A Study on anisotropically assembled Ceramic-polymer composites and their Application for high heat spreaders

다국어 초록 (Multilingual Abstract)

The thermal conductive properties of anisotropically assembled ceramic-polymer composites were investigated and their potential for application as high heat spreader device was studied in this work.
Various insulating fillers with high thermal conductive property were utilized to fabricate composite materials. Anisotropic assemble of fillers within composite material was achieved by applying electric field. Silicone resin was selected as polymer matrix in order to apply high electric field strength to fabricate composite material. According to filler material, filler morphology, loading amount, applied electric field type and electric field strength a variety of microstructure fabrication was enabled.
Alumina filler loaded composites formed anisotropic microstructures with applied DC electric and AC electric field. According to morphology of filler different anisotropic microstructures were fabricated. For 20vol% spherical shape filler loaded composite by applying DC electric field of 1kV/mm resulted in composite with increased thermal conductivity of 0.46W/mK. For plate shaped filler with 20vol% filler loading the thermal conductivity increased up to 0.44W/m K. Also by increasing the applied DC electric field strength the thermal conductivity increased to 0.54W/m K. By applying AC electric field even higher thermal conductivity of 0.71W/m K was obtained which was estimated to be due to aggregation of the fabricated anisotropic microstructures. For 40vol% filler loaded composite, thermal conductivity of 1W/m K was enabled but the thermal conductive property decreased with increasing electric field strength. But by filler loading with bi-modal size distribution the fabricated anisotropic composite retained its thermal conductive property even increasing electric field strength.
For boron nitride filler loaded composites no detectable formation of anisotropic microstructure was observed regardless of the type of the applied electric field. However due to the inherent high thermal conductive property of boron nitride filler, the 20vol% filler loaded composite achieved thermal conductivity of 0.75W/ m K.
For aluminum nitride filler loaded composite no anisotropic microstructure was fabricated with applying DC electric field. Rather the fillers showed distinct separation from the polymer matrix resulting in reduced thermal conductive properties. But by applying AC electric field, assembly of fillers into anisotropic microstructure was achieved. Thermal conductivity of 0.91W/m K was obtained with 20vol% filler loaded composite.
Diamond filler loaded composites achieved various anisotropic microstructures according to applied electric field type and strength. For 20vol% filler loaded composite the highest thermal conductivity of 0.74W/m K was obtained by applying AC electric field.
It was determined that by assemble of fillers into anisotropic microstructure by applying electric field, the thermal conductivity of the composite was increased drastically. To acquire a solution for obtaining the optimum electric field condition for fabricating anisotropic microstructure a Rheometer was designed and utilized. From the measured signal values the storage shear modulus of the composite suspension was calculated. Samples were fabricated according to obtained electric field condition and it was found that for the electric field condition with highest storage shear modulus value the composite with highest thermal conductivity was obtained.
Finally a high heat spreader device was fabricated with the anisotropically assembled composite material. Compared to device fabricated with conventionally prepared composite material the developed composite material showed significantly lowered thermal resistance of 1.4W/K thus promising to be a good solution for high power devices where thermal heat dissipation is a critical issue for device performance and reliability.

목차 (Table of Contents)

• Contents
• Abstract i
• List of Figures v
• List of Tables x
• Chapter 1. Introduction 1
• Chapter 2.Literature survey and theoretical background 4
• 2-1. Review of thermal interface materials status and technology issues 4
• 2-1-1. Overseas technology development status 11
• 2-1-2. Domestic technology development status 13
• 2-1-3. Development trend of new high thermal conductive and insulating material 13
• 2-2. Composite theory 19
• 2-2-1. Connectivity 19
• 2-2-2. Theoretical modeling of thermal conductivity in composites 21
• 2-3. Electric field phenomena in suspension 23
• 2-2-1. Basic mechanisms 23
• 2-2-2. Electro-rheological effect 29
• 2-4. Materials issues for electric field assembly of composite materials 31
• 2-5. Principal of laser flash method for measurement of thermal properties 32
• Chapter 3.Experimental Procedure 35
• 3-1. Formulation of composite and fabrication of specimens 35
• 3-2. Analysis of micro structural and thermal properties 35
• 3-3. Device fabrication 39
• 3-4. Measurement of device properties 40
• Chapter 4.Results and Discussion 56
• 4-1. Optical microscopy and Scanning electron microscopy studies
• on composites 56
• 4-1-1. Alumina filler loaded composite 56
• 4-1-2. Boron nitride filler loaded composite 62
• 4-1-3. Aluminum nitride filler loaded composite 64
• 4-1-4. Diamond filler loaded composite 68
• 4-2. Effect of anisotropically assembled composite
• on thermal conductive properties 71
• 4-2-1. Alumina filler loaded composite 71
• 4-2-2. Boron nitride filler loaded composite 86
• 4-2-3. Aluminum nitride filler loaded composite 92
• 4-2-4. Diamond filler loaded composite 99
• 4-3. Rheometer studies on anisotropic microstructure fabrication condition 106
• 4-4. Application of anisotropically assembled composite
• to heat spreader device 114
• Chapter 5.Conclusions 118
• 5-1. Anisotropically assembled composites 118
• 5-1-1. Alumina filler loaded composite 118
• 5-1-2. Boron nitride filler loaded composite 118
• 5-1-3. Aluminum nitride filler loaded composite 119
• 5-1-4. Diamond filler loaded composite 119
• 5-2. Rheometer study on composite assembled according to electric field 119
• 5-3. Application of anisotropically assembled composite to heat spreader device 120
• Acknowledgement 121
• References 122