Aluminum nitride (AlN) is a kind of advanced ceramic material with excellent comprehensive performance. It is a kind of new packaging material which is favored by domestic and foreign experts. It is also recognized as the most promising high thermal conductivity ceramic material at present. Research on it began more than a century ago, but it was only used as a nitrogen-fixing fertilizer. As a covalent compound, aluminum nitride is difficult to be sintered due to its high melting point and low self-diffusion coefficient. It wasn’t until the 1950s that aluminum nitride ceramics were first made and used as a refractory,
Then it is widely used in the smelting of pure iron, aluminum and aluminum alloy. Since the 1970s, with the further development of research, the preparation technology of aluminum nitride has gradually matured, and its application field and scale have also been expanding.
Aluminum nitride is a covalent bond compound with hexagonal wurtzite structure and lattice constants a=3.11, C =4.98. Its theoretical density is 3.26g/cm3, Mohs hardness is 7~8, and decomposition temperature is 2200~2250℃
Aluminum nitride ceramics have high thermal conductivity, suitable for high power, high lead and large size chips; Its thermal expansion coefficient matches that of silicon and its dielectric constant is lower. Its material has high mechanical strength and can still work under harsh conditions. Therefore, aluminum nitride can be made into very thin substrates to meet the requirements of different packaging substrates. Aluminum nitride ceramics as high thermal conductivity, high sealing material has great development potential, is an important research field of ceramic packaging materials. It is expected that aluminum nitride ceramics will eventually replace the current alumina ceramics and beryllium oxide ceramics in both substrate and packaging areas. [2]
The main characteristics of aluminum nitride ceramics are as follows: 1) High thermal conductivity, 5~10 times that of alumina ceramics, and equivalent to highly toxic beryllium oxide; 2) The thermal expansion coefficient (4.3×10-6/℃) matches the semiconductor silicon material (3.5-4.0×10-6/℃); 3) Good mechanical properties, higher than beryllium oxide ceramics, close to alumina; 4) Excellent electrical performance, with high insulation resistance and low dielectric loss; 5) Multi-layer wiring can be carried out to achieve high density and miniaturization of packaging; 6) Non-toxic, beneficial to environmental protection.
