alumina ceramic substrate overview of manufacturing process
Alumina ceramic substrate is widely used in multilayer wiring ceramic substrate, electronic packaging and high-density packaging substrate due to its high mechanical strength, good insulation and light proof. But at present, there are some problems in the production of alumina ceramic substrate in China, such as the high sintering temperature, which leads to the application of this component mainly depends on imports.
With the continuous development of modern communication technology, electronic components are becoming more and more simple, miniaturized and highly integrated. The requirements for circuit packaging technology are also increasing, and the requirements for alumina ceramic packaging substrate are also increasing. Alumina ceramics have good properties in strength, heat resistance, impact resistance, electrical insulation and corrosion resistance, and the raw materials are sufficient, the price is affordable, and the manufacturing and processing system is perfect, which plays an important role in industrial packaging.
1、 Crystal structure, classification and properties of alumina ceramic substrate
Alumina has many homogeneous and heterogeneous crystals, such as α - Al2O3, β - Al2O3, γ - Al2O3 and so on. Among them, α - Al2O3 has high stability, its crystal structure is compact, its physical and chemical properties are stable, it has the advantages of high density and mechanical strength, and it is also widely used in industry.
Alumina ceramics are classified by alumina purity. Alumina ceramics with alumina purity of more than 99% are called corundum ceramics. Alumina ceramics with alumina purity of 99%, 95% and 90% are called 99 ceramics, 95 ceramics and 90 ceramics. Alumina ceramics with alumina content of more than 85% are generally called high alumina ceramics. The volume density of 99.5% alumina ceramics is 3.95g/cm3, the bending strength is 395mpa, the linear expansion coefficient is 8.1 × 10-6, the thermal conductivity is 32W / (m · K), and the insulation strength is 18kV / mm.
2、 Manufacturing process of black alumina ceramic substrate
Black alumina ceramic substrate is mostly used in semiconductor integrated circuits and electronic products. This is mainly because most electronic products have high photosensitivity, and the packaging materials need to have strong blackout to ensure the clarity of digital display. Therefore, black alumina ceramic substrate is mostly used for packaging. With the continuous update of modern electronic components, the demand for black alumina packaging substrate is also expanding. At present, research on the manufacturing process of black alumina ceramics has been actively carried out at home and abroad.
Based on the requirements of its application field, the selection of black coloring materials needs to combine the properties of ceramic raw materials. For example, it is necessary to consider that its ceramic raw materials need to have good electrical insulation. Therefore, in addition to the final chromaticity and mechanical strength of the ceramic substrate, the black coloring material should also consider its electrical insulation, thermal insulation and other functions of electronic packaging materials.
In the process of ceramic coloring, the low temperature environment may cause the volatility of the coloring materials to be affected and keep warm for a certain period of time. In this process, the free state coloring materials may aggregate into spinel compounds, which can avoid the continuous volatilization of the coloring materials in the high temperature environment and ensure the coloring effect.
3、 Technology of producing black alumina ceramic substrate by tape casting
The casting process is a manufacturing process of adding solvents, dispersants, binders, plasticizers and other substances into the ceramic powder to make the slurry evenly distributed, and then making different specifications of ceramic chips on the casting machine, also known as the scraper forming process. The process first appeared in the late 1940s and was used to produce ceramic chip capacitors. The advantages of the process are as follows:
(1) The equipment is simple in operation, efficient in production, capable of continuous operation and high in automation;
(2) The density of embryo and the elasticity of membrane were high;
(3) Mature technology;
(4) The production specification is controllable and the scope is wide.
The ceramic substrates used in modern production are mostly multilayer substrates. The purity of alumina ceramics is 90.0 ~ 99.5%. The higher the purity is, the better the performance is. However, the key problem lies in the higher requirements of sintering temperature for this part, which leads to the higher manufacturing difficulty.