合金成分对Sn-Ag-Cu焊料性能和显微组织的影响

ReviewArticle

EffectofalloyingelementsonpropertiesandmicrostructuresofSnAgCusolders

LiliGaoa,SongbaiXuea,*,LiangZhanga,ZhongShenga,FengJia,WeiDaia,Sheng-linYua,b,GuangZenga

ab

CollegeofMaterialsScienceandTechnology,NanjingUniversityofAeronauticsandAstronautics,Nanjing210016,ChinaThe14thResearchInstitute,ChinaElectronicsTechnologyGroupCorporation,Nanjing210013,China

articleinfoabstract

Recentyears,theSnAgCufamilyofalloyshasbeenfoundawidelyapplicationasareplacementfortheconventionalSnPbsoldersinelectronicindustry.InordertofurtherenhancethepropertiesofSnAgCusolderalloys,alloyingelementssuchasrareearth,Bi,Sb,Fe,Co,Mn,Ti,In,Ni,Geandnano-particleswereselectedbylotsofresearchersasalloysadditionintothesealloys.Rareearth(RE)elementshavebeencalledthe‘‘vitamin”ofmetals,whichmeansthatasmallamountofREelementscangreatlyenhancethepropertiesofmetals,suchasmicrostructurere nement,alloyingandpuri cationofmaterialsandmetamorphosisofinclusions.Inaddition,asmallamountofZnadditionhastheabilitytoreduceundercoolingef cientlyandsuppresstheformationofmassiveprimaryAg3Snplates,andBi/GahastheabilitytoenhancethewettabilityofSnAgCualloysaswellasNi.Moreover,addingCo/Fe/Gecaneffec-tivelyre nemicrostructure,modifyinterfacialCu–SncompoundsandincreasetheshearstrengthofjointswithCu.Thispapersummarizestheeffectsofalloyingelementsonthewettability,mechanicalproperties,creepbehaviorandmicrostructuresofSnAgCulead-freesolderalloys.

Ó2010ElsevierB.V.Allrightsreserved.

Articlehistory:

Received27February2010Accepted8April2010

Availableonline14April2010Keywords:

SnAgCusoldersAlloyingelementsWettability

MechanicalpropertiesCreepbehavior

1.Introduction

TraditionaleutecticSnPbsoldershavebeenwidelyusedinmicroelectronicpackagingindustry.Atpresent,increasedhealthconcernsoverthetoxicityofPbineutectictin–leadsolderhavepromotedthedevelopmentofnewlead-freesoldersformicroelec-tronicpackaging[1–3].AcloselyrelatedsetofSnAgCunear-eutec-ticalloyshaverisenthroughtheranksofmanyexperimentalstudiestostandasthemostlikelycandidatesforwidespreadreplacementofSnPbsolders[4–6].Themainbene tsofthisalloysystemareitsrelativelylowmeltingtemperaturecomparedwithSnAgbinaryeutecticalloyanditsgenerallysuperiormechanicalproperties,aswellasrelativelygoodsolderability[7].However,manyproblemsofSnAgCualloysstillexist,suchastheargumentonlargebrittleintermetallicphasesandhighcost[8].

Withthewiderapplicationsofsurfacemounttechnologyandpopulartrendsofultra ne-pitchdesign,aswellastheincreasingservice-environmentrequirements,itisimperativetodevelopandinvestigatenewlead-freesolderswithhighermechanicalproperties[9,10].InordertofurtherenhancethepropertiesofSnAgCusolderalloys,alloyingelementssuchasrareearth,Bi,Sb,In,Co,Ga,Ni,Geandnano-particleswereselectedbylotsofresearchersasalloysadditionintothesealloys[11,12].Inthispa-per,wesummarizethedevelopmentinSnAgCusolderalloyswith

*Correspondingauthor.Tel.:+862584896070.E-mailaddress:xuesb@nuaa.edu.cn(S.Xue).

0167-9317/$-seefrontmatterÓ2010ElsevierB.V.Allrightsreserved.doi:10.1016/j.mee.2010.04.007

additionofalloyingelements,andtheireffectsonthewettingbehavior,meltingtemperature,mechanicalproperties,creepbehavior,andmicrostructuresofSnAgCusolderalloys.

2.Wettingandspreadingproperties

Thesolderingprocessconsistsintheformationofajointbetweenthemoltensolderandasolidmetalsurface.Theabilityofaliquidalloytowetandspreadonthesubstrateiscrucialfortheformationofametallurgicalbondingdrivenbythephysical–chemicalpropertiesofthesystem[13].Usually,thefollowingfamousYoung’sequationisextensivelyusedtodiscussthewetta-ÀcSL

bilityofsolders[14]:cosh¼cSG

LGwherecSGisthesolid–gas

interfacetension,cSListhesolid–liquidinterfacetension,cLGistheliquid–gasinterfacetension,andhisthecontactangle.

ThewettingpropertiesofSnAgCu–REwereinvestigatedbyYuetal.[15].ComparativewettingforceofthefoursoldersusingRMA uxisdisplayedinFig.1a.ThewettingforceofSn3.5Ag0.7CuishigherthanSn2.5Ag0.7Cuduetoitsrelativelylowmeltingpoint.Theadditionof0.1%REtoSn3.5Ag0.7Cucansigni cantlyimprovethewettingforce.Moreover,thewettingforceofSn3.5Ag0.7-Cu0.25REisstillhigherthanthatofnoRE-bearingsolder,butlowerthan0.1%REaddition.ThewettinganglesofthesesoldersareshowninFig.1b.ItisnodoubtthatSn3.5Ag0.7Cu0.1REsoldergotthesmallestwettingangleandthatofSn2.5Ag0.7Cusolderisthebiggest.Shietal.[16]havereportedthatwhenrareearthEr