Views: 0 Author: Site Editor Publish Time: 2019-05-07 Origin: Site
Pyrolytic graphite is a better heat conducting material than copper, aluminum and other metals, the main reason is that graphite has a special hexagonal plane network structure, which can evenly distribute heat in the two-dimensional plane and effectively transfer it. In the horizontal direction, the thermal conductivity of graphite is 300-1900 W / (m · K), while that 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 heat conduction and vertical heat resistance effect. At the same time, the specific heat capacity of graphite is equal to that of aluminum, which is about 2 times of that of copper, which means that the temperature rise of graphite after absorbing the same heat is 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. Therefore, it can be lightweight and can adhere to any plane and curved surface smoothly.
With the improvement of technology, the processing technology of graphite film is more mature. At present, the thinnest graphite film is 0.01M m, and the heat transfer efficiency of its horizontal axis is as high as 1900w / (m · K). However, the graphite heat sink is not the thinner the better; the key is to fill the gap between the power device and the radiator. Therefore, the graphite cooling film used in different application scenarios is different.
There are three main types of cooling films: natural graphite, synthetic graphite and Nano carbon.
(1) Natural graphite film: it is completely made of natural graphite, and will not be degassed under vacuum condition. It can be used continuously at a temperature above 400 ℃, with a minimum of about 0.1mm. It is mainly used in data center, base station, charging station, etc.
(2) Artificial graphite heat dissipation film: made of polyimide (PI film) through carbonization and graphitization, it is currently the thinnest heat dissipation film material, the thinnest can be 0.01mm, widely used in mobile phones, computers and other intelligent terminal products.
(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 processing procedure of the Nano carbon heat sink film, only need to open the mold and cut, the cost is low and the price is low.
Synthetic graphite film is mainly used in smart phones. The amount depends on the performance and requirements of mobile phones, about 3-6 pieces. The components used include lens, CPU, OLED display screen, Wi-Fi antenna, wireless charging and battery, etc. Among them, CPU has the highest requirement for heat dissipation, followed by wireless charging, lens and battery, display screen and Wi-Fi antenna. At present, the price of high thermal conductivity graphite film is about 0.2-0.3 USD / piece. It is estimated that the value of single graphite film is 1-2 US dollars. In the future, with more innovative electronic design of smart phones, the value of single machine graphite film is expected to further improve.
PI film is the core material of artificial graphite film. The artificial graphite heat dissipation film widely used in mobile phones is made of polyimide (PI film) through carbonization and graphitization. Polyimide, tape and protective film are the key raw materials in the upstream, among which polyimide (PI film) is the main one, and the cost accounts for up to 30%. PI film is a kind of high performance insulating material, which can be widely used in satellite navigation, digital products, computers, mobile phones and other fields.