Preparation And Properties Of Thermal Conductive Composites Used In CPU Heat Sink

In this article, the PET/graphite, PP/graphite, PA66/graphite heat conducting composites were prepared by twin screw extrusion and injection molding to obtain high thermal conductivity material used in CPU heat sink. Thermal conductivity, mechanical properties, melt flow rate, melting temperature and the crystallinity of composites were tested. The results were analyzed by SEM and ultrasonic test. Effects of graphite content and heating rate on melting and crystallization behavior of PET and effects of heat treatment and mold temperature on thermal conductivity and mechanical properties of PET/graphite composites were studied. We also analyzed effects of lamella structure and orientation of graphite on thermal conductivity of PP/graphite, PA66/graphite and effects of process parameters on orientation, distribution of graphite and properties of composites. Conductive plastic formula has been achieved and we used it in thermal analysis of metal-plastic heat sink. Heat dissipation experiment of PA66/graphite composites was done.The results are as follows:1. Mold temperature rises will help improving the crystallinity of PET within a certain range. Within an appropriate heat treatment temperature, thermal stress in blend will relax which can promote rearrangement of polymer chains and improve the crystallinity of PET, thermal conductivity of composites were increased. 2. The smaller particle size is, the higher planar orientation degree is, which makes the difference between the planar and vertical thermal conductivity of the composites bigger. The excessive shear of twin screw extruder can destroy lamella structure of graphite, influence the formation of the heat conducting network and reduce the thermal conductivity, but improve the uniformity of heat conducting in different directions of the composites. The moderate shear can open the lamellar structure of flake graphite and improve the thermal conductivity of the composites, the injection molding influence the anisotropy of heat conducting of composites at a large degree. With the increase of screw speed, melt flow property of mixtures meliorates.3. The use of metal-plastic heat sink can reduce cost and weight. Heat dissipation achieves optimal performance when diameter of center aluminum-cylinder:D=20mm, height:H=40mm, Number of fins:N=60, fin thickness:t=1mm, fins are straight. Designed microstructures onto fins can increases heat dissipation area and improve the heat dissipation effect. Metal-plastic heat sink with microstructures on fins has the same heat dissipation performance as metal heat sink, it can meet heat dissipation demand of CPU chip.4. When the heating power of block is20W and time is18min, temperature of the heating block reduces5.3℃through PA66/graphite wafer,and the temperature between the upper and lower surfaces is5.9℃.