Mainstream heat dissipation material, single cell phone usage is 3 ~ 6 pieces
Graphite is a better heat-conducting material than metals such as copper and aluminum. The main reason is that graphite has a special hexagonal planar network structure, which can distribute heat evenly in a two-dimensional plane and efficiently transfer it. In the horizontal direction, the thermal conductivity of graphite is 300 ~ 1900W / (m〃K), while the thermal conductivity of copper and aluminum is about 200 ~ 400W / (m〃K). In the vertical direction, the thermal conductivity of graphite is only 5 ~ 20W / (m〃K). Therefore, graphite has good horizontal thermal conductivity and vertical thermal resistance. At the same time, the specific heat capacity of graphite is equivalent to that of aluminum, which is about twice that of copper, which means that after absorbing the same amount of heat, the temperature of graphite rises by only half of that of copper. In addition, the density of graphite is only 0.7 ~ 2.1g / cm3, which is lower than 8.96g / cm3 of copper and 2.7g / cm3 of aluminum, so it can be lightened and can be smoothly adhered to any flat and curved surface.
Based on the performance advantages of high thermal conductivity, high specific heat capacity and low density, graphite has been used in consumer electronics products in batches since 2009 and large-scale applications in smartphones in 2011. It has now replaced traditional metals and has become the mainstream heat dissipation material in the field of consumer electronics. . In theory, the thinner the graphite film, the higher the thermal conductivity. The thickness of early graphite film was mainly between 20 ~ 50μm, and the thermal conductivity of its horizontal axis was between 300 ~ 1,500W / (m〃K). With the improvement of technology, the processing technology of graphite film is more mature, and the thinnest can be up to 0.01mm, and the thermal conductivity of its horizontal axis is also up to 1,900W / (m〃K). However, the graphite heat sink is not as thin as possible, the key is to fill the gap between the power device and the heat sink. Therefore, the graphite heat dissipation films used in different application scenarios are different.
There are three main types of heat dissipation film: natural graphite heat dissipation film, synthetic graphite heat dissipation film and nano carbon heat dissipation film.
(1) Natural graphite film: completely made of natural graphite, no degassing will occur under vacuum conditions, and it can continue to be used at temperatures above 400 ° C, with a minimum of about 0.1mm, mainly used in data centers , Base stations and charging stations.
(2) Artificial graphite heat dissipation film: made of polyimide (PI film) through carbonization and graphitization, it is currently the thinnest heat dissipation film material, and the thinnest can be 0.01mm.
(3) Nano carbon heat dissipation film: made of nano carbon (graphite isomer), the thinnest can be 0.03mm, and the heat dissipation power can be as high as 1000 ~ 6000. Due to the simple process of nano-carbon heat dissipation film, it only needs mold opening and punching, and the cost is low and the price is low.
The artificial graphite film is mainly used in smart phones, and the amount depends on the performance and requirements of the mobile phone. It is about 3 to 6 pieces. The components used include the lens, CPU, OLED display, WiFi antenna, wireless charger and battery. Among them, the CPU has the highest performance requirements for heat dissipation, followed by wireless charging, then the lens and battery, and finally the display and WiFi antenna. At present, the price of high thermal conductivity graphite film is about 0.2 ~ 0.3 USD / piece. According to preliminary estimates, the value of the stand-alone graphite film is US $ 1-2. In the future, with more innovative electronic design of smart phones, the value of stand-alone graphite film is expected to further increase.
At present, the main participants in the thermal conductive graphite film industry are domestic and foreign enterprises such as Panasonic of Japan, Graftech of the United States, Kaneka of Japan, CZTY Carbon Material Technology Company, BJZS Electronic Material Technology Company and SZFR Electronic Material Technology Group. Panasonic of Japan and Graftech of the United States entered the field earlier, and the technology is more mature. CZTY Carbon Material Technology Company, BJZS Electronic Material Technology Company and SZFR Electronic Material Technology Group, etc. China's leading thermal conductive graphite material technology is mature and relatively leading, and successfully entered the supply chain system of major mobile phone manufacturers such as Samsung and Huawei.
2.3. PI membrane is the core material of artificial graphite membrane
The artificial graphite heat dissipation film widely used in smart phones is made of polyimide (PI film) through carbonization and graphitization. From the perspective of production process, it mainly passes through 6 processes, which are substrate treatment, carbonization, graphitization, calendering, lamination, and die cutting in that order. Among them, carbonization refers to the disorder of the radial arrangement of the structure molecules of the PI film at high temperature, the carbonyl group is broken, all or most of the non-carbon components are volatilized, and finally the polyimide carbide film (a polycyclic compound) with a chaotic layer structure ). Graphitization is to further reform the polycyclic compound molecules at high temperature, the order is increased, the disorder is reduced, and the hexagonal plane layered graphite structure is transformed, and finally a large-scale graphite original film with high crystallinity is formed. After carbonization and graphitization, it is calendered (extruded and stretched to form a soft and high-density graphite original film), laminated (laminated release film and protective film on the upper and lower surfaces) and die-cutting (processing and cutting make the material customized zero Components), and finally form a finished high thermal conductivity graphite film.
Polyimide, adhesive tape and protective film are the key upstream raw materials. Among them, polyimide (PI film) is the main raw material, and the cost accounts for up to 30%. PI film is a high-performance insulating material, which can be widely used in satellite navigation, digital products, computers, mobile phones and other fields. The product has high technical barriers, and there are few manufacturers worldwide. The high-end products are mainly DuPont from the United States, Kaneka from Japan, and SKPI from South Korea. Among them, DuPont from the United States occupies more than 40% of the global high-performance polyimide film market PI film manufacturer is the leader, with a full range of products, which can meet the needs of various PI film applications.