电镀共晶锡铋焊膏凸点的特性

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ThePropertiesofElectroplatedEutecticSnBiSolderPasteBumps

Theelectronicsindustryhasanincreasingdemandforlighter,smaller,andmoreflexibleproducts.Inordertorealizetheminiaturizationofchips,thepadpitchbecomessmallerandsmaller.Inaddition,inordertomakefulluseofchipspace,moreandmoremanufacturersadoptflip-chippackagingtechnology,whichcanproducemoreI/Ointerfaces,betterelectricalperformance,andsmallerpackagesize.Theresearchersfoundthattheuseofelectroplatedsolderpastetomakebumpscanmeettherequirementsofflip-chippackaging.Theelectroplatingsolderpasteprocesscansolvecostandmassproductionproblemsandmeetfine-pitchrequirements.Eutectictin-bismuthsolderpasteissuitableforproducingmicro-bumpswithlowmeltingpointsandgoodmechanicalproperties.

Theflipchiprequiresplacingametallayerunderthebumps.Solderpasteisthendepositedonthepadsandreflowedtoformsolderjoints.TheeutecticSn-BisolderpastecanbeelectroplatedontothepadsusingacommercialelectroplatingDCpulseelectroplatingapparatus.Rohetal.(2014)conductedexperimentsonelectroplatingeutecticSnBisolderpasteandtestedsolderjointreliability.Constantpotentialandcurrentdensityarethekeystostableelectroplating.Platingat30mA/cm2for15minutesresultedincolumnarSn-Bibumpswithanaveragebumpdiameterandheightof22±0.4and18±06lm,respectively(Rohetal.,2014).Figure1.TheschematicdiagramofelectroplatedSnBisolderbumpprocess(Rohetal.,2014).

Figure2.Thecross-sectionalimageofsolderbumpafter20minutesofreflowat170℃(Rohetal.,2014).After20minutesofreflowat170°C,theSnBisolderpastewettedthepadsandformedhemisphericalsolderjoints.ThewhitepartofFigure2isthebismuth-richphase,andthegraysectionisthetin-richphase.Atthesametime,thegrowthoftheintermetalliccompoundCu6Sn5canbeobservedinthesolderjoints.ThegrowthofCu6Sn5isrelatedtothereflowtime.LongerreflowtimecanresultinexcessivelyCu6Sn5formation.OtherIMCs,suchasCu3Sn,areunlikelytogenerateduringreflow.Generallyspeaking,Cu3Snappearsgraduallyintheagingtestandincreaseswiththeagingtime.Figure3.Therelationshipbetweenreflowtimeandshearstrength(Rohetal.,2014).AsshowninFigure3,theshearstrengthoftheelectroplatedeutecticSnBibumpsincreasesasthereflowtimeincreases.Reflowsolderingtimeshouldbetoolong.Otherwise,thesolderjointswillbecomebrittleandcausefractureduetotheovergrowthoftheIMCs.Brittlefracturealsooccursduringthermalaging.Withincreasingagingtime,brittleIMCsgrowspontaneously,eventuallyleadingtobrittlefracture.Atpresent,manyexperimentalconclusionsshowthatdopingnanometalparticlescanreducethebrittlefractureissue.EutecticSnBibumpshavelowhardnessandcanbeappliedtospecificcomponentsaccordingtoactualneeds.

Fitechisamanufacturerdedicatedtotheproductionofhigh-reliabilitysolderpaste.Theproductscovervariousalloycombinations,suchastin-bismuthandtin-silver-copper.Welcometolearnmoredetails.ReferenceRoh,M.H.,Jung