Foam is a high molecular polymer with many small cells, the solid phase is a polymer matrix, and the small cells are filled with gas.

The foam is divided into open and closed cells according to the structure of the cell. The cell connected with the cell is called the open cell structure, and the cell that is not connected with the cell is called the closed cell structure.

Example of application of polyurethane foam in mobile phone:

Application example of polyurethane foam in automobile:

Summary of the main uses of foam:

(1) Panel interlayer: function-no pollution, prevent loosening, prevent impact noise, prevent adhesion.

(2) Around the LED: prevent light leakage, absorb shock, and increase air tightness.

(3) Lower perimeter of PCB: absorb shock, absorb vibration, fill gaps, heat insulation effect.

(4) Keyboard gasket: rebound, no pollution, and good dimensional stability.

(5) Around the battery: no pollution, absorb impact sound, improve air tightness.

(6) Foot pads: good friction, no pollution, and good dimensional stability.

(7) Rear pad of disk drive: absorb vibration, prevent impact noise, and improve air tightness.

(8) Friction pads: good friction, no pollution, and good dimensional stability.

(9) Disk cover cushion: absorb vibration, block motor noise, prevent vibration and improve air tightness.

(10) Around the speaker: prevent noise and fill gaps.

(11) Around the LCD: Dustproof, absorb shock, fill gaps, improve shading.

2 Application Case of Graphite Sheet in Xiaomi Mobile Phone

1. What is "graphite heat sink"

First, let's take a look at such things as "graphite". Graphite is an allotrope of elemental carbon. Let's take a look at it if we have studied chemistry. We can associate some characteristics of graphite with carbon element, including the very famous stability of carbon, so carbon element is common in many industrial uses.

Graphite element structure

At present, the graphite we know has high temperature resistance, electrical and thermal conductivity, lubricity, chemical stability, plasticity and thermal shock resistance. Using graphite as part of mobile phone design, we can see many suitable uses. For example, the current graphite heat sinks used in mobile phones mainly use the thermal conductivity of graphite.

2. What is "graphite heat sink"

Thermally conductive graphite sheet (LGS), also known as graphite heat sink, is a brand-new thermally conductive heat dissipation material with unique grain orientation and uniform heat conduction in both directions. The sheet structure can be well adapted to any surface, shielding heat sources and Components while improving the performance of consumer electronics.

Wide use of graphite heat sink

The reason why it can be designed as a graphite heat sink also uses the plasticity of graphite. We can make the graphite material into a sheet like a sticker and let it be attached to the circuit board inside the mobile phone. Not only can block the contact between the originals, but also play a certain role in earthquake resistance.

3. Introduction of the cooling principle of Xiaomi mobile phone

At the press conference of the Xiaomi mobile phone, Lei Jun solemnly announced the heat dissipation characteristics of the Xiaomi mobile phone. Although it is not the first time that the graphite heat sink is present in the mobile phone, it is relatively rare to promote it as an advantage.

The first graphite heat sink between the CPU chip and the middle layer

Previously, we have explored the internal structure of the Xiaomi mobile phone through the disassembly of the Xiaomi mobile phone (disassembly diagram tour, first evaluation, disassembly and installation video), and also completely saw two graphite heat sinks. Although I saw the graphite heat sink and the location of the graphite heat sink, it is not clear to everyone how the heat dissipation principle is. Here we try to introduce a simple status:

One of the heat sources of Xiaomi mobile phones is the CPU and Flash chips. Therefore, on the encapsulation layer of these chips, a "7" shaped graphite heat sink is attached. The other side of the heat sink will be attached in the middle of the fuselage. Above the metal plate. Another large graphite heat sink is attached to the other side of the metal plate in the middle of the Xiaomi mobile phone, which corresponds to the back of the screen.

The second graphite heat sink between the screen and the middle layer

Therefore, when the phone is not disassembled, you can see that the heat behind the screen and the CPU/Flash will be transferred to each other through the middle metal layer, which will eventually distribute the heat evenly and dissipate heat through the air flow. Therefore, we can say that part of the heat of the Xiaomi mobile phone will be assisted by the LCD side to dissipate heat. In addition, the back side of the mobile phone is also another heat dissipation surface.

Xiaomi mobile phone with graphite heat sink can control the calorific value at a reasonable level

Therefore, we can say that the graphite heat sink of Xiaomi mobile phone actually conducts heat and distributes the heat evenly, indirectly, it also plays a role of heat dissipation. So we can control the Qualcomm MSM8260 electric tiger)