PCB Design and Assembly Process Development of 010

PresentedatIPCPrintedCircuitsExpo®,APEX®andtheDesignersSummit2006S01-02-1PCBDesignandAssemblyProcessDevelopmentof01005ComponentswithLeadFreeSolderYueliLiu,ShaunteRodgers,R.WayneJohnsonLaboratoryforElectronicsAssembly&Packaging,AuburnUniversity162BrounHall/ECEDept.Auburn,AL36849AbstractThecontinuingdemandforsmaller,lightermultifunctionalportableelectronicproductshasdriventheuseofminiaturecomponents.Tosatisfythisdemand,01005chipcomponentsarenowcommerciallyavailable.Howevertheimplementationforsuchtinycomponentsintonewproductspresentssomedesignandassemblyprocesschallenges.Inthisstudy,atestvehiclewasdesignedtoinvestigatetheeffectofPCBpaddesignonassemblyyield.Processcapabilityofthe01005testboardmanufacturingwasevaluated.ADesignofExperiments(DOE)wasusedtooptimizethesolderpasteprintingbasedon3Dsolderpasteinspection.Leadfreesolderwasusedforallassemblytrials.Severaltestswereperformedtoexploretheinfluencesofprocessparametersonplacementaccuracyandreflowdefects.Throughtheanalysisofexperimentalresultsandpost-reflowinspectionforassemblydefects,recommendationsforPCBdesignandassemblyprocessesaremade.IntroductionDuetothedesiretomakeelectronicproductssmallerandlighter,miniaturizationandreducingspacingbetweencomponentsisthegeneraltrendintheelectronicsindustry,particularlyforhandheldelectronicproductssuchascamcorders,cameras,cellphonesandlaptops.Infact,anotherdrivingforceforsmallercomponentsistheincreasingcomplexityoffeaturesandfunctions.PassivecomponentsoccupysignificantareaonthePCB,especiallyforanalogandmix-signalapplicationsthatusealargernumberofpassivescomparedtoatypicaldigitalsystem[1].Reducingthesizeofthepassivecomponentsandthespacingbetweenthemwouldincreasethepackagingdensity,andisanefficientwaytominiaturizemanyelectronicproducts.ThesecondtrendimpactingtheelectronicsindustryistheswitchtoleadfreesolderinresponsetotheRoHSandWEEEDirectivesinEurope,recyclinglawsinJapanandpendingregulationsinChinaandCalifornia.ThewettingcharacteristicsofleadfreesoldersaredifferentfromeutecticSn/Pb[2],andhigherreflowtemperaturesarerequired.Recently,0201componentshavebeenimplementedinveryhighdensityapplicationssuchasmobilephones,bluetoothmodules,andwirelessLANsafterextensiveprocessoptimization[3-10].Resistorsandcapacitorsarenowbeingproducedintheextremelyminiaturized01005size(0.4mmx0.2mm).However,theuseofsuchatinycomponentposeschallengesforSMTassembly.Themainfactorsaffectingthe01005assemblyprocesscanbedividedintothefollowingcategories:PCBdesign,components,stencil,solderpaste,PCBhandling,printing,pickandplacement,reflowandinspection[11,12].InordertoinvestigatetheeffectofPCBdesignonassemblyyield,a01005testvehiclewasdesignedwithdifferentpadsizes,resistor-to-resistorspacing,shapesandorientations.Experimentswereperformedtooptimizeandcharacterizethesolderpasteprinting,componentplacementandreflowprocesses.TestVehicleDesignInordertooptimizepaddesignsandevaluateassemblyprocessesfor01005components,atestvehiclewasdesigned.ThepaddimensionsareshowninTable1.PadSizeType1isconsidered‘nominal’.Thepadswerenon-soldermaskdefined(NSMD).TheothervariablesinthePCBdesignincluded:onelaserdrilledviainoneofthetwopads;alaserdrilledviainbothofthepads;noviaineitherpad;differentresistororientations(0o,45oand90o);resistor-to-resistorspacing;andintentionalsoldermaskmisalignment.S01-02-2Table1.-PadDimensions(unit:mils).StencilAreaRatioPadSizeTypePadTypeabcrm3milstencil4milstencilPadsize1,100%Rectangular8.08.77.00.6950.521Padsize2,90%Rectangular7.27.87.00.6240.468Padsize3,110%Rectangular8.89.57.00.7610.571Padsize4,120%Rectangular9.610.47.00.8320.624Padsize5,130%Rectangular10.411.37.00.9030.677Padsize6,Homebase17.05.623.00.7550.566Padsize7,Homebase27.04.019.00.7480.561RectangularHomebase1Homebase2Thetestvehicle,showninFigure1,wasadoublesided,highTg(Tg170oC)FR-4boardwith9600resistorssites,8CSPsitesand1BGAsiteononeside.Thepadshadanimmersionsilverfinishandwereallnon-soldermaskdefined(NSMD).Thetestboardwas8.0by6.0by0.042thickandreplicatedthebasictestpatternina2x2array.Thereareatotalof20designgroupslocatedineachquadrantoftheboard:Sevengroups(PadSizeTypes1-7,5padspacingsforeach)with90oorientation;Sevengroups(PadSizeTypes1-7,5padspacingsforeach)with0oorientation;Onegroup(PadSizeType1,5padspacings)with45oorientation;OneGroup(PadSizeType1,5padspacings)with0oand90oorientationandaviainonepad;OneGroup(PadSizeType1,5padspacings)with0oand90oorientationandviasinbothpads;andOnegroup(PadSizeType1)with0oand90oorientation,,soldermaskintentionallyshifted2milsalongthelengthofresistor.Roundglobalandlocal(asetforeachquadrant)fiducialswerealsoincludedinthedesign.Figure1-01005TestVehicle.ProcessCapabilityEvaluationofBoardManufacturingTheboardqualityisimportantforreliableandconsistentSMTassembly.Todetermineiftheboardmanufacturingwascapable,andiftheboardsmetthespecificationlimits,capabilityanalysiswasperformedontheincomingboards.Fiverectangularpadsizedesignsandfivedifferentspacingdesignswerechosenformeasurement.Fiftysamplesperboardweremeasuredfortwoboards.Basedonthedesignspecifications,thepadwidthandspacing