Zeon Co., Ltd. developed a single-layer carbon nanotube thermal interface sheet

Japan’s Zeon Corporation (Zeon) announced on November 10, 2016 that it has developed a thermal interface sheet that uses single-layer carbon nanotubes (SGCNT) with high thermal conductivity, and is used for servers and personal computers that require high heat dissipation. For example, CPU, SiC (silicon carbide) power modules, etc., are targeted, and samples of 'heat sink' sheets that can significantly improve heat dissipation are started.

　　SGCNT is a single-layer sheet of carbon nanomaterials rolled into a cylindrical shape (Figure 1). The single-layer sheet is a structure in which carbon atoms are arranged in a regular hexagonal grid. The thermal conductivity of SGCNT is excellent, about 10 times that of copper. Zeon disperse a small amount of SGCNT (with a diameter of 0.3 to 0.4 nm and a length of several 100 μm) and graphite particles into the fluorine-based rubber to form a fine mesh of carbon nanomaterials in the rubber, successfully realizing the thickness of the thermal interface sheet The thermal conductivity in the direction and the hardness to ensure the flexibility of the rubber.

Figure 1: Single-walled carbon nanotube (SGCNT). The picture was produced by Japan's Single-layer CNT Fusion New Material Research and Development Agency (TASC).

　　 Specifically, the thermal conductivity of the thermal interface sheet (Figure 2) in the thickness direction was greatly increased to 38W/m·K, and the Asker hardness, which represents the hardness of the rubber, was reduced to 59. Previously, the thermal conductivity of the thermal interface sheet in the thickness direction was only 2W/m·K, and the hardness was as high as 88. If the Asker hardness is high, when the thermal interface sheet is sandwiched between the CPU and the heat dissipation module, due to poor adhesion, a part with high thermal resistance will be formed locally, resulting in poor thermal conductivity.

Figure 2: Thermal interface sheet developed by Zeon, Japan

　　 Due to the low Asker degree, Therefore, it can be closely attached to the surface of the CPU and the discrete module at the same time to fully ensure thermal conductivity (Figure 3). The specific measure is to fix the CPU and the cooling module with screws. According to reports, the original method used was to apply grease-like thermal interface materials to thermally combine the CPU and the heat dissipation module, but 'there are problems such as the difficulty of applying grease, uneven parts and droplets.'

Figure 3: Schematic diagram of the thermal interface sheet in use

　　 Japan Zeon introduced that the development of the hot The outstanding performance of the interface sheet is that it 'shows low thermal resistance in a large pressure range of the use range.' As shown in Figure 4, 'The curve of the thermal interface sheet developed this time (the blue curve marked with ZEON) has a thermal resistance value of only about 0.05°C/W in the pressure range of 0.2 to 0.4 MPa, which can conduct sufficient heat conduction.' The thermal resistance of the original grease-based thermal interface material is about 2 times higher, reaching 0.1°C/W. The grease-based thermal interface material reduces thermal resistance by dispersing silver nanoparticles in the interior.

Figure 4: The relationship between the pressure and thermal resistance of the thermal interface sheet

　　 Japan Zeon said that this development The heat sink has already supplied samples to a company for server and power electronic components, and is currently discussing the direction of actual adoption. The current goal is to ship about 60,000 m2 of the thermal interface sheet developed this time within one year. To this end, Zeon Japan plans to build a pilot plant for this type of heat sink at its subsidiary Zeon Chemicals' Ibaraki plant on December 15 this year, and start stable production on April 30, 2017. By the way, SGCNT is produced by Zeon's Tokuyama factory in Japan.

The person in charge of Zeon said, 'Although the improvement of the thermal conductivity in the surface direction has been achieved before, it is very difficult to increase the thermal conductivity in the thickness direction perpendicular to the surface.' 'The technology realized this time allows SGCNT and graphite particles to be fully dispersed in the fluorine rubber and arranged to a certain extent along the thickness direction. We are confident in this independent technology that other companies cannot imitate.' It is estimated that Zeon has adopted an intellectual property strategy to ensure this.

　　 The heat sink material developed this time can not only promote the miniaturization and high performance of electronic and electrical components, but also is expected to obtain derivative effects, such as the 'mass production effect' that currently reaches as high as 100 per kilogram. The high cost of SGCNT materials of 10,000 yen has been reduced, the high-performance rubber added with SGCNT has been promoted to achieve low prices, and the hydraulics and other institutions can achieve high performance. SGCNT will thus move towards industrial materialization. It can be said that this is the greatest achievement of this development.