Alumina is a widely known and commonly used precision ceramic material. For decades, because of its high electrical insulation, it was once used in electrical components. Its high strength, high corrosion resistance and high wear resistance are widely used in our lives. Because alumina is a material with relatively balanced mechanical performance parameters, it is widely used, including wear-resistant products used in high-temperature industrial furnaces and various electronic components. Due to stable chemical and physical properties, alumina ceramic substrate is widely known as a precision ceramic material.
Alumina ceramics are divided into high purity type and ordinary type
High purity alumina ceramics refer to ceramic materials with Al2O3 content of more than 99.9%. Because the sintering temperature is up to 1650-1990 ℃, the transmission wavelength is 1-6 μ m. Generally, molten glass is made to replace platinum crucible; The utility model can be used as a sodium lamp because of its light transmission property and alkali metal corrosion resistance; It can be used as integrated circuit substrate and high-frequency insulating material in the electronic industry.
Ordinary alumina ceramics can be divided into 99 porcelain, 95 porcelain, 90 porcelain and 85 porcelain according to the content of Al2O3. Sometimes those with Al2O3 content of 80% or 75% can also be classified as ordinary alumina ceramics. 99 alumina ceramic materials are used to make high-temperature crucibles, refractory furnace tubes and special wear-resistant materials, such as ceramic bearings, ceramic seals and water valve pieces; 95 alumina ceramics are mainly used as corrosion resistant and wear-resistant parts; 85 ceramics can be sealed with molybdenum, niobium, tantalum and other metals, and some of them can be used as electric vacuum devices, because some of them are often mixed with talc, which improves the electrical properties and mechanical strength.
Surface metallization process of alumina ceramics
Because of its good electrical performance, alumina ceramics are most widely used in electronic and electrical fields. As a substrate material for electronic and electrical appliances, surface metallization must be involved. Because ceramics are insulating materials, only surface metallization can lead to electrical conduction.
Ceramic metallization is to firmly adhere a layer of metal film on the ceramic surface to realize the welding between ceramics and metals. More advanced application is to form circuits on the ceramic surface, which can not only be welded, but also be used as a wire to transmit current. At present, the traditional metallization methods include thick film method, DBC method, DPC method, LTCC, HTCC. The advantages and disadvantages of these processes are described one by one as follows:
01 Thick film method
Through screen printing, various circuits, resistors and capacitors are printed on the ceramic substrate. It is undeniable that this process is widely used and can carry large currents. Most applications of ceramics are realized by thick film method, but can it really cure all diseases? As we all know, the precision of screen printing is very unsatisfactory. The combination of silver paste and ceramics is not satisfactory. At the same time, silver paste can only be solidified after sintering at a certain temperature. I believe that many people in the industry have been deeply troubled by these shortcomings. In addition, the circuit of thick film method is relatively thick, which is a big obstacle to the miniaturization of electronic products, so we have to come up with other methods.
02 DBC method
This process is often applied to high-power modules. The copper layer is thick, which can carry large current, has good thermal conductivity, high strength, strong insulation, and the thermal expansion coefficient matches with semiconductor materials such as Si. However, the reaction ability of ceramic substrate and metal materials is low, the wettability is poor, and the implementation of metallization is quite difficult. It is not easy to solve the problem of micro pores between Al2O3 and copper plates. In addition, the high sintering temperature and high cost can only be used in fields with special needs.
03 OPC method
It is widely used in the LED field. The technology is mainly in the hands of Taiwan manufacturers. Tongxin Electronics accounts for more than half of the annual shipments. In addition, Aisipei has the advantages of high circuit precision and smooth surface, which is more suitable for cladding/eutectic packaging. International LED manufacturers Cree, Osram, etc. are using Tongxin's substrate. Its cost is lower than DBC method. At present, the DPC technology of Siliton has been officially mass produced in China.
04 LTCC
Because LTCC uses thick film printing technology to complete the line production, the line surface is relatively rough and the alignment is not accurate. Moreover, the multilayer ceramic laminated sintering process also has the problem of shrinkage ratio, which limits its process resolution, and greatly challenges the promotion and application of LTCC ceramic substrate.
05 HTCC
Due to the high sintering temperature, this process has few users and is basically replaced by LTCC.