Conductive paste, conductive film, ceramic circuit substrate, and electronic component

Abstract

Provided are a conductive paste capable of forming a circuit pattern by a screen printing method and capable of forming a conductive film having high adhesion to a ceramic substrate, a conductive film, a ceramic circuit substrate, and an electronic component. The conductive paste of the present invention comprises (A) a conductive powder, (B) a glass powder, and (C) an organic vehicle, wherein the (B) glass powder comprises a glass powder that, when the glass powder is disposed on a ceramic substrate and the glass powder is melted at 900°C in a nitrogen atmosphere, the contact angle of the melted glass powder with respect to the ceramic substrate is 40 degrees or less as measured according to JIS R3257.

Description

Technical Field

[0001] This invention relates to conductive pastes, conductive films, ceramic circuit boards, and electronic components. Background Technology

[0002] Ceramic substrates used in power devices for power control, such as converters and inverters, often require substrates with good heat dissipation, such as DBC (Direct Bonded Copper) substrates or AMC (Active Metal Brazed Copper) substrates. For example, in the fabrication of AMC substrates, the active metal method is used. In the active metal method, a solder or other bonding agent is applied to the surface of the ceramic substrate, and a metal plate, such as a copper plate, is stacked on top. Metallization is then performed, for example, by firing at a high temperature of 900°C to 1200°C, thereby forming a metal layer for forming wiring patterns, etc.

[0003] DBC or AMC substrates have a metallized layer on a ceramic substrate. To form complex wiring patterns, cumbersome operations such as etching are required. If etching is performed, drainage is required, which can cause environmental problems.

[0004] In order to form wiring patterns directly on the surface of a ceramic substrate, for example, Patent Document 1 discloses a conductive paste containing copper powder for forming wiring patterns by directly coating, drying, and firing on a ceramic substrate.

[0005] Patent Document 2 discloses a copper conductor paste that requires strict atmospheric control during firing, particularly strict control of oxygen in the atmosphere. The copper conductor paste disclosed in Patent Document 2 contains zinc borosilicate glass powder and borosilicate glass powder. The zinc borosilicate glass powder has a contact angle of 60 degrees or less with respect to a film formed from unoxidized copper powder, and a softening point of 700°C or less. The borosilicate glass powder has a solubility within a specific range relative to concentrated sulfuric acid aqueous solution, and a softening point of 700°C or less. Although the copper conductor paste disclosed in Patent Document 2 contains zinc borosilicate glass powder with a contact angle of 60 degrees or less when molten relative to a film formed from copper powder, since the contact angle of the glass powder is not relative to the contact angle of the ceramic substrate, there is still room for improvement in terms of adhesion to the ceramic substrate.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2015-149162

[0009] Patent Document 2: Japanese Patent Application Publication No. 2008-226771 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] Conductive pastes containing copper as a conductive powder have poor adhesion to ceramic substrates, thus requiring improvements in the adhesion between the ceramic substrate and the conductive paste. For example, if a conductive paste is applied to a ceramic substrate to achieve a thickness of 100 μm or more after firing and then fired to obtain a conductive film, the poor adhesion between the conductive film and the ceramic substrate leads to localized peeling of the conductive film, resulting in undesirable conditions such as poor appearance.

[0012] Therefore, the object of the present invention is to provide a conductive paste, a conductive film, a ceramic circuit board, and an electronic component that can form circuit patterns by screen printing and can form a conductive film with high adhesion to a ceramic substrate.

[0013] Methods for solving problems

[0014] The means for solving the above-mentioned problems are as follows, and the present invention includes the following methods.

[0015] [1] A conductive paste comprising (A) a conductive powder, (B) a glass powder, and (C) an organic carrier, wherein the (B) glass powder comprises a glass powder such that, when the glass powder is disposed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, the contact angle of the melted glass powder relative to the ceramic substrate is 40 degrees or less, as determined by JIS R3257.

[0016] [2] According to the conductive paste described in [1] above, the conductive powder (A) above contains copper powder, and contains more than 50 parts by mass of the copper powder relative to 100 parts by mass of the conductive powder (A) above.

[0017] [3] According to the conductive paste described in [1] or [2] above, the average particle size (D50) of the conductive powder (A) above, as determined by laser diffraction scattering, is in the range of 0.5 μm or more and 10.0 μm or less.

[0018] [4] The conductive paste described in any one of [1] to [3] above, wherein the glass powder (B) above includes at least one selected from bismuth-based glass powder, tellurium-based glass powder, and zinc borosilicate-based glass powder.

[0019] [5] According to any one of [1] to [4] above, the content of the glass powder (B) is in the range of 1 part by mass or more and 30 parts by mass or less relative to 100 parts by mass of the conductive powder (A).

[0020] [6] According to any one of [1] to [5] above, the temperature difference between the softening point of the glass powder (B) and the decomposition temperature of the organic carrier (C) in a nitrogen atmosphere, as measured by a differential thermal-thermogravimetric analyzer, is within 200°C in absolute terms.

[0021] [7] According to any one of [1] to [6] above, the temperature of the softening point of the glass powder (B) is lower than the decomposition temperature of the organic carrier (C) in a nitrogen atmosphere as measured by a differential thermal-thermogravimetric analyzer.

[0022] [8] According to any one of [1] to [7] above, the content of the resin solid component in the organic carrier of (C) is in the range of 0.5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the conductive powder of (A).

[0023] [9] The conductive paste described in any one of [1] to [8] above is used to form a conductive film with a thickness of 100 μm or more.

[0024]

[10] The conductive paste described in any one of [1] to [9] above is used for the formation of a conductive film formed by coating the conductive paste onto the ceramic substrate and firing it.

[0025]

[11] The conductive paste described in any one of [1] to

[10] above, wherein the ceramic substrate comprises at least one selected from alumina (Al2O3), aluminum nitride (AlN) and silicon nitride (Si3N4).

[0026]

[12] A conductive film is formed by coating a ceramic substrate with a conductive paste described in any one of [1] to

[11] above and then firing it.

[0027]

[13] The conductive film described in

[12] above has a thickness of 100 μm or more.

[0028]

[14] According to the conductive film described in

[12] or

[13] above, wherein the ceramic substrate is an alumina (Al2O3) substrate, and the conductive film with a thickness of 250 μm formed by coating the conductive paste onto the alumina (Al2O3) substrate and firing it has a compressive shear bond strength of 1.0 N / mm as measured according to JIS K6852. 2above.

[0029]

[15] According to the conductive film described in

[12] or

[13] above, wherein the ceramic substrate is an aluminum nitride (AlN) substrate, and the conductive film with a thickness of 250 μm formed by coating the conductive paste onto the aluminum nitride (AlN) substrate and then firing it has a compressive shear bond strength of 1.0 N / mm as measured according to JIS K6852. 2 above.

[0030]

[16] According to the conductive film described in

[12] or

[13] above, wherein the ceramic substrate is a silicon nitride (Si3N4) substrate, and the conductive film with a thickness of 250 μm formed by coating the conductive paste onto the silicon nitride (Si3N4) substrate and then firing it has a compressive shear bond strength of 1.0 N / mm as measured according to JIS K6852. 2 above.

[0031]

[17] A ceramic circuit board comprising a conductive film formed by coating a conductive paste as described in any one of [1] to

[11] onto a ceramic substrate and firing it.

[0032]

[18] An electronic component comprising a conductive film formed by coating a conductive paste, any one of the conductive pastes described in [1] to

[11] above onto a ceramic substrate and then firing it.

[0033] Invention Effects

[0034] According to the present invention, a conductive paste, a conductive film, a ceramic circuit board, and an electronic component are provided, which are capable of forming circuit patterns by screen printing and can form a conductive film with high adhesion to the ceramic substrate even when the conductive paste is applied to a ceramic substrate with a thickness of 100 μm or more after firing and then fired. Attached Figure Description

[0035] Figure 1 This is an example of a pattern in which a conductive paste is applied to a ceramic substrate. Detailed Implementation

[0036] The conductive paste, conductive film, ceramic substrate, and electronic component of this disclosure will be described below based on embodiments. The embodiments shown below are examples to embody the technical concept of the present invention, and the present invention is not limited to the conductive paste, conductive film, ceramic substrate, and electronic component described below. In this specification, "~" indicates an upper limit or lower limit, encompassing numerical values ​​or symbols containing numerical values ​​listed before or after it.

[0037] The conductive paste of the present invention comprises (A) conductive powder, (B) glass powder, and (C) organic carrier. The glass powder comprises glass powder that, when the glass powder is disposed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, has a contact angle of 40 degrees or less with respect to the ceramic substrate after melting, as determined by JIS R3257.

[0038] The conductive paste contains (B) glass powder, which, when melted under specific conditions, has a contact angle of less than 40 degrees relative to the ceramic substrate. Therefore, it exhibits good wettability to the ceramic substrate and can form a conductive film with high adhesion between the conductive powder and the ceramic substrate. Furthermore, since the conductive paste contains (A) conductive powder, as well as the aforementioned (B) glass powder and (C) organic carrier, it eliminates the need for etching and allows for the precise formation of circuit patterns using screen printing.

[0039] The conductive powder (A) preferably contains copper powder, and more preferably contains 50 parts by mass or more of copper powder relative to 100 parts by mass of the conductive powder (A). In this specification, copper powder is sometimes also referred to as "(A-1) copper powder". The conductive powder (A) is included to impart conductivity and heat dissipation to the conductive film. Examples of conductive powder (A) include copper powder, nickel powder, silver powder, palladium powder, etc. Since the conductive powder (A) can improve conductivity and heat dissipation, and can form a circuit pattern of copper wiring by screen printing, the conductive powder (A) preferably contains copper powder. More preferably, it contains 60 parts by mass or more of (A-1) copper powder relative to 100 parts by mass of the conductive powder (A), further preferably, it contains 80 parts by mass or more, particularly preferably, it contains 90 parts by mass or more, or the conductive powder (A) can be entirely copper powder, that is, the conductive powder (A) can be 100 parts by mass of copper powder. By including copper powder within the above range, migration can be suppressed, and a circuit pattern of copper wiring can be formed by screen printing.

[0040] (A-1) Copper powder is an aggregate of particles with copper as the main component. It may contain particles formed from copper oxide, or unavoidable impurities other than copper oxide. The copper oxide may be copper oxide (I) (Cu2O) or copper oxide (II) (CuO). The main component referred to here is the component with the largest content among the components constituting copper powder. For the purposes of conductivity and / or heat dissipation, copper powder is preferably an aggregate of particles formed from copper. In the case where the copper powder in (A-1) contains both particles formed from copper and particles formed from copper oxide, when the total amount of copper powder is set to 100 parts by mass, it is preferable to include copper oxide powder in the range of 1 part by mass or more and 20 parts by mass or less.

[0041] (A) The conductive powder preferably has an average particle size (D50) of 0.5 μm or more and 10.0 μm or less, more preferably 1.0 μm or more and 8.0 μm or less, and even more preferably 1.5 μm or more and 5.0 μm or less. If the average particle size of the conductive powder (A) is within the above range, the conductive paste containing the conductive powder (A) can be easily formed into a circuit pattern with excellent precision by screen printing. In addition, it is easy to form a thick conductive film with a film thickness of 100 μm or more by multiple printing. In order to obtain a dense conductive film, the conductive powder (A) can be mixed with one or more conductive powders with different average particle sizes (D50). The average particle size (D50) measured by laser diffraction scattering refers to the median diameter equivalent to the cumulative 50% in the particle size distribution on a volume basis.

[0042] The particles constituting the conductive powder (A) can be spherical, flake-like (thin), conical, fibrous, or other shapes. Because of their good smoothness and ease of printing by screen printing, the shape of the particles constituting the conductive powder (A) is preferably spherical and / or flake-like.

[0043] Preferably, the conductive powder (A) is included in the range of 70% to 95% by mass relative to 100% of the total amount of the conductive paste; more preferably, it is included in the range of 75% to 90% by mass; and even more preferably, it is included in the range of 75% to 88% by mass. If the conductive powder (A) is included in the range of the above within 100% by mass relative to the total amount of the conductive paste, a thick conductive film with good conductivity and heat dissipation and a film thickness of 100 μm or more can be obtained.

[0044] (B) The glass powder includes glass powder that, when the glass powder is disposed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, has a contact angle of 40 degrees or less with the ceramic substrate after melting, as determined according to JIS R3257. In this specification, glass powder with a contact angle of 40 degrees or less with the ceramic substrate after melting is sometimes referred to as "(B-1) glass powder".

[0045] In this specification, the nitrogen atmosphere preferably contains 99% by volume or more nitrogen. The nitrogen atmosphere may also contain 99.9% by volume or more nitrogen. The nitrogen atmosphere may also contain less than 1% by volume oxygen, preferably 0.5% by volume or less, or 0.1% by volume (1000 ppm by volume) or less, or 0.01% by volume (100 ppm by volume) or less, preferably 0.001% by volume (10 ppm by volume) or less, or 0.00001% by volume (0.1 ppm by volume) or more. To determine the contact angle of the (B) glass powder relative to the substrate, when melting the (B) glass powder disposed on the ceramic substrate, a nitrogen atmosphere is preferably used to suppress the reaction of the glass powder. There is no particular limitation on the melting time of the (B) glass powder at 900°C, as long as the melting time of the glass powder is sufficient. For example, after the furnace temperature reaches 900°C, it is preferably 5 minutes or more and 15 minutes or less, and preferably 8 minutes or more and 12 minutes or less.

[0046] (B) The glass powder is preferably formed into a cylindrical shape with a diameter of 5 mm and a height of 5 mm by molding and then placed on a ceramic substrate. A belt furnace, for example, can be used to measure the contact angle of the (B) glass powder relative to the ceramic substrate. The contact angle of the molten (B) glass powder is relative to the ceramic substrate, not relative to the copper plate or copper oxide powder.

[0047] (B) The glass powder includes (B-1) glass powder in which the contact angle between the molten glass powder and the ceramic substrate is 40 degrees or less. The contact angle between the molten glass powder and the glass substrate is preferably 30 degrees or less, more preferably 20 degrees or less, and even more preferably 10 degrees or less. There is no particular limitation on the lower limit value of the contact angle between the molten glass powder and the glass substrate, but it is, for example, 1 degree or more.

[0048] If the conductive paste contains glass powder with a contact angle relative to the ceramic substrate within the aforementioned range (B-1), the wettability of the conductive paste to the ceramic substrate improves, enabling the formation of a conductive film that adheres closely to the ceramic substrate, and allowing the formation of a thick conductive film with a thickness of 100 μm or more. It should be noted that when forming a thick conductive film with a thickness of 100 μm or more, the shrinkage of the coating increases compared to a thin film with a thickness less than 100 μm, thus weakening the adhesion strength with a large coating thickness. This invention has found that even with a conductive film thickness of 100 μm or more, the adhesion to the ceramic substrate is improved.

[0049] Regarding the content of glass powder (B), in the conductive paste, it is preferably in the range of 1 part by mass or more and 30 parts by mass or less relative to 100 parts by mass of conductive particles (A), more preferably in the range of 2 parts by mass or more and 20 parts by mass or less, and even more preferably in the range of 3 parts by mass or more and 15 parts by mass or less. If the content of glass powder (B) in the conductive paste is within the above range, the molten glass powder (B) will bond the conductive powder (A) to the ceramic substrate, forming a thick conductive film with excellent adhesion and a film thickness of 100 μm or more. If the content of glass powder (B) in the conductive paste is less than 2 parts by mass relative to 100 parts by mass of conductive powder (A), the adhesion between the ceramic substrate and the conductive film may not be sufficiently improved. If the content of (B) glass powder in the conductive paste is greater than 30 parts by mass relative to 100 parts by mass of (A) conductive particles, then the content of (A) conductive particles is relatively smaller relative to the total amount of the conductive paste, resulting in a decrease in the conductivity or heat dissipation of the obtained conductive film.

[0050] When (B) is (B-1) glass powder in which the contact angle between the molten glass powder and the ceramic substrate is 40 degrees or less, the softening point of (B-1) glass powder is preferably 600°C or less, more preferably 500°C or less, even more preferably 400°C or less, and particularly preferably 380°C or less. It should be noted that the lower limit of the softening point is not particularly limited and can be 250°C or more, or 300°C or more. When (B) is (B-1) glass powder in which the contact angle between the molten glass powder and the ceramic substrate is 40 degrees or less, if the softening point is within the above range, the (B-1) glass powder will melt sufficiently during firing, which can improve the adhesion between the ceramic substrate and the conductive film. The softening point of the glass powder can be measured using a differential thermal-thermogravimetric analyzer (e.g., TG-DTA2000SA, manufactured by BRUKERAXS).

[0051] (B) The glass powder preferably includes at least one of the following: bismuth-based glass powder, tellurium-based glass powder, and zinc borosilicate-based glass powder.

[0052] Bismuth-based glass powder is a glass powder that contains Bi as the main component in terms of oxides as an essential ingredient, and may also contain other optional components. In this specification, the term "main component" of the glass powder refers to the component with the highest content in terms of oxides among the components constituting the glass powder. (B) Preferably, the (B-1) glass powder, in which the contact angle between the molten glass powder and the ceramic substrate is 40 degrees or less, contains bismuth-based glass powder. Relative to the total amount of bismuth-based glass powder, the bismuth-based glass powder preferably contains 50-95% by mass of Bi (Bi₂O₃) in terms of oxides, more preferably 70-90% by mass, and even more preferably 75-90% by mass. Relative to the total amount of bismuth-based glass powder, the bismuth-based glass powder preferably contains 2-40% by mass of B (B₂O₃) in terms of oxides, more preferably 3-30% by mass, and even more preferably 3-15% by mass.

[0053] Bi(Bi₂O₃) converted from oxides is the main component of bismuth-based glass powder. If the Bi₂O₃ content in the bismuth-based glass powder is less than the lower limit of the above range, the softening point of the glass powder increases. The contact angle between the molten glass powder and the ceramic substrate, as measured by the aforementioned method, will be greater than 40 degrees, which is excessive. This reduces the wettability of the molten glass powder on the ceramic substrate, resulting in reduced adhesion between the ceramic substrate and the conductive film. If the Bi(Bi₂O₃) content in the bismuth-based glass powder is greater than the upper limit of the above range, vitrification is difficult to occur, resulting in reduced adhesion between the ceramic substrate and the conductive film.

[0054] Tellurium-based glass powder is a glass powder that contains Te as the main component in oxide form as an essential ingredient, and may also contain other optional components. Tellurium-based glass powder preferably contains Te as an essential component and V as an optional component, and is preferably tellurium-vanadium-based glass powder. (B) Glass powder preferably includes tellurium-based glass powder and / or tellurium-vanadium-based glass powder as (B-1) glass powder in which the contact angle between the molten glass powder and the ceramic substrate is less than 40 degrees. Tellurium-based glass powder may substantially not contain alkali metal oxides, and preferably contains 14 to 55% by mass of Te (TeO2) in oxide form relative to the total amount of tellurium-based glass powder, more preferably 20 to 50% by mass, and even more preferably 30 to 45% by mass. By making the Te (TeO2) in oxide form contained in the tellurium-based glass powder within the above range, a glass powder with a low softening point and good adhesion strength to the ceramic substrate is obtained. Furthermore, when the tellurium-based glass powder contains V, it is preferable to include 10-50% by mass of V (V₂O₅ converted from oxides) relative to the total amount of tellurium-based glass powder, more preferably 15-35% by mass, and even more preferably 20-30% by mass. By ensuring that the V (V₂O₅ converted from oxides) contained in the tellurium-based glass powder is within the above range, a glass powder with a low softening point and good adhesion strength to the ceramic substrate is obtained. In tellurium-based glass powder or tellurium-vanadium-based glass powder, TeO₂ and V₂O₅ are components that form the glass framework. If the content of TeO₂ and V₂O₅ in tellurium-based glass powder or tellurium-vanadium-based glass powder is low, the adhesion between the ceramic substrate and the conductive film may decrease. When the softening point of tellurium-based glass powder or tellurium-vanadium-based glass powder increases, the contact angle between the molten glass powder and the ceramic substrate, as measured by the aforementioned method, will be greater than 40 degrees, which is too large. This reduces the wettability of the molten glass powder on the ceramic substrate, resulting in a decrease in the adhesion between the ceramic substrate and the conductive film.

[0055] Zinc borosilicate glass powder may also contain at least one of B and Si and Zn as essential components, and may also contain other optional components.

[0056] (B) Zinc borosilicate glass powder can be used as (B-1) glass powder in which the contact angle between the molten glass powder and the ceramic substrate is 40 degrees or less. However, when using zinc borosilicate glass powder, from the viewpoint of improving wettability to the ceramic substrate, it is preferable that the glass powder does not contain zinc borosilicate glass powder containing more than 50% by mass of Zn (ZnO) converted from oxides.

[0057] (B) The glass powder is preferably a zinc borosilicate glass powder containing less than 40% by mass of Zn (ZnO) converted from oxides, which is a (B-1) glass powder with a contact angle of less than 40 degrees relative to the ceramic substrate after molten glass powder. The zinc borosilicate glass powder contains 2-20% by mass of B (B₂O₃) converted from oxides, 5-30% by mass of Si (SiO₂) converted from oxides, and 10-35% by mass of Zn (ZnO) converted from oxides. It may also contain 0-20% by mass of Na (Na₂O) converted from oxides and 0-5% by mass of Al (Al₂O₃) converted from oxides. In the zinc borosilicate glass powder, Si (SiO₂) and B (B₂O₃) are components that form the glass framework. In the zinc borosilicate glass powder, Zn (ZnO) converted from oxides is a component that adjusts the viscosity of the glass during melting. If the content of Zn (ZnO) in the zinc borosilicate glass powder is more than 50% by mass, the contact angle of the molten glass powder relative to the ceramic substrate, as determined by the aforementioned method, will be greater than 40 degrees, which is too large. This reduces the wettability of the molten glass powder on the ceramic substrate, resulting in a decrease in the adhesion between the ceramic substrate and the conductive film.

[0058] It should be noted that (B) glass powder may also include glass powder (B-2) that is, when glass powder is placed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, the contact angle of the molten glass powder relative to the ceramic substrate is greater than 40 degrees, as determined by JIS R3257. If glass powder (B-2) with a contact angle greater than 40 degrees is also included, it is sufficient to mix glass powder (B-1) with a contact angle of 40 degrees or less with (B-2) and press it to form a molded body, and the contact angle obtained by the test method described later is 40 degrees or less.

[0059] (B) SnO-P2O5 glass powder, which contains Sn and P as essential components, is preferably excluded. Although SnO-P2O5 glass has a low melting point, its contact angle relative to the ceramic substrate, as measured by the aforementioned method, is greater than 40 degrees, which is too large. The wettability of the molten glass powder to the ceramic substrate is reduced, resulting in a decrease in the adhesion between the ceramic substrate and the conductive film. (B) SnO-P2O5 glass powder, which contains 40-50 mol% SnO, 10-20 mol% P2O5, 15-25 mol% SiO2, 5-15 mol% Al2O3, and 10-15 mol% of at least one of MgO, CaO, and SrO, is preferably excluded.

[0060] The conductive paste comprises (C) an organic carrier. The organic carrier comprises a resin and a solvent, and examples include organic carriers formed by dissolving the resin in a solvent. The resin contained in the organic carrier is preferably at least one selected from cellulose-based resins and (meth)acrylic resins.

[0061] When a conductive paste is coated onto a ceramic substrate, the organic carrier (C) imparts thixotropic properties to the conductive paste, improving its coatability. After the conductive paste is coated onto the ceramic substrate, even with a film thickness greater than 100 μm, the organic carrier, being a resin contained within it, maintains the shape of the coating. When the conductive paste is sintered after being coated onto the ceramic substrate to obtain a conductive film, the organic carrier (C) is decomposed and removed.

[0062] (C) The organic carrier preferably comprises, for example, at least one cellulose-based resin selected from methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, benzylcellulose, propylcellulose, and nitrocellulose as the resin, and at least one solvent selected from α-terpineol, texanol, butyl carbitol acetate, and ethyl carbitol acetate as the solvent. When the resin contained in the organic carrier (C) is a cellulose-based resin, it is preferable to impart thixotropy to the conductive paste compared to (meth)acrylic resins, and to maintain the shape of the coating film after application.

[0063] (C) The organic carrier preferably comprises, for example, at least one (meth)acrylic resin selected from methyl methacrylate, ethyl methacrylate, butyl methacrylate and 2-hydroxyethyl methacrylate, and at least one solvent selected from methyl ethyl ketone, α-terpineol, ester-12 (Texanol), butyl carbitol acetate and ethyl carbitol acetate.

[0064] Regarding the content of the resin solids in the organic carrier (C), it is preferably in the range of 0.5 parts by mass or more and 15 parts by mass or less, more preferably in the range of 0.7 parts by mass or more and 7 parts by mass or less, and even more preferably in the range of 1 part by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the conductive particles (A) in the conductive paste. If the content of the resin solids in the organic carrier (C) in the conductive paste is within the above range, the conductive paste can be endowed with thixotropic properties suitable for screen printing, and the shape of the coating film can be maintained after the coating film is formed. It can also be decomposed and removed when the conductive film is obtained by firing.

[0065] Regarding the ratio of resin to solvent contained in the (C) organic carrier, in order to adjust the viscosity of the conductive paste by means of the (C) organic carrier, the resin to solvent ratio (resin:solvent) is preferably 1:99 to 30:70, more preferably 2:98 to 25:75, and even more preferably 3:97 to 20:80.

[0066] The temperature difference between the softening point of the glass powder (B) and the decomposition temperature of the organic carrier (C), as measured by a differential thermal-thermogravimetric analyzer in a nitrogen atmosphere, is preferably within 200°C in absolute terms, more preferably within 150°C in absolute terms, and even more preferably within 100°C in absolute terms. Specifically, the decomposition temperature of the organic carrier (C), as measured by the differential thermal-thermogravimetric analyzer in a nitrogen atmosphere, is the decomposition temperature of the resin contained in the organic carrier (C). If the temperature difference between the softening point of the glass powder (B) and the decomposition temperature of the organic carrier (C) is within the above range, when a conductive paste is coated onto a ceramic substrate, for example, with a film thickness of 100 μm or more, the shape of the coated film can be maintained by the organic carrier (C). During firing, before and after the decomposition of the organic carrier (C), the glass powder (B) softens, allowing a conductive film with high adhesion to the ceramic substrate to be obtained while maintaining the shape of the coated film. This enables the precise formation of circuit patterns formed from the conductive film. Regarding the temperature difference between the softening point of the glass powder (B) and the decomposition temperature of the organic carrier (C) measured by a differential thermal-thermogravimetric analyzer in a nitrogen atmosphere, although no lower limit is specifically specified, it is preferably 10°C or higher, and may also be 50°C or higher.

[0067] Regarding the nitrogen atmosphere used when determining the decomposition temperature of the (C) organic support using a differential thermal-thermogravimetric analyzer, to suppress the reaction of the (C) organic support, the nitrogen atmosphere is preferably 99% by volume or more, and can also be 100% by volume. The nitrogen atmosphere used when determining the decomposition temperature of the (C) organic support using a differential thermal-thermogravimetric analyzer may also contain less than 1% by volume of hydrogen. The decomposition temperature of the organic support can be determined using a differential thermal-thermogravimetric analyzer (e.g., TG-DTA2000SA, manufactured by BRUKERAXS).

[0068] Preferably, the softening point of (B) glass powder is lower than the decomposition temperature of (C) organic carrier as measured by a differential thermal-thermogravimetric analyzer in a nitrogen atmosphere. If the softening point of (B) glass powder is lower than the decomposition temperature of (C) organic carrier as measured by a differential thermal-thermogravimetric analyzer in a nitrogen atmosphere, then after the conductive paste is coated onto the ceramic substrate with a film thickness of, for example, 100 μm or more, the softening of (B) glass powder begins during firing before the decomposition of (C) organic carrier. This allows the shape of the coated film to be maintained, resulting in a conductive film with high adhesion to the ceramic substrate, and enabling the formation of circuit patterns from the conductive film with greater precision.

[0069] Examples of (B) glass powders with a softening point below 600℃ include bismuth-based glass powders, tellurium-based glass powders, tellurium-vanadium-based glass powders, and zinc borosilicate glass powders containing less than 40% by mass of Zn (ZnO) converted from oxides.

[0070] Organic carriers (C) whose decomposition temperature, measured by differential thermal-thermogravimetric analysis in a nitrogen atmosphere, is within 200°C in absolute terms, can be exemplified by organic carriers containing ethyl cellulose and α-terpineol in the range of 3:97 to 20:80.

[0071] Organic carriers with a decomposition temperature of less than 200°C in absolute terms, as determined by differential thermal-thermogravimetric analysis in a nitrogen atmosphere, include, for example, organic carriers containing methyl methacrylate and α-terpineol in the range of 3:97 to 20:80.

[0072] The conductive paste is preferably used for forming conductive films with a thickness of 100 μm or more. The conductive paste exhibits good thixotropy and coatability, enabling the formation of circuit patterns via screen printing and maintaining its shape after coating. Even thick conductive films with a thickness of 100 μm or more can be formed. It should be noted that in applications where the conductive paste is directly coated onto a ceramic substrate used in power devices and then dried and fired to form wiring patterns, thick wiring patterns are required to supply high currents to semiconductor elements. Based on this requirement, the conductive paste is more preferably used for forming conductive films with a thickness of 150 μm or more, further preferably for forming conductive films with a thickness of 200 μm or more, and particularly preferably for forming conductive films with a thickness of 250 μm or more. After firing, the conductive film thickness decreases compared to the thickness when the conductive paste is applied due to the decomposition of the (C) organic carrier. Therefore, the thickness of the coating obtained by applying the conductive paste can be 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, or 300 μm or more. Preferably, the conductive paste forms a coating with a thickness of 1.2 to 1.5 times that of the conductive film obtained by sintering the conductive paste.

[0073] The conductive paste is preferably formed, for example, by screen printing, into a coating that becomes a conductive film after firing. The conductive paste can also be used to form a conductive film by laminating multiple layers of coating and firing them. For example, after applying a conductive paste to a ceramic substrate and drying the first layer, spacers thicker than the first layer are placed, and the conductive paste is applied onto the first layer (dried film) to form a second layer. After drying, spacers thicker than both the first and second layers are further placed, forming a third layer. This process is repeated until the target thickness is achieved. The dried film formed in multiple layers is then fired in a belt furnace at 900°C for 1 hour using an in-out (nitrogen atmosphere) firing process, thereby forming a conductive film with a thickness of 100 μm or more.

[0074] The number of coating layers is not limited to 3 layers; it can be repeated multiple times to form multiple layers. The number of layers in the conductive paste coating can be 2 or more but less than 20 layers, or 3 or more but less than 15 layers, preferably 3 or more but less than 10 layers. Spacers, for example, can be made of plastics such as polyethylene terephthalate.

[0075] The conductive paste is preferably used to form a conductive film by coating a ceramic substrate with the conductive paste and then firing it. The conductive paste can be used to form circuit patterns by screen printing, which can maintain the shape of the coating and form a conductive film with high adhesion to the ceramic substrate.

[0076] The ceramic substrate preferably comprises at least one material selected from alumina (Al2O3), aluminum nitride (AlN), and silicon nitride (Si3N4). Among these, aluminum nitride (AlN) substrates with high thermal conductivity and silicon nitride (Si3N4) substrates with high fracture toughness are preferred. When forming a conductive film of 100 μm or more on aluminum nitride (AlN) substrates and silicon nitride (Si3N4) substrates, it is more difficult to improve the adhesion strength compared to alumina (Al2O3). The present invention can form a conductive film with high adhesion even when forming a conductive film of 100 μm or more on aluminum nitride (AlN) substrates and silicon nitride (Si3N4) substrates.

[0077] Good ceramic substrates may contain zirconium oxide (ZrO) in addition to alumina (Al2O3).

[0078] The ceramic substrate is preferably an alumina (Al2O3) substrate, an aluminum nitride (AlN) substrate, or a silicon nitride (Si3N4) substrate. These substrates have high thermal conductivity and good heat dissipation. An alumina substrate refers to a ceramic substrate whose main component is alumina (Al2O3). In this specification, the main component of a ceramic substrate refers to the most abundant component among the components of the ceramic substrate, and specifically, a component comprising 50% by mass or more. An alumina substrate preferably contains 95% by mass or more of alumina. An aluminum nitride substrate has aluminum nitride as its main component, and preferably contains 95% by mass or more of aluminum nitride in the ceramic substrate. A silicon nitride substrate has silicon nitride as its main component, and preferably contains 95% by mass or more of silicon nitride in the ceramic substrate.

[0079] The conductive film is a film formed by coating the aforementioned conductive paste onto a ceramic substrate and then firing it. Methods for coating the conductive paste onto the ceramic substrate include screen printing, gravure printing, rod coating, blade coating, slot coating, gravure coating, and spraying. To facilitate the formation of precise patterns on the ceramic substrate, the aforementioned conductive paste is preferably formed into a coating film by screen printing.

[0080] The thickness of the coating film (dry film) formed by the conductive paste after applying it to a ceramic substrate and then drying and firing it is preferably 100 μm or more, more preferably 150 μm or more, and may also be 200 μm or more. By producing a film thickness within the above range, it is possible to handle large currents of tens to about 100 A, and the ceramic wiring substrate can be used as a wiring substrate for power devices. There is no particular limitation on the upper limit of the film thickness; for example, it may be 1000 μm or less, 800 μm or less, or 700 μm or less. The coating film formed by applying the conductive paste to the ceramic substrate may be a coating film formed by screen printing and laminating multiple layers. In addition, when applying the conductive paste to the ceramic substrate, the thickness of the first layer may be different from the thickness of the second and subsequent layers.

[0081] The conductive film is preferably formed by applying the aforementioned conductive paste to a ceramic substrate and then firing it. The firing temperature of the coating film is simply a temperature at which the (C) organic carrier in the aforementioned conductive paste volatilizes and the (B) glass powder melts. The firing temperature of the coating film formed by applying the aforementioned conductive paste to the ceramic substrate is preferably in the range of 700°C or higher and 1500°C or lower, more preferably in the range of 800°C or higher and 1200°C or lower, and even more preferably in the range of 850°C or higher and 1100°C or lower. If the firing temperature of the coating film formed by applying the aforementioned conductive paste to the ceramic substrate is in the range of 700°C or higher and 1500°C or lower, the (C) organic carrier in the conductive paste volatilizes, and the (B) glass powder melts and acts as a binder, resulting in a conductive film in which the (A) conductive particles are tightly adhered to the ceramic substrate. Regarding the firing atmosphere of the coating film, a nitrogen atmosphere is preferred in order to obtain a conductive film with good adhesion to the ceramic substrate.

[0082] Furthermore, the thickness of the conductive film (conductive film) formed by applying a conductive paste to a ceramic substrate, drying it, and then firing the conductive paste is preferably 100 μm or more, more preferably 200 μm or more, and even more preferably 250 μm or more. By achieving a film thickness within the above range, large currents of tens to approximately 100 A can be handled, allowing the ceramic wiring substrate to be used as a wiring substrate for power devices. There is no particular limitation on the upper limit of the film thickness (conductive film); for example, the film thickness can be less than 1000 μm, less than 800 μm, or less than 750 μm. Since the conductive paste has good wettability on the ceramic substrate, the conductive film formed by applying and firing the conductive paste can be repeatedly applied, thus obtaining a conductive film with a thickness of 100 μm or more. Sometimes, films with a thickness of 100 μm or more are also referred to as thick films. In addition, conductive pastes that can form conductive films with a thickness of 100 μm are also called conductive pastes for thick films. For example, a coating film formed by stacking multiple layers through screen printing cannot be distinguished from each other after firing, becoming a conductive film of a single thickness.

[0083] Preferably, the ceramic substrate is an alumina (Al2O3) substrate, and the conductive film with a thickness of 250 μm, formed by coating the alumina (Al2O3) substrate with the aforementioned conductive paste and then firing it, has a compressive shear bond strength of 1.0 N / mm² as measured according to JIS K6852. 2 The above is preferred, and more preferably is 1.5 N / mm. 2 The above is further preferred to be 2.0 N / mm. 2The above is an explanation of the advantages of aluminum oxide (Al2O3) substrates. While alumina (Al2O3) substrates exhibit high thermal conductivity and excellent heat dissipation, the conductive paste has lower wettability compared to typical copper substrates, resulting in lower adhesion as expressed by compressive shear strength. The conductive paste disclosed herein contains glass powder with a contact angle of 40 degrees or less relative to the ceramic substrate after molten glass. Therefore, even when forming a conductive film with a thickness of 100 μm or more by coating the conductive paste and then firing, a conductive film with high compressive shear strength can be obtained.

[0084] Preferably, the ceramic substrate is an aluminum nitride (AlN) substrate, and the conductive film with a thickness of 250 μm, formed by coating the aluminum nitride (AlN) substrate with the aforementioned conductive paste and then firing it, has a compressive shear bond strength of 1.0 N / mm² as measured according to JIS K6852. 2 The above is preferred, and more preferably is 1.5 N / mm. 2 The above is further preferred to be 2.0 N / mm. 2 above.

[0085] While aluminum nitride (AlN) substrates offer higher thermal conductivity and superior heat dissipation compared to alumina (Al2O3) substrates, they suffer from lower adhesion, as expressed by compressive shear strength. The conductive paste disclosed herein, by including molten glass powder with a contact angle of less than 40 degrees relative to the ceramic substrate, achieves a compressive shear strength of 1.0 N / mm² when forming a conductive film with a thickness of 250 μm. 2 The above are conductive films with high adhesion.

[0086] Preferably, the ceramic substrate is a silicon nitride (Si3N4) substrate, and the conductive film with a thickness of 250 μm, formed by coating the silicon nitride (Si3N4) substrate with the aforementioned conductive paste and then firing it, has a compressive shear bond strength of 1.0 N / mm as measured according to JIS K6852. 2 The above is preferred, and more preferably is 1.5 N / mm. 2 The above is further preferred to be 2.0 N / mm. 2 The above is an explanation of the advantages of silicon nitride (Si3N4) substrates over alumina (Al2O3) substrates. While silicon nitride (Si3N4) substrates offer higher thermal conductivity and better heat dissipation, they suffer from lower adhesion, as expressed by compressive shear strength. The conductive paste disclosed herein comprises molten glass powder with a contact angle of 40 degrees or less relative to the ceramic substrate. When the conductive paste is coated and sintered to achieve a film thickness of 100 μm or more, a compressive shear strength of 1.0 N / mm can be obtained when forming a conductive film with a thickness of 250 μm. 2 The above are conductive films with high adhesion.

[0087] The conductive film formed by coating the aforementioned conductive paste onto a ceramic substrate and firing it can form circuit patterns by screen printing. It can form a conductive film with high adhesion to the ceramic substrate and a large film thickness, and can be used to form the circuit pattern of a ceramic circuit board.

[0088] The conductive film formed by coating the aforementioned conductive paste onto a ceramic substrate and firing it can form circuit patterns by screen printing. It can form a conductive film with high adhesion to the ceramic substrate and large film thickness, and can be suitable for use in electronic devices that include wiring substrates for power devices.

[0089] Example

[0090] The present invention will now be specifically described through examples. The present invention is not limited to these examples. In the following examples and comparative examples, unless otherwise specified, the figures representing the proportions of each component in the resin composition are as follows: the composition of glass powder in Table 1 represents % by mass; the components of the conductive paste in Table 2 represent parts by mass.

[0091] (B) Glass powder

[0092] Table 1 provides the glass composition, softening point, and contact angle relative to each ceramic substrate, measured under the conditions described below, for glass powders (B) GF1 to GF9. GF1, GF3, GF7, and GF8 are bismuth (Bi2O3)-based glass powders containing Bi (Bi2O3) as the main component. GF2 and GF9 are tellurium-vanadium (TeO2-V2O5)-based glass powders containing Te (TeO2) and V as the main components. GF4 is a zinc borosilicate (ZnO)-based glass powder containing less than 50% by mass of Zn (ZnO) as the main component. GF5 is a SrO-based glass powder containing silicon and strontium as essential components, and GF6 is a SiO2-based glass powder containing silicon (SiO2) as the main component. In Table 1, the symbol "-" indicates a value for no corresponding item.

[0093] Ceramic substrate

[0094] Alumina (Al2O3) substrate: The content of alumina (Al2O3) is 96% by mass relative to the total amount, the thermal conductivity is 30 W / m·K, and the thickness is 0.15 mm or more and 1.2 mm or less.

[0095] Aluminum nitride (AlN) substrate: The aluminum nitride (AlN) content is 96% by mass relative to the total amount, the thermal conductivity is 200 W / m·K, and the thickness is 0.25 mm or more and 1.5 mm or less.

[0096] Silicon nitride (Si3N4) substrate: The content of silicon nitride (Si3N4) is 96% by mass relative to the total amount, the thermal conductivity is 80 W / m·K, and the thickness is 0.25 mm to 0.63 mm.

[0097] Measurement of contact angle

[0098] The (B) glass powders shown in Table 1 were pressed into cylindrical shapes with a diameter of 5 mm and a thickness of 5 mm to form molded bodies. The (B) glass powders with molded bodies were then placed on ceramic substrates to prepare samples for contact angle measurement. The samples were melted using a belt furnace (manufactured by JTEKT Thermo System Co., Ltd.) at a temperature of 850°C to 900°C for 10 minutes in a nitrogen atmosphere (nitrogen: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less). The contact angle of the molten glass powder relative to the ceramic substrate was measured according to JIS K3257. The time from placing the sample in the belt furnace to removing it was 60 minutes. The contact angles of each glass powder relative to each ceramic substrate are shown in Table 1. It should be noted that the contact angle relative to a copper substrate was also measured for reference.

[0099] Determination of the softening point of glass powder

[0100] The softening point of the glass powder was determined using a differential thermal-thermogravimetric analyzer (TG-DTA2000SA, manufactured by BRUKERAXS) at a temperature of 900°C in a nitrogen atmosphere (nitrogen: ≥99.9% by volume, oxygen: ≤0.001% by volume (10 ppm by volume)).

[0101]

[0102] The following materials are used: (B) glass powders of GF1 to GF9 as shown in Table 1, (A) conductive particles, and (C) organic carriers.

[0103] (A) Conductive particles

[0104] Copper powder (Cu powder) 1: An aggregate of copper-containing particles, spherical in shape, with an average particle size of 2.5 μm, produced by atomization.

[0105] Copper powder (Cu powder) 2: An aggregate of copper-containing particles, spherical, with an average particle size of 3.5 μm, produced by atomization.

[0106] Copper powder (Cu powder) 3: An aggregate of copper-containing particles produced by atomization, in the form of flakes (thin sheets), with an average particle size of 4.0 μm.

[0107] (C) Organic carrier

[0108] Resin 1: Ethyl cellulose

[0109] Resin 2: (Meth)acrylate

[0110] Solvent: α-terpineol

[0111] Examples 1-10 and Comparative Examples 1-2

[0112] A conductive paste was prepared by mixing and dispersing (A) conductive particles, (B) glass powder, and (C) organic carrier using a three-roll mill in the proportions shown in Table 2. The values ​​for each component in Table 2 represent parts by mass. In Table 2, the symbol "-" indicates a value for which there is no corresponding item.

[0113] (A) Volume average particle size D50 of conductive powder based on laser diffraction scattering method

[0114] The volume average particle size (median diameter) D50 of Cu powders 1 to 3, which are (A) conductive powders, was determined by laser diffraction scattering method using a particle size distribution measuring device (trade name: Microtrac MT3000II, manufactured by Microtrac Bel Co., Ltd.).

[0115] (C) Determination of the decomposition temperature of the resin contained in the organic carrier

[0116] (C) The decomposition temperature of the organic carrier was determined using a differential thermal-thermogravimetric analyzer (TG-DTA2000SA, BRUKERAXS) at a nitrogen atmosphere (nitrogen: ≥99.9 vol%, oxygen: ≤0.001 vol% (10 vol ppm)). Specifically, the decomposition temperature of the organic carrier (C) is the decomposition temperature of the resin contained in the organic carrier (C). The results are recorded in Table 2.

[0117] Determination of viscosity and thixotropic index (TI) of conductive pastes

[0118] Using an HB type viscometer (BrookFields) (SC4-14 rotor), the viscosity of each conductive paste in the examples and comparative examples was measured at various rotational speeds (first viscosity (1 rpm), second viscosity (20 rpm)) at 25°C and 1 rpm. The viscosity V measured at 1 rpm for each conductive paste was recorded. 1rpm Viscosity V measured at a rotational speed of 20 rpm 20rpm The ratio is set as the thixotropic index (TI) and is calculated using the following formula (1). The results are recorded in Table 2.

[0119] TI = V 1rpm / V 20rpm (1)

[0120] From the viewpoint of being able to form a coating film (dry film) of 100 μm or more, the thixotropic index (TI) is preferably in the range of 1 to 22, more preferably in the range of 1.5 to 15, and even more preferably in the range of 2 to 10. By being within the above range, the diffusion of the paste coating surface can be suppressed, ensuring that the amount of conductive paste applied from the opening of the screen-printed mask is maintained, and the height of the coating film is preserved.

[0121] conductive film

[0122] Using the following printing apparatus and mask, the conductive pastes of the examples and comparative examples were applied to the ceramic substrates by screen printing to form... Figure 1 The pattern shown was dried at 150°C for 10 minutes using a box dryer to obtain a dried film. Figure 1 This is an example of a pattern in which a conductive paste is applied to a ceramic substrate. Figure 1 This refers to a conductive film formed by applying a conductive paste in a given pattern onto a ceramic substrate, or a conductive film formed by firing the coating. Figure 1 The pattern shown is a coating that appears as a quadrilateral when viewed from above.

[0123] One side of the coating is 2 mm. Subsequently, the coating formed on the ceramic substrate was fired in a belt furnace at a maximum temperature of 900°C in a nitrogen atmosphere (nitrogen: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less) to obtain the conductive film for testing. The time from placing the coating formed on the ceramic substrate into the belt furnace to removing it was 60 minutes. The thickness of the fired conductive film was 250 μm.

[0124] The printing equipment uses a screen printing machine (MT-650TVC, manufactured by Micro-tec Co., Ltd.).

[0125] Specifically, the coating is formed as shown below.

[0126] For the first layer of the coating, a conductive paste is applied using a 60-mesh mask with an emulsion film thickness of 20 μm to form a coating film (dried film) with a thickness of 20 μm after drying.

[0127] Then, for the first layer of dried film, a conductive paste was repeatedly coated and dried using a 150-mesh mask with an emulsion film thickness of 102 μm to form the second to seventh layers of coating film. As a result, a dried film with an overall thickness of 300 μm was obtained.

[0128] Subsequently, the coating formed on the ceramic substrate was fired in a belt furnace at a maximum temperature of 900°C under a nitrogen atmosphere (nitrogen: ≥99.9 vol% and oxygen: ≤0.001 vol% (10 vol ppm)) to obtain the conductive film for testing. The time from placing the coating formed on the ceramic substrate into the belt furnace to removing it was 60 minutes. The thickness of the fired conductive film was 250 μm.

[0129] Determination of compressive shear bond strength of conductive film

[0130] Using the conductive film used in the test, the compressive shear bond strength of a 250 μm thick conductive film formed on each ceramic substrate was measured using a strength testing machine (Model 1605HTP, manufactured by Aikoh Engineering Co., Ltd.) according to JIS K6852. The compressive shear bond strength was 2.0 N / mm². 2 Under the above conditions, the rating is "A" (good), with a compressive shear bond strength of 1.0 N / mm. 2 Above and less than 2.0 N / mm 2 In this case, the rating is "B" (good), with a compressive shear strength of less than 1.0 N / mm². 2 In the case of failure, the evaluation is "C" (NG: unacceptable). The results are recorded in Table 2.

[0131]

[0132] As shown in Tables 1 and 2, the conductive pastes of Examples 1 to 10 contain (B-1) glass powder with a contact angle of less than 40 degrees relative to the ceramic substrate, thus exhibiting good wettability to the ceramic substrate and enabling the formation of a conductive film with high adhesion between the conductive powder and the ceramic substrate. Specifically, the conductive pastes of Examples 1 to 10 all demonstrate excellent adhesion to alumina (Al2O3) substrates, and their compressive shear bond strength is 1.0 N / mm². 2 That's all. Furthermore, the conductive pastes of Examples 1-3 and Examples 5-7 also exhibited good adhesion to the aluminum nitride (AlN) substrate, and their compressive shear bond strength was 1.0 N / mm². 2 That's all. Furthermore, the conductive pastes of Examples 1, 2, and 5-7 also exhibited good adhesion to the silicon nitride (Si3N4) substrate, and their compressive shear bond strength was 1.0 N / mm². 2That's all. Furthermore, comparing Example 2, which uses GF2 as a tellurium-vanadium (TeO2-V2O5) based glass powder, with Example 10, which uses GF9, the conductive paste from Example 2 using GF2 exhibits better adhesion to both the aluminum nitride (AlN) and silicon nitride (Si3N4) substrates. This can be presumably because the GF2 glass powder has a lower softening point, allowing it to melt sufficiently during firing, thereby further improving adhesion.

[0133] Figure 1 This is a photograph showing the appearance of the conductive film 1 obtained by screen printing the conductive paste of Example 1 onto an alumina (Al2O3) substrate, which serves as a ceramic substrate 2, and then firing it. Figure 1 As shown, even small quadrilateral patterns can be formed with excellent precision by screen printing, which is used to fire the conductive film 1 obtained by coating a conductive paste onto a ceramic substrate 2.

[0134] The conductive pastes in Comparative Examples 1 and 2, because they do not contain (B-1) glass powder with a contact angle of less than 40 degrees relative to the ceramic substrate, have lower wettability to the ceramic substrate, and their compressive shear bond strength to each ceramic substrate is as low as less than 1.0 N / mm. 2 .

[0135] Industrial availability

[0136] The conductive paste and conductive film of the present disclosure can be suitably used for circuit patterns on ceramic circuit boards, or circuit boards such as wiring boards for power devices, and electronic devices including these boards.

[0137] Explanation of reference numerals in the attached figures

[0138] 1. A coating or conductive film formed by a conductive paste; 2. A ceramic substrate.

Claims

1. A conductive paste comprising (A) a conductive powder, (B) a glass powder, and (C) an organic carrier. The glass powder (B) comprises glass powder that, when the glass powder is disposed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, has a contact angle of less than 40 degrees relative to the ceramic substrate after melting, as determined by JIS R3257.

2. The conductive paste according to claim 1, wherein, The conductive powder (A) comprises copper powder, and contains more than 50 parts by mass of the copper powder relative to 100 parts by mass of the conductive powder (A).

3. The conductive paste according to claim 1 or 2, wherein, The conductive powder of (A) has an average particle size D50 of 0.5 μm or more and 10.0 μm or less, as determined by laser diffraction scattering.

4. The conductive paste according to any one of claims 1 to 3, wherein, The glass powder (B) comprises at least one type selected from bismuth-based glass powder, tellurium-based glass powder, and zinc borosilicate-based glass powder.

5. The conductive paste according to any one of claims 1 to 4, wherein, The content of the glass powder in (B) is in the range of more than 1 part by mass and less than 30 parts by mass relative to 100 parts by mass of the conductive powder in (A).

6. The conductive paste according to any one of claims 1 to 5, wherein, The temperature difference, in absolute value, between the softening point of the glass powder (B) and the decomposition temperature of the organic carrier (C) in a nitrogen atmosphere, as measured by a differential thermal-thermogravimetric analyzer, is within 200°C.

7. The conductive paste according to any one of claims 1 to 6, wherein, The softening point of the glass powder (B) is lower than the decomposition temperature of the organic carrier (C) in a nitrogen atmosphere as determined by a differential thermal-thermogravimetric analyzer.

8. The conductive paste according to any one of claims 1 to 7, wherein, The content of the resin solid component in the organic carrier (C) is in the range of 0.5 parts by mass and 10 parts by mass relative to 100 parts by mass of the conductive powder (A).

9. The conductive paste according to any one of claims 1 to 8, used for forming a conductive film with a thickness of 100 μm or more.

10. The conductive paste according to any one of claims 1 to 9, used in a conductive film, Formation of a conductive film formed by coating a conductive paste onto the ceramic substrate and firing it.

11. The conductive paste according to any one of claims 1 to 10, wherein, The ceramic substrate comprises at least one of alumina (Al2O3), aluminum nitride (AlN), and silicon nitride (Si3N4).

12. A conductive film, which is formed by coating a ceramic substrate with the conductive paste according to any one of claims 1 to 11 and then firing it.

13. The conductive film according to claim 12, wherein the film thickness is 100 μm or more.

14. The conductive film according to claim 12 or 13, wherein, The ceramic substrate is an alumina (Al2O3) substrate. The conductive film with a thickness of 250 μm, formed by coating the conductive paste onto the alumina (Al2O3) substrate and then firing it, has a compressive shear bond strength of 1.0 N / mm², as measured according to JIS K6852. 2 above.

15. The conductive film according to claim 12 or 13, wherein, The ceramic substrate is an aluminum nitride (AlN) substrate. The conductive film with a thickness of 250 μm, formed by coating the conductive paste onto the aluminum nitride (AlN) substrate and then sintering, has a compressive shear bond strength of 1.0 N / mm², as measured according to JIS K6852. 2 above.

16. The conductive film according to claim 15 or 16, wherein, The ceramic substrate is a silicon nitride (Si3N4) substrate. The compressive shear bond strength of a 250 μm thick conductive film, measured according to JIS K6852, formed by coating the conductive paste onto the silicon nitride (Si3N4) substrate and then sintering, is 1.0 N / mm². 2 above.

17. A ceramic circuit board comprising a conductive film formed by coating a conductive paste according to any one of claims 1 to 11 onto a ceramic substrate and then firing it.

18. An electronic component comprising a conductive film formed by coating a conductive paste, as described in any one of claims 1 to 11, onto a ceramic substrate and then firing it.

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