JP2982447B2 - Method for manufacturing mullite ceramic substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a mullite ceramic substrate which can be sintered at a low temperature without being calcined. More specifically, the present invention relates to a method for manufacturing a mullite ceramic substrate suitable for a multilayer wiring board for precision electronic products.

[0002]

2. Description of the Related Art Conventionally, this type of mullite ceramic substrate for multilayer wiring is manufactured by a powder method. In this manufacturing method, first, alumina (Al ₂ O ₃ ) powder and silica (Si
O ₂ ) A predetermined amount of powder is mixed, calcined at a high temperature, and then pulverized to prepare a mullite powder. Next, an organic binder is blended with the mullite powder to form a slurry, and the slurry is dried to form a green sheet. Next, a paste of a refractory metal such as tungsten (W) or molybdenum (Mo) is printed on the green sheet in a predetermined pattern. A plurality of the printed green sheets thus obtained are prepared, an adhesive is applied to both sides or one side thereof, laminated, and fired at a high temperature of 1500 ° C. or more in a reducing atmosphere to form a multilayer wiring board. I have.

[0003]

It is known that mullite has a low dielectric constant and a thermal expansion coefficient close to that of silicon, and is a promising material for an LSI chip mounting substrate. However, the firing temperature required to produce mullite is 1500
Because of the high temperature of ℃, the ceramic green sheet and the printed conductor formed by printing on the surface of this green sheet need to be fired at the same time to produce a multilayer wiring board. Metals had to be used, and firing in a reducing atmosphere was necessary. In the case of producing a mullite ceramic green sheet, alumina powder (Al ₂ O ₃ ) and silica (SiO ₂ ), which are components of mullite ceramics, are ground and mixed in a ball mill in advance, and calcined to prepare mullite powder. And
Although this is used as a starting material, there is a problem that a large amount of heat energy is consumed in this calcining step. An object of the present invention is to perform high-temperature firing in a reducing atmosphere,
Another object of the present invention is to provide a method for producing a mullite-based ceramic substrate capable of producing mullite at a low temperature without performing calcination.

[0004]

SUMMARY OF THE INVENTION A mullite-based cella according to the present invention.
The production method of the mix substrate is an alumina sol and a silica sol.
B by firing_TwoO_ThreeAnd the first compound capable of producing
Generate MgO by baking with a second compound capable of generating CaO
A ceramic slurry is obtained by mixing with a third compound which can be formed.
Preparation process and film drying of this ceramic slurry
To form a green sheet by
Baking the glass. Its characteristic structure
The result is that the alumina sol is converted to an aluminum alkoxide.
After hydrolysis, the hydrolysis product is prepared by peptization,
After the silica sol hydrolyzes the silicon alkoxide,
Prepared by peptizing the hydrolysis product of
Silica particles are coated with boehmite, and the ceramics
Rally is 100% by weight of its total inorganic components.
Al alumina sol_TwoO_Three50 to 70% by weight before conversion
The silica sol is converted to SiO_Two20-30% by weight in conversion
The first compound is B_TwoO _Three1 to 15% by weight in conversion to the second
1 to 20% by weight of the compound in terms of CaO and the third compound
1 to 7% by weight in terms of MgO, and the green
The baking of the sheet is performed at a temperature of 800 to 1200 ° C.
And there.

Hereinafter, the present invention will be described in detail. In the present invention, the alumina sol constituting the ceramic slurry is prepared by hydrolyzing an aluminum alkoxide and then peptizing the hydrolysis product. As the aluminum alkoxide, aluminum isopropoxide [A
1 (OC ₃ H ₇ )]. The silica sol constituting the ceramic slurry is coated with boehmite (AlOOH) on the silica particles of the dispersed phase. The silica sol is prepared by hydrolyzing a silicon alkoxide and then hydrolyzing the hydrolyzate by adding aluminum chloride or the like to a silica particle dispersion obtained by peptizing the hydrolysis product. Examples of the silicon alkoxide include ethyl silicate (tetraethoxysilane) [Si (OC ₂ H ₅ ) ₄ ]. Examples of the first compound that can generate B ₂ O ₃ by firing include boric acid (H ₃ BO ₃ ). Ca by firing
Examples of the second compound that can generate O include calcium acetate and the like. Examples of the third compound that can generate MgO by firing include magnesium acetate.

The above-mentioned alumina sol, silica sol,
Mixing the compound, the second compound, the third compound and preferably a plasticizer such as glycerin and heating if necessary,
Preferably, after adding a binder such as polyvinyl alcohol, the mixture is cooled to prepare a ceramic slurry. When the total inorganic component of this slurry is 100% by weight, alumina sol is converted to 5% in terms of Al ₂ O ₃ in order to obtain a mullite composition.
And 0-70% by weight, 20 to a silica sol in terms of SiO ₂
Mix 30% by weight. The mullite - to the glass composition, 1 to 15 wt% further a first compound terms _of B ₂ O ₃
Mix. The mixing amount is determined within the above range depending on the use of the finally obtained ceramic substrate. The second and third compounds as sintering aids are added in an amount of 1 to 20% by weight and 1 to 7% by weight, respectively, so as not to impair the properties of the substrate.
The ceramic slurry is formed into a film and dried to form a green sheet. As a molding method, a doctor blade method is preferable. When a multilayer wiring board is not manufactured, the green sheet is fired at a temperature of 800 to 1200 ° C. to obtain a desired mullite ceramic substrate. When manufacturing a multilayer wiring board, a paste of a printed metal is printed on a green sheet in a predetermined pattern, and a plurality of obtained printed green sheets are prepared. Next, after applying an adhesive to both sides or one side of these printed green sheets, laminating and, if necessary, heating and pressurizing, followed by 800 to 120
It is fired at a temperature of 0 ° C. to obtain a multilayer wiring board. Firing temperature 8
When the temperature is lower than 00 ° C., the obtained ceramic substrate is not dense, and when the temperature exceeds 1200 ° C., Ag-Pd, A
Printing with a printed metal paste made of a good conductor having a melting point of about 1000 ° C. such as g becomes impossible, and a large amount of heat energy is consumed.

[0007]

The ceramic slurry of the present invention is mostly alumina sol and silica sol, each of which is composed of fine colloid particles obtained by hydrolysis of alkoxide. These colloid particles are composed of other components of the ceramic slurry. And mixed uniformly. A boehmite layer is formed on the surface of the silica particles of the silica sol. Therefore, when firing a green sheet made from this slurry, alumina particles and silica particles easily sinter,
Mullite is produced at relatively low temperatures, such as 800-1200 ° C.

[0008]

As described above, according to the conventional method for producing a mullite-based ceramic substrate by the powder method, after the raw material powder is calcined to prepare the mullite powder, a green sheet is produced, and the green sheet is produced in a reducing atmosphere. It was necessary to fire at a high temperature of 1500 ° C. or more. On the other hand, according to the present invention, mullite can be generated by low-temperature firing without performing high-temperature firing in a reducing atmosphere and without performing calcination. Therefore, the manufacturing process is simplified, and heat energy can be saved. In addition, since low-temperature baking at 800 to 1200 ° C. can be performed, a melting point of 10
It is possible to print a paste of a good conductor such as Ag-Pd, Ag or the like at about 00 ° C. on a green sheet.

[0009]

Next, embodiments of the present invention will be described. <Preparation of ceramic slurry> Aluminum isopropoxide [Al (OC ₃ H ₇ ) ₃ ] was added to water at a ratio of aluminum alkoxide / water = 1 mol / 100 mol to carry out hydrolysis, and further, hydrochloric acid / aluminum isoform was added. Hydrochloric acid is added at a ratio of propoxide = 0.33 mol / 1 mol to peptize the hydrolysis product, and boehmite sol (AlOOH)
Was prepared. Ethyl silicate [Si (OC ₂
H ₅ ) ₄ ] was slowly added, and hydrolysis was carried out for 24 hours. Hydrochloric acid was further added at a ratio of hydrochloric acid / ethyl silicate = 0.33 mol / 1 mol to obtain a silica particle dispersion. Further, 0.03 mol of aluminum chloride was gradually added to the silica particle dispersion and hydrolyzed at 80 ° C. to prepare a silica sol having a boehmite layer formed on the surface of SiO ₂ colloidal particles. The alumina sol and the silica sol thus prepared were mixed at a ratio of Al ₂ O ₃ / SiO ₂ = 65/25 (weight ratio), and (1) glycerin was added as a plasticizer to 8% by weight of the total inorganic component, (2) 5% by weight of boric acid as a first compound capable of generating B ₂ O ₃ by firing, (3) 2.5% by weight of magnesium acetate as a second compound capable of generating MgO by firing, and (4) CaO by firing. 2.5% by weight of calcium acetate is sequentially added as a third compound capable of forming a polymer, and the temperature is increased to 75 ° C. by heating, and after adding polyvinyl alcohol as a binder at this temperature, the mixture is naturally cooled to prepare a ceramic slurry. did.

<Preparation of Green Sheet> This ceramic slurry was formed into a film having a thickness of 3 mm by a doctor blade method, and was naturally dried at a belt speed of 0.07 m / min to obtain a green sheet.

<Sintering of Green Sheet> This green sheet is placed in an electric furnace under atmospheric pressure, up to 250 ° C. and 0.5 ° C.
/ Min., Heated at 250 ° C. for 1 hour, and calcined at 1000 ° C. for 4 hours to obtain a desired mullite ceramic substrate. This mullite ceramic substrate exhibited a low dielectric constant and a thermal expansion coefficient close to that of silicon, and was found to be useful as a substrate for mounting an LSI chip.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jiro Oishi 2270 Yokoze, Yokoze-cho, Chichibu-gun, Saitama Mitsubishi Materials Corporation Ceramics Research Laboratory (56) References JP-A-4-367557 (JP, A) 3-177352 (JP, A) JP-A-2-102169 (JP, A) JP-A-58-153604 (JP, A) JP-A-57-88075 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/10 C04B 35/18 H05K 1/03

Claims (4)

(57) [Claims] 1. A ceramic obtained by mixing an alumina sol, a silica sol, a first compound capable of generating B ₂ O ₃ by firing, a second compound capable of generating CaO by firing, and a third compound capable of generating MgO by firing. A step of preparing a rally, a step of forming a green sheet by film-forming and drying the ceramic slurry, and a step of firing the green sheet, wherein the alumina sol is an aluminum alkoxide. Is prepared by peptizing the hydrolysis product, and the silica sol is prepared by peptizing the hydrolysis product after hydrolyzing the silicon alkoxide, and the silica particles of the dispersed phase are boehmite. The ceramic slurry is coated with the alumina when the total inorganic component is 100% by weight. Le in terms of Al ₂ O ₃ 50
７０70% by weight and the silica sol in an amount of 20 ₂
30% by weight, the first compound is 1 to 15% by weight in terms of B ₂ O ₃ , the second compound is 1 to 20% by weight in terms of CaO, and the third compound is 1 to 7% by weight in terms of MgO. Including
And sintering the green sheet at a temperature of 800 to 1200 ° C. 2. The method for manufacturing a mullite ceramic substrate according to claim 1, wherein the first compound is boric acid, the second compound is calcium acetate, and the third compound is magnesium acetate. 3. The method according to claim 1, wherein the ceramic slurry further contains a plasticizer and a binder. 4. The method for manufacturing a mullite ceramic substrate according to claim 1, wherein the aluminum alkoxide is aluminum isopropoxide and the silicon alkoxide is tetraethoxysilane.