金属间化合物的形成机理

深圳市福英达工业技术有限公司/一站式锡膏解决方案供应商MechanismofIntermetallicCompoundFormationIntermetalliccompoundsareaclassofsubstancesformedbychemicalbondingofmetallicelementsinspecificatomicproportions.Inordertoobtainagoodweldingresult,ametallurgicalreactionmusttakeplacebetweenthesoldercomponentandthebasemetalcomponentthatcreatesastrongbond,i.e.,anappropriatealloylayer(intermetalliccompound,orIMC)attheinterface.Therefore,intheweldedjointinterface,theformationofIMCortheformationofgoodorbadquality,themechanical,chemical,electricalandotherpropertiesoftheweldedjointhasacriticalimpact.IntermetalliccompoundformationconditionsSolderjointsservetwokeypurposeswhenjoiningtwomaterials:goodelectricalconductivityandlong-lastingmechanicaljointstrength.Sn-Pbsolder,forexample,whenthetwoareconnectedtothebasemetalareCu,toachieveadurableandstrongmechanicalconnection,itmustbeheatedtothesolderjointtemperatureabovethemeltingpointofthesoldermorethan15°C,thetimefor2~15s.Atthistime,thesoldermaybeinthepadandcomponentsbetweentheformationofpinsbetweenthepinsofanewchemicalsubstance,andtoachieveadurableandfirmlyconnectedtothetwopurposes.Obviouslytheformationprocessofintermetalliccompoundsiscloselyrelatedtotemperatureandtime,especiallybythetemperatureismoreobvious.Figure1depictstheintermetalliccompoundswithintheweldedjointinthegenerationprocess,undertheactionofdifferenttemperatures,theintermetalliccompoundsgeneratedthicknessanditsimpactonthestrengthoftheweldedjoint.Theinternalstructureofthesolderjointatthistimeisshowninthefigure.Theintermetalliccompoundlayer(IMC),seenundertheelectronmicroscope,consistsoftwosubstances,Cu3SnandCu6Sn5,asshowninFig.2.TheformationmechanismandmorphologyofCu3SnandCu6Sn5varyduringthesolderingprocess.Generallyspeaking,Cu6Sn5islocatedonthesolderside,thicker,andscallopedtogrowintotheliquidsolder,resultinginaroughmorphologyattheboundarybetweenIMCandsolder;whileCu3SnislocatedbetweenthecoppersubstrateandCu6Sn5,thinner,andintheformofasmooththinlayer.Thisisbecauseatthesolid-solidinterface(i.e.,betweenthecoppersubstrateandthesolidsolder),tinatomsdiffusefastertothecoppersubstratethantothecopperatomstothesolder,resultingintheformationoftin-richCu6Sn5phasefirst;whileatthesolid-liquidinterface(i.e.,betweenthecoppersubstrateandtheliquidsolder),tinatomsdiffuseslowertothecoppersubstratethantothecopperatomstothesolder.Atthesolid-liquidinterface(i.e.betweenthecoppersubstrateandtheliquidsolder),thediffusionoftinatomsintothecoppersubstrateisslowerthanthediffusionofcopperatomsintothesolder,resultingintheformationofthecopper-richCu3Snphase.InfluenceofintermetalliccompoundsonthereliabilityofthesolderinterfaceIntermetalliccompoundshaveanimportantinfluenceonthereliabilityofthesolderinterface.Ontheonehand,intermetalliccompoundscanimprovethebondingstrengthandcorrosionresistanceoftheinterface;ontheotherhand,intermetalliccompoundsalsoincreasethebrittlenessandstressconcentrationoftheinterface,andgrow,transformorcrackwithchangesintime,temperature,pressureandotherfactors.Therefore,whendesigningandfabricatinglead-freetin-basedsolderingsystems,itisnecessarytoconsiderthechara