JP2010159184A - Method for producing aluminum nitride sintered compact - Google Patents

Abstract

A method of manufacturing an aluminum nitride sintered body with less warpage is provided.
An aluminum nitride sintered body is manufactured by a manufacturing method characterized in that the degreasing and firing processes are characterized by the following (1) and (2).
(1) Degreased and fired by placing a weight on the laminated body that is alternately laminated so that the front surfaces or back surfaces of the molded body face each other.
(2) The weight of the weight applied to the laminate is A represented by the following formula per 1 cm ² .
10 <= A <= 100- (n-1) * a (The unit of mass is g.)
However, n is the number of stacked molded bodies, and a is the mass per 1 cm ² of the surface of the molded body after drying.

[Selection figure] None

Description

The present invention relates to a method for producing an aluminum nitride sintered body.

Conventionally, a circuit board is used in which a conductive metal circuit layer is bonded to a surface of a ceramic substrate for mounting a semiconductor with a brazing material and a semiconductor element is mounted at a predetermined position of the metal circuit layer. In order for a circuit board to operate with high reliability, it is important to dissipate the heat generated by the semiconductor element so that the temperature of the semiconductor element does not become excessive. Therefore, high thermal conductivity is required so as to exhibit excellent heat dissipation characteristics. In recent years, with the progress of miniaturization of circuit boards and higher output of power modules, aluminum nitride substrates have attracted attention as miniaturization and weight reduction modules. Further, along with the demand for miniaturization of the circuit itself of the aluminum nitride substrate, the aluminum nitride sintered body has been required to reduce warpage.

An aluminum nitride sintered body that becomes an aluminum nitride substrate is generally manufactured by the following method. That is, an additive such as a sintering aid, a binder, a plasticizer, a dispersion medium, and a release agent is mixed with the aluminum nitride powder and processed into a sheet-like molded body by extrusion molding or the like. Next, the molded body is heated in air or in a non-oxidizing atmosphere such as nitrogen to 350 to 700 ° C. to remove the binder (degreasing), and then in a non-oxidizing atmosphere such as nitrogen at 1800 to 1900 ° C. Manufactured by holding for 0.5-10 hours (firing).

As a method of reducing deformation (warpage) of the aluminum nitride sintered body during firing, a method of surrounding the periphery with a ceramic spacer or setter when firing the aluminum nitride molded body (Patent Document 1), containing ceramic powder There has been proposed a method (Patent Document 2) or the like in which aluminum nitride molded bodies are laminated and fired in multiple stages through sushi powder. However, these methods do not provide sufficient warping improvement effects to meet today's requirements, and it is essential to arrange setters and spacers, and to use a dust, in terms of productivity. There was a problem.
On the other hand, in the degreasing step, after debinding in a nitrogen atmosphere, a method of manufacturing an aluminum nitride sintered body having a small warpage by further debinding in air has been proposed (Patent Document 3). . However, even in this method, it is necessary to repeat the degreasing process twice, and it has been difficult to increase the productivity.

JP-A-5-229873 Japanese Patent Laid-Open No. 5-229872 Japanese Patent Laid-Open No. 5-9077

  An object of the present invention is to provide a method for producing an aluminum nitride sintered body with less warpage.

That is, the present invention relates to a method for producing an aluminum nitride sintered body in which a molded body containing an aluminum nitride powder and a sintering aid comprising a rare earth compound is fired. (1) The front surfaces or the back surfaces of the molded bodies face each other. (2) The weight of the weight applied to the laminate is fired with a weight in the range of A represented by the following formula per 1 cm ^2. A method for producing a featured aluminum nitride sintered body,
10 ≦ A ≦ 100− (n−1) × a
However, n is the number of laminated molded bodies, a is a weight of 1 cm ² of the surface of the molded body after drying is made of tungsten, molybdenum, or an alloy containing these, and the warp of the sintered body is 5 μm / cm or less. This is a method for producing aluminum nitride. Further, the present invention is an aluminum nitride circuit board using an aluminum nitride sintered body manufactured by the aluminum nitride manufacturing method, and a module using the aluminum nitride circuit board.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of an aluminum nitride sintered compact with few curvature is provided.

The production method of the present invention goes through the steps of raw material preparation, molding, lamination, degreasing, and firing, but the major features are in the lamination step, degreasing step, and firing step, and the raw material preparation step and molding step are conventional. It may be the same.

  As the aluminum nitride raw material powder used in the present invention, a powder produced by a known method such as a direct nitriding method or an alumina reduction method can be used.

  As sintering aids, rare earth elements such as Y, La, Ce, Ho, Yb, Gd, Nb, Sm, Dy, alkaline earth elements such as Mg, Ca, Sr and / or Al, Ga, In, etc. One kind or two or more kinds of oxides such as 3B group elements and fluorides are used.

As the binder, one or more of polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyvinyl butyral, nitrocellulose, polyvinyl alcohol, methyl cellulose and the like are used.
A solvent in which the binder is soluble is used so that the binder is more uniformly dispersed. An example of the solvent is water. By pre-treating the aluminum nitride powder with an organic compound having a hydrophobic group such as oleic acid, water-based molding becomes possible.

  For mixing the aluminum nitride powder, the sintering aid, the binder, and the like, for example, a known mixer such as a stirring mixer, a ball mill, or a rod mill can be used.

  The molded body is an aluminum nitride powder, a sintering aid, an organic binder, and if necessary, a plasticizer, a dispersant and the like are mixed, and molded into a desired shape by an extrusion molding method, a doctor blade method, a press molding method, It is manufactured by producing a sheet by the forming method and then cutting it into a desired shape. The thickness of the molded body is suitably 2 mm or less, preferably 1 mm or less. When the thickness of the molded body exceeds 2 mm, the density distribution in the molded body becomes non-uniform. Due to the non-uniformity, non-uniform thickness occurs after sintering, or cracks occur in the molded body during firing. May occur. Furthermore, a slurry made of boron nitride may be applied to one side or both sides to the extent that fusion between the molded bodies during degreasing and firing is prevented.

One of the features of the present invention is to provide a laminate in which the molded bodies are alternately laminated so that the front surfaces or the back surfaces thereof face each other. This is because in the drying process after extrusion molding, the molded body warps due to the difference in drying in the thickness direction of the molded body. When the front and back surfaces are laminated together and degreased and fired, the sintered body remains warped. As for the front and back of the molded body, warping of the molded body after drying has a convex surface on the top and a concave surface on the back.
The number of sheets to be stacked is not particularly limited, but it is desirable to stack 10 to 100 sheets.

Furthermore, the laminate of the molded body of the present application is housed in a container made of boron nitride, graphite, or aluminum nitride, placed on a boron nitride plate, and further placed on top of it. It is preferable that the mass of the weight applied per 1 cm ^{2 of the} laminate is in the range of A represented by the following formula.
10 <= A <= 100- (n-1) * a (The unit of mass is g.)
However, n is the number of stacked molded bodies, and a is the mass per 1 cm ² of the surface of the molded body after drying.
In the present invention, “mass per 1 cm ² of the surface of the molded body” means a mass obtained by cutting the molded body after drying into 1 cm ² .

A metal such as tungsten or molybdenum or an alloy thereof can be suitably used as a weight.

If the mass of the weight per 1 cm ^{2 of the} laminate is out of the range, the warp generated during firing may not be suppressed, or deformation or cracking may occur before or during firing. is there.

  After removing the binder (degreasing) by performing heat treatment at 300 to 700 ° C. for 0.5 to 10 hours in an air flow such as nitrogen gas or air, it is 1500 to 1900 ° C. in a non-oxidizing atmosphere such as nitrogen gas or argon gas. Bake in the temperature range. When the firing temperature is less than 1500 ° C., firing is insufficient, and it becomes difficult to produce an aluminum nitride sintered body. On the other hand, when the firing temperature exceeds 1900 ° C., the vapor pressure of aluminum nitride in the firing furnace becomes high, and aluminum nitride is scattered to make it difficult to make it dense.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.

4 parts by mass of yttrium oxide powder was added to 100 parts by mass of the aluminum nitride powder, and mixed for 1 hour by a ball mill. Furthermore, 6 parts by mass of a cellulose ether binder, 5 parts by mass of glycerin, and 10 parts by mass of ion-exchanged water were added to 100 parts by mass of the raw material powder, and mixed for 1 minute by a Henschel mixer. Next, a sheet (width 80 mm, thickness 0.8 mm) was formed with a screw-type molding machine, dried at 100 ° C. for 1 hour, and then cut into a 60 × 60 mm shape to form a molded body. The formed body was 0.19 g per 1 cm ² . Boron nitride powder slurry is applied to the sheet surface as a release agent, and 20 sheets are laminated alternately so that the front surfaces or back surfaces of the molded bodies face each other, and then left on the boron nitride setter. Then, a boron nitride plate material was placed, and a tungsten plate was placed on the uppermost surface so that the weight of the weight per 1 cm ^{2 of} the laminate was 86 g.

Thereafter, this laminate was degreased by heating at 570 ° C. for 5 hours in an air atmosphere. After degreasing, the aluminum nitride sintered body was obtained by heating at 1780 ° C. for 2 hours in a nitrogen atmosphere.

An aluminum plate was bonded to the obtained aluminum nitride substrate as a metal circuit and a metal heat sink by the following method to produce an aluminum nitride circuit substrate.
Ten sheets of aluminum alloy substrate each having a 60 mm × 50 mm × 0.2 mmt brazing alloy foil adhered thereto and a 60 mm × 50 mm × 0.2 mmt aluminum plate sandwiched between the both surfaces were laminated with a carbon spacer therebetween. After placing it on a carbon jig, it was held at 620 ° C. for 2 hours to join the aluminum nitride sintered body and the aluminum plate. In order to form a circuit pattern of a predetermined shape on one main surface of the joined body and a heat sink pattern on the other main surface, a UV curable resist ink is screen-printed and then irradiated with a UV lamp to form a resist film. Was cured. Next, the portion other than the resist-coated portion was etched with an aqueous sodium hydroxide solution, and then the resist was peeled off with an aqueous ammonium fluoride solution to produce an aluminum nitride circuit board.

<Materials used>
Aluminum nitride powder: It was produced by a direct nitriding method in which aluminum powder was sprayed from the top of a tubular electric furnace heated to 1850 ° C. or more to form aluminum vapor and reacted with nitrogen gas supplied into the tube to synthesize aluminum nitride. Average particle size 1.5μm, oxygen content 0.80% by mass
Yttrium oxide powder: manufactured by Shin-Etsu Chemical Co., Ltd., trade name “Yttriumu Oxide”
Binder: Shin-Etsu Chemical Co., Ltd., trade name “Metrozu”
Glycerin: Product name “Exepal” manufactured by Kao Corporation
Aluminum plate: Mitsubishi Aluminum Co., Ltd., trade name “1085”
Brazing alloy foil: manufactured by Toyo Seiki Co., Ltd., trade name “A2017R-H alloy foil”
UV curable resist ink: Product name “PER-27B-6” manufactured by Kyoyo Chemical Industry Co., Ltd.

An aluminum nitride sintered body was produced in the same manner as in Example 1 except that a tungsten plate having a weight of 76 g per 1 cm ^{2 of the} laminate was used.

An aluminum nitride sintered body was produced in the same manner as in Example 1 except that a tungsten plate having a weight of 36 g per 1 cm ^{2 of the} laminate was used.

An aluminum nitride sintered body was manufactured in the same manner as in Example 1 except that a tungsten plate having a weight of 20 g per 1 cm ^{2 of the} laminate was used.

An aluminum nitride sintered body was produced in the same manner as in Example 1 except that a tungsten plate having a weight of 10 g per 1 cm ^{2 of the} laminate was used.

Moreover, the aluminum nitride circuit board was produced similarly to Example 1 using the sintered compact produced in Examples 2-5.

(Comparative Examples 1-2)
The mass of the weigh according to 1cm per ^second laminate has a tungsten plate with a 5 g (Comparative Example 1) that the weigh of the mass according to 1cm per ^second laminate has a tungsten plate with a 100 g ( An aluminum nitride sintered body was produced in the same manner as in Example 1 except for Comparative Example 2).

(Comparative Example 3)
An aluminum nitride sintered body was produced in the same manner as in Example 5, except that the front and back surfaces of the molded body were laminated to form a laminated body.

(Comparative Example 4)
An aluminum nitride sintered body was produced in the same manner as in Example 3, except that the front and back surfaces of the molded body were laminated to form a laminated body.

(Comparative Example 5)
An aluminum nitride sintered body was manufactured in the same manner as in Example 1 except that the front and back surfaces of the molded body were laminated to form a laminated body.

Moreover, the aluminum nitride circuit board was produced similarly to Example 1 using the sintered compact produced by the comparative examples 1 and 3-5.

About the aluminum nitride sintered compact and aluminum nitride circuit board which were obtained by the Example and the comparative example, it measured about the item of following (1)-(3). The results are shown in Table 1.
(1) Warpage (sintered aluminum nitride)
Using a contact-type two-dimensional contour shape measuring machine (Tokyo Seimitsu Co., Ltd .; TOURCORED1600D), the amount of warpage per unit length (μm / cm) was calculated from the detected amount of warpage and the measured length. The warpage was measured at the center in the longitudinal direction of the aluminum nitride sintered body, and the maximum value was obtained in addition to the average value of 10 measurements.
(2) Three-point bending strength at room temperature (aluminum nitride sintered body)
A strength test body (40 × 20 × 1 mm) was ground from the aluminum nitride sintered body, and measured at a room temperature of 25 ° C. using a bending strength tester according to JIS R 1601.
(3) Thermal history impact test (aluminum nitride circuit board)
Thermal history with one cycle of exposure to -25 ° C. for 10 minutes, 25 ° C. for 10 minutes, 125 ° C. for 10 minutes, and 25 ° C. for 10 minutes is 3000 for the fabricated aluminum nitride circuit board excluding Comparative Example 2. Cycle giving test. Presence / absence of joint cracks is determined by conducting a thermal history impact test, symbol C when joining cracks occur in less than 2000 cycles, and joining symbols B and 3000 cycles when joining cracks occur in 2000-3000 cycles. The case where no crack occurred was designated as symbol A. The reliability assurance standards for circuit boards are symbols A and B.

表１からわかるように、本発明の製造方法によれば、反りが５μｍ／ｃｍ以下である窒化アルミニウム焼結体を、焼結体間のばらつきを少なくして（歩留まりよく）、生産性を高めて製造することができた。

As can be seen from Table 1, according to the production method of the present invention, the aluminum nitride sintered body having a warp of 5 μm / cm or less is reduced in variation between the sintered bodies (high yield), and the productivity is increased. Could be manufactured.

According to the present invention, an aluminum nitride sintered body having a warp of 5 μm / cm or less is provided. The circuit board produced using the aluminum nitride sintered body of the present invention is a material suitable as a circuit board used under severe usage conditions, for example, a ceramic substrate of a circuit board for a power module. In addition, according to the method for producing an aluminum nitride sintered body of the present invention, an aluminum nitride sintered body having the above characteristics can be produced with high yield without using spacers or squeezing powder or repeatedly performing a degreasing process. It can be manufactured at a higher level.

Claims (5)

A method for producing an aluminum nitride sintered body characterized in that the degreasing and firing processes are characterized by the following (1) and (2).
(1) Degreased and fired by placing a weight on the laminated body that is alternately laminated so that the front surfaces or back surfaces of the molded body face each other.
(2) The weight of the weight applied to the laminate is A represented by the following formula per 1 cm ² .
10 <= A <= 100- (n-1) * a (The unit of mass is g.)
However, n is the number of stacked molded bodies, and a is the mass per 1 cm ² of the surface of the molded body after drying. 2. The method for producing an aluminum nitride sintered body according to claim 1, wherein the weight is made of tungsten, molybdenum, or an alloy containing either tungsten or molybdenum. The method for producing an aluminum nitride sintered body according to claim 1 or 2, wherein the warp of the sintered body is 5 µm / cm or less.   The aluminum nitride circuit board using the aluminum nitride sintered compact obtained by the manufacturing method as described in any one of Claims 1-3. A module using the aluminum nitride circuit board according to claim 4.