合金成分对Sn-Ag-Cu焊料性能和显微组织的影响

contentislessthan0.25wt.%,thespreadingareaofSn3.8Ag0.7CuincreaseswithErincreases.ThenthespreadingareadecreaseswhenErcontentincreasesupto1.0wt.%.ItissuggestedthatappropriaterangeaddingrareearthErshouldbe0.1–0.4wt.%.Wangetal.[17]demonstratedthatthewettabilityofSnAgCusol-deronCusubstratescanbeimprovedbyaddingsmallamountsofrareearthCeinadditiontoN2protectionandincreasingsolderingtemperature,andtheoptimalrareearthCecontentsforwettabilityareintherangeof0.03–0.05%forSn3.8Ag0.7Cualloys.

Inthepaper[18],Rizviassessedtheeffectsof1.0wt.%BionthewettabilityofSn2.8Ag0.5CusolderalloyonCuandNisubstratesbythewettingbalancetestsandcomparedwiththatoftheSnPbal-loy.Ingeneral,thewettabilityofSn2.8Ag0.5Cu1.0BisolderisworsethanthatoftheconventionalSnPbsolder,andahighersolderingtemperatureenhancesthediffusionprocess,resultinginadecreaseincontactanglesandimprovementofthewettability.However,newlydevelopedSn2.8Ag0.5Cu1.0BisolderiswettableonCuandNisubstratesandstronglydependentonthetypeof ux.Huetal.[19]foundthattheadditionofBicanimprovethewettabilityofSn0.3Ag0.7Culead-freesolderalloy,Sn0.3Ag0.7Cu3.0Bilead-freesolderhasafavorablewettabilityat240°C.ButtheamountofBishouldbelimited,becausetheexcesselementofBicouldin-creasethemeltingrangeofsolder,decreasetheplasticityofsolderandresultinthe awof llet-lifting[20].Inaddition,Panetal.[21]proposedthatasmallamountofGaadditionhastheabilitytoen-hancethewettabilityofSnAgCualloysaswellasBielement.

ThewettabilitytestofSnAgCuwiththeadditionofMgwascon-ductedbyLuetal.[22],itisfoundthattheadditionofMgworsensthewettabilityofsoldersdramatically.ItisconsiderthatMgispronetooxidize,andtheoxide lmproducedinthethermalpro-cessincreasesthesurfacetensionoftheliquidsolder,thuspre-ventsthesolderfromspreadingoverthecopperwiresurface.Yuetal.[23,24]foundthattheadditionofsmallamountofIndidsig-ni cantlyimprovethewettabilityofSnAgCusolderatthere owtemperatureof230–240°C.Moreover,solderwettabilityresultsrevealedthatthecompositesolderswithdifferentNicontentshadanacceptablespreadareacomparedwiththeoriginalSnAgCusolders[25].WhiletheadditionofGepreventedtheoxidationofSnandimprovedsolderwettabilityofSnAgCualloys[26].

3.Meltingtemperature

Theeffectsofrareearthelementshaveattractedpeoples’atten-tionlongbefore,astherareearthelementswererecognizedasthe‘‘vitamin”ofalloys,whichindicatesthattraceamountofREcaneffectivelyimprovethepropertiesandmicrostructuresofalloys.

Buttheadditionoftracerareearthhasatri ingeffectonthemelt-ingtemperatureofSnAgCusolderalloys[27,28].

Lotsofstudieshaverevealedthatadditionsoftransitionmetals(TM)toSnAgCualloyprovidedamarkedimprovementinmeltingcharacterizationproperties[29].Fig.2aandbillustratestheDSCendothermicandexothermicpeaksofthesamplesuseduponheat-ingandcooling,respectively.ItisfoundthatuponheatingtheonlyendothermalpeakfortheSn3.0Ag0.5Cu(SAC305)sampleswasseparatedintodoublepeaksforthelowAgsamples(SAC105).Theoneathightemperatureswascausedbythemeltingofproeu-tecticSnandthelowtemperaturepeakwasfortheeutecticstruc-ture.Duetoundercooling,theexothermicpeaksuponcoolingforallthesamplesappearedatalowertemperaturecomparedtotheirendothermalpeakbutthereductionsintemperaturewerenotidentical.Remarkably,thetemperatureofexothermicpeaksforthealloyedsampleswithalloyingadditions(MnTi)wasmuchhigherthantheunalloyedsamples.ItisworthyofnoticingthatthedegreeofundercoolingforproeutecticSnwasstronglyaffectedbythecomposition,inthedecreasingorderwasSAC305,SAC105,0.15Mn,0.15Ti,0.5Mnand0.5Ti.The0.5Tisampleexhibitedanex-tremelysuppressedundercoolingofonly4°C.ComparedwiththesolderofSn4.0Ag–0.5Cu,itcanbeseenobviouslythattraceaddi-tionofMgintoSnAgCusolderscanmodi esthemetingcharacter-istics.ThemeltingtemperatureoftheSnAgCusolderalloyswiththeadditionofMgdecreasesobviously[22].

Fig.3[30]showstheDSCendothermicandexothermicpeaksofthesamplesuseduponheatingandcooling,respectively.Fig.3arevealsthatuponheating,thetemperaturesoftheendo-thermalpeaksfortheeutecticreactionofthesamplesdidnotdif-ferverymuch,andthatoftheSAC–Znspecimenwasslightlylowerthantheothers.Duetoundercooling,theexothermicpeaksuponcoolingforallthesamplesappearedatalowertemperaturecomparedtotheirendothermalpeak,butthereductionsintem-peraturewerenotidentical(Fig.3b).Remarkably,theexothermicpeaksforthesampleswithTMadditionswereobservedathighertemperaturesthantheunalloyedsample,especiallyforSAC–ZnandSAC–Co.ItisworthnotingthatthedegreeofundercoolingdecreasedinturnfromSAC,SAC–Ni,SAC–Co,toSAC–Zn.TheSAC–Znsampleexhibitedadrasticallyreducedundercoolingofonly5.2°C.Jiangetal.[31]proposedthatminordopingelementsdidnotcausesigni cantdifferenceinmeltingrangebutdidin-ducedifferentundercoolingduringsolidi cation.AdditionofSbwouldincreasetheundercoolingbutZnadditionwouldreducetheundercooling.

Meltingbehaviorofdifferentlead-freesolderalloyswerestudiedbyLiuandLee[32].Table1showscomparativemeltingbehaviorofthesolderalloysinvestigated.Ascanbeseen,the

addi-