AlN has a high thermal conductivity, with a theoretical value of 320W/(mK), which is 7-10 times that of Al2O3. With such a high “heat dissipation gene”, aluminum nitride naturally becomes the focus of attention in efficient heat dissipation.
At present, the application of aluminum nitride in the field of high thermal conductivity is mainly concentrated in two aspects: packaging substrate and thermal conductive filler.
Packaging substrate
AlN: an ideal electronic packaging substrate material
The packaging substrate mainly uses the high thermal conductivity of the material itself to export heat from the chip (heat source) to achieve heat exchange with the external environment. For power semiconductor devices, the packaging substrate must meet the following requirements:
High thermal conductivity;
Match with the thermal expansion coefficient of the chip material;
Good heat resistance, meet the high temperature use requirements of power devices, and have good thermal stability;
Good insulation, meet the electrical interconnection and insulation requirements of the device;
High mechanical strength, meet the strength requirements of device processing, packaging and application processes;
Affordable price, suitable for large-scale production and application
Currently, commonly used electronic packaging substrates can be mainly divided into polymer substrates, metal substrates (metal core circuit boards, MCPCB) and ceramic substrates. Ceramic materials themselves have high thermal conductivity, good heat resistance, high insulation, high strength, and thermal matching with chip materials. They are very suitable as power device packaging substrates. At present, commonly used electronic packaging ceramic substrate materials include aluminum oxide, aluminum nitride, silicon nitride, beryllium oxide, etc.
The theoretical thermal conductivity of AlN ceramics is very high, and the thermal conductivity of its commercial products can reach 180W/(mK)~260W/(mK). The thermal expansion coefficient is only 50% of that of alumina ceramics. In addition, it has the advantages of high insulation strength, low dielectric constant, and good corrosion resistance. In addition to the high cost, the comprehensive performance of aluminum nitride ceramics is better than that of alumina ceramics. It is an ideal electronic packaging substrate material, especially suitable for fields with high thermal conductivity requirements.
Thermally conductive fillers
With the miniaturization and high integration of electronic products and their devices, heat dissipation has become an important bottleneck restricting the development of electronic technology, and thermally conductive composite materials such as thermally conductive interface materials that determine the heat dissipation effect have received more and more attention.
At present, commercial thermally conductive composite materials are generally composed of polymers and thermally conductive fillers. Since the thermal conductivity of polymers is very low, generally less than 0.5W/m·K, the thermal conductivity of thermally conductive composite materials is mainly determined by thermally conductive fillers. At present, the most widely used fillers in the market are oxide fillers represented by Al2O3, etc., but the intrinsic thermal conductivity of aluminum oxide is only 38~42W/m·K. Due to its limitation, it will be difficult to prepare thermally conductive composite materials that meet the future market demand for heat dissipation materials.
In comparison, the theoretical thermal conductivity of AlN is as high as 320W/m·K, and it has excellent properties such as small thermal expansion coefficient, good insulation performance, low dielectric constant, and matching with silicon expansion coefficient. Therefore, the preparation of thermally conductive composite materials using AlN powder as filler has been popular in recent years.
It should be pointed out that although the comprehensive performance of aluminum nitride is far superior to that of aluminum oxide, beryllium oxide, and silicon carbide. It is considered to be an ideal material for high-integration semiconductor substrates and electronic device packaging, it easily absorbs water in the air to undergo hydrolysis, so that its surface is coated with a layer of aluminum hydroxide film, resulting in interruption of the heat conduction path and affected transmission of phonons. Its large content filling will greatly increase the viscosity of the polymer, which is not conducive to molding processing.
To overcome the above problems, the aluminum nitride thermal conductive particles must be surface modified to improve the interface bonding problem between the two. There are currently two main methods for modifying the surface of inorganic particles. One is the surface chemical reaction method, which is the adsorption or reaction of small molecules such as coupling agents on the surface of inorganic particles. The other is the surface grafting method, which is the grafting reaction of polymer monomers with hydroxyl groups on the surface of inorganic particles.
Currently, coupling agent surface modification is commonly used, such as silane and titanate coupling agents and other types of surface treatment agents. Compared with the surface chemical reaction method, the surface grafting method has greater flexibility. It can select monomers and grafting reaction processes that meet the conditions according to different characteristic requirements.
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