STUDY ON THE NANOCOMPOSITE UNDERFILL FOR FLIP-CHIP APPLICATION
STUDY ON THE NANOCOMPOSITE UNDERFILL FOR FLIP-CHIP APPLICATION
A Thesis Presented to The Academic Faculty by Yangyang Sun
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in the
School of Chemistry and Biochemistry
Georgia Institute of Technology
December, 2006
TABLE OF CONTENTS
ACKNOWLEDGEMENTS III
TABLE OF CONTENTS V
LIST OF TABLES IX
LIST OF FIGURES XI
SUMMARY XVII
CHAPTER 1. INTRODUCTION 1
1.1. ELECTRONIC PACKAGING AND FLIP-CHIP TECHNOLOGY 1
1.1.1. Packaging technology development 1
1.1.2. Flip-chip technology 3
1.2. UNDERFILL MATERIALS AND NANO SIZE FILLER 5
1.2.1. Overview of underfill materials 5
1.2.2. Underfill classifications 7
1.2.3. Composition of epoxy underfill 10
1.2.4. Filler in the underfill 14
1.3. PARTICLE DISPERSION 18
1.3.1. Energy state of particle in the medium 18
1.3.2. Attractive force 19
1.3.3. Repulsive force 20
1.3.4. Filler stabilization in underfill 22
1.4. IMPACT OF NANOPARTICLES ON THE RHEOLOGY 25
1.4.1. Definition of viscosity 25
1.4.2. Einstein Equation for dilute suspension 27
1.4.3. Kreigher-Dougherty Equation for concentrated suspension 27
1.4.4. Particle size effect to viscosity 29
1.5. RESEARCH OBJECTIVES 31
CHAPTER 2. NANOSILICA SYNTHESIS AND MODIFICATION 34
2.1. SILICA SYNTHESIS 34
2.1.1. Pyrogenic silica 34
2.1.2. Sol-gel method 37
2.1.3. Size control of nanosilica by Stöber method 40
2.2. SURFACE MODIFICATION OF SILICA BY SILANE 44
2.2.1. Contact angle and surface wetting 44
2.2.2. Silane coupling agent 47
2.3. EXPERIMENT 49
2.3.1. Material 49
2.3.2. Surface tension measurement after treatment 50
2.3.3. Surface modification of nanosilica 51
2.3.4. Particle characterization 51
2.3.5. Underfill composite preparation and characterization 52
2.4. RESULTS AND DISCUSSION 53
2.4.1. Surface tension measurement of silicon dioxide after treatment 53
2.4.2. Optimal experimental conditions for nanosilica modification 57
2.4.3. Characterizations of treated nanosilica 64
2.4.4. Viscosity of nanocomposite no-flow underfill 71
CHAPTER 3. MATERIAL PROPERTIES CHARACTERIZATION OF THE
NANOCOMPOSITE UNDERFILL AFTER CURING 73
3.1. EXPERIMENTS 73
3.1.1. Materials 73
3.1.2. Underfill composite preparation 74
3.1.3. Underfill composite characterization 75
3.2. RESULTS AND DISCUSSIONS 77
3.2.1. Anhydride epoxy polymerization mechanism 77
3.2.2. Curing Behaviors and Tg of composite underfills 79
3.2.3. Rheological and optical behavior of composite underfills 81
3.2.4. Thermal mechanical properties 83
3.2.5. Moisture absorption and density measurement 86
3.2.6. Morphology 91
3.2.7. Wetting test 92
3.3. GLASS TRANSITION AND RELAXATION BEHAVIORS OF NANOCOMPOSITES 94
3.3.1. Experiments 95
3.3.2. Characterization 96
3.3.3. Results and discussion 97
CHAPTER 4. INFLUENCE OF INTERPHASE AND MOISTURE ON THE
DIELECTRIC SPECTROSCOPY OF EPOXY/SILICA COMPOSITES 108
4.1. DIELECTRIC PROPERTIES OF COMPOSITE MATERIALS 108
4.1.1. Theory and background 108
4.1.2. Existing dielectric study for composite material 112
4.1.3. Dielectric properties measurement 113
4.2. RESULTS AND DISCUSSIONS 114
4.2.1. Dielectric properties 114
4.2.2. TTS shifting of dielectric loss curve 116
4.2.3. Dielectric loss in composites 119
4.2.4. Moisture influence for dielectric properties 122
CHAPTER 5. THE HARDENER EFFECTS TO COLLOIDAL SILICA
DISPERSION 127
5.1. EXPERIMENT 128
5.1.1. Materials 128
5.1.2. Dynamic rheology 129
5.1.3. Dielectric constant of liquid sample 131
5.2. RESULTS AND DISCUSSIONS 131
5.2.1. Rheology measurement 131
5.2.2. Van der Waals interaction 137
CHAPTER 6. PHOTO-POLYMERIZATION OF EPOXY NANOCOMPOSITE FOR
WAFER LEVEL APPLICATION 143
6.1. PHOTO-POLYMERIZATION OF EPOXY 143
6.2. EXPERIMENTS 145
6.2.1. Materials 145
6.2.2. Preparation of nanocomposites 146
6.2.3. Characterization 146
6.3. PREPARATION OF PHOTO-CURABLE NANOCOMPOSITES 151
6.3.1. Filler size of nanosilica 151
6.3.2. UV absorption of compositions in the photo-curable nanocomposite 152
6.4. REACTION MECHANISM AND KINETICS OF PHOTO-CURABLE NANOCOMPOSITE 155
6.4.1. Mechanism of cationic photo-polymerization 155
6.4.2. Reaction process measured by real-time FTIR 157
6.4.3. Two-steps curing of underfill by cationic photo-polymerization 160
6.4.4. Reaction kinetics of underfill by photo-polymerization 164
6.5. MATERIAL PROPERTIES CHARACTERIZATION 170
6.5.1. Optical properties 170
6.5.2. Glass transition temperature 173
6.5.3. Thermal degradation behavior 174
6.5.4. Thermal expansion 175
6.5.5. Thermal mechanical properties of photo-cured nanocomposites 176
6.5.6. Nanocomposite morphology 179
6.5.7. Surface hardness 180
6.6. APPLICATION OF PHOTO-CURABLE EPOXY NANOCOMPOSITE IN WAFER LEVEL
PACKAGING 182
6.6.1. Novel wafer level packaging process 182
6.6.2. Advantages of photo-curable nanocomposites 185
6.6.3. Pattern formation with photo-curable nanocomposite 186
CHAPTER 7. CONCLUSIONS AND SUGGESTED WORK 190
7.1. CONCLUSIONS 190
7.2. SUGGESTED WORK 195
7.2.1. Chemical bond between filler and epoxy matrix 195
7.2.2. Molecular level reinforcement in epoxy 197
7.2.3. High performance polymer matrix 199
7.2.4. Nanocomposite polymeric optical waveguide 200
APPENDIX A AUTHOR’S AWARDS, PATENTS, AND PUBLICAITONS 201
REFERENCE 207
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