Electrostatic Discharge Awareness - Solar...
Transcript of Electrostatic Discharge Awareness - Solar...
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