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MECHANICAL

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MECHANICALMECHAN

    MECHANICAL

;CHINESEJOURNALOFMECHANICALENGINEERING

    ;‘82.Vo1.21,No.6,2008

    ;DOI:10.3901/CJME.2008.06.082,availableonlineatwww.cjmenet.com;www.cjmenet.tom.cn

    ;ZHANGLiang

    ;XUESongbai

    ;HANZongjie

    ;WANGJianxin

    ;GAOLili

    ;SHENGZhong

    ;CollegeofMatedaisScienceand

    ;Technology,

    ;NanjingUniversityofAeronautics

    ;andAstmnautics

    ;Nanjing210016.China

    ;OINTRODUCTIoN

    ;MECHANICALPROPERTlESOFFINE

    ;PITCHDEVICESSOLDEREDJOINTS

    ;BASEDONCREEPMODEL

    ;Abstract:Nonlinearanalysesofquadfiatpackage(QFP)onprintedcircuitboardf1CB)assemblies

    ;subiectedtothermalcyclingconditionsarepresented.Twodifferentsoldersareconsidered,namely,

    ;Sn37PbandSn3,5Ag.Thestressandstrainresponseoffinepitchdevicessolderedjpintswas ;investigatedbyusingfiniteelementmethodbasedonGRiofaloArrheninusmode1.Thes

    imulated

    ;resultsindicateereepdistributionofsolderedjpintsisnotunifo1”111,theheelandtoeofsold

    eredjoints,

    ;theareabetweensolderediointsand1cadsaretl1eere

    concentratedsites.Thesimilarphenomenaof

    ;stresscurvessimulatedbasedonGarofalo—An’heninusmode1andAnandequationsisco

    nfirmed,and

    ;theereepstrainvalueofSn3.5AgsolderedipintsisIowerthanthatofSn37Pbsolderedjoints. ;Therina1cyclingresultsshowthatSn3.5AgstronglyoutperformsSn37PbforQFPdevicesunderthe

    ;studiedtestcondition.Thisiswellmatchedwiththeexperimentaloutcomeanalyzed.Inaddition,the

    ;soldereddevicesweretestedbymicro-jointstester,thetensilestrengthofSn3.5Agsoldered

{ointsis

    ;foundtobehigherthallthatofSn37Pbsolderedipints.Byanalyzingthefracturemicrostmct

    ureof

    ;soldered{pints,itisfoundthatfracturemechanismofSn3.5Agsolderedjointsistoughnessf

    racture,

    ;whilefracturemechanismofSn37Pbsoldered{pintsincludesbrittlefractureandtoughnes

    sfracture.

    ;Theresultsofthisstudyprovideanimportantbasisofunderstandingthemechanicalpropert

    iesoffine

    ;pitchdeviceswithtraditionalSn37PbandSn3.5Agleadfreesolderedjpints.

    ;Keywords:Finiteelementmethod,creepproperties,tensilestrength,fracturemicrostructu

    re

    ;AsthebanofthePbuseinelectronicsproductsislegislated ;duetothewasteelectricalandelectronicequipmentfWEEE)and ;restrictionofhazardoussubstances(RollSdirectives.electronies ;companiesstarttodelivertheproductsusingthePbfleesolders.

    ;Severa1promisingleadfreesolderstoreplacelcad.containing

    ;soldersineleconicapplicationshavebeenproposedand

    ;investigated.However.understandingofthesenewlead.free ;soldersisstillinitsinfancycomparedtotraditionalSnPbsolders. ;thus,furtherstudiesareneeded.

    ;Insurfacemounttechnologies.thesolderinterconnectionis ;requiredtoactasnotonlyanelectronicandlogicalpathbutalsoa ;mechanica11inkbetweenthecomponentandtheprintedcircuit ;boardllJ_Itiswel1.knownthattheprinciplecauseoffailuresin ;solderintercOnnectscanbeattributedtothedeformationthatis ;causedbythemismatchinthermalexpansionamongthematerials. ;becauseofchangesintheambienttemperatureoftemperature ;gradientduringpowercycling.Therefore,thereliabilityof ;electricalcomponentreliesonmepropertiesofsolderedipints. ;Recently,thereliabilltyinvestigationofsolderedipintscomprises ;experimentalanalysisandnumeriealsimulationathomeand ;abroad,thereliabilityexperimentsanalysisfocusesonthermal ;stressofsolderedipintsanddroptesting.Finiteelementmethod ;isthemainmediumfornumerica1simulation.andthe

    ;establishmentofconstitutiveequationsistheimportantpartfor ;simulation,someconstitutiveequationsareusedwidely,suchas ;Anandequation,Garofalo.Arrheninusequation,Nortonequation. ;Wongequation,WieseequationandsoonL,however,some

    ;parametersoftheseunifiedmodelsareempiricalanddependent ;ontemperatureandstrainrate,resultingincomplexcalculationof ;thestress?strainresponseandsomescaReringpredictionsfrom ;experiments.Therefore.theinvestigationofconstitutiveequations ;mustbedonefurtherforstress.strainresponseofinteriorsoldered

    ;joints.Manystudieshavebeenperformedinthepastto ;ThisprojectissupposedbySixKindSkilledPersonnelProjectofJiangsu ;Province,China(No.06-E-02o1,JiangsuGeneralCollegesandUniversities ;PostgraduateScientificResearchInnovativePlan,China(No.CX07B_087z). ;ReceivedMarch27,2008;receivedinrevisedformOctober9,2008; ;acceptedOctober28,2008

    ;investigatethepropertiesofsolderedipintsunderthermalfatigue ;loading(RIDOUT,etal,2006;XUE,etat,2007;SPRAUL,etal, ;2007;ZHANG.eta1.2008)L/-IUJ.SObasedonconstitutive ;equations,theinvestigationoflead.fleesolderedipintsproperties ;underthermalloadingbecomeamajorconcern.

    ;Theobjectiveofthisstudyistoevaluatethestress-strain ;responsesofSn37Pb/Sn3.5Agsolderedpintsoffinepitchdevice ;usingfiniteelementcodebasedonGarofa1oArrheninusequation.

    ;Thecreepconstitutiveequationrepresentsgenerallyaccepted ;industryvaluesfromcompressionsamplestestedoverthe ;temperaturerangefrom218Kto398K.Additionally,tensile ;strengthtestswereconductedbvITlicro-jointsstrengthtesterto ;analyzethequadflatpackagewithtwokindsofsolderedjoints, ;Sn37Pb/Sn3.5Ag.respectively.

    ;1FINITEELEMENTSIMULATIoN

    ;Threedimensionalf3D)nonlinearfiniteelementsimulation ;methodswereutilizedtoanalyzethestress-sainresponsein

    ;Sn37PbandSn3.5Agsolderedjpints.Thedeviceoffiniteelement ;simulationincludedareflowedsolderedioint,thePCBsubstrate, ;theCupad.theplasticcarrie~TheSOLID186wasselectedto ;modelthecomplexgeometry,andthecreatedmodelcontaineda ;totalof2388elements.ThesolderedipintwasrefinedwitI1 ;acceptablesolutionaccuracv’thecoarsermeshwasprovidedfor

    ;plasticcarderandPCBsubsateduetoitslocationfurtheraway

    ;fromthesolderedjpint.Fig.1aandbshowthegeneral ;cross.sectionalviewofareflowsOFPsolderediointandthe3D ;finiteelementmOde1.

    ;Fig.1cr0sssectiona1viewofarlenowedso1deredjoint(a) ;andnIliteelementmodelf0rsimulation(b)

    ;CHINESEJ0URNAL0FMECHANICALENG|NEERING?83?

    ;DuetothelowmeltingpointofSn37Pb/Sn3.5Agsolders. ;creepdeformationwasdramaticsinceroomtemperatureexceeded ;halfofthesolder’smeltingpoint.SoGarofalo—Arrheninusmodel

    ;wasusedtodescribethenonlinearbehaviorofsolderedioints.

    ;Theothermaterialswereassumedtobe1inearelastic.asshownin ;Table1.

    ;Table1Parametersofmaterials

    ;ACOOrdingtoMIL.STD.883specification.temperature

    ;loadingwasselectedtobeireposedontheQFPassembly.The ;temperaturerangesfrom2l8Kto398K,dwel1.timeatallDeak ;temperatureis15min,therateofdescendandascendtemperature ;are12K/rnin.Temperatureloadingbeganat298Kandthefinite ;elementsimulationwasassumedtobethestressfleeatthe

    ;temperature.ThetemperatureprofileisshowninFig.2. ;

    ;

    ;&

    ;E

    ;Timet/100s

    ;Fig.2Temperatureprofileinthermalcyclingtest ;0

    ;Garofalo—Arrheniusf”creepconstitutiveequationsare

    ;shownasfollows.

    ;SnPb:

    ;7658915

    )J1Ir/ ;(_

    ;SnAg:

    ;0300796T]『唧(-)ll44..l/

    ;Fig.3showstypicalcreepstraincontourofthe1cad.free ;solderediointinthequadflatpackageattheendofthe3rdcycle. ;Thelocationfortllemaximumcreepstraincanbeseennearthe ;copperpad.andtheareabetweenthesolderediointandlead. ;Thetoeofthesolderediointarealsocreepstrainconcentrated ;location.Thephenomenaiswel1matchedwiththeoutcomes ;calculatedbasedontheAnandequationt.Thecreepstrain ;contourisverysimilartothepreviouslystudiedcauseL”J.Ithas

    ;beenproventhatthecrackinitiationandpropagationoccurredat ;thebottomedgenearthecopperpadduringexperimentsJ.Itis

    ;observedthatthesimulatedresultshavegoodagreementwith ;practicalcondition.

    ;Fig.4plotsthehistoryofyonMisesstressatthemostcritical ;locationsOfa1lstudiedauadflatpackages.Itisfoundthatthe ;tendencyofcurvesbasedonGarofaIoArrheninusmodelissimilar

    ;tothatofcurvesbasedonAnandequationt13J:stressrelaxaDpears ;attheinitialstageoftemperatureloading.periodicvarietycan ;alsobefoundinthefigure.ThevonMisesstressofSn37Pb ;solderedfointsexceedsthatofSn3.5Agsolderedioints,which ;meansSn3.5Agsolderediointsaremorereliable.

    ;000012

    ;OO0199

    ;Ooo387

    ;000574

;000761

    ;000949

    ;001136

    ;001324

    ;O15l14

    ;0l6988

    ;Fig.3Equivalentcreepstraindistribution

    ;inthesolderedjoint

    ;0102030405060708090100110

    ;Timet/100s

    ;Fig.4Stresscurveddiagramsofsolderedjoints

    ;InordertocomparethestrainresponsesoftheSn37Pband ;Sn3.5Agalloysunderthermalcyclicloading.the

    ;thermo.mechanicalfiniteelementmodelwasusedtosimulatethe ;creepstrainasafunctionoftheacceleratedtherma1cycling ;temperatureusingtheisothermalfiniteelementmode1.Fig.5 ;showstheequivalentcreepstraintimehistorynearthecritical ;locationofthesolderedjointmostlikelytofailinthequadflat ;packages.Itcanbeseenthataccumulatedenhancementtendency ;ofequivalentcreepstrainisobvious,andthecreeprateof ;Sn3.5AgsolderediointsiSlowerthanthatofSn37Pbsoldered ;iointsevidently.Fig.6plotsthevonMisesstress/vonMisescreeD ;strainhysteresisloopsatthemostcriticallocationsofesoldered

    ;ioints.Itwasnotedthatthelooptendstobesteadyafterthefirst ;cycleinthetwoconditions.Thisfurtherprovedthesupefiorityof ;Sn3.5Agsolderedjoints.

    ;

    ;

    ;2

    ;=

    ;

    ;

    ;Timet/lO0s

    ;Fig.5Equivalentcreepstraincurveddiagramsofsolderedjoints ;口时j1Qo0tI一时>;

    ;???0

    ;

    ;84’ZHANGLiang,etal:Mechanicalpropertiesoffinepitchdevicessolderedjointsbasedo

    ncreepmodel

    ;Vonmisescreepstrain%

    ;Fig.6Hysteresisloopofsolderedjoints

    ;2EXPEIUMENT

    ;Pulltestwasadoptedtoevaluatedthetensilestrengthofthe ;twosoldersbySTR1000microqointsstrengthtester.Duringthe

    ;pulltestofthe1cad.theanglebetweenthehookandthePCBwas ;45..asshowninFig.7.Totalnumberofleadspal1testedwas40 ;foreachsolderingcondition.Thetestedaveragevalueoftensile ;forcewasconducted.Fig.8showsthepmIstrengthdataofthe ;QFPsolderedioints,thetensilestrengthofSnAgsolderediointsis ;foundtobeslightlystrongerthanthatofSnPbsolderedioints, ;whichiswellconsentaneouscomparedwithsimulatedresults. ;

    ;

    ;

    ;

    ;Solderedjoint

    ;45.

    ;Copperpad

    ;Fig.7Tensiletestsofquadflatpackage

    ;Fig.8ResultsoftensileforceforQFPdevices

    ;SolderingexperimentswerecarriedoutusingIRreflow ;solderingmethOd.IRreflowsolderingmethodisakindofintegral ;heatsolderingmethod.inwhichtheentireassemblyispassed ;throughanoven.Fig.9andFig.10showthefracture

    ;microstrueturesofSn3.5AgsolderediointsandSn37Pbsoldered ;joints.Thefracturemorphologiesofhomogeneousdimplesand ;manglededgesaredisplayedinFig.9,whichbelongsto ;toughnessfracture.ThefracturemicrostruetureofSn37Pb ;solderediointsisshowninFig.10.inhomogeneousgrainsizeand ;minimdimplesappearednarratethebrittledeformationand ;toughnessdeformationhappenedbeforefracture,andbrittle ;deformationisthemainfactorforfracture

    ;Fig.9FracturemicrostructuresofSnAg

    ;solderedjoints

    ;Fig.10FracturemicrostructuresofSnPb

    ;solderedjoints

    ;3CoNCLUSIoNS

    ;(1)ThesimulatedresultsindicatethattheerecDdistribution ;ofsolderedjointsisnotuniforln.Theheelandtoeofsoldered ;ioints,andtheareabetweensolderediointsandlcadsarethecreep ;concentratedsites.ThecreepstrainvalueofSn3.5Agsoldered ;iointsislowerthanthatofSn37Pbsolderedjoints.Thetensile ;strengthofSn3.5Agsoldered{ointsisfoundtobehigherthanthat ;ofSn37Pbsoldered{oints.

    ;(2)FracturemorphologyofQFPSn3.5Agsolderedjoints ;exhibitsthecharacteristicoftoughnessfracture,whilefracture ;mechanismofSn37Pbsolderedointsincludesbrialefractureand ;toughnessfracture.

;References

    ;fl1QIANZF,LIUS.onthe1irepredictionandacceleratedtestingofsolder ;joints[J].TheIntemationaiJournalofMicrocireuiISandElectronic ;Packaging,1999,22(4):288-304.

    ;f21XIAYanghua.Interfacialreactionandreliabilityinleadfreeelectronics

    .Shanghai:ShanghaiInstituteofMicrosystemandInformation ;fD

    ;Technology2006:5-20.finChinese)

    ;f31CHENZN,WANGGZ,CHENL,eta1.ViscoplasticAnandmodelfor ;solderalloysandiIsapplication[J].SoldngandSurfaceMotmt ;Technology,2000.12(21:3136.

    ;41TSENGSC,CHENRS,LIOCC.Stressanaiysisoflcadfreesolders ;withunderbumpmetallurgyinawaferlevelchipscalepackage[J].The ;lntemationa1JoumalofAdvancedManufacturingTechnology,2006, ;31f1.2,:l9.

    ;[5]STOECKLS,YEOA,LEEC,eta1.Impactoffatiguemodelingon2nd ;leveljointreliabilityofBGApackageswithSnAgCusolderbailsC]//

    ;7thElectronicsPackagingTechnologyConference,Singapore,December ;2005:857-862.

    ;61WONGB,HELL?GDE,CLARKRW.Acreeprupturemodelfor

    ;twophaseeutecticsolders[J].IEEETransactionsonComponents. ;Hrids,andMannfacturingTechnology,1998,l1(3):284-290. ;71RIDOUTS,DUSEKM,BAILEYC,eta1.Assessingtheperformanceof ;crackdetectiontestsforsolderjoinis[J].MicroeleconicsReliability.

    ;2006.46(12,:2122-2l30.

    ;f81xUESongb4i,wuYuxiu,HANZongiie,eta1.Effecisof1cadwidthand ;pitchesonreliabilityofquadflatpackage(QFP)solderedjoints[J]. ;ChineseJournalofMechanicaiEngineering.2007,20(4):4043.

    ;91SPRAULM,NUCHTERW,MOLLERA,eta1.ReIiilityofSnPband

    ;Pb.freeflip.chipsolders[J].MicroelectronicsReliability.2007,47f231:

    ;Edl,\??2??一口0

    ;d—??—

    ;

    ;l

    ;,

    ;CHINESEJOURNALOFMECHANICALENGINEERING?85?

    ;[1O

    ;[12]

    ;[13

    ;252-258.

    ;ZGLiang,XUESongbai,LUFangyan,eta1.Nuinericalsimulation ;ofsolderediointsandreliabilityanalysisofPLCCcomponentswim ;JshapeleadsfJ].ChinaWelding,2008,l7(2):3741.

    ;GONZALEZM.VANDEVELDEB,BEYNEE.TherlllOmechanical

    ;analysisofachipscalepackage(cse)usingleadfreeandleadcontaining

    ;soldermaterials[C]//EuropeanMicroelectronicsandPackaging ;Symposium,CzechRepublic,June,2004:247-252.

    ;ZHANGLiang,XUESongbai,LUFangyan,eta1.Finiteelementanalysis ;onsolderedjointreliabilofQFPdevicewithdifferentsolders[J].

    48.(in ;TransactionsoftheChinaWeldiI1gInstitution,2007,28(11):45

    ;Chinese.

    ;LEESW.ZHANGXW.Sensitivitystudyonmaterialpropertiesforthe ;fatigue1ifepredictionofsolderiointsundercyclicthermalloading[J]. ;CircuitWorld,1998,24f3):2631.

    ;[14]LAUJ,PAOYH,LARNERC,eta1.Reliabilityof0.4mmpitch,256pin

    ;plasticquadflatpacknoncleanandwatercleansolderjoints[C]//43rd

    ;ElectronicComponentsandTechnologyConference,Orlando,USA,June, ;1993:3953.

    ;[15]ZHANGLiang,XUESongbai,LUFangyan,eta1.Numericalsimulation ;onsolderedjointsofQFPdevicewithdifferentsubstratematerialsand ;thickness[J].TransactionoftheChinaWeldingInstitution,2008,29(1): ;3539.(inChinese)

    ;Biographicalnotes

    ;ZHANGLiangisadoctorcandidateinCollegeofMaterialsScienceand ;Technology,NanjingUniversityofAeronauticsandAstronautics,China.His ;researchinterestsincludemicroelectronicsweldingandleadfreesolde~Hehas

    ;publishedover10papers.

    ;Tel:+86-013505193457;Email:zhangliang@nuaa.edu.cn

    ;XUESongbaiiscurrentlyaprofessorinCollegeofMaterialsScienceand ;Technology,NanjinUniversityofAeronauticsandAstronautics,China.He ;receivedhisPhDdegreeomCollegeofMaterialsScienceandTeehnology,

    ;HarbinInstituteofTechnology,China.in2002.Hisresearchinterestsinclude ;microelectronicswelding,SMlcad.fleesolderandlasersoldering,etc.He ;haspublishedover150papers.

    ;Tel:+862584896070;E,mail:xuesb@nuaaedu.cn

    ;HANZongjieisadoctorcandidateinCollegeofMaterialsScienceand ;Technology,NanjingUniversityofAeronauticsandAstronautics,China.His ;researchinterestsincludemicroelectronicsweldingandlasersoldering.Hehas ;published8papers.

    ;Tel:+86-025-52112911;E-mail:hanzongjiel13@nuaa.edu.cn ;WANGJianxinisadoctorcandidateinCollegeofMaterialsScienceand ;Technology,NanjingUniversityofAeronauticsandAstronautics,China.His ;researchinterestsincludemicroelectronicsweldingandlead-freesolder.Hehas ;published7papers.

    ;Tel:+860255211291l;Email:wjx1816@163.corn

    ;GAOLiliisamastercandidateinCollegeofMaterialsScienceandTechnology, ;NanjingUniversityofAeronauticsandAstronautics,China.Herresearch ;interestsincludemicroelectronicsweldingandleadfleesolder.Shehas

    ;published2papers.

;Tel:+86?025-52112911:E?mail:gaolyly@126.corn

    ;SHENGZhongisamastercandidateinCollegeofMaterialsScienceand ;Technology,NanjingUniversityofAeronauticsandAstronautics,China.His ;researchinterestsincludemicroelectronicsweldingandleadfreesolder.Hehas

    ;published2papers.

    025-52112911;E-mall:orochiai@126.c? ;Tel:+86

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