Comparison of several LED substrate materials

Comparison of several LED substrate materials

 

When selecting substrate materials, materials with high thermal conductivity are generally selected as substrates, and the equivalent thermal resistance of these materials is calculated and compared, and then materials that are more favorable to high-power LED heat dissipation are selected. Let's take a look at the performance comparison of the following substrate materials.

Beryllium oxide substrate

 

Beryllium oxide is an excellent thermal conductor with high hardness and strength, and the thermal conductivity of the oxide substrate is more than ten times that of the alumina substrate, which is suitable for high-power circuits, and its dielectric constant is low, and it can also be used for high-frequency circuits. But its cost is higher.

 

Aluminum nitride substrates

Aluminium nitride, unlike alumina, is not naturally occurring in nature. Therefore, aluminum nitride needs to be manufactured artificially, and the price of aluminum nitride is more expensive than that of aluminum oxide. Its outstanding excellent properties are the same thermal conductivity as beryllium oxide, as well as good electrical insulation properties and dielectric properties. Compared with alumina, the insulation resistance, insulation withstand voltage is higher, and the dielectric constant is lower, especially the thermal conductivity of aluminum nitride is more than 10 times that of alumina, and CTE matches the silicon wafer. Aluminum nitride is one of the few materials that has good thermal conductivity and good electrical insulating properties.

 

Ceramic substrates

Among the practical ceramic substrate materials, alumina has a low price, and its comprehensive performance is the best in terms of mechanical strength, insulation, thermal conductivity, heat resistance, thermal shock resistance, chemical stability, etc., and it is used the most as a substrate material. The glass composition of alumina ceramics is generally composed of silica and other oxides, and the glass content can vary from very high to very low, because the thermal conductivity of glass is very poor, therefore, the thermal conductivity of ceramics with high glass content must be paid attention to when manufacturing high-density and high-power circuits.

 

SiC substrates

SiC is a strong covalent bond compound, second only to diamond in hardness, and it has excellent wear resistance and chemical resistance. The thermal conductivity of high-purity single crystals is also second only to diamond. Compared to other materials, its thermal diffusion coefficient is large, even greater than that of copper, and its coefficient of thermal expansion is close to that of silicon. At room temperature, its thermal conductivity is higher than that of aluminum, up to more than 20 times that of alumina substrates, but its thermal conductivity decreases significantly with the increase of temperature. Compared to alumina, it has a high dielectric constant, and it has a differential insulation withstand voltage.

 

AlSiC substrates

As a reinforcing material, SiC particles have the advantages of excellent performance and low cost, and their CTE is the closest to the CTE of Si, and the thermal conductivity

 

It is 80-170W/(mK), the elastic modulus is 450GPa, and the density is 3.2g/; As a substrate material, Al has the advantages of high thermal conductivity (170-220 W/(mK)), low density (279 g/), low price, and easy processing, but its disadvantage is that the CTE is high. However, after the two composite materials are formed, they can give full play to the advantages of A1 and their respective advantages, and overcome their respective shortcomings, so they can show excellent overall performance.

 

The thermal conductivity of AlSiC is about 10 times that of Kovar alloy and alumina, and comparable to that of Si and Cu-W. The CTE of AlSiC is similar, and the CTE can be adjusted by the amount of addition, so that the exact coefficient of thermal expansion can be matched, so that the interfacial stress of adjacent materials can be minimized, and high-power chips can be mounted directly on the substrate without worrying about their mismatch stress.