JP2778783B2 - Method for producing BN-AlN-based sintered body having anisotropy - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anisotropic BN that can be used as an IC substrate, a material for an IC package, or an electrically insulating heat dissipation material.
The present invention relates to a method for producing an AlN-based sintered body.

More specifically, an anisotropic BN-AlN-based sintered body having an anisotropy of thermal conductivity of 2 or more and a higher value of thermal conductivity of 150 W / m · K or more. It relates to a manufacturing method.

2. Description of the Related Art A hexagonal BN sintered body is widely used in various fields because of its excellent properties such as machinability, corrosion resistance, thermal shock resistance, and electrical insulation. A hexagonal BN sintered body is usually manufactured by a hot press method using an oxide-based auxiliary agent. The sintered body obtained by this method is hexagonal BN
It is known to have structural anisotropy due to the layered crystal structure of (for example, ceramics, vol. 7, No.
4, p.243 (1972)) and physical properties such as thermal conductivity also have anisotropy. However, even in a sintered body having anisotropy, the thermal conductivity is not so high, and a value of up to about 60 W / mK (for example, electronics ceramics, vol.
17, No. 84, p. 68 (1986)). It is considered that the reason for this is that a large amount of oxide-based auxiliaries or reaction products of auxiliaries and other components are present in the sintered body.

On the other hand, research on the improvement of the thermal conductivity of AlN sintered bodies has been actively conducted for the purpose of developing materials for IC substrates and IC packages (for example, Japanese Patent Application Laid-Open No. 61-27026).
4, JP-A-62-36069, JP-A-62-41766), and a high value of thermal conductivity at room temperature of about 110 to 195 W / mK. However, AlN sintered bodies have the disadvantage that, like ordinary structural ceramics, cutting is difficult, and it takes time and costs to process into a desired shape.

Accordingly, an invention relating to a sintered body in which AlN is combined with hexagonal BN and a method for producing the same to mainly improve the machinability of the sintered body while maintaining the high thermal conductivity of the Al N sintered body is disclosed. Have been. For example, Japanese Patent Application Laid-Open No. 60-195059 discloses Al N,
BN, and a Group IIa metal, a Group IIIa metal compound,
There is a description of a sintered body in which Al N particles having a fractured surface are filled and a thin layer of BN is interposed in part or all of the grain boundaries.

The feature of this sintered body is that it is a so-called machineable ceramic composite sintered body that can be cut at a high speed with an ordinary tool. The sintered body is homogeneous and isotropic, and reports a value of about 55 to 122 W / m · K as an example of the thermal conductivity.

Also, Japanese Patent Application No. 62-329626 filed by the present inventors discloses 40 to 95 parts by weight of BN, 5 to 60 parts by weight of a total amount of AlN and AlON, and at least one of a calcium compound and an yttrium compound. There is a description of a composite sintered body consisting of 0.01 to 5 parts by weight and a method for producing the same by a pressure heating method. The features of the sintered body include that it has excellent thermal conductivity, electrical insulation, low thermal expansion coefficient, low dielectric constant, and excellent machinability. 40 ~ 135W / m ・ K as an example of thermal conductivity
Reported values of the degree.

However, these sintered bodies have excellent machinability, but have a thermal conductivity of at most 135 W / mK, which is a material for IC substrates, IC packages, or electrical insulation. Considering application to conductive heat dissipation materials,
It is hard to say that the thermoelectric reading rate is sufficient.

On the other hand, Japanese Patent Application Laid-Open No. 58-32073 discloses that cubic or hexagonal BN is compounded in Al N up to 30% by weight and then molded and then sintered in a vacuum or in a non-oxidizing atmosphere. Alternatively, a sintered body having high thermal conductivity and electrical insulation is obtained by hot press sintering. This sintered body is 85 ~ 195w / m
It is reported to have a thermal conductivity of about K. However, there is no description regarding the anisotropy of the sintered body and the cutting workability with a normal tool or the like.

Also, depending on the production method, these Al N-BN composite sintered bodies may have structural anisotropy due to the structural anisotropy of BN and anisotropy of physical properties as in the case of the BN sintered body ( JP
62-56377) However, a manufacturing method for eliminating this anisotropy and a method for using a material having extremely small anisotropy have been studied.

On the other hand, Japanese Patent Application Laid-Open No. 63-135562 filed by the present inventors discloses that the structural anisotropy of BN is maximally utilized by using a manufacturing method called hot pressing, and the anisotropy of thermal conductivity is 2%. And the higher thermal conductivity value is 150W / m
There is a description on a BN-Al N-type sintered body having anisotropy of K or more and a method for producing the same.

The sintered body is characterized by high thermal conductivity and its anisotropy, and is excellent in machinability. However, the sintered body has a disadvantage of low mechanical strength, for example,
For materials with a composition of BN / Al N = 50/50 (weight ratio), the three-point bending strength also shows anisotropy as well as the thermal conductivity.
It is about 140 to 150 MPa, and the lower value is about 70 to 75 MPa. Particularly when the lower value is used for an IC substrate or the like, it may be a problem in terms of reliability.

Problems to be Solved by the Invention The inventors have conducted intensive studies for the purpose of remarkably improving the strength of a BN-AlN-based sintered body having the above-described anisotropy while maintaining high thermal conductivity. As a result, the object was achieved by devising the particle size of boron nitride which is one of the raw material powders, and the present invention was completed.

The present invention has excellent machinability, exhibits high thermal conductivity of 150 W / m · K or more in a biaxial direction having a three-dimensional space, and has anisotropy in which mechanical strength is significantly improved.
The present invention relates to a method for producing a BN-AlN-based composite sintered body.

Means for Solving the Problems That is, the present invention provides (1) 20 to 80 parts by weight of hexagonal boron nitride, 80 to 20 parts by weight of aluminum nitride, and a sintering aid.
Anisotropic BN-AlN based sintering consisting of 0.2 to 5 parts by weight, having an anisotropy of thermal conductivity of 2 or more and a value of higher thermal conductivity of 150 W / m · K or more In producing the body, the average particle size as a raw material powder of hexagonal boron nitride is 2 to 100 μm
Of coarse powder and fine powder of 0.01 to 1 μm in combination,
This and a mixed powder comprising aluminum nitride powder and a sintering aid in a vacuum or in an inert gas stream, at 1700 to 2200 ° C,
The present invention relates to a manufacturing method characterized by hot pressing at 5 to 50 MPa.

(2) The anisotropic BN-AlN-based ceramic according to the above (1), wherein the content of the fine powder in the hexagonal boron nitride raw material powder is 3 to 30% by weight. The present invention relates to a method for manufacturing a unit.

The particle diameter (particle diameter) of the hexagonal boron nitride or aluminum nitride powder used in the present specification means the primary particle diameter.

Action Hereinafter, the present invention will be described in detail.

The BN-AlN-based sintered body having anisotropy of the present invention has a total of 100 parts by weight of hexagonal boron nitride 20 to 80 parts by weight and aluminum nitride 80 to 20 parts by weight, and a sintering aid 0.2 to Consists of 5 parts by weight. In a composition in which boron nitride is close to 20% by weight with respect to the total amount of hexagonal boron nitride and aluminum nitride, the sintered body has relatively large bending strength and Vickers hardness and relatively low anisotropy. A small sintered body can be obtained. Conversely, in a composition in which boron nitride is close to 80% by weight,
The sintered body exhibits remarkable anisotropy, and a sintered body having extremely good machinability can be obtained. If the composition exceeds these ranges and boron nitride is less than 20% by weight, the anisotropy of the sintered body will not be remarkable, and the higher thermal conductivity is almost equal to the thermal conductivity of the aluminum nitride sintered body. In addition, since most of the constituent components are aluminum nitride, a sintered body having poor machinability is not obtained. Also, boron nitride
If the sintered body exceeds 80% by weight, the bending strength is low and the thermal conductivity is low.

The sintered body having anisotropy of the present invention has a structure in which flaky boron nitride particles are oriented and laminated in the z-axis direction, as shown in the schematic view of the sintered body in FIG. For this reason, anisotropy occurs in physical property values such as thermal conductivity. Now consider the anisotropy figure. This anisotropy is defined as the ratio of the thermal conductivity in the z-axis direction to the thermal conductivity in an arbitrary direction on a plane (xy plane) including the x-axis and the y-axis in FIG. Thermal conductivity in any direction / thermal conductivity in the z-axis direction.
When the hot press pressure axis is set in the z-axis direction, BN is laminated in the z-axis direction, and this direction is a direction in which the thermal conductivity is poor. On the other hand, the x-axis, the y-axis, and a plane including both axes (xy plane) show high thermal conductivity. In the sintered body of the present invention, besides thermal conductivity, bending strength, thermal expansion coefficient, anisotropy also exists in physical property values such as Vickers hardness, but the anisotropy referred to in the present specification is to the last Consider only thermal conductivity.

The sintered body of the present invention has an anisotropy of 2 or more and has a higher thermal conductivity value (thermal conductivity in any direction on a plane (xy plane) including the x-axis and the y-axis). Is 150 W / m · K or more. As a range of a composition satisfying these characteristics, the content of boron nitride is 20 to 80% by weight of the total amount of boron nitride and aluminum nitride. This anisotropy exists even in a sintered body of boron nitride alone, but its thermal conductivity is not so high, up to about 60 W / m · K, and the thermal conductivity of 150 W / m · K or more is aluminum nitride. 20% by weight to 80% by weight
This is achieved only by blending up to

The grain size of the crystal grains constituting the sintered body, particularly the grain size of boron nitride, greatly affects the anisotropy and mechanical strength of the sintered body. That is, it was found that the anisotropy increased as the size of the coarse particles increased, and the strength increased as the size of the fine particles increased.

In the sintering of the composite material BN-AlN, the BN particles almost maintain the shape and size of the raw material BN powder even after sintering,
In order to obtain BN particles having a desired size in the sintered body, BN raw material powder having a size corresponding to the BN particles and having as high a purity as possible may be used.

The boron nitride powder used in the production of the sintered body of the present invention is composed of coarse powder and fine powder, and the coarse powder has an average particle size of 2 μm or more,
μm or less, preferably 5 μm or more and 100 μm or less. The average particle size of the fine powder is 0.01 μm or more and 1 μm or less, preferably 0.01 μm or more and 0.1 μm or less. However, the particle size of the boron nitride powder here is the size in the plane direction of the flaky boron nitride particles, not the size in the thickness direction.

When the average particle size of the coarse powder is less than 2 μm, the anisotropy of the thermal conductivity is hardly 2 or more, and when it is more than 100 μm, sintering becomes difficult. On the other hand, if the average particle size of the fine powder is more than 1 μm, it is difficult to improve the mechanical strength. If the average particle size is less than 0.01 μm, the purity of the BN particles decreases and the material has many impurities (oxides). Would.

The particle size used in the present specification means the primary particle size as described above, which is roughly measured by observing a powder sample with a transmission electron microscope, for example. be able to. According to such observations by the inventors, fine powder, for example, powder having an average particle size of 0.02 μm, was remarkably agglomerated, and many of the fine powders were aggregated particles having a size of about 0.5 to 3 μm. In comparison, it was found that coarse powder, for example, powder having an average particle diameter of 10 μm was not so aggregated.

When the particle size distribution of the powder having an average particle diameter of 10 μm was measured by a centrifugal sedimentation method, about 10 parts by weight of particles having a particle diameter of less than 1 μm, about 80 parts by weight of particles having a particle diameter of 1 μm to 30 μm, About 10 parts by weight of particles larger than 30 μm were measured. Average particle size
Since the 0.02 μm powder was agglomerated, it was difficult to accurately measure the primary particle size distribution.

The abundance of fine powder in the hexagonal boron nitride powder was 3% by weight.
-30%, preferably 5-25%. If it is less than 3%, the effect of improving the strength is hardly expected, and if it exceeds 30%, it is difficult to achieve an anisotropy of thermal conductivity of 2 or more, or the higher thermal conductivity is 150 W / m · K. It is difficult to achieve the above.

On the other hand, as the aluminum nitride raw material powder, known ones can be used, but from the viewpoint of increasing the thermal conductivity, the average particle diameter is preferably 1 μm or less, and the oxygen content is preferably 3.0 wt% or less.
An oxygen content of 1.5 wt% or less is particularly preferred.

Known sintering aids such as calcium oxide, calcium carbide, calcium cyanamide, yttrium oxide, and yttrium carbide can be used. At least one of these compounds is added in an amount of 0.2 to 5% by weight based on the total amount of hexagonal boron nitride and aluminum nitride to obtain a mixed powder. If the amount of the auxiliary agent is less than 0.2% by weight, the function as the auxiliary agent is not sufficiently exhibited, and if it is more than 5% by weight, the auxiliary agent remaining in the obtained sintered body or the reaction formation between the auxiliary agent and other components. Since the amount of the substance becomes excessive, the thermal conductivity decreases. Also, the value of the thermal conductivity of the sintered body, especially the higher value of the thermal conductivity is sensitive to the amount of the sintering aid added, so that the amount to be added needs to be determined with care.

For mixing the raw material and the sintering aid, dry mixing and wet mixing by a known method such as a ball mill can be used, but wet mixing is preferable. The dispersion medium used for the wet mixing is not particularly limited, and alcohols, hydrocarbons, and ketones are preferably used. Since water can react with the nitride powder and generate ammonia gas,
It is better not to use it unless it is particularly necessary.

For the sintering to obtain the sintered body of the present invention, a hot press method which is uniaxial pressing is used. Atmospheric pressure sintering after press molding and isotropic pressure sintering such as HIP
Since lamination does not occur or occurs even if it does not occur, it is not preferable as a sintering method.

Hot press sintering is performed under the conditions of 1700 to 2200 ° C. and 5 to 50 MPa. If the temperature is lower than 1700 ° C., a desired physical property value, particularly a sintered body having a high thermal conductivity cannot be obtained, and if it exceeds 2200 ° C., it is not economical. If the pressure is less than 5 MPa, the sintered body may be insufficient to densify and orient the BN particles,
If it exceeds 50 MPa, the dies that can be used for hot pressing are limited. The atmosphere during sintering is preferably an inert gas atmosphere such as nitrogen gas to prevent oxidation of nitrides. However, when a specific sintering aid is used, by performing sintering in a vacuum, these sintering aids or reaction products of the sintering aids and other components are relatively quickly formed. It may be released outside the system, resulting in an improvement in thermal conductivity. In such a case, sintering in a vacuum is preferred.

The anisotropy of the sintered body due to the orientation and lamination of the BN particles, and the resulting high thermal conductivity are achieved by the manufacturing method described above.

In more detail, calcium oxide, calcium carbide and calcium cyanamide added as sintering aids during hot press sintering react with aluminum oxide inevitably formed on the aluminum nitride surface, It becomes an oxide and begins to melt at about 1400 ° C. In addition, when yttrium oxide or yttrium carbide is added, it also reacts with aluminum oxide to form aluminum-yttrium oxide.
This starts melting.

These melts gradually surround boron nitride and aluminum nitride, react almost completely with the oxide layer remaining on the surface of the nitride particles, purify the surface of the particles, and conduct heat transfer of the sintered body. Improve rate. In addition, due to the presence of the melt, the densification between the particles proceeds by so-called liquid phase sintering through a process of rearrangement, dissolution-precipitation, and coalescence. Due to this liquid phase-related densification mechanism, orientation and lamination of BN by uniaxial pressing are promoted, and boron nitride particles are almost completely laminated in a direction equilibrium with the hot press pressure axis, and have anisotropy. A sintered body is obtained.

In addition, the anisotropic BN-AlN-based sintered body of the present invention can be easily mechanically processed in any composition having a boron nitride content of 20 to 80% by weight.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to only these examples.

Example 1 Aluminum nitride powder having an average particle diameter of 0.6 μm,
As shown in Nos. 1 to 29 in the table, the powder of boron nitride and the sintering aid mixed in particle size were wet-mixed in a ball mill using acetone as a solvent. After the obtained powder was dried, it was filled in a graphite die, and was heated at 1800 ° C. for 2 hours in a nitrogen stream at 2 minutes per minute.
Hot press sintering was performed at a pressure of 40 MPa. Cooling rate is 1
0 ° C / min.

The bulk density, thermal conductivity, and three-point bending strength (according to JIS standards) of the obtained sintered body were measured. Since the sintered body has anisotropy, the values of the thermal conductivity and the bending strength in the direction perpendicular to and parallel to the hot press pressure axis are also listed.
Thermal conductivity was measured by a laser flash method.

The results are shown in Table 1. As can be seen from Table 1, when the boron nitride content is in the range of 80 to 20% by weight, the anisotropy is 2.1 to
A remarkable anisotropy of 7.8 was observed, and the higher thermal conductivity was 150 W / m · K or more in any composition range.

Also, the flexural strength tends to increase with decreasing boron nitride content in both values perpendicular and parallel to the hot press pressure axis. The bending strength of the BN / Al N = 80/20 composition is slightly lower in the direction perpendicular to the hot pressing pressure axis, slightly higher than 100 MPa, but becomes 20 when the BN / Al N = 60/40 composition.
Over 0MPa, further increase with increasing AlN composition, BN / Al
N = 20/80 composition shows a high value of around 380 MPa. The bending strength in the direction parallel to the hot press pressure axis is smaller for each sample than the value in the vertical direction, and is approximately half the value.

Next, as a comparative example, characteristics of a sintered body material outside the scope of the present invention will be described. Aluminum nitride powder having an average particle diameter of 0.6 μm and an average particle diameter of 10 μm as shown in Nos. 30 to 35 in Table 1.
m of boron nitride and a sintering aid were wet-mixed in a ball mill using acetone as a solvent, and a sintered body was prepared and evaluated in the same manner as described above.

The results are shown in Table 1 Nos. 30 to 35. Table 1 (No.
As can be seen from 1 to 35), the bending strength of each BN / Al N composition was higher than that in the case where fine particles were mixed with the boron nitride powder used as a raw material, and the particle size was not mixed. Both the value in the direction perpendicular to the axis and the value in the direction parallel to the axis are significantly improved (increased by about 20 to 60%). On the other hand, it can be seen that the thermal conductivity has hardly changed.

Effect of the Invention As described above, the anisotropic BN-AlN-based sintered body according to the production method of the present invention has high thermal conductivity and significantly improved mechanical strength. It is a material suitable as a highly reliable IC substrate, a material for an IC package, or an electrically insulating heat dissipation material, and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a hot press sintered body.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-305586 (JP, A) JP-A-62-116967 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/583-35/5833 C04B 35/581-35/582

Claims (2)

(57) [Claims] The present invention comprises 20 to 80 parts by weight of hexagonal boron nitride, 80 to 20 parts by weight of aluminum nitride, and 0.2 to 5 parts by weight of a sintering aid, and has an anisotropy of thermal conductivity of 2 or more, and Anisotropic with higher thermal conductivity value of 150 W / mK or more
In producing a BN-Al N-based sintered body, it is composed of a coarse powder having an average primary particle diameter of 2 to 100 μm as a raw material powder of hexagonal boron nitride, and a fine powder having an average primary particle diameter of 0.01 to 1 μm. Using a powder, the mixed powder consisting of aluminum nitride powder and a sintering aid is hot-pressed at 1700 to 2200 ° C. and 5 to 50 MPa in a vacuum or in an inert gas stream to provide anisotropy. Of producing a BN-AlN-based sintered body having the same. 2. The anisotropic BN-AlN according to claim 1, wherein the content of the fine powder in the hexagonal boron nitride raw material powder is 3 to 30% by weight. A method for producing a sintered body.