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1、附錄1WIREBONDING:PRESENTANDFUTURETRENDSABSTRACTGoldwirebondinghasbeenastandardoperationinplasticICpackageassemblyforseveraldecades.However,asthepackagesgrowlarger,thinner,anddenser,thecapabilitiesofequipment,andofthewireitself,arebeingtakentothelimit.Recently,specialtywireshavebeenintroducedwithdiffer
2、entdopantsandprocessingproceduresgivinghigherstrengthandstiffness.Theseimprovedpropertiescanofferbetterwirewashprotectionaswellascapabilityforlongspansandlowloops.Disadvantagescomefromhighercostandpotentialreliabilityissuesfromthehighdopantlevels.Advancesinthewirebondersallowbettermachinemotioncontr
3、olwithpreciseplacementofthewires.Improvedcontrolsoftwarecanproducelowloopsandlongstraightspansbysimultaneouslyregulatingmotionalongallthreeaxes,fromballplacementtothewedgebondontheleadtip.Somemanufacturersevenbelievethatallimprovementscanbeachievedthroughtheequipmentalone,withouthavingtoresorttothes
4、pecialtywires.Thecombinationofbetterwiresandbettermachinesshouldbeabletoproducethetypeofwirebondsdesiredinthinfinepitchplasticpackages.Nevertheless,thephysicallimitsofballbondingmayeventuallybereached,ifthecurrenttrendoffinerandfinerpitchcontinues.Inthiscase,othertypesofinterconnectionwillstartlooki
5、ngattractive,suchasTAB,flip-chip,orthedevelopmentofhighspeed,flexiblewedgebonding.1.0CURRENTSTATUSThegold(Au)bondingwiregenerallyusedintheindustryforautomatedthermosonicbondingisprimarilyberyllium(Be)doped,atabout3to8parts-per-million(ppm).Inthisrange,berylliumgivesthewireincreasedstrengthbyprecipit
6、ationhardeninginthematrixoftheintermetallicsformedfromthetwoelements.Italsoallowsthegoldtobemoreeasilydrawn,asverypuregoldistoosoftforshapingintoafinewire(1,2).Strongerandharderwireshavebeenintroducedintothemarketrecentlyinresponsetotheneedsforfinepitchandlongerspans.Thesewiresarealsoformulatedtopro
7、ducelowerloopsforthinoutlinepackages(3).Whileadequateformostplasticpackagingbondingneeds,thepreviousgenerationofbondersdonothavetheabilitytobondaccuratelyforthenextgenerationofhighdensitypackages.Thesemachinestendtohaveanalogmotioncontrol,whichdoesnotlendtoprecisetravelandplacementofthewires.Also,be
8、inganalog,eachmachineisuniquewithrespecttoitsset-up.Parametersoptimizedononebondercannoteasilybetransferredtoanother.2.0TRENDSINGOLDBONDINGWIRE2.1MATERIALREFINEMENTSTable1comparesthepropertiesofsometypicalcommerciallyavailablewires.Generallyallthe“new”wireshaveimprovedproperties,suchasgreaterbreakin
9、gload,lowerloopheight,andincreasedpullandshearstrengths.DopantsincreasethestrengthofAuwires.Forinstance,Beincreasesgrainrefinementandstrengthbyintroducingintermetallicprecipitates,sinceitisasmallatomcomparedtogoldandiselectronicallyissimilar.Eveninminuteamounts,theatomswilldistortthelattice,makingBe
10、aneffectivehardeningagent.Thisiscurrentlytheprimarydopantusedintheindustry.However,increasingtheamounttoabove12ppmwillcauseBetocomeoutofsolution,andinduceintergranularfractureduringbonding(1).Othermetalsarealsousedtomaximizemechanicalproperties.Silver(Ag),palladium(Pd),copper(Cu),andplatinum(Pt)area
11、ddedforsolidsolutionstrengtheningandchemicalstability.Threeofthefourelementscitedareinthesamegroupintheperiodictableasgold.Inaddition,justaswithgold,allfourelementsarefacecenteredcubic(FCC)withsimilarlatticeconstantsandelectronicstructure.Strengtheningisbysubstitutionoflatticeatomswithdopantatomstop
12、rovidethechemicalstability(4).Othermetals,likecalciumandlanthanum,canalsobeusedforstrengtheningbyprecipitationhardening,inmuchthesamemannerasBe.Inadditiontothedopants,theproductionprocessalsoinfluencesthewireproperties.Carefulrolling,annealing,anddrawingimprovethewirepropertiesbyinsuringgrainuniform
13、ityandevendispersionoftheprecipitates(1).2.2LOWLOOPINGCHARACERISTICSAnotherpurposefortheserefinementsistoincreasestrengthandhardnessandtoreducethelengthoftheheataffectedzone(HAZ).TheHAZisthelocationwheretheloopisformed,andshouldideallybebetween25pmto100pmfromtheballbond.Throughrecrystallizationandgr
14、aingrowth,theHAZcaneasilybedeformed.Largergrainsaregenerallyweakerfromalackofdislocationsduetoworkhardening.Opantprecipitatestieupthegrainboundariesduringheatingandpreventgraingrowth.Onereasonforthehighdopantlevelistoinsurethatanadequateamountofprecipitatesexistsintheatomiclattice.Thus,thequalityoft
15、hewireloopingcapabilitiesrequiresgoodcontroloftheHAZ.FigureIillustratesthehardnessprofileofastandardAuwireafterballformation(6).Hardnessismeasuredfromtheneckpositiontowardtheballbondwitha2gmload.ThedistributionisU-shapedwithaminimumacertaindistanceawayfromtheballbond.Thewirebendsattheminimumhardness
16、position,whichusuallyisinthe00.10.20.30.40.5centeroftheHAZ.Thispointcorrespondstothepositionoflargestcurvatureandaffectstheloopheight.ShorteningtheHAZshouldproducealowerloop.Fortheexamplegiven,wireAisharderandhasaHAZclosertotheneckthanwireBresultinginalowerloop(5-7).2.3LONGSPANCHARACERISTICSAsthewir
17、espanfromthebondpadsonthechiptotheleadfingersincreases,theriskofwiresagging,andsweepingduringmoldingalsogrows.calciumandlanthanum,canalsobeusedforstrengtheningbyprecipitationhardening,inmuchthesamemannerasBe.Inadditiontothedopants,theproductionprocessalsoinfluencesthewireproperties.Carefulrolling,an
18、nealing,anddrawingimprovethewirepropertiesbyinsuringgrainuniformityandevendispersionoftheprecipitates(1).Figure2showshowthemoldflowaffectswirewashing(8a).&I.istheratiooftheamountofwiredeflection,6,overthebondpadpitchs.Thus,if6sisequalto1,thewirebondhasdrapedovertotheadjacentpad.Thisratioisusedasamet
19、ricfordescribingtheextentofwiresweepinapackage.Inpractice,however,sweepisdefinedasanydeformationthatexceedsaratiospecifiedbytheICmanufacturer.Typically,thisvaluecouldbefromonetothreewirediametersdependingontheassemblydesignrulesofthemanufacturer.Thepolarplotillustratesthelocationofthewiresonthetestd
20、evice,withtheanglemadebyeachwirewithrespecttotheflowdescribedbythepositionofthedatapoint.Comerwiresexhibitthehighestamountofsweepcomparedtothecenterwiresduetotheirlongerspans.Asthefrontvelocityofthemoldingencapsulantisincreased,higherflow-inducedforcesareobservedresultinginmoresweep.Towithstandthemo
21、ldcompoundflow,theAuwiremustbestronger.Theincreasedstrengthandstiffnessofthespecialtywires,indicatedbythehighbreakingloadandelongationvalues,providemoreresistancetomoldsweep.Table2comparesthetypicalsweepobservedbetweenthestandardwiresandthenewerhigh-strengthwiresfordifferentwirespans.Thesamerefineme
22、ntswhichgivetheAuspecialtywireslowloopingcapabililitiesalsoprovidethemeansforlongspans.Itshouldbepointedoutthatwiresweepresultsfromacombinationoffactorssuchasmoldcavitydesign,moldingparameters,anddevicelayout(8b,c).Thesefactorscontroltheextentofsweepjustasmuchasthepropertiesofthewiresandtheprofilesofthebonds.Thus,inordertoreduceoreliminatemolding-inducedwiresweep,a
外文翻譯--引線鍵合的現(xiàn)狀與發(fā)展趨勢.doc
