Master Defense
Christoph Pluess
Oregon State University
Corvallis
September 10, 2004
Application of Controlled
Thermal Expansion in
Diffusion Bonding for the
High-Volume Microlamination
of MECS Devices
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 Table of Contents
 Introduction
 Literature & Patent Review
 Theoretical Concept & Device Design
 Finite Element Analysis (FEA)
 Experimental Approach
 Results & Conclusions
 Questions & Discussion
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 Introduction
Bulk m-Fluidic Devices
(MECS)
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 Introduction
Microlamination (Paul et al.,
1999)
Patterning
• Laser Micromachining
• Chemical Etching
Registration

• Pin Alignment
• TEER (Thermal Enhanced Edge
Registration)
t
p
T
p
Bonding
• Diffusion
Bonding
• Diffusion
Brazing
OSU Device
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 Introduction
Why is this topic relevant?
Example: Solid-State Diffusion Bonding within a
Vacuum Hot Press
Vacuum Hot Press,
Nano/Micro Fabrication Facility
 Production
Capability:
• Pump-down:
0.75-1h
• Ramp-up: 0.75-1h
• Bonding: 0.5-1h
• Cool-down: 2-3h
Cycle Time: 4-6h
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 Introduction
Why is this topic relevant?
Example: Solid-State Diffusion Bonding within a
Vacuum Hot Press
 Device Size:
• Large Substrate MECS
Devices
• Large Hot Press System ($)
• Pressure Uniformity
Vacuum Hot Press,
Nano/Micro Fabrication Facility
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 Introduction
Using thermal expansion? Possible solution?
Conveyor Furnace “Sequoia”,
MRL Industries
DCTE Fixture
• DCTE, free source of
pressure
• low expanding frame
• high expanding inner parts
Continouous Furnace
System
• Similar to microelectronics
industry
• high-volume microlamination
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 Introduction
DCTE Bonding Fixture
• Is this a plausible approach for microlamination?
• Can a particular fixture design provide control over:
• Pressure magnitude?
• Pressure timing?
• Pressure sensitivity?
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 Literature & Patent Review
Is this idea unique?
• Use of thermal expansion for pressure application
first stated by PNNL in 1999
• Most papers/publications try to minimize effects of
thermal expansion
• Patents where thermal expansion is used to apply
pressure/force:
• Clamping ring for wafers
• Belt press using DCTE
US 5,460,703 (1995)
US 6,228,200 (2001)
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 Literature & Patent Review
Is this idea unique?
Patent Application Publication US 2003/0221777 A1
McHerron et al.
International Business Machines Corp. (IBM)
Method and Apparatus
for Application of
Pressure to a Workpiece
by Thermal Expansion
 2003, McHerron, IBM
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 Literature & Patent Review
IBM Patent Application
• Lamination of multilayer thin film structures (MLTF)
• Use for continuous production and high throughput
• Reduction of capital expenditures for lamination of
MLTF
• Is this a plausible approach for microlamination?
• Can a particular fixture design provide control
over:
• Pressure magnitude?
• Pressure timing?
• Pressure sensitivity?
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 Theoretical Model
Theoretical Study and Model Development
Gap closure
function:
Resulting strain in zdirection:
Resulting pressure in zdirection :
g (T )  g0  Dz(T )  g0  (e,i  ze,i   f ,i  z f ,i )  (T  TR )
 total 
g (TB )
h f  Dz f (TB )
 lam   total  Elam
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 Theoretical Model
Sensitivity
Analysis
Applying reasonable material
properties and sizes:
• initial gap variations of 1mm  pressure change 1.6 MPa
assumed accuracy with feeler gage 5mm  8.0
MPa
Geometrical Sensitivity: 1.6 MPa/mm
• temperature fluctuations of 5°C  pressure change 4.7
MPa
Thermal Sensitivity: 0.94 MPa/°C
• Lowering thermal sensitivity  increases geometrical
sensitivity
• Lowering geometrical sensitivity  increases thermal
sensitivity
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 Fixture Concept
Pressure Timing:
Initial gap adjustment
Low expanding
fixture frame
High expanding
engagement block
Pressure Magnitude:
Preloading and force
storage with spring
elements
Pressure Sensitivity:
Spring constant
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 Fixture Design
Fixture
Frame:
Initial gap
setting
Inner
Parts:
Load
Cell
Bonding
Platens
Inconel
Disc Springs
Engagemen
t Block
Cu
Laminae
• Designed to fit in hot press ( 3”)
• Max. service temperature 800°C
• Bonding area 25x25mm (2
stations)
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 Fixture Model (FEM)
Purpose of FE-Model
• Validation of developed fixture design
• Proof of feasibility
• Theoretical assessment of pressure
magnitude, timing and sensitivity
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 Fixture Model (FEM)
Expansion Behavior (in zdirection)
• gap closure
function:
Dz gap 
Dze (T ) Dz f (T )

 1.056mm / C  0.665mm / C  0.391mm / C
DT
DT
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 Fixture Model (FEM)
p-Timing, p-Magnitude, p-Sensitivity
D FEM (T ) 
Dp  0.13MPa

 0.0065MPa / C
DT
 20C
• 150 times less sensitive
than simple fixture model
(0.94MPa/°C)
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 Fixture Simulation
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 Experimental
DCTE-Fixture
Prototype
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 Experimental
Experimental Overview
Validation Experiments
Test Article Orientation
Means and 95.0 Percent Confidence Intervals
5.2
4.7
Deflection
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4.2
3.7
3.2
2.7
0
90
Orientation
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 Experimental
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
• Theoretical: 10’960 N/mm
• Practical: 11’215 N/mm (+2.3%)
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 Experimental
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
• Fuji Pressure Sensitive
Film
before:
3.0
3.5
4.0
4.5
5.0
5.5
6.0
MPa
after:
3.0
3.5
4.0
4.5
5.0
5.5
6.0
MPa
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 Experimental
Experimental Overview
Validation Experiments
DT
0°
C
300°C
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
400°C
p-Timing during Lamination
600°C
800°C
• Experimental
• Theoretical (FEM)
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 Experimental
Experimental Overview
Validation Experiments
• At low temperature
(180°C):
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing during Lamination
p-Timing of DCTE-Fixture
g0=0mm
g0=30mm
g0=50mm
g0=70mm
• T-limit of Fuji film 180°C
• No contact situation with g0 >
63mm based on theoretical model
• Experimental validation of DCTEFixture at low temperature!
• Uniform pressure distribution
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 Experimental
• T-profile optimization by
Experimental Overview connecting TC directly to
temperature control unit:
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing during Lamination
• Furnace cool down
optimization with helium
cooling:
p-Timing of DCTE-Fixture
TC Measurements
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 Experimental
Experimental Overview
Validation Experiments
Final Experiment
Test Article Orientation
Fin warpage (timing)
Load Cell Validation
Void fraction (p-magnitude)
p-Uniformity Bonding Platens
p-Timing during Lamination
DCTEFixture
Hot
Press
p-Timing of DCTE-Fixture
vs.
TC Measurements
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 Experimental
DOE Final Experiment
• 24 full-factorial design with 1 replicate (32 runs)
• Mode: Hot Press / Fixture
• Pressure: 3 MPa / 6 MPa
• Temperature: 500°C / 800°C
• Time: 30’ / 60’
• 2 samples each run for a total of 64 test samples
32
32
• ANOVA on fin warpage (128
measurements)
• ANOVA on void fraction (160
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 Results
ANOVA Fin Warpage
• No statistical significant difference observed (p-value
0.92)
3.99 mm  0.44 mm
• Average fin warpage hot press:
• Average fin warpage DCTE-fixture: 4.02 mm  0.44 mm
Means and 95.0 Percent Confidence Intervals
Interactions and 95.0 Percent Confidence Intervals
5.6
4.5
Pressure
3
6
5.1
Warpage
4.3
Warpage
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4.1
3.9
3.7
4.6
4.1
3.6
3.1
2.6
3.5
Fixture
Hot Press
Mode
Fixture
Hot Press
Mode
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 Results
Void Fraction Inspection
• Metallographic preparation of the 16 samples
• 10 inspection locations for each DB set (160
measurements)
• Voids were marked on a
transparency at 384X
• Calculation of void fractions
(reference length 250 mm)
vf 
l
void
l0
 100%
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 Results
Metallographic Pictures Bond Lines (Void Shrinkage)
Hot Press
DCTEFixture
500°C
3 MPa
60 min
78.8%
70.5%
15.8%
23.2%
8.0%
9.6%
800°C
3 MPa
60 min
800°C
6 MPa
60 min
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 Results
ANOVA & Table of Means for Void Fraction
Bonding
Conditions
Void
Fraction
Hot Press
S.D.
Void
Fraction
Fixture
S.D.
500°C/3MPa/30min
100.0%
0%
100.0%
0%
500°C/3MPa/60min
78.8%
8.4%
70.5%
8.7%
500°C/6MPa/30min
65.7%
10.3%
80.0%
6.2%
500°C/6MPa/60min
35.9%
12.0%
62.0%
7.3%
800°C/3MPa/30min
20.1%
6.9%
30.3%
10.3%
800°C/3MPa/60min
15.8%
9.5%
23.2%
4.2%
800°C/6MPa/30min
15.5%
3.7%
19.5%
8.5%
800°C/6MPa/60min
8.0%
2.4%
9.6%
2.8%
42.5%
6.7%
49.4%
6.0%
Overall
Means and 95.0 Percent Confidence Intervals
52
Void Fraction
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50
48
46
44
42
40
Fixture
Hot Press
Mode
• Statistical significant difference observed
• Since T & t are equal, variation is due to pressure applied
 2004 Christoph Pluess
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 Results
ANOVA for Void Fraction (Interactions)
• Less significant difference at low pressures
(frame stiffness maintained)
• Less significant differences at high temperatures
(void fraction less pressure sensitive at high temp.)
68
Pressure
3
6
58
48
38
28
Interactions and 95.0 Percent Confidence Intervals
100
Void Fraction
Interactions and 95.0 Percent Confidence Intervals
Void Fraction
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Temperature
500
800
80
60
40
20
0
Fixture
Hot Press
Mode
Fixture
Hot Press
Mode
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 Results
Comments
• Timing of pressure within the DCTE-fixture did not show
any problems
• Although void fractions showed a difference, bond quality
is comparable
• Source of p-variation due to the use of high expanding
stainless steel bolts (potential loss of preload)
• Level of pressure was dampened due to spring
implementation in frame (loss of rigidity)
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 Conclusions
• Is this a plausible approach for
microlamination?
 yes
• Can a particular fixture design
provide control over:
( yes)
• Pressure magnitude?
• Pressure timing?
• Pressure sensitivity?
 yes
 yes
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 Future Research
• DCTE-Fixture design for large substrates
• Validation of large substrate fixture design with
FEM:
• Structural, p-uniformity
• Thermal, T-gradients
• Process optimization for continuous production
line
• Experimental investigation of large substrate
 2004 Christoph Pluess
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 Questions & Discussion
Thanks for your
attention!
M.S. Defense Presentation
Christoph Pluess
September 10th 2004
Oregon State University
Corvallis
USA
Special thanks to:
Major Professor Dr. Brian K. Paul
Committee Members:
Dr. Sundar V. Atre
Dr. Kevin M. Drost
Dr. Timothy C. Kennedy
Dr. Zhaohui Wu
 2004 Christoph Pluess
 Additional Slides
 2004 Christoph Pluess
 Experimental
First DCTE-Prototype
• 7 MPa at 800°C
• 5 Cu-layers bonded: 02/20/2004
• 1st successful DCTE-bond
 2004 Christoph Pluess
 Fixture Model (FEM)
FE-Model Features (ANSYS)
• ¼ model
6655 elements (17’000 nodes)
• LINK10 prevented use of contact
elements
• One solid structure (SOLID95)
• Spring constant, initial gap, preload
of load cell defined over real
constants
• Input of bonding parameters over
Scalar Parameter Menu
• Automatic load step definition and
execution with APDL-macro
 2004 Christoph Pluess
 FE-Model Settings
Real Constant Settings
Bonding Data Input
Room Temperature
20
Bonding Temperature
200
Temperature of Contact
200
Bonding Area (Test Article)
625
Desired Bonding Pressure
4.0
°C
°C
°C
mm2
MPa
CTE Fixture Data Output: Preload Load Cell
Active Warpage Temperature Range
0
Load Cell Force at Bonding Temperature
2500
Load Cell Force at Contact Temperature
2500
Load Cell Force at Room Temperature
3034
Preload Force (Hot Press)
682
CTE Fixture Data Input
CTE Fixture Data Output: Initial Gap
Gap Closure Function
0.391 mm/°C Additional Load Cell Compression
-49
CTE Load Cell Fasteners
16.2 10-6/°C Spring Constant per Stack
2740
CTE Load Cell Platens
6.5 10-6/°C Active Force per Spring Stack at Room T.
758
Active Expanding Bolt Length 16.7
mm
Active Force per Spring Stack at Contact
625
Thickness Load Cell Top
mm
Active Force per Spring Stack at Bonding T.
625
Tensile Stress Area Bolt
20.5
mm2
Tensile Stress of Bolts at Room Temp.
37
Nominal Load Disc Spring
800
N
Tensile Stress of Bolts at Contact Temp.
30
Nominal Compression D.S.
0.292
mm
Load Cell Compression at Room Temp.
277
Number of Springs per Stack
1
Load Cell Compression at Contact Temp.
228
Number of Spring Stacks
4
Load Cell Compression at Bonding Temp.
228
Expansion Potential CTE Fixture
70
Active CTE Compression of Load Cell
0
Starting Pressure at Contact Temperature
4.0
Pressure Sensitivity CTE Fixture in f(T)
0.0069
Pressure Sensitivity CTE Fixture in f(z)
0.0175
Adjustable Initial Gap
70
FEM Model Data Input
Element Length LINK10 (T.o.) 13.668
Element Length LINK10 (C.o.) 7.332
mm
mm
°C
N
N
N
lbs
mm
N/mm
N
N
N
MPa
MPa
mm
mm
mm
mm
mm
MPa
MPa/°C
MPa/mm
mm
FEM Model Data Output: Real Constant Settings
ISTRN Value for LINK10 (Tension only)
0.02025
277
ISTRN Value for LINK10 (Compr. only)
-0.02816
-206
Important Comments
Check with fin buckling limit equation!
Min. adjustable load of hot press is 400 lbs
(+): add. compression / (-): relaxation
Flat load of disc springs 1620 N
Flat load of disc springs 1620 N
Flat load of disc springs 1620 N
Max. stress limit of ceramic bolts 55 MPa
Max. stress limit of ceramic bolts 55 MPa
>nominal compression, increase # of springs
RC Set #3, Element Type 5 (Fasteners)
RC Set #4, Element Type 6 (Set Screw)
 2004 Christoph Pluess