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GreatHumanTechnology,INC.FundamentalsofElectrostaticDischargeAnIntroductiontoESDHistory&BackgroundTomanypeople,staticelectricityislittlemorethantheshockexperiencedwhentouchingametaldoorknobafterwalkingacrossacarpetedroomorslidingacrossacarseat.However,staticelectricityhasbeenaseriousindustrialproblemforcenturies.Asearlyasthe1400's,EuropeanandCaribbeanfortswereusingstaticcontrolproceduresanddevicestopreventelectrostaticdischargeignitionofblackpowderstores.Bythe1860's,papermillsthroughouttheU.S.employedbasicgrounding,flameionizationtechniques,andsteamdrumstodissipatestaticelectricityfromthepaperwebasittraveledthroughthedryingprocess.Theageofelectronicsbroughtwithitnewproblemsassociatedwithstaticelectricityandelectrostaticdischarge.And,aselectronicdevicesbecamefasterandsmaller,theirsensitivitytoESDincreased.Today,ESDimpactsproductivityandproductreliabilityinvirtuallyeveryaspectoftoday'selectronicsenvironment.Manyaspectsofelectrostaticcontrolintheelectronicsindustryalsoapplyinotherindustriessuchascleanroomapplicationsandgraphicarts.Despiteagreatdealofeffortduringthepastdecade,ESDstillaffectsproductionyields,manufacturingcosts,productquality,productreliability,andprofitability.Industryexpertshaveestimatedaverageproductlossesduetostatictorangefrom8-33%(Table1).OthersestimatetheactualcostofESDdamagetotheelectronicsindustryasrunningintothebillionsofdollarsannually.Thecostofdamageddevicesthemselvesrangesfromonlyafewcentsforasimplediodetoseveralhundreddollarsforcomplexhybrids.Whenassociatedcostsofrepairandrework,shipping,labor,andoverheadareincluded,clearlytheopportunitiesexistforsignificantimprovements.Table1InformalSummaryofStaticLossesbyLevelStaticLossesReportedDescriptionMin.LossMax.LossEst.Avg.LossComponentManufacturers4%97%16-22%Subcontractors3%70%9-15%Contractors2%35%8-14%ReportbySammyLu1GreatHumanTechnology,INC.User5%70%27-33%ThisfirstinaseriesofsixarticlesonthefundamentalsofESDanditscontrolfocusesonhowelectrostaticchargeanddischargeoccur,howvariousmaterialsaffectthelevelofcharge,typesofESDdamage,andhowESDeventscandamageelectroniccomponents.Futurearticleswillcovervariouswaystocontroltheproblem.StaticElectricity:CreatingChargeStaticelectricityisdefinedasanelectricalchargecausedbyanimbalanceofelectronsonthesurfaceofamaterial.Thisimbalanceofelectronsproducesanelectricfieldthatcanbemeasuredandthatcaninfluenceotherobjectsatadistance.Electrostaticdischargeisdefinedasthetransferofchargebetweenbodiesatdifferentelectricalpotentials.Electrostaticdischargecanchangetheelectricalcharacteristicsofasemiconductordevice,degradingordestroyingit.Electrostaticdischargealsomayupsetthenormaloperationofanelectronicsystem,causingequipmentmalfunctionorfailure.Anotherproblemcausedbystaticelectricityoccursincleanrooms.Chargedsurfacescanattractandholdcontaminants,makingremovalfromtheenvironmentdifficult.Whenattractedtothesurfaceofasiliconwaferoradevice'selectricalcircuitry,theseparticulatescancauserandomwaferdefectsandreduceproductyields.Controllingelectrostaticdischargebeginswithunderstandinghowelectrostaticchargeoccursinthefirstplace.Electrostaticchargeismostcommonlycreatedbythecontactandseparationoftwomaterials.Forexample,apersonwalkingacrossthefloorgeneratesstaticelectricityasshoesolescontactandthenseparatefromthefloorsurface.Anelectronicdeviceslidingintooroutofabag,magazineortubegeneratesanelectrostaticchargeasthedevice'shousingandmetalleadsmakemultiplecontactsandseparationswiththesurfaceofthecontainer.Whilethemagnitudeofelectrostaticchargemaybedifferentintheseexamples,staticelectricityisindeedgenerated.ReportbySammyLu2GreatHumanTechnology,INC.Figure1TheTriboelectricCharge.MaterialsMakeIntimateContactFigure2TheTriboelectricCharge-SeparationCreatingelectrostaticchargebycontactandseparationofmaterialsisknownastriboelectriccharging.Itinvolvesthetransferofelectronsbetweenmaterials.Theatomsofamaterialwithnostaticchargehaveanequalnumberofpositive(+)protonsintheirnucleusandnegative(-)electronsorbitingthenucleus.InFigure1,MaterialAconsistsofatomswithequalnumbersofprotonsandelectrons.MaterialBalsoconsistsofatomswithequal(thoughperhapsdifferent)numbersofprotonsandelectrons.Bothmaterialsareelectricallyneutral.Whenthetwomaterialsareplacedincontactandthenseparated,negativelychargedelectronsaretransferredfromthesurfaceofonematerialtothesurfaceoftheothermaterial.Whichmaterialloseselectronsandwhichgainselectronswilldependonthenatureofthetwomaterials.Thematerialthatloseselectronsbecomespositivelycharged,whilethematerialthatgainselectronsisnegativelycharged.ThisisshowninFigure2.Staticelectricityismeasuredincoulombs.ThechargeqonanobjectisdeterminedbytheproductofthecapacitanceoftheobjectCandthevoltagepotentialontheobject(V):q=CVCommonly,however,wespeakoftheelectrostaticpotentialonanobject,whichisexpressedasvoltage.Thisprocessofmaterialcontact,electrontransferandseparationisreallyamorecomplexmechanismthandescribedhere.Theamountofchargecreatedbytriboelectricgenerationisaffectedbytheareaofcontact,thespeedofseparation,relativehumidity,andotherfactors.Once