As a high-speed and high-power communication technology, 5G has extremely strict requirements on heat conduction. Traditional heat conduction schemes cannot meet the requirements. The new heat conduction technology must undergo qualitative changes to cope with such a complicated overheated environment. Especially for core components such as chips, in order to achieve the operation and processing capabilities that are compatible with 5G, we must always remain "calm" and put forward new requirements for heat conduction solutions. In the past, high thermal conductivity mesophase pitch-based carbon fibers, which have been important applications in the aerospace industry, have aroused widespread concern in the field of thermal conductivity. Its excellent orientable thermal conductivity is subverting the traditional chip heat dissipation solution. The mesophase pitch-based carbon fiber will become the core material to solve the thermal conductivity problem in the 5G field.
It is estimated that there will be 6.5 million 5G base stations and 2.8 billion 5G users in the world by 2025. Among them, there will be more than 4 million base stations in China and users will exceed 1 billion. At the same time, it will drive the production or construction of a large number of mobile phones, automobiles, smart medical systems, smart wearable devices, servers and data centers. 5G has become a disruptive revolution in the communications technology industry, bringing great development opportunities to the entire industry chain and also put forward more demanding technical requirements, especially the demand for quality and quantity of heat dissipation materials and electromagnetic shielding materials will grow rapidly. According to the forecast of the Prospective Industry Research Institute, the compound annual growth rate of the heat dissipation industry will reach 8% from 2018 to 2023, and the market size is expected to increase from 149.7 billion yuan in 2018 to 219.9 billion yuan in 2023. According to BCC Research's forecast, the global EMI (electromagnetic interference) and RFI (radio frequency interference) shielding materials market is expected to reach US $ 7.9 billion in 2020, with a compound annual growth rate (CAGR) of 5.6%.
The mesophase pitch is formed by a series of reactions of heavy aromatic hydrocarbons through polycondensation, and has optically anisotropic fused ring aromatic hydrocarbon structure polymer, which is a melt-induced liquid crystal polymer. The mesophase pitch becomes mesophase pitch-based carbon fiber after melt spinning, oxidation, carbonization, graphitization and other processes. The synthesis of mesophase pitch with good spinnability and high purity is the core technology in the entire process chain. The mesophase pitch of the plane molecular structure is highly oriented in the fiber axis direction in the fiber. During the high temperature graphitization process, a layered graphite crystallite is formed. It is a mesophase pitch-based carbon fiber capable of high modulus, high thermal conductivity, electrical conductivity, electromagnetic The structural basis of shielding performance. Mesophase pitch-based carbon fiber has important applications in aerospace, high-end manufacturing and other fields. As a key strategic material, it has been monopolized by the United States and Japan. The product is strictly prohibited from sale to China. The price has been extremely expensive for a long time, and it has also made civilian products prohibitive. . In recent years, with the development of technological level in the civil field, product competition has become increasingly fierce, and the performance requirements of key materials have become higher and higher. Mesophase pitch-based carbon fibers have gradually received widespread attention.
The thermal conductivity of mesophase pitch-based carbon fiber along the fiber axis can reach more than 1100W / mK, which is more than four times that of aluminum and more than twice that of copper. Although some nanomaterials currently have a high theoretical thermal conductivity, it is difficult to make high thermal conductivity especially directional due to factors such as difficulty in dispersion in the matrix polymer, difficulty in aligning the array, and limited filling amount. Thermally conductive material. The composite material with mesophase pitch-based carbon fiber as thermal conductive filler can achieve a thermal conductivity of more than 30W / mK through a reasonable design.
Mesophase pitch-based chopped fibers and ground fibers have good dispersion properties in the polymer matrix. It does not require any auxiliary means. It itself exists in an independent dispersed granular form, and the filling process is good, which will not cause problems such as excessive viscosity, low elasticity, and poor mechanical properties of the system. Good dispersion is very important to obtain high thermal conductivity. Figure 1 is a comparison of the thermal conductivity of a thermally conductive filler when it is filled in a dispersed state and an aggregated state. It can be seen that good dispersion can increase the thermal conductivity by more than double.
When the mesophase pitch-based carbon fiber is filled into the polymer matrix, it can be array-oriented by means of flow field, electric field, magnetic field, etc. to achieve excellent thermal conductivity in a specific direction. When the filler reaches a certain content, the thermal conductivity of the same filler ratio and good orientation is more than 3 times the thermal conductivity when the filler is disorderly arranged. And the influence of orientation on thermal conductivity is much greater than dispersion. Figure 2 is a comparison of thermal conductivity of polymer thermal conductive materials composed of different fillers.
Silicone thermal pads made by Japanese companies by orienting mesophase pitch-based carbon fiber arrays have been increased from a maximum thermal conductivity of 10w / m · k to 50w / m · k. This is a disruptive improvement, not only in the 5G application field, even in the 6G field, but also to adopt this directional heat conduction scheme. At present, the mesophase pitch-based carbon fiber is a directional thermal conductive material with excellent overall performance.
In China, some advanced enterprises in the field of thermal conductivity materials in the communications field have begun to use mesophase pitch-based carbon fibers as a new generation of thermally conductive materials, directional array of mesophase pitch-based carbon fibers, so as to achieve the improvement of thermal conductivity performance indicators, has been mass production Flexible thermal pad with thermal conductivity up to 25W / mK.
In the heat dissipation scheme of mobile phones, the heat pipe and the heat conduction sheet are often combined. The heat conduction sheet acts on the chip part, and the heat pipe is connected to the heat conduction sheet to conduct heat to other areas for heat dissipation. However, metal heat pipes have many disadvantages. For example, (1) metal heat pipes cannot be arbitrarily designed into desired shapes, and it is difficult to effectively conduct heat in narrow and irregular spaces of electronic equipment; (2) inevitable existence in the heat transfer path of heat pipes For other precision components, the direction of metal heat conduction is uncontrollable, and the coefficient of thermal expansion is large, which will inevitably affect the stability of other components; (3) Although metals such as copper have good thermal conductivity, due to their high density, they do not meet the development trend of thin and thin electronic products .
The mesophase pitch-based carbon fiber has excellent thermal conductivity and very low thermal expansion coefficient in the axial direction, while the thermal conductivity in the radial direction is low, and has anisotropy in thermal conductivity. The composite material made of it can achieve thermal conductivity. Designability, light weight and low coefficient of thermal expansion. The composite material formed by combining the mesophase pitch-based carbon fiber with the thermal conductivity of 500W / mK and the epoxy resin can achieve a thermal conductivity of 300W / mK along the fiber axis.
There have been prospective studies to rationally design the mesophase pitch-based carbon fiber so that it can play the heat conduction role of the heat pipe and solve the problem of the heat pipe in use. A well-known foreign mobile phone brand has planned to use the "carbon fiber liquid cooling system" to make the mobile phone better thermal conductivity and maintain the best running state for a long time.
The application of mesophase pitch-based carbon fibers in the field of 5G thermal conductivity has caused widespread concern in the 5G industry. In the future, 5G's demand for high thermal conductivity mesophase pitch-based carbon fibers will continue to increase.
In addition to thermal conductivity, in terms of electromagnetic shielding, mesophase pitch-based carbon fibers also perform well.
Shielding effectiveness rating
The mesophase pitch-based carbon fiber has a reasonable design, and the electromagnetic shielding effectiveness SE value can reach more than 90db. At the same time, it has light weight, corrosion resistance, oxidation resistance, difficult to deposit, good dispersion, strong designability, adjustable electromagnetic shielding effect, applicable The advantages such as wide range are excellent electromagnetic shielding solutions.
Mesophase pitch-based carbon fiber is a key strategic material for the development of China's aerospace industry and high-end equipment manufacturing. Its high modulus performance is the basic guarantee for the precise and efficient operation of equipment such as satellite antennas, aircraft high-rigidity panels, large aircraft wings, robot arms, and large industrial rollers. Its high thermal conductivity is a rare material that meets the high thermal conductivity needs of aircraft engine cooling systems, missile nose cones, and electronic product thermal management. Its excellent electromagnetic shielding performance is an excellent material for electromagnetic shielding protection of aerospace information systems and civil electronic products. Due to its important applications in many fields, Japan and the United States have been strictly blocking related technologies, and products have been strictly banned from sale in China. To promote the development of related industries in China and improve product competitiveness, China urgently needs to produce and supply mesophase pitch-based carbon fiber products independently. .