High Performance Flexible Heat Dissipating Materials-Design, Preparation And Application

A new concept of flexible heat dissipating materials was proposed accordingto the emerging application scenarios in the microelectronics industry. Flexibleheat dissipating materials point a new research direction in thermal managementby integrating and enhancing the preparation, design, measurement andapplication technology of related materials.Elongated β-Si3N4powders of controllable aspect ratio were prepared byfoaming combustion synthesis method. Together with other powders, the β-Si3N4powders were applied into various organic matrices to form flexible compositesof different physical states. The resulting composites included thermal adhesive,thermal mud, thermal grease and thermal pad. Thermal adhesive and thermal mudwere chosen as focuses, on which the design, preparation and applicationtechnology were studied. The main applications of thermal adhesives and thermalmud were as in-plane heat dissipating and temperature uniforming materials,which were an important trend in thermal management.Thermal adhesive was prepared with silicon rubber encapsulants as thematrix material and β-Si3N4powders as the main fillers. The thermal conductivityand fluidity of the resulting composites varied with the intrinsic properties, aspectratio and surface modification of the fillers. To reveal the thermal conductingmechanisms, MG equation and percolation theory were introduced to describe thevariation rules of discontinuous filler phase and continuous filler phase,respectively. With the consideration of interface thermal resistance,pseudo-grain-boundary model and exclusive volume assumption, using two-stepmethod and other mathematical means, we revised the MG equation and the scalelaw of percolation theory. For the first time, we give the physical meaning of theslope of the scale law.Thermal mud was prepared with silicone rubber of high molecular weight,moderate hardness and the spherical Al2O3powders. The resulting compositescould be compressed with no limit. The influences of filler properties and fillingmethods on thermal conductivities and application effects were systematically examined. The use of the coupling agent, dispersing agent, thixotropic agent andcuring agent were also discussed.An in-plane thermal diffusivity measuring equipment was developed basedon Angstrom method. This equipment is a necessary supportive hardware forresearching anisotropic flexible heat dissipating materials. The way ofsample-holding and thermocouple loading, the choices of input waveform, circuitamplification method, testing temperature and the sample length were determined.The as-developed equipment can effectively measure the materials with highthermal diffusivity such as flexible graphite sheet and copper. The error can becontrolled within10%.