new rheology design considerations for one step chip attach … base... · 2016. 6. 1. · ieee...

IEEE 65th ECTC – San Diego, CA, USA May 26–29, 2015

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Rheology Design Considerations for One Step Chip Attach Materials (OSCA) used for Conventional Mass Reflow Processing

D. Duffy, M. Desai, H. Bhavsar L. Xin, J. Liu, B. Tolla

Kester Inc. Itasca, IL 60143

2


IEEE 65th ECTC – San Diego, CA, USA

May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla 2


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

• OSCA Materials for Reflow Processing ( OSCA-R ) – OSCA-R Material Design – Rheology Design for Jet Dispense – Forces During Die Placement

– Compression & Squeeze Flow Rheology – High TC OSCA-R, Interconnected Assemblies

• Summary & Conclusions • Acknowledgements

Agenda / Outline / Overview

3



May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla

Conventional Flip Chip Assembly Process

New and Improved Process Flow

Flux / Chip Place Reflow De-flux Underfill Post Cure

Flux & Die Placement

Reflow

Cleaning

Post Cure Underfill

Underfill

4




Why Use a One Step Chip Attach (OSCA-R) ?

• OSCA-R Materials Enable OSCA Process – Process Simplification + Throughput

Dispense OSCA-R

Place Die

Next Process

Step

Dispense OSCA-R Die Placement Conventional Reflow Processing

5




Dispensing Die Placement Reflow Processing Post Cure or Additional Assembly

Steps OSCA-R Material

OSCA-R Process

• OSCA-R Materials Enable OSCA Process – Process Simplification + Throughput

Why Use a One Step Chip Attach (OSCA-R) ?

Rheology Wetting & Flow Design

Cure Kinetics & Thermomechanical Design

6




One Step Chip Attach Process & Materials

Dispensing

Die Placement

Fluxing

Reflow Processing

Controlled Flow & Wetting

Filet Formation

Solder Wetting & Interconnection OSCA Curing Assembled Device

1/ Rheological Profile designed for Assembly

2/ Fluxing & Cure Kinetics balanced for appropriate sequencing

• Key formulation design considerations for OSCA-R materials – Rheology/flow for dispensing and die placement – Balance of fluxing & cure chemistry during reflow processing – Final cured properties, interconnection and reliability

7





OSCA-R Material Design

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

Fillers Rheology

Color Density

Monomers Viscosity

Flow, tack Wetting

Cure Chemistry

Activators Fluxing

Adhesion

Hardeners Viscosity Flow, tack Wetting

Cure Chemistry Monomers Cross Links

Tg, CTE Modulus Adhesion

Hardeners & Activators Cross Links

Thermal Stability Tg, CTE Modulus Adhesion

Fillers CTE

Modulus Hardness

Toughness Thermal Conductivity

Reliability Moisture Resistance

Thermal Cure ∆

Catalyst Cure Kinetics

1k Liquid Material High Tg Polymer Composite

Fluxing

8




One Step Chip Attach Process & Materials

Dispensing

Die Placement

Controlled Flow & Wetting

Filet Formation

1/ Rheological Profile designed for Assembly

• Filled system that can dispense by auger or jet

• Stays where it is intended to after dispense

• Retains dispense pattern

• Presents proper height profile

• Yields and flows during die placement

• Maintains alignment, no die floating, drift or tilt

• No placement voids

• Forms fillet and remains in intended area after placement

• Flows during reflow to allow wetting and interconnection

• Design Considerations ( CTQs )

9




OSCA-R Rheology Design – Die Placement

• 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

10




Wetting & Flow Control During

Dispense

Clean ReleaseNo Stringing

Controlled FlowPattern & Shape

Retention

Controlled Flow from

Needle

PDP Jet

Formation of Stable Droplets


dispenseNo Stringing

Controlled FlowPattern & Shape

Retention

Performance Considerations During Dispense

11




OSCA-R Rheology Design - Dispensing

• OSCA-R materials designed for compatibility with different dispense processes

Time-Pressure Auger Jet

oder

or

Pisto

ble Module

wetted parts)

Yoke

e (Orifice)

Chamb

Shaft

O-R

Bump

O-Nut S

SmartStreamTM

Assembly Equipment R&D Equipment

Finetech Asymtek NanoShotTM

Speedline

Assembly Equipment

12




• Both fluids jet dispensable but fluid with shear thinning behavior meets patterning & post dispense flow control CTQs

1

10

100

0.01 0.1 1 10 100 1000

Visc

osity

( Pa

-s )

at 2

5C

Shear Rate ( Hz )

Formation of Stable Droplets


dispense No Stringing

Controlled Flow Pattern & Shape

Retention

Reology & Dispensing Behavior

13




Properties of OSCA-R Materials

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

• Comparison of OSCA-R properties – Rheology, viscosity, flow properties related to dispensing and

flow during die placement

Flow Properties

14




Reology & Dispensing Behavior

• All three materials are jet dispensable – Material C, is near Newtonian

and continues to flow after dispense

– Material D, higher in viscosity but also Newtonian and flows after dispense

– Material A, with shear thinning behavior and a yield stress retains shape after dispense but will thin during die placement 1

10

100

1000

0.01 0.1 1 10 100

Visc

osity

( Pa

-s )

Shear Rate ( Hz )

OSCA-R, Material C

OSCA-R, Material D

OSCA-R, Material A

b.Material A

Material C

Material D

15




Rheology & Dispensing Behavior

• Highly filled materials can exhibit shear thickening behavior – Thickening under shear

strain leads to poor jet dispensability

– Material showed excessive stringing at ambient temperature

– Increasing the jet dispense nozzle to 75C enabled jet dispensability 0.1

1

10

100

1000

0 50 100 150 200

Com

plex

Vis

cosi

ty (

Pa-s

)

Strain Amplitude ( % ) at f=1Hz

25 C

50 C

75 C

a.

25C

50C

75C

16




Jet Dispensing Trials; OSCA-R Materials

• OSCA-R formulation jet dispense performance – Rheology enables dispense pattern stability – No flow or bleeding after patterning, will shear thin during die placement – Rheology also enables tall z-profile of deposition

17




OSCA-R Rheology Design - Die Placement

• OSCA-R materials designed to overcome key placement challenges

Traps voids

Air Escapes

Rebound (viscoelasticity)

Placement Voids

Pick & Place

Kester Pilot Equipment

KE 1080 (±50 micron)

Production Equipment Advantis (25-50um)

Genesis SC (± 5-10um)

Juki Universal Kester

R&D Equipment

Finetech

18




• Material Factors – Rheology – Filler loading

• Process Factors – Temperature – Placement Speed – Peak Force – Dwell Time

• Component Factors – Die Area – Bump Pitch – Bump Configuration – Substrate Topology

Approach Contact

with OSCA-R

Compression and flow of

OSCA Contact with

substrate

Release

die

quill

substrate OSCA-R

Considerations During Die Placement

19





• Studies of compression forces using normal force transducer and a rheometer – Identify scaling behaviors and critical material properties

Experimental Compression Force Measurement

• abc

Parallel Plate Configuration

Fundamental Work

Die on Top Explore Effects of Die

Size, Bump Pitch, Bump Size,

Configuration

Die & Substrate Effects of Both Die

and Substrate

Use of Silicon-Silicon Test Vehicles

Effects on Inorganic Substrates

20




Analysis of Compression Force Curves

• Force versus distance measured during compression experiments and analyzed for several responses

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 500 1000 1500 2000 2500

Axia

l Com

pres

sion

For

ce (

Nt )

Z = Axial Compression Distance (micron)

F(0) = force at zero gap

Fmax = maximum force observed

( zo,Fo) = Onset

= rate of force build upRheometer Fixture

Rheometer Stage Temperature Controlled

OSCA-R

Axial Compression Distance (z)Compression Speed (dz/dt)

Terminal Gap (z*)

Normal (z-axis) Force

Transducer

21




Process and Material Variables Explored

Property Symbol Range

Compression Speed U = dZ/dt 5 - 500 microns/sec

Terminal Gap Z* 5 to 250 microns Fixture Area Ax 55 to 1200 mm2 Stage Temperature T 10 to 100C Filler Content Wt% 0 to 80wt%

Filler Type & Shape Silica, High TC Sphere, Plate, Rod

Filer Size < d > 0.5 to 20 micron

Shear Thinning Index STI 0.2 to 5

Temperature Thinning Ea 1000 to 8000 Kelvin

Process

Material (rheology)

22




Compressional Force Response to Terminal Gap & Placement Speed • Force increases with filler loading and decreases with

increasing temperature – Implies that compression forces can be moderated for highly filled

systems using mild stage heating ( 40 to 50C )

0

1

2

3

0 20 40 60 80

Max

. For

ce (

Nt )

Filler Loading ( wt % )

Overlay of 3 replicate data sets

0

2

4

6

8

10

0 20 40 60 80

Max

. For

ce (

Nt )

Filler Loading ( wt % )

10

25

40

Placement Temperature

( oC )

23




Compressional Force Response to Terminal Gap & Placement Speed

• Force increases as the terminal gap decreases and as placement speed increases – Implies placement conditions need to be adjusted for small features

0

4

8

12

16

20

0 50 100 150 200 250

Max

. For

ce (

Nt )

Terminal Gap ( micron )

60%40%

Filler Loading

0

2

4

6

8

0 25 50 75 100 125 150 175 200

Max

. For

ce (

Nt )

Velocity ( micron / sec )

60

Filler Loading( wt% )

24




Design of Placement Process

• Placement process studies conducted using Finetech die bonder system – Multi step placement procedure ensures die contact and alignment

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

25




Design of High TC OSCA-R Materials

• High thermal conductivity OSCA-R – High filler loading – Balance rheology for dispensing and

device placement – Design of cure kinetics for reflow

processing

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 10 20 30 40

Ther

mal

Con

duct

ivity

( W

/m-K

)

Viscosity ( Pa-s )

10 micron silica spheres

10 micron alumina spheres

10 micron BN plates

SiO2

Al2O3 BN

0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

Tem

pera

ture

(oC)

Time (sec)

26




Summary & Conclusions

• One Step Chip Attach (OSCA-R) materials can be used to eliminate steps in flip chip assembly processing using convection or conduction mass reflow – Reduced complexity of manufacturing – Higher throughput with use existing processing equipment

• Approaches to overcoming the key technical challenges presented – Systematic studies of rheology and filler effects on 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 process

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

27




Thank you for your attention

Questions?

• Acknowledgements • Kester Inc.

• David Eichstadt, Maulik Shah, Chris Klimaszewski, Jim Lowe, Kal Chokshi • ITW Innovation Center

• Marina Litvinsky • Research Triangle Institute, Research Triangle Park, NC.

• Chris Gregory, Alan Huffman • TA-nstruments

• Gregory Kamykowski PhD, Kushal Modi • Finetech

• Neil O’Brian, Adrienne Gerard, Wade Gay • Sonoscan

• Michelle Forbes

new rheology design considerations for one step chip attach … base... · 2016. 6. 1. · ieee...

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