What is HTCC
High temperature co fired ceramic HTCC (high temperature co fired ceramic) is made of tungsten, molybdenum, molybdenum, manganese and other high melting point metal heating resistance paste, which is printed on 92 ~ 96% alumina cast ceramic green body according to the requirements of heating circuit design, and 4 ~ 8% sintering additives are then laminated in multiple layers, and burned together at 1500 ~ 1600 ℃ under high temperature.
Thus, it has the advantages of corrosion resistance, high temperature resistance, long service life, high efficiency and energy saving, uniform temperature, good thermal conductivity, fast thermal compensation speed, etc., and it does not contain harmful substances such as lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, polybrominated diphenyl ethers, and meets the environmental protection requirements of the European Union, such as RoHS.
Due to the high firing temperature, HTCC cannot use low melting point metal materials such as gold, silver and copper, but must use refractory metal materials such as tungsten, molybdenum and manganese. These materials have low conductivity and will cause defects such as signal delay, so they are not suitable for making substrates for high-speed or high-frequency micro assembly circuits. However, because HTCC substrate has the advantages of high structural strength, high thermal conductivity, good chemical stability and high wiring density, it has a wide application prospect in high-power micro assembly circuits.
Classification of HTCC
Alumina, mullite and aluminum nitride are the main components of high temperature co fired ceramics.
alumina
Alumina ceramic technology is a relatively mature microelectronic packaging technology. It is sintered at 1500-1700 ℃ with 92-96% alumina and 4-8% sintering additives. Its conductor materials are tungsten, molybdenum, molybdenum manganese and other refractory metals.
The substrate technology is mature, the cost of dielectric materials is low, and the thermal conductivity and bending strength are high. However, alumina multilayer ceramic substrates have the following disadvantages:
(1) High dielectric constant affects the improvement of signal transmission speed;
(2) High conductor resistivity and large signal transmission loss;
(3) The coefficient of thermal expansion is quite different from that of silicon, which limits its application in supercomputers.
Mullite
The dielectric constant of mullite is 7.3-7.5, while the dielectric constant of alumina (96%) is 9.4, which is higher than mullite, so the signal transmission delay time of mullite can be about 17% smaller than that of alumina. Moreover, the thermal expansion coefficient of mullite is very close to that of silicon, so this substrate material has been developed rapidly.
For example, Hitachi, shinko and other companies have developed mullite multilayer ceramic substrates, and their products have good performance indicators. However, the wiring conductors of this substrate can only be tungsten, nickel, molybdenum, etc., with high resistivity and lower thermal conductivity than alumina substrate.
Aluminum nitride
For aluminum nitride substrate, due to its high thermal conductivity and thermal expansion coefficient matching with semiconductor materials such as Si, SiC and GaAs, its dielectric constant and dielectric loss are better than alumina, and AlN is a relatively hard ceramic, which can still work well under harsh environmental conditions.
For example, AlN Ceramics still have excellent stability at high temperature. Therefore, aluminum nitride as multilayer substrate material has been widely studied at home and abroad and has made remarkable progress.
The disadvantages of aluminum nitride substrate are:
(1) The wiring conductor has high resistivity and large signal transmission loss;
(2) High sintering temperature and high energy consumption;
(3) The dielectric constant is higher than that of low temperature co fired ceramic dielectric materials;
(4) The thermal conductivity of aluminum nitride substrate decreases after CO firing with tungsten, molybdenum and other conductors;
(5) Screen printed resistors and other passive components cannot be incorporated into the high-temperature co firing process, because the metal oxides in the slurry of these passive components will react in the reducing atmosphere of the process and deteriorate their performance;
(6) The outer conductor must be nickel plated and gold plated to protect it from oxidation, while increasing the surface conductivity and providing a metallized layer that can be used for wire welding and tin welding components.
Despite these shortcomings, in general, aluminum nitride substrates have more advantages than other high-temperature co fired ceramic substrates, and have a good development prospect in the field of high-temperature co fired ceramics.
Application of HTCC HTCC ceramic heating element is a new type of high-efficiency, environment-friendly and energy-saving ceramic heating element. Compared with PTC ceramic heating element, it can save 20 ~ 30% electric energy under the same heating effect. Therefore, the products are widely used in daily life, industrial and agricultural technology, military, science, communication, medical treatment, environmental protection, aerospace and many other fields.
Such as small warm air heaters, hair dryers, dryers, clothes dryers, heaters, cold and warm dehumidifiers, hand warmers, dryers, electric heating splints, electric irons, electric irons, curling irons, electronic thermos bottles, incubators, incubators, kerosene vaporizers, electric cookers, toilet ceramic heaters, water heaters, infrared Physiotherapeutics, intravenous injection heaters, small special crystal device thermostatic troughs, industrial drying equipment Electric heater, heating element of water, oil and acid-base liquid. As shown in the figure, there are arc-shaped heating plates and circular heating plates made of HTCC.
