JP6991917B2 - Aluminum nitride green sheet - Google Patents

Description

The present invention relates to a novel aluminum nitride green sheet. More specifically, the present invention provides an aluminum nitride green sheet having excellent storage stability, in which the flexibility does not easily decrease even when the aluminum nitride green sheet is stored for a long period of time.

Aluminum nitride substrates are used for IGBT substrates, LED heat dissipation substrates, etc. due to their characteristics, and the demand for them has been increasing in recent years.

The aluminum nitride sintered body to be the aluminum nitride substrate is generally manufactured by the following method. First, aluminum nitride powder, a thermoplastic resin, a sintering aid, a plasticizer, a solvent, etc. are mixed, and the obtained molding composition is formed into a sheet, and the solvent is dried and removed to remove the aluminum nitride green sheet. To get. Next, a mold is placed on the aluminum nitride green sheet, punched to a required size, heated to 450 to 650 ° C. in an air atmosphere to remove organic components such as a thermoplastic resin, and in a non-oxidizing atmosphere such as nitrogen. Hold at 1600 to 1900 ° C. for 0.5 to 10 hours to produce an aluminum nitride sintered body (see Patent Document 1).

Since stress such as tension and bending is applied to the aluminum nitride green sheet in the manufacturing process, a plasticizer is used to impart flexibility to the aluminum nitride sheet so as to withstand such stress. ing. However, the present inventors have confirmed that when the aluminum nitride green sheet is stored in the state of the green sheet, its flexibility is gradually lost. When such an aluminum nitride green sheet is punched out, burrs and chips are generated, and the fragments adhere to the aluminum nitride green sheet, so that the obtained aluminum nitride sintered body becomes a defective product due to poor foreign matter adhesion. In some cases.

Japanese Unexamined Patent Publication No. 2014-066993

Therefore, an object of the present invention is to provide an aluminum nitride green sheet having excellent storage stability, in which the flexibility does not easily decrease even if the aluminum nitride green sheet is stored for a long period of time.

As a result of repeated studies to solve the above problems, the present inventors have obtained the finding that polyvinyl butyral resin should be used as a thermoplastic resin because the aluminum nitride green sheet is excellent in moldability and flexibility. rice field. Then, the present inventors further developed the above findings and found that the use of a specific plasticizer for the polyvinyl butyral resin can effectively suppress the decrease in flexibility of the aluminum nitride green sheet. The present invention has been completed by a combination of these.

That is, in the present invention, in an aluminum nitride green sheet containing an aluminum nitride powder, a sintering aid, a thermoplastic resin, and a plasticizer, the thermoplastic resin is a polyvinyl butyral resin, and the plasticizer has a molecular weight of 300 or more. And an ester of an aliphatic polyvalent carboxylic acid and an aliphatic monoalcohol or an ester of an aliphatic polyhydric alcohol and an aliphatic monocarboxylic acid, and having two or more ester bonds. It is an aluminum nitride green sheet characterized by.

The aluminum nitride green sheet of the present invention has good flexibility even after being stored for a long period of time, and further, the aluminum nitride green sheet stored for a long period of time is less likely to cause burrs and chips and has good punching properties. Have.

Further, the aluminum nitride green sheet of the present invention can be prepared by taking advantage of the excellent storage stability, for example, by winding it into a roll, and as a result, considering the balance with the next process. It has high industrial utility value because it enables efficient work.

6 is an image obtained by observing a videomicroscope about a cross section of the aluminum nitride green sheet obtained in Example 1 when punched out. It is an image obtained by videomicroscope observation about the cross section of the sheet when the aluminum nitride green sheet obtained in Comparative Example 1 was punched out.

(Aluminum Nitride Green Sheet of the Present Invention)
The aluminum nitride green sheet of the present invention is composed of an aluminum nitride powder, a sintering aid, a thermoplastic resin, and a plasticizer.

<Composition>
[Aluminum nitride powder]
As the aluminum nitride powder which is a component of the aluminum nitride green sheet of the present invention, known ones can be used without any limitation. In general, in order to obtain an aluminum nitride sintered body having excellent thermal conductivity, it is preferable that the oxygen content and cation impurities are low. The aluminum nitride in the present invention is a 1: 1 compound of aluminum and nitrogen, and all other compounds are treated as impurities. However, the surface of aluminum nitride is inevitably oxidized in the air, and the Al—N bond is replaced with the Al—O bond, but this bonded Al is not regarded as a cationic impurity. Therefore, metallic aluminum without Al—N and Al—O bonds is a cationic impurity.

Further, the particles of the aluminum nitride powder used in the present invention are preferably those having a small particle size. For example, it is preferable that the average particle size (D50) is 5 μm or less, more preferably 3 μm or less by a laser diffraction method using a particle size distribution measuring device, for example, MICROTRACK-HRA (trade name) manufactured by Nikkiso Co., Ltd.

[Sintering aid]
The sintering aid used in the aluminum nitride green sheet of the present invention promotes the sintering of aluminum nitride powder, and known ones are used without particular limitation, specifically, alkali metal and alkaline soil. Oxides of similar metals or rare earth elements can be used. Examples of the alkali metal include lithium. Examples of the alkaline earth metal element include beryllium, magnesium, calcium, strontium, barium and the like. Examples of the rare earth element include ytterbium, lanthanum, cerium, placeodim, neodym, promethium, samarium, europium, gadolinium, terbium, dysprosium, formium, erbium, thulium, ytterbium, lutetium and the like. Of these, oxides of calcium, strontium, barium, yttrium, lanthanum, cerium, and neodymium are preferably used. These compounds may be used alone or in combination of two or more.

The amount of the sintering aid contained in the aluminum nitride green sheet of the present invention is preferably 0.05 to 10 parts by mass in terms of oxide with respect to 100 parts by mass of the aluminum nitride powder, and is preferably 1 to 7 parts by mass. Is more preferable, and 3 to 6 parts by mass is particularly preferable.

[Thermoplastic resin]
In the present invention, the thermoplastic resin is used as a binder for the aluminum nitride powder, and since the aluminum nitride green sheet is excellent in moldability and flexibility, it is a feature of the present invention to use a polyvinyl butyral resin. It is one.

The molecular weight of the polyvinyl butyral resin used in the present invention is not particularly limited, but generally 15,000 to 150,000, preferably 30,000 to 100,000, an aluminum nitride green sheet having excellent moldability and flexibility can be obtained. Suitable for.

As the polyvinyl butyral resin used in the present invention, it may be appropriately produced, it may be a commercially available product, or a material known per se can be used. As commercially available products, for example, Mobile (Mobile B 14S, Mobile B 16H, Mobile B 20H, Mobile B 30T, Mobile B 30H, Mobile B 30HH, Mobile B 45H, Mobile B 60T, Mobile B 60T, Mow B 75H, Mobile BA 20S) (above, product name manufactured by Kuraray Co., Ltd.), Eslek B (BL-1, BL-1H, BL-2, BL-2H, BL-5, BL-10, BL-S, BX -1, BX-5, BX-L, BM-1, BM-2, BM-5, BM-S, BH-3, BH-6, BH-S (above, Sekisui Chemical Co., Ltd. product name) ) And the like, and examples thereof include polyvinyl butyral resin.

The amount of the thermoplastic resin contained in the aluminum nitride green sheet of the present invention is preferably 3 to 20 parts by mass, preferably 5 to 10 parts by mass with respect to 100 parts by mass of the aluminum nitride powder. By setting the amount of the thermoplastic resin in the above range, the aluminum nitride powder, the sintering aid, and the plasticizer can be uniformly dispersed in the thermoplastic resin.

[Plasticizer]
In the present invention, the plasticizer plasticizes the thermoplastic resin and imparts flexibility, and the greatest feature of the present invention is a specific plasticizer, specifically, 300 or more, with respect to the polyvinyl butyral resin. An ester of an aliphatic polyvalent carboxylic acid and an aliphatic monoalcohol or an ester of an aliphatic polyvalent alcohol and an aliphatic monocarboxylic acid having a molecular weight of 2 or more. It is in the point that it was used as a plasticizer. Thereby, the aluminum nitride green sheet of the present invention can have good flexibility even after long-term storage. The reason why such an effect was obtained is not necessarily clear, but as a result of the combination of the thermoplastic resin and the plasticizer effectively suppressing the volatility of the plasticizer, the plasticizer is an aluminum nitride green sheet. The present inventors believe that it may exist in the drug for a long period of time.

Examples of the aliphatic polyvalent carboxylic acid include aliphatic divalent carboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelli acid, suberic acid, azelaic acid and sebacic acid, propantricarboxylic acid and butane. Examples thereof include aliphatic trivalent carboxylic acids such as tricarboxylic acid and pentantricarboxylic acid.

Examples of the aliphatic monoalcohol include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) ethanol, and 2 -(2-Butoxyethoxy) ethanol and the like can be mentioned.

Examples of the aliphatic polyhydric alcohol include aliphatic dihydric alcohols such as ethylene glycol, propylene glycol, butanediol, pentandiol and hexanediol, and aliphatic trihydric alcohols such as glycerin and butanetriol.

Examples of the aliphatic monocarboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, behenic acid, and coconut fatty acid.

Particularly preferred plasticizers in the present invention include bis [2- (2-butoxyethoxy) ethyl] adipate and glycerin diacet monolaurate.

The plasticizer may be used alone or in combination of two or more.

The amount of the plasticizer contained in the aluminum nitride green sheet of the present invention is preferably 20 to 60 parts by mass, more preferably 30 to 50 parts by mass, and 35 parts by mass with respect to 100 parts by mass of the thermoplastic resin. It is particularly preferable that the amount is up to 40 parts by mass. By setting the amount of the plasticizer in the above range, the effect of the plasticizer can be sufficiently obtained.

<Physical characteristics>
In the present invention, the thickness of the aluminum nitride green sheet cannot be unconditionally determined because it depends on the use of the aluminum nitride sintered body, but it is preferably 0.1 to 5 mm, preferably 0.2 to 1.5 mm.

In the present invention, the flexibility of the aluminum nitride green sheet is evaluated by the values of tensile strength and elongation. The aluminum nitride green sheet of the present invention preferably has a tensile strength of 1.2 to 2.0 MPa and an elongation of 30 to 50%, more preferably a tensile strength of 1.5 to 50%. It is preferably 1.8 MPa and its elongation is preferably 32 to 48%. Since the tensile strength and elongation values are within the above ranges immediately after the aluminum nitride green sheet is manufactured and after long-term storage, the aluminum nitride green sheet is cracked even when stress such as tension or bending is applied. hard. The tensile strength and elongation can be obtained by a tensile test using a dumbbell test piece described later.

The storage conditions for the aluminum nitride green sheet of the present invention are not particularly limited, but it is preferable to store the aluminum nitride green sheet in the range of 0 to 25 ° C. Within this temperature range, even if it is stored for 100 days or more, the decrease in flexibility can be suppressed.

(Manufacturing Method of Aluminum Nitride Green Sheet of the Present Invention)
In the present invention, the aluminum nitride green sheet is specifically manufactured through the following steps. That is, a step of kneading aluminum nitride powder, a sintering aid, a thermoplastic resin, a plasticizing agent, etc. to obtain a molding composition (kneading step), and the obtained molding composition is plate-shaped or formed by a doctor blade method or the like. It is manufactured through a step of molding into a sheet (molding step) and a step of drying and removing the solvent to obtain an aluminum nitride green sheet (drying step).

Hereinafter, each process will be described step by step.

<Kneading process>
In the kneading step, the amount of each component to be kneaded may be appropriately determined so that the obtained aluminum nitride green sheet has the above composition. Further, a dispersant or a solvent may be used as needed.

Further, the method of kneading each component can be mixed using a known kneading device. Examples of the kneading device include known kneading devices such as a pressure kneader, a Banbury mixer, a disc kneader, and a single-screw or twin-screw extruder. In addition, in order to sufficiently knead and disperse each component, it is generally kneaded in two portions. The first time, the aluminum nitride powder, the sintering aid, the dispersant and the solvent are added and kneaded, and the second time, the thermoplastic resin, the plasticizer and the solvent are added to the first mixture. Is kneaded. In this way, a molding composition is produced.

The dispersant is preferably used to enhance the dispersibility of the aluminum nitride powder, the sintering aid and the like in the molding composition, and in general, a surfactant is preferably used.

As the surfactant, known ones are used without any limitation. Specific examples of surfactants that can be suitably used in the present invention are carboxylated trioxyethylene tridecyl ether, diglycerin monooleate, diglycerin monostearate, carboxylated heptaoxyethylene tridecyl ether, and tetraglycerin mono. Examples thereof include oleate, hexaglycerin monooleate, sorbitan laurate, sorbitan oleate, sorbitan triolate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan triolate. In addition, you may use these surfactants in mixture of 2 or more types.

The amount of the dispersant is selected from the range of 1 to 5 parts by weight and used with respect to a total of 100 parts by mass, which is the sum of the amount of the aluminum nitride powder and the amount of the sintering aid.

Further, the solvent is preferably used to improve the kneadability and moldability of the molding composition, and generally, an organic solvent is preferably used.

Examples of those preferably used as the organic solvent are ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohols such as ethanol, propanol and butanol; aromatic hydrocarbons such as benzene, toluene and xylene; or Examples thereof include one or a mixture of two or more halogenated hydrocarbons such as trichloroethylene, tetrachloroethylene and bromchloromethane.

The amount of the solvent ranges from 50 to 150 parts by mass with respect to a total of 100 parts by mass, which is the sum of the amount of the aluminum nitride powder, the amount of the sintering aid, the amount of the thermoplastic resin, and the amount of the plasticizer. Selected and used.

If the viscosity of the molding composition obtained by using the solvent is low, an operation of removing a part of the solvent in the molding composition is performed to adjust the viscosity to be suitable for the next step. May be good. Examples of the above operation include an operation of stirring in a vacuum atmosphere to distill off the solvent.

<Molding process>
In the molding step, the method for molding the molding composition into a sheet is not particularly limited, and known methods and devices can be used. For example, it is molded into a sheet shape using a sheet forming machine such as the doctor blade method.

<Drying process>
In the drying step, the method for drying the molded product formed into a sheet is not particularly limited, and known methods and devices can be used. Generally, the aluminum nitride green sheet can be obtained by drying in an air or nitrogen atmosphere at the boiling point temperature of the solvent and removing the solvent.

The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement and evaluation results described in the examples were obtained by the following methods.

<Tensile strength and elongation of aluminum nitride green sheet>
The tensile strength and elongation of the aluminum nitride green sheet of the present invention were evaluated in accordance with JIS K 7161.

Specifically, a test piece is punched along the sheet forming direction of the aluminum nitride green sheet using a sheet punching dumbbell (JIS standard product ASTM D1822 L type), and the test piece is used as a universal material testing machine (stro). Graph M2 (manufactured by Toyo Seiki Seisakusho) was used to measure the measured load and elongation. The measurement conditions at this time were load cell capacity; 100 kgf, crosshead speed; 10 mm / min, load selector; x50, chart speed; 20 mm / min. Then, the value of the tensile strength was calculated by dividing the value of the measured load by the value of the cross-sectional area (width × thickness) of the test piece. The values of tensile strength and elongation were taken as the average value of the measured values of five test pieces.

<Punching property of aluminum nitride green sheet>
The punching property of the aluminum nitride green sheet was evaluated using a punching machine (SSP-1000, manufactured by Japan Automatic Machine) at a punching pressure of 98 kN, a press lowering speed of 80 mm / sec, and a sheet feeding speed of 280 mm / sec. Under the conditions, the mold of the 2-inch substrate was pressed, the aluminum nitride green sheet was punched out, and the cross section was observed with a video microscope. The evaluation criteria are shown below.

Evaluation Criteria ◯: The cross section is generally smooth Δ: Unevenness is seen in the upper part in the direction in which the blade is inserted ×: The cross section is generally uneven. In addition, the following raw materials were used in the examples.

[Aluminum nitride powder]
・ H-No. Made by Tokuyama Corporation. 1 grade, particle diameter (D50) 1.6 μm
[Thermoplastic resin]
-Polyvinyl butyral resin: Sekisui Chemical Co., Ltd. Eslek B BM-S
[Sintering aid]
・ Yttrium oxide: Made by Nippon Yttrium Co., Ltd. [Plasticizer]
-Bis [2- (2-butoxyethoxy) ethyl] adipate: BXA-N manufactured by Daihachi Chemical Industry Co., Ltd.
・ Glycerin diacet monolaurate :: Riken Vitamin Co., Ltd. Rikemar PL-012
・ Dibutyl phthalate: DBP manufactured by Daihachi Chemical Industry Co., Ltd.
・ Dibutyl phthalate: DBA manufactured by Daihachi Chemical Industry Co., Ltd.
[Dispersant]
・ Sorbitan triorate: Riken Vitamin Co., Ltd. Rikemar OR-85
Example 1
Aluminum nitride powder 2000 g, yttrium oxide 100 g, sorbitan triolate 50 g, toluene 400 g, ethanol 234 g, and butanol 34 g, using a 10 L rotary ball mill, mill ball (alumina φ10 mm) 9.3 kg, 25 ° C., mill rotation speed 38 ± 1 rpm It was kneaded for 14 hours under the conditions of. Next, 160 g of polyvinyl butyral resin, 60 g of bis [2- (2-butoxyethoxy) ethyl] adipate, 558 g of toluene, 326 g of ethanol, and 48 g of butanol were added to the obtained kneaded product, and the mixture was kneaded under the above conditions for 18 hours. Further, the obtained molding composition was subjected to the above-mentioned conditions under a vacuum, a stirring speed of 50 rpm, and a heater setting of 23 ° C. using a stirring defoaming viscosity adjusting device (KD-15 type, manufactured by Daiwa Seiki Co., Ltd.). The viscosity was adjusted by removing the solvent until the viscosity of the molding composition became 21,000 to 26,000 mPa · s. Then, the viscosity-adjusted molding composition was molded into a sheet by a doctor blade method using a medium-sized sheet molding machine (manufactured by Hirano Metal Co., Ltd.). The sheet forming conditions at this time were a blade gap of 2.10 mm, a coating speed of 0.27 m / min, and a forming width of 280 mm. Next, the molded sheet was dried in the medium-sized sheet molding machine with a circulation fan; 1200 rpm, temperature and time; at a temperature of 78 ° C. for 0.5 h, and further dried at a temperature of 118 ° C. for 0.3 h, and aluminum nitride green. A sheet was prepared.

The tensile strength, elongation, and punching property of the obtained aluminum nitride green sheet were evaluated immediately after the aluminum nitride green sheet was produced and after the aluminum nitride green sheet was stored in air at 25 ° C. for 100 days. Is shown in Table 1.

The obtained aluminum nitride green sheet had excellent flexibility immediately after production and after storage for 100 days. Further, the cross section of the aluminum nitride green sheet when punched out was smooth as a whole, and good punching property was recognized.

Example 2
Table 1 shows the results of evaluation of the tensile strength, elongation, and punching property of the obtained aluminum nitride green sheet using the plasticizer shown in Table 1 and other than that in the same manner as in Example 1.

The obtained aluminum nitride green sheet had excellent flexibility immediately after production and after storage for 100 days. Further, the cross section of the aluminum nitride green sheet when punched out was smooth as a whole, and good punching property was recognized.

Comparative Examples 1 and 2
Table 1 shows the results of evaluation of the tensile strength and elongation of the obtained aluminum nitride green sheet using the plasticizer shown in Table 1 and other than that in the same manner as in Example 1.

The flexibility of the obtained aluminum nitride green sheet was good immediately after production, but after storage for 100 days, the flexibility was greatly reduced and it was difficult to handle. Further, regarding the cross section of the sheet when the aluminum nitride green sheet was punched out, unevenness was generated in the upper part in the direction in which the blade was inserted or in the entire cross section.

Claims (1)

In an aluminum nitride green sheet containing an aluminum nitride powder, a sintering aid, a thermoplastic resin, and a plasticizer.
The thermoplastic resin is polyvinyl butyral resin,
An aluminum nitride green sheet, wherein the plasticizer is bis [2- (2-butoxyethoxy) ethyl] adipate or glycerin diacet monolaurate .

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