IWLPC October 13-15, 2015

Daniel Duffy Ph.D., Hemal Bhavsar, Lin Xin, Jean Liu, Bruno Tolla Ph.D.

Kester Inc., Itasca, IL, USA

Introduction◦ Conventional Flip Chip Assembly Process◦ One Step Chip Attach Process & Materials ( OSCA )

OSCA Materials for Reflow Processing ( OSCA-R )◦ Copper Pillar Test Vehicle◦ Design for Dispensing & Die Placement◦ Fluxing and Curing Kinetics During Reflow◦ Assembly by Conventional Reflow

Summary & Conclusions Acknowledgements

2

New and Improved Process Flow

Flux / Chip Place Reflow De-flux Underfill Post Cure

Flux & Die Placement

Reflow

Cleaning

Post Cure Underfill

Underfill

3

Process Simplification + Throughput

Dispense OSCA-R

Place Die

Next Process

Step

Dispense OSCA-R Die Placement Conventional Reflow Processing

4

Wafer level assembly 3D assembly Fine pitch where flux residue

removal is challenging

5

High device density Use where capillary

underfill materials face limitations

Dispensing

Die Placement Reflow Processing Post Cure or Additional Assembly

StepsOSCA-R Material

OSCA-R Process

OSCA-R materials enable assembly process simplification ( no need to clean flux residues )

Rheology Wetting & Flow Design

Cure Kinetics & Thermomechanical Design

6

Dispensing

Die Placement

Fluxing

Reflow Processing

Controlled Flow & Wetting

Filet Formation

Solder Wetting & Interconnection OSCA CuringAssembled Device

1/ Rheological Profile designed for Assembly

2/ Fluxing & Cure Kinetics balanced for appropriate sequencing

7

OSCA-R materials have a range of flow and functional requirements during processing

OSCA-R materials are multi functional reactive mixtures that thermally cure to a high performance thermoset polymer composite during reflow processing

FillersRheology

ColorDensity

Monomers Viscosity

Flow, tackWetting

Cure Chemistry

ActivatorsFluxing

Adhesion

HardenersViscosity Flow, tack

WettingCure Chemistry

Monomers Cross Links

Tg, CTEModulusAdhesion

Hardeners & ActivatorsCross Links

Thermal StabilityTg, CTEModulusAdhesion

FillersCTE

ModulusHardness

ToughnessThermal Conductivity

ReliabilityMoisture Resistance

Thermal Cure

CatalystCure Kinetics

1k Liquid MaterialHigh Tg Polymer Composite

Fluxing

OSCA-R materials have been investigated using a number device configurations

◦ Silicon & ceramics tend to have better outgassing than organics and lower voiding with OSCA-R materials

◦ Solder capped structures are found to exclude fillers from the joint during reflow

9

Organic Substrate Silicon Substrate

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

Cu pillar test vehicle used for OSCA-R evaluations

10

Wafer thickness = 0.75mm Die size = 6.35x 6.35mm. Two daisy chained arraysCentral Array 20x 20 bumps (400)Perimeter Array is 5x 70 bumps per side (1300) 128 interstitial bumps

Pitch = 80 microns Cu Pillar Height = Diameter = 40 micron 10 micron SnAg cap on pillarsCu Pad Diameter = 40 micronsCu Pad Height = 10 micron

OSCA-R materials designed for use with different dispense technologies

11

Time-Pressure Auger Jet

Optical Encoder

Voice-Coil Linear Motor

Material Piston

Removable Fluidic Module (houses wetted parts)

Yoke

Nozzle (Orifice)

Chamber

SmartStream

Shaft

A piston is used to displace the material from a chamber through a nozzle or needle.

O-Ring

Bumper

O-RingNut Seal

Positive Displacement Pump

SmartStreamTM

Time-Pressure PDP - Auger

NanoShotTM

Jet Dispense

1

10

100

0.01 0.1 1 10 100 1000

Vis

cosi

ty (

Pa-s

) at

25C

Shear Rate ( Hz )

Formation of Stable Droplets

Wetting & Flow Control During

dispenseNo Stringing

Controlled FlowPattern & Shape

Retention

Reology & Dispensing Behavior

Fluids with shear thinning / yield stress behavior meet patterning & flow control CTQs

12

1

10

100

0.01 0.1 1 10 100 1000

Vis

cosi

ty (

Pa-s

) at

25C

Shear Rate ( Hz )

Reology & Dispensing Behavior

OSCA-R materials have good jet dispensing characteristics and pattern retention

Controlled flow keeps materials out of “no-go” zones and avoids bleed out

13

OSCA-R Dispensed on Test Vehicle

OSCA-R materials designed to overcome key placement challenges

Traps voids

Air Escapes

Rebound (viscoelasticity)

Void Elimination

• Flow properties enable dispense pattern and void elimination

• Flow behavior during die placement under compression can complicate accurate die placement

14

OSCA-R materials designed to overcome key placement challenges and to be compatible with common placement technologies

15

Board Level Assembly

Flip Chip Assembly

R&D Bonder Thermo Compression Bonding

Using a Finetech die bonder system◦ Multi step placement procedure ensures die contact, and flow

High Speed

Low Speed0.5 to 3mm/sec

Dwell0.05 to 0.2 Sec

Force1 to 15 Nt

( 10x10 mm die )

Approach Step 1Approach Step 2

+ ContactApply Force

Hold Retract Placement

Tool

Change Over Distance 0.5 to 2 mm

High Speed

Make Contact with SubstrateDrive to Target z-position

Depends on Deposit Profile & Die Size / Shape

16

Timing kinetics of fluxing, solder melting, interconnection and cure

17

0

50

100

150

200

250

0 60 120 180 240

Tem

pera

ture

( oC

)

Time ( seconds )

Fluxing

Solder Wetting & Interconnection

OSCA Curing

Assembled Device

OSCA-R cure kinetics tunable to meet a given reflow profile Ensure fluxing, interconnection and cure occur in the proper

sequence and at desired times during reflow

18

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

50

100

150

200

250

300

0 100 200 300

Frac

tion

al C

onve

rsio

n

Tem

pera

ture

(oC)

Time ( sec )

Temperature

Conversion

TAL

BD Model Parameter

Definition Units Unfilled, 0% Filled, 40%

NReaction

order-- 0.4 0.6

EActivation

EnergykJ/mol 44 52

Log ( Z ) Pre Factor 1/min 3.9 4.9

HReaction Enthalpy

J/g 360 235

Reaction Kinetics Modeling via DSC

Examples of reflow profiles used to assemble devices with OSCA-R materials

19

0

50

100

150

200

250

300

0 20 40 60 80 100120140160180200220240260280300320340360

Tem

pera

ture

(oC)

Time (sec)

1 2 3 Range of profiles for different assembly applications

Illustration of relationship between placement voids and ORCA-R rheology design

20

(a)

(b)

1

10

100

0.01 0.1 1 10 100 1000

Vis

cosi

ty (

Pa-s

) at

25C

Shear Rate ( Hz )

0

50

100

150

200

250

300

0 20 40 60 80 100120140160180200220240260280300320340360

Tem

pera

ture

(oC)

Time (sec)

Successful assembly of devices with copper pillar features using conventional reflow processing and OSCA-R materials

21

Property (method) Units A B C DFiller % Wt% 40 55 0 40Filler Size micron 0.5 0.5 5Tg (a) °C 159 125 116 125CTE-1 (a) ppm/K 46 36 68 49CTE-2 (a) ppm/K 138 117 212 163H (b) J/g 235 165 348 212T-onset (b) °C 129 118 160 157T-peak (b) °C 197 162 204 203Viscosity(c) Pa-s 49 26 2.6 6.8Viscosity(d) Pa-s 14 40 2.6 6.7STI (e) Ratio 3.5 0.5 1.0 1.1Yield Stress (f) Pa 2 0 0 0Temperature Thinning (g) Kelvin 2200 7300 5000 6900

Flo

w

22

Rheology, viscosity, flow properties tunable for target dispensing/flow during die placement, cure kinetics and thermomechanical properties

Th

ermo

.C

ure

One Step Chip Attach (OSCA-R) materials can be used to assemble devices with copper pillar features using convection or conduction mass reflow◦ Single die devices assembled in this work◦ Can be extended to wafer level◦ Can be used for 3D assembly◦ Device density increase, close placement◦ Approach reduces complexity of manufacturing with respect to

conventional processing◦ Higher throughput with use existing processing equipment

23

Approaches to overcoming the key technical challenges presented◦ Systematic studies of soldering, rheology cure kinetics

and used to design OSCA-R materials for dispensing and successful assembly

◦ Die and substrate size, configuration and type are integral considerations for OSCA-R materials and processing

24

Process integration is key to enabling OSCA-R materials◦ Chemistry matched to desired reflow processing◦ Rheology adjusted for dispensing and die placement

process

25

Kester Inc. David Eichstadt, Maulik Shah, Chris Klimaszewski, Jim Lowe, Kal Chokshi

ITW Innovation Center Marina Litvinsky Research Triangle Institute, NC. Chris Gregory, Alan

Huffman TA-Instruments Gregory Kamykowski PhD, Kushal

Modi Finetech Neil O’Brian, Adrienne Gerard, Wade Gay Sonoscan Michelle Forbes

26

Thank You for Your Attention

Questions?

27