【SMT资料】ESD介绍(英文资料)ppt课件

1、ESD;ESD Presentation OutlinePart 1: Introduction/Background Part 2: Electrostatic Problems Part 3: ResistancePart 4: IonizationPart 5: Charge Measurement;Charging MechanismsTriboelectric ChargingInduction Charging;Triboelectrification+ +-+ +-MATERIAL CONTACT;Triboelectrification+ +-+ +-MATERIAL SEPA

2、RATION-;Triboelectric ChargingThe amount of charge transferred depends onTypes of materials involved Area of contactNumber of contacts Rate of separationSurrounding environment;Triboelectric ChargingGlass Human Hair NylonWool Aluminum Paper Cotton Steel RubberNickel, Copper Brass, SilverPolyester Po

3、lyurethane Polyethylene Polypropylene PVCSilicon Teflon_+Triboelectric Series;Typical Charge LevelsTypical charge (voltage) measured for different activitiesWalking on an untreated vinyl floor12 kV for 10% RH3 kV for 55% RHWorker standing up6 kV for 10% RH400 V for 55% RH;Typical Charge LevelsTypica

4、l charge (voltage) measured on common objectsWafers5 kVWafer Carriers35 kV Quartz Ware15 kVPlastic Film 40 kVSmocks10 kV;Induction Charging- - -+- - -+;Charge by Induction_ _ _ _ _ _+_+;ProblemsElectrostatic AttractionContamination “Static ClingESDDevice Damage Equipment Latch Up(ESC);ProblemsElectr

5、ostatic AttractionContamination“Static Cling;ProblemsElectrostatic AttractionContamination“Static Cling;ProblemsESDDevice DamageEquipment Latch Up;ProblemsESDDevice DamageEquipment Latch UpOften misdiagnosed as software bugs.Induced EM DisturbanceAn Extra Pulse;Discharge ModelsTribocharging or induc

6、tion charging + metal contact = ESDHuman Body Model (HBM) Machine Model (MM)Charged Device Model (CDM)are used to simulate ESD events from various sources;1500 ohmsHuman Body Model100k ohmsHVPower Supply100 pFDUT;Machine ModelZero ohms andlow L100k ohmsHVPower Supply200 pFDUT;Charged Device ModelHVP

7、ower SupplyCharge Plate;Charged Device ModelHVPower SupplyCharge Plate;Grounding (first line of defense)Grounding prevents charging.Ground everything- floors, mats, personnel, chairs, garments, machine parts.;Soft Grounds Use soft grounds to control discharges. Using dissipative materials limits dis

8、charge current to a level that does not cause damage.;Resistance MapInsulative103 104 105 106 107 1081091013 1014 10151010 1011 1012Surface Resistance (Ohms)101102DissipativeConductiveShielding;The Need for StandardsMany common items are rendered dissipative to control discharges.ESD control program

9、s require qualification of these items. Thus a need for standardized test methods.Flooring Work Surfaces ChairsGloves Garments Packaging;ESD Association StandardsGarments WorksurfacesFlooring ChairsPlanar Materials10V100V103104105106 107 108 109101310101011 1012Surface Resistance (ohms);TEST VOLTAGE

10、INPUTSHIELD/GROUNDVIPoint-To-Point MeasurementsFacility GroundRegulated Test Voltage;INPUTITEST VOLTAGEVSHIELD/GROUNDRTG MeasurementsFacility Ground;Measuring Small Objects5 lb probes are tool large to measure many objects of interest.ThermoformedTrays ClamshellsTape and Reel CarriersPick and Place

11、Suction Cups;IonizationInsulators cannot be grounded.Methods of Ion Generation Ionization by Radiation Electrical (Corona) Ionization;Ionization by RadiationRadioactive Decay Alpha particlesElectromagnetic Radiation Soft X-RayUltravioletInherently balanced;Corona Ionization+_HIGH VOLTAGE (+);Corona

12、IonizationHIGH VOLTAGE (+)+;Corona IonizationTypes of Electrical IonizersAC DCPulse DC;AC and Pulse DC Ionization+_HIGH VOLTAGE (AC);AC IonizationStep up line voltageLow costHigh airflow required to prevent recombination No control of balance;Pulsed DC IonizationFast transport of ions without air fl

13、owMinimum recombination Good for room ionization;DC IonizationAir ions will recombine and drift in the electric field.+_HIGH VOLTAGE (+)HIGH VOLTAGE (-);Efficiency and Balance_+HIGH VOLTAGE (+)HIGH VOLTAGE (-);Testing IonizersSuitability for ApplicationIncoming Test Periodic Verification;How We Test

14、 IonizersTest efficiency of ion 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.;How We Test IonizersThe instrument used to test ionizers is the Charged- Plate Monitor.;Discharge (Dec

15、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.;Float (Balance) TestEvaluate the balance of positive and negative ions produced by the ionizer.;Charged-Plate Monitors (CPMs)Conven

16、tional Construction;Properties 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) object.C;Properties of Charged Insulators

17、_GROUNDQ 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 characterize.Strictly speaking, the behavior of charged ins

18、ulators cannot be characterized by Q = CV.X XC C;Direct Measurement of ChargeGROUNDDischarge isolated conductive objects into a coulombmeter.Destructive test.Cant test insulators this way.C_+_Q = CV;Direct Measurement of ChargeOther objects (charged insulators) must be placed in a Faraday enclosure

19、that is connected to a coulombmeter.+_;Direct Measurement of ChargeIt is challenging to place object into a Faraday enclosure without adding or subtracting charge.Measuring charge using these direct methods may be impractical. (Objects may be too large to place into a Faraday enclosure or not remova

20、ble.)+_;Measuring Voltages on Isolated Conductors0000GROUNDFamiliar test equipment, such as digital voltmeters and oscilloscopes, cannot be used to characterize electrostatic charges.Contacting charged conductive objects quickly discharges the object.Contacting insulators discharges the contact poin

21、t and doesnt measure the un-contacted surface._;Contacting ElectrometersVery high input impedance.GROUNDMinor loading of the charged conductor.Okay for measuring isolated conductors. Doesnt work for insulatorsC_+_;GROUNDVoltage followerMinimal loading of the charged conductorStill cant measure an in

22、sulatorC+_Contacting Electrometers;Properties of Charged ObjectsWe often evaluate a charged object indirectly by evaluating its electric field.Instruments that sense electric fields includeElectrostatic FieldmetersElectrostatic Voltmeters Non-contacting test method.+;FieldmetersFieldmeters were orig

23、inally used to measure large objects.Measuring in a uniform electric field is desired.Point-to-point or point-to-plane measurements yield different measurement results.;FieldmetersElectrostatic fieldmeters measure the field strength associated with a charge.The unit of measure is the volt/meter (or

24、some other convenient distance).Indicates the presence and approximate level of charge.Usually hand-heldBest suited for making general auditsCost-effective for measuring voltages above 3kV.;FieldmetersFieldmeters do not resolve low voltages.Fieldmeter measurements vary significantly with distance fr

25、om the charged object.Fieldmeters do not resolve small surface areas. Two common types of fieldmeters areInduction FieldmetersChopper-Stabilized Fieldmeters;Simplest type of fieldmeterNo system to improve drift and instabilityWont operate reliably in the presence of ionizationFieldmeters are grounde

26、d instruments and modify the data.Induction Fieldmeters;Chopper-Stabilized FieldmetersDo operate in the presence of ionizationFeedback systems to improve drift and instability performanceStill require a fixed spacing;Electrostatic VoltmetersElectrostatic voltmeters use voltage feedback to null the e

27、lectric field between the surface under test and the voltmeter 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 fieldmet

28、ers, and are better suited for making accurate and repeatable measurements.;Electrostatic 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 installa

29、tion in equipment. Not a grounded probePresence of high voltage on the reference surfaceWorks in ionization because they are chopper-stabilized;AC-Feedback VoltmeterAC-feedback electrostatic voltmeters are part fieldmeter and part electrostatic voltmeter- a hybrid instrument with some characteristic

30、s of fieldmeters and some characteristics 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

31、of electrostatic voltmeters.Resolve small surface areas.;AC Feedback Electrostatic Voltmeter;AC Feedback Electrostatic VoltmeterAlso known as a spacing compensated fieldmeter, spot meterHow it is like a voltmeter How it is like a fieldmeter Reports surface voltageLow costSpacing independent accuracy

32、A grounded instrumentResolves small objectsArc over if used too close Good stability and drift performance;ComparisonsVoltmetersNot cost effective above 3kVExcellent spatial resolutionIntended for close spacing, measuring small objectsNot grounded Spacing independentaccuracyLow driftAC-FeedbackCost

33、effective above 3 kVGood spatial resolutionGood at close spacings, measuring small objectsGroundedSpacing independent accuracyLow driftFieldmetersCost effective above 3 kVL o w s p a t i a l resolutionI n t e n d e d f o r wide spacing, measure large objectsGrounded;Using Voltmeters and Fieldmetersd

34、4d - 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.;Using Voltmeters and Fieldmeters_ _ _ _ _ _+ + + + + +Insulators do not have uniform cha

35、rge distribution.As charge density is non- uniform, surface potentials are non-uniform.What is measured is nebulous. Provides a figure of merit.;AuditingHand-held meters are particularly useful for auditing.Grounding is important, especially for battery-operated instruments. Charge up objects of int

36、erest and see if they retain charge.;Diagnostics 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. Probes can be fixtured to monitor a surface of interest.Probes must b