These "high thermal conductivity graphite films" are very different

Graphite heat dissipation film is a standard product for chip heat dissipation and is widely used in electronic products.

At present, the technical routes for preparing high thermal conductivity graphite films mainly include: expanded graphite calendering method, PI thin film carbonization-graphitization method, petroleum coke/coal pitch carbonization, highly oriented "pyrolytic graphite",

Graphite heat dissipation film is a common type of material in the heat dissipation system of electronic equipment

1.

The expanded graphite (flexible graphite) calendering method takes natural flake graphite as raw material, conducts intercalation chemical reaction through acidification, and then obtains high-expansion graphite worms through water washing, drying and high-temperature expansion, and finally obtains high thermal conductivity flexible graphite worms through calendering and pressing process.

0.

The degree of graphite crystallization and crystallite orientation of the expanded graphite after chemical oxidation decreases, resulting in a decrease in the thermal conductivity of the fabricated flexible graphite material; at the same time, the material microchip layers are only extruded and stacked with each other under the action of external force, and their mechanical strength is mainly The tensile strength is lower due to internal friction and shear forces between the lamellae

Rolled flexible graphite sheet and its production line (Nihon Carbon Company)

TIPS: Expandable Graphite & Expanded Graphite:

Expandable graphite is a graphite interlayer compound formed by the oxidation and intercalation of natural flake graphite to insert dissimilar substances into the graphite flakes.

Electron Micrograph of Expanded Graphite

2.

A long time ago, scientists found that graphite can be made by carbonizing polyimide (PI) under pressure in an inert atmosphere and graphitizing it at 2800-3200 °C, and the resulting product has similar properties to highly oriented pyrolytic graphite.
The highly preferentially oriented graphite layer along the surface of the film has high crystallinity.
This method has a simpler preparation process than the pyrolysis method to prepare graphite, which greatly promotes the development of graphite as a heat dissipation material
.
The carbonization-graphitization method of PI-type thin films has more advantages in preparing highly crystalline and highly oriented graphite films with high thermal conductivity.
Low structural defects, high degree of carbon atomic order, thermal conductivity in the range of 1400-2000W·m-1·K-1, in addition, in terms of thickness, this process route can produce heat dissipation films as thin as 0.
01mm (10μm) Yes, it has a good performance in the thin and light heat dissipation design of mobile phones
.

Process route reference: The PI film is sent to the carbonization furnace, and the PI film is heated and carbonized at a heating temperature of 1100°C-1300°C, and the PI film is carbonized to form a PI carbide sheet, and then the PI carbide sheet is cooled to room temperature.
(It takes about 6 hours), and then send the PI carbide sheet into the graphite furnace, at a heating temperature of 2800 ℃-3000 ℃, the PI carbide sheet is subjected to a cartoon, the PI carbide sheet is graphitized to form a PI graphite heat sink, The PI graphite heat sink was cooled before, and after cooling to room temperature (about 6 hours), the thickness of the PI graphite heat sink was rolled with a calendering device, so that the graphite heat sink was rolled to form a finished graphite heat sink with a thickness of 15-30 μm
.

TIPS: What is the difference between carbonization and graphitization?

The key difference between carbonization and graphitization is that carbonization involves converting organic matter to carbon whereas graphitization involves converting carbon to graphite
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Therefore, carbonization is a chemical change whereas graphitization is a microstructural change
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Graphitization is the use of thermal activation to realize the orderly transformation of thermodynamically unstable carbon atoms from a turbostratic structure to a graphite crystal structure.
energy
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In order to improve the degree of graphitization of the refractory carbon materials, the method of adding catalysts, which is called catalytic graphitization, can also be used
.

3.
Carbonization of petroleum coke/coal pitch, etc.

Petroleum coke is a by-product of petrochemical industry, and pitch coke is a by-product of coal chemical industry
.
Therefore, these two raw materials are cheap and easy to produce, and they are the main raw materials of artificial graphite
.
Both petroleum coke and pitch coke have a certain ordered structure and are easy to graphitize, so they also have relatively strong anisotropy
.

Such raw materials are rich in sources, relatively simple in preparation process, and short in production cycle, but have large energy consumption, serious pollution, and low thermal conductivity.
field
.

4.
Highly oriented "pyrolytic graphite"

Pyrolytic graphite is a pyrolytic carbon with high crystal orientation deposited by chemical vapor deposition on a graphite matrix of 1800℃~2000℃ under a certain furnace pressure of high-purity hydrocarbon gas.
Highly oriented pyrolytic graphite HOPG (Highly Oriented Pyrolytic Graphite ) is a new type of high-purity carbon, which is a new type of graphite material obtained from pyrolytic graphite after high temperature and high pressure treatment, and its performance is close to that of single crystal graphite
.

Because the material needs to be prepared under high temperature (10 MPa) at 3400-3600 °C, the production cycle is long and the production cost is high, so its application is greatly limited
.
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