JPH0524928A - Ceramic substrate and production thereof - Google Patents

Abstract

PURPOSE:To provide a compsn. grade in the thickness direction of the substrate and to impart a cutting property to the substrate as well as to lower its dielectric constant while maintaining the mechanical strength as a substrate material by adding boron nitride to an AlN material by a special method and to impart a high thermal conductivity with AlN and the mechanical strength with Al2O3 to the substrate by constituting the material of AlN-Al2O3 as well as to lower the dielectric constant with porous glass and to impart the mechanical strength with the Al2O3 by constituting the substrate of a porous glass-Al2O3 system. CONSTITUTION:The ceramic substrate is constituted of the Al1-xBxN system (0.37>=X>=0) formed by calcining a mixture composed of aluminum nitride powder (AlN) and boron nitride powder (BN) and is graded in the compsn. in the thickness direction. The machinability is imparted and the cutting property is imparted in the thickness direction by the BN.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate having high thermal conductivity for electronic circuits, and more particularly to a ceramic substrate having a composition which is graded to give the substrate a machineability and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field,
For example, (1) "Functional Ceramics" Metal January 1989, pp. 72-76, (2) "Concept and Development Trend of Functionally Graded Materials" Industrial Materials Vol. 38, No. 12 (October 1990) 18- Some were described on page 25.

There is a great demand for miniaturization, high functionality, high reliability and low cost of electronic devices, and accordingly, semiconductor chips have been remarkably developed in the direction of high integration density and high speed. There is. Along with this, ceramic substrates are also required to have characteristics higher than those of conventionally used alumina substrates. One of the drawbacks of alumina substrates is that their thermal conductivity is 20 W / (m
It is about K) and the heat dissipation is not so good.

[0004]

[Problems to be Solved by the Invention] With the miniaturization of electronic equipment, the integration degree of hybrid modules has increased significantly, and the amount of heat generated per unit area has become a problem. Substrates are needed. Several materials have already been studied for the high thermal conductivity substrate, and SiC-BeO obtained by adding a small amount of beryllium oxide (BeO) to silicon carbide (SiC).
The system has obtained a thermal conductivity of 270 W / (m · K). This value is more than 10 times the thermal conductivity of alumina and is a very promising material, but its relative permittivity ε _r is 1 MH.
There is also 40 in z, which is four times or more the relative dielectric constant of alumina.

In general, the relative permittivity of the substrate greatly affects the propagation speed of the circuit, and the signal delay time is proportional to √ε _r .
Therefore, the one with large ε _r like the above SiC system is
It is not suitable as a substrate ceramic. On the other hand, as high thermal conductivity ceramics, aluminum nitride (AlN)
Is also promising. Thermal conductivity has also improved and is now 270
The value of W / (mK) has come to be obtained. Furthermore, the relative permittivity is slightly smaller than that of alumina, that is, about 8.7, and its development is urgently required for practical use. However, AlN generally has the drawback of being hard and brittle.

In order to solve the above problems, the present invention provides
Due to the selected material with composition gradient in the thickness direction,
An object of the present invention is to provide a ceramic substrate having various excellent characteristics and a method for manufacturing the same. More specifically, A
By adding boron nitride to a 1N-based material by a special method, a composition gradient is provided in the thickness direction, while maintaining mechanical strength as a substrate material, it also has machinability and also reduces the dielectric constant. A ceramic substrate to be obtained and a method for manufacturing the same are provided.

Al having a composition gradient in the thickness direction
Provided is a ceramic substrate which is made of N-Al ₂ O ₃ system, has high thermal conductivity with AlN, and has mechanical strength with Al ₂ O ₃ , and a manufacturing method thereof. Furthermore, a ceramic substrate and a method for producing the same, which are composed of a porous glass-Al ₂ O ₃ system having a composition gradient in the thickness direction, have a low dielectric constant with the porous glass, and have mechanical strength with Al ₂ O _3. provide.

[0008]

According to the present invention, in order to achieve the above object, in a ceramic substrate, an Al _1-x B _x N system (0.3 ≧ X) having a composition gradient in the thickness direction is provided.
≧ 0), high thermal conductivity and machinable.
In addition, the total weight of CaO and Ca added to impart high thermal conductivity to the Al _1-x B _x N system is 10 mol% or less.
It has a composition containing at least one selected from F ₂ , AlF ₃ , Y ₂ O ₃ , and YF ₃ .

Further, one side of the substrate surface (X = 0 or a minute X
Has a high thermal conductivity and a high mechanical strength, and the other one side (X ≠ 0) enables cutting. In addition, AlN-Al having a composition gradient in the thickness direction
₂ O ₃ system, AlN with high thermal conductivity, Al
It is made to have mechanical strength with ₂ O ₃ .

Further, it is composed of a porous glass-Al ₂ O ₃ system having a composition gradient in the thickness direction, the dielectric constant is lowered by the porous glass, and Al ₂ O ₃ has mechanical strength. Is.

[0011]

As described above, according to the present invention, the ceramic substrate is (1) an Al _1-x B _x N system obtained by sintering a mixture of aluminum nitride powder (AlN) and boron nitride powder (BN). (0.3 ≧ X ≧ 0), and the composition is graded in the thickness direction. Then, BN can provide machineability and machinability in the thickness direction. (2) Aluminum nitride powder (AlN) and alumina (A
It is formed by sintering a mixture of 1 ₂ O ₃ ) and has a composition gradient in the thickness direction. The thermal conductivity can be covered with AlN, and the mechanical strength can be covered with alumina, so that a high-strength and high-thermal-conductivity substrate can be obtained. (3) A mixture of porous glass (B ₂ O ₃ —SiO ₂ ) and alumina (Al ₂ O ₃ ) is sintered,
The composition is graded in the thickness direction. Then, the upper part is made of porous glass having a low dielectric constant (porous glass: the dielectric constant ε _r is 4 or less) to lower the dielectric constant ε _r, and the lower part is made of alumina to increase the strength of the substrate. Moreover, a substrate having mechanical strength can be obtained.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of a ceramic substrate showing a first embodiment of the present invention. The ceramic substrate of this example is formed by sintering a mixture of aluminum nitride powder (AlN) and boron nitride powder (BN), and is characterized in that the composition is graded in the thickness direction. . In general, AlN and BN do not form a solid solution but form a composite,
The BN precipitated in the 1N matrix absorbs the breaking energy and enables cutting. That is, the BN is used to provide the machineability and the machinability in the thickness direction.

Here, a method of providing a composition gradient in the thickness direction can be generally performed as follows. That is,
In the Al _1-x B _x N system, some values of X are selected from 0 to 0.3 and several kinds of mixed powders are prepared. For example,
X = 0, 0.05, 0.1, 0.15, 0.20, 0.
Suppose you choose 25, 0.30 and 7 types. These powders are made into discs (pellets) having a thickness of 0.5 mm and a diameter of 10 mmφ according to a usual ceramics manufacturing method. These 7
By stacking and integrating discs (pellets) of plates and firing them at a predetermined temperature and atmosphere, ceramic substrates having different composition gradients of X can be obtained almost continuously in the thickness direction.

Thus, in the Al _1-x B _x N system,
Prepare several kinds of pellets in the range of X = 0 to 0.3,
They are combined and fired to obtain a ceramic substrate having a graded composition. Here, the side of X = 0 is
High thermal conductivity and high mechanical strength. On the other hand, on the side of X ≠ 0 and including BN, the thermal conductivity decreases with an increase in BN, but the machinability is improved.

Here, X = 0.3 means that the thermal conductivity decreases as X increases, and when X exceeds 0.3, 100 W / (m · K) is desirable as a substrate material.
This is because the above value cannot be obtained. Basically, A
Although a high thermal conductive substrate can be obtained in the l _1-x B _x N system,
Generally, AlN is a difficult-to-sinter body, and various additives enhance the sinterability, and are also effective in achieving high thermal conductivity. CaO, CaF ₂ , Al that has a useful effect as an additive is
Oxides and fluorides such as F ₃ , Y ₂ O ₃ and YF ₃ ;
A total weight of 10 mol% or less is effective. When it is 10 mol% or more, a material having a thermal conductivity of 100 W / (m · K) or more cannot be obtained.

A specific embodiment will be described below. "Example 1" CaO 2 mol%, CaF ₂ 2 mol%
Containing AlN, Al _0.96 B _0.04 N, Al _0.91 B
_0.09 N, Al _0.87 B _0.13 N, Al _0.82 B _0.18 N,
Six types of powder of Al _0.76 B _0.24 N are prepared. An organic binder or the like is added to these powders to form a 0.2 mm thick sheet by the doctor blade method. These six sheets are stacked in order and integrated by pressure compression. This laminated sheet is fired, for example, at 1900 ° C. for 6 hours in a nitrogen stream. The obtained substrate has the following characteristics.

[0017] Thermal conductivity (AlN surface) 180 W / mK Relative permittivity (1MHz) 8.5 Cutting time (Comparison between AlN and counter surface) 1/10 "Example 2" AlF₃  1 mol%, Y₂O₃  3 mol
% Containing Al_0.99B_0.01N, Al _0.96B_0.04N,
Al_0.90B_0.10N, Al_0.86N_0.14N, Al_0.75B
_0.25Prepare 5 kinds of N powder and add organic binder
Then, a circular plate having a thickness of 10 mm and a thickness of 0.3 mm is prepared.
These five discs are stacked in order and integrated by pressure compression
To do. This laminated disc was placed in a nitrogen stream at 1850 ° C. for 10
Bake for hours. The obtained disc has the following characteristics.
It

Thermal conductivity (Al _0.99 B _0.01 N face) 195 W / (m ·
K) Relative permittivity (1MHz) 8.6 Cutting time (Al _0.99 B _0.01 N face vs. counter face)
1/18 "Example 3" Y ₂ O ₃ 1.5 mol%, YF ₃ 4 mol%, AlN containing CaO 1 mol%, Al _0.95 B
_0.05 N, Al _0.90 B _0.10 N, Al _0.88 B _0.12 N,
_{Al 0. 86 B 0.14 N, Al} 0.78 B 0.22 N, Al 0.78 B
7 kinds of powder of _0.29 N are prepared. Add 0.15 m of these powders with the doctor blade method by adding an organic binder.
Create an m-thick sheet. These sheets are stacked in order and integrated by pressure compression. This laminated sheet is fired in a nitrogen stream at 1940 ° C. for 5 hours to obtain a substrate. The characteristics of the obtained substrate show the following characteristics.

Thermal conductivity (AlN surface) 145 W / (m · K) Relative permittivity (1 MHz) 8.5 Cutting time (comparison between AlN and counter surface) 1/15 “Example 4” CaO 0.5 Mol%, CaF ₂ 1.
AlN, A containing 2 mol% and Y ₂ O ₃ 1.4 mol%
l _0.96 B _0.04 N, Al _0.92 B _0.08 N, Al _0.88 B
_0.12 N, Al _0.83 B _0.17 N, Al _0.80 B _0.20 N,
Seven kinds of powders of Al _0.76 B _0.24 N are prepared. An organic binder is added to each to make a disk with a thickness of 15 mm and a thickness of 0.35 mm, and these seven disks are stacked in order and integrated by pressure compression. This laminated disc was placed in a nitrogen gas stream at 192
A disc is obtained by firing at 0 ° C. for 8 hours. The resulting disc has the following properties.

Thermal conductivity (AlN surface) 210 W / (m · K) Relative permittivity (1 MHz) 8.7 Cutting time (Comparison between AlN and opposing surface) 1/13 Further, lower dielectric constant of ceramic substrate From the perspective of
The Al _1-x B _x N system has a limit in reducing the dielectric constant to that extent as compared with AlN. However, it was found that by adding various additives in an amount of 10 mol% or less, it was possible to make the content lower than that of AlN alone, and it was found that the additives also have an action effect for lowering the dielectric constant.

Here, for the evaluation of cutting, as an example, a weight of 200 g is loaded at a speed of 72 m / sec and the time required to cut a thickness of 1 mm is compared. It takes about 50 minutes at X = 0, about 10 minutes at X = 0.1, about 5 minutes at X = 0.2, and 2.5 minutes at X = 0.3. It turned out to be greatly shortened.

As described above, the advantage of the present invention is that the surface required as a substrate has high mechanical strength and high thermal conductivity.
Further, the relative dielectric constant can be reduced. In addition, by grading the composition, there is an advantage that cutting can be performed from the other side. For example, from the BN surface, holes (through holes) for upper and lower wiring can be easily formed with a fine drill (0.5 mmφ).

In this way, a highly heat conductive machinable substrate using a functionally graded material can be obtained. Such a substrate is suitable as a substrate for multilayer high-density wiring.
Next, FIG. 2 is a configuration diagram of a ceramic substrate showing a second embodiment of the present invention. The ceramic substrate of this example is composed of aluminum nitride powder (AlN) and alumina (Al
_It is formed by sintering a mixture of ₂ O ₃ ) and has a composition gradient in the thickness direction.

With this structure, the AlN-based material has high thermal conductivity (200 W / mK) and the alumina has large mechanical strength, that is, the thermal conductivity is AlN.
Therefore, the mechanical strength can be covered with alumina, and a high strength and high thermal conductivity substrate can be obtained. Incidentally, the thermal conductivity of alumina is 20 W / m · K or less.

The manufacturing method is as follows:
N, AlON, and Al ₂ O ₃ are prepared. In order to make the composition gradient in the thickness direction, the following mixed powders are prepared. For example, AlN, 0.75AlN-0.25A
1ON, 0.5AlN-0.5AlON, 0.75
AlON-0.25Al ₂ O ₃ , 0.50AlON-
0.5Al ₂ O ₃ , 0.25AlON-0.75Al
_It is assumed that 7 kinds of ₂ O ₃ and Al ₂ O ₃ are selected. These powders have a thickness of 0.5 m according to the usual ceramic manufacturing method.
A disk having a diameter of 10 mm and a diameter of 10 mmφ. By integrating these seven discs and firing them in a predetermined temperature and atmosphere, ceramics having different composition gradients of nitrogen N can be obtained almost continuously in the thickness direction. In this system, additives such as MgO, Y ₂ O ₃ and CaO are effective for improving the mechanical strength.

Specific examples will be described below. "Example 1" AlN containing 1 mol% of MgO, 0.
8AlN-0.2AlON, 0.5AlN-0.5A
1ON, 0.2AlN-0.8AlON, 0.8A
lON-0.2Al ₂ O ₃ , 0.5AlON-0.5
_{Al 2 O 3, 0.2AlON-0.8Al} 2 O 3,
Prepare 8 kinds of Al ₂ O ₃ powders, add these powders with organic binder, etc.
Create a thick sheet. Stack these sheets in order,
It is integrated by pressure compression. This laminated sheet is, for example, at 1830 ° C. in a controlled nitrogen stream at 5 ° C.
Bake for hours. The obtained substrate has the following characteristics.

Thermal conductivity (AlN surface) 130 W / (m · K) Dielectric constant (1 MHz) 8.9 Hardness (Vickers) (Al ₂ O ₃ surface) 2500 kg /
mm ² Hardness (Vickers) (AlN surface) 1300kg /
mm ² Next, FIG. 3 is a configuration diagram of a ceramic substrate showing a third embodiment of the present invention.

The ceramic substrate of this embodiment is composed of porous glass (B ₂ O ₃ --SiO ₂ ) and alumina (Al.
_It is formed by sintering a mixture of ₂ O ₃ ) and has a composition gradient in the thickness direction. With this structure, the upper part is made of porous glass having a low dielectric constant (porous glass: dielectric constant ε _r is 4 or less) to lower the dielectric constant ε _r ,
By lowering the strength of the substrate with alumina at the bottom,
It is possible to obtain a substrate having a small dielectric constant and mechanical strength. Since such a ceramic substrate has a low dielectric constant, the capacitance component of the wiring is reduced, and the signal delay can be eliminated.

Therefore, it is suitable for a substrate for high speed computers.
It is suitable. The manufacturing method is as follows:
Acid glass (B₂O₃-SiO₂) And alumina
It To grade the composition in the thickness direction, the following types
Prepare a kind of mixed powder. For example, in mol%, (B₂
O₃-SiO₂) 30-Al ₂O₃70, (B₂O₃
-SiO₂) 40-Al₂O₃60, (B₂O₃-S
iO₂) 30-Al₂O₃70 types should be selected.
It These powders are processed according to the usual ceramics manufacturing method.
A disk with a thickness of 0.3 mm and a diameter of 10 mmφ.
It Integrate these three discs, and
By firing with air, A
l₂O₃Ceramics having different composition gradients are obtained.
In this system, in order to make it porous, 500 to 70
Heat treatment is performed at about 0 ° C to precipitate glass, and then glass
It is obtained by removing the soot component with an acid stream. Well
The same applies to glasses other than borosilicate glass, which is the glass component.
The same effect can be obtained.

Specific examples will be described below. In "Example 1" _{mol%, (B 2 O 3 -SiO} 2) 35
-Al ₂ O ₃ 65, (B ₂ O ₃ -SiO ₂ ) 40-A
l ₂ O ₃ 60, (B ₂ O ₃ —SiO ₂ ) 50-Al _{2
O 3 50, (B 2 O} 3 -SiO 2) 60-Al 2 O 3
40 kinds of 40 kinds of powders are prepared, an organic binder or the like is added to these powders, and a sheet of 0.25 mm thickness is prepared by a doctor blade method. These sheets are stacked in order and integrated by pressure compression. This laminated sheet is fired in air at 1050 ° C. for 3 hours. The porous ceramic substrate obtained by subjecting this sintered body to heat treatment at 600 ° C. for 2 hours to precipitate a glass component and removing the glass component with hydrochloric acid (Hcl) is:
It has the following characteristics.

The dielectric constant (the surface of the _{B 2 O 3 -SiO 2 60-} Al 2 O 3 40) (1MHz) 4.3 Hardness _{(Vickers) (B 2 O 3 -SiO 2} 35-Al 2
The surface of O ₃ 65) 1500 kg / mm ^{2 The} present invention is not limited to the above embodiment,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0032]

As described above in detail, according to the present invention, it is possible to obtain a ceramic substrate having various excellent characteristics by using the selected material having the composition gradient in the thickness direction. That is, by adding boron nitride to an AlN-based material by a special method, a composition gradient is provided in the thickness direction and mechanical strength as a substrate material is maintained,
It is possible to obtain a ceramic substrate that has a machinability and can also reduce the dielectric constant. Further, by grading the composition, a practical effect that cutting can be performed from the other side is achieved.

Further, Al having a composition gradient in the thickness direction
It is possible to obtain a ceramic substrate composed of N-Al ₂ O ₃ system, AlN having high thermal conductivity, and Al ₂ O ₃ having mechanical strength. Further, it is possible to obtain a ceramic substrate which is composed of a porous glass-Al ₂ O ₃ system having a composition gradient in the thickness direction, the dielectric constant is reduced by the porous glass, and mechanical strength is provided by Al ₂ O _3. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of a ceramic substrate showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a ceramic substrate showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a ceramic substrate showing a third embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H05K 1/03 B 7011-4E

Claims (10)

[Claims] _1. An Al _1-x having a composition gradient in the thickness direction.
A ceramic substrate characterized by being B _x N based (0.3 ≧ X ≧ 0), having high thermal conductivity and being machinable. 2. The ceramic substrate according to claim 1, wherein the total weight of CaO and CaF added to impart high thermal conductivity to the Al _1-x B _x N system is 10 mol% or less.
A ceramic substrate having a composition containing at least one selected from ₂ , AlF ₃ , Y ₂ O ₃ , and YF ₃ . 3. The ceramic substrate according to claim 1, wherein one side (X = 0 or a minute value of X) of the substrate surface has high thermal conductivity and strong mechanical strength, and the other side (X ≠).
0) is a ceramic substrate that can be cut. 4. An Al _1-x having a composition gradient in the thickness direction.
In a method for manufacturing a B _x N system (0.3 ≧ X ≧ 0) ceramic substrate, (a) prepare a plurality of pellets obtained by selecting some values of X from 0 to 0.3. ,
(B) A ceramic substrate characterized in that the pellets are sequentially stacked and integrated, (c) fired at a predetermined temperature and atmosphere, and (d) the composition gradient of X is substantially continuously changed in the thickness direction. Manufacturing method. 5. The method of manufacturing a ceramic substrate according to claim 4, wherein the total weight of the additive is at least 10 mol% and is selected from CaO, CaF ₂ , AlF ₃ , Y ₂ O ₃ , and YF _3. A method of manufacturing a ceramic substrate, comprising: 6. AlN--having a composition gradient in the thickness direction
It is made of Al ₂ O ₃ system and has high thermal conductivity with AlN,
A ceramic substrate characterized by having mechanical strength with Al ₂ O ₃ . 7. The ceramic substrate according to claim 6, wherein MgO, Y ₂ O ₃ and C are added to have mechanical strength.
A ceramic substrate having at least one additive selected from aO. 8. An AlN-having a composition gradient in the thickness direction.
In a method of manufacturing an Al ₂ O ₃ -based ceramic substrate,
(A) Prepare a plurality of pellets whose raw material powders are AlN, AlON, and Al ₂ O ₃ , (b) stack the pellets one after another to integrate them, (c) fire at a predetermined temperature and atmosphere, and (d) ) A method of manufacturing a ceramic substrate, characterized in that composition gradients of N different from each other are made substantially continuous in the thickness direction. 9. A porous glass-Al ₂ O ₃ system having a composition gradient in the thickness direction, wherein the porous glass lowers the dielectric constant and Al ₂ O ₃ provides mechanical strength. Ceramic substrate to be used. 10. A method for producing a porous glass-Al ₂ O ₃ -based ceramic substrate having a composition gradient in the thickness direction, comprising: (a) a plurality of raw material powders made of porous glass and Al ₂ O ₃ ; Pellets are prepared, (b) the pellets are sequentially stacked and integrated, (c) fired at a predetermined temperature and atmosphere, and (d) a composition gradient of Al ₂ O ₃ having different compositions is continuously formed in the thickness direction. A method of manufacturing a ceramic substrate, comprising: