Commonly used heat dissipation substrate materials include silicon, metals (such as aluminum and copper), ceramics (aluminum nitride and aluminum oxide), and composite materials. Although metal materials have high thermal conductivity, their high thermal mismatch with LED chip substrates makes it difficult to meet the requirements of high-power LED packaging; However, the low thermal conductivity of composite materials cannot solve the heat dissipation problem of high-power LEDs.

The heat dissipation substrate, as the main pathway for heat flow, is essential in the packaging application of high-power LEDs. It plays a very important role in improving the heat dissipation efficiency of devices, reducing junction temperature, and improving the reliability and lifespan of devices.

The function of LED heat dissipation substrate is to absorb the heat generated by the chip and conduct it to the heat sink, thereby achieving heat exchange with the outside of the chip.

Therefore, as an ideal heat dissipation substrate for LED, it must have the following characteristics in terms of physical, chemical, and electrical properties:

1) Good chemical stability and corrosion resistance

2) High thermal conductivity, coefficient of thermal expansion matching with chip material

3) Low dielectric constant and dielectric loss

4) Good electrical insulation and high mechanical strength

5) Low price and easy processing

6) Low density, non-toxic

Below are several ceramic substrates made of different materials:

1) Beryllium oxide substrate

An excellent thermal conductor with high hardness and strength. The substrate made of this material has a thermal conductivity more than ten times that of aluminum oxide substrate, making it suitable for high-power circuits with low dielectric constant. It can also be used in high-frequency circuits, but the cost is high. Beryllium oxide powder and its vapor are harmful to human health and pose environmental problems.

2) Alumina substrate

Aluminum oxide is the material with the lowest price and the most comprehensive performance among all ceramic substrates used. The glass composition of alumina ceramics is generally composed of silicon dioxide and other oxides, and the glass content can vary from high to low. Due to the poor thermal conductivity of glass, ceramics with high glass content need to pay special attention to their thermal conductivity when manufacturing high-density and high-power circuits. The matching between alumina raw materials and processed products needs to be strictly controlled.

3) Silicon carbide substrate

The hardness of silicon carbide is second only to diamond, and the thermal conductivity of high-purity single crystals is also second only to diamond. Compared with other materials, its thermal diffusion coefficient is very large, even larger than that of copper, and its coefficient of thermal expansion is close to that of silicon. At room temperature, the thermal conductivity is higher than that of aluminum, which can reach more than 20 times that of aluminum oxide substrates. However, the thermal conductivity significantly decreases with increasing temperature. Compared with alumina, it has a high dielectric constant and poor insulation and voltage resistance.

4) Aluminum nitride substrate

As a material with excellent properties such as high thermal conductivity, high strength, high resistivity, low density, low dielectric constant, non-toxic, and coefficient of thermal expansion matching with silicon, aluminum nitride ceramics have good insulation and mechanical properties, and are gradually popularized in commercial applications in emerging fields such as high-frequency telecommunications, LED lighting, new energy vehicles, high-speed iron, wind energy, and photovoltaic power generation.

Aluminum nitride, unlike aluminum oxide, does not form naturally in nature and requires manual preparation of aluminum nitride. This makes the production process of AlN materials more complex, with higher production costs, and currently, most domestic AlN materials cannot achieve high thermal conductivity and high strength application research.

5) Aluminum silicon carbide substrate (AI/SiC)

In recent years, aluminum silicon carbide substrates (AI/SiC) have attracted increasing attention due to their advantages such as low raw material cost, high thermal conductivity, low density, and strong plasticity. The coefficient of thermal expansion of SiC particles is similar to the coefficient of thermal expansion of LED chip substrate, with high elastic modulus and low density; At the same time, the high thermal conductivity, low density, low cost, and easy processing characteristics of aluminum give it unique advantages when used as a substrate material. Therefore, the aluminum silicon carbide substrate obtained by combining the two materials has excellent comprehensive performance and can be applied to high-power LED substrates.