Underfill Design and Trend for 2.5D/3D with TSV Package

Haruyuki Yoshii NAMICS Corporation

Outline

IntroductionIntroduction

# Flip Chip Package trend# Flip Chip Package trend

CUF design for 2.5D/3D with TSV PackageCUF design for 2.5D/3D with TSV Package# Reliability requirement for CUF# Reliability requirement for CUF

# # Thermal conductivity requirementThermal conductivity requirement

# Void elimination process for narrow gap# Void elimination process for narrow gap

PAM challenges for 2.5D/3D with PAM challenges for 2.5D/3D with TSV TSV PKGPKG# Features of PAM# Features of PAM

# Types of NCF and challenges# Types of NCF and challenges

Flip-Chip Package Integration

Void/Flowability issue

Bleeding issue Low-k Crack issue

Bump Crack issueWarpage issue

Flow Flow markmarkVoidVoid

Substrate

BumpUnderfill

Low k wafer

stressstress

Substrate

Bump

stressstress

UF Properties to be RequiredGeneral issue in FC-BGA/CSP Package

Outline

IntroductionIntroduction

# Flip Chip Package trend# Flip Chip Package trend

CUF design for 2.5D/3D with TSV PackageCUF design for 2.5D/3D with TSV Package# Reliability requirement for CUF# Reliability requirement for CUF

# # Thermal conductivity requirementThermal conductivity requirement

# Void elimination process for narrow gap# Void elimination process for narrow gap

PAM challenges for 2.5D/3D with PAM challenges for 2.5D/3D with TSV TSV PKGPKG# Features of PAM# Features of PAM

# Types of NCF and challenges# Types of NCF and challenges

2.5D/3D Packaging trend

Year 20122012 20132013 20142014 20152015

Microbump gap (um)

3D TSV

2.5D

Underfill development target for 2.5D/3D Packaging

Year 20122012 20132013 20142014 20152015

Filler size (um)

CTE (ppm/C)

Thermal conductivity (W/m.K)

ray emission (count/cm2h) <0.001

Underfilling method CUF / VCUF NCF

0.3 ~ 0.6 0.330 ~ 40 20 ~ 30

< 2.0 > 2.0

2.5D/3D packaging roadmap and CUF requirement

20 - 30 <20

Filler size (um)

Gap size (um)

10 20 50

2 Stop Stop

0.6 Flowmark /Void

0.3

Only fine filler type underfill can be applied to stacked die PKG

Test specimen for flowability

Gap:10um

Underfill

Glass

Glass

10mm

20mm

Hot plate

Target for 2.5D/3D PKGFiller content = 50wt%

Flowability test result

Underfill filler size and applicability to various gaps

FEM result: SAC solder strain (at -55C)

Cu pillarCu pillar

SAC solderSAC solder

1st Die

Substrate

2nd Die

Cu pillar/ SAC solder Cu pillar/

SAC solder

Creep Strain 【SAC-1】

0

0.005

0.01

0.015

5000

MPa

8000

MPa

1100

0MPa

50M

Pa20

0MPa

350M

Pa

120C

145C

160C

19pp

m/C

27pp

m/C

35pp

m/C

80pp

m/C

110p

pm/C

140p

pm/C

5000

MPa

8000

MPa

1100

0MPa

50M

Pa20

0MPa

350M

Pa

120C

145C

160C

19pp

m/C

27pp

m/C

35pp

m/C

80pp

m/C

110p

pm/C

140p

pm/C

E1 E2 Tg CTE1 CTE2 E1 E2 Tg CTE1 CTE2

1st UF(TOP) 2nd UF(Bottom)

Stra

in(-

)

FEM result Concern

Proper Underfill property directionProper Underfill property direction

1st UF1st UF 2nd UF2nd UF

Tg E CTE Tg E CTE

1st bump strain •Bump crack High Low E1 Low CTE No effect

Effect of CUF Property on 1st bump strain

FEM result: Eu bump strain (at -55C)

1st Die

Substrate

2nd Die

EuEu

Creep Strain 【Eu-2】

0

0.01

0.02

0.03

5000

MPa

8000

MPa

1100

0MPa

50M

Pa20

0MPa

350M

Pa

120C

145C

160C

19pp

m/C

27pp

m/C

35pp

m/C

80pp

m/C

110p

pm/C

140p

pm/C

5000

MPa

8000

MPa

1100

0MPa

50M

Pa20

0MPa

350M

Pa

120C

145C

160C

19pp

m/C

27pp

m/C

35pp

m/C

80pp

m/C

110p

pm/C

140p

pm/C

E1 E2 Tg CTE1 CTE2 E1 E2 Tg CTE1 CTE2

1st UF(TOP) 2nd UF(Bottom)

Stra

in(-

)

FEM result Concern

Proper Underfill property directionProper Underfill property direction

1st UF1st UF 2nd UF2nd UF

Tg E CTE Tg E CTE

2nd bump strain •Bump crack No effect High High E1 Low CTE

Effect of CUF Property on 2nd bump strain

Filler size (um)

Gap size (um)

10 20 50

2 Stop Stop

0.6 Flowmark /Void

0.3

Test specimen for flowability

Gap:10um

Underfill

Glass

Glass

10mm

20mm

Hot plate

Target for 2.5D/3D PKG Target for 2.5D/3D PKG

Current:Filler content = 50wt%

In future:Filler content = 65wt%

Low CTE

Increasing the filler content will be needed to reduce underfill CTE.

Need for improvement in flow marks and voids.

Filler size (um)

Gap size (um)

10 20 50

2 Stop Stop

0.6 Flowmark /Void

Flowmark /Void

0.3 Flowmark /Void

Flowmark /Void

Flowability test result

Concern of higher filler loading for lower CTE

Mechanism of flow mark

Filler cohesion during underfill flow slows the flow partly. This will cause flow marks and capture voids.

Filler cohesion during underfill flow slows the flow partly. This will cause flow marks and capture voids.

Flow

dire

ctio

n

FlowmarkFlowmark

FastFastSlowSlow

Captured void Captured void

Cross-sectional schematics

Uniform flow = Flows fast

Filler cohesion / stuck = Flows slow

Flow direction Flow direction

Applying special treatment to the filler prevented it from cohesion.

Conventional UnderfillMany flow marks and voids

Improved with special treatment

No flow mark

Flow markFlow mark

Test specimen for flowability

Gap:10um

Underfill

Glass

Glass

10mm

20mm

Hot plate

Captured voidCaptured void

10um GapFiller size (mean/max):

0.6/3umFiller loading:

62wt%

Improvement of voids caused by flow marks

2.5D/3D Packaging trend

Year 20122012 20132013 20142014 20152015

Microbump gap (um)

3D TSV

2.5D

Underfill development target for 2.5D/3D Packaging

Year 20122012 20132013 20142014 20152015

Filler size (um)

CTE (ppm/C)

Thermal conductivity (W/m.K)

ray emission (count/cm2h) <0.001

Underfilling method CUF / VCUF NCF

0.3 ~ 0.6 0.330 ~ 40 20 ~ 30

< 2.0 > 2.0

2.5D/3D packaging roadmap and underfill requirement

20 - 30 <20

Flip chip PKG 3D PKG

Logic

Memory

3D packages has multiple heat sources and are more likely to retain the heat inside than 2D packages because of their structure. For the heat dispersion, thermal resistance between chips needs to be reduced. This is why high thermal conductivity is required for underfill.

COOL HOT

Thermal conductivity CUF requirement

Conventional UF Developed New type

Filler

Type SiO2 Al2O3 Al2O3

wt% 60 67 77

Mean / Max. 0.6 / 3 0.7 / 5 0.7 / 5

Viscosity Pa.s 80 33 25

Tg(DMA) C 119 118 113

Storage modulus GPa 10.7 9.2 14.0

CTE 1 ppm/C 29 30 29

CTE 2 ppm/C 100 116 91

Thermal conductivity W/mK 0.4 0.6 1.3

Alpha ray emission count/cm2h <0.001 <0.008 <0.001

Thermal conductivity CUF

A type of filler and its loading volume are the keys to higher thermal conductivity. Our CUF has achieved a thermal conductivity of 1.3W and we are exploring it further. Considering an influence on viscosity, however, a new material other than CUF needs to be explored as well.

2.5D/3D Packaging trend

Year 20122012 20132013 20142014 20152015

Microbump gap (um)

3D TSV

2.5D

Underfill development target for 2.5D/3D Packaging

Year 20122012 20132013 20142014 20152015

Filler size (um)

CTE (ppm/C)

Thermal conductivity (W/m.K)

ray emission (count/cm2h) <0.001

Underfilling method CUF / VCUF PAM(NCF)

0.3 ~ 0.6 0.330 ~ 40 20 ~ 30

< 2.0 > 2.0

2.5D/3D packaging roadmap and underfill requirement

20 - 30 <20

Vacuum assisted process Curing process with Pressure oven

Equipment Vacuum system Pressure oven

Void reduction process At underfilling At curing

A sort of void to eliminate Capture Capture, Moisture

Size of void to eliminate Large ~ Small Small

Underfill VCUF CUF

Dispensing Underfilling Curing Completion

Vacuum assisted process

Void elimination

Curing process with Pressure oven

Void elimination

Void elimination process

In vacuum conditionIn vacuum condition

Dispense Complete Underfilling

Flow by Capillary action and differential pressure No void

Gap: 20um

Demonstration 1

Tem

pera

ture

Tem

pera

ture

Pre

ssur

eP

ress

ure

TimeTime Leak

20sec 20secAbout About

Vacuum process can accelerate penetration speed

Set onto heated stage in vacuum chamber (130Pa, 70 – 110C) Penetration process

Demonstration 1

Round shape dispensing

Vacuum assisted process

Leak

U8410-73C

Before cure

After cure

UF Pressure-oven Type Pressure value

U8410-73C VFS-60A-JP 7 kg/cm2

Voids disappear.

Capture void

Voids remain.

Pressure oven profile

2030405060708090

100110120130140150160170180

0 15 30 45 60 75 90 105 120 135 150 165 180Time (min.)

Tem

pera

ture

(deg

.C)

12345678910

Pres

sure

(Kg/

cm2 )

Temperature Pressure

Pressure-ovenOven

TEST vehicleDie size : 20mmx20mmx0.73mm(t)Passivation : PIBump material : Sn/3Ag/0.5CuBump pitch : 175umFlux : non-cleanSubstrate size : 52.5mmx30.0mmx0.73mm(t)

Pressure oven process

Outline

IntroductionIntroduction

# Flip Chip Package trend# Flip Chip Package trend

CUF design for 2.5D/3D with TSV PackageCUF design for 2.5D/3D with TSV Package# Reliability requirement for CUF# Reliability requirement for CUF

# # Thermal conductivity requirementThermal conductivity requirement

# Void elimination process for narrow gap# Void elimination process for narrow gap

PAM challenges for 2.5D/3D with PAM challenges for 2.5D/3D with TSV TSV PKGPKG# Features of PAM# Features of PAM

# Types of NCF and challenges# Types of NCF and challenges

Capture VoidCapture Void

Capture vCapture voidoid issueissue

Difficulty in dispensing at narrow KOZDifficulty in dispensing at narrow KOZ

No space to No space to dispense CUFdispense CUF

Flux residue issueFlux residue issueDDifficult for the packageifficult for the packagesswithwith a narrow gap to a narrow gap to ccleanlean fluxflux..

CleaningCleaningFlux residueFlux residue

Concerns for 3D PKG with CUF

Likely to generate capture voids Likely to generate capture voids among stack dies with a narrow gap.among stack dies with a narrow gap.

LaminatLaminationion

NCPNCP

DispenseDispense LaminationLamination

DicingDicing

TCBTCB

UFUF applicationapplication

To To SubstrateSubstrate

To To WaferWafer

NCFNCF NCFNCF

TCBTCB

UFUF applicationapplication

Introduction of Pre-applied materials (PAM)

Application Process of NCF

Laminate Bonding Post cureDicing

Laminate Bonding Post cureDicingBackgrind

Applied onthe Wafer

Applied afterBackgrind

Applied beforeBackgrind

Laminate Bonding Post cure

Applied on theSubstrate

- NCF needs to be higher than bump height.- NCF needs to be flat.- No void.

Method Item

Appearances by Microscope

Voids

Evaluation Method

Test vehicleWafer Size 29.2mm x 29.2mm

(wafer /16 Chips)

Wafer Thickness 125 um

Bump Substance Cu pillarw/ Sn-Ag solder

# of bumps 544

NCF Thickness 55um

Lamination test “Over the bump type”Objectives

Lamination test “Over the bump type”

Check the void by C-SAM Cross section

Solder joints are good for each bump.

Chip / NCF

NCF / Sub.

Bonding test “Over the bump type”

X 500 X 1500

Summery• High filler loading to reduce underfill CTE will cause flow marks and

voids. Applying special treatment to the filler can prevent it from cohesion and reduce the voids.

• We has successfully developed high thermal conductive CUF by adjusting the filler. For further improvement, new materials need to be explored as well.

• A vacuum assisted process and a pressure oven process have been examined for void reduction. Although the processes should be done in batches, they are an effective way to reduce the voids.

• NCF has been explored to be applicable to any structure as well as a small Keep Out Zone. We are aiming to expand the applicability by widening the process window and improving control of film thickness.

Thank you!