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Material classification-"ultra-high thermal conductivity" materials

Time : 2023-12-05 Hits : 8

"Ultra-high thermal conductivity" materials forced out by 5G

The 5G base station has indeed greatly improved compared to 4G in terms of transmission power, bandwidth, number of user connections, etc. However, if you look at the base station power consumption comparison test of 4G/5G equipment, you will find that the single station power consumption of the 5G base station is approximately 2.5~3.8 times that of 4G single station! Industry insiders claim that the substantial increase in AAU power consumption is the main reason for the increase in 5G power consumption. The Chinese name of AAU is "Active Antenna Unit", which is mainly responsible for converting baseband digital signals into analog signals, and then modulating them into high-frequency radio frequency signals, which are then amplified to sufficient power by a PA (power amplifier) and then emitted by the antenna.

 

In addition, the transistors of 5G circuits are getting smaller and smaller, which will lead to increased leakage current and leakage power consumption. The leakage current of the chip will change with temperature. When the chip temperature increases, the static power consumption will increase exponentially. Therefore, introducing advanced heat dissipation technology to ensure that the base station operates within a reasonable temperature range can significantly reduce the power consumption of the base station.

 

This means that 5G equipment will generate three times the heat of 4G, but the internal space will be reduced to 30% of that of 4G equipment! In other words, the heat density of 5G equipment is nearly 10 times that of 4G equipment!

 

Such a huge increase in heat density shows how prominent the contradiction between the development of 5G technology and heat dissipation is. No wonder the demand for ultra-high thermal conductivity gaskets has exploded!

 

Judging from the current status of the industry, the more reliable candidates as thermal conductive fillers include the following materials:

MaterialThermal conductivity(W/mK)StabilityInsulationDensity(g/cc)
Al2O338GoodGood4
Si15GoodGood2.6
SiC83.6-220GoodBad3.2
AlN80-320BadGood3.3
BN60-300GoodGood2.3


The thermal conductivity must be much higher than that of alumina, and the only two players that have good insulation properties are AlN aluminum nitride and BN boron nitride.

The surface of aluminum nitride AlN is extremely active. After absorbing moisture, it is easily hydrolyzed to produce Al(OH)3, which interrupts the phonon path and seriously affects heat conduction.

AlN+3H2O=Al(OH)3↓+NH3↑

Studies have shown that the hydrolysis reaction of AlN can occur even at lower temperatures, and it is an all-weather hydrolysis player.

40nm aluminum nitride hydrolysis TEM micrograph. However, as an electronic grade material, it must pass the test of double 85 high temperature and humidity to be qualified. Therefore, the surface of the AlN filler is treated to form a nanoscale dense oxide layer, so that It is equivalent to wrapping each AlN particle with a raincoat. In theory, the problem of moisture absorption and hydrolysis is easily solved.

 

BN boron nitride has high thermal conductivity and very good insulation properties, so it is nicknamed "white graphene". If a large amount is added to the silicone rubber base material, the thermal conductivity can be improved by several orders of magnitude on its own.

 

However, the surface of BN lacks active functional groups and its chemical properties are too stable, which makes it difficult for BN nanoparticles to be wetted and compatible with polymer substrates, has poor dispersion, and is very easy to agglomerate. This will affect the effective establishment of phonon conduction pathways.

Studies have shown that when the amount of BN added exceeds 180 parts, the viscosity increases sharply and the mechanical properties decrease significantly. If you refer to the surface treatment scheme for alumina, you will find that BN modification treatment lacks a green, simple and efficient method.

However, most of the current market-oriented thermal conductive products are concentrated in alumina Al2O3 filler systems, and there are still very few thermal conductive gasket products using metal nitrides.

-------------------------------------------------------------------------Reprinted from Zhihu-Bondme(知乎-胶我选Bondme).

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