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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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla 2
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• 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
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IEEE 65th ECTC – San Diego, CA, USA
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla 7
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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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
Wetting & Flow Control During
Dispense
Clean ReleaseNo Stringing
Controlled FlowPattern & Shape
Retention
Controlled Flow from
Needle
PDP Jet
Formation of Stable Droplets
Wetting & Flow Control During
dispenseNo Stringing
Controlled FlowPattern & Shape
Retention
Performance Considerations During Dispense
11
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
• 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
Wetting & Flow Control During
dispense No Stringing
Controlled Flow Pattern & Shape
Retention
Reology & Dispensing Behavior
13
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
• 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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla 19
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• 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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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IEEE 65th ECTC – San Diego, CA, USA
May 26 – 29, 2015 D. Duffy, M. Desai, H. Bhavsar, J. Liu, L. Xin, B. Tolla
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
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