JPH04198062A - Method for sintering ceramics and sintering tool used for the method - Google Patents

Abstract

PURPOSE:To sinter a ceramic molded product in improved efficiency by placing the ceramic molded product on each of ceramic sintered product-made setters arranged through tungsten-made spacers and subsequently sintering the ceramic molded product. CONSTITUTION:Ceramic sintered product-made setters 12 comprising aluminum nitride having a relative density of >=99% are arranged on the bottom of a graphite-made bottomed specimen case 10 through tungsten-made spacers 14. Ceramic molded products 16 each comprising an aluminum nitride substrate metallized with a tungsten paste are set on the setters 12, and sintered at 1800-2000 deg.C in a sintering atmosphere in which carbon is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic firing method and a firing jig used therein.

(Prior Art) In the firing of ceramics, ceramics formed into a predetermined shape are heated and fired in a firing furnace. An appropriate firing furnace is used depending on the type of ceramic to be fired, but for ceramics such as aluminum nitride that are fired at extremely high temperatures of over 1800°C, it is recommended to use graphite, which has high heat resistance, as the furnace material. is normal.

The aluminum nitride has excellent material properties such as high thermal conductivity, high electrical insulation, and a low coefficient of thermal expansion that matches silicon elements, and is also low in toxicity, so it can replace the conventionally used alumina ceramics and beryllia ceramics. Aluminum nitride is attracting attention as a substrate material for semiconductor devices, but a good sintered body cannot be obtained from aluminum nitride in a firing furnace using graphite as the furnace material. This is because aluminum nitride is affected by carbon in the firing atmosphere, which inhibits sintering and causes uneven coloring.

Therefore, boron nitride was used as a material that also has high heat resistance. When this boron nitride is used, a well-densified aluminum nitride sintered body can be obtained. However, when boron nitride is used, the boron released into the firing atmosphere reacts with tungsten and molybdenum, resulting in an abnormally high resistance of the metallized part when fired after being metallized with tungsten paste or the like. The point became clear.

(Problem to be Solved by the Invention) Therefore, in order to avoid the influence of carbon appearing in the firing atmosphere from graphite and to enable metallization with tungsten paste, a firing jig was created using tungsten or molybdenum. The method used was to set a ceramic molded body in a firing jig and fire it.

When using this firing jig made of tungsten or molybdenum, the aluminum nitride is fired to become suitably a-densified, and the metallized portion has high resistance even if it is pre-metalized using tungsten paste or molybdenum paste. Such problems do not arise.

However, firing jigs made of tungsten or molybdenum are heavy due to the high specific gravity of these metals, and there are problems in manufacturing that the amount of fired products that can be input is limited due to the load capacity of the furnace. , tungsten or molybdenum are brittle materials and have the problem of being susceptible to deterioration when used repeatedly. Note that when cleaning the baking jig, it is usually treated with a strong base solution or an acid solution.

For this reason, there was a problem in that work efficiency was significantly reduced.

Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to be able to suitably sinter ceramics such as aluminum nitride while avoiding the influence of furnace materials, etc. Another object of the present invention is to provide a method for firing ceramics that can suitably sinter even products that have been metalized in advance using tungsten paste or the like, and a firing jig for use in the method.

(Means for solving problems) The present invention has the following configuration to achieve the above object.

That is, in a ceramic firing method in which ceramic is fired in a firing furnace in which carbon appears in the firing atmosphere, a ceramic sintered body is used as a setter that supports the ceramic molded body in the furnace, and the ceramic molded body is mounted. The ceramic molded body is made of aluminum nitride and the setter is made of an aluminum nitride plate. It is effective to use a compact formed by metallizing an aluminum nitride substrate with tungsten paste, or an aluminum nitride plate setter having a relative density of 99X or more.

Furthermore, it is effective to use a spacer made of a tungsten plate, or a spacer made of tungsten powder piled up to a predetermined thickness on a setter.

It is also a firing jig for firing a ceramic molded body by setting it in a firing furnace in which carbon appears in the firing atmosphere, the firing jig being a ceramic molded body formed into a plate shape on which the ceramic molded body is placed. It is characterized by comprising a setter and a spacer that is sandwiched between the upper and lower parts of the setter to provide a space for placing the ceramic molded body.

Further, in the firing jig, the setter is an aluminum nitride plate and the spacer is a tungsten plate;
It is effective that the setter is an aluminum nitride plate and the spacer is made of tungsten powder.

(Function) By using a ceramic setter and a tungsten material spacer, it is possible to reduce the weight of the jig, and the spacer part blocks out components that have a negative effect on the molded product, such as carbon or boron, so that good products can be fired. do.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is an explanatory view showing an embodiment of a ceramic firing jig according to the present invention. In the example, a firing jig used for firing aluminum nitride is shown.

In FIG. 11, 10 is a sample case for accommodating a ceramic molded body. The sample case 10 is made of graphite and is shaped like a pyramid with a bottom.

12 is a setter placed inside the sample case 10. In the example, a sintered aluminum nitride plate (density 3.26 g/cm') formed into a 2 mm thick plate was used.

14 is a spacer arranged around the periphery of the setter 12. This spacer 14 is provided to provide a space on the setter 12 for placing an aluminum nitride molded body 16 to be fired. In the example, the spacer 14 was made of tungsten material with a thickness of 3 mm and a width of 3 mm, and was formed into a frame shape so as to cover the outer peripheral edge of the setter 12.

The setter 12 places molded bodies 16 of aluminum nitride in a predetermined arrangement, and the spacers 14 are sandwiched between the setters 12 and stacked and set in the sample case 10 as shown in the figure.

The aluminum nitride molded body 16 is formed by screen printing a desired metallization pattern using tungsten paste, and contains 3% by weight of Y and Ch.

The sample case 10 containing the aluminum nitride molded body 16 was set in an electric furnace, and after removing the binder, it was fired at 1900° C. for 10 hours in a nitrogen gas atmosphere.

The sintered body was obtained as a transparent body without yellowing or other uneven color. In addition, a suitable value for thermal conductivity was obtained at l96W/mK, and the resistivity of the metallized part was approximately 7XlO-''Ω・cm.
A very low value was obtained, and a sintered body with excellent properties was obtained.

The method of firing aluminum nitride in this example is as follows:
The setters 12 are set using an aluminum nitride plate, the spacers 14 are made of tungsten material, and the setters 12 are stacked via the spacers 14.

The aluminum nitride sintered body used for the setter 12 needs to be a densely sintered, high-purity aluminum nitride plate with a relative density of 99% or more.

A densely sintered aluminum nitride sintered body does not exhibit any problematic interaction with carbon or boron nitride in a non-oxidizing atmosphere up to at least about 1950°C. Therefore, even if graphite or boron nitride materials are used in the furnace chamber or the sample case 10 as in the above embodiment, there is an advantage that deterioration due to mutual reactions does not occur.

Furthermore, the reason why aluminum nitride must be dense and highly pure is to prevent contamination when the setter is used repeatedly.

Generally, when firing aluminum nitride, a secondary phase (liquid phase) is generated in the initial stage of sintering, and densification progresses through the liquid phase sintering mechanism.
At the final stage, this secondary phase is removed from the system. The liquid or gas phase produced from aluminum nitride products, which is mainly composed of sintering aids, often contaminates the setter, causing deterioration of the setter, or is transferred from the setter side to the product side when used for the next step. This may cause problems such as transcription etc. If the aluminum nitride used in the setter is not sufficiently dense, secondary phase components from the product may be unevenly incorporated into the setter and transferred to the product, but if the aluminum nitride sintered body is not sufficiently dense, If the purity is high, secondary phase components from the product will not be taken into the setter, and therefore the above-mentioned problem of transfer from the setter to the product will not occur. This also makes cleaning the setter easier.

Moreover, the use of tungsten material for the spacer 14 is because
This is because tungsten material is superior to aluminum nitride spacers in controlling the atmosphere within the firing jig.

The spacer 14 of the embodiment is sandwiched between the outer periphery of the setter 12 and overlapped with the setter 12, thereby shielding the outer periphery of the setter 12 and preventing carbon, boron, etc. from entering the molded body 16 or the molded body 16 from entering from the outside. It has the effect of blocking components that have an adverse effect on the metallized parts. Moreover, the spacer 14 also has the purpose of preventing the accumulation of components such as the above-mentioned secondary phase components which are generated when the molded body is fired and which are to be discharged from the inside to the outside of the system.

Tungsten material has sufficient effects for these purposes. That is, since tungsten easily interacts with carbon, boron, etc., when carbon or boron tries to enter from the outside, it interacts with tungsten and is blocked at the outer peripheral edge of the setter 12. Further, since tungsten and the aluminum nitride setter 12 do not easily interact with each other, the setter 12 and the spacer 14 do not adhere to each other, and components to be discharged, such as secondary phase components, are preferably discharged. Note that spacer 1 using tungsten material
4, a plate made of rolled tungsten may be used, or tungsten powder may be applied to the outer peripheral edge of the setter 12, and the setters 12 may be stacked on top of each other.

Using a tungsten plate for the spacer 14 is easier to handle, but if the sintering aid component in aluminum nitride is particularly large, a method using tungsten powder will yield better results.

When the molded body 16 is set on the setter 12 with tungsten powder piled up on the outer periphery of the setter 12 and fired, the tungsten powder on the outer periphery of the setter 12 is often integrated after firing. It is thought that grain growth occurs during the process of discharging the secondary phase components of the compact to the outside of the jig during firing.

Furthermore, in this embodiment, a part of the setter, which is the main part of the firing jig, is formed of a sintered body of aluminum nitride, which has the advantage that it can be made lighter compared to a case where the firing jig is made of tungsten.

The specific gravity of aluminum nitride is about 3.3 g/cm3, which is about one-sixth that of tungsten, and when a 2 mm thick aluminum nitride plate is used as a practical setter, the thickness I,
Compared to the case where a 5 mm tungsten plate is used, it is possible to store approximately four times as much molded product within the load tolerance of the furnace.

Incidentally, in the above embodiments, the firing of aluminum nitride has been described, but the present invention can be similarly applied to the firing of ceramics which are fired at extremely high temperatures of 1800 to 2000°C.

The present invention has been variously explained above using preferred embodiments, but the present invention is not limited to these embodiments.
Of course, many modifications can be made without departing from the spirit of the invention.

(Effects of the Invention) As described above, the ceramic firing method and firing jig according to the present invention are suitable for firing ceramics that require extremely high firing temperatures, even when carbon appears in the firing atmosphere. Furthermore, it is possible to obtain fired metallization with low resistivity even in products metallized using tungsten paste, and it is possible to manufacture good quality ceramic products. Furthermore, since it can be made lighter in weight compared to conventional firing jigs, it has great effects such as being able to fire more products at once and making it more efficient to manufacture.

[Brief explanation of the drawing]

FIG. 1 is an explanatory view showing an embodiment of a ceramic firing jig according to the present invention. 10... Sample case, 12... Setter, 14
...Spacer, 16... Aluminum nitride molded body.

Claims (9)

[Claims] 1. In a ceramic firing method in which ceramic is fired in a firing furnace where carbon appears in the firing atmosphere, a ceramic sintered body is used on a setter that supports the ceramic molded body in the furnace, and the ceramic molded body is placed on the setter. A ceramic firing method characterized by using tungsten material for a spacer sandwiched between upper and lower setters to form a space. 2. The ceramic molded body is aluminum nitride,
2. The ceramic firing method according to claim 1, wherein an aluminum nitride plate is used as the setter. 3. 3. The method for firing a ceramic according to claim 2, wherein the ceramic molded body is a molded body formed by metallizing an aluminum nitride substrate with tungsten paste. 4. Relative density of aluminum nitride plate setter is 99%
The ceramic firing method according to claim 2 or 3, wherein the method is as follows. 5. 5. The ceramic firing method according to claim 1, wherein the spacer is made of a tungsten plate. 6. Claims 1 and 2, characterized in that the spacer is a setter with tungsten powder piled up to a predetermined thickness.
4. The ceramic firing method according to 3 or 4. 7. A firing jig for firing a ceramic molded body by setting it in a firing furnace where carbon appears in the firing atmosphere, comprising a ceramic setter formed into a plate shape on which the ceramic molded body is placed; A firing jig comprising: a spacer sandwiched between the upper and lower sides of the setter to provide a space for placing the ceramic molded body. 8. Claim 7, wherein the setter is an aluminum nitride plate and the spacer is a tungsten plate.
The firing jig described. 9. 8. The firing jig according to claim 7, wherein the setter is an aluminum nitride plate and the spacer is made of tungsten powder.