JP2020111797A - Method for manufacturing composite body of ceramic and conductor - Google Patents

Abstract

To provide a method for manufacturing a composite body of a ceramic and a conductor having three following characteristics: (1) excellent in conductivity of a conductor; (2) contributing to productivity improvement of a composite body of a ceramic and a conductor; and (3) suitable for manufacturing a composite body excellent in adhesion between the ceramic and the conductor.SOLUTION: A method for manufacturing a composite body of a ceramic and a conductor includes: a step of coating a conductive composition containing first copper powder having a BET specific surface area of 1.0-10.0 m2/g and a compacted bulk density of 3.0 g/cm3 or less, second copper powder having a BET specific surface area smaller than that of the first copper powder, a binder resin and a dispersion medium onto a ceramic substrate; and a step of firing the ceramic substrate and the coated conductive composition in a non-oxidation atmosphere at a steam partial pressure of 0.02-0.15 atm and at a peak temperature of 400-700°C.SELECTED DRAWING: None

Description

The present disclosure relates to a method of making a composite of ceramic and conductor.

Conventionally, metal particles such as Ag, Cu, Ni or Pt and glass powder having a low softening point have been used as a conductive material for producing a composite of a ceramic and a conductor when forming an electrode or a circuit on the surface of a ceramic substrate. A conductive composition in which and are mixed in an organic vehicle is generally known. As a method for manufacturing a composite of a ceramic and a conductor, there is known a method in which a green sheet is baked to manufacture a ceramic substrate, and then a conductive composition is applied on the ceramic substrate and baked (post-fire method). ..

Such a conductive composition is required to have excellent adhesion to a ceramic substrate after firing. Therefore, for example, Japanese Patent Application Laid-Open No. 2006-73836 (Patent Document 1) discloses a conductive composition for a ceramic electronic component, which contains a rosin or terpene oil-polymerized resin taken from pine resin in order to improve adhesion with a ceramic body. Is disclosed.

Further, Japanese Patent Laid-Open No. 2004-311605 (Patent Document 2) discloses an external electrode of a multilayer ceramic capacitor for the purpose of improving the denseness of the external electrode and improving the electrical bondability between the external electrode and the internal electrode. A technique is disclosed in which steam is introduced into the atmosphere after the peak firing temperature is reached.

JP, 2006-73836, A JP, 2004-311605, A

When industrially producing a composite of a ceramic and a conductor, high adhesion between them is of course an important characteristic, but not only that, but also high electrical conductivity of the conductor and high productivity. It is desirable to combine them.

Therefore, an object of the present disclosure in one aspect is to provide a method of manufacturing a composite of a ceramic and a conductor, which has the following three characteristics.
(1) The conductor has excellent conductivity.
(2) Contributes to improvement in productivity of a composite of ceramic and conductor.
(3) It is suitable for producing a composite having excellent adhesion between the ceramic and the conductor.

In order to solve the above problems, the present inventor first produced a composite of a ceramic and a conductor by using a post-fire method in which a conductive composition containing copper powder is applied onto a ceramic substrate and fired. We examined the improvement of sex. When the conductive composition is sintered at a high temperature, excessive stress acts on the ceramic substrate and the ceramic substrate is deformed. Therefore, in the post-fire method, it is preferable to sinter the conductive composition at a low temperature. Thereby, the deformation of the ceramic substrate can be suppressed. In addition, if the firing peak temperature is low, it is possible to reduce the difference between the shrinkage amount of ceramics and the shrinkage amount of copper that occur during the cooling process after firing. In other words, peeling (delamination) between copper and ceramic can be suppressed, and the adhesion between them can be improved. On the other hand, if the firing temperature is low, firing will be insufficient, and thus there will be a problem in that the adhesion between the ceramic and the conductor tends to deteriorate.

Therefore, the present inventor diligently studied an effective method for sufficiently sintering the conductive composition even at a low temperature, and by performing the firing in a non-oxidizing atmosphere containing water vapor, the firing peak temperature was lowered. I found that I can do it. It is presumed that this is due to the large penetration effect of the heated steam into the material to be fired. Further, the present inventor has stated that “a first copper powder having a BET specific surface area of 1.0 to 10.0 m ² /g and a compacted bulk density of 3.0 g/cm ³ or less; It was found that a composite having excellent adhesion between a conductor and a ceramic can be produced even at a low firing temperature by using a conductive composition containing a second copper powder having a BET specific surface area smaller than that of copper powder.

The present invention has been completed based on the above findings and is exemplified below.
(1)
A first copper powder having a BET specific surface area of 1.0 to 10.0 m ² /g and a compacted bulk density of 3.0 g/cm ³ or less, and a BET specific surface area smaller than that of the first copper powder. Applying a conductive composition containing a second copper powder, a binder resin, and a dispersion medium to the ceramic substrate,
Firing the ceramic substrate and the applied conductive composition in a non-oxidizing atmosphere having a water vapor partial pressure of 0.02 to 0.15 atm with a peak temperature of 400 to 700° C.;
A method of manufacturing a composite of a ceramic and a conductor.
(2)
The manufacturing method according to (1), wherein the conductive composition contains glass frit.
(3)
The manufacturing method according to (1) or (2), wherein the non-oxidizing atmosphere is an inert atmosphere.
(4)
In the firing step, at the time of temperature increase, at least the ceramic substrate and the applied conductive composition are non-oxidized at a steam partial pressure of 0.02 to 0.15 atm until the peak temperature is reached from 100°C. The manufacturing method according to any one of (1) to (3), which is performed in a volatile atmosphere.
(5)
The firing step includes
Raising the temperature to the peak temperature at 0.1 to 10° C./min,
Maintaining the peak temperature for 1 to 180 minutes,
The manufacturing method as described in any one of (1)-(4) containing.
(6)
The manufacturing method according to any one of (1) to (5), wherein the mass ratio of the first copper powder to the total mass of the first copper powder and the second copper powder is 50% or more.
(7)
The BET specific surface area of a 2nd copper powder is 0.1 m< ² >/g or more, The manufacturing method as described in any one of (1)-(6).
(8)
A method for producing a monolithic ceramic capacitor, comprising the step of obtaining a composite of a ceramic and a conductor by using the production method according to any one of (1) to (7).
(11)
A method for manufacturing a ceramic circuit board, comprising the step of obtaining a composite of a ceramic and a conductor by using the method for manufacturing according to any one of (1) to (7).

According to an embodiment of the method for producing a composite of a ceramic and a conductor according to the present disclosure, a composite having excellent conductor conductivity can be obtained. Further, according to the embodiment of the method for manufacturing the composite of the ceramic and the conductor according to the present disclosure, low-temperature firing is possible, so that the productivity is improved. Further, according to the embodiment of the method for producing the composite of the ceramic and the conductor according to the present disclosure, it is possible to produce the composite having excellent adhesion between the ceramic and the conductor.

Hereinafter, the present disclosure will be described in detail with reference to embodiments. The present disclosure is not limited to the specific embodiments described below.

[Conductive composition]
In one embodiment, the conductive composition according to the present disclosure has a BET specific surface area of 1.0 to 10.0 m ² /g and a first copper powder having a compacted bulk density of 3.0 g/cm ³ or less. And a second copper powder having a BET specific surface area smaller than that of the first copper powder, a binder resin, and a dispersion medium. The conductive composition can be produced by kneading these various components. The kneading can be performed using a known means. The conductive composition is provided as a paste in one embodiment. The electrically conductive composition according to the present disclosure can be used to produce a composite of ceramic and conductor.

[Production of composite]
In one embodiment, a method of manufacturing a composite of a ceramic and a conductor according to the present disclosure includes a step of applying a conductive composition to a ceramic substrate, and the ceramic substrate and the applied conductive composition having a water vapor partial pressure. Firing at a peak temperature of 400 to 700° C. in a non-oxidizing atmosphere of 0.02 to 0.15 atm.

The coating method is not particularly limited, and examples thereof include screen printing, gravure printing, inkjet method, offset printing, gravure offset printing, flexo printing, and other printing methods, as well as dipping and spraying.

The firing peak temperature can be lowered by performing the firing in a non-oxidizing atmosphere containing water vapor. The calcination is preferably carried out at a steam partial pressure of 0.02 atm or more for the purpose of enhancing the penetration of heat into the material to be calcined and promoting the sintering at a low temperature. However, if the water vapor partial pressure becomes too high, water is taken into the fired body during the sintering process, and the water taken into the vicinity of the interface easily separates the ceramic and the conductor. It is carried out at a water vapor partial pressure of 0.15 atm or less, more preferably 0.1 atm or less.

The lower the peak temperature during firing, the more the time required for raising and lowering the temperature is saved, and the productivity is improved. Further, a lower peak temperature during firing can suppress delamination due to a difference in thermal contraction between the ceramic and the conductor during the temperature lowering process, which is advantageous in preventing a decrease in adhesion between the ceramic and the conductor. Further, in the case of a ceramic substrate containing a low melting point material (for example, glass), if the firing temperature is too high, the ceramic substrate will be deformed and the flatness of the composite cannot be ensured. Therefore, the peak temperature during firing is preferably 700° C. or lower, and more preferably 550° C. or lower. However, even in the case of firing in a steam atmosphere, if the peak temperature during firing is too low, the sintering of the copper powder becomes insufficient and the adhesion between the ceramic and the conductor tends to become insufficient. Therefore, the peak temperature during firing is preferably 400° C. or higher, and more preferably 450° C. or higher.

In a preferred embodiment, the step of calcining comprises:
Raising the temperature to the peak temperature at 0.1 to 10°C/min, more preferably 0.3 to 2.0°C/min,
Maintaining at the peak temperature for 1 to 180 minutes, more preferably 10 to 120 minutes;
including.
By setting the heating rate up to the peak temperature in the above range, combustion and decomposition of organic matter in the conductive composition including the binder resin will surely occur before sintering of the copper powder, and thus a low resistance conductor can be obtained. In addition, since the combustion and decomposition of the organic matter gradually progress, there is an advantage that a conductor with few cracks can be obtained. By setting the time for maintaining at the peak temperature within the above range, there is an advantage that the sintering between the copper powders is promoted and a conductor having a low resistance is obtained. The time of maintaining the peak temperature refers to the time of maintaining the firing temperature substantially equal to the peak temperature, and is not required to be maintained at the temperature that completely matches the peak temperature. Specifically, in the present disclosure, the time of maintaining at the peak temperature refers to the time of maintaining the temperature range from the temperature 20° C. lower than the peak temperature to the peak temperature.

By performing the firing at the peak temperature in a non-oxidizing atmosphere, it is possible to prevent the copper powder from oxidizing. Further, by adopting a reducing atmosphere as the non-oxidizing atmosphere, even if the copper powder is oxidized, it can be reduced. Therefore, firing may be performed in an oxidizing atmosphere before reaching the peak temperature. For example, in the post-fire method, conventionally, firing was usually performed in two or more steps including switching from an oxidizing atmosphere to a reducing atmosphere. Also in the present disclosure, for example, as the first step, after firing the binder resin contained in the conductive composition in an air atmosphere at about 200 to 500° C., the second step is oxidation at the first step. The copper can be reduced by firing the copper in a reducing atmosphere at a temperature higher than that in the first stage.

However, when hydrogen is used as the reducing gas in the second stage, there is a demerit that explosion-proof measures are required. Therefore, in one embodiment of the method for producing a composite of a ceramic and a conductor according to the present disclosure, firing at a peak temperature is performed in an inert atmosphere (for example, a nitrogen atmosphere or a rare gas atmosphere such as argon). According to the present embodiment, explosion-proof measures are unnecessary, which is advantageous in terms of safety, productivity, and production cost.

Further, in one embodiment of the method for manufacturing a composite of a ceramic and a conductor according to the present disclosure, the firing step includes at least the ceramic substrate and the coating at the time of temperature increase until a peak temperature is reached from 100°C. The conductive composition thus obtained is subjected to a non-oxidizing atmosphere with a steam partial pressure of 0.02 to 0.15 atm. As described above, in the post-fire method, conventionally, firing is usually performed in two steps. However, according to the present embodiment, the binder resin is also decomposed in a steam atmosphere, so that firing in one step produces a ceramic. A composite of conductors can be manufactured. Therefore, it is advantageous in terms of productivity and production cost. The preferable range of the water vapor partial pressure is the same as that during the firing at the peak temperature.

Since the sintered body obtained by firing the conductive composition according to the present disclosure is a conductor, it can be used, for example, as an electrode or a circuit. For example, a monolithic ceramic capacitor can be manufactured by applying a conductive composition for an electrode layer on a ceramic substrate by a screen printing method or the like and then performing a firing process. In this case, the sintered body of the conductive composition is used as the internal electrode of the laminated ceramic capacitor. Similarly, a ceramic circuit board can be manufactured by applying a conductive composition for forming a circuit on the ceramic board by a screen printing method or the like and then performing a firing process.

[Copper powder]
The copper powder includes pure copper powder and copper alloy powder (in particular, copper alloy powder having a Cu content of 80 mass% or more).

As the copper powder, a first copper powder having a large BET specific surface area (small size) and a second copper powder having a small BET specific surface area (large size) are used. As a result, the first copper powder enters between the second copper powder to reduce the voids, and a dense conductor can be obtained after sintering. This improves the adhesion to the ceramic substrate and also improves the conductivity of the conductor. Assuming that the specific surface area of the first copper powder is A ₁ and the specific surface area of the second copper powder is A ₂ , the smaller A ₂ /A ₁ is, the easier the first copper powder is to enter between the second copper powder. Therefore, A ₂ /A ₁ ≦0.15 is preferable, A ₂ /A ₁ ≦0.1 is more preferable, and A ₂ /A ₁ ≦0.08 is further more preferable. preferable. However, when A ₂ /A ₁ becomes excessively small, the substantial size of the second copper powder becomes large, so that the coating film becomes rough when the conductive composition is applied to the ceramic substrate, As a result of the formation of voids at the interface between the ceramic and the conductor, the adhesiveness between the two tends to deteriorate, so 0.02≦A ₂ /A ₁ is preferable, and 0.03≦A ₂ /A ₁ is satisfied. Is more preferable, and 0.04≦A ₂ /A ₁ is even more preferable. The BET specific surface area is measured in accordance with JIS Z 8830:2013 after degassing copper powder in vacuum at 200° C. for 5 hours.

BET specific surface area of the first copper powder is preferably 1.0~10.0m ² / g, more preferably 1.5~5m ² / g, even more preferably 2 to 4 m ² / g Is. When the BET specific surface area of the first copper powder is 1.0 m ² /g or more, sintering at a low temperature of 400 to 700° C. is promoted. If the first copper powder having a small size, that is, a large surface area and a low sintering start temperature can be used as the starting point for sintering, the sintering of the second copper powder may be insufficient to some extent. If the first copper powder is sufficiently sintered, the void between the copper and the ceramic is suppressed, the adhesion between the copper and the ceramic is improved, and the specific resistance can be lowered. No particular upper limit is set on the BET specific surface area of the first copper powder. However, since copper powder having an excessively large BET specific surface area is difficult to manufacture and the cost is high, 10.0 m ² /g The following is preferable.

If the BET specific surface area of the second copper powder is too small, the coating film becomes rough when the conductive composition is applied to the ceramic substrate, and voids are formed at the interface between the ceramic and the conductor, resulting in adhesion between the two. Is preferably 0.1 m ² /g or more, and more preferably 0.2 m ² /g or more.

The higher the dispersibility of the first copper powder, the easier the first copper powder enters the gap between the second copper powders. Therefore, it is preferable that the compacted bulk density, which is an index of the dispersibility of the first copper powder, is low. Specifically, the compacted bulk density of the first copper powder is preferably 3.0 g/cm ³ or less, and more preferably 2.5 g/cm ³ or less. However, the compacted bulk density of the copper powder is preferably 1.0 g/cm ³ or more, because if the copper powder is too low, the bulk of the copper powder becomes large and it is difficult to handle when adjusting the conductive composition. It is more preferably 5 g/cm ³ or more. The compacted bulk density can be lowered, for example, by improving the disintegration property by performing a pH treatment step in which copper powder is brought into contact with an alkaline aqueous solution having a pH of 8 to 14.

The compacted bulk density is measured by the following procedure. A guide is attached to a 10 cc cup having a diameter of 2 cm, powder exceeding 10 cc is put therein, and tapping is performed 1000 times. Next, leaving the guide, the portion exceeding the volume of 10 cc was cut off, and in this state, the density determined based on the weight of the powder contained in the cup and the volume (10 cc) of the cup is the compacted bulk density. The compacted bulk density can be measured using, for example, Powder Tester PT-X (Hosokawa Micron Co., Ltd.).

The mass ratio of the first copper powder to the total mass of the first copper powder and the second copper powder is preferably 50% or more, more preferably 60% or more, and more preferably 70% or more. Even more preferable. By increasing the mixing ratio of the first copper powder having a small size, it is possible to prevent the coating film from becoming rough when the conductive composition is applied to the ceramic substrate. However, if the mass ratio of the first copper powder to the total mass of the first copper powder and the second copper powder is too large, the voids in the conductor increase and the conductivity of the conductor tends to decrease, It is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

The copper powder concentration (that is, the total concentration of the first copper powder and the second copper powder) in the conductive composition becomes too high in fluidity when the conductive composition is applied to the ceramic substrate, and the application pattern In order to prevent bleeding, it is preferably 30% by mass or more, and more preferably 35% by mass or more. Further, the concentration of the copper powder in the conductive composition is 90 mass from the viewpoint of preventing the metal powder from aggregating and increasing the coating roughness when the conductive composition is applied to the ceramic substrate. % Or less, and more preferably 85% by mass or less.

As the copper powder, both copper powder manufactured by a dry method and copper powder manufactured by a wet method can be used. A suitable method for producing copper powder by the wet method will be described as an example. The manufacturing method is a step of adding a dispersant (eg, gum arabic, gelatin, collagen peptide, a surfactant, etc.) to the cuprous oxide powder slurry, and then adding dilute sulfuric acid to the slurry at once within 5 seconds. And a step of carrying out a disproportionation reaction. In a preferred embodiment, the slurry can be maintained at room temperature (20 to 25° C.) or lower and dilute sulfuric acid similarly maintained at room temperature or lower to add the disproportionation reaction. The BET specific surface area (size, compacted bulk density) of the copper powder can be controlled by the addition amount of the dispersant, the addition rate of dilute sulfuric acid, and the like. As an example, when the amount of organic substances such as gum arabic is large, the BET specific surface area becomes large, and when the addition rate of dilute sulfuric acid is fast, the BET specific surface area tends to become large. In a preferred embodiment, the dilute sulfuric acid can be added so that the slurry has a pH of 2.5 or less, preferably pH 2.0 or less, more preferably pH 1.5 or less. In a preferred embodiment, the addition of dilute sulfuric acid to the slurry is performed within 5 minutes, preferably within 1 minute, more preferably within 30 seconds, further preferably within 10 seconds, and further preferably within 5 seconds. , Can be added. In a preferred embodiment, the disproportionation reaction can be completed within 10 minutes, for example within 5 seconds when the addition of dilute sulfuric acid to the slurry is carried out instantaneously. In a preferred embodiment, the concentration of the dispersant such as gum arabic in the slurry before the addition of dilute sulfuric acid can be 0.2 to 1.2 g/L. The principle of this disproportionation reaction is as follows:
Cu ₂ O+H ₂ SO ₄ → Cu↓+CuSO ₄ +H ₂ O
The copper powder obtained by this disproportionation can be washed, rust-proofed, filtered, dried, crushed, and classified, if desired.

Metal powder other than copper powder, for example, one or more metal powders selected from the group consisting of Pt powder, Pd powder, Ag powder and Ni powder can be blended in the conductive composition. Pt powder includes pure Pt powder and Pt alloy powder (particularly Pt alloy powder having a Pt content of 80 mass% or more), and Pd powder includes pure Pd powder and Pd alloy powder (particularly Pd content of 80 mass%). The above Pd alloy powder) is included, the Ag powder includes pure Ag powder and Ag alloy powder (in particular, Ag alloy powder with an Ag content of 80% by mass or more), and the Ni powder includes pure Ni powder and Ni alloy. Powder (particularly Ni alloy powder having a Ni content of 80% by mass or more) is included. However, usually, the mass ratio of copper powder in the metal powder is 90% or more, typically 95% or more, and more typically 99% or more.

In one embodiment, the copper powder may be surface-treated. As such a surface treatment, for example, an anticorrosion treatment with an organic anticorrosion agent such as benzotriazole or imidazole can be mentioned. Therefore, the person skilled in the art can carry out such known surface treatments as desired without departing from the purpose of the present invention. That is, the metal powder obtained by further performing the surface treatment on the surface of the surface-treated metal powder according to the present disclosure is also within the scope of the present disclosure, as long as the object of the present invention is not lost.

[Binder resin]
Examples of the binder resin used in the conductive composition include cellulose resins, acrylic resins, alkyd resins, polyvinyl alcohol resins, polyvinyl acetals, ketone resins, urea resins, melamine resins, polyesters, polyamides and polyurethanes. it can. The binder resins may be used alone or in combination of two or more. The binder resin in the conductive composition can be contained in a proportion of, for example, 0.1 to 10%, preferably 1 to 8% with respect to the mass of the copper powder. By setting the blending ratio of the binder resin within the above range, it is possible to enhance the structural stability and uniform coating property of the conductive composition.

[Dispersion medium]
The dispersion medium used in the conductive composition is, for example, one or more selected from the group consisting of alcohol solvents (for example, terpineol, dihydroterpineol, isopropyl alcohol, butylcarbitol, terpineloxyethanol, dihydroterpineloxyethanol). ), a glycol ether solvent (eg butyl carbitol), an acetate solvent (eg butyl carbitol acetate, dihydroterpineol acetate, dihydrocarbitol acetate, carbitol acetate, linalyl acetate, terpinyl acetate) 1 Or more), a ketone solvent (for example, methyl ethyl ketone), a hydrocarbon solvent (for example, one or more selected from the group consisting of toluene and cyclohexane), and a cellosolve (for example, one or more selected from the group consisting of ethyl cellosolve and butyl cellosolve). , Diethyl phthalate, or a propyneate-based solvent (for example, one or more selected from the group consisting of dihydroterpinyl propyneate, dihydrocarbyl propineate, and isobonyl propineate). As the dispersion medium, one kind may be used alone, or two or more kinds may be used in combination. The conductive composition may contain a dispersion medium in a ratio of, for example, 10 to 400% with respect to the mass of the copper powder.

[Other additives]
The conductive composition according to the present disclosure may appropriately contain known additives such as glass frit, a dispersant, a thickener, and a defoaming agent.

The glass frit is useful for improving the adhesion between the ceramic and the conductor. When low-temperature firing is performed in a steam atmosphere, the first copper powders having a small size are sintered together, or the first copper powders and the second copper powders are sintered together, and the sintering between the second copper powders is insufficient. There is a possibility of finishing the sintering as it is. In such a case, minute voids may occur in the sintered body. Therefore, by adding glass frit to the conductive composition, this void (particularly, the void existing at the interface between the sintered body and the ceramic) can be filled, and the adhesion between the ceramic and the conductor can be improved. it can. In addition, since the wettability of the glass frit is improved by firing in a steam atmosphere, the sinterability of both the first copper powder and the second copper powder is improved, and copper is sintered at a lower temperature side. You can wake it up.

As the glass frit, for example, a BET specific surface area of 1 to 10 m ² g ^-1, preferably 2 to 10 m ² g ^-1, more preferably may use a glass frit 2 to 8 m ² g ^-1. The conductive composition may contain glass frit in a proportion of, for example, 0 to 5% with respect to the mass of the copper powder.

Examples of the dispersant include oleic acid, stearic acid and oleylamine. The conductive composition may contain a dispersant in a proportion of, for example, 0 to 5% with respect to the mass of the copper powder.

Examples of the defoaming agent include organic modified polysiloxane and polyacrylate. The conductive composition may contain an antifoaming agent in a proportion of, for example, 0 to 5% with respect to the mass of the copper powder.

In addition, the ratio of the copper powder, the filler, the binder resin, and the dispersion medium in the conductive composition may be appropriately determined within a range that does not impair the coating property according to the application of the conductive composition.

Hereinafter, the present disclosure will be described in more detail with reference to Examples. The present disclosure is not limited to the following examples.

(Procedure 1: Examples 1-6, 9-13, 1st copper powder of Comparative Examples 1-4)
6 L of pure water was added to a 50 L container and heated so that the liquid temperature became 70°C. 3.49 kg of copper sulfate pentahydrate was added thereto, and it was visually confirmed that all the crystals of copper sulfate were dissolved while stirring at 350 rpm. D-glucose 1.39kg was added here. A 5 wt% aqueous ammonia solution was added thereto at a rate of 300 mL/min until a pH of 5 was reached with a liquid feed pump. When the pH reached 5, an aqueous ammonia solution was added dropwise with a dropper to raise the pH to 8.4. From here, the liquid temperature was maintained at 70±2° C. and pH 8.5±0.1 for 3 hours. The pH was adjusted with an aqueous ammonia solution. After the completion of the reaction, decantation, discharge of the supernatant, and washing with pure water were repeated until the pH of the supernatant fell below 8.0 to obtain a cuprous oxide powder slurry. A part of the solid content was taken out and dried at 70° C. in nitrogen, and it was confirmed by XRD that the solid content was cuprous oxide.

The water content of the cuprous oxide powder slurry obtained above was adjusted to 20% by mass, and the cuprous oxide powder slurry (25° C.) was added with pure water (25 (° C.) was added, 4 g of glue was further added, and the mixture was stirred at 500 rpm. 2 L of 25 vol% dilute sulfuric acid (25° C.) was instantaneously added thereto to adjust the pH to 0.7. The powder was settled by decantation, the supernatant was removed, 7 L of pure water (25° C.) was added, and the mixture was stirred at 500 rpm for 10 minutes. The decantation and water washing operations were repeated until the Cu concentration derived from Cu ²⁺ in the supernatant liquid fell below 1 g/L. Then, the mixture was poured into 3 L of ammonia water adjusted to pH 13 and stirred. Stirring was performed at 25° C. for 1 hour. Then, solid-liquid separation was performed by suction filtration to obtain a cake of pH-treated copper powder. The cake thus obtained was washed with pure water by using the pH of pure water after filtration as a guide. The washed cake was dried under a nitrogen atmosphere at 100° C. for 2 hours. The obtained dry powder was crushed with a pestle mortar until it passed through a sieve having 0.7 mm holes, and further crushed with a jet mill. It was confirmed by XRD that the obtained powder was copper.

(Procedure 2: Determination of compacted bulk density)
The compacted bulk density of the copper powder obtained in Procedure 1 was measured by the above-described method using a powder tester PT-X manufactured by Hosokawa Micron Corporation. The results are shown in Table 1.

(Procedure 3: BET specific surface area)
The BET specific surface area of the copper powder obtained in Procedure 1 was measured after pretreatment by heating at 200° C. for 5 hours in vacuum using BELSORP-miniII manufactured by Microtrac Bell. The results are shown in Table 1.

(Procedure 4: First copper powder of Example 7)
In Procedure 1, 2 L of 25 vol% dilute sulfuric acid was not instantaneously added to the cuprous oxide powder slurry (25° C.) stirred at 500 rpm, but was added at 50 mL/min. The decantation and water washing operations were repeated until the Cu concentration derived from Cu ²⁺ in the supernatant liquid fell below 1 g/L. Then, the cake obtained by solid-liquid separation by suction filtration was further washed with pure water until the pH fell below 8.0. The washed cake was dried under a nitrogen atmosphere at 100° C. for 2 hours. The obtained dry powder was crushed with a pestle mortar until it passed through a sieve having 0.7 mm holes, and further crushed with a jet mill. Then, the solidified bulk density and the BET specific surface area were determined according to the same procedure as Procedures 2 and 3. The size of the copper powder was large (the BET specific surface area was small) due to the fact that the addition rate of dilute sulfuric acid was slower than in Example 1. Since the compacted bulk density basically becomes larger as the size becomes larger, it becomes larger in accordance with the size of the copper powder.

(Procedure 5: First copper powder of Example 8)
In Procedure 1, copper powder was produced according to Procedure 1 except that the pH of 3 L of ammonia water was changed from 13 to 8. Then, the solidified bulk density and the BET specific surface area were determined according to the same procedure as the procedure 2 and the procedure 3. Due to the decrease in the pH of the ammonia water, the hydroxide ions adsorbed on the copper powder are reduced. As a result, the absolute value of the zeta potential of the copper powder is reduced and the repulsion degree between the copper powders is reduced. A copper powder having a high compacted bulk density was obtained.

(Procedure 6: First Copper Powder of Comparative Example 5)
A copper powder was prepared according to the procedure 1 except that the addition rate of 2 L of 25 vol% dilute sulfuric acid to the cuprous oxide powder slurry (25° C.) stirred at 500 rpm was changed to 10 mL/min. Then, the solidified bulk density and the BET specific surface area were determined according to the same procedure as Procedures 2 and 3.

(Procedure 7: First Copper Powder of Comparative Example 6)
6 L of pure water was added to a 50 L container and heated so that the liquid temperature became 70°C. 3.49 kg of copper sulfate pentahydrate was added thereto, and it was visually confirmed that all the crystals of copper sulfate were dissolved while stirring at 350 rpm. D-glucose 1.39kg was added here. A 5 wt% aqueous ammonia solution was added thereto at a rate of 300 mL/min until a pH of 5 was reached with a liquid feed pump. When the pH reached 5, an aqueous ammonia solution was added dropwise with a dropper to raise the pH to 8.4. From here, the liquid temperature was maintained at 70±2° C. and pH 8.5±0.1 for 3 hours. The pH was adjusted with an aqueous ammonia solution. After the completion of the reaction, decantation, discharge of the supernatant, and washing with pure water were repeated until the pH of the supernatant fell below 8.0 to obtain a cuprous oxide powder slurry. A part of the solid content was taken out and dried at 70° C. in nitrogen, and it was confirmed by XRD that the solid content was cuprous oxide.

The water content of the cuprous oxide powder slurry obtained above was adjusted to 20% by mass, and the cuprous oxide powder slurry (25° C.) was added with pure water (25 (° C.) was added, 4 g of glue was further added, and the mixture was stirred at 500 rpm. 2 L of 25 vol% dilute sulfuric acid (25° C.) was instantaneously added thereto to adjust the pH to 0.7. The powder was settled by decantation, the supernatant was removed, 7 L of pure water was added, and the mixture was stirred at 500 rpm for 10 minutes. The decantation and water washing operations were repeated until the Cu concentration derived from Cu ²⁺ in the supernatant liquid fell below 1 g/L. Then, solid-liquid separation was performed by suction filtration to obtain a cake of copper powder. The cake was dried under a nitrogen atmosphere at 100° C. for 2 hours. The obtained dry powder was crushed with a pestle mortar until it passed through a sieve having 0.7 mm holes, and further crushed with a jet mill. It was confirmed by XRD that the obtained powder was copper.

(Procedure 8: Second Copper Powder of Examples and Comparative Examples)
Copper powders having BET specific surface areas of 0.24 m ² g ^-1 , 0.15 m ² g ^-1 , and 0.08 m ² g ^-1 were produced by the atomization method.

(Procedure 9: Preparation of pastes of Examples 1 to 12 and Comparative Example)
A vehicle was prepared in advance by passing terpineol and ethyl cellulose through an orbiting/revolving mixer AR-100 and three rolls to sufficiently knead them. Then, two kinds of copper powder were mixed according to the mass ratio in Table 1 according to the test number. The powder after this mixing is called copper powder. Vehicle powder and copper powder are mixed so that copper powder: ethyl cellulose: terpineol = 80: 2.3: 17.7 (weight ratio), pre-kneaded in a rotation-revolution mixer, and then passed through three rolls (finish roll gap 5 μm), and defoamed by using a rotation/revolution mixer to prepare pastes of Examples 1 to 12 and Comparative Example.

(Procedure 10: Preparation of paste of Example 13)
The silica particles were crushed with a bead mill to obtain a glass frit. For this glass frit, the BET specific surface area measured by Procedure 3 was 6 m ² g ^-1 . This glass frit, the vehicle prepared by the procedure 9, two kinds of copper powder mixed in the mass ratios shown in Table 1, and terpineol were used as copper powder:ethyl cellulose:glass frit:terpineol=80:2.3:1. The mixture was mixed so as to have a weight ratio of 6:16.1, preliminarily kneaded by a rotation revolution mixer, passed through three rolls (finishing roll gap 5 μm), and defoamed using a rotation revolution mixer. 13 pastes were made.

(Procedure 11: Specific resistance of sintered body (conductor))
Using each paste and screen plate (stainless steel mesh, wire diameter 18 μm, gauze thickness 38 μm, opening 33 μm, opening ratio 42%) of the examples and comparative examples obtained by the above procedure, the surface roughness Ra was 0.04 μm. Three lines with a width of 5 mm and a length of 20 mm were printed on an alumina substrate (purity 99.5%). While supplying the remaining nitrogen gas having a total pressure of 1 atm and a steam partial pressure of 0.03 atm at 2 L/min, the nitrogen gas was supplied at a rate of 0.75° C./min up to a predetermined peak temperature shown in Table 1 according to the test number. Hold for 20 minutes at a given peak temperature. Then, it was cooled to room temperature at a rate of 5° C./min in a pure nitrogen atmosphere containing no water vapor. In this way, a fired body of the paste was formed on the ceramic substrate to obtain a fired body/ceramic laminate. The surface resistance and the thickness of a circuit having a width of 5 mm and a length of 20 mm obtained by cooling to room temperature were measured, and the specific resistance was calculated as a three-point average. The results are shown in Table 1.

(Procedure 12: Tape peeling test)
Using the carbon double-sided tape (manufactured by Nisshin EM Co., Ltd.) for the circuit and substrate obtained by the above procedure, according to JIS Z 0237:2009, a tape peeling test was performed at a peeling angle of 90° and a peeling speed of 5 mm/s. It was confirmed that the circuit did not adhere to the adhesive surface of. In one peeling test, at least a part of the circuit (sintered body) was peeled off from the substrate, and when peeled off twice or three times, it was judged as Δ, and when peeled off after four times or more, it was judged as ○. The results are shown in Table 1.

[Discussion]
According to the manufacturing methods of Examples 1 to 13 in which the BET specific surface area, the compacted bulk density, and the firing atmosphere were appropriate, the conductor-ceramic laminate having a low specific resistance of the conductor and excellent adhesion between the ceramics was gotten.
On the other hand, in Comparative Example 1, since the peak temperature during firing was too high, the degree of delamination during cooling was large, and the adhesion between the ceramic and the conductor was insufficient.
In Comparative Example 2, the peak temperature during firing was too low, resulting in insufficient sintering and insufficient adhesion between the ceramic and the conductor. Also, the conductivity of the conductor deteriorated.
In Comparative Example 3, since the water vapor partial pressure during firing was too high, water was taken into the sintered body, and the water taken into the vicinity of the interface caused insufficient adhesion between the ceramic and the conductor.
In Comparative Example 4, the partial pressure of water vapor during firing was too low, resulting in insufficient sintering and insufficient adhesion between the ceramic and the conductor. Also, the conductivity of the conductor deteriorated.
In Comparative Example 5, the size of the first copper powder was large and the BET specific surface area was insufficient. For this reason, sintering becomes insufficient at a low firing temperature, resulting in insufficient adhesion between the ceramic and the conductor. Also, the conductivity of the conductor deteriorated.
In Comparative Example 6, since the compacted bulk density of the first copper powder was too high, voids were generated between the ceramic and the conductor, and the adhesion between the ceramic and the conductor was insufficient. In addition, the conductivity of the conductor was insufficient due to the formation of voids in the conductor.

Claims (9)

A first copper powder having a BET specific surface area of 1.0 to 10.0 m ² /g and a compacted bulk density of 3.0 g/cm ³ or less, and a BET specific surface area smaller than that of the first copper powder. Applying a conductive composition containing a second copper powder, a binder resin, and a dispersion medium to the ceramic substrate,
Firing the ceramic substrate and the applied conductive composition in a non-oxidizing atmosphere having a water vapor partial pressure of 0.02 to 0.15 atm with a peak temperature of 400 to 700° C.;
A method of manufacturing a composite of a ceramic and a conductor. The manufacturing method according to claim 1, wherein the conductive composition includes a glass frit. The manufacturing method according to claim 1, wherein the non-oxidizing atmosphere is an inert atmosphere. In the firing step, at the time of temperature increase, at least the ceramic substrate and the applied conductive composition are non-oxidized at a steam partial pressure of 0.02 to 0.15 atm until a peak temperature is reached from 100°C. The manufacturing method according to any one of claims 1 to 3, which is performed in a neutral atmosphere. The firing step includes
Raising the temperature to the peak temperature at 0.1 to 10° C./min,
Maintaining the peak temperature for 1 to 180 minutes,
The manufacturing method according to claim 1, further comprising: The manufacturing method according to claim 1, wherein a mass ratio of the first copper powder to a total mass of the first copper powder and the second copper powder is 50% or more. The manufacturing method according to claim 1, wherein the BET specific surface area of the second copper powder is 0.1 m ² /g or more. A method of manufacturing a monolithic ceramic capacitor, which comprises the step of obtaining a composite of a ceramic and a conductor by using the method of manufacturing according to claim 1. A method of manufacturing a ceramic circuit board, comprising the step of obtaining a composite of ceramic and conductor using the method of manufacturing according to claim 1.