Thermal Properties of Active Solder Bonds-IMAPS TATW 2004

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


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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

Thermal Properties of Active Solder Bonds-IMAPS TATW 2004

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