1、ESDdocin/sundae_mengESD Presentation OutlinePart 1:Introduction/Background Part 2:Electrostatic Problems Part 3:ResistancePart 4:IonizationPart 5:Charge Measurementdocin/sundae_mengCharging MechanismsTriboelectric ChargingInduction Chargingdocin/sundae_mengTriboelectrification+-+-MATERIAL CONTACTdoc
2、in/sundae_mengTriboelectrification+-+-MATERIAL SEPARATION-docin/sundae_mengTriboelectric ChargingThe amount of charge transferred depends onTypes of materials involved Area of contactNumber of contacts Rate of separationSurrounding environmentdocin/sundae_mengTriboelectric ChargingGlass Human Hair N
3、ylonWool Aluminum Paper Cotton Steel RubberNickel,Copper Brass,SilverPolyester Polyurethane Polyethylene Polypropylene PVCSilicon Teflon_+Triboelectric Seriesdocin/sundae_mengTypical Charge LevelsTypical charge(voltage)measured for different activitiesWalking on an untreated vinyl floor12 kV for 10%
4、RH3 kV for 55%RHWorker standing up6 kV for 10%RH400 V for 55%RHdocin/sundae_mengTypical Charge LevelsTypical charge(voltage)measured on common objectsWafers5 kVWafer Carriers35 kV Quartz Ware15 kVPlastic Film40 kVSmocks10 kVdocin/sundae_mengInduction Charging-+-+docin/sundae_mengCharge by Induction_
5、 _ _ _+_+docin/sundae_mengProblemsElectrostatic AttractionContamination“Static Cling”ESDDevice Damage Equipment Latch Up(ESC)docin/sundae_mengProblemsElectrostatic AttractionContamination“Static Cling”docin/sundae_mengProblemsElectrostatic AttractionContamination“Static Cling”docin/sundae_mengProble
6、msESDDevice DamageEquipment Latch Updocin/sundae_mengProblemsESDDevice DamageEquipment Latch UpOften misdiagnosed as software bugs.Induced EM DisturbanceAn Extra Pulsedocin/sundae_mengDischarge ModelsTribocharging or induction charging+metal contact=ESDHuman Body Model(HBM)Machine Model(MM)Charged D
7、evice Model(CDM)are used to simulate ESD events from various sourcesdocin/sundae_meng1500 ohmsHuman Body Model100k ohmsHVPower Supply100 pFDUTdocin/sundae_mengMachine ModelZero ohms andlow L100k ohmsHVPower Supply200 pFDUTdocin/sundae_mengCharged Device ModelHVPower SupplyCharge Platedocin/sundae_me
8、ngCharged Device ModelHVPower SupplyCharge Platedocin/sundae_mengGrounding(first line of defense)Grounding prevents charging.Ground everything-floors,mats,personnel,chairs,garments,machine parts.docin/sundae_mengSoft Grounds Use soft grounds to control discharges.Using dissipative materials limits d
9、ischarge current to a level that does not cause damage.docin/sundae_mengResistance MapInsulative1031041051061071081091013 1014 10151010 1011 1012Surface Resistance(Ohms)101102DissipativeConductiveShieldingdocin/sundae_mengThe Need for StandardsMany common items are rendered dissipative to control di
10、scharges.ESD control programs require qualification of these items.Thus a need for standardized test methods.Flooring Work Surfaces ChairsGloves Garments Packagingdocin/sundae_mengESD Association StandardsGarments WorksurfacesFlooring ChairsPlanar Materials10V100V103104105106107108109101310101011 10
11、12Surface Resistance(ohms)docin/sundae_mengTEST VOLTAGEINPUTSHIELD/GROUNDVIPoint-To-Point MeasurementsFacility GroundRegulated Test Voltagedocin/sundae_mengINPUTITEST VOLTAGEVSHIELD/GROUNDRTG MeasurementsFacility Grounddocin/sundae_mengMeasuring Small Objects5 lb probes are tool large to measure man
12、y objects of interest.ThermoformedTrays ClamshellsTape and Reel CarriersPick and Place Suction Cupsdocin/sundae_mengIonizationInsulators cannot be grounded.Methods of Ion Generation Ionization by Radiation Electrical(Corona)Ionizationdocin/sundae_mengIonization by RadiationRadioactive Decay Alpha pa
13、rticlesElectromagnetic Radiation Soft X-RayUltravioletInherently balanceddocin/sundae_mengCorona Ionization+_HIGH VOLTAGE(+)docin/sundae_mengCorona IonizationHIGH VOLTAGE(+)+docin/sundae_mengCorona IonizationTypes of Electrical IonizersAC DCPulse DCdocin/sundae_mengAC and Pulse DC Ionization+_HIGH V
14、OLTAGE(AC)docin/sundae_mengAC IonizationStep up line voltageLow costHigh airflow required to prevent recombination No control of balancedocin/sundae_mengPulsed DC IonizationFast transport of ions without air flowMinimum recombination Good for room ionizationdocin/sundae_mengDC IonizationAir ions wil
15、l recombine and drift in the electric field.+_HIGH VOLTAGE(+)HIGH VOLTAGE(-)docin/sundae_mengEfficiency and Balance_+HIGH VOLTAGE(+)HIGH VOLTAGE(-)docin/sundae_mengTesting IonizersSuitability for ApplicationIncoming Test Periodic Verificationdocin/sundae_mengHow We Test IonizersTest efficiency of io
16、n generation.How quickly will the ionizer discharge a charged surface.Test the balance of positive and negative air ions.An imbalance will charge an uncharged surface.docin/sundae_mengHow We Test IonizersThe instrument used to test ionizers is the Charged-Plate Monitor.docin/sundae_mengDischarge(Dec
17、ay)TestsEvaluate the quantity of ions produced by the ionizer.Charge a surface and measure the time to neutralize the charge.Perform for positive and negative charges.docin/sundae_mengFloat(Balance)TestEvaluate the balance of positive and negative ions produced by the ionizer.docin/sundae_mengCharge
18、d-Plate Monitors(CPMs)Conventional Constructiondocin/sundae_mengProperties of Charged,Isolated Conductors_GROUNDQ=CVCharges are mobile.They are free to redistribute themselves on the surface of the objectCharge(Q)is fixed.Capacitance and voltage depend on the location of the charged(conductive)objec
19、t.Cdocin/sundae_mengProperties of Charged Insulators_GROUNDQ X X=CVCharges are not mobile.They cannot redistribute themselves on the surface of the object.Charges on an insulator cannot be removed by connecting the surface of the insulator to ground.Charged insulators are more troublesome to charact
20、erize.Strictly speaking,the behavior of charged insulators cannot be characterized by Q=CV.X XCdocin/sundae_mengDirect Measurement of ChargeGROUNDDischarge isolated conductive objects into a coulombmeter.Destructive test.Cant test insulators this way.C_+_Q=CVdocin/sundae_mengDirect Measurement of Ch
21、argeOther objects(charged insulators)must be placed in a Faraday enclosure that is connected to a coulombmeter.+_docin/sundae_mengDirect Measurement of ChargeIt is challenging to place object into a Faraday enclosure without adding or subtracting charge.Measuring charge using these direct methods ma
22、y be impractical.(Objects may be too large to place into a Faraday enclosure or not removable.)+_docin/sundae_mengMeasuring Voltages on Isolated Conductors0000GROUNDFamiliar test equipment,such as digital voltmeters and oscilloscopes,cannot be used to characterize electrostatic charges.Contacting ch
23、arged conductive objects quickly discharges the object.Contacting insulators discharges the contact point and doesnt measure the un-contacted surface._docin/sundae_mengContacting ElectrometersVery high input impedance.GROUNDMinor loading of the charged conductor.Okay for measuring isolated conductor
24、s.Doesnt work for insulatorsC_+_docin/sundae_mengGROUNDVoltage followerMinimal loading of the charged conductorStill cant measure an insulatorC+_Contacting Electrometersdocin/sundae_mengProperties of Charged ObjectsWe often evaluate a charged object indirectly by evaluating its electric field.Instru
25、ments that sense electric fields includeElectrostatic FieldmetersElectrostatic Voltmeters Non-contacting test method.+docin/sundae_mengFieldmetersFieldmeters were originally used to measure large objects.Measuring in a uniform electric field is desired.Point-to-point or point-to-plane measurements y
26、ield different measurement results.docin/sundae_mengFieldmetersElectrostatic fieldmeters measure the field strength associated with a charge.The unit of measure is the volt/meter(or some other convenient distance).Indicates the presence and approximate level of charge.Usually hand-heldBest suited fo
27、r making general auditsCost-effective for measuring voltages above 3kV.docin/sundae_mengFieldmetersFieldmeters do not resolve low voltages.Fieldmeter measurements vary significantly with distance from the charged object.Fieldmeters do not resolve small surface areas.Two common types of fieldmeters a
28、reInduction FieldmetersChopper-Stabilized Fieldmetersdocin/sundae_mengSimplest type of fieldmeterNo system to improve drift and instabilityWont operate reliably in the presence of ionizationFieldmeters are grounded instruments and modify the data.Induction Fieldmetersdocin/sundae_mengChopper-Stabili
29、zed FieldmetersDo operate in the presence of ionizationFeedback systems to improve drift and instability performanceStill require a fixed spacingdocin/sundae_mengElectrostatic VoltmetersElectrostatic voltmeters use voltage feedback to null the electric field between the surface under test and the vo
30、ltmeter probe.Also known as voltage follower or electrometerHigh degree of accuracy that is independent of the distance from the charge.Electrostatic voltmeters generally provide a better approximation of the charge level as compared to fieldmeters,and are better suited for making accurate and repea
31、table measurements.docin/sundae_mengElectrostatic VoltmetersThe sensor can be placed very close to the charged surface without arc-over.The sensor can resolve small surface areas.Very free of drift and environmental instability.Well suited for fixed installation in equipment.Not a grounded probePres
32、ence of high voltage on the reference surfaceWorks in ionization because they are chopper-stabilizeddocin/sundae_mengAC-Feedback VoltmeterAC-feedback electrostatic voltmeters are part fieldmeter and part electrostatic voltmeter-a hybrid instrument with some characteristics of fieldmeters and some ch
33、aracteristics of electrostatic voltmeters.AC-feedback electrostatic voltmeters sense electric field and sense capacitance(distance)changes between the surface under test and the probe to indicate surface voltage even if the distance changes.Spacing independent accuracy of electrostatic voltmeters.Re
34、solve small surface areas.docin/sundae_mengAC Feedback Electrostatic Voltmeterdocin/sundae_mengAC Feedback Electrostatic VoltmeterAlso known as a spacing compensated fieldmeter,spot meterHow it is like a voltmeterHow it is like a fieldmeter Reports surface voltageLow costSpacing independent accuracy
35、A grounded instrumentResolves small objectsArc over if used too close Good stability and drift performancedocin/sundae_mengComparisonsVoltmetersNot cost effective above 3kVExcellent spatial resolutionIntended for close spacing,measuring small objectsNot grounded Spacing independentaccuracyLow driftA
36、C-FeedbackCost effective above 3 kVGood spatial resolutionGood at close spacings,measuring small objectsGroundedSpacing independent accuracyLow driftFieldmetersCost effective above 3 kVLow spatial resolutionIntended for wide spacing,measure large objectsGroundeddocin/sundae_mengUsing Voltmeters and
37、Fieldmetersd4d-5dAs electrostatic voltmeters can be operated close to a charged surface without fear of arc-over,they can resolve smaller surface areas.Extraneous fields can negate the whole notion of spatial resolution.docin/sundae_mengUsing Voltmeters and Fieldmeters_ _ _ _ _ _+Insulators do not h
38、ave uniform charge distribution.As charge density is non-uniform,surface potentials are non-uniform.What is measured is nebulous.Provides a figure of merit.docin/sundae_mengAuditingHand-held meters are particularly useful for auditing.Grounding is important,especially for battery-operated instrument
39、s.Charge up objects of interest and see if they retain charge.docin/sundae_mengDiagnostics and Continous MonitoringHand-held instruments are cumbersome for monitoring inside of process equipment,but many do have electrical outputs.Both fieldmeters and electrostatic voltmeters can have remote probes.
40、Probes can be fixtured to monitor a surface of interest.Probes must be fixtured in holders that isolate them from ground.Probes are available with various aperture locations and housing shapes.Most chopper-stabilized instruments are limited in temperature range.Most fieldmeters and electrostatic vol
41、tmeters can be interfaced to facilities monitoring systems.docin/sundae_mengSummaryTriboelectric charging and induction charging are common causes of charges in electronic manufacturing.Electrostatic charge cause electrostatic attraction of contaminants and causes objects to stick together.Electrost
42、atic discharges cause device damage and equipment lock up.These problems are reduced by using an ESD control program.Electrostatic measurements tell you how well you are doing,and allow informed choices about where to properly place ESD countermeasures and to determine the effectiveness of those cou
43、ntermeasures.docin/sundae_mengSummaryDifferent instruments will excel in different situations.Understanding your instruments allows you to obtain the greatest benefit and best results from them.Measuring and monitoring for charge accumulation allows informed choices about where to properly place ESD countermeasures and to determine the effectiveness of those countermeasures.2002 Trek Incorporateddocin/sundae_meng
