GRAPHITE HEAT DISSIPATION FILM

Content

 

1. Preface

2. What is graphite heat dissipation film 

3. Classification of graphite 

4. Characteristic of heat dissipating graphite film 

5. What is graphite sheet 

6. Application of graphite materials 

 

1. Preface

With the development of electronic devices and products in the field of high integration and high computing, the dissipated power is doubled, and heat dissipation is becoming an urgent problem to be solved.

On September 16, 2011, Xiaomi mobile phone held a conference in Beijing 798. At the meeting, Lei Jun, CEO of Xiaomi Technology, said that heat dissipation is critical because Xiaomi mobile phones use dual-core 1.5G processors and large screens.

How to solve this problem?

Graphite heat dissipation film can effectively solve the heating problem caused by high performance.

 

2. What is graphite heat dissipation film?

 

First of all, let's look at something like graphite. Graphite is an allotrope of elemental carbon. Each carbon atom is surrounded by three other carbon atoms (arranged in honeycomb-like hexagons) which are covalently bonded to form a covalent molecule.

 

Graphite has the following special properties because of its special structure: a) high temperature resistance; b) conductivity and thermal conductivity; c) lubricity; d) chemical stability; e) plasticity; f) thermal shock resistance.

 

3. Classification of graphite

 

1). Natural graphite

The technological properties of graphite mainly depend on its crystalline morphology. Graphite minerals with different crystalline forms have different industrial values and uses. In industry, according to different crystalline forms, natural graphite is divided into three categories: block graphite, flake graphite and cryptocrystalline graphite.

2). Artificial graphite

In general, all graphite materials obtained by high temperature treatment through organic carbonization and graphitization can be called artificial graphite, such as carbon fiber, pyrolytic carbon and foam graphite. In the narrow sense, artificial graphite usually refers to bulk solid materials, such as graphite electrodes, isostatic graphite, which are prepared by mixing, kneading, shaping, carbonization and graphitization with low impurity carbon as aggregate and coal tar pitch as binder.

Artificial graphite is usually formed by vibration, extrusion, moulding and isostatic pressing.

Heat-dissipating graphite film is a very thin GTS, comprehensive thermal conductive material, also known as heat-conducting graphite film, heat-conducting graphite sheet, graphite heat sink sheet and so on, which provides a possibility for the development of thin electronic products. The heat dissipating graphite film has good reprocessing property and can be compounded or glued with other film materials such as PET according to its use. The material is elastic, can be cut and stamped into arbitrary shape, and can be bended many times. It is suitable for fast heat conduction from point heat source to surface heat source, and has high thermal conductivity, and is made of a highly oriented graphite polymer film. In addition to traditional methods, heat dissipation graphite film is an ideal material for heat dissipation management, heat dissipation of power devices in limited areas or heat dissipation of auxiliary power devices.

 

4. Characteristic of heat dissipating graphite film

 

1). Excellent thermal conductivity: 700-1300 w/(m-k) (2-4 times as much as copper and 3-6 times as much as aluminium), thermal resistance 40% lower than aluminium and 20% lower than copper.

2). Light weight: 0.75-2.1 g/cm3 (1/4 to 1/10 of copper and 1/1.3 to 1/3 of aluminium).

3). Low thermal resistance, soft and easy to cut (can bend repeatedly).

4). Ultrathinity: thickness (0.025-0.1mm).

5). Surface can be combined with other materials such as metal, plastic, self-adhesive to meet more design functions and needs.

 

 

5. What is graphite sheet?

 

Graphite sheet is a new heat conducting and heat dissipating material. It conducts heat uniformly in both directions; shields heat sources and components, and improve the performance of consumer electronic products. We also call it graphite foil, graphite film, graphite paper or graphite tape.

    

 

 

Heat dissipation principle of graphite heat sink sheet

Typical thermal management system is composed of external cooling device, radiator and thermal section. The important function of the radiator is to create the maximum effective surface area on which the heat is transferred and taken away by external cooling media. Graphite heat sink sheet can transfer heat effectively by distributing heat evenly in two-dimensional plane to ensure that the components work at the temperature they are subjected to.

 

Fig. 1 Thermal diffusion diagram of TCGS-S graphite heat sink sheet

 

The following is the relationship of several materials and heat three important parameters (thermal conductivity, specific heat capacity and density) of the reference value:

 

Material Thermal conductivity (W/mK) Specific heat capacity (J/kg.K) Density (g/cm3)

Aluminum 200 880 2.7

Copper 380 385 8.96

Graphite Horizontal 100~1500, vertical 5~20 710 0.7~2.1

 

Thermal conductivity is very easy to understand, popular understanding is the speed of heat conduction, for heat dissipation, of course, the faster the better, the greater the value of the better, the opposite for thermal insulation materials.

 

This is a parameter of thermal conductivity:

 

Thermal conductivity of various materials (a-b direction)

 

Diamond

Graphite sheet 25um

Graphite sheet 70um

Graphite sheet 100um

Copper

Aluminum

Magnesium oxide alloy

Stainless steel

Heat conduction sheet

 

 

 

 

 

 

 

 

 

 

 

 

 

Thermal conductivity W/(m.K)

From the data shown in the figure, it can be concluded that the horizontal thermal conductivity of graphite heat dissipation film has great advantages over that of traditional heat dissipation materials. At the same time, we should also note that graphite has a good thermal insulation effect on this parameter because its vertical thermal conductivity is only 5-20W/mk (as shown in the figure below). The heat is well diffused and evenly distributed, thus eliminating local hot spots and avoiding local overheating.

 

 

Comparison of parameters between graphite heat dissipation film and traditional heat dissipation material (thermal conductivity)

 

Now let's look at the second parameter: specific heat capacity. This parameter represents the heat required to increase the temperature of the material by 1℃ per KG. So for the radiator, the higher the specific heat capacity is, the better, because the larger the specific heat capacity of the radiator is, the lower the temperature rises after it absorbs heat, that is, the larger the specific heat capacity is. From this parameter, graphite is close to aluminium, almost twice as much as copper. Popular understanding is equivalent to heat storage capacity, but also did not dissipate heat. When heat production is not very large, the larger the specific heat capacity the better, because the degree of temperature rise is lower. However, when the heat continues to increase rapidly, the specific heat capacity has little effect on heat dissipation.

 

Comparison of parameters between graphite heat dissipation film and traditional heat dissipation material (specific heat capacity)

 

Another application environment may have nothing to do with heat itself. Because of the softness of graphite, the film-shaped radiator needs to be attached to a plane. That is to say, it basically needs to be attached to some parts. This is why we see it mostly on the shield, the empty PCB surface and the LED substrate. At the same time, because of its good thermal conductivity, it can also play a very good shielding effect.

 

In order to better adapt to the fluctuating surface of electronic devices and circuit modules, it is necessary to process graphite thermal conductive sheets. The main processing methods are: 1. Gum. 2. Back film. According to the actual demand of the product, choose the appropriate processing method.

 

Gum processing: For better adhesion to IC and PCB, gum processing is carried out on the surface of thermal conductive graphite sheet.

 

Processing of graphite heat dissipating film gum

 

Back film processing: In some circuit designs requiring insulation or heat insulation, in order to achieve better function optimization, back film processing is carried out on the surface of graphite sheets.

 

 

Back film processing of graphite heat dissipating film

 

 

With the acceleration of the upgrading of electronic products and the increasing demand for heat dissipation management of miniature, highly integrated and high-performance electronic devices, Dasen has introduced a new heat dissipation technology for electronic products, i.e. a new solution of graphite material heat dissipation. This new artificial graphite solution has the characteristics of high heat dissipation efficiency, small occupancy space and light weight. It conducts heat evenly along two directions, eliminates "hot spot" areas, shields heat sources and components, and improves the performance of consumer electronic products. Widely used in PDP, LCD TV, Notebook PC, UMPC, Flat Panel Display, MPU, Projector, Power Supply, LED lighting and other electronic products graphite heat dissipation materials. Graphite heat dissipation materials have been widely used in communication industry, medical equipment and other heat dissipation.  

 

Some pictures of product application:

Application in iPhone

 

 

Application in Samsung mobile phone

 

 

Application in HTC mobile phone

 

Application in Xiaomi mobile phone

 

 

Application in SONY VAVIO laptop