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How to prepare ceramic substrates

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Method for Preparing Ceramic Substrate A typical molding method before ceramic firing is as follows: powder-limited molding (molding molding, isostatic pressing), kneading molding, tape casting, and the like. In the meantime, the tape casting method has been widely used in the production of substrates for LSI packages and hybrid integrated circuits because of its ease of completion of multilayering and high consumption efficiency.
Various types of ceramic substrates (1) Alumina (Al2O3) substrate? Material: Al2O3 material is usually produced by the Buy method. In this method, the raw material is bauxite (aluminite/boehmite and corresponding compounds). ); Preparation method: Al2O3 ceramics are generally formed by green sheet lamination method, the adhesive is generally selected from polyvinyl alcohol polybutyraldehyde (PVB), the firing temperature varies depending on the added combustion aid, generally 1550 ~ 1600 °C. The metallization method of the Al2O3 substrate is now mainly selected by the thick film method and the co-firing method, from the application of the slurry to the process skill, and is now satisfactory for all kinds of applications; use: hybrid integrated circuit substrate, LSI package substrate , multilayer circuit substrate. (2) Aluminum nitride (AlN) substrate material: AlN is an unnaturally occurring but an artificial mineral, which was first synthesized by Genther et al. in 1862. The representative preparation method of AlN powder is the recovery nitriding method and the direct nitriding method. The former is made of Al2O3 as a material, recovered by high-purity carbon, and then reacted with nitrogen. The latter is directly reacted with N2 to directly nitrite. Production method: Various methods for making Al2O3 substrate can be used for the production of AlN substrate, and the most used one is the green sheet lamination method, which is made by mixing AlN powder, organic binder, solvent and external active agent into ceramic. Slurry, cast, laminated, hot pressed, degreased, fired; AlN substrate characteristics: AlN thermal conductivity is more than 10 times that of Al2O3, CTE is matched with silicon wafer, AlN material is relative to Al2O3 It is said that the insulation resistance and the insulation withstand voltage are higher and the dielectric constant is lower. These characteristics are very valuable for the use of the package substrate; use: for VHF (Ultra High Frequency) band power amplifier module, high power equipment And laser diode substrate, etc.; (3) silicon carbide (SiC) substrate material: SiC is not naturally occurring but is made by artificially produced minerals, which are mixed in powder form by silica, coke and a small amount of salt, and heated by a graphite furnace. The reaction occurs at 2000 °C or higher to form α-SiC, and then the precipitates are increased to obtain a dark green block-like polycrystalline aggregate. The production method: SiC has good chemical stability and thermal stability, and it is difficult to use general methods for firing. Arrival densification, so the need to add sintering aids and special methods of firing, generally selected by vacuum hot pressing method; SiC substrate characteristics: its most characteristic property is that compared with other materials, its thermal diffusivity is particularly large So that it is larger than copper, and its heat shrinkage coefficient is closer to Si. Of course, it also has some defects. Relatively speaking, its dielectric constant is high and its dielectric withstand voltage is worse. Use: Regarding SiC substrate, it is long and short, and is used for low-voltage circuits and VLSI high-heat-dissipation packages with low pressure resistance. The substrate is, for example, a high-speed, high-integration logic LSI with a heat-dissipating tissue package, and a substrate for a super-large computer or a laser diode for optical communication. (4) The mullite (3Al2O3·2SiO2) substrate 3Al2O3·2SiO2 is one of the most stable crystal phases in the Al2O3-SiO2 binary system. Compared with Al2O3, the mechanical strength and thermal conductivity are lower, but the dielectric constant is lower. Low, so it is expected to further improve the signal transmission speed. The heat shrinkage coefficient is also low, and the thermal stress on the LSI can be reduced, and the difference in thermal shrinkage coefficient from the conductor materials Mo and W is also small, and then the stress generated between the conductor and the conductor is low. (5) The yttrium oxide (BeO) substrate has a thermal conductivity of more than ten times that of Al2O3, is suitable for high-power circuits, and has a low dielectric constant, and can be used for high-frequency circuits. The BeO substrate is basically made by a dry pressing method, and a small amount of MgO and Al2O3 may be added therebetween to form a BeO substrate by a green sheet method. Because of the toxicity of BeO powder, there are environmental problems. It is not allowed to consume BeO substrates in Japan and can only be imported from the United States.

Low-temperature co-fired ceramic multilayer substrate (LTCC) The substrate of the above review is quite high because its sintering temperature is 1500-1900 °C. Therefore, if simultaneous firing is used, the conductor material can only select refractory metals Mo and W, etc. It is bound to constitute a series of difficult problems: if the co-firing demand is carried out in a restorative atmosphere, the process difficulty is added, the sintering temperature is too high, and a special sintering furnace is needed; because Mo and W have higher resistivity and large wiring resistance, Signal transmission tends to constitute distortion, increase loss, and wiring miniaturization is limited; dielectric materials have a large dielectric constant, which increases signal transmission delay time, especially for UHF circuits. In order to solve the above problems, a low temperature co-fired ceramic substrate (LTCC) in which glass and ceramic are co-fired has been developed. Since the firing temperature is around 900 ° C, various resistivities can be selected. The low material can complete the fine wiring, during which the precious metal paste can be fired in the atmosphere. Preparation of low-temperature co-fired multi-layer ceramic substrate: This skill requires first adding inorganic alumina powder and about 30% to 50% of glass material to the organic binder to make it evenly mixed into a slurry. Then use a scraper. The slurry is scraped into a sheet shape, and then the sheet slurry is formed into a thin piece of green embryo through a boring process, and then the through hole is drilled according to the design of each layer, and the internal circuit of the LTCC is used as a signal transmission of each layer. Screen printing skills, do not leave the raw embryos to fill holes and printed circuits, the internal and external electrodes can be separated from the use of silver, copper, gold and other metals, and finally the layers are stacked, placed in a sintering furnace 850 ~ 900 ° C In the middle of sintering, it can be finished.

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