                                                                          Initiated Explosive Devices), ESD Association, 1999.
                                                                                       2. ESD TR 20.20, Handbook for the Development of an
                                                                                          Electrostatic Discharge Control Program for the Protection
                                                                                          of Electronic Parts, Assemblies and Equipment
                                                                                       3. ANSI/ESD S1.1: Wrist Straps.
                                                                                       4. ANSI/ESD STM2.1: Garments
                                                                                       5. ESD SP3.3: Periodic Verification of Air Ionizers.
                                                                                       6. ANSI/ESD S4.1: Worksurfaces – Resistance Measurements
                                                                                       7. ESD STM7.1: Resistive Characterization of Materials —
                                                                                          Floor Materials
                                                                                       8. ANSI/ESD STM12.1: Seating - Resistive Measurement
                                                                                       9. ANSI/ESD STM97.1: Floor Materials and Footwear –
www.conformity.com




                                                                                          Resistance Measurement in Combination with a Person.
                                                                                       10. ANSI/ESD STM97.2: Floor Materials and Footwear –
                                                                                          Voltage Measurement in Combination with a Person.




                              Go to www.conformity.com/INFODIRECT   Input #17
                     28     CONFORMITY MARCH 2004
                                               ®

				
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