PCB制程设计PCBA制程改善-DFM-DFT

06/06/2020,1,PCBAPresentation,06/06/2020,2,ContentStructure,1,DFM/DFTIntroduction,2,PCBProcessandMaterial,3,PCBAProcessandSAC305,4,ICTTesting,06/06/2020,3,1,DFM/DFTIntroduction,1.1,WhyweneedtodoDFx(DFM/DFT)analysisforPCBcheckingbeforewefinalizetheGerberfiles?,First,thePCBsorPCBAswedesignshouldmatchwithPCBorPCBAsuppliercapability.,ThisisHATPCBPanelizationDuetolimitedGPCBcapabilities,5mmclearancearerequired.ButLPCBsuppliercanaccept2mm.,06/06/2020,4,Second,findsomepotentialissues,InordertosuretoavoidproblemsforPCBorproductassembly.,A,Smallissue:noULlogoandPCBsupplierinformationonthePCB.Actually,thesewordswereprintedunderheatsink.,D,Criticalissue:HcomponentcantbelocatedinthecenterofmagneticCore.ItaffectsPCBAassembly.Werethinkingofsomemethodstofixit.,B,Balancedtracecanpreventtombstoneissue.,C,ThermalreliefforPTH(PlatedThroughHole)componentsinsufficientsolderissue.,06/06/2020,5,Drawaconclusion:ItsnecessarytodoDFxanalysisbeforeGerberout.ThevalueofDFxinPCBAdesignandmanufacturingcanbefactoreddirectlyintothecosttoproduceaprintedcircuitboardorassembly.IfthePCB/PCBAismanufacturedwithdefects,themanufacturersorLEMwillhavetobearthehighcostfordefectsandrepairs.Theonlywaythosedefectscanbeidentifiedisbytestsorassembly.,1.2,DFxBenefits,ImproveddesignDecreasethetime-to-marketDecreaseproductcostIncreasemarketshareandprofitability,06/06/2020,6,1.3,HowtoimplementDFxprocess,06/06/2020,7,1.4,DFM/DFTcheckItem,DFMcheckItemincluding:ToolingholeMountingholeFiducialmarksPTH,NPTHsizeSoldersideclearanceComponentclearanceCopperconnectionSilkscreenSoldermaskcolorULlogo/PCBvendorBoardsizePostassemblyissue,DFTcheckItemincluding:TestcoverageTestpointsonbottom/topsideTestpointstyleTestpointsneedtoaddedormodified,06/06/2020,8,2,PCBProcessandMaterial,2.1,PCBMaterial,Laminates,06/06/2020,9,2.2,PCBcharacterexplain,Tg:Glasstransitiontemperature,Td:Delaminationtemperature,T260:Testat260oCTestingforsolderability,T288:Testat288oCTestingforthermalstressat3times10seconds,Dicy:Curingagent(Dicy-freeforAnti-CAF;Dicy-cureforprocess),Halogen:HalogenfreegoodforCTE,Moistureabsorption:below5%,CTE:Temperatureexpansioncoefficient,06/06/2020,10,2.3,RoHSandReach,SnPbMeltingpoint183oCSAC305Meltingpoint217oC(Sn-3.0Ag-0.5Cu),RoHS:RestrictionoftheuseofcertainHazardousSubstancesinelectricalandelectronicequipment.Takeeffecton1July2006andrequiresthatsuchequipmentmustnotcontainthefollowingchemicals:,Lead(Pb)ChromiumVI(Cr6+)Mercury(Hg)Cadmium(Cd)PolybrominatedBiphenyls(PBB)Polybrominateddiphenylethers(PBDE),06/06/2020,11,2.4,PCBManufactureProcess,06/06/2020,12,06/06/2020,13,06/06/2020,14,2.5,Laminate:4layerPCB,06/06/2020,15,Thecouponindicatesthenumberofthelayerinawindow.Incaseofapressedmultilayer,alllayersarelegibleinthecorrectorder.,06/06/2020,16,2.6,PCBsurfacefinish,HALSnAgCuHotAirSolderLeveling,specifiedatLEMfileChemicalTinSecondchoiceatLEMfileImmersionSilverEasiertoprocess;sufficientbarrelfillforPTH;goodsolderability;nocontactissueduringICTtestingprobecontactissue,CAFandWickingissue;Ioniccontaminationtest;migrationCAF:ConductiveAnodefilament,06/06/2020,17,3,PCBAProcessandSAC305,06/06/2020,18,3.2,SAC305,WhydontuseSn/Pb(63/37)?,Advantage:ExcellentplatingfeasibilityWellcharacterizedandunderstandsolderabilityperformanceGooddepositproperties,assemblycompatibilityMeltingpoint183oC,Disadvantage:TheonlydisadvantageistheTOXICITYofPb,SAC305Sn-3.0Ag-0.5CuMeltingpoint217oCSN100C(Sn-Cu-Ni+Ge)Meltingpoint227oC,06/06/2020,19,3.3,Reflowprofile,06/06/2020,20,Open/ShortAnalogComponentsDigitalComponentsPower(Voltagetesting),Coverage,4,ICTInCircuitTesting,InordertokeeptheproductqualityandfindPCBAdefect(Open-Short,Componentvalue,Missing,SolderVoids,Polarityreverse)inashorttime.,06/06/2020,21,4.1,FigurehelpstounderstandICTtesting.,Itlookslikethesameboard,Actuallyitisdifferent.SofarICTisthebestwaytofindthedifferentarea.ICTcanfinishitin1secondforthisPCBAchecking.,A,B,06/06/2020,22,Good,NG,ICTcanfindthedifferentareainashorttime.,A,B,06/06/2020,23,1,Short,NGBoard,2,ComponentMissingComponentMismatch,3,Polarityreverse,NGphenomenon,06/06/2020,24,4.2,Guardingtheoryincomplexcircuit,Ipcurrentwilleffecttestresult.SokeeptheIp=0A.,GuardingtheorykeeptheGVoltageequal0V.,06/06/2020,25,4.3,Somecomponentscantbedetected.,RxR1*R2(R1+R2),R2cantbedetected,R=0.999ohm,Resistorparallelwithresistor,Capacitorparallelwithcapacitor,