ELECTRONICSASSOCIATIONELECTRONICS

StencilDesignMay Astandarddevelopedby2215SandersRoad,Northbrook,IL60062-Tel.847.509.9700FaxThePrinciplesof

InMay1995theIPC’sTechnicalActivitiesExecutiveCommitteeadoptedPrinciplesofStandardizationasaguidingprincipleofIPC’sstandardizationefforts.StandardsShowrelationshiptoDesignforManufacturability(DFM)andDesignfortheEnvironment(DFE)MinimizetimetoContainsimple(simplified)JustincludespecFocusonendproductIncludeafeedbacksystemonuseandproblemsforfutureimprovement

StandardsShouldInhibitIncreasetime-to-KeeppeopleIncreasecycleTellyouhowtomakeContainanythingthatcannotbedefendedwithdata IPCStandardsandPublicationsaredesignedtoservethepublicinterestthrougheliminatingmisunderstandingsbetweenmanufacturersandpurchasers,facilitatinginterchangeabilityandimprovementofproducts,andassistingthepurchaserinselectingandobtainingwithminimumdelaytheproperproductforhisparticularneed.ExistenceofsuchStandardsandPublicationsshallnotinanyrespectprecludeanymemberornonmemberofIPCfrommanufacturingorsell-ingproductsnotconformingtosuchStandardsandPublication,norshalltheexistenceofsuchStandardsandPublicationsprecludetheirvoluntaryusebythoseotherthanIPCmembers,whetherthestandardistobeusedeitherdomesticallyorinternationally.RecommendedStandardsandPublicationsareadoptedbyIPCwithoutregardtowhethertheiradoptionmayinvolvepatentsonarticles,materials,orprocesses.Bysuchaction,IPCdoesnotassumeanyliabilitytoanypatentowner,nordotheyassumeanyobligationwhatevertopartiesadoptingtheRecommendedStandardorPublication.Usersarealsowhollyresponsibleforprotectingthemselvesagainstallclaimsofliabilitiesforpatentinfringement.IPCPositionStatementon

ItisthepositionofIPC’sTechnicalActivitiesExecutiveCommittee(TAEC)thattheuseandimplementationofIPCpublicationsisvoluntaryandispartofarelationshipenteredintobycustomerandsupplier.WhenanIPCstandard/guidelineisupdatedandanewrevisionispub-lished,itistheopinionoftheTAECthattheuseofthenewrevisionaspartofanexistingrelationshipisnotautomaticunlessrequiredbythecontract.TheTAECrecommendstheuseofthelastestrevision. AdoptedOctober6.1998Whyisthereachargethis

Yourpurchaseofthisdocumentcontributestotheongoingdevelopmentofnewandupdatedindustrystandards.Standardsallowmanufacturers,customers,andsupplierstounderstandoneanotherbetter.Standardsallowmanufacturersgreaterefficiencieswhentheycansetuptheirprocessestomeetindustrystandards,allowingthemtooffertheircustomerslowercosts.IPCspendshundredsofthousandsofdollarsannuallytosupportIPC’svolunteersinthestandardsdevelopmentprocess.Therearemanyroundsofdraftssentoutforreviewandthecommitteesspendhundredsofhoursinreviewanddevelopment.IPC’sstaffattendsandparticipatesincommitteeactivities,typesetsandcirculatesdocumentdrafts,andfollowsallnecessaryprocedurestoqualifyforANSIapproval.IPC’smembershipdueshavebeenkeptlowinordertoallowasmanycompaniesaspossibletoparticipate.Therefore,thestandardsrevenueisnecessarytocomplementduesrevenue.Thepricescheduleoffersa50%discounttoIPCmembers.IfyourcompanybuysIPCstandards,whynottakeadvantageofthisandthemanyotherbenefitsofIPCmembershipaswell?FormoreinformationonmembershipinIPC,pleasevisitorcall847/790-5372.Thankyouforyourcontinued?Copyright2000.IPC,Northbrook,Illinois.AllrightsreservedunderbothinternationalandPan-Americancopyrightconventions.Anycopying,scanningorotherreproductionofthesematerialswithoutthepriorwrittenconsentofthecopyrightholderisstrictlyprohibitedandconstitutesinfringementundertheCopyrightLawoftheUnitedStates.標準分享網(wǎng)標準分享網(wǎng)免費下載ELEELECTRONICSINDUSTRIE

StencilDesignDevelopedbytheStencilDesignTaskGroup(5-21e)oftheAssemblyandJoiningProcessCommitteeofIPCUsersofthisstandardareencouragedtoparticipateinthedevelopmentoffuturerevisions.2215SandersRoadNorthbrook,IllinoisTel847Fax847MayMayMayMay標準分享網(wǎng)標準分享網(wǎng)免費下載AnyStandardinvolvingacomplextechnologydrawsmaterialfromavastnumberofsources.WhiletheprincipalmembersoftheStencilDesignTaskGroup(5-21e)oftheAssemblyandJoiningProcessesCommitteeareshownbelow,itisnotpos-sibletoincludeallofthosewhoassistedintheevolutionofthisstandard.Toeachofthem,themembersoftheIPCextendtheirgratitude.Processes

StencilDesignTaskGroup

TechnicalLiaisonsoftheIPCBoardofDirectorsJamesMaguireIntelCorporation

WilliamE.Coleman,Ph.DPhotoStencilInc.

StanPlzakPensarCorp.

PeterBigelowBeaverBrookCircuitsInc.StencilDesignTaskKermitAguayo,XeTelCorporationSyedSajidAhmad,MicronShermanM.Banks,Finisar,Inc.RickyBennett,DEKUSAInc.CraigP.Brown,DEKUSAInc.MaureenA.Brown,KesterSolderMagdalenChristopher,LittonSystemsCanadaLtd.RichardClouthier,AMTX/DivisionofPhotoStencilWilliamE.Coleman,Ph.D.,PhotoStencilInc.JerryCupples,InterphaseCorp.CharlieDavis,RadiSysCorporationAshokDhawan,C-MACSystemsKanteshDoss,PhD,NokiaMobilePhonesLtd.CaldonDriscoll,EMPF/ACIFrankV.Grano,SCISystemsInc.GovernmentDivisionRyanGrant,MCMSAndyHilbert,PlexusCorp./ElectronicAssembly

JayB.Hinerman,DEKUSAInc.JavierJaramillo,SchneiderAutomationDenisJean,3COMCorporationKathyJenczewski,Syscon-MicroRichardKennady,BahiatechBahiaTechnologiaLtdaJohnKnowles,DEKPrintingMachinesLtd.RichardLieske,DEKUSAInc.AndyC.Mackie,PraxairInc.NicholasC.Mescia,GeneralDynamics-ChristineA.Miller,FORESystemsSteveM.Moore,JohnOliver,AcumenTechnologyAhneOosterhof,A-Laser,Inc.DeepakK.Pai,C.I.D.,GeneralDynamicsInformationSys.Inc.TimothyM.Pitsch,PlexusCorp.JimR.Reed,RaytheonSystems

JosephRenda,SpeedlineRobertRowland,RadiSysSteveSangillo,DMCManufacturing,MarkA.Schwarz,VitronicsSoltecDr.R.Sengupta,ElectronicsRegionalTestHansL.Shin,PacificTestingJan-ChristerStalnert,EricssonMobileDaanTerstegge,SignaalRichardThompson,VenturaElectronicsAssemblyDavidP.Torp,KesterSolderDivisionNancyTrumbull,TRMI,Inc.RaymondJ.Turner,CabletronSystemsInc.Rongxiang(Davis)Yang,HuaweiTechnologiesCo.,Ltd.MichaelW.Yuen,Tableof Termsand APPLICABLE JointIndustry STENCIL Stencil Data Gerber? Aperture SolderPaste Data Panelized Image Image Aperture Aperture ApertureSizeVersusBoardPad GlueApertureChip MixedTechnologySurface-Through-Hole(Intrusive SolderPaste MixedTechnologySurface-Flip Two-PrintStencilforSurface-Flip StepStencil Step-Down Step-Up StepStencilforContainedTransfer Relief-Etch Global Local STENCIL

Stencil StencilFabrication Chemical Laser Trapezoidal Additional STENCIL LocationofImageon AdditionalDesign STENCIL USERSTENCIL STENCIL ENDOF APPENDIX EXAMPLEORDER Figure CrossSectionalViewofAStencil Figure HomePlateAperture Figure BowTieAperture Figure OblongAperture Figure ApertureDesignforMELF Figure GlueStencilAperture Figure Through-HoleSolderPaste Figure Overprintwithout Figure OverprintwithStep(Squeegee Figure OverprintwithStep(Contact/Board Figure Two-PrintThrough-Hole Figure Two-PrintStencilforMixed Figure GeneralApertureDesignGuidelinesSurface-Mount ProcessWindowforIntrusive MayMayMayMay標準分享網(wǎng)標準分享網(wǎng)免費下載StencilDesignThisdocumentprovidesguidesforthedesignandfabrica-tionofstencilsforsolderpasteandsurface-mountadhe-sive.Itisintendedasaguidelineonly.TermsandDefinitionsAlltermsanddefinitionsusedthroughoutthishandbookareincompliancewithIPC-T-50.Definitionsdenotedwithanasterisk(*)belowarereprintsfromIPC-T-50.Otherspecifictermsanddefini-tions,essentialforthediscussionofthesubject,arepro-videdbelow.ApertureAnopeninginthestencilAspectRatioandAreaAspectRatio=WidthofAperture/ThicknessofStencilAreaRatio=AreaofApertureOpening/AreaofApertureBorderPeripheraltensionedmesh,eitherpolyesterorstainlesssteel,whichkeepsthestencilfoilflatandtaut.Theborderconnectsthefoiltotheframe.ContainedPasteTransferHeadAstencilprinterheadthatholds,inasinglereplaceablecomponent,thesqueegeebladesandapressurizedchamberfilledwithsol-derpaste.EtchFactorEtchFactor=EtchedDepth/LateralEtchinachemicaletchingprocessFiducialsReferencemarksonthestencilfoil(andotherboardlayers)foraligningtheboardandthestencilwhenusingavisionsysteminaprinter.Fine-PitchBGA/ChipScalePackage(CSP)Ballgridarraywithlessthan1mm[39mil]pitch.ThisisalsoknownasChipScalePackage(CSP)whenthepackagesizeisnomorethan1.2Xtheareaoftheoriginaldiesize.Fine-PitchTechnology(FPT)*Asurface-mountassemblytechnologywithcomponentterminationsoncen-terslessthanorequalto0.625mm[24.61mil].FoilThesheetusedtocreatethe

FrameAdeviceontowhichthefoilismounted.Thismaybetubularorcastaluminumwiththeborderper-manentlymountedusinganadhesive.Somefoilscanbemountedintoatensioningmastercaseanddonotrequireaborderorapermanentfixturingofthefoiltotheframe.IntrusiveSolderingIntrusivesolderingmayalsobeknownaspaste-in-hole,pin-in-hole,orpin-in-pastesol-dering.Thisisaprocessinwhichthesolderpasteforthethrough-holecomponentsisappliedusingthestencil,thethrough-holecomponentsareinsertedandreflow-solderedtogetherwiththesurface-mountcomponents.ModificationTheprocessofchanginganapertureinsizeorshape.OverprintingTheuseofstencilswithapertureslargerthanthepadsorannularringsontheboard.PadMetallizedshapeonthecircuitboardtowhichtheterminalofasurfacemountcomponentiselec-tricallyormechanicallyattached.SqueegeeAmetalorrubberbladeusedtowipeacrossthestenciltoforcesolderpasteintoopeningsinthestencil.Normally,squeegeeismountedatananglesuchthattheprintingedgeofthesqueegeetrailsbehindtheprintheadandthefaceofthesqueegeeslopesforward.StandardBGABallgridarraywith1mm[39mil]pitchorlarger.StencilAtoolwhichmayconsistofaframe,bor-der,andfoilcontainingaperturesthroughwhichsolderpaste,adhesive,orothermediaistransferred.StepStencilAstencilwithmorethanonefoilthicknesslevel.Surface-MountTechnology(SMT)*Theelectri-calconnectionofcomponentstothesurfaceofaconduc-tivepatternthatdoesnotutilizecomponentholes.Through-HoleTechnology(THT)*Theelectricalconnectionofcomponentstoaconductivepatternbytheuseofcomponentholes.Ultra-FinePitchTechnologyAsurface-mountassemblytechnologywithcomponentterminationsoncen-terslessthanorequalto0.40mm[15.7mil]MayMayMayMay標準分享網(wǎng)標準分享網(wǎng)免費下載APPLICABLEIPC-T-50TermsandDefinitionsforInterconnectingandPackagingElectronicCircuitsIPC-A-610AcceptabilityofElectronicIPC-SM-782SurfaceMountDesignandLandPatternIPC-2511GenericRequirementsforImplementationofProductManufacturingDescriptionDataandTransferIPC-7095DesignandAssemblyProcessImplementationofBGAsJointIndustryJ-STD-005RequirementsforSolderingGerberRS-274DFormatReferenceGuide,PartNumberGerberRS-274XFormatUser’sGuide,PartNumber414-STENCILStencilDataFormatRegardlessofthestencilfabricationmethodused,Gerber?dataisthepreferreddataformat.PossiblealternativeformatsareGenCAM?3,DXF,HP-GL,Barco,etc;however,theymayneedtobecon-vertedtoGerber?formatpriortothestencilmanufactur-ingprocess.Gerber?datadescribesthefileformatthatprovidesalan-guageforcommunicatingwiththephotoplottingsystemtoproduceatoolforchemicallyetchedstencils.Itisalsousedtoproducethelasercutorelectroformedstencils.Whiletheactualdataformatmayvaryfromfiletofiledependingonthesoftwarepackageordesigner,thedataformatcom-monlyusedbyphotoplotterandlaserequipmentisknownasGerber?.Gerber?FormatTherearetwostandardGerber?formatsavailable:RS-274D-requiresadatafilelistingtheX-Ycoordinatesonthestencilwhereaperturesaretobeplacedandformed,andaseparateGerber?aperturelistthat

describesthesizeandshapeofthevariousGerber?aper-turesusedtopreparetheimage.RS-274X-inthisformattheGerber?aperturelistisembeddedinthedatafile.ApertureListTheaperturelistisanASCIItextfilecontainingDcodesthatdefinethesizeandshapeforallaperturesusedwithintheGerber?file.Withouttheaper-turelist,thesoftwareandphotoplottingsystemcannotreadtheGerber?data.OnlytheX-Ycoordinateswouldbeavailablewithnosizeandshapedata.SolderPasteLayerThesolderpastelayerdataisnecessarytoproduceastencil.Iffiducialsarerequiredonthestencil,theyshouldalsobeincludedinthesolderpasteDataTransferDatacanbetransmittedtothesten-cilsupplierviamodem,FTP(filetransferprotocol),e-mailattachmentordisk.Toensuredataintegrityaftertransmit-tingandduetothelargesizeofdatafiles,itissuggestedthatthefilesbecompressedpriortosendingdata.Itisrec-ommendedthatthefulldatafile(thesolderpaste,soldermask,silkscreenandcopperlayers)senttotheprintedcir-cuitboardmanufacturerbesuppliedtothestencilmanufac-turer.ThisallowsthestencilmanufacturertooptimizeormakerecommendationsonaperturesizesbasedonactualpadsizesfortheSMTland.PanelizedStencilsInthosecaseswhereitisdesiredtohavemorethanoneimageonthestencil,thestencilpatternswillbepanelizedandincludedinthedatafile.Inthoseinstanceswherethedatafiledoesnotalreadycontainthepanelizedstencildesign,areadmefile,paneldrawingororderinformationmustspecifythelocationofthetwoormoredesigns.Thiscouldbeareferencefromtheedgeoftheframe,distancesbetweenpatterns,etc.Step-and-RepeatInthosecaseswheremorethanoneimageofthesamedesignistobeprinted,thedatafileforstencilfabricationshouldcontainthestencildesigninthestep-and-repeatarray.Inthoseinstanceswherethedatafiledoesnotcontainthestep-and-repeatpattern,areadmefile,paneldrawing,ororderinformationshouldspecify:TotalnumberofstepsforthefinalNumberofstepsintheX-directionalongwithdimensionsfromaspecificfeaturetocorrespondingfeature(suchasfiducials,componentpadlocations,etc.).NumberofstepsintheY-directionalongwithdimensionsfromaspecificfeaturetocorrespondingfeature(suchasfiducials,componentpadlocations,etc.).IPC,2215SandersRoad,Northbrook,ILBarco/ETSinNorthAmerica,Telephone860-291-7000,Fax860-291-ForEuropeandAsia,Telephone+3292169441,Fax+3292169870,EmailIPCGenericComputerAidedManufacturing(GenCAM?)format.Moreinformationavailableatthebackofdocument.RefertoIPC-2511forImageOrientation/RotationInthosecaseswhereimageorientationisnotparalleltotheframeorthestep-and-repeatisnotrecti-linear(oneormoreimagesisrotated),thedataforstencilfabricationshouldcontaintheorientedimage.Inthosecaseswhereitdoesnot,areadmefile,paneldrawingororderinformationshouldspecifythisinformation(X-andY-offsets)referencingstencilfeatures.ImageLocationToaccommodatespecificprinters,thestencilimagemayhavetobelocatedindifferentposi-tionsinsidetheframe:centercenterboard/panel–requiresboard/paneloffsetboard/panel–requiresboard/paneloutlinesandreferencelocationsInthosecaseswherethisdataisnotincludedinthe

Whenthestencilseparatesfromtheboard,pastereleaseencountersacompetingprocess:solderpastewilleithertransfertothepadontheboardorsticktotheaperturesidewalls.Whenthepadareaisgreaterthan0.66oftheinsideaperturewallarea,acompletepastetransfershouldFigure1CrossSectionalViewofAber?data,areadmefile,paneldrawingororderinforma-tionshouldspecifythisinformationreferencingstencilfea-

AspectRatio

WidthofAperture W IdentificationStencilshouldcontainidentifica-tioninformationsuchaspartnumber,revisionnumber,

LxW 2xLWxthickness,supplier’snameandcontrolnumber,dateandmethodofmanufacture.ApertureDesignAgeneralaperturedesignguidelineforvariousSMTcomponentsisshowninTable1.Someofthefactorsinfluencingstencilaperturedesignare:compo-nenttype,padfootprint,soldermaskopening,boardfinish,aspect/arearatio,solderpastetypeanduserprocessApertureSizeThevolumeofsolderpasteappliedtotheboardismainlydeterminedbytheaperturesizeandfoilthickness.Solderpastefillsthestencilapertureduringthesqueegeecycleoftheprintoperation.Thepasteshouldcompletelyreleasetothepadsontheboardduringtheboard/stencilseparationcycleoftheprintoperation.Fromthestencilviewpoint,theabilityofthepastetoreleasefromtheinneraperturewallstotheboardpaddependspri-marilyonthreemajorfactors:theareaandaspectratiosfortheaperturedesign(Seetheaperturesidewallgeometry(SeeSectiontheaperturewallfinish(SeeSectionreducestoafactoroftheaspectAreaRatio/AspectRatioBotharearatioandaspectratioareillustratedinFigure1.Ageneraldesignguideforacceptablepastereleaseis>1.5foraspectratioand>0.66forarearatio.Theaspectratioisaone-dimensionalsimplificationofthearearatio.Whenthelengthismuchreducestoafactoroftheaspect

ApertureSizeVersusBoardPadSizeAsagen-eraldesignguide,theaperturesizeshouldbereducedcom-paredtotheboardpadsize.Thestencilapertureiscom-monlymodifiedwithrespecttotheoriginalpaddesign.Reductionsintheareaorchangesinapertureshapeareoftendesirabletoenhancetheprocessesofprinting,reflow,orstencilcleaning.Forinstance,reducingtheaperturesizewilldecreasethepossibilityofstencilaperturetoboardpadmisalignment.Thisreducesthechanceforsolderpastetobeprintedoffthepad,whichmayleadtosolderballsorsolderbridging.Havingaradiusedcornerforallaperturescanpromotestencilcleaning.LeadedSMD’sForleadedSMD’s,e.g.,J-leadedorgull-wingcomponentswith1.3-0.4mm[51.2-15.7mil]pitch,thereductionistypically0.03-0.08mm[1.2mil]inwidthand0.05-0.13mm[2.0-5.1mil]inPlasticBGA’sReducecircularaperturediameterby0.05mm[2.0mil].CeramicBGA’sIncreasecircularaperturedimensionby0.05-0.08mm[2.0-3.1mil]whenthisdoesnotinterferewiththesoldermaskand/orincreasethesten-cilfoilthicknessto0.2mm[7.9mil]andgoonetoonewiththeboardpad.RefertoIPC-7095forsolderpastevol-umerequirements.Fine-PitchBGAandCSPSquareapertureW

thewidthofthesquareequalto,or0.025mm[0.98lesslessthan,thediameterofthepadcircleontheboard.Table1GeneralApertureDesignGuidelinesforSurface-MountPartStencilFoilThicknessRangeAreaRatio1.25[49.20.65[25.62.00[78.70.60[23.61.95[76.80.15-0.25[5.91-9.842.3-0.88-0.65[25.60.35[13.81.50[59.10.30[11.81.45[57.10.15-0.175[5.91-6.891.7-0.71-0.50[19.70.30[11.81.25[49.20.25[9.84[1.2047.20.125-0.15[4.92-5.911.7-0.69-0.40[15.70.25[9.841.25[49.20.20[7.87[1.2047.20.10-0.125[3.94-4.921.6-0.68-0.30[11.80.20[7.871.00[39.40.15[5.910.95[37.40.075-0.125[2.95-3.941.5-0.65-0.50[19.70.65[25.60.45[17.70.60[23.60.125-0.15[4.92-5.910.84-0.25[9.840.40[15.70.23[9.060.35[13.80.075-0.125[2.95-3.940.66-1.25[49.20.80[31.50.80[31.50.75[29.50.75[29.50.15-0.20[5.91-7.870.93-1.00[39.40.38[15.00.38[15.00.35[13.80.35[13.80.115-0.135[4.53-5.310.67-0.50[19.70.30[11.80.30[11.80.28[11.00.28[11.00.075-0.125[2.95-3.940.69-Itisassumedthatthefine-pitchBGApadsarenotsoldermaskN/AimpliesthatonlythearearatioshouldbeLL1/2ChipComponents-ResistorsandCapacitorsSeveralaperturegeometriesareeffectiveinreducingtheoccurrenceofsolderballs.Allthesedesignsareaimedatreducingexcesssolderpastetrappedunderthechipcom-ponent.ThemostpopulardesignsareshowninFigure2,3and4.Thesedesignsarecommonlyusedforno-cleanpro-2/31/2Figure2HomePlate2/31/2

Figure3BowTieApertureMELF,Mini-MELFComponentsForMELFandMini-MELFcomponents,‘‘C’’shapedaperturesaresug-gested.(SeeFigure5).DimensionsoftheseaperturesshouldbedesignedtomatchthegeometryofcomponentGlueApertureChipComponentThegluestencilistypically0.15-0.2mm[5.9-7.9mil]thick.Theglueapertureisplacedinthecenterofthecomponentsolderpads.Itis1/3thespacingbetweenpadsand110%ofthecomponentwidth.(SeeFigure6.)Moreinformationaboutgluestencilwillbemadeavailableinthenextrevisionofthisdocument.MayMayMayMay標準分享網(wǎng)標準分享網(wǎng)免費下載1/21/2fullTable2Process1/21/2fullMaximum0.65-1.60[25.6-63.00.75-1.25[29.5-49.2Holediameter0.075mm[2.95Holediameter0.125mm[4.926.35mm[250<4.0mm[157StencilFoil0.125-0.635[4.92-25.00.15mm[5.910.20mm[7.87mil]forfine-pitchFigure4OblongAperture

VisvolumeofsolderpasteAllcornersAllcornersSisthesolderpasteshrinkAHisthecrosssectionalareaofthethrough-holeAPisthecrosssectionalareaofthethrough-holepinTBisthethicknessoftheboardFT+FBisthetotalfilletvolumeTSisthethicknessofthestencilLOisthelengthoftheoverprintLPisthelengthoftheFigure5ApertureDesignforMELF1/31/3glueFigure6GlueStencilApertureMixedTechnologySurface-Mount/Through-Hole(IntrusiveReflow)ItisdesirabletohaveaprocesswhereSMTandTHTdevicescanbothbe:providedwithprintedsolderplacedonorinthereflowedTheobjectiveofstencilprintingofsolderpastefortheintrusivereflowprocessistoprovideenoughsoldervolumeafterreflowtofilltheholeandcreateacceptablesolderfilletsaroundthepins.Table2showsprocesswin-dowforatypicalintrusivesolderingprocess.SolderPasteVolumeAsimpleequationlistedbelowdescribesthevolumeofsolderpasterequiredasshowninFigure7.V=TS(LOx

WOisthewidthoftheoverprintapertureWPisthewidthofthepadVHissolderpastefillingtheholeduringtheprintingItisdesirabletokeepthecopperpadaroundthethrough-holeassmallaspossible.Itisalsodesirabletokeeptheclearancebetweenthepinandthethrough-holeandthelengthofthepinassmallaspossible.Bydoingthislesssolderpastevolumewillberequired.Note:Solderpastevolumefillingtheholecanvaryfrom0%to100%dependingontheprintsetup.Containedpastetransferheadsareeffectiveinachievingcloseto100%whilemetalsqueegeebladeswithahighattackangleandhighprintspeedwilldeliverminimumpasteintotheFollowingarethreestencildesignsusedtodeliverthethrough-holesolderpaste:Non-stepStepTwo-printOverprintWithoutStepThisisthestencilofchoicewhenitcandeliverenoughsolderpastetosatisfythethrough-holerequirement.AcrosssectionofthistypestencilisshowninFigure8.Anexampleofwhenthisstencilcouldbeusedisatwo-rowconnectoron2.5mm[98.4mil]pitchwith1.1mm[43.3mil]diameterthough-holes,0.9mm[35.4mil]diam-eterpins,1.2mm[47.2mil]thickboardandnoothercom-ponentswithin3.8mm[150mil]ofthethrough-hole=1{T(A-A)+

+F)+V}-

ings.Anoverprintstencilapertureof2.2mm[86.6

Through- Through-SMTAnnularStencilAnnularStencilCrossSectionalshouldbe36xthestep-downthickness.Forexample,a0.2mm[7.9mil]stencilfoilwithastepdownto0.15mm[5.9mil]wouldrequireaK1keep-outdistanceof1.8mm[70.9mil].Itisalsopossibletoputthesteponthecontactsideofthestencilinsteadofthesqueegeeside.ThisisshowninFigure10.Thistypeofstepissometimesmoreconve-nientwhenusingmetalsqueegeebladesandishighlyrec-ommendedforcontainedpastetransferheads.Thesamekeep-outrulesapply.Through- Through-SMTThrough- Through-SMTwideand5.1mm[200mil]longwithastencilfoilthick-nessof0.15mm[5.91mil]candeliversufficientsolderThrough- Through-SMTFigure10Through- Through-SMTFigure8OverprintwithoutOverprintWithStepIftheboardisthicker,theholeisbigger,orthepinissmaller,moresolderpastevol-umewillberequired.Inthiscase,astepstencilmaybeneededtoprovidesufficientsolderpastevolumefortheTHTpartswithoutprovidingtoomuchpasteontheSMTpads.AnexampleofthistypestencilisshowninFigureK1andK2arekeep-outdistances.K2isthedistancebetweenthethrough-holeapertureandthestepedge.AsageneraldesignguideK2canbeaslowas0.65mm[25.6mil].K1isthedistancefromthestepedgetothenearestapertureinthestep-downarea.Asageneraldesignguide,K1shouldbe0.9mm[35.4mil]forevery0.025mm[0.98mil]ofstep-downthickness.Asasimpleguideline,

Two-PrintStencilSomethrough-holedeviceshavesmallpinswithlargeholesordensespacingwiththickboards.Ineithercaseinsufficientsolderpastevolumeisdeliverableusingthefirsttwostencildesigns.Thetwo-printstencilcandeliverlargeamountsofsolderpasteintothethrough-holes.Inthisdesign,anormalsurface-mountstencil,typically0.15mm[5.9mil]thick,isusedtoprintthesurface-mountsolderbricks.Whilethesurface-mountpasteisstilltacky,athickstencilisusedtoprintthethrough-holepaste.Normallythisrequiresasecondstencilprintersetupinlinetoperformthisprinting.Thisstencilcanbeasthickasrequired.However,0.4to0.75mm[16to30mil]istypical.Whenstencilfoilthicknessrequire-mentsexceed0.5mm[20mil],lasercutelectropolishedaperturesprovidebetterpastereleaseandoverallprintper-formanceduetotheexcellentwallgeometry.Thecontactsideofthisstencilfoilisreliefetchedatleast0.25mm[9.84mil]deepinanyareawheresurface-mountbrickshavebeenpreviouslyprinted.Acrosssectionofthetwo-printthrough-holestencilisshowninFigure11.MayMayMayMay標準分享網(wǎng)標準分享網(wǎng)免費下載SolderreliefetchareaforThrough