Wire Bonding Technology.docx
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Wire Bonding Technology.docx
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WireBondingTechnology
WireBondingProcess
Editor:
Thomas-ma
1.BallShearTest-FailureModeGradingMethod
Thefailuremodesusedintheballsheartesthelptoevaluatethebondingresultsandassessthebondingprocess.
FailureModes:
∙Ballliftindicatesbadresults(low F):
∙Goldremainindicatesgoodresults(high F)
∙Padpeelingorcrateringindicatesaflowthatshouldbeinvestigated
Factorsaffectingthe F:
∙Bondedarea(D)
∙Process
∙Shearheight(5um)
∙Toolsize(min2X D)
∙Balltoolcentering
∙Cleanliness
∙Testercalibration,accuracyandvacuum
2.WirePullTest-FailureModeGradingMethod
Thefailuremodesusedinthewirepulltesthelptoevaluatethebondingresultsandassessthebondingprocess.
Grade
Brokenat
Reason
Quality
1
Balllift
Badprocess
Poor
2
Ballneck
H.A.Z
Good
3
Wire
Dependsonconditions
Verygood
4
Weld
Welddeformation
Good
5
Stitchlift
Badprocess
Poor
Factorsaffectingthe F:
∙Wirediameter
∙Wirelength
∙Loopheight
∙Padtoleadplanegap
∙Process
∙Hooklocation
∙
Testercalibration,accuracyandvacuum
3.ballheight(thickness)
ball(1stbond)
3.Bottleneck(BTNK)CapillaryBonding
4.Bottleneck CapillariesTolerancesTable
Family/Design
BondPadPitch
SpecRange
Tolerances(mils)
Tip
Hole
CD
OR
4149X
4849X
Above
100um
Regular
ForTip>10�0.3
ForHole≥2.5
+0.25/-0.1
�0.2
ForOR>3.5
�0.3
ForTip≤10�0.2
For1.8 +0.2/-0.1 �0.2 ForOR≤3.5 �0.2 ForHole≤1.8 +0.15/-0.1 �0.2 High Spec �0.1 -0.1/-0.0 �0.1 �0.2 5.Loopheight measuring 6.OpticalMeasurements Usuallythisisthefirstsetofexaminationstobeperformed,usingaScanningElectronMicroscope(SEM)andadvancedopticalequipment. Theseexaminationsareperformedbothpriortothebondingprocess-todeterminethebesttoolandprocessparameters-andafteritscompletion-toevaluatethebondingresults.Theseexaminationsconsistof: ∙Inspectionofthe package/devicedimensions,whichassistsinsettingtheprocessspecifications,determiningthewiringconstraintsanddesigningthebest-suitedcapillary. ∙Inspectionofthe bondpadandpitch andrelateddimensions,whichassistsindeterminingtherequiredbondpadopening,padsgap,padsizeandpadpitch.Thisalsohelpstodeterminethebondableareaandtherequiredcrosssection(accordingtopassivationlayer andpadlayerthickness). ∙Inspectionofthe wiringmeasurements,whichassistindefiningtherequiredballsize,ballheight,ballplacementaccuracy,loopheightandwireswaytolerances. ∙Thepostbondinginspectionsinclude ball(1stbond)diameter measuring, ballheight(thickness)measuringand Loopheight measuring. 7.BondPadPitch Thebondpadpitchisadefineddistancebetweenthecentersoftwoadjacentpads.Thedesiredpadpitch,derivedfromtheapplicationconstraints,prescribesthetypeofcapillaryoneshoulduse. Thecapillary'sexternaldimensions(Tip, BTNK, CA)needtobeoptimizedinordertoavoidcontactbetweenthecapillaryandtheadjacentwirewhilemaintainingoptimalbondingperformances. 8.The1stbonddiameterisderivedfromthe padopening. Mostapplicationsrequirea100%bondonpad.Themostimportantcapillaryparameteraffectingthein-specaccuracyofthe1stbondisthe IC volume,whichconsistsofthe Hole diameter,the ICA and CD. Thisparameterneedstobecarefullycontrolledandoptimizedinwaysthatshallbediscussedlater. 9.WireDiameter Thewirediameterisdefinedbytheapplication-finerprocessesnaturallyemploythinnerwires.Therefore.thecapillary Hole isdefinedbythedesiredwirediameter. Generally,thickwiresarepreferableduetotheirstrengthandbetterresistancetosweepduringmolding.However,thereisadelicatebalancebetweenHoleandwirethatneedstobeobservedinordertomaintainthecriticalgapthatallowsthefreeanduninhibitedmovementofthewire.Thiscriticalgapisimperativeforthesuccessoftheprocessandeliminatingincidentsofwireswayandwirefriction. Anotherfactorinfluencingthewirediameterselectionisthecostofthe goldwire. 10.K&SCapillaryDesignRecommendations WireDiameter(mil) RecommendedHole(mil) Min.RecommendedHole(mil) 2.00 3.00 2.40 1.50 2.20 1.80 1.30 1.80 1.50 1.20 1.70 1.40 1.10 1.60 1.30 1.00 1.50 1.20 0.90 1.20 1.10 0.80 1.00 0.95 0.70 0.90 0.85 11.TechnicalGuide Goodbondingresultsaretheprimarygoalofeverybondingprocess.Theseresultsarethencomparedto thespecifications(SPEC)definedbythesemiconductormanufacturerandjudgedbytheirdeviationfromthatSPEC. Thesemiconductormanufacturerseeksprocessreliabilityatlowercostsandhigheryields.Theseobviousbusinesstargetsareachievedthrougharepeatableandstablebondingprocess.Processstabilityismeasuredaccordingtothefollowingperformancespecifications: ∙FreeAirBalldiameter(min,max,std,Cpk) ∙Balldiameter&height(min,max,std,Cpk) ∙Loopheight&shape(min,max,std,Cpk) ∙Ballshearforce&Strength(min,Cpk) ∙Wirepullforce(min,Cpk) ∙Ballplacementaccuracy(min,Cpk) ∙Confirmationrun(stability,numberofassists,visualinspection, UPH) ∙Capillarydimensionstolerances(SPECs,effectonprocess,lifetime) ∙Overallprocessfeasibility(cost,demand,timetomarket) K&SBondingToolshasdesigned advancedperformancetests todeterminewhetherspecificationsweremet. Understandingtherelationshipbetweencapillarydimensionsandbondingresultsisthekeytocontrollingthebondingprocess.Everytoolhasmorethan15differentparametersthatdeterminethebondingresults.Theseparameters,alongwithvariousotherfactorssuchasthebondingmachine,thewireandthedevicemakeupthecomplexenvironmentthatinfluencestheprocess.ThisenvironmentisanalyzedbybondingexpertsinK&SapplicationlabsandR&Dcenters.Thefollowingisageneraldescriptionofthecapillary-processrelationsthatbynomeansconcludethebondingresultsanalysis. 12.BallShearTest TheballsheartestisperformedusingaShearTester(BT-24,BT-2400PC,DAGE4000)andaShearTool. Thetestisconsistentwiththefollowingmethodology: 1.Measureballdiameter(D)andballheight(H),andthencalculatethe"bondedarea"(S). S=[(D^2)/4]*p in[mil]^2or[um]^2. 2.Fixshearheightaccordingtoballheightandpassivationthickness. 3.PerformShearforcetest.TheShearforce(F)ismeasuredin[gr.]. 4.Theforcevalueobtainediscalculatedasfollows: S/u_a(Shearperunitarea)=Shear/[pD2/4]. Reasonablestrengthrange=5.5andabove[gr.]/[mil]2 13.TheEffectonthe1stBond The1stbondisprimarilyaffectedbythe IC.TheICcentersthe FAB priortotheformationofthebond,transmitsultrasonicpowertotheball,andhelpstocontrolthesizeofthebond.The CD andthe ICAdeterminetheICvolume,whichinturndeterminestheshape,diameterandstrengthofthe1stbond. Therearetwomainfactorsaffectingthestrengthofthe1stbond: 1.TheforcevectorsappliedbytheICAand Tip face. 2.TheultrasonicvibrationsappliedtotheFAB,whichiscapturedintheICvolume. TheICAalsoaffectstheforcevectorappliedonthegoldsquash.InmostcasesthelargertheICA,thehigherthepressureappliedonthesquash. K&SBondingToolsoffersvariousICAsfordifferentapplicationrequirements,rangingfrom60°to130°.ThemostcommonICAdimensionsare90°and120°.The120°ICAisusuallyappliedtostandardapplicationswherealargersquashispermitted.The120°ICAallowsmoregoldtoflowoutsidetheIC,thusutilizingthetipfaceforastronger1stbond. InFinePitchapplications,wheresmallersquashesarerequired,enlargedICvolumeisneededtocapturemoregold.Intheseinstances,90°ICAisappropriate.Inthiscase,theICvolumeisofmoreimportancethantheTipfaceasameansoftransmittingtheforceandultrasonicvibrationsneededtostrengthenthe1stbond. 14.TheEffectonLooping Themaincapillaryparametersaffectingloopingarethe ICtypeandthe Hole.Toensurestablelooping,itiscriticaltoreduceoccurrencesoffrictionbetweenthewireandthecapillary. Duringlooping,thewirecomesincontactwiththecapillaryalongtheHole,whentouchingthecorneroftheHoleandICandwhengoingthroughthecorneroftheICandthe Tip face.Whenexcessfrictionoccurs,thesecontactscanresultinwiredamageandloopsways. ToavoidthesesetbacksinloopingoneneedstodefineanappropriategapbetweentheHoleandthewire,determinethebest ICA,andselectadditionalfeaturessuchas D/IC or IR. Theminimumhole-wireclearanceisusuallysetat0.2milforFinePitchapplications;whenfinerclearancesarerequired,thereisdifficultyinreducinggapswithoutdamaginglooping. Kulicke&Soffaindustry-leadingtolerancesallowsuchreductionswhilemaintainingastableprocess. InStandardcapillarydesign,theloopheightdeterminestheCA,whileinFinePitchcapillarydesign,theloopheightdeterminesthe BTNKheight, BTNKangle andBTNKradius. Forlongandhighlooping,aD/ICwitha90°or120°angleisusuallyrecommended.Forlongandlowlooping,anIRandICAof120°areadvisable.Naturally,theserecommendationsaresubjecttoapplicationconstraintsandoptimizationconsiderations. 15.TheEffectonthe2ndBond Thecapillaryaffectsthe2ndbondintwomainaspects: ∙Thestitchbond-thisbondpermanentlyconnectsthewiretothelead.(Moreaboutthestitchbond) ∙Thetailbond-thisbondtemporarilyconnectsthewiretothelead.Itenablesthecapillarytorisetothetailposition,t
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