惠普绝密SMT资料 SMT Process HP XXXX

©2006Hewlett-PackardDevelopmentCompany,L.P.TheinformationcontainedhereinissubjecttochangewithoutnoticeSMTProcessGESREPEPCAProcessEngineeringRevision1.0January15th,201028March2010Whatiscoveredinthistrainingmodule?•SolderPastePrintingProcess•Pick&PlaceProcess•ReflowProcessHPConfidential38March2010SolderPastePrintingProcess•Area’sCovered−Keyfactorsinsolderpasteprintingprocess−Stencildesign−Stencilcleaningprocess−Identification&Storage−Mis-printboardcleaningprocess−Solderpastestorageandhandling−Solderpasteinspectionprocess−KeytoSuccessfulScreenPrintingProcessHPConfidential48March2010SMTAssemblyDefectStatisticsHPConfidential58March2010StencilPrint•ThestencilprintingsubprocessappliessolderpastetothePCBpriortoplacementoftheelectroniccomponents.Thegoalistodeposittherightamountofsolderpasteontoasetofbondingpadsonaboard.HPConfidential68March2010FactorsInfluencingStencilPrintingSolderPastePrintingFactorsStencilEquipmentMaterialParametersEnvironmentMaterialsDimensionalAccuracySurfaceandwallfinishCalculatingareaaspectratiosSolderpasteefficiencytransferandAreaAspectRatio(AAR)AperturesizeStencilthicknessPrintheadSqueegeematerialsPrintingtableandsupportVisionsystemAccuracyBoardsupportPrintingrepeatabilitySolderPasteAlloycompositionAlloyparticlesizePCBPCBflatnessSolderlandflatnessDownstopSqueegeepressureSnapoffPrintspeedSeparationspeedStencilundersidewipeStencilCleaningProductionareaAirhumidityTemperatureDust&dirtAircirculationOperatorsTrainingExperience&KnowledgeAwarenessAuthorityHPConfidential78March2010StencilDesign•Stencildesignisacriticalprocessandisdirectlyrelatedtoproductyield,costandthroughput.•Stencilaperturedesignforeachcomponentshouldtakeintoconsiderationsolderjointreliabilityandthecomponentsupplier’srecommendationtomeetsolderpastecoverageandsolderpastevolume.•Keyconsiderationstostencildesignare:−ApertureSizevsPadSize−ApertureShape−ApertureDesign−StencilThickness−StencilManufacturingMethodHPConfidential88March2010StencilDesign-ApertureSizevs.PadSize•Generallypadsareprinted1to1,butinsomecasesreducedoroverprintisneeded.•CBGA(CeramicBallGridArray)mayrequireaperturesizeslightlylargerthanpadsizetoensuresuppliersrecommendedsoldervolumecanbeachieved.ReducedAperture1:1ratio(FullAperture)OversizeApertureHPConfidential98March2010StencilDesignApertureShape•Differentapertureshapeshavebeenfoundtoofferthebenefitsoflesspasteutilization,consistentpastereleaseandreducedoreliminatedsolderballing.Shapestoconsiderinclude:•Asexamplethe“homeplate”isdesignedtoeliminate“solderbeads”.HPConfidential108March2010StencilManufacturingMethodHPConfidential118March2010StencilManufacturingMethod•Step-downstencil−Toreducesoldervolumeandheightforsmall/finepitchcomponentswhilemaintainingsufficientsoldervolumeforothercriticalcomponentssuchasBGAandlargechipcomponents.Theneedforstep-downwillbebasedontheprimarystencilthicknesscomparedtosmall/finepitchpartssoldervolumerequirements.Astepdownmaybeneededtoallowsolderpasterelease(AreaRatio)fromthestencilapertureinfinepitchBGA’s,CSP’sandsmalldiscreteparts.•Step-upstencil−ToincreasesoldervolumeandheightforcomponentssuchasCBGAandPTHPIPprocess.*Stepstencilsarehardonsqueegee’s,requiretransitionarea,cancausebridgesandopensifnotdesignedcorrectly..HPConfidential128March2010StencilDesign–StencilThickness•StencilthicknessisimportanttoensureoptimumsolderpastedepositionisachievedonSMT/PTHpadtoavoiddetectssuchas−insufficientsolder−excesssolder−solderbridging−solderballingStencilTypeRatioofFoilThicknesstoMinimumApertureWidthChemicallyEtched1:1.5Laser-Cut1:1.3Electroformed1:1.1HPConfidential138March2010PrintVariablesPrintvariables•Thefollowingaresomeoftheimportantprintvariableswhicharetobeconsideredbeforeanyprintcycle.−Solderpasteviscosity−Solderpasteheight−Solderpastevolume−Squeegeewear,pressure,andhardness−Stencilwear,damage−Printspeed−PCBsupport−Tempandhumidity(environment)HPConfidential148March2010CommonlyUsedFormulasHPConfidential*Useapertureareaifapertureisnotthesamesizeasthepad.**Note:Releasepropertieschangewithdryingpaste.StencilInspection•Inspecttheincomingstencilfromthestencilsupplieraccordingtotheorderedrequirements.−StencilapertureopeningsmatchPCBpartlocationlayout−Stencilaperturesarecorrectaccordingtoorder−Stencilfoilthicknessiscorrect−Stenciltension−Stencilmarkings−Framecondition−Meshcondition158March2010HPConfidential168March2010StencilCleaning•Stencilsmustbekeptcleanandfreeofdentsorblemishestoensuregoodqualityprint.•Whenstencilisbeingusedinscreenprintingmachine,autostencilwipeshouldbeusedonregularbasis(frequencyofwipemustbedeterminedthroughtest–typicalstartingsetpointofevery2to5boards,ultrafinepitchmayrequireeveryboard).•Stencilsmustbecleanedbystencilcleaningmachine−Atleastonceashift−Afterusage(beforestorage)topreventsolderpastefromdryingintheapertures.•ThesuppliermustuseaseparatededicatedstencilwashmachineforSn-PbandPb-free.SolderpasteresiduebuildupinstencilapertureHPConfidential178March2010StencilCleaning•Thestencilmustbecleanedinstencilcleanerequipmentpriortostoragetop