ASM Cu bond informationWord文档格式.docx
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ASM Cu bond informationWord文档格式.docx
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-Copperwirebondinghasbeenacceptedandbecomeahigh-volumeassemblyprocess.Ithascapturedasubstantialportionofthelow-costpowerdevicemarketwherethesignificantcostreductionofcopper(asmuchas90%inmaterialscost)inlargerdiameterwirebondingapplicationsprovidesalargeincentive.
-Now,copperballbondingisenteringthehighI/O,finepitchmarketplacewhereitoffersbothlowercostandimprovedperformance.
-CurrentqualificationsincludeGPU(GraphicProcessUnit)devicesrequiringhighI/Oandfine-pitch(20umwirediameter,<
50umpitch).Inthisapplication,copperoffersadvantageswithitsbettermechanicalandelectricalproperties.Copperhashigherstrengthandstiffnessthangold.Inaddition,itismoreconductive,allowingtheuseofasmallerdiameterwireforequivalentconductivity.
Copyfrom:
CopperBallBondingAdvancesforleadingEdgePackaging
Preparedby:
SammyChan
CuBondinginformation
1Cubondinglimitation
I)Cuoxidationreadilyatrelativelowtemperature
II)Cuharderthangold(20–30%higher)
i)Bondingparameteradjusttoavoidcatering
ii)Bestsolution:
CubondontoCupad
(Butpadcan’tbeprotectedformoxidation)
iii)MouldingcompoundonCuwirehasnotbeendevelopedenoughasyet.
iv)Mainlydrivebutcostreduction
v)Finepitchdrivebyexcellentmechanical&
electricalproperties.
III)HarderCuFABisachallengetolowKdevice.
5CuFAB
1ComparewithAuwireEFOwands(20mils),usethickerEFOwandsisadvantagetoCuwire(32mils).
232milsEFOwandshaveshorterEFOtimetoformsamesizeFAB
3Highermaxballtemperature(highcurrent,shortspark)ispreferredasitislikelytoresultinsofterFAB(ShortHAZ–HeatAffectiveZone).
4EFOcurrentisdependentontypeofcovergasandisnotdirectlyrelatedtomaxballtemperature.
5Forminggasisneeded(Forminggas(5%H2)isbetterthanpurenitrogengas).
6Forminggascontrolisnecessary(Higherforminggasflowrateisbetterthanlowerflowrate).
7EFOgapalsorelativetoFABsize
8FABoxidationformation
2CuBondProcess
I)5%H2ismaxusingforminggas.(Morethan5%isflammablegas)
II)N2(95%)+H2(5%)freeofoxidation.
III)Hightemperaturestorage(HTS)test.
i)Achieves175DegreeCfor800hrs
ii)Lesssensitivetohightemperature
iii)Highpowergivebestresultat:
Balllift,ballshear,wirepull.
iv)Slowinter-metallicgrowth
v)DoesnotproduceKirkendallvoids.
IV)Cost:
Compare2mm50umAuwire&
Cuwire,Cuwiremax90%cheaper.
V)Lowelectricalresistivity(Conductivity23%morethanAu)
VI)Highthermalconductivity
i)21%higherthermalconductivitythanAu
ii)Highthermalconductivityeffect(HeatAffectedZoneHAZ)
(ShorterHAZ,lowerloopcanbeachieves.)
VII)Slowinter-metallicgrowth
i)Cu-Alinter-metallicapproximate10XlifeexpectancythanAl-Al.
3CuAdvantage
4)ParameterApplication
I)CuBallcrushedreliefstress
II)Ballstressdistribution
-StresscanbedecreaseifCuballwasmadeasflataspossible.
III)Since,stressneedtobereleasedouble1stBondforcewasneeded.
DoubleForcebondingisgoodprocess=>
Stressrelief
i)ThecornerdamageAlpad,peeling&
cateringoccur.
ii)HiforcethenlowforcecanreleasestressinsideCuball.
IV)UseLowbondforceHighbondforce,stresscan’tberelease.
-Bondpaddamageorcateringoccur
V)CuballHTStestin250C
VI)2ndBond
SmallercapillaryORcangetbetter2ndbondflatness.Increasestitchbond.
6Cuinter-metallic/Cubondtest
I)UseNitricacid(NaOH)toremoveCuball&
Wire.(AuuseKOH)
i)Wiremustberemovedbeforethebondpadisetched.
ii)Otherwise,etchingwillundercutthepadleavingtheballonthispedestalofresidualbondpad.
iii)Asthispedestalisdissolvedtheresidualstresswillnucleateacrackthatisanartefact.
II)EtchingtheballfirstwithnitricacidwillnotattacktheAlbondpadandwilleliminatepossibleartefacts.
III)Opticalinspectionshouldbeat400~500X.
7Development
Cuwirealloys
i)Mustmaintainmechanical&
ii)Improvedbondabilityon
a)Multi-layer
b)LowKmetallization.
8Conclusion
-Inter-metalliccoverageascommonlyunderstoodfromgoldballbonding(Inter-metalliccoverage–IMC)cannotbemeasuredincopperballbondsusingroutineanalysistechniques.
-Itisstillunclearifbondingformsinter-metallicorthinalloyphase(Inter-metallicPhase–IP)
-Extremeagingconditionsat250CledtocorrosiononBGAtestdevicesafteralready16hrsisothermalagingprobablyduetochlorineout-gassingoftheFR4substrate.
-PLCCbonddevicesdemonstratehighreliabilitywhenagedat250Cfor500hrswherenovoidingorcorrosionwasobserved.
END
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