JP2828998B2 - Manufacturing method of aluminum nitride sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for producing an aluminum nitride sintered body.

(Conventional technology) Aluminum nitride (AlN) has many excellent properties such as maintaining high strength from room temperature to high temperature, not getting wet with molten metal, high electrical insulation, high thermal conductivity, etc. Therefore, it is attracting attention as a new material. In particular, in recent years, Al
The application of N-sintered bodies to heat-dissipating substrates has been actively studied, and as a result, the thermal conductivity was limited to 100 W / m · k until several years ago due to improvements in raw materials and sintering technology. It has been improved to 260 W / m · k by adopting a special sintering method.

By the way, an AlN sintered body is usually manufactured by molding AlN powder by a desired method and then sintering it. Sintering is performed by normal pressure sintering method or hot press method,
Since AlN is a hardly sinterable substance, it is necessary to add a sintering aid in the normal pressure sintering method in order to obtain a dense sintered body. AlN sintering aids include compounds of alkaline earth elements and compounds of rare earth elements. These compounds react with oxygen which is inevitably mixed in the AlN powder raw material during sintering, and R-Al-O-based compounds (R; alkaline earth elements) and Ln-Al-O-based compounds ( Ln; rare earth element)
And densify the sintered body. In addition, oxygen contained in the AlN powder raw material generates an Al-NO-based compound or dissolves in the AlN particles to lower the original high thermal conductivity of AlN. Since the alkaline earth compound or the rare earth compound reacts with oxygen and fixes this product as a grain boundary phase, the sintering aid also contributes to increasing the thermal conductivity.

By adding the sintering aid to the AlN powder raw material as described above, it is possible to surely achieve the densification of the AlN sintered body and increase in the thermal conductivity.
Sintering at a high temperature of 1700-1900 ° C is required. as a result,
This has been a factor in soaring the manufacturing cost of the AlN sintered body.
Further, in the conventional AlN sintered body using the sintering aid, there are problems that color defects, cracks, swelling, and other defects frequently occur, resulting in an increase in cost due to a decrease in yield. Such AlN
The high cost of the sintered body is an extremely important obstacle in widely using the AlN sintered body. In other words, the AlN sintered body is far superior in characteristics such as heat dissipation and matching of thermal expansion coefficient with silicon compared to alumina ceramics widely used as a highly reliable circuit board at present. However, since the market price is about an order of magnitude higher than that of alumina ceramics, at present the application is limited to very limited fields. Therefore, in order to reduce the manufacturing cost of the AlN sintered body, it is extremely important to reduce the sintering temperature and further suppress the decrease in yield due to poor shape and appearance.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and provides an aluminum nitride sintered body having excellent sinterability by low-temperature sintering and having a uniform shape and appearance. It is intended to provide a method that can be manufactured.

[Constitution of the Invention] (Means for Solving the Problems) The present invention comprises aluminum nitride (AlN) as a main component,
To this, at least an additive containing at least one compound selected from the group consisting of an oxide of an alkaline earth element, a rare earth element aluminum compound and an alkaline earth oxide, a fluoride, a carbide and a rare earth oxide, a fluoride, and a carbide is added.
A method for producing an aluminum nitride sintered body, characterized by sintering at a temperature of not more than ℃.

It is desirable to use AlN containing 0.01 to 7% by weight of oxygen. Such AlN has an average particle size of 4
For low-temperature sintering, it is desirable to use a powder having a particle size of 2 μm or less.

Examples of the additive include the following forms.

. An additive comprising a mixture of an alkaline earth element rare earth aluminum compound and an alkaline earth oxide, fluoride, carbide and at least one compound selected from rare earth oxides, fluorides, and carbides.

. An additive comprising a mixture of a transition metal compound and at least one compound selected from oxides, fluorides, carbides, and oxides, fluorides, and carbides of a rare earth element, an alkaline earth element rare earth element aluminum compound and an alkaline earth element.

. An additive comprising a mixture of an aluminum oxide and at least one compound selected from oxides, fluorides, carbides, and oxides, fluorides, and carbides of a rare earth element and an alkaline earth element rare earth element aluminum compound.

. Alkaline earth element rare earth element aluminum compound and alkaline earth oxide, fluoride, carbide and rare earth element oxide, fluoride, carbide at least one compound selected from a transition metal compound and aluminum oxide mixture Additives.

As the alkaline earth element rare earth element aluminum compound contained in the additive, for example, when the alkaline earth element is R and the rare earth element is Ln, a composite oxide having an R-Ln-Al-O diameter may be mentioned. Yes, more preferably RLnAlO
_4. It is desirable to use a composite oxide of RLnAl ₃ O ₇ . Here, examples of the alkaline earth element include Mg, Ca, Sr, and Ba, and Ca and Sr are particularly preferable. As rare earth elements, Sc, Y, La, Ce, Sm, Eu, Tm, Tb, Dy, Nd, Gd,
Pr, Ho, Er, Yb and the like can be mentioned, and in particular, Y, La, Ce
Is preferred.

Examples of the alkaline earth element compound contained in the additive include oxides, fluorides, and carbides of Mg, Ca, Sr, and Ba, and compounds of Ca and Sr are particularly preferable.

As the rare earth element compound contained in the additive,
For example, Sc, Y, La, Ce, Sm, Eu, Tm, Tb, Dy, Nd, Gd,
Oxides, fluorides or carbides of Pr, Ho, Er, and Yb can be mentioned, and compounds of Y, La, and Ce are particularly preferable.

Examples of the transition metal compound contained in the additive include oxides, fluorides, nitrides, and carbides of Ti, Zr, Hf, Ni, Cr, Mn, Fe, Co, and V, and in particular, T
Compounds of i, Zr and Hf are preferred.

Examples of the aluminum oxide contained in the additive include α-Al ₂ O ₃ and γ-Al ₂ O ₃ .

The amount of the above additives with respect to AlN powder is calculated in terms of cation.
It is desirable to be in the range of 0.05 to 30% by weight, more preferably 0.1 to 20% by weight. The reason for this is that if the amount of the additive is less than 0.05% by weight, the effect of improving the properties of the sintered body is not sufficient, while if the amount exceeds 30% by weight, the properties such as thermal conductivity and high-temperature strength deteriorate. This is because it may not be ignored. The amount of the alkaline earth element rare earth element aluminum compound in the additive is preferably 5% by weight or more, more preferably 15% by weight or more. The reason for this is that if the amount of the alkaline earth element rare earth element aluminum compound in the additive is less than 5% by weight, the effect of improving the properties of the sintered body may not be sufficient. Further, when a transition metal compound and an aluminum oxide are contained in the additive, the amount of each component in the additive is preferably 5% by weight or less, more preferably 3% by weight or less. The reason for this is that if the amount of each of the transition metal compound and the aluminum oxide in the additive exceeds 5% by weight, the thermal conductivity of the sintered body may be reduced.

 Next, the production method of the present invention will be described more specifically.

First, an additive is added to AlN powder, and ground and mixed using a ball mill or the like to prepare a raw material. However, in the case of normal pressure sintering, a raw material is prepared by adding a binder to the mixture obtained by pulverizing and mixing with a ball mill or the like, kneading and granulating. Subsequently, after the raw material containing the binder is molded by means such as a mold, hydrostatic pressure or sheet molding, the molded body is heated in a stream of N ₂ gas to remove the binder. Next, the compact is set in a container made of graphite, boron nitride or aluminum nitride, and subjected to normal pressure sintering at 1400 to 1850 ° C. in an N ₂ gas atmosphere. On the other hand, in the case of hot press sintering, the raw material prepared by pulverizing and mixing with the ball mill is hot pressed at a temperature of 1400 to 1800 ° C.

(Action) According to the present invention, aluminum nitride is used as a main component, and an additive containing at least an alkaline earth element and a rare earth element aluminum compound is added thereto and sintered.
The sinterability at a lower sintering temperature is improved as compared with the related art, and a dense and high thermal conductivity AlN sintered body can be manufactured. Although this effect is not clear, it is presumed to be due to the following mechanism.

That is, in general, an alkaline earth element compound or a rare earth element compound is effective for densification and high thermal conductivity as a sintering aid because it mainly reacts with impurities in the AlN raw material at the sintering temperature to form a liquid phase. It is believed that the liquid phase sintering of AlN proceeds. For example, considering the case of yttrium, Y ₂
When O ₃ is added to the AlN raw material as an additive, first, a Y—Al—O-based composite oxide is generated during the temperature rise, and these products become a liquid phase at the sintering temperature. In this case, if the generated phase is Y ₃ Al ₅ O ₁₂ , the liquidus temperature is considered to be 1760 ° C., and the dense Al
It is necessary to sinter at a higher temperature in order to obtain an N sintered body. To describe this mechanism in more detail, Y ₂ O ₃
The reaction with impurity oxygen in AlN powder is thought to involve nitrogen (N) in some form, and pure Y ₂ O ₃ and Al ₂ O
_Although it is expected that this reaction is different from the reaction of _3, the temperature at which the liquid phase is formed has not been elucidated exactly at present. However, according to previous studies, it has been confirmed that a liquid phase is formed at a temperature close to 1760 ° C. The formation of such a liquid phase is the same when other rare earth elementization is used, and when the rare earth element is represented by Ln, Ln ₃ Al ₅ O ₁₂ , L
Rare earth element aluminum composite oxides such as nAlO ₃ , Ln ₄ Al ₂ O ₉ , LnAl ₁₁ O ₁₈ are generated, and a dense and high thermal conductivity AlN sintered body can be obtained as with Y ₂ O ₃ . The same applies to the case where an alkaline earth element compound is used. When the alkaline earth element is represented by R, R ₃ Al ₁₂ O ₁₉ , RAlO ₇ , RAl
Alkaline earth element aluminum composite oxides such as ₂ O ₄ , R ₁₂ Al ₇ O ₃₃ , R ₃ Al ₂ O are generated and, like when Y ₂ O ₃ is used,
A dense, high thermal conductivity AlN sintered body can be obtained. Furthermore, when an alkaline earth element compound and a rare earth element compound are simultaneously added, R-
Ln-Al-O based composite oxide, for example, RLnAlO ₄ or RLnAl ₃ O
₇ oxide phases are formed.

The present invention relates to an alkaline earth element rare earth element aluminum compound (R-Ln-Al-
O-based composite oxide) is synthesized in advance, and an additive containing at least this is added to the AlN raw material and sintered, thereby improving the sinterability at a lower sintering temperature as compared with the conventional one as described above. , A dense and high thermal conductivity AlN sintered body has been obtained, which is that the alkaline earth element rare earth element aluminum compound can lower the liquidus temperature, high reactivity with the AlN raw material It is thought to be due to the above.

Also, by using an additive containing at least an alkaline earth element rare earth element aluminum compound, an AlN sintered body having a uniform shape and appearance can be manufactured.
This is presumed to be due to the following mechanism.

In other words, the shape and appearance of the AlN sintered body are intricately involved in the properties of the AlN powder during the sintering process, especially factors such as the amount and size of impurities and the type and amount of additives, and further sintering conditions. In particular, the composition and amount of the liquid phase are important factors. When sintering is performed using a conventional additive, the composition and amount of the liquid phase are almost uniquely determined by the type and amount of the additive and the amount of impurity oxygen in the AlN raw material. For this reason, it was difficult to control the liquid phase for homogenizing the shape and appearance of the AlN sintered body. In the present invention, since the composition and amount of the liquid phase by the alkaline earth element rare earth element aluminum compound contained in the additive during sintering are easily controlled, AlN sintering having a uniform shape and appearance as described above is performed. It is presumed that the body can be manufactured.

Furthermore, by using the above-mentioned additive of the system containing the alkaline earth element rare earth element aluminum compound, the densification and the thermal conductivity can be further improved by further improving the sinterability. In particular, the use of a system additive containing a transition metal compound can achieve high strength and coloring of the AlN sintered body. That is, the additive of the system containing the transition metal compound is uniformly distributed in the sintered body without impairing the sinterability of the AlN raw material, and the strength of the sintered body can be increased by the pinning effect. Moreover, when the sintered body is colored and various colors are obtained by combining with other components, the unevenness of the color of the sintered body is concealed to enhance the aesthetic appearance. Light that causes a malfunction of the memory can be blocked. Further, the use of a system additive containing aluminum oxide can improve the sinterability of the AlN sintered body. In particular, it is possible to effectively improve the sinterability of a compact having a small residual oxygen content due to insufficient sintering of the AlN powder having a small impurity oxygen content and a large particle diameter and insufficient binder removal after compaction.

(Examples of the Invention) Hereinafter, examples of the present invention will be described in detail.

Example 1 First, an AlN powder containing 1.4% by weight of oxygen as an impurity and having an average particle diameter of 2.2 μm was added to an AlN powder having an average particle diameter of 2.5 μm in a weight ratio.
Of Y ₂ O ₃ , CaYAlO _{4 having} an average particle size of 2.0 μm, and having an average particle size of 3 μm
5.7% by weight of an additive obtained by mixing ZrO ₂ and α-Al ₂ O ₃ having an average particle size of 1.0 μm in a ratio of 3: 2: 0.5: 0.2 was added, and the mixture was crushed and mixed using a ball mill to prepare a raw material. . Then, after adding 7% by weight of paraffin to this raw material and granulating,
Press molding was performed under a pressure of g / cm ² to obtain a green compact having dimensions of 50 cm × 50 cm × 8 cm. Subsequently, the green compact was heated to 700 ° C. in a nitrogen gas atmosphere to remove paraffin. Next, the green compact was set in a carbon container and sintered under normal pressure at 1700 ° C. for 2 hours under a nitrogen gas atmosphere to produce an AlN sintered body.

Examples 2 to 10, Comparative Examples 1 to 3 12 kinds of AlN were prepared in the same manner as in Example 1 except that the raw material was composed of the AlN powder shown in Table 1 below and a mixed powder as an additive. A sintered body was manufactured. However, CaO in Table 1 is obtained by adding CaCO ₃ in terms of weight, and the average particle size is shown as a centrifugal sedimentation diameter when n-butanol is used as a dispersion medium.

The densities of the AlN sintered bodies obtained in Examples 1 to 10 and Comparative Examples 1 to 3 were measured. Further, each AlN sintered body was ground to produce a disk having a diameter of 10 mm and a thickness of 2.5 mm, and the thermal conductivity at room temperature was measured by a laser flash method using these as test pieces. Furthermore, each AlN sintered body is ground to a width of 4m.
6 bars each of m, thickness 3mm and length 40mm were prepared, and these were used as test pieces for measuring bending strength. The three-point bending strength was measured under the conditions of distance between fulcrums of 20mm and crosshead speed of 0.5mm / min. It was measured. The results are shown in Table 1 below.

As is clear from Table 1 described later, Examples 1 to 10
It can be seen that the AlN sintered body is superior to the AlN sintered bodies of Comparative Examples 1 to 3 in all of the properties of denseness, thermal conductivity, and three-point bending strength.

Example 11 First, an AlN powder containing 0.9% by weight of oxygen as an impurity and having an average particle size of 1.9 μm was added to an AlN powder having an average particle size of 2.5 as an additive.
A raw material was prepared by adding 2% by weight of Y ₂ O ₃ μm and 1% by weight of CaYAlO ₄ having an average particle size of 2.0 μm, and crushing and mixing using a ball mill. Subsequently, 7 wt% of paraffin was added to this raw material.
After adding and granulating, it was press-molded at a pressure of 500 kg / cm ² to obtain a green compact having a size of 30 cm × 30 cm × 8 cm. Subsequently, the green compact was heated to 700 ° C. in a nitrogen gas atmosphere to remove paraffin. Next, the green compact was set in a carbon container, and heated at 1500 ° C. and 16 ° C. in a nitrogen gas atmosphere.
Atmospheric pressure sintering was performed at 00 ° C., 1700 ° C. and 1800 ° C. for 2 hours, respectively, to produce four types of AlN sintered bodies.

Comparative Example 4 First, an AlN powder containing 0.9% by weight of oxygen as an impurity and having an average particle size of 1.9 μm was added to an AlN powder having an average particle size of 2.5% as an additive.
Add 3% by weight of Y ₂ O _{3 of} μm and crush using a ball mill.
The raw materials were prepared by mixing. Subsequently, using these raw materials, normal pressure sintering was performed in the same manner as in Example 11 to produce four types of AlN sintered bodies.

Thus, each of the AlNs obtained in Example 11 and Comparative Example 4
The density and the thermal conductivity at room temperature of the sintered body were measured.
The results are shown in Table 2 below.

As is clear from Table 2 below, in Example 11,
It can be seen that even at sintering at a low temperature of 1600 ° C., an AlN sintered body having high density and high thermal conductivity can be obtained.

Examples 12 to 27 Sixteen types of AlN sintered bodies were produced in the same manner as in Example 1, except that AlN powder shown in Table 3 below and a mixed powder as an additive were used as raw materials. . However, CaO in Table ₃ is obtained by adding CaCO ₃ in terms of weight, and the average particle size is shown as a centrifugal sedimentation diameter when n-butanol is used as a dispersion medium.

The density and the thermal conductivity at room temperature of the AlN sintered bodies of Examples 12 to 27 were measured in the same manner as in Example 1. The results are shown in Table 3 below.

Example 28 As a raw material, the same composition as in Example 9 shown in Table 1 (additive;
Y ₂ O _3, used as the CaO and mixed powder of CaYAlO _4), after a sheet by which a doctor blade method, and cut
One hundred sheets having dimensions of 6.2 mm × 6.2 mm × 0.77 mm were produced. Subsequently, these sheets were subjected to binder removal and normal pressure sintering in the same manner as in Example 1 to obtain 100 sheets of A
An 1N sintered body was manufactured.

Comparative Example 5 As a raw material, the same composition as in Comparative Example 3 shown in Table 1 (additive;
Y ₂ O ₃ powder), which was formed into sheets by the doctor blade method, and then cut to produce 100 sheets having dimensions of 6.2 mm × 6.2 mm × 0.77 mm.
Perform binder removal and normal pressure sintering in the same manner as
Zero sheet-like AlN sintered bodies were produced.

The AlN sintered bodies of Example 28 and Comparative Example 5 were visually and visually inspected for defects in appearance and shape using a microscope. The inspection criteria for appearance and shape defects were as follows.

(1) Uneven color: no color unevenness is visually observed.

(2) Swelling; no bubbles or gaseous inclusions on the surface of the AlN sintered body (a pinhole if broken near the surface).

(3) Sticking: No AlN sintered body composition or foreign matter pieces adhered to the surface.

(4) Chipping: No dropout due to chipping including the AlN sintered body surface.

(5) Cracks: Elongated grooves or tear lines generated on the surface can be seen, but there are no gaps without gaps between them.

(6) Streaks; no elongated projections on the surface.

(7) Foreign matter; no embedded foreign matter or dirt.

As a result, in Example 28, out of 100 sheets, the number of defects was two due to uneven color and one due to cracks, and the defect rate was only 3%. On the other hand, in Comparative Example 5, 10
Of the 0 sheets, 26 were defective due to uneven color, 7 were due to cracks, and 4 were due to blistering.
It was as high as 37%.

Example 29 As a raw material, the same composition as in Example 1 shown in Table 1 (additive;
Y ₂ O ₃ , CaYAlO ₄ , ZrO _2, and α-Al ₂ O ₃ mixed powder), and sheet it by the doctor blade method, then cut and measure 6.2 mm × 6.2 mm × 0.77 mm 50 sheets
0 sheets were produced. Subsequently, these sheets were subjected to binder removal and normal pressure sintering in the same manner as in Example 1 to produce 500 sheet-like AlN sintered bodies.

Thus, with respect to the AlN sintered body of Example 29, Example 28
Inspection of appearance and shape defect by visual observation and microscope was carried out in the same manner as in the above. As a result, there were three defects due to uneven color, and the defect rate was only 0.6%. In addition, the sheet-like AlN sintered bodies all exhibited a brown color, the average value of the thermal conductivity was 173 W / m · k, and the average value of the strength was 56 kg / mm ² . Further, when the surface roughness of the baked surface of the AlN sintered body was measured, the maximum roughness (Rmax) <5 μm and the minimum roughness (Rmin) <0.8 μm, which were sufficiently excellent in use as a circuit board. It was confirmed that it had characteristics.

Examples 30 to 46 and Reference Examples 1 to 4 21 kinds of AlN powders were prepared in the same manner as in Example 1, except that AlN powders shown in Table 4 below and a mixed powder as an additive were used as raw materials. A sintered body was manufactured. However, CaO in Table 4 is obtained by adding CaCO ₃ in terms of weight, and the average particle size is shown as the centrifugal sedimentation diameter when n-butanol is used as the dispersion medium.

The density and the thermal conductivity at room temperature of the AlN sintered bodies of Examples 30 to 50 were determined in the same manner as in Example 1.
The point bending strength and the surface roughness (Ra) were measured. The results are shown in Table 4 below.

[Effects of the Invention] As described above in detail, according to the present invention, low-temperature sintering is excellent in sinterability, and the shape and appearance have high homogeneity, high strength,
It is possible to provide a method capable of producing an aluminum nitride sintered body having high thermal conductivity and useful for a circuit board or the like at a high yield and at low cost.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihiko Tsuge 1 Toshiba-cho, Komukai, Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-61-201671 (JP, A) JP-A-63-166765 (JP, A) JP-A-62-153173 (JP, A) JP-A-63-17262 (JP, A) JP-A-61-219763 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) C04B 35/58

Claims (1)

(57) [Claims] 1. An aluminum nitride as a main component and at least an alkaline earth element rare earth element aluminum compound and an alkaline earth oxide, fluoride, carbide and at least one selected from rare earth oxides, fluorides and carbides. A method for producing an aluminum nitride sintered body, comprising adding an additive containing one compound and sintering at a temperature of 1700 ° C. or less.