Electrosta*cDischargeAwareness

AFRLSatFab,Jan2010

Defini*ons

•  STATICELECTRICITY–  Asta*onaryelectricalchargethatresidesonthesurfaceofan

object.•  ELECTROSTATICDISCHARGE(ESD)

–  Therapiddischargeofasta*cchargetoground(ortoalowerpoten*al).Bothobjectsinvolvedmustbeconduc*ve.

–  Duringadischargelas*ngafewnanoseconds,currentlevelscanexceedseveralamps.

–  Thecombina*onofavoltagehighenoughtobreakdowninternalinsula*onfollowedbythesuddensurgeofcurrentthroughaverysmallareacausesmostESDdamage.

•  ELECTROSTATICDISCHARGESENSITIVE(ESDS)–  Aclassifica*ongiventopartsanddevicesthatcanbedamaged

ordestroyedbycommonlevelsofsta*ccharge.

HowisSta*cElectricityGenerated?

•  Twowaystogenerate:–  Triboelectric–generatedbyfric*on/separa*onofmaterials.–  Induc*ve‐generatedbyelectricfields(Nophysicalcontact

required)•  Threefactorsdeterminehowmuchchargegeneratedby

fric*on/separa*on:– Material

•  Somematerialsgeneratemorethanothers.Insulatorsgeneratethemost,conductorsgeneratetheleast.

–  In*macyofcontact•  Thecloserthetwoobjects,themorechargeisgenerated.

–  SpeedofSepara*on•  Thefastertheyarepulledapart,thegreaterthechargegenerated.

CommonSta*cChargeSources

•  Worksurfaces Plas*corwoodbenchtops.

•  Floors Carpets,*le,paintedorsealedconcrete.•  Clothes Allcommonfabrics,co^ongenerates

theleast,woolandsynthe*csthemost.

•  Chairs Synthe*cfabricupholstery,plas*cs.•  PackingMaterial Styrofoam,plas*cbags,foamcushions,

cardboardandpaper.

•  Tools Solderingirons,heatguns,plas*ccases

SingleBiggestESDHazard

People

• Alwaysconduc*ve• Normallyisolated• Mobile• Toucheverything• Impossibletoeliminate• Resistanttotrainingandhabitua*on• Pronetora*onalizeimproperbehavior

CommonElectrosta*cVoltagesAc#on 10‐30%Humidity 30‐70%Humidity 70‐90%Humidity

Walkingoncarpet 35,000V 7,500V 1,500V

Walkingonvinylfloor

12,000V 3,000V 250V

Workingatbench 6,000V 400V 100V

Removingpaperfromvinylsleeve

7,000V 1,500V 600V

Pickinguppolybagfrombenchtop

20,000V 6,500V 1,200v

Usingpolyurethanepaddedchair

18,000V 5,000V 1,500V

Howmuchsta*cdoesittaketodamagehardware?

Device RangeofminimumESDsuscep#bility

MOSFET 30To1,800volts

EPROM 100volts

OpAmp 190to2,500volts

CMOS 250to3,000volts

Filmresistors 300to3,000volts

TypesofESDDamage

•  ImmediateFailure–  ESDdamagesthepartandrendersituselessimmediately.–  Iden*fyingthefailedpartcanbedifficultand*meconsuming.

•  LatentFailure–  ESDdamageisnotsevereenoughtocauseimmediatefailure.–  Maycauseasmallincreaseincurrentdraw,usuallynotdetectable.–  Partdegradesover*me(metalmigra*on,etc)un*lfailureoccurs.

•  CircuitUpset–  PulsefromESDeventiserroneouslydetectedasanormalcircuit

func*onwithunintendedandundesirableresults.–  Usuallyimpossibletoduplicate,canresultinlargeamountsof*me

beingspentexamininghardwareandsojwareinana^empttodeterminecauseofproblem.

SomeExamples

Bipolartransistor,dischargethroughunderlyingsilicon

SomeExamples

ESDAtLarge

•  Cellphonemanufacturerses*matethat1/3ofallphonefailurescausedbyESD.

•  PCandperipheralmanufacturersconsiderESDasthecauseofbetween50%and66%ofhomeandofficecomputerfailures.

• Mostfuelingfiresthatoccuratgassta*onsarecausedbyESD.– Don’tgetbackinthecarwhilefueling!

HowdoweprotectESDHardware?

•  Humidity Keephumidityabove30%

•  Training Teachallpersonnelhowtominimizesta*c buildupandhowtosafelydissipatesta*c charge.

•  ESDAreas Iden*fyareaswhereESDsensi*veitems maybe.

•  ESDWorkSta*ons Provideworksta*onswithdissipa*ve surfaces,commonpointground.

•  Properpackaging Useshieldingbags,secondarypackaging, ESDwarninglabels.

PersonalESDProtec*on

•  WristStrap–  Mustfitsnugly,metalpor*onmustbeincontactwithskinatall*mes.–  Mustbeconnectedtoapprovedgroundingpointbeforeyoutouch

hardware.–  Mustbetestedbeforeuse.

•  ESDLabCoat–  Checkforconduc*vegrid,collarlabelshouldindicateESDsafe.–  Mustbeincontactwithyourskintowork.

•  Ifyou’rewearingalongsleevesweater,thelabcoatislikelynotdoinganything.

•  Habits–  Testyourwriststrap,wearyourwriststrap,connectyourwriststrap.–  Wearyoulabcoat.Bu^onupyourlabcoat.–  Moveslowly.Fastmovementbuildsupmorecharge.

ESDWorksta*ons

•  StandardESDControlledWorksta*on– Commonpointground– Sta*cdissipa*vematorbenchtop– Wriststrapgroundpoint– Placardandevidenceofinspec*on– Absenceofplas*cs,papers,otherchargebuildingmaterials.

•  LargeObjectESDControlledWorksta*on(cleantents)– MustbeinanESDcontrolledarea– Largeobjectmustbegrounded– Scaffoldsorsupportsmustbegrounded– Wriststrapgroundpointsmustbeprovided

HandlingPrecau*ons

•  ConnectyourwriststraptoapprovedgroundbeforehandlingESDsensi*veitems.

•  WearyourESDsafelabcoatinESDcontrolledareas.•  Onlyhandlesensi*veitemsinESDcontrolledareas.•  KeepESDsensi*veitemsinclosedshieldingbagsforstorageor

movement.•  OnlyplaceESDitemsondissipa*vesurfaces.•  Avoidtouchingexposedcircuitry,pins,orcontacts,handleboards

bytheiredges.•  Keeplargesensi*veitemsinESDcontrolledareasandkeepthem

groundedatall*mes.•  Groundlargeshippingcontainersbeforeopening.•  Usenitrilegloveswhenglovesarerequired.

Contamina*onControl&CleanRoomPrac*ces

AFRLSatFab,Jan2010

Defini*ons

•  CONTAMINATION–  Par*culateContamina*on–  Materialwithanobservablelength,width,andthickness.Examplesincludefibers,hair,dust,lint,etc.

–  MolecularContamina*on–  Foreignmaterialthatlacksreadilydefineddimensions.Examplesincluderesidues,fingerprints,etc.

•  CLEANROOM–  Aroomdesignedtoreduceambientpar*culatecontamina*ontoaspecificlevel

•  SOURCESOFCONTAMINATION•  Environment:– Dust,fumes,vapor,fungi,bacteria,pollen,etc.

•  People:– Skinflakes,dandruff,hair,fingerprints,spit,etc.

•  Ac*vi*es:– Machining,cleaning,packaging,soldering,tes*ng,etc.

BasicCleanRoomDesign

•  Efficientairfiltra*on–HEPA(HighEfficiencyPar*culateAir)Filters

•  Posi*vePressure‐Keepsunfilteredairout•  Laminarairflow‐Minimizesturbulence,purgescontamina*on

fromroom

•  Materials‐Walls,floors,furniture,&fixturesdesignednottogenerateorshedpar*cles

•  Layout‐Anteroomforgowning,storage•  Classes‐#designa*onindicatesthenumberof.4micronor

largerpar*clespercu.j.

CleanRoomPrac*ces

•  Goals:– Thegoalofcleanroomsistominimizegrosspar*culatecontamina*onandpreventaccumula*onofresidues.

•  Specifics:– Cleanroomsprac*cesvarybyclasses.– The204roomisclass100.Accordingly,weneedtowearthefullcoveralls(“bunnysuits”),leggings,andshoecovers.AsMOSESisanop*calpayload,itneedstobekeptcoveredwhennotinuse.

Prac*cesCont’d

•  Ifyouknowyouwillbeworkinginthecleanroomregularly:–  It’sbesttoshoweratnightratherthanthemorningbeforework.

–  Avoidcosme*cs(Especiallyyou,Tom)–  Avoidheavyuseofaerosols,perfumesandcologne

•  Beforeentering:–  Makesureyouhaveallthetoolsyouwillneed–  Pre‐cleantoolsandequipmentwithalcohol

–  Removeouterpackagingbeforebringingdelivereditemsintotheroom

–  Usethes*ckymetintheanteroom

Prac*cescont’d

•  Preparingtoenterthecleanroom:–  Cleanshoesontackymat

–  Leavepersonalitemsinanteroom

–  Makesureyouhaveacleanbunnysuit,hairnet,facecover,andpowderfreegloves

•  Whileinthecleanroom:–  Avoidfastmo*ons(itgeneratespar*clemovement)

–  Avoidleaningoverhardware

–  Nogum

–  Donotremoveitemsfromunderthesuit

–  Donottouchyourface

•  Packaging–  Cutpackagingopen(don’ttear)

–  Promptlydiscardorstowpackaging

Prac*cesCont’d

•  Ifyoumust:– Movehardwareintoandoutofthecleanroom,useafreshsuitwhenyoure‐enterthecleanroom

– Unpackageanitemofques*onablecleanlinessinthecleanroom,doitasfarfromflighthardwareaspossible,removethepackagingimmediatelyandwipedowntheitem.

OpenAreaContamina*onControl

• Whenmovingflighthardwaretotestareasoutsidethecleanroom:– Wearatminimumacleanroomsmock,hairnet,maskandgloves

– Installprotec*vecoversonhardwareandifpossible,completelycoverhardware

– Ifusingacraneforheavyloads,adripshieldisrecommendedtoprotectfrompossibleoilleakage