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8/14/2019 Thermal Properties of Active Solder Bonds-IMAPS TATW 2004
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Initial Results: ThermalInitial Results: Thermal
Properties of Active SolderProperties of Active SolderBondsBonds
Randall Redd & Dr. Ronald SmithRandall Redd & Dr. Ronald Smith
SS--Bond Technologies, LLCBond Technologies, LLCrredd@[email protected]
S-BondTechnologies, LLC
8/14/2019 Thermal Properties of Active Solder Bonds-IMAPS TATW 2004
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SS--Bond TechnologiesBond Technologies
Original technology patent in 1996 withinOriginal technology patent in 1996 within
another companyanother company SBT formed in 2003 to developSBT formed in 2003 to develop
applications in the electronics, aerospace,applications in the electronics, aerospace,
defense, and general industrial marketsdefense, and general industrial markets Small team of scientists/engineers thatSmall team of scientists/engineers that
develop materials and applications, thendevelop materials and applications, thenlicense the technology to OEMlicense the technology to OEMs ands andcontract assembly service providerscontract assembly service providers
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Study ObjectiveStudy ObjectiveTo examine the relative thermal conductivity ofTo examine the relative thermal conductivity of
bonded packaging/thermal managementbonded packaging/thermal managementmaterials in a way that provides relativematerials in a way that provides relative
performance data to compare active solderperformance data to compare active solder
materials to commonly used conventionalmaterials to commonly used conventionalsolderssolders
Why?Why?-------- TIM1 and bond lines between materials areTIM1 and bond lines between materials arefrequently the limiting item in high performance thermalfrequently the limiting item in high performance thermal
management systemsmanagement systems
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Active Solder ChemistryActive Solder Chemistry Based onBased on
conventional leadconventional lead--freefreesolder materialssolder materials
Addition of specificAddition of specific
elements creates aelements creates aself fluxing systemself fluxing system
No need to preNo need to pre--plate,plate,
metallize, ormetallize, oradd/remove fluxadd/remove flux
Material # 2Material # 1
S-Bond Alloy
Ti/Rare Earth IntermetallicsThin oxide layer acting as stabilizer
Air
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Study ProcedureStudy Procedure Test apparatusTest apparatus
follows ASTM Dfollows ASTM D--54705470 Testing done onTesting done on
substratessubstrates
approximately 2approximately 2square x 0.125square x 0.125thickthick
Materials wereMaterials wereconsistent inconsistent in
thickness within samethickness within samematerial, but notmaterial, but notbetween materialsbetween materials
H
Insulator
Guard Heater
Insulator
Heater
T1UpperMeterBarT2
Specimen
T3LowerMeter
BarT4
T5Reference
CalorimeterT6
Cooling Plate
Insulator
FORCE
H
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Bonding MethodsBonding Methods Substrates were bonded using 4 materialsSubstrates were bonded using 4 materials
Indium based Active Solder (SIndium based Active Solder (S--BondBond 130)130)
Tin/silver based Active Solder (STin/silver based Active Solder (S--BondBond 220)220)
32.5 tin/67.5 lead conventional solder32.5 tin/67.5 lead conventional solder
96 tin/4 silver conventional solder96 tin/4 silver conventional solder
Active solder materials bonded directly to the substrateActive solder materials bonded directly to the substrate
surfacesurface Other materials bonded using fluxOther materials bonded using flux -------- significantsignificant
bonding issues with certain substratesbonding issues with certain substrates
Bond thickness controlled by weight applied to assemblyBond thickness controlled by weight applied to assembly
prior to coolingprior to cooling No evaluation of bond strengthNo evaluation of bond strength
Bond quality evaluated by Scanning Acoustic MicroscopyBond quality evaluated by Scanning Acoustic Microscopy
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Active Solder JoiningActive Solder Joining Substrate material is heated to joiningSubstrate material is heated to joining
temperaturetemperature Indium based materialIndium based material -- 140140CC
Tin/Silver based materialTin/Silver based material -- 250250CC
Surfaces are coated with thin layer of materialSurfaces are coated with thin layer of materialby brushingby brushing
Additional material added and parts assembledAdditional material added and parts assembled
Weight is placed on top of assembly duringWeight is placed on top of assembly duringcooling to establish consistent bond thicknesscooling to establish consistent bond thicknessand minimize voidingand minimize voiding
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Conventional Solder JoiningConventional Solder Joining
Joined using fluxes recommended forJoined using fluxes recommended for
particular material, where available, andparticular material, where available, andfollowing recommended practicesfollowing recommended practices
For certain materials, acceptable bondsFor certain materials, acceptable bondscould not be obtained without plating thecould not be obtained without plating the
surfacesurface [testing in progress][testing in progress]
AlSiC with nickelAlSiC with nickel Si with goldSi with gold
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Test MatrixTest Matrix
XXCuW
XXXSi
XXXXCu
AlAlSiCCuWSi
Difficult to achieve bond w ith conventional solders
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Anticipated ResultsAnticipated Results Bond conductivity isBond conductivity is
governed by severalgoverned by severalfactors:factors:
Bulk thermalBulk thermal
impedance of joiningimpedance of joiningmaterialmaterial
Bond line thicknessBond line thickness
Degree of substrateDegree of substrate
surface wettingsurface wetting
Void fractionVoid fraction 1.251.25Tin/Silver/Tin/Silver/CopperCopper
1.221.22Tin/LeadTin/Lead
1.251.25SB220SB220
1.001.00SB130SB130
Relative BulkRelative Bulk
ThermalThermal
ImpedanceImpedanceMaterialMaterial
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Bond Quality EvaluationBond Quality Evaluation
Scanning Acoustic MicroscopyScanning Acoustic Microscopy
Si bonded to CuW w / SB220 AlSiC bonded to Cu w/ tin-lead
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Bond Line ThicknessBond Line Thickness Bond thickness is determined by surface tension,Bond thickness is determined by surface tension,
melt rheology, assembly process, and surfacemelt rheology, assembly process, and surfaceroughness of substratesroughness of substrates
Experience shows normal variation of ~1 mill forExperience shows normal variation of ~1 mill for
a capable processa capable process Difficult to make substantial changes inDifficult to make substantial changes in
thickness without use of greatly increasedthickness without use of greatly increased
pressurepressure All bond thickness fell in the range of 1All bond thickness fell in the range of 1--4 mills4 mills
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Measured Relative ThermalMeasured Relative Thermal
ImpedanceImpedance
0
1
2
Si-CuW
0
1
2
Si-Cu
0
1
2
AlSiC-Cu
0
1
2
Al-Cu SB130
SB220
Sn/Pb
Sn/Ag/Cu
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Initial ConclusionsInitial Conclusions Bulk thermal impedance drives thermalBulk thermal impedance drives thermal
performance if the bonding material completelyperformance if the bonding material completelywets the substratewets the substrate
Active Solders wet and join to a wider variety ofActive Solders wet and join to a wider variety of
materials than conventional solders, producingmaterials than conventional solders, producingequal or lower thermal impedanceequal or lower thermal impedance
Further study is needed with plated substratesFurther study is needed with plated substrates
to fully compare conventional solders to activeto fully compare conventional solders to activesolders in silicon, AlSiC, and CuW substratessolders in silicon, AlSiC, and CuW substrates