JPH0478563B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an aluminum nitride sintered body with excellent thermal conductivity and a raw material for producing the same. Aluminum nitride (AlN) sintered body is a high-temperature material with excellent heat resistance, corrosion resistance, and thermal shock resistance. It is also a highly thermally conductive and insulating material with excellent scientific stability, so it is particularly popular in the field of electronic equipment. It is attracting attention as a substrate material for insulating heat dissipation in integrated circuits, etc. [Prior Art] Aluminum nitride sintered bodies are 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. In this case, it is said that the average particle size of the aluminum nitride powder is preferably 3 μm or less. On the other hand, aluminum nitride powder is usually produced by nitriding a metal aluminum powder compact under nitrogen or ammonia gas. Since the shape after nitriding becomes block-like, it is pulverized to a particle size of several microns using a coarse pulverizer such as a geocrusher, and further a fine pulverizer such as a ball mill. Generally available powders are coarse, several microns in size, and therefore, in order to obtain a sintered body, a pulverization and mixing treatment is performed together with a sintering aid and the like as a pretreatment. During the above-mentioned grinding process, aluminum nitride powder becomes contaminated with metal and oxygen due to contamination or oxidation from the material of the grinder, and these impurities have a large effect even when trying to obtain high thermal conductivity. Often worsens thermal conductivity. [Problems to be solved by the invention] The present inventor has developed aluminum nitride powder and a sintered body that can suppress contamination by metal impurities and oxygen as much as possible and fully exhibit the high thermal conductivity inherent to aluminum nitride. As a result of various studies aimed at achieving this goal, it was discovered that instead of conventional diyoke crushers, ball mills, etc., a pot made of an organic polymer and a zirconia ball could be used in combination, and the present invention was completed. . [Means for Solving the Problems] The present invention is an aluminum nitride powder for sintering and an aluminum nitride sintered body having the following gist. (1) Aluminum nitride powder alone or a mixture with one or more substances selected from the group of sintering aids, binders, dispersants, and plasticizers is mixed into a pot made of an organic polymer and a zirconia ball. An aluminum nitride powder for sintering, characterized in that it is made by combining and pulverizing to an average particle size of 3μ or less. (2) aluminum nitride powder, one or more sintering aids selected from a-oxide and a-oxide;
If necessary, one or more substances selected from the group of organic polymer binders, organic dispersants, and plasticizers are dispersed in an organic solvent, and a pot made of an organic polymer and a zirconia ball are combined. After preparing a slurry containing aluminum nitride powder with an average particle size of 3μ or less, forming a green sheet and removing organic matter, 1700 μm under an inert atmosphere.
An aluminum nitride sintered body characterized by being sintered at a temperature of ℃ or higher. The present invention will be explained in more detail below. The first feature of the present invention is that the raw material aluminum nitride powder is pulverized using a combination of an organic polymer pot and zirconia balls instead of the conventional diyoke crusher or ball mill. have Thereby, the contamination of oxygen and metal impurities can be significantly reduced. That is, aluminum nitride usually has a particle size of 5
Since particles with a diameter of ~10μ are obtained, they are ground in an alumina ball mill to reduce the particle size to 3μ or less, which is suitable for sintering. However, as a result, aluminum oxide of the order of % is mixed in, and the thermal conductivity of the sintered body becomes 50 w/mk, but this does not occur in the present invention. Organic polymers for pot materials include nylon,
polyethylene, fluororesin, polycarbonate,
Examples include epoxy resins, silicone resins, phenolic resins, and polyethylene terephthalate, with nylon and polyethylene being particularly preferred. Examples of organic solvents include aromatic solvents such as toluene, trichlene,
Chlorine type such as chlorocene, ketone type such as acetone,
Paraffinic materials such as hexane and alcoholic materials such as butyl alcohol are used, but urethane pots are not preferred because they may swell during wet mixing and pulverization using organic solvents. The material of the ball is zirconia, and may also be zirconia stabilized with, for example, CaO, MgO, _Y2O3 , or _the like. In order to reduce the amount of oxygen mixed in, it is possible to use non-oxide ceramics such as silicon nitride or aluminum nitride, but even if these balls can prevent oxygen mixed in, the silicon nitride In this case, the contamination of Si ₃ N ₄ , that is, Si, cannot be avoided. When Si content is mixed into the sintered body,
Forms phases such as AlSiON that severely degrade thermal conductivity. On the other hand, in the case of aluminum nitride, the disadvantages due to impurity contamination can be eliminated because the ingredients are the same as the raw material powder, but the specific gravity is
Since it is as small as 3.2 g/cm ³ , its pulverization efficiency is extremely poor, and it is difficult to obtain because it is not as easy to sinter as silicon nitride. On the other hand, it is also conceivable to use pots and balls coated with an organic polymer, but this is not preferred because the organic polymer will be subject to severe wear. The size of the pot is not particularly limited, but the pot should be filled with 30 to 60% of the pot volume. The amount of aluminum nitride powder is preferably 5 to 30% of the pot volume, preferably enough to fill the voids in the ball. Further, the diameter of the ball is usually about 5 to 20 mmφ, preferably about 5 to 15 mmφ. Next, the second invention will be explained. Generally, aluminum nitride sintered bodies are produced by dispersing aluminum nitride powder, a sintering aid, and, if necessary, one or more substances selected from the group of binders, dispersants, and plasticizers in an organic solvent. Adjust the slurry using
After forming a green sheet, it undergoes a degreasing process to remove organic matter, and is then sintered in an inert atmosphere. There is also a method of forming a green molded product and sintering it using a cold press method. In such a method, the present invention selects one or more selected from a oxide and a oxide as a sintering aid, and as in the first invention described above,
In addition to wet mixing and pulverization using a combination of an organic polymer pot and zirconia balls,
The main feature is that the green sheet is sintered at a temperature of 1,700℃ or higher. The sintering aids a and the oxides of a include yttrium oxide, cerium oxide, calcium oxide, lanthanum oxide, niobium oxide, praseodymium oxide, europium oxide, barium oxide,
Examples include strontium oxide. moreover,
It is also possible to use compounds that convert into oxides during sintering, for example in the form of hydroxides. Among these, preferred are yttrium oxide, cerium oxide, and lanthanum oxide. One or more sintering aids selected from the oxides of a and a have an advantage over other sintering aids in that aluminum nitride can be sintered without impairing its thermal conductivity. The appropriate amount of the sintering aid according to the present invention is 1 to 10% relative to the external volume of the raw material aluminum nitride powder. The reason for using a pot made of an organic polymer in combination with a zirconia ball was detailed in the first invention. The organic solvents mentioned above can be used, but chlorine-based solvents such as chlorocene are easy to handle. Note that water and alcohol are unsuitable because they hydrolyze aluminum nitride. Degreasing after forming the green sheet is carried out at a temperature of 400 to 800°C under an inert atmosphere or an atmosphere containing a little oxygen, and then at a temperature of 1700°C or higher under an inert atmosphere such as nitrogen or argon. By sintering the aluminum nitride sintered body of the present invention, the aluminum nitride sintered body of the present invention can be produced. If the sintering temperature is less than 1700°C, a dense sintered body cannot be obtained. Preferably the temperature is 1800°C or higher. Incidentally, binders to be added as necessary include polyvinyl butyral, polyvinyl alcohol, acrylic polymers, etc. Dispersants include triolein, glycerin, etc., and plasticizers include phthalate esters such as dioctyl phthalate. Usual amounts can be used, and the amount used is sufficient. Hereinafter, the present invention will be explained in more detail with reference to Examples. [Example] Example 1 200g of solvent and 100g of commercially available aluminum nitride powder (average particle size 7μ) were put into a ball mill with a volume of 1, and the material of the pot of the ball mill and the material and diameter of the balls were changed to produce aluminum nitride powder. The time required for the average particle size to reach 3μ and the amount of metal impurities and oxygen mixed in were measured. Note that the rotation speed of the ball mill was 80 rpm. As a solvent, chlorocene,
Trichlene and acetone were used, and almost the same good results were obtained with both, so Table 1 shows the results using only chlorocene.

[Table] Example 2 Raw material aluminum nitride powder (commercial product: average particle size
7 μ), 5 g of an organic binder (polyvinyl butyral), 1 g of an organic dispersant (triolein), 2 g of a plasticizer (diocryl phthalate), and 10 g (4.3 volume %) of a sintering aid (cerium oxide).
The mixture was dispersed in 200 g of chlorocene, placed in a ball mill, and mixed and pulverized under various conditions such that the average particle size of the aluminum nitride powder was 3 μm or less to prepare a slurry. This slurry is processed using a doctor blade device.
Apply to polyethylene terephthalate film,
It was dried to produce a green sheet. After peeling the green sheet from the film, it was made into a 40 mm square sheet, and after laminating and pressing four sheets, the temperature
The polyvinyl butyral was removed by holding in a nitriding gas atmosphere at 700°C for 2 hours, and then sintered in a nitrogen atmosphere at 1800°C for 1 hour. The density and thermal conductivity of the obtained sintered body were measured. The results are shown in Table 2.

【table】

[Table] Example 3 Similar measurements were carried out in Example 2, using yttrium oxide or calcium oxide with an average particle size of 1.2μ as the sintering aid, and adding an amount of 8g (volume %: 5.1 and 7.3, respectively). . The results are shown in Table 3.

[Table] Example 4 Under the conditions of Experiment No. 21 of Example 2, sintered bodies were manufactured by varying the sintering temperature and the amount of sintering aid, and their thermal conductivity was measured. The results are shown in Table 4.

〔Effect of the invention〕

(1) According to the first aspect of the present invention, it is possible to obtain aluminum nitride powder having an average particle size of 3 μm or less and containing a small amount of metal impurities and oxygen. (2) Moreover, since the specific gravity of zirconia is as high as 7.6 g/cm ³ , the grinding efficiency is extremely high, and the grinding time is reduced to one-third compared to balls made of alumina, silicon nitride, or aluminum nitride. That is, since efficient pulverization is possible, surface oxidation of aluminum nitride during pulverization can be suppressed. (3) According to the second aspect of the present invention, aluminum nitride exhibits high thermal conductivity without impairing its inherent thermal conductivity, has good sinterability, and has sufficient density required for the substrate. A sintered body can be obtained.

Claims (1)

[Claims] 1. Aluminum nitride powder alone, or 1 selected from the group of sintering aids, binders, dispersants, and plasticizers.
1. An aluminum nitride powder for sintering, which is obtained by pulverizing a mixture of more than one substance to an average particle size of 3 μm or less using a pot made of an organic polymer and a zirconia ball. 2 Aluminum nitride powder, one or more sintering aids selected from a oxide and a oxide, and if necessary, an organic polymer binder, an organic dispersant, and a plasticizer selected from the group. The average particle size is obtained by dispersing one or more substances in an organic solvent, and combining a pot made of an organic polymer and a zirconia ball.
An aluminum nitride sintered body characterized by preparing a slurry containing aluminum nitride powder of 3μ or less, forming a green sheet, removing organic matter, and sintering at a temperature of 1700°C or higher in an inert atmosphere.