JPH0510298B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to a method for producing a sintered aluminum nitride plate. (Prior art and its problems) In recent years, electronic components have become significantly smaller and more highly integrated.
Along with this, the amount of heat generated per unit area continues to increase. How to dissipate this heat is an important design point for electronic components, and it is desired to develop a substrate made of a material with high thermal conductivity. For this purpose, a silicon carbide sintered body or aluminum nitride sintered body substrate has been proposed as an alternative to the conventionally widely used alumina substrate. However, although silicon carbide has high thermal conductivity, it has poor electrical insulation properties and must be hot pressed to make it dense, which limits its field of use. On the other hand, aluminum nitride sintered body has a thermal conductivity of 2 to 5 that of alumina, although its thermal conductivity is inferior to that of silicon carbide.
Moreover, its electrical insulation properties are comparable to alumina, and it can be densified by pressureless sintering, making it a highly versatile material. The aluminum nitride sintered body is usually obtained by molding aluminum nitride powder by a cold press method, a doctor blade method, or the like, and then firing it in an inert atmosphere such as nitrogen. Generally, aluminum nitride sintered bodies are processed into thin plates and used for hybrid substrates or discrete electronic components by baking conductive paste, resistive paste, or dielectric paste onto the plates, and in the near future they will be used for ceramic packages. It is a material that is also used for various purposes, and basically requires a plate-like shape, and for general use, a low-cost sintered plate is required. Currently, in the case of the most commonly used alumina substrate, a mixture of alumina powder, an organic binder, an organic dispersant, and a plasticizer is mixed and dispersed in an organic solvent using an alumina ball mill, and the viscosity is 1 to 1.
The method used is to create a slurry of 30,000 cps, make it into a green sheet using the doctor blade method, remove organic matter, and then sinter it at 1,500 to 1,700 degrees Celsius under normal pressure to make an alumina substrate. In the case of alumina substrates, the history is long and more than 20 years have passed, so the type and amount of organic substances used have been optimized, and currently, from safety and economical points of view, organic melting is not used. Progress has been made to such an extent that attempts are being made to create slurry using aqueous systems. (Problem to be solved by the invention) On the other hand, in the case of aluminum nitride sintered bodies, forming sheets by the doctor blade method is considered to be the most advantageous economically, but since the history is short and there are no such conditions, it is still at the stage of trial-and-error investigation. It is. The reason for this is that aluminum nitride has various problems compared to alumina. That is, firstly, aluminum nitride is easily oxidized. For example, the surface of aluminum nitride powder may be oxidized during the organic matter removal process or raw material crushing process after green sheets are made. When oxidized, an alumina layer is formed on the surface, and the resulting aluminum nitride sintered body often has poor thermal conductivity and loses the properties of aluminum nitride. Second, aluminum nitride powder is susceptible to hydrolysis. If the type of organic solvent used in the slurry manufacturing process or the water content in the solvent is not controlled, the same problems as those caused when the particles undergo hydrolysis and undergo the first oxidation will occur. Thirdly, metal impurities in aluminum nitride, especially silicon,
Similarly, aluminum nitride loses its thermal conductivity when impurities such as iron and chromium are mixed into it. As described above, aluminum nitride has several problems that alumina does not have, so it is necessary to consider conditions and formulations suitable for aluminum nitride, such as the slurry preparation process before applying the doctor blade and the subsequent organic matter removal (debinding) process. It is. The present invention solves these problems and uses sintered aluminum nitride, which has uniform and high thermal conductivity, has no stains, uneven color, or cracks, and has a high surface smoothness, and is inexpensive and has a high yield in manufacturing. The object of the present invention is to provide a manufacturing method for obtaining a highly thermally conductive ceramic sintered plate consisting of a ceramic body. (Means for Solving the Problems) That is, the present invention mixes aluminum nitride powder, a sintering aid, an organic binder, a plasticizer, a dispersant, and an organic solvent, molds it, removes the binder, and then forms a non-oxidized When producing a sintered aluminum nitride plate by firing in a neutral atmosphere, 4 to 12 parts by weight of polyvinyl butyral as an organic binder and dibutyl phthalate and/or dioctyl phthalate as a plasticizer are added to 100 parts by weight of aluminum nitride powder. 2 to 10 parts by weight,
1 to 3 parts by weight of an aliphatic ester as a dispersant, together with a sintering aid, in a mixed solvent of two or more selected from chlorine-based, ketone-based, aromatic-based, alcohol-based, and paraffin-based organic solvents. , a relative density of 95% or more, characterized by mixing an organic polymer pot and a zirconia ball, forming it into a sheet using a doctor blade method, removing the binder, and firing in a non-oxidizing atmosphere. , a method for producing aluminum nitride sintered plates with a thermal conductivity of 100W/mk or more. The present invention will be explained in more detail below. First, in order to obtain a high-density sintered body by pressureless sintering of aluminum nitride powder, it is necessary to make the aluminum nitride powder a fine powder with an average particle size of 3 microns or less to avoid contamination with impurities. Since the average particle size of commonly available commercial products is about 7 to 8 microns, they must be pulverized. We have found that wet ball milling using an organic polymer pot and zirconia balls is a good grinding method that is efficient and reduces contamination. Furthermore, since aluminum nitride itself is difficult to sinter, it is necessary to add a sintering aid. There are no particular restrictions on the type of sintering aid, but using a cerium oxide-yttrium oxide compound or a mixture of two or more selected from cerium oxide, yttrium oxide, and lanthanum oxide will result in a good yield and reduce uneven color and warpage. This method is suitable for the present invention because it provides a sintered aluminum nitride plate that is free from heat and has good thermal conductivity. The mixing state of the sintering aid and the aluminum nitride powder has a subtle effect on sintering, so in order to obtain a sufficient mixing state, it is desirable to mix the aluminum nitride powder at the same time as the aluminum nitride powder is wet-pulverized in a ball mill. The amount of the sintering aid added depends on the amount of oxygen contained in the aluminum nitride powder, but is preferably about 4 to 20 parts by weight per 100 parts by weight of the aluminum nitride powder. It is important that the green sheet obtained by forming the slurry into a sheet using a doctor blade has flexibility and stiffness necessary for handling such as punching in subsequent steps. For this purpose, organic binders such as polyvinyl butyral, poval, acrylic polymers, etc. are used in the case of alumina substrates. In the case of aluminum nitride, an organic binder is also required, but in the present invention, polyvinyl butyral,
Among them, it has been found that polyvinyl butyral having two or more molecular weight distributions with different degrees of polymerization is suitable. Especially mixtures with polymerization degrees of 300 and 1700 or 600 and
A mixture of about 1700 has excellent flexibility and stiffness. Polyvinyl butyral has excellent film-forming properties compared to other organic binders, and can produce crack-free sheets. Since polyvinyl butyral is a resin that is difficult to dissolve in organic solvents, it is not preferable to add the resin itself during wet mixing and pulverization of aluminum nitride powder and sintering aid. It is preferable to prepare a solution in which the plasticizer and the plasticizer are dissolved in an organic solvent in advance and to mix the solution. The concentration of polyvinyl butyral in the organic solvent is preferably 10 to 45% by weight in terms of ease of dissolution and handling. The mixed solution of polyvinyl butyral and plasticizer is weighed and mixed so that the amount of polyvinyl butyral is 4 to 12 parts by weight and the amount of plasticizer is 2 to 10 parts by weight per 100 parts by weight of aluminum nitride powder. . Note that it is not preferable to add a solution containing only polyvinyl butyral during the pulverization and mixing process of aluminum nitride powder because the viscosity of the slurry during pulverization increases and the pulverizability deteriorates. As the plasticizer, dibutyl phthalate and/or dioctyl phthalate, which are said to be compatible with polyvinyl butyral, can be used. If the amount of polyvinyl butyral is less than 4 parts by weight, a crack-free sheet cannot be obtained, and if it exceeds 12 parts by weight, shrinkage during sintering will increase. Furthermore, if the plasticizer is less than 2 parts by weight, the above-mentioned effect of reducing the viscosity of the slurry cannot be obtained, and there is no advantage to adding more than 10 parts by weight. Furthermore, the aliphatic ester dispersant that improves the dispersibility of powder, which is used in the case of alumina, is also used in the case of aluminum nitride powder. As the aliphatic ester, for example, triolein is preferred, but other aliphatic esters can also be used. The amount of dispersant is 100% aluminum nitride powder.
It is about 1 to 3 parts by weight. Further, it is preferable to add the aluminum nitride powder when the aluminum nitride powder and the sintering aid are wet-pulverized and mixed, since this improves the dispersibility. Slurry made as above ()
The viscosity of the green sheet is 50 to 5,000 cps, and if it were to be formed into a sheet using a doctor blade device, the slurry would flow while it was being applied to a polyethylene phthalate film as a carrier film and drying, resulting in a green sheet with a uniform thickness. is not obtained. Furthermore, if air bubbles are involved in the slurry, problems such as holes in the green sheet will occur. So slurry with viscosity 50~5000cps ()
is passed through a deaerator to remove the solvent and remove air bubbles. Usually, defoaming is performed under a vacuum of 0.01 to 0.1 atm, and the final viscosity is thickened to a slurry () with a viscosity of 10,000 to 30,000 cps. This slurry () is applied onto a polyethylene terephthalate film using a doctor blade device, dried at room temperature to 120°C to remove the organic solvent, and made into a green sheet with a thickness of 0.5 to 1.5 mm. Since it is undesirable if bumping occurs during drying, it is desirable that the organic solvent used has a boiling point that is not too low and is capable of dissolving the organic binder, plasticizer, and dispersant. Therefore, it is usually difficult to use a single solvent and a mixed solvent is used. That is, in the present invention, two or more solvents are selected from chlorine solvents such as trichloroethane, ketone solvents such as acetone, aromatic solvents such as toluene, alcohol solvents, and paraffin solvents. in particular,
Trichlorethylene/tetrachlorethylene/butanol/chlorocene, toluene/ethanol/
Butanol, toluene/isopropanol/butanol, etc. As mentioned above, aluminum nitride dislikes moisture, so when using organic solvents, keep the moisture content below 500 ppm, preferably
Care must be taken to keep it below 100ppm. The amount of the mixed solvent to be used is usually approximately equal to the weight of the aluminum nitride powder. After punching the green sheet into a predetermined shape,
After debinding (removal of organic matter) by heating in an oxidizing atmosphere at a temperature of 400 to 600°C for about 0.5 to 2 hours, it is heated in an inert gas atmosphere such as nitrogen or argon.
By performing sintering under normal pressure in the temperature range of 1700 to 1900°C, a sintered body with a relative density of 95% or more can be obtained. The thermal conductivity of the aluminum nitride sintered plate produced through this process is over 100W/mk, and the original properties of aluminum nitride can be maintained, and the color and stains and cracks are not a problem for practical use. It is possible to obtain a good sintered plate without any unevenness. (Example) A more detailed explanation will be given below using examples. Example 1 A 1:1 compound of cerium oxide and yttrium oxide was prepared by baking 3 kg of commercially available aluminum nitride powder with an average particle size of 7 μm at 1400°C for 3 hours.
200 g and 32 g of triolein were weighed and loaded into 10 nylon ball mill pots. Furthermore, after putting a 10φ zirconia ball into a 20Kg pot, 2.4Kg of a mixed solvent consisting of trichlorethylene, butanol, and tetrachlorethylene in a weight ratio of 60:24:16 was added, and after the pot was sealed, the pot was mixed and pulverized for 24 hours at 80 rpm. death,
An aluminum nitride powder slurry () with an average particle size of 2.0μ was prepared. On the other hand, 300 g of a mixture of polyvinyl butyral with a polymerization degree of 300 and 1700 in a weight ratio of 3:2 and 150 g of dibutyl phthalate were dissolved in 1.5 kg of the above mixed solvent to make a mixed solution, and 800 g of the mixed solution was slurried ().
In addition, the viscosity is further mixed in the ball mill for 24 hours.
200cps slurry (). The slurry () was taken out from the ball mill and defoamed using a vacuum defoaming machine to prepare a slurry with a viscosity of 15,000 cps. Thereafter, the slurry was applied onto a polyethylene terephthalate film having a width of 330 mm using a pipe doctor blade device under conditions of a clearance of 2.2 mm and a coating width of 250 mm. The drying zone was 15 m long and had a temperature gradient from room temperature to 120°C. A green sheet was prepared at a film feed speed of 10 cm/min. The resulting green sheet had a tensile strength of 20 Kg/cm ² and a thickness of 1.1 mm, and was highly flexible and did not exhibit any cracks. This green sheet was punched out into 50 mm square pieces using a punching die. The cross section of the punched sheet was clean and no burrs were observed. Next, 50 sheets of 50 mm square were set in a graphite dish and treated under air circulation at 450° C. for 1 hour to remove organic substances (organic binder, dispersant, and plasticizer).
The amount of carbon remaining after removing organic matter was 0.3% by weight, which was confirmed to be reduced to the amount of carbon in the raw material aluminum nitride powder. After that, the green sheet along with the graphite plate was set in a large sintering furnace, and heated at 1850℃ for 1 hour at normal pressure in a nitrogen atmosphere.
Baked for an hour. The dimensions of the 50 sintered aluminum nitride sheets are 40 mm square, and their relative density is 95%.
The warpage was less than 0.1 mm/25 mm.
Furthermore, when the thermal conductivity was measured using a laser flash method device manufactured by Shinku Riko, it was found to be 130 W/mk on average and 112 W/mk at the minimum. Example 2 An aluminum nitride sintered plate was produced in the same manner as in Example 1, except that the sintering aid was a mixture of lanthanum oxide, cerium oxide, and yttrium oxide, and the mixing ratio was 1:1:2 by volume. . However, the sintering temperature was 1800°C. The obtained green sheet had no abnormalities such as cracks, and the relative density and warpage of the sintered body were the same as in Example 1. The average value of thermal conductivity was 125W/mk. Example 3 In Example 1, the amount of mixed solvent in the slurry () was reduced to 1.2 kg, but the particle size of the aluminum nitride powder was a little coarse at 2.8μ, so the grinding and mixing time was extended by 10 hours. It was set to 2.1μ. The results obtained were almost the same as in Example 1. Examples 4 to 10 Comparative Examples 1 to 3 Green sheets were prepared in the same manner as in Example 1 by changing the types and amounts of the sintering aid, dispersant, plasticizer, and organic binder, and 50 sheets were sintered. The average values of the relative density and thermal conductivity of the bonded plates were determined. The results are shown in the table.

[Table] (Note) Comparative Example 1 uses polyvinyl butyral, Comparative Example 2 uses a dispersant, and Comparative Example 3 uses a dispersant and plasticizer outside the scope of the present invention.
(Effects of the Invention) According to the present invention, the following effects are achieved. (1) The high thermal conductivity of aluminum nitride can be exhibited because it can be sintered under conditions with few metal impurities and where the aluminum nitride powder is not oxidized or hydrolyzed. (2) The resulting green sheet is free from cracks and other cracks, improving product yield. Furthermore, no burrs or the like occur even when the green sheet is punched out. (3) Especially when using chlorine-based solvents, the risk of explosion etc. is reduced, which is advantageous in terms of equipment.

Claims (1)

[Claims] 1. Mix aluminum nitride powder, sintering aid, organic binder, plasticizer, dispersant, and organic solvent, mold, remove binder, and then bake in a non-oxidizing atmosphere to produce a sintered aluminum nitride plate. Hits the,
4 to 12 parts by weight of polyvinyl butyral as an organic binder to 100 parts by weight of aluminum nitride powder;
2 to 10 parts by weight of dibutyl phthalate and/or dioctyl phthalate as a plasticizer, 1 to 3 parts by weight of an aliphatic ester as a dispersant, and chlorine-based, ketone-based, aromatic-based, alcohol-based and paraffin-based In a mixed solvent of two or more selected from organic solvents, a pot made of an organic polymer and a zirconia ball are used to mix the mixture, which is then formed into a sheet using a doctor blade method, after which the binder is removed and the non-oxidized Relative density 95% or more, thermal conductivity 100w/mk, characterized by firing in a warm atmosphere
The above method for producing an aluminum nitride sintered plate.