China's thermal conductivity field started late, as high-end product technology is still monopolized in Europe, the United States and Japan and a few other enterprises, many domestic manufacturers of thermal conductivity interface materials are still mainly low-end product output, sales accounted for only about 10% of the total market.
Traditional cell phone heat dissipation materials such as graphite sheet and thermal gel and other TIM materials (thermal interface materials), graphite sheet has a relatively low thermal conductivity, relatively large thickness and other problems.
At present, heat pipes and VC (homogeneous thermal plates) are beginning to penetrate from computers and servers to smartphone terminals, and graphene materials are also beginning to be used. Relatively speaking, VC and graphene are better performance heat dissipation materials with high thermal conductivity and low thickness.

Graphite film: the mainstream material for thermal solutions

Mainstream heat dissipation material, single phone usage is 3~6 pieces

Graphite is a better thermal conductivity material than metals such as copper and aluminum, mainly because of its special hexagonal planar mesh structure, which can evenly distribute and effectively transfer heat in two-dimensional planes. In the horizontal direction, the thermal conductivity of graphite is 300~1900 W/(m〃K), while that of copper and aluminum is about 200~400 W/(m〃K). In the vertical direction, the thermal conductivity of graphite is only 5~20 W/(m〃K). Therefore, graphite has good horizontal thermal conductivity and vertical thermal resistance.
At the same time, the specific heat capacity of graphite is comparable to that of aluminum, about twice that of copper, which means that the temperature rise of graphite is only half that of copper after absorbing the same amount of heat. 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 lightweight and can adhere smoothly 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 in batch since 2009 and in smartphones on a large scale since 2011, and has now replaced traditional metals as the mainstream heat dissipation material in consumer electronics.

Theoretically, the thinner the graphite film, the higher the thermal conductivity. In the early days, the thickness of graphite film mainly ranged from 20 to 50µm, and the thermal conductivity of its horizontal axis ranged from 300 to 1,500W/(m〃K). With the improvement of the technology, the processing of graphite film has become more mature, and now the thinnest film can be as thin as 0.01mm, and its thermal conductivity in the horizontal axis is as high as 1,900W/(m〃K). However, the thinner the graphite heat sink, the better. The key is to fill the gap between the power device and the heat sink. Therefore, the graphite heat sink used in different application scenarios varies.

The mainstream heat sink films are natural graphite heat sink film, synthetic graphite heat sink film and nano carbon heat sink film.

(1) Natural graphite film: Made entirely of natural graphite, it will not degas under vacuum conditions and can continue to be used at temperatures above 400°C. It can be used as low as 0.1mm and is mainly used in data centers, base stations and charging stations, etc.

(2) Artificial graphite heat sink film: made of polyimide (PI film) after carbonization and graphitization, it is the thinnest heat sink film material, the thinnest can be 0.01mm, widely used in cell phones, computers and other intelligent terminal products.
(3) Nano carbon heat sink film: made of nano carbon (graphite isomer), the thinnest can be 0.03mm, and the heat sink power can be up to 1000~6000, because the processing process of nano carbon heat sink film is simple, only mold opening and punching, the cost is low and the price is low.
Synthetic graphite films are mainly used in smartphones, and the amount of film used depends on the performance and requirements of the phone, about 3~6 pieces.
The CPU has the highest performance requirements for heat dissipation, followed by the wireless charger, 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 US dollars per piece. Initially, the value of a single graphite film is estimated to be US$1 to US$2. In the future, with more innovative electronic designs for smartphones, the value of a single graphite film is expected to increase further.

Industry competition is fierce, prices continue to fall

At present, the main players in the industry of thermally conductive graphite film are domestic and foreign enterprises such as Panasonic (Japan), Graftech (USA), Kaneka (Japan), Carbon Technology, Zhongshi Technology and Fei Rongda. Matsushita and Graftech entered the field earlier and are the pioneers with more mature technology. Domestic companies such as Kaneka, Zhongshi and Fei Rongda have mature technology and are relatively advanced, and have successfully entered the supply chain system of major cell phone manufacturers such as Samsung and Huawei.
Due to the relatively low entry threshold of the industry, many manufacturers are involved, resulting in fierce price competition and continuously low product prices. According to the prospectus and other announcements of Carbon Element Technology and Sinostone Technology, the price of single-layer and multi-layer high thermal conductivity graphite film has continued to decline since 2014, and has fallen from 400 yuan/m2 in 2014 to about 180 yuan/m2 in 2017.

PI film is the core material of artificial graphite film, high-end production capacity is concentrated in the hands of foreign manufacturers
The artificial graphite heat sink film widely used in smartphones is made of polyimide (PI film) by carbonization and graphitization. From the production process point of view, it goes through 6 processes, namely substrate treatment, carbonization, graphitization, calendering, laminating, and die-cutting. Carbonization refers to the disruption of the radial arrangement of the structural molecules of the PI film at high temperatures, the carbonyl group is broken, and all or most of the non-carbon components are volatilized, resulting in a polyimide carbonized film (a polycyclic compound) with a disordered layer structure.
Graphitization is a further reorganization of the molecules of the polycyclic compound at high temperature, which increases the order and decreases the disorder and transforms it into a hexagonal planar laminar graphite structure, resulting in a large graphite primary film with high crystallinity. After carbonization and graphitization, the graphite film is calendered (extrusion and stretching to form a soft, high-density graphite film), laminated (lamination of top and bottom surfaces with release and protective films) and die-cut (processing and cutting to make customized parts) to produce a finished, highly thermally conductive graphite film that meets your needs.

Polyimide, tape and protective film are the key upstream raw materials, among which polyimide (PI film) is the main one, accounting for up to 30% of the cost.
PI film is a high-performance insulation material, which can be widely used in satellite navigation, digital products, computers, cell phones and other fields. The product has high technical barriers, and there are few manufacturers in the world. The high-end products mainly include DuPont, Kaneka and SKPI, among which DuPont occupies more than 40% of the global high-performance polyimide film market and is the leading PI film manufacturer. Domestic manufacturers mainly produce low-end products.

Graphene film: rich physical and chemical properties, obvious domestic advantages
1. the highest thermal conductivity, good electrical conductivity, downstream lithium materials and thermal conductive film space is huge

Graphene is the substance with the highest known thermal conductivity, with a theoretical thermal conductivity of 5300W/m〃K, much higher than graphite. It is a honeycomb-like two-dimensional crystal formed by the hybridization of single layer of carbon atoms by electron orbitals, and its thickness is only 0.335nm. According to the standard of China Graphene Industry Technology Innovation Alliance, monolayer graphene refers to a two-dimensional carbon material composed of one layer of carbon atoms.

Graphene's fast thermal conductivity and fast heat dissipation properties make it an ideal replacement material for traditional graphite heat dissipation films, which are widely used for heat dissipation in smartphones, tablet PCs, high-power energy-saving LED lighting, and ultra-thin LCD TVs.
In addition to high thermal conductivity, graphene has other excellent physicochemical properties and therefore has a wide range of downstream applications. For example, high electrical conductivity can be used in integrated circuits, conductive agents, sensors and lithium batteries; high specific power can be used as super capacitors and energy storage components; strong flexibility, bending does not affect the performance, can be used as a flexible material for curved screens and wearable devices; with high light transmission, can be used for transparent conductive films.

Graphene product forms include both thin films and powders, and the application areas of graphene powders include.

(1) Conductive additives for positive and negative electrode materials of lithium batteries, which can improve charging and discharging speed and cycling performance.
(2) Electrode materials for supercapacitors with strong energy storage activity and excellent cycling performance.
(3) Characteristic coatings, as additives in anti-corrosion coatings, heat dissipation coatings and conductive coatings to improve the performance of the coating
(4) High efficiency catalysts for energy and chemical applications.

Applications of graphene films include.

(1) Thermally conductive film, used as a heat sink layer for smartphones and tablet PCs, etc.
(2) Flexible displays, for use in fields such as flexible displays and wearable devices.
(3) Sensor materials for wearable devices, medical and environmental monitoring, etc.
(4) Integrated circuit base materials for supercomputers, high-frequency chips and precision electronic components, etc.
Lithium materials and thermal conductive films are expected to be the largest downstream applications. Huawei's Mate 20 X smartphone released in 2019 will use graphene as a heat dissipation material for the first time, and graphene lithium battery is also expected to be commercially promoted in the cell phone. In terms of market size, according to the calculation of China Business Industry Research Institute, the market space of lithium battery materials is expected to be the largest, reaching 4~5 billion yuan, followed by thermal film, which is expected to reach 1.5~2 billion yuan, and the market space of composite materials is also around 2 billion yuan.
According to the China Graphene Industry Alliance, the size of China's graphene industry grew from $16.3 million in 2015 to $38.42 million in 2016. With the solution of graphene mass production and the expansion of downstream, China's graphene market size is expected to reach $200 million in 2020, exceeding 50% of the global market and becoming the largest graphene consuming country.

2. China's graphene industry is a global leader with many players

Graphene-related research began to appear in 1994, and in 2004, British scientists Andrei Heim and Konstantin Novoselov successfully isolated graphene and won the Nobel Prize in Physics in 2010. In recent years, graphene research has continued to heat up and the number of patents has been increasing, while the industrialization process is also advancing.

Theoretical research and industrialization of graphene in China are both in the forefront of the world. In terms of theoretical research, according to the Graphene Industry Alliance, as of 2016, China's graphene patents accounted for 58% of the world's major priority patent applications (followed by Korea and the United States); in terms of industrialization, graphene occupies a key position in strategic frontier materials, and China plans to achieve a graphene industry "with an industrial scale of 10 billion by 2020 and 100 billion by 2025. In terms of industrialization, graphene occupies a key position in strategic frontier materials, and China plans to achieve the development goal of "forming a $10 billion industry scale by 2020 and breaking $100 billion by 2025.

According to the China Graphene Industry Alliance, the number of graphene manufacturers in China has grown from more than 300 in 2015 to more than 400 in 2016. In terms of graphene heat-conducting film, Changzhou Fulene is the technological leader and the first to be commercially available in smartphones. According to the official website of Changzhou Wujin District Government, the company's graphene heat-conducting film has been widely used in Huawei mate 20 series, P30 series and other terminal products.

3. many preparation methods, CVD method has good development prospects

The upstream of graphene includes resources such as graphite, devices and systems, etc. The downstream applications include thermal conductivity, electrical conductivity, flexible displays and ink coatings, etc. The midstream has two product forms: graphene powder and graphene film.

Graphene powders and graphene films have significant differences in preparation methods.
In general, graphene preparation methods include physical, chemical and biological methods. Among them, physical methods mainly include mechanical exfoliation, liquid phase exfoliation and gas phase exfoliation; chemical methods include redox, vapor deposition (CVD) and SiC epitaxial growth; biological methods include redox.

Graphene powder is mainly prepared by mechanical exfoliation, liquid phase exfoliation, vapor phase exfoliation and redox method, and graphene film is mainly prepared by mechanical exfoliation, vapor phase deposition (CVD) and epitaxial growth method.

From the perspective of technology maturity and mass production, the graphene powder has the least number of layers and relatively simple process flow under the redox method; the graphene film has the largest size under the CVD method, thus becoming the two directions with better industrialization and development prospects.

TIM: A wide range of products and a mature domestic supply chain
1. Matching thermally conductive filler materials, with numerous and indispensable application scenarios

Thermal Interface Materials (TIM), one of the common heat dissipation methods, is commonly used for IC packaging and electronic heat dissipation.
When assembling microelectronic materials and heat sinks, there are very small uneven gaps between them, and if installed directly, the actual contact area between them is only 10% of the heat sink base area, and the rest are air gaps. The air is a poor conductor of heat, which will seriously impede the conduction of heat, ultimately causing the radiator to be ineffective. The role of the thermally conductive interface material is to fill these air gaps to establish an effective heat transfer channel between the electronic components and the heat sink, reducing the thermal resistance to heat transfer and improving thermal performance.

There are many types of thermally conductive interface materials, including thermally conductive silicone grease, thermally conductive silicone film, thermally conductive phase change material and thermally conductive double-sided adhesive. Among them, thermally conductive silicone grease has good fluidity and can be placed on heat generating devices by dispensing and printing, and is suitable for thermally conductive composite materials with smaller or zero gap.
The thermal conductive silicone has ultra-low thermal resistance, so it is suitable for high heat generation close fitting scenarios, and has the lowest thickness for thermal conductive products, so it can quickly transfer heat out of the equipment to achieve good temperature control. In addition, depending on different scenarios and needs, thermally conductive silicone film, phase change material and double-sided adhesive are also widely used.

The usage of TIM for smartphones alone is not large, but the price is higher than graphite film. According to the prospectus of Sinostone Technology, the unit price of synthetic graphite in 2017 was $129.94/m2 , while the unit price of TIM thermal conductive material was $783.35/m2 . According to our estimation, the value of a single TIM for smartphone is about 0.5~2.5 US dollars.

2. domestic manufacturers continue to enter, the market competition pattern is increasingly full

According to a report published by BCC Research in 2015, the global thermal interface materials market size will increase from USD 716 million in 2014 to USD 1.1 billion by 2020, growing at a CAGR of 7.28% during 2014 to 2020.
According to a report published by Credence Research in 2016, the global thermal interface materials market size is expected to reach $1.711 billion in 2022, growing at a CAGR of 12.0% between 2014 and 2022. Data from the Ministry of Industry and Information Technology show that the largest country in the global thermal interface materials market size was China in 2016, accounting for 45%, and the share is expected to increase to 53% by 2020.

In the international market, the field of thermal conductive interface materials has formed a relatively stable market competition pattern, with Chomerics and Bergquist as the representatives of the United States and European companies in the international and domestic high-end market in a monopoly position.
In the domestic market, stimulated by the huge market demand, the number of manufacturers has increased rapidly in recent years, but due to the late start in the field of thermal conductivity in China, most of the enterprises have few varieties, strong homogeneity and low technological content, and mostly seize the market by way of price war. On the other hand, because the high-end product technology is still monopolized in Europe and the United States and Japan and a few other enterprises, many domestic manufacturers of thermal conductive interface materials are still mainly low-end product output, with sales accounting for only about 10% of the total market.

3. A wide variety of preparation processes to meet the needs of various levels of heat dissipation

There are a variety of processes for making thermally conductive interface materials. Take graphite phase change thermally conductive silicone grease as an example, starting from melting paraffin wax, it goes through a total of 5 procedures to finally obtain high thermally conductive silicone grease. This preparation process is simple and easy, with low production difficulty. One of the materials, nanoporous graphite, has high adsorption to high-precision paraffin wax and long service life. The final product, high thermal conductivity silicone grease, can reduce temperature efficiently and can be reused at the same time.
The production process of composite thermally conductive silicone grease is relatively complicated. It mainly uses the special properties of carbon nanotubes to form a thermally conductive network inside the colloid together with alumina, and the thermal conductivity of the final product composite thermally conductive silicone grease is significantly higher than that of the existing technology, with excellent thermal conductivity performance.

The upstream of thermally conductive interface materials include structural stabilizers, anti-corrosion additives, silica gel, alumina and thickening agents, etc. Most of these materials can be obtained through market-based procurement, and the market supply is sufficient and there is no scarcity, so the upstream bargaining power is weak. The downstream applications are very wide, mainly including communication equipment, electronic equipment, automotive and household appliances.

In addition to the traditional downstream industries with growing demand for thermally conductive interface materials, emerging technologies and industries are also increasing their demand for thermally conductive interface materials. According to the forecast of the Ministry of Industry and Information Technology, the demand for thermal conductive interface materials in VR will reach RMB 3.78 billion in 2021, with a CAGR of 99.37% from 2016 to 2021; the demand for thermal conductive interface materials in new energy vehicles will reach RMB 12.24 billion in 2021, becoming one of the most demanded downstream areas with a CAGR of 44.84%.

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