ASM Cu bond informationWord文档格式.docx

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