Anisotropic thermal conductive composite constructed by carbon fiber for thermal management in electronic package

Abstract

Because of the high-power density of chips, thermal management material has become a key node of electronic system development. Thermal management material with high thermal conductivity can dissipate the waste heat on time to avoid heat damage to system stability and arithmetic speed. However, polymer as traditional packaging material used in electronic system by virtue of low processing temperature and good mechanical properties can hardly satisfy the demand for high thermal conductivity. So, scientist tend to endow the polymers with high thermal conductivity by mixing them with fillers which can enhance the heat transport.
However, how to construct such composites which possess high thermal conductivity and meanwhile can satisfy the requirement of a specific application is still a challenge facing engineers and scientists.
In the rest of this thesis, carbon fiber, a thermal conductive filler with , was applied to construct a thermal conductive composite with the assistance of a mechanical force field. To make full use of the anisotropic thermal conductivity of carbon fiber to obtain directional high thermal conductivity composites, carbon fiber was supposed to be aligned along a specific direction. By compressing the carbon fiber powder, an orientated thermal conductive network was fabricated to transport heat efficiently, which resulted in a 32 W m-1 K-1 thermal conductivity.
Compared with compressing, stretching is a more efficient method to achieve the alignment of carbon fiber in a single direction. However, the difficulty of applying the tensile force on carbon fiber powder blocked the realization of the strategy. Here, a novel strategy was proposed. A medium was introduced to control the movement of carbon fiber powder by transferring the mechanical force applied on it to the carbon fiber. Then the medium was graphitized into sheets of carbon crystal enhancing the heat exchange between carbon fibers. The thermal transport speed in different carbon structure and the alignment of carbon fiber during the stressing process were calculated with molecular dynamics and mathematics. As a result, with the novel strategy, metal-level thermal conductive but lighter composite was constructed.
Besides thermal conductivity, in this thesis, a thermal management material with phase change function was constructed using phase change matrix which can suppress temperature fluctuation during the overloading of electronic equipment. The extra heat generated by the overloading would be stored as latent heat of matrix during the phase change process avoiding the rise of equipment temperature. As a result, the hurt of high temperature to equipment can be avoided. The resulted material has a 23 W m-1 K-1 thermal conductivity accompanied with 62 J g -1 K-1 latent heat.
In summary, different mechanical methods manufacturing directional thermal conductive materials were talked in the thesis. Accompanied with them, characterization of structure and thermal properties was done with experimental, simulative and mathematical methods. Various applications are given in the thesis to prove the materials’ practicability. The materials manufactured with these methods were supposed to be applied in different fields because of their promising properties. Meanwhile, it is possible for some different analysis methods used here to inspire the researchers and accelerate the development of the field.

Date of Award	Mar 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Jim Greer (Supervisor), Hainam Do (Supervisor) & Nan Jiang (Supervisor)