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Feature ArticleTesting is typically performed using awrist strap/ ESD footwear combo testerlocated at the entrance to the ESDProtected Area, and results should belogged.ESD Control PrerequisitesThe prerequisites of ESD control are:1) identifying the ESD Protected Area;2) identifying all ESD sensitive items;and 3) providing ESD control training.www.conformity.comSignsA typical periodictesting programwould include aquarterly check thatthe ESD ProtectedArea is clearlyidentified using signs(see Figure 1) & aisletape. (Ref: S20.20,Paragraph 6.2.3.1)Figure 1: ESDprotected areawarning signESD Susceptible Items Clearly IdentifiedESD Susceptible Items should beclearly identified and handled only inan ESD ProtectedArea. The ESDsusceptibility symbol(see Figure 2) exists todo this (Ref: S20.20,Paragraphs 6.2.3.1 &6.2.5.1). However,Figure 2: The ESDmany companies find susceptibilitythat it is more costsymboleffective to considerall electronic components andsub-assemblies containing electroniccomponents as ESD sensitive, requiringthat ESD precautions be followed whenhandling. In addition, employees are tobe grounded and follow all ESDcontrol procedures while working at anESD-protected workstation, regardlessof what they are working on (even nuts& bolts!). If running different systemsdependent upon identifying ESD susceptible items, then periodic verificationof this should occur at least quarterly.Protected Area.” This is oftenaccomplished by equipping theentrance to an ESD Protected Areawith a wrist strap / ESD footwearcombo tester, where test results arelogged (Ref: S20.20, paragraph6.2.2.2). This daily visual verificationcheck should verify that controlledaccess procedures are being followed.ESD Control BasicsThe basics of ESD control are: Ground all conductors Remove all non-essential insulators,or convert to ESD protective versions,& neutralize essential insulators withionizers if the electrostatic charge isconsidered a threat Use low charging and dissipativepackaging including static dischargeshielding property to store ortransport ESD susceptible itemsoutside the ESD protected areaGroundingEquipment GroundThe most important element of ESDcontrol is to ground all conductors,including people. Personal groundingdevices used to ground human beingsshould be checked daily while beingworn. In addition, there are ESDprotective product dissipative orconductive versions of commonproduction supplies such as mats,flooring, garments, gloves, chairs,packaging, etc. For example,dissipative loose-leaf binders ordocument holders can have chargesremoved from them when handled bygrounded personnel or when in contactwith a properly grounded ESDworksurface. Since “the third wire(green) AC equipment ground is thepreferred choice for ground,” theControlled Access to An ESD ProtectedAreaAccess to an ESD Protected Area is tobe controlled. Per S20.20, Paragraph6.2.3.1, “access to the Protected Areashall be limited to personnel who havecompleted appropriate ESD training.Trained personnel shall escortuntrained individuals while in a24CONFORMITY MARCH 2004Figure 3: Data loggergrounding system is dependent uponthe electrical outlets being wiredproperly. This can be easily checkedwith an AC outlet analyzer. A typicalcompany would verify their electricalreceptacles quarterly.Figure 4: ESD workstationWorksurface / Floors / Seating /ShelvesThe ESD Association standards,primarily used for test lab qualificationtesting, details RTT and RTG testswhere the RTG test is to the mat’sgroundable snap. Steve Halperin ofStephen Halperin & Associates advisesusing a three-wire extension cord andmeasuring RTG to equipment ground.The electrical outlet and the extensioncord should be checked to ensure thatthey are properly wired. Using asurface resistance megohmmeter withone 5# electrode, the sensing lead canbe plugged into the extension cord(equipment ground), and then one canmove the 5# electrode on manysurfaces and quickly take manymeasurements. We refer to this test asusing modified test methods inaccordance with concepts outlined inESD S4.1.Figure 5: Surface resistance meter

Feature ArticlePeriodic testing would typically not beperformed on every item. Non-randomsampling should be used, for example,particularly with worn or dirtyworksurfaces, and at least one each ofdifferent types should be tested. If thefollowing elements are part of the ESDcontrol program, measuring RTG toequipment ground would include: Worksurfaces 1 x 10E6 –less than 1 x 10E9 ohms 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 ohmsIf the measurement is high,troubleshooting would includemeasuring each component separatelyto determine which item is out of spec.The first troubleshooting measurementwould typically be RTT of the surface,which can measure high if dirty (as dirtis typically insulative), or coated withsilicone from non-ESD cleaners. Ifsurface RTT measures high, it shouldbe re-tested after cleaning with an ESDcleaner and letting the surface drycompletely. Ground snaps, commonpoint grounds, and ground cords can bechecked for less than 1 ohm resistanceusing a multimeter. If the ground cordincludes a 1 Megohm resistor, themeasurement should be 1E6 ohms.Flooring-Footwear System Resistancein Combination with a PersonThe above noted RTG to equipmentIdeally, particularly if unpackaged ESDsensitive items are placed upon thesurface, it should be dissipative withRTG of 1 x 10E6 to less than 1 x 10E9ohms. Per ESD S4.1, paragraph 8,Resistance Guidelines, “Resistance-togroundable point 1 x 10E6 to 1 x 10E9ohms. These guidelines represent arange of resistance that has generallybeen proven to provide protection inthe manufacturing environment.”ESD Handbook, TR20.20, paragraph5.3.1.7, Electrical Considerations,states:“[RTG is] the most importantfunctional consideration forworksurfaces. This establishes theresistance of the primary path toground for items, placed on thesurface. When worksurface materialsare being selected, considerationshould be given to possible ChargedDevice Model (CDM) damage toESD sensitive products. If CDMdamage is a concern then setting alower resistance limit for theworksurface should be considered.Typically, the lower limit for thesetypes of worksurfaces is 1 X10E6ohms.”Go to www.conformity.com/INFODIRECTInput #14MARCH 2004 CONFORMITY 25www.conformity.comResistance TroubleshootingIf the overall resistance RTG toequipment ground measurement isgood, this system method provides theinformation that all the components aregood: RTT of the surface material Snap or other conductor connectionsto surface material Ground cord or other path-to-ground

Feature Articleground systems test provides overall information, makingperiodic testing more effective and productive. Instead oftesting program components, it verifies that they are workingtogether properly. Another such systems test is in accordancewith ESD STM 97.1, Floor Materials and Footwear Resistance Measurement in Combination with a Person,which measured the path-to-ground of the ESD floor andESD footwear and the person together not separately.Per S20.20, paragraph 6.2.2.2, Personnel GroundingGuidance, “ESD protective flooring, used with approvedfootwear, may be used as an alternative to the wrist strapsystem for standing operations.” That is, both ESD floor andESD footwear need to be used together. Personnel will likelybe testing their ESD footwear daily, but doing so standing ona metal plate. As part of a quarterly periodic verification plan,we suggest using a Megohmmeter with one lead attached toequipment ground and electrode held by person wearing ESDfootwear standing on factory’s ESD protective floor measuredat 10 volts. RTG should be less than 3.5E7 ohms.Flooring-Footwear System Voltage Measurement inCombination with a PersonAlternatively, the proper functioning of the flooring-footwearsystem can be verified by measuring less than 100 Volts onthe person in accordance with ESD STM 97.2, where voltageon the person is measured using a charged plate analyzer. Awalking pattern is suggested Figure 1 in the standard.However, per Appendix A, “the user of this test methodshould choose a step pattern typical of the majority of theworkers.” This test can be approximated using a charged plateanalyzer where the electrostatic charge on the person istransferred to the conductive plate clipping worn wrist strapcord to the plate. The charged plate analyzer will measure thecharge on a person wearing ESD footwear walking upon ESDFloor taking a few normal steps.ESD Protective Product Version of InsulatorsESD workstations should be checked to verify that all nonessential insulators are removed. Ideally, all ESD protectiveitems are marked or identified. A grounded static field metershould be used to measure the ability of questionable items togenerate a charge. Per S20.20, “all nonessential insulators,such as those made of plastics and paper (e.g. coffee cups,food wrappers and personal items) must be removed from theworkstation.” Instead of removing them altogether, manyinsulative items are replaced with ESD protective versionswhich will be low charging, conductive/dissipative, or both.These include ESD protective packaging, material handlingcontainers, tape, document holders, loose leaf binders, etc.The worksurface RTG test can be repeated with the 5#electrode placed upon the dissipative ESD protective item,verifying a path-to-ground.Per ESD Handbook, TR 20.20, paragraph 2.4:“It should be understood that any object, item, material orperson could be a source of static electricity in the workenvironment. Removal of unnecessary nonconductors,replacing nonconductive materials with dissipative orconductive materials and grounding all conductors are theprinciple methods of controlling static electricity in theworkplace, regardless of the activity.”www.conformity.comGarmentsESD garments are not required by S20.20, but can be aneffective means of complying with Paragraph 6.2.3.2,Protected Areas Guidance. “All process essential insulatorsthat have electrostatic fields that exceed 2,000 volts should bekept 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 whoseelectrical continuity wears out over time can do more harmthan good. Per ESD Handbook, TR 20.20, paragraph5.3.13.2.6, Proper Use, “the garment should be electricallybonded to the grounding system of the wearer so as not to

ESD control program to protect electrical or electronic parts, assemblies and equipment susceptible to ESD damage. S20.20 is a process document, and provides ESD control plan guidance; one of its requirements is having a “compliance verification plan” as a component of the ESD c