High Performance Thermal Conductive Sheets Made of Carbon Fibers

Today, the quality of LCD (Liquid Crystal Display) TVs has improved along with the quality of the installed LSI (Large Scale Integration) Thus, the cooling system needs to have high performance. However, LCD TV requires a large area but thin cooling system, so the TIM in which used in LCD TV requires highly softness. Thus we have developed high-quality yet soft thermal conductive sheets in which carbon fibers are directed in the thickness direction. The thermal conductivity of the 2-mm-thick sheets is more than 23 W/mK, and the compressibility is more than 10%. In this case the thermal conductivity was measured in accordance with ASTM D5470. The compressibility means the ratio of the difference between the initial thickness and the thickness when the sheets were loaded. The carbon fibers are more than 100 μm long and about 10 μm in diameter. This sheet contains alumina and aluminum nitride particles. The manufacturing process for the sheet is as follows. Step 1: The mixing process. Step 2: The resin including the carbon fibers and the particles is pressed into a long rectangular cast. Step 3: The resin is heated to harden it. Step 4: The resin is sliced into sheets. In step 1, because the carbon fibers are long, the fibers are likely affected by shear stress. Thus, the fibers are aligned in a lengthwise direction. In Step 4, we used a supersonic wave cutter to achieve ideal slicing, thereby reducing the thermal contact resistance. These processes produced high-quality yet soft thermal conductive sheets. In these processes, the carbon fibers aligned in the thickness direction, which was determined in an SEM observation. Moreover, we found that, by slicing in the orientation direction at inclining angles, only the softness improved, without any deterioration in the thermal conductivity.