ProfileTroubleShooting(英文资料)

Profiling&Troubleshooting,Reflow,SolderPasteReflow,TheactualsolderingprocessUsuallycarriedoutusinganovenOvenmaybeInfra-redorconvection,theatmosphereairornitrogenButanycontrollableheatingmethodcanwork,SurfaceMountLine,Printer,Pick&Place,Pick&Place,ReflowOven,Reflow,IdealisedReflowProfile,WhatisanIdealProfile?,Inmostcasestheprofileisdeterminedbytherequirementsoftheboard&componentsandthecapabilityoftheovenModernsolderpasteswilltolerateawidevarietyofprofilesHowever,certainaspectsmustbenotedinordertogetthemostfromthematerial,WhyProfile?,SolderinginvolvesachemicalreactionInordertogetconsistentresultstheprocessmustbemonitoredEveryboardtypehasdifferentthermaldemandsEveryovenbehavesdifferentlyandmayevenchangefromweektoweek,daytodayorhourtohour,WhyProfile?,StatisticalProcessControlEnsureConsistencySpottrends&adjustaccordinglyEnabletheuseofmax/minlines,ProcessWindow(Example),HowDoIProfile?,HowDoIProfile?,UseaprofilersuchasaSoldaProoraSlimlineSoldaProOracleAttachthermocouplestovariousareasofascrap,populated(orpartpopulated)boardHighdensityorheavyareasLowdensityorlightareaSensitivecomponentsPassboard&profilerthroughtheoventhendownloadtoaPCorprinter,Tackcomponents&thermocouplesusingHMPsolder,SoldaPro,Lightlypopulatedarea,Heavilypopulatedarea,Temperaturesensitivedevice,Passthroughthereflowoven,DownloadtoaPC,TypicalReflowProfile,ProfileGuidelines,InitialHeatingRamp,InitialHeatingRamp,Objectistogetprofiletopre-heatstageLimitedbyboard&components(thermalshock)Explosiveout-gassingfromthesolderpastewillonlyoccurunderextremeconditions(eglasersoldering)Commonramp-ratesare1-3C.s-1,Pre-heatSoak,Pre-HeatSoak,Thepre-heatallowsallareasoftheboardtoreachasimilartemperaturebeforereflowWithmodernovensitispossibletoreduceoreliminatethe“plateau”partoftheprofileThereisnospecificactivationtemperatureforsolderpastes.HoweverTheactivatorsbecomemoreeffectiveoncetheyaremoltenordissolvedinmoltenresin,Pre-HeatSoak,Rosinsbegintosoftenandflowattemperaturesbetween70-120CAsimplelawofchemistrysaysthatreactionsbecomefasterathighertemperaturesDuringthepre-heat(inaerobicreflow),oxidationwilloccuronexposedmetalsurfaces,ReflowSpike,ReflowSpike,ThisiswhenthesolderingoccursAllareasmustexceedthemeltingpointofthealloytoallowpowderparticlestocoalesce,wetthesurfacesandfillcapillariesAhighertemperaturewilllowerthesurfacetensionofthesolderandincreasetheefficiencyoftheflux,ReflowSpike,Ahighertemperaturewillincreaseoxideformation,discolourresidues&boardandmaydamgecomponentsAgoodreflowspikeisusuallyabout30-40Cabovetheliquidusofthealloy(eg.210-220CforSn62)andwillbeabovethemeltingpointfor30-60seconds,SolderSolidification,SolderSolidification,RapidcoolingwillgivebrightshinyjointsSlowcoolingallowsmoredissolutionofsubstrateswhichwillgiveroughordulllookingjoints.Takentoextreme,thiscanleadtode-wettingandpoorstrengthTheboardsshouldbeascoolaspossiblebeforebeinghandledforHealth&Safetyreasonsaswellasensuringthatnojointsaredisturbedwhilstmolten,Soldercreamreflowbehaviour,RoomTemperature-StablePrint-Fluxheldbetweenpowderparticles90oC-Resinssoften-Solventplasticisesresin-Gelstructurebeginstobreakdown,SolderCreamReflowBehaviour,150oC-Solventlosssignificant-Resinmeltveryfluid-Metalsurfaces(powderandsubstrates)cleanedandre-oxidisedrapidlyReflow(soldermelting)-Solderwetsfluxedmetalsandfillscapillaries.Intermetallicisformed,FluxSpreadDuringReflow,FluxspreadcancarrypowderparticlesawayfromthejointsiteFluxspreadcanreducethebarrieragainstre-oxidationFluxspreaddependson:-ResinblendPlasticisingsolventsActivators,FactorsFavouringNitrogenReflow,Ultra-finepitchcomponentsUseoflowactivityfluxesUseoflowresiduefluxesNon-idealprintingconditionsPoordimensionaltolerancesVarietyofboard&componentfinishes,Somecommonreflowproblems,Off-padsolderballingMid-chipsolderballingTombstoning(Manhattaneffect)Bridging(shorts)onfinepitchQFPleadsOpenjoints-usuallyfinepitchQFPsDullorroughsoldersurface,Off-PadBalling,Off-PadBalling,ReasonsPrintmisregistrationExcessivepreheatOxidisedsolderpaste,SolutionsAdjustprinterAdjustreflowprofile(Increasebeltspeedorreducepre-heatsettings)Freshsolderpaste,Mid-ChipBalling,SolutionstoMid-ChipBalling,DesignAlterpaddimensionsand/orshapeThinnerstencil,ProcessReduceplacementheight(notalwayspossible)Increasepre-heatsoak(effectiveinmarginalcases),DesignSolutionsforMid-ChipBalling,D-Shapeortriangularpadsratherthansquareorrectangular,SolderBridging,GenerallyonfinepitchQFPsOftenduetoexcesspastedepositorpoordefinition(smudged)deposits,Bridging,SolderBridgingSolutions,ThinnerstencilNarrowerapertures-caretoavoidaperturecloggingMorefrequentunder-stencilwipingAdjustprinterregistration(printontopad),Tombstoning,TombstoningSolutions,Adjustplacementmachine(offset)Increasepre-heatsoakLessactivefluxmediumUse63S4alloy,Antitombestonepaste,Smallercomponents,Duetotheuseofsmallercomponentssuchas0402,0201andeven01005.Placement(handlingandpositioning)andprintingcanbecomeaproblem.PrintingcanbeovercomewithgoodqualitystencilsandagoodprintersuchasaDEK(aswellastherightpaste).Poorplacementhowevercanleadto.,ExamplesofTombstoneDefects,ComponentTombstoning,PastewetsoneendofthecomponentsignificantlybeforeitwetstheotherendSurfacetensionactstoliftthenon-wettedendoutofcontactwiththepasteContributingfactorsDifferentsolderabilityofcomponentterminationsPoorpaddesignPoorcomponentplacementHighactivityfluxPooractivityflux,TombstoningSolutions,Adjustplacementmachine(offset)Lessactivefluxmedium.Changingthedesignorprocessperameters.,PreventingComponentTombstoning,ThebestwayCarefulpaddesignandcomponentplacementThe“fix”ModifyreflowprofileFasterprofile,orairnitrogentopreventfluxexhaustionSlowerprofileornitrogenairtoreducefluxactivityHitandmissprocesschangedependingonspecificcircumstancesProcesswindowimprovementAnti-tombstonepaste,TraditionalAnti-tombstoneSolderPastes,SlowdownthewettingandsolderflowprocessestoencouragecomponentterminationstosolderatthesametimeMixtureofsolderalloypowderswithdifferentmeltingtemperaturesSn/Pb+Sn/BiSolderpowderalloywithameltingrangeSn/Pb/BiBothtechniquesmayleavesolderjointswithasignificantmeltingrangeandreducedfatiguereliability,ImprovedAnti-tombstoneSolderPaste,PrincipleofoperationunchangedUsesmixtureofalloypowderswithverysimilarmeltingtemperaturesSn63(183C)+Sn62(179C)FinaljointreliabilitynotcompromisedSmallmeltingtemperaturedifferencenotsufficientforgoodanti-tombstoneeffectUsesmixtureofpowderparticlesizesEnhancesanti-tombstoneeffect,MulticoreAnti-tombstonesolderpastes,Multicorepowdersizecode“ACP”Mixedalloypowders(code63S4)meltingrange179-183CsolidifiedalloyisSn63withlowAg(silver)“contamination”Mixedpowdersizesincreasestheeffecto