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Application of ControlledThermal Expansion inDiffusion Bonding for theHigh-Volume Microlaminationof MECS Devices
Christoph PluessOregon State University
Corvallis
September 10, 2004
Master Defense
Table of Contents
2004 Christoph Pluess
Literature & Patent Review
Questions & Discussion
Theoretical Concept & Device Design
Introduction
Results & Conclusions
Experimental Approach
Finite Element Analysis (FEA)
1of 36
Introduction
2004 Christoph Pluess
Bulk -Fluidic Devices (MECS)
2of 36
Introduction
2004 Christoph Pluess
Microlamination (Paul et al., 1999)
Patterning• Laser Micromachining• Chemical Etching
Bonding• Diffusion Bonding• Diffusion Brazing
Registration• Pin Alignment• TEER (Thermal Enhanced Edge Registration)
p
p
T
t
OSU Device
3of 36
Introduction
2004 Christoph Pluess
Why is this topic relevant?
Example: Solid-State Diffusion Bonding within a Vacuum Hot Press
Vacuum Hot Press, Nano/Micro Fabrication Facility
• Pump-down: 0.75-1h• Ramp-up: 0.75-1h• Bonding: 0.5-1h• Cool-down: 2-3hCycle Time: 4-6h
Production Capability:
4of 36
Introduction
2004 Christoph Pluess
Why is this topic relevant?
Example: Solid-State Diffusion Bonding within a Vacuum Hot Press
• Large Substrate MECS Devices• Large Hot Press System ($)• Pressure Uniformity
Device Size:
5of 36
Vacuum Hot Press, Nano/Micro Fabrication Facility
Introduction
2004 Christoph Pluess
Using thermal expansion? Possible solution?
CTE Fixture• CTE, free source of pressure• low expanding frame• high expanding inner parts
Continouous Furnace System• Similar to microelectronics industry• high-volume microlamination
Conveyor Furnace “Sequoia”,MRL Industries
6of 36
Introduction
2004 Christoph Pluess
CTE Bonding Fixture
• Is this a plausible approach for microlamination?
• Can a particular fixture design provide control over:
• Pressure magnitude?
• Pressure timing?
• Pressure sensitivity?
7of 36
Literature & Patent Review
2004 Christoph Pluess
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 US 5,460,703 (1995)• Belt press using CTE US 6,228,200 (2001)
8of 36
Literature & Patent Review
2004 Christoph Pluess
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
9of 36
Literature & Patent Review
2004 Christoph Pluess
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?
10of 36
Theoretical Study and Model Development
Theoretical Model
2004 Christoph Pluess
)()()()( ,,,,00 Rififieie TTzzgTzgTg Gap closure function:
)(
)(
Bff
Btotal Tzh
Tg
Resulting strain in z-
direction:Resulting pressure in z-direction :
lamtotallam E
11of 36
Sensitivity Analysis
Theoretical Model
2004 Christoph Pluess
Applying reasonable material properties and sizes:
• initial gap variations of 1m pressure change 1.6 MPa
assumed accuracy with feeler gage 5m 8.0 MPa
Geometrical Sensitivity: 1.6 MPa/m
• 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
12of 36
Fixture Concept
2004 Christoph Pluess
Low expanding fixture frame
High expanding engagement block
Pressure Timing:Initial gap adjustment
Pressure Sensitivity:Spring constant
Pressure Magnitude:Preloading and force storage with spring elements
13of 36
Fixture Design
2004 Christoph Pluess
Fixture Frame:
Inner Parts:
•Designed to fit in hot press ( 3”)
•Max. service temperature 800°C
•Bonding area 25x25mm (2 stations)
Initial gap
setting
Load Cell
Bonding
Platens
Engagement Block
Cu Laminae
InconelDisc Springs
14of 36
Fixture Model (FEM)
2004 Christoph Pluess
Purpose of FE-Model
•Validation of developed fixture design
•Proof of feasibility
•Theoretical assessment of pressure magnitude, timing and sensitivity
15of 36
Fixture Model (FEM)
2004 Christoph Pluess
Expansion Behavior (in z-direction)
CmCmCmT
Tz
T
Tzz fegap
/391.0/665.0/056.1
)()( • gap closure function:
16of 36
Fixture Model (FEM)
2004 Christoph Pluess
p-Timing, p-Magnitude, p-Sensitivity
CMPaC
MPa
T
pTFEM
/0065.020
13.0)(
•150 times less sensitive than simple fixture model (0.94MPa/°C)
17of 36
Fixture Simulation
2004 Christoph Pluess
18of 36
ExperimentalCTE-FixturePrototype
2004 Christoph Pluess
19of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Means and 95.0 Percent Confidence Intervals
Orientation
De
flect
ion
0 902.7
3.2
3.7
4.2
4.7
5.2
20of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
• Theoretical: 10’960 N/mm
• Practical: 11’215 N/mm (+2.3%)
21of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
• Fuji Pressure Sensitive Film
22of 36
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
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing during Lamination
• Experimental
• Theoretical (FEM)
0°C300°C
400°C
600°C
800°C
T
23of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing of CTE-Fixture
p-Timing during Lamination
•T-limit of Fuji film 180°C
•No contact situation with g0 > 63m based on theoretical model
•Experimental validation of CTE- Fixture at low temperature!
•Uniform pressure distribution
• At low temperature (180°C):
g0=0m
g0=30m
g0=50m
g0=70m
24of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing of CTE-Fixture
p-Timing during Lamination
•T-profile optimization by connecting TC directly to temperature control unit:
TC Measurements
•Furnace cool down optimization with helium cooling:
25of 36
Experimental
2004 Christoph Pluess
Experimental Overview
Validation Experiments Final Experiment
Hot Press
CTE-Fixture
vs.vs.
Fin warpage (timing)
Void fraction (p-magnitude)
Test Article Orientation
Load Cell Validation
p-Uniformity Bonding Platens
p-Timing of CTE-Fixture
p-Timing during Lamination
TC Measurements
26of 36
Experimental
2004 Christoph Pluess
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
• ANOVA on fin warpage (128 measurements)
• ANOVA on void fraction (160 measurements)
32 32
27of 36
Results
2004 Christoph Pluess
ANOVA Fin Warpage
Means and 95.0 Percent Confidence Intervals
Mode
War
page
Fixture Hot Press3.5
3.7
3.9
4.1
4.3
4.5
Interactions and 95.0 Percent Confidence Intervals
Mode
War
page
Pressure36
2.6
3.1
3.6
4.1
4.6
5.1
5.6
Fixture Hot Press
•No statistical significant difference observed (p-value 0.92)
•Average fin warpage hot press: 3.99 m 0.44 m
•Average fin warpage CTE-fixture: 4.02 m 0.44 m
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Results
2004 Christoph Pluess
Void Fraction Inspection
•Metallographic preparation of the 16 samples
•10 inspection locations for each DB set (160 measurements)
•Voids were marked on atransparency at 384X
•Calculation of void fractions(reference length 250 m)
%1000
l
lv
voidf
29of 36
Results
2004 Christoph Pluess
Metallographic Pictures Bond Lines (Void Shrinkage)
500°C3 MPa60 min
800°C3 MPa60 min
800°C6 MPa60 min
Hot Press CTE-Fixture
8.0%
9.6%
15.8% 23.2%
78.8%
70.5%
30of 36
Means and 95.0 Percent Confidence Intervals
Mode
Voi
d F
ract
ion
Fixture Hot Press40
42
44
46
48
50
52
Results
2004 Christoph Pluess
ANOVA & Table of Means for Void Fraction
BondingConditions
Void Fraction
Hot PressS.D.
Void FractionFixture
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%
Overall 42.5% 6.7% 49.4% 6.0%
•Statistical significant difference observed
•Since T & t are equal, variation is due to pressure applied
31of 36
Results
2004 Christoph Pluess
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.)
Interactions and 95.0 Percent Confidence Intervals
Mode
Vo
id F
ract
ion
Pressure36
28
38
48
58
68
Fixture Hot Press
Interactions and 95.0 Percent Confidence Intervals
Mode
Vo
id F
ract
ion
Temperature500800
0
20
40
60
80
100
Fixture Hot Press
32of 36
Results
2004 Christoph Pluess
Comments
• Timing of pressure within the CTE-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)
33of 36
•Is this a plausible approach for microlamination?
•Can a particular fixture design provide control over:
• Pressure magnitude?
• Pressure timing?
• Pressure sensitivity?
Conclusions
2004 Christoph Pluess
( yes)
yes
yes yes
34of 36
Future Research
2004 Christoph Pluess
• CTE-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 bonding
35of 36
Thanks for your attention!M.S. Defense Presentation
Christoph Pluess
September 10th 2004
Oregon State UniversityCorvallis
USA
Special thanks to:Major Professor Dr. Brian K. Paul
Committee Members:Dr. Sundar V. AtreDr. Kevin M. Drost
Dr. Timothy C. KennedyDr. Zhaohui Wu
Special thanks to:Steven Etringer
Questions & Discussion
2004 Christoph Pluess
36of 36
Additional Slides
2004 Christoph Pluess
Experimental
2004 Christoph Pluess
First CTE-Prototype
• 7 MPa at 800°C
• 5 Cu-layers bonded: 02/20/2004
• 1st successful CTE-bond
Fixture Model (FEM)
2004 Christoph Pluess
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
FE-Model Settings
2004 Christoph Pluess
Real Constant Settings
Important CommentsRoom Temperature 20 °C Active Warpage Temperature Range 0 °C Check with fin buckling limit equation!Bonding Temperature 200 °C Load Cell Force at Bonding Temperature 2500 NTemperature of Contact 200 °C Load Cell Force at Contact Temperature 2500 N
Bonding Area (Test Article) 625 mm2 Load Cell Force at Room Temperature 3034 NDesired Bonding Pressure 4.0 MPa Preload Force (Hot Press) 682 lbs Min. adjustable load of hot press is 400 lbs
Gap Closure Function 0.391 m/°C Additional Load Cell Compression -49 m (+): add. compression / (-): relaxation
CTE Load Cell Fasteners 16.2 10-6/°C Spring Constant per Stack 2740 N/mm
CTE Load Cell Platens 6.5 10-6/°C Active Force per Spring Stack at Room T. 758 N Flat load of disc springs 1620 NActive Expanding Bolt Length 16.7 mm Active Force per Spring Stack at Contact 625 N Flat load of disc springs 1620 NThickness Load Cell Top mm Active Force per Spring Stack at Bonding T. 625 N Flat load of disc springs 1620 N
Tensile Stress Area Bolt 20.5 mm2 Tensile Stress of Bolts at Room Temp. 37 MPa Max. stress limit of ceramic bolts 55 MPaNominal Load Disc Spring 800 N Tensile Stress of Bolts at Contact Temp. 30 MPa Max. stress limit of ceramic bolts 55 MPaNominal Compression D.S. 0.292 mm Load Cell Compression at Room Temp. 277 m >nominal compression, increase # of springsNumber of Springs per Stack 1 Load Cell Compression at Contact Temp. 228 mNumber of Spring Stacks 4 Load Cell Compression at Bonding Temp. 228 m
Expansion Potential CTE Fixture 70 mActive CTE Compression of Load Cell 0 mStarting Pressure at Contact Temperature 4.0 MPaPressure Sensitivity CTE Fixture in f(T) 0.0069 MPa/°CPressure Sensitivity CTE Fixture in f(z) 0.0175 MPa/m
Adjustable Initial Gap 70 m
Element Length LINK10 (T.o.) 13.668 mm ISTRN Value for LINK10 (Tension only) 0.02025 277 RC Set #3, Element Type 5 (Fasteners)Element Length LINK10 (C.o.) 7.332 mm ISTRN Value for LINK10 (Compr. only) -0.02816 -206 RC Set #4, Element Type 6 (Set Screw)
FEM Model Data Input
Bonding Data Input
CTE Fixture Data Input
CTE Fixture Data Output: Preload Load Cell
CTE Fixture Data Output: Initial Gap
FEM Model Data Output: Real Constant Settings