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 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 includes (A) a conductive powder, (B) a glass frit, and (C) an organic vehicle. The (B) glass frit may be a glass frit in which, when the glass frit is disposed on a ceramic substrate and is melted under the condition of 900°C in a nitrogen atmosphere, the contact angle of the molten glass frit with respect to the ceramic substrate measured in conformance with JIS R3257 is 40 degrees or less.　

Description

Conductive paste, conductive film, ceramic circuit board and electronic components

[0001] The present invention relates to a conductive paste, a conductive film, a ceramic circuit board, and an electronic component.

[0002] As ceramic substrates for use in power devices used in power control of converters, inverters, and the like, substrates with good heat dissipation properties, such as DBC (Direct Bonded Copper) substrates and AMC (Active Metal Brazed Copper) substrates, are desired. For example, an active metal method is used to manufacture AMC substrates. In the active metal method, a bonding agent such as a brazing material is applied to the surface of a ceramic substrate, and a metal plate such as a copper plate is placed on top of the applied bonding agent. The metallization process is performed by firing the substrate at a high temperature of, for example, 900°C to 1200°C, thereby forming a metal layer for forming a wiring pattern, etc.

[0003] DBC substrates or AMC substrates have a metallized metal layer on a ceramic substrate, and require complicated processes such as etching to form complex wiring patterns. Etching processes require wastewater treatment, which places a burden on the environment.

[0004] In order to form a wiring pattern directly on the surface of a ceramic substrate, for example, Patent Document 1 discloses a conductive paste containing copper powder that is applied directly to a ceramic substrate, dried, and fired to form a wiring pattern.

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

[0006] JP 2015-149162 A JP 2008-226771 A

[0007] A conductive paste containing copper as a conductive powder has poor adhesion to a ceramic substrate, and there is a need to improve the adhesion between the ceramic substrate and the conductive paste. For example, when a conductive paste is applied to a ceramic substrate and then fired to a thickness of 100 μm or more after firing to obtain a conductive film, the poor adhesion between the conductive film and the ceramic substrate can cause partial peeling of the conductive film, resulting in defects such as poor appearance.

[0008] Therefore, an 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 a circuit pattern by a screen printing method and can form a conductive film that has high adhesion to a ceramic substrate.

[0009] The means for solving the above problems are as follows, and the present invention includes the following aspects.

[0010] [1] A conductive paste comprising (A) a conductive powder, (B) a glass frit, and (C) an organic vehicle, wherein the (B) glass frit is a glass frit such that, when the glass frit is placed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, the contact angle of the molten glass frit with the ceramic substrate is 40 degrees or less, as measured in accordance with JIS R3257. [2] The conductive paste according to [1], wherein the (A) conductive powder contains copper powder, and the copper powder is contained in an amount of 50 parts by mass or more per 100 parts by mass of the (A) conductive powder. [3] The conductive paste according to [1] or [2], wherein the average particle size (D50) of the (A) conductive powder, as measured by a laser diffraction scattering method, is in the range of 0.5 μm or more and 10.0 μm or less. [4] The conductive paste according to any one of [1] to [3], wherein the (B) glass frit comprises at least one selected from the group consisting of a bismuth-based glass frit, a tellurium-based glass frit, and a zinc borosilicate-based glass frit. [5] The conductive paste according to any one of [1] to [4], wherein the content of the (B) glass frit is in the range of 1 part by mass to 30 parts by mass per 100 parts by mass of the (A) conductive powder. [6] The conductive paste according to any one of [1] to [5], wherein the difference between the softening point of the (B) glass frit and the decomposition temperature of the (C) organic vehicle measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere is within 200°C in absolute value. [7] The conductive paste according to any one of [1] to [6], wherein the softening point of the (B) glass frit is lower than the decomposition temperature of the (C) organic vehicle measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere. [8] The conductive paste according to any one of [1] to [7], wherein the content of the resin solid content in the (C) organic vehicle is in the range of 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the (A) conductive powder. [9] The conductive paste according to any one of [1] to [8], which is used to form a conductive film with a film thickness of 100 μm or more.

[10] The conductive paste according to any one of [1] to [9] for a conductive film, which is used to form a conductive film by applying the conductive paste to the ceramic substrate and firing the same.

[11] The ceramic substrate is made of aluminum oxide (Al. ２ O ３ ), aluminum nitride (AlN) and silicon nitride (Si ３ N ４ The conductive paste according to any one of the above [1] to

[10] , which contains at least one selected from the group consisting of aluminum oxide (Al).

[12] A conductive film obtained by applying the conductive paste according to any one of the above [1] to

[11] to a ceramic substrate and firing the applied paste.

[13] The conductive film according to the above

[12] , which has a film thickness of 100 μm or more.

[14] The ceramic substrate is made of a conductive material containing aluminum oxide (Al ２ O ３ ) substrate, and the aluminum oxide (Al ２ O ３ ) The conductive paste is applied to a substrate and fired to form a conductive film having a thickness of 250 μm, and the compressive shear adhesive strength measured in accordance with JIS K6852 is 1.0 N / mm ２

[15] The conductive film according to

[12] or

[13] , wherein the ceramic substrate is an aluminum nitride (AlN) substrate, and the conductive film is formed by applying the conductive paste to the aluminum nitride (AlN) substrate and firing the conductive paste to a thickness of 250 μm, and the compressive shear adhesive strength measured in accordance with JIS K6852 is 1.0 N / mm ２

[16] The conductive film according to the above

[12] or

[13] . ３ N ４ ) substrate, and the silicon nitride (Si ３ N ４ ) The conductive paste is applied to a substrate and fired to form a conductive film having a thickness of 250 μm, and the compressive shear adhesive strength measured in accordance with JIS K6852 is 1.0 N / mm ２The conductive film according to

[12] or

[13] above.

[17] A ceramic circuit board comprising a conductive film obtained by applying the conductive paste according to any one of [1] to

[11] above to a ceramic substrate and firing the same.

[18] An electronic component comprising a conductive film obtained by applying the conductive paste according to any one of [1] to

[11] above to a ceramic substrate and firing the same.

[0011] According to the present invention, a conductive paste, a conductive film, a ceramic circuit board, and an electronic component are provided which can form a circuit pattern by a screen printing method and can form a conductive film that has high adhesion to a ceramic substrate even when the conductive paste is applied to the ceramic substrate and fired so that the thickness after firing is 100 μm or more.

[0012] FIG. 1 is a diagram showing an example of a pattern in which a conductive paste is applied to a ceramic substrate.

[0013] The conductive paste, conductive film, ceramic substrate, and electronic component according to the present disclosure will be described below based on embodiments. The embodiments shown below are examples for embodying 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, "to" means that the preceding and following numerical values ​​or symbols including numerical values ​​are included as upper and lower limits, and represent values ​​from above to below.

[0014] A conductive paste according to an embodiment of the present invention includes (A) a conductive powder, (B) a glass frit, and (C) an organic vehicle, and the glass frit (B) includes glass frit such that when the glass frit is placed on a ceramic substrate and melted at 900°C in a nitrogen atmosphere, the contact angle of the molten glass frit with the ceramic substrate measured in accordance with JIS R3257 is 40 degrees or less.

[0015] The conductive paste contains (B) glass frit, which has a contact angle of 40 degrees or less with respect to a ceramic substrate when melted under specific conditions, and therefore has good wettability with respect to the ceramic substrate, and can form a conductive film with high adhesion between the conductive powder and the ceramic substrate. Furthermore, the conductive paste contains (A) conductive powder, as well as the above-mentioned (B) glass frit and (C) organic vehicle, and therefore can form a circuit pattern with high precision by screen printing without requiring an etching process.

[0016] The (A) conductive powder preferably contains copper powder, and preferably contains 50 parts by mass or more of copper powder per 100 parts by mass of the (A) conductive powder. In the present specification, copper powder may also be referred to as "(A-1) copper powder." The (A) conductive powder is contained to impart electrical conductivity and heat dissipation to the conductive film. Examples of the (A) conductive powder include copper powder, nickel powder, silver powder, and palladium powder. The (A) conductive powder preferably contains copper powder because the (A) conductive powder improves electrical conductivity and heat dissipation and enables the formation of a circuit pattern using copper wiring by a screen printing method. The (A) conductive powder preferably contains 60 parts by mass or more of (A-1) copper powder per 100 parts by mass of the (A) conductive powder, more preferably 80 parts by mass or more, even more preferably 90 parts by mass or more. Alternatively, the (A) conductive powder may be entirely copper powder, and the (A) conductive powder may be 100 parts by mass of copper powder. By including copper powder in the above range, migration can be suppressed, and a circuit pattern with copper wiring can be formed by screen printing.

[0017] (A-1) Copper powder is an aggregate of particles mainly composed of copper, and may contain particles made of copper oxide, or may contain unavoidable impurities other than copper oxide. Copper oxide is copper(I) oxide (Cu ２Alternatively, copper(II) oxide (CuO) or copper(II) oxide (CuO) may be used. Here, the term "main component" refers to the component with the largest content among the components constituting the copper powder. The copper powder is preferably an aggregate of copper particles for electrical conductivity and / or heat dissipation. When the (A-1) copper powder contains both copper particles and copper oxide particles, it is preferable that the copper oxide powder be contained in an amount of 1 part by mass or more and 20 parts by mass or less, when the total amount of the copper powder is taken as 100 parts by mass.

[0018] The (A) conductive powder preferably has an average particle size (D50) measured by laser diffraction scattering in the range of 0.5 μm to 10.0 μm, more preferably 1.0 μm to 8.0 μm, and even more preferably 1.5 μm to 5.0 μm. When the average particle size of the (A) conductive powder is within the above range, a conductive paste containing the (A) conductive powder can easily form a circuit pattern with high precision using a screen printing method, and can easily form a thick conductive film with a film thickness of 100 μm or more by multiple printing processes. To obtain a dense conductive film, the (A) conductive powder may be a mixture of one or more types of conductive powders with different average particle sizes (D50). The average particle size (D50) measured by laser diffraction scattering refers to the median diameter corresponding to the cumulative 50% in the volume-based particle size distribution.

[0019] The particles constituting the (A) conductive powder may be spherical, scaly (flake-like), conical, fibrous, etc. The particles constituting the (A) conductive powder are preferably spherical and / or scaly, because they have good smoothness and are easy to print by screen printing.

[0020] The (A) conductive powder is preferably contained in a range of 70% by mass to 95% by mass, more preferably 75% by mass to 90% by mass, and even more preferably 75% by mass to 88% by mass, based on 100% by mass of the total amount of the conductive paste. When the (A) conductive powder is contained within this range based on 100% by mass of the total amount of the conductive paste, a thick conductive film having good electrical conductivity and heat dissipation properties and a film thickness of 100 μm or more can be obtained.

[0021] (B) Glass frit includes glass frit that, when placed 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 as measured in accordance with JIS R 3257. In the present specification, glass frit that has a contact angle of 40 degrees or less with the ceramic substrate may be referred to as "(B-1) glass frit."

[0022] In the present specification, the nitrogen atmosphere preferably contains 99% or more by volume of nitrogen gas. The nitrogen atmosphere may also contain 99.9% or more by volume of nitrogen gas. The nitrogen atmosphere may contain less than 1% by volume of oxygen, and the oxygen content in the nitrogen atmosphere is preferably 0.5% or less by volume, may be 0.1% by volume (1000 ppm by volume) or less, may be 0.01% by volume (100 ppm by volume) or less, preferably 0.001% by volume (10 ppm by volume) or less, and may be 0.00001% by volume (0.1 ppm by volume) or more. In order to measure the contact angle of the (B) glass frit with respect to the substrate, the atmosphere in which the (B) glass frit placed on the ceramic substrate is melted is preferably a nitrogen atmosphere in order to suppress the reaction of the glass frit. The time for melting the glass frit (B) at 900°C is not particularly limited as long as it is a time sufficient for melting the glass frit. For example, after the temperature inside the furnace reaches 900°C, the time is preferably 5 minutes or more and 15 minutes or less, and may be 8 minutes or more and 12 minutes or less.

[0023] The (B) glass frit is preferably formed into a cylindrical molded body having a diameter of 5 mm and a height of 5 mm by a mold press molding method, and then placed on a ceramic substrate. A furnace, such as a belt furnace, can be used when measuring the contact angle of the (B) glass frit with the ceramic substrate. The contact angle of the molten (B) glass frit is the contact angle with the ceramic substrate, not with a copper plate or copper oxide powder.

[0024] The (B) glass frit includes a (B-1) glass frit having a contact angle of 40 degrees or less when molten with a ceramic substrate. The contact angle of the molten glass frit with the glass substrate is preferably 30 degrees or less, more preferably 20 degrees or less, and even more preferably 10 degrees or less. The lower limit of the contact angle of the molten glass frit with the glass substrate is not particularly specified, but is, for example, 1 degree or more. When the conductive paste includes a (B-1) glass frit having a contact angle with the ceramic substrate within the above range, the wettability of the conductive paste with the ceramic substrate is improved, allowing for the formation of a conductive film adhered to the ceramic substrate, and a thick conductive film having a thickness of 100 μm or more can be formed. Note that when forming a thick conductive film having a thickness of 100 μm or more, the shrinkage of the coating film is greater than that of a thin film having a thickness of less than 100 μm, and therefore, a thicker coating film may result in weaker adhesion strength. The present invention has discovered that even a conductive film having a thickness of 100 μm or more can have improved adhesion to a ceramic substrate.

[0025] The content of the (B) glass frit in the conductive paste is preferably in the range of 1 part by mass to 30 parts by mass, more preferably 2 parts by mass to 20 parts by mass, and even more preferably 3 parts by mass to 15 parts by mass, per 100 parts by mass of the (A) conductive particles. When the content of the (B) glass frit in the conductive paste is within the above range, the molten (B) glass frit bonds the (A) conductive powder to the ceramic substrate, forming a thick conductive film with excellent adhesion and a film thickness of 100 μm or more. When the content of the (B) glass frit in the conductive paste is less than 2 parts by mass per 100 parts by mass of the (A) conductive powder, the adhesion between the ceramic substrate and the conductive film may not be sufficiently improved. When the content of the (B) glass frit in the conductive paste is more than 30 parts by mass per 100 parts by mass of the (A) conductive particles, the content of the (A) conductive particles relative to the total amount of the conductive paste becomes relatively small, and the electrical conductivity or heat dissipation of the resulting conductive film may be reduced.

[0026] When the (B) glass frit is a (B-1) glass frit having a contact angle of 40 degrees or less when molten with a ceramic substrate, the softening point of the (B-1) glass frit 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. The lower limit of the softening point is not particularly limited, but may be 250°C or more or 300°C or more. When the (B) glass frit is a (B-1) glass frit having a contact angle of 40 degrees or less when molten with a ceramic substrate, as long as the softening point is within the above range, the (B-1) glass frit will be sufficiently melted during firing, thereby improving the adhesion between the ceramic substrate and the conductive film. The softening point of the glass frit can be measured using a simultaneous differential thermal and thermogravimetric analyzer (e.g., TG-DTA2000SA, manufactured by BRUKERAX).

[0027] The glass frit (B) preferably includes at least one selected from the group consisting of a bismuth-based glass frit, a tellurium-based glass frit, and a zinc borosilicate-based glass frit.

[0028] The bismuth-based glass frit is a glass frit containing Bi as a main component in terms of oxide as an essential component, and may contain other optional components. In this specification, the main component of the glass frit refers to the component with the largest content in terms of oxide among the components constituting the glass frit. The (B) glass frit preferably contains a bismuth-based glass frit as a (B-1) glass frit having a contact angle of the molten glass frit with the ceramic substrate of 40 degrees or less. The bismuth-based glass frit contains Bi (Bi ２ O ３ The bismuth-based glass frit preferably contains 50 to 95 mass %, more preferably 70 to 90 mass %, and even more preferably 75 to 90 mass % of B (B ) in terms of oxide relative to the total amount of the bismuth-based glass frit. ２ O ３) is preferably contained in an amount of 2 to 40 mass %, more preferably in an amount of 3 to 30 mass %, and even more preferably in an amount of 3 to 15 mass %. ２ O ３ ) is the main component of bismuth-based glass frit. ２ O ３ If the content of Bi contained in the bismuth-based glass frit is less than the lower limit of the above range, the softening point of the glass frit will be high, and the contact angle of the molten glass frit with respect to the ceramic substrate measured by the above method will be large, exceeding 40 degrees, and the wettability of the molten glass frit with respect to the ceramic substrate will be reduced, which may result in a reduction in the adhesion between the ceramic substrate and the conductive film. ２ O ３ If the value of (I) exceeds the upper limit of the above range, vitrification becomes difficult, and the adhesion between the ceramic substrate and the conductive film may decrease.

[0029] The tellurium-based glass frit is a glass frit containing Te as a main component in terms of oxide as an essential component, and may contain other optional components. The tellurium-based glass frit preferably contains Te as an essential component and V as an optional component, and is preferably a tellurium-vanadium-based glass frit. The (B) glass frit preferably contains a tellurium-based glass frit and / or a tellurium-vanadium-based glass frit as a (B-1) glass frit in which the contact angle of the molten glass frit with the ceramic substrate is 40 degrees or less. The tellurium-based glass frit may be substantially free of alkali metal oxides, and may contain Te (TeO ２ The tellurium-based glass frit preferably contains 14 to 55 mass %, more preferably 20 to 50 mass %, and even more preferably 30 to 45 mass % of Te (TeO ２ ) in the above range, the softening point is low and the adhesive strength to the ceramic substrate is good. In addition, when the tellurium-based glass frit contains V, the oxide equivalent of V (V ２ O ５The tellurium-based glass frit preferably contains 10 to 50 mass %, more preferably 15 to 35 mass %, and even more preferably 20 to 30 mass % of V (V ２ O ５ When the content of TeO in the tellurium-based glass frit or the tellurium-vanadium-based glass frit is within the above range, the softening point is low and the adhesive strength to the ceramic substrate is good. ２ and V ２ O ５ is a component that forms the glass framework. In tellurium-based glass frit or tellurium-vanadium-based glass frit, TeO ２ and V ２ O ５ If the content of is low, the adhesion between the ceramic substrate and the conductive film may decrease. If the softening point of the tellurium-based glass frit or the tellurium-vanadium-based glass frit is high, the contact angle of the molten glass frit with respect to the ceramic substrate measured by the above-mentioned method may become large, exceeding 40 degrees, and the wettability of the molten glass frit with respect to the ceramic substrate may decrease, thereby decreasing the adhesion between the ceramic substrate and the conductive film.

[0030] The zinc borosilicate glass frit contains at least one of B and Si, and Zn as essential components, and may contain other optional components. The (B) glass frit may be a zinc borosilicate glass frit as the (B-1) glass frit, the contact angle of which when molten with a ceramic substrate is 40 degrees or less. However, when using a zinc borosilicate glass frit, from the viewpoint of improving wettability with a ceramic substrate, it is preferable that the glass frit does not contain a zinc borosilicate glass frit containing 50 mass % or more of Zn (ZnO) calculated as an oxide. The (B) glass frit is preferably a zinc borosilicate glass frit containing less than 40 mass % of Zn (ZnO) calculated as an oxide, the (B-1) glass frit, the contact angle of which when molten with a ceramic substrate is 40 degrees or less, the zinc borosilicate glass frit containing less than 40 mass % of B (B ２ O ３ ) 2 to 20 mass%, oxide equivalent Si (SiO２ ) in an oxide equivalent amount of 5 to 30 mass %, Zn (ZnO) in an oxide equivalent amount of 10 to 35 mass %, Na (Na ２ O) in an amount of 0 to 20 mass %, Al (Al ２ O ３ In the zinc borosilicate glass frit, Si(SiO ２ ) and B(B ２ O ３ ) is a component that forms the skeleton of the glass. In the zinc borosilicate glass frit, Zn (ZnO) in terms of oxide is a component that adjusts the viscosity of the glass during melting. If the content of Zn (ZnO) in terms of oxide in the zinc borosilicate glass frit is 50 mass % or more, the contact angle of the molten glass frit with the ceramic substrate measured by the above-mentioned method may become large, exceeding 40 degrees, and the wettability of the molten glass frit with the ceramic substrate may decrease, resulting in a decrease in adhesion between the ceramic substrate and the conductive film.

[0031] The glass frit (B) may include a glass frit (B-2) in which, when the glass frit is placed on a ceramic substrate and melted at 900° C. in a nitrogen atmosphere, the contact angle of the molten glass frit with the ceramic substrate exceeds 40 degrees as measured in accordance with JIS R 3257. When the glass frit (B-2) having a contact angle of more than 40 degrees is also included, glass frits (B-1) and (B-2) having a contact angle of 40 degrees or less are combined and pressed into a molded body, and the contact angle is measured by the test method described below. It is sufficient that the contact angle is 40 degrees or less.

[0032] (B) The glass frit contains Sn and P as essential components, SnO—P ２ O ５ It is preferable to exclude SnO-P based glass frit. ２ O ５Although the (B) glass frit has a low melting point, the contact angle with the ceramic substrate measured by the above-mentioned method exceeds 40 degrees, which may decrease the wettability of the molten glass frit with the ceramic substrate, thereby decreasing the adhesion between the ceramic substrate and the conductive film. ２ O ５ 10 to 20 mol % of SiO ２ 15 to 25 mol % of Al ２ O ３ and SnO-P containing 5 to 15 mol % of MgO, CaO and SrO in an amount of 10 to 15 mol %. ２ O ５ It is preferable to exclude glass frit.

[0033] The conductive paste includes an organic vehicle (C). The organic vehicle (C) includes a resin and a solvent, and the resin is preferably dissolved in the solvent. The resin included in the organic vehicle (C) is preferably at least one selected from the group consisting of a cellulose-based resin and a (meth)acrylic resin.

[0034] The (C) organic vehicle imparts thixotropy to the conductive paste when the conductive paste is applied to a ceramic substrate, thereby improving the coatability of the conductive paste. After the conductive paste is applied to a ceramic substrate, the organic vehicle becomes a resin contained in the organic vehicle, and can maintain the shape of the coating film, even when the conductive paste is applied to a thickness of, for example, more than 100 μm. The (C) organic vehicle is decomposed and removed when the conductive paste is applied to a ceramic substrate and then fired to obtain a conductive film.

[0035] The (C) organic vehicle preferably contains, for example, at least one cellulose-based resin selected from the group consisting of methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, and nitrocellulose as the resin, and at least one solvent selected from the group consisting of α-terpineol, texanol, butyl carbitol acetate, and ethyl carbitol acetate as the solvent. When the resin contained in the (C) organic vehicle is a cellulose-based resin, it is preferable because, compared to (meth)acrylic resins, it can impart thixotropy to the conductive paste and maintain the shape of the coating film after application.

[0036] The (C) organic vehicle preferably contains, for example, at least one (meth)acrylic resin selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-hydroxyethyl (meth)acrylate, and at least one solvent selected from the group consisting of methyl ethyl ketone, α-terpineol, texanol, butyl carbitol acetate, and ethyl carbitol acetate.

[0037] The content of the resin solids in the (C) organic vehicle is preferably in the range of 0.5 parts by mass to 15 parts by mass, more preferably in the range of 0.7 parts by mass to 7 parts by mass, and even more preferably in the range of 1 part by mass to 5 parts by mass, relative to 100 parts by mass of the (A) conductive particles in the conductive paste. When the content of the resin solids in the (C) organic vehicle in the conductive paste is within the above range, the conductive paste can be imparted with thixotropy suitable for screen printing, the shape of the coating film can be maintained after formation, and the coating film can be decomposed and removed when fired to obtain a conductive film.

[0038] The ratio of the resin to the solvent contained in the (C) organic vehicle is preferably 1:99 to 30:70 (resin:solvent), more preferably 2:98 to 25:75, and even more preferably 3:97 to 20:80, so that the viscosity of the conductive paste can be adjusted by the (C) organic vehicle.

[0039] The temperature difference between the softening point of the (B) glass frit and the decomposition temperature of the (C) organic vehicle measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere is preferably within 200°C in absolute value, more preferably within 150°C in absolute value, and even more preferably within 100°C in absolute value. The decomposition temperature of the (C) organic vehicle measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere is specifically the decomposition temperature of the resin contained in the (C) organic vehicle. If the temperature difference between the softening point of the (B) glass frit and the decomposition temperature of the (C) organic vehicle is within the above range, when the conductive paste is applied to a ceramic substrate with a film thickness of, for example, 100 μm or more, the shape of the film applied by the (C) organic vehicle can be maintained. Before and after the decomposition of the (C) organic vehicle during firing, the (B) glass frit softens, and a conductive film with high adhesion to the ceramic substrate can be obtained while maintaining the shape of the applied film, and a circuit pattern made of the conductive film can be formed with high precision. The temperature difference between the softening point of the (B) glass frit and the decomposition temperature of the (C) organic vehicle measured by a differential thermal-thermogravimetric simultaneous analyzer in a nitrogen atmosphere does not have a particular lower limit, but is preferably, for example, 10°C or more, and may be 50°C or more.

[0040] The nitrogen atmosphere used to measure the decomposition temperature of the organic vehicle (C) using a simultaneous differential thermal / thermogravimetry analyzer preferably contains 99% by volume or more of nitrogen gas, and may also contain 100% by volume, in order to suppress the reaction of the organic vehicle (C). The nitrogen atmosphere used to measure the decomposition temperature of the organic vehicle (C) using a simultaneous differential thermal / thermogravimetry analyzer may contain 1% by volume or less of hydrogen gas. The decomposition temperature of the organic vehicle can be measured using a simultaneous differential thermal / thermogravimetry analyzer (for example, TG-DTA2000SA, manufactured by BRUKERAX).

[0041] The softening point of the (B) glass frit is preferably lower than the decomposition temperature of the (C) organic vehicle as measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere. When the softening point of the (B) glass frit is lower than the decomposition temperature of the (C) organic vehicle as measured by a simultaneous differential thermal and thermogravimetry analyzer in a nitrogen atmosphere, after the conductive paste is applied to a ceramic substrate in a film thickness of, for example, 100 μm or more, softening of the (B) glass frit begins before the (C) organic vehicle decomposes during firing, and the shape of the applied film is maintained, making it possible to obtain a conductive film that has high adhesion to the ceramic substrate, and thus making it possible to form a circuit pattern made of the conductive film with higher accuracy.

[0042] Examples of the (B) glass frit having a softening point of 600° C. or less include bismuth-based glass frit, tellurium-based glass frit, tellurium-vanadium-based glass frit, and zinc borosilicate glass frit containing less than 40 mass % of Zn (ZnO) calculated as oxide.

[0043] Examples of the (C) organic vehicle having a decomposition temperature of 200°C or less in absolute value as measured by a simultaneous differential thermal and thermogravimetric analyzer in a nitrogen atmosphere include organic vehicles containing ethyl cellulose and α-terpineol in a ratio of 3:97 to 20:80.

[0044] Examples of the (C) organic vehicle having a decomposition temperature of 200°C or less in absolute value as measured by a simultaneous differential thermal and thermogravimetric analyzer in a nitrogen atmosphere include organic vehicles containing methyl (meth)acrylate and α-terpineol in a ratio of 3:97 to 20:80.

[0045] The conductive paste is preferably used to form a conductive film having a thickness of 100 μm or more. The conductive paste has good thixotropy and coatability, allowing circuit patterns to be formed by screen printing, maintaining the shape after application, and even thick conductive films having a thickness of 100 μm or more can be formed. In applications where a conductive paste is directly applied to a ceramic substrate used in a power device, dried, and fired to form a wiring pattern, a thick wiring pattern is required to supply a large current to the semiconductor element. For this reason, the conductive paste is more preferably used to form a conductive film having a thickness of 150 μm or more, even more preferably used to form a conductive film having a thickness of 200 μm or more, and particularly preferably used to form a conductive film having a thickness of 250 μm or more. After firing, the conductive film is reduced in thickness compared to the thickness obtained when the conductive paste is applied due to decomposition of the (C) organic vehicle. Therefore, the thickness of the coating film formed by applying the conductive paste may be 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, or 300 μm or more. The conductive paste preferably forms a coating film 1.2 to 1.5 times thicker than the thickness of the conductive film obtained by firing the conductive paste.

[0046] The conductive paste is preferably formed into a coating film that becomes a conductive film upon firing, for example, by a screen printing method. The conductive paste may be laminated in multiple layers and fired to form a conductive film. For example, after applying the conductive paste to a ceramic substrate and drying the first coating film, a spacer thicker than the first coating film is disposed, and the conductive paste is applied on the first coating film (dried film) to form a second coating film. After drying, a spacer thicker than the first and second coating films is disposed, and a third coating film is formed on the second coating film. The layers are then stacked to the target thickness. The dried films formed in multiple layers can then be fired, for example, in a belt-type firing furnace at a temperature of 900°C in an in-out environment for 1 hour (in a nitrogen atmosphere), to form a conductive film of 100 μm or more.

[0047] The number of times the coating film is laminated is not limited to three layers, and may be repeated multiple times to form multiple layers. The conductive paste may have 2 to 20 laminated coating layers, or 3 to 15 laminated coating layers, and preferably 3 to 10 laminated coating layers. The spacer may be made of a plastic such as polyethylene terephthalate.

[0048] The conductive paste is preferably used to form a conductive film by applying the conductive paste to a ceramic substrate and firing the paste. The conductive paste allows a circuit pattern to be formed by a screen printing method, can maintain the shape of the coating film, and can form a conductive film that has high adhesion to the ceramic substrate.

[0049] The ceramic substrate is made of aluminum oxide (Al ２ O ３ ), aluminum nitride (AlN) and silicon nitride (Si ３ N ４ Among these, it is preferable to use at least one selected from the group consisting of aluminum nitride (AlN) substrates having high thermal conductivity and silicon nitride (Si) substrates having high fracture toughness. ３ N ４ It is preferable to use an aluminum nitride (AlN) substrate or a silicon nitride (Si ３ N ４ When forming a conductive film of 100 μm or more on a substrate, aluminum oxide (Al ２ O ３ ), it has been difficult to improve the adhesive strength. ３ N ４ Even when forming a conductive film with a thickness of 100 μm or more on a ceramic substrate, a conductive film with high adhesion can be formed. ２ O ３ ), zirconium oxide (ZrO) may also be included.

[0050] The ceramic substrate is made of aluminum oxide (Al ２ O ３) substrate, aluminum nitride (AlN) substrate, or silicon nitride (Si ３ N ４ These substrates have high thermal conductivity and good heat dissipation. Aluminum oxide substrates are ceramic substrates whose main component is aluminum oxide (Al ２ O ３ ) refers to a ceramic substrate. In this specification, the term "major component constituting a ceramic substrate" refers to the component that is present in the largest amount among the components constituting the ceramic substrate, and refers to a component that accounts for 50 mass% or more of the components constituting the ceramic substrate. An aluminum oxide substrate preferably contains 95 mass% or more of aluminum oxide. An aluminum nitride substrate preferably contains aluminum nitride as the main component, and the ceramic substrate preferably contains 95 mass% or more of aluminum nitride. A silicon nitride substrate preferably contains silicon nitride as the main component, and the ceramic substrate preferably contains 95 mass% or more of silicon nitride.

[0051] The conductive film is formed by applying the conductive paste to a ceramic substrate and firing the paste. Methods for applying the conductive paste to a ceramic substrate include screen printing, gravure printing, a bar coater, a doctor blade, a slit coater, a gravure coater, and a spray coater. Since the conductive paste can be easily applied to a ceramic substrate in a precise pattern, it is preferable to form the coating film by screen printing.

[0052] The thickness of the coating film (dried film) made of the conductive paste after applying it to the ceramic substrate and before drying and firing is preferably 100 μm or more, more preferably 150 μm or more, and may be 200 μm or more. By achieving a film thickness within this range, it becomes possible to handle large currents of several tens to 100 A, and the ceramic wiring substrate can be used as a wiring substrate for power devices. The upper limit of the film thickness is not particularly limited, but may be, for example, 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 formed by applying and stacking multiple layers by screen printing. Furthermore, when applying the conductive paste to the ceramic substrate, the film thickness of the first layer may be different from the film thickness of the second and subsequent layers.

[0053] The coating film formed by applying the conductive paste to a ceramic substrate is preferably fired to form a conductive film. The temperature at which the coating film is fired may be any temperature at which the (C) organic vehicle in the conductive paste volatilizes and the (B) glass frit melts. The firing temperature for the coating film formed by applying the conductive paste to a ceramic substrate is preferably within the range of 700°C to 1500°C, more preferably within the range of 800°C to 1200°C, and even more preferably within the range of 850°C to 1100°C. If the firing temperature for the coating film formed by applying the conductive paste to a ceramic substrate is within the range of 700°C to 1500°C, the (C) organic vehicle in the conductive paste volatilizes, the (B) glass frit melts and functions as an adhesive, and a conductive film in which the (A) conductive particles are adhered to the ceramic substrate is obtained. The atmosphere in which the coating film is fired is preferably a nitrogen atmosphere in order to obtain a conductive film with good adhesion to the ceramic substrate.

[0054] Furthermore, the thickness of the coating film (conductive film) obtained by applying the conductive paste to a ceramic substrate, drying the paste, 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 this range, it is possible to handle large currents of several tens to 100 A, and the ceramic wiring substrate can be used as a wiring substrate for power devices. The upper limit of the film thickness of the coating film (conductive film) is not particularly limited, but for example, the conductive film may have a thickness of 1000 μm or less, 800 μm or less, or 750 μm or less. A conductive film obtained by applying and firing a conductive paste to a ceramic substrate has good wettability with the ceramic substrate, and the conductive paste can be applied multiple times, resulting in a thick conductive film with a thickness of 100 μm or more. A film with a thickness of 100 μm or more is sometimes referred to as a thick film. A conductive paste capable of forming a thick conductive film with a thickness of 100 μm is also called a thick-film conductive paste. For example, a coating film formed by stacking multiple layers using a screen printing method becomes a single conductive film with a single thickness after firing, with each layer indistinguishable.

[0055] The ceramic substrate is made of aluminum oxide (Al ２ O ３ ) substrate, and aluminum oxide (Al ２ O ３ ) The conductive paste is applied to a substrate and fired to form a conductive film having a thickness of 250 μm, and the compressive shear adhesive strength measured in accordance with JIS K6852 is 1.0 N / mm ２ It is preferable that the strength is 1.5 N / mm or more. ２ More preferably, it is 2.0 N / mm or more. ２ It is more preferable that the content of aluminum oxide (Al ２ O ３) substrates have high thermal conductivity and excellent heat dissipation, but compared to general copper substrates, they have low wettability of conductive pastes and may have low adhesion, as expressed by compressive shear bond strength.The conductive paste of the present disclosure contains glass frit that has a contact angle of 40 degrees or less when molten with respect to the ceramic substrate, so that even when a thick conductive film with a film thickness of 100 μm or more is formed by applying and firing the conductive paste, a conductive film with high compressive shear bond strength can be obtained.

[0056] The ceramic substrate is an aluminum nitride (AlN) substrate, and the conductive film having a thickness of 250 μm, which is formed by applying the conductive paste to the aluminum nitride (AlN) substrate and firing the paste, has a compressive shear adhesive strength of 1.0 N / mm, as measured in accordance with JIS K6852. ２ It is preferable that the strength is 1.5 N / mm or more. ２ More preferably, it is 2.0 N / mm or more. ２ The aluminum nitride (AlN) substrate is preferably made of aluminum oxide (Al ２ O ３ ) substrate, but the adhesiveness expressed by compressive shear bond strength may be low. The conductive paste of the present disclosure contains glass frit with a contact angle of 40 degrees or less when molten with respect to the ceramic substrate, and therefore the compressive shear bond strength when a conductive film with a film thickness of 250 μm is formed is 1.0 N / mm ２ As described above, a conductive film with high adhesiveness can be obtained.

[0057] The ceramic substrate is made of silicon nitride (Si ３ N ４ ) substrate, and silicon nitride (Si ３ N ４ ) The conductive paste is applied to a substrate and baked to form a conductive film having a thickness of 250 μm, and the compressive shear adhesive strength measured in accordance with JIS K6852 is 1.0 N / mm ２ It is preferable that the strength is 1.5 N / mm or more. ２ More preferably, it is 2.0 N / mm or more. ２ More preferably, the silicon nitride (Si ３ N ４The substrate is aluminum oxide (Al ２ O ３ The conductive paste of the present disclosure contains glass frit having a contact angle of 40 degrees or less when molten with respect to a ceramic substrate, and when the conductive paste is applied and fired to a thickness of 100 μm or more, a conductive film having a thickness of 250 μm has a compressive shear adhesive strength of 1.0 N / mm. ２ As described above, a conductive film with high adhesiveness can be obtained.

[0058] The conductive film obtained by applying the above-mentioned conductive paste to a ceramic substrate and firing it can be used to form a circuit pattern by a screen printing method, and can form a conductive film with high adhesion to the ceramic substrate and a thick film thickness, making it suitable for use as a conductive film that constitutes the circuit pattern of a ceramic circuit substrate.

[0059] The conductive film obtained by applying the conductive paste to a ceramic substrate and firing it can form a circuit pattern by a screen printing method, and can form a thick conductive film that has high adhesion to the ceramic substrate, making it suitable for use in electronic devices including wiring boards for power devices.

[0060] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. In the following examples and comparative examples, unless otherwise specified, the numbers indicating the blending ratio of each component contained in the resin composition represent mass % for the glass frit composition in Table 1 and parts by mass for each component in the conductive paste in Table 2.

[0061] (B) Glass Frit Table 1 shows the glass composition of each (B) glass frit GF1 to GF9, its softening point, and the contact angle with each ceramic substrate measured under the conditions described below. GF1, GF3, GF7, and GF8 contain Bi (Bi ２ O ３ ) containing bismuth (Bi ２ O ３GF2 and GF9 are glass frits containing Te (TeO ２ ) and V-containing tellurium-vanadium (TeO ２ -V ２ O ５ GF4 is a zinc borosilicate (ZnO)-based glass frit containing less than 50 mass% of Zn (ZnO) in oxide equivalent. GF5 is a SrO-based glass frit containing silicon and strontium as essential components, and GF6 is a SrO-based glass frit containing silicon (SiO) in oxide equivalent as the main component. ２ ) including SiO ２ In Table 1, the symbol "-" indicates that there is no numerical value for the corresponding item.

[0062] Ceramic substrate Aluminum oxide (Al ２ O ３ ) Substrate: Aluminum oxide (Al ２ O ３ ) content of 96 mass% of the total amount, thermal conductivity of 30 W / m·K, thickness within the range of 0.15 mm to 1.2 mm. Aluminum nitride (AlN) substrate: Aluminum nitride (AlN) content of 96 mass% of the total amount, thermal conductivity of 200 W / m·K, thickness within the range of 0.25 mm to 1.5 mm. Silicon nitride (Si ３ N ４ ) Substrate: Silicon nitride (Si ３ N ４ ) content is 96 mass% of the total amount, thermal conductivity is 80 W / m·K, and thickness is in the range of 0.25 mm or more and 0.63 mm or less.

[0063] Contact Angle Measurement: The (B) glass frits of each composition 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 molded (B) glass frits were placed on ceramic substrates to form samples for contact angle measurement. The samples were then melted in a belt-type firing furnace (manufactured by JTEKT Thermosystems Corporation) at a temperature of 850°C to 900°C for 10 minutes in a nitrogen atmosphere (nitrogen gas: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less). The contact angle of the molten glass frit with the ceramic substrate was measured in accordance with JIS K3257. The samples for contact angle measurement were left in the belt-type firing furnace for 60 minutes before being removed. The contact angles of each glass frit with each ceramic substrate are shown in Table 1. For reference, the contact angle with a copper substrate was also measured.

[0064] Measurement of Softening Point of Glass Frit The softening point of the glass frit is measured by raising the temperature to 900°C in a nitrogen atmosphere (nitrogen gas: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less) using a differential thermal-thermogravimetric simultaneous analyzer (TG-DTA2000SA, manufactured by BRUKERAX).

[0065]

[0066] Each of the (B) glass frits GF1 to GF9 shown in Table 1, the following (A) conductive particles, and (C) organic vehicle are used.

[0067] (A) Conductive particles Copper powder (Cu powder) 1: an aggregate of particles made of copper by atomization, spherical, with an average particle size of 2.5 μm. Copper powder (Cu powder) 2: an aggregate of particles made of copper by atomization, spherical, with an average particle size of 3.5 μm. Copper powder (Cu powder) 3: an aggregate of particles made of copper by atomization, flake-like, with an average particle size of 4.0 μm.

[0068] (C) Organic vehicle Resin 1: ethyl cellulose Resin 2: methyl (meth)acrylate Solvent: α-terpineol

[0069] Examples 1 to 10 and Comparative Examples 1 and 2 Conductive pastes were produced by mixing and dispersing (A) conductive particles, (B) glass frit, and (C) organic vehicle using a three-roll mill so as to obtain the blending ratios shown in Table 2. The numerical values ​​for each component in Table 2 represent parts by mass. In Table 2, the symbol "-" indicates that there is no numerical value for the corresponding item.

[0070] (A) Volume average particle diameter D50 of conductive powders by laser diffraction scattering method The volume average particle diameters (median diameters) D50 of (A) Cu powders 1 to 3, which are conductive powders, were measured by a laser diffraction scattering method using a particle size distribution measuring device (product name: Microtrac MT3000II, manufactured by Microtrac Bell Co., Ltd.).

[0071] Measurement of decomposition temperature of resin contained in (C) organic vehicle The decomposition temperature of the (C) organic vehicle is measured using a simultaneous differential thermal-thermogravimetric analyzer (TG-DTA2000SA, manufactured by BRUKERAXS) by raising the temperature to 900°C in a nitrogen atmosphere (nitrogen gas: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less). The decomposition temperature of the (C) organic vehicle is specifically the decomposition temperature of the resin contained in the (C) organic vehicle. The results are shown in Table 2.

[0072] Measurement of viscosity and thixotropy index (TI) of conductive paste Using an HB type viscometer (manufactured by Brookfield) (SC4-14 spindle), the paste was rotated at 25°C at rotation speeds of 1 rpm and 20 rpm, and the viscosity of each conductive paste of the Examples and Comparative Examples at each rotation speed (first viscosity (1 rpm), second viscosity (20 rpm)) was measured. For each conductive paste, the viscosity V measured at a rotation speed of 20 rpm was ２０ｒｐｍ , whereas the viscosity V measured at a rotation speed of 1 rpm １ｒｐｍ The ratio of V to V was determined as the thixotropy index (TI) using the following formula (1). The results are shown in Table 2. TI = V １ｒｐｍ / V ２０ｒｐｍ(1) From the viewpoint of enabling the formation of a coating film (dry film) of 100 μm or more, the thixotropy 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 having the thixotropy index (TI) in this range, spreading on the paste application surface can be suppressed, the amount of conductive paste applied from the screen printing mask opening can be secured, and the height of the coating film can be maintained.

[0073] Conductive Film: Using the following printing device and mask, each conductive paste of the Examples and Comparative Examples was applied to each ceramic substrate by screen printing to form the pattern shown in FIG. 1 , and then dried for 10 minutes at 150°C using a box dryer to obtain a dried film. FIG. 1 is a diagram showing an example of a pattern in which a conductive paste is applied to a ceramic substrate. FIG. 1 shows a coating film formed by applying a conductive paste to a ceramic substrate in a predetermined pattern, or a conductive film formed by firing the coating film. The pattern shown in FIG. 1 represents a coating film with a rectangular pattern in plan view. Each side of the coating film is 2 mm. The coating film formed on the ceramic substrate was then fired in a belt-type firing furnace at a maximum temperature of 900°C in a nitrogen atmosphere (nitrogen gas: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less) to obtain a conductive film for testing. The time from when the coating film formed on the ceramic substrate was placed in the belt-type firing furnace until it was removed was 60 minutes. The thickness of the fired conductive film was 250 μm. The printing device used was a screen printer (MT-650TVC, manufactured by Micro-Tec Co., Ltd.). The coating film was formed specifically as follows. For the first layer of the coating film, a conductive paste was applied using a mask with a 60 mesh and an emulsion film thickness of 20 μm, forming a coating film (dried film) with a thickness of 20 μm after drying. Next, a mask with a 150 mesh and an emulsion film thickness of 102 μm was used to repeatedly apply and dry the conductive paste to the dried first layer of coating film, forming the second to seventh layers of coating film. As a result, a dried film with a total thickness of 300 μm after drying was obtained. The coating film formed on the ceramic substrate was then fired in a belt-type firing furnace at a maximum temperature of 900°C in a nitrogen atmosphere (nitrogen gas: 99.9% by volume or more, oxygen: 0.001% by volume (10 ppm by volume) or less) to obtain a conductive film for testing. The time from when the coating film formed on the ceramic substrate was placed in the belt-type firing furnace until it was removed was 60 minutes. The thickness of the conductive film after firing was 250 μm.

[0074] Measurement of compressive shear adhesive strength of conductive film Using the test conductive film, the compressive shear adhesive strength of the conductive film with a thickness of 250 μm formed on each ceramic substrate was measured in accordance with JIS K6852 using a strength tester (Model 1605HTP, manufactured by Aiko Engineering Co., Ltd.). ２ If the compressive shear adhesive strength is 1.0 N / mm or more, the adhesive is evaluated as "A" (Good). ２ 2.0N / mm or more ２ If the compressive shear strength is less than 1.0 N / mm, it is evaluated as "B" (Better). ２ If the value was less than 100%, the evaluation was "C" (NG: No good). The results are shown in Table 2.

[0075]

[0076] As shown in Tables 1 and 2, the conductive pastes of Examples 1 to 10 contain (B-1) glass frit with a contact angle of 40 degrees or less with respect to the ceramic substrate, and therefore have good wettability with respect to the ceramic substrate, and can form a conductive film with high adhesion between the conductive powder and the ceramic substrate. Specifically, all of the conductive pastes of Examples 1 to 10 contain aluminum oxide (Al ２ O ３ ) Excellent adhesion to the substrate, compressive shear adhesive strength of 1.0 N / mm ２ Furthermore, the conductive pastes of Examples 1 to 3 and Examples 5 to 7 also had good adhesion to aluminum nitride (AlN) substrates, with a compressive shear adhesive strength of 1.0 N / mm ２ Furthermore, the conductive pastes of Examples 1, 2 and 5 to 7 contain silicon nitride (Si ３ N ４ ) It also has good adhesion to the substrate, with a compressive shear adhesive strength of 1.0 N / mm ２ The results were as above. In addition, tellurium-vanadium (TeO ２ -V ２ O ５ When Example 2 using GF2, which is a glass frit based on GF2, is compared with Example 10 using GF9, the conductive paste of Example 2 using GF2 has a better adhesion to the aluminum nitride (AlN) substrate and silicon nitride (Si３ N ４ ) The adhesion to the substrate was good. This is presumably because the softening point of the glass frit was lower in GF2, and the glass frit was sufficiently melted during firing, which resulted in improved adhesion.

[0077] FIG. 1 shows the conductive paste of Example 1 applied to a ceramic substrate 2 made of aluminum oxide (Al ２ O ３ 1 is a photograph showing the appearance of a conductive film 1 obtained by applying a coating film 1 to a substrate by screen printing and then firing the coating film 1. As shown in Fig. 1, the conductive film 1 obtained by applying a conductive paste to a ceramic substrate 2 and then firing the coating film 1 can be formed with high precision by screen printing, even in the case of small rectangular patterns.

[0078] The conductive pastes of Comparative Examples 1 and 2 did not contain the (B-1) glass frit, which has a contact angle of 40 degrees or less with respect to the ceramic substrate, and therefore had low wettability with respect to the ceramic substrate, with a compressive shear adhesive strength of 1.0 N / mm ２ It was lower than that.

[0079] The conductive paste and conductive film according to the embodiments of the present disclosure can be suitably used in circuit patterns of ceramic circuit boards, circuit boards such as wiring boards for power devices, and electronic devices including these boards.

[0080] 1: Coating film or conductive film made of conductive paste, 2: Ceramic substrate

Claims

1. A conductive paste comprising (A) conductive powder, (B) glass frit, and (C) organic vehicle, wherein the (B) glass frit includes a glass frit having a contact angle of 40 degrees or less with respect to the ceramic substrate, which is measured in accordance with JIS R3257 when the glass frit is melted under the condition of 900 ° C. in a nitrogen atmosphere after the glass frit is disposed on the ceramic substrate.

2. The conductive paste according to claim 1, wherein the (A) conductive powder includes copper powder, and the copper powder is included in an amount of 50 parts by mass or more based on 100 parts by mass of the (A) conductive powder.

3. The conductive paste according to claim 1 or 2, wherein the average particle size (D50) of the (A) conductive powder measured by the laser diffraction scattering method is in the range of 0.5 μm or more and 10.0 μm or less.

4. The conductive paste according to any one of claims 1 to 3, wherein the (B) glass frit includes at least one selected from the group consisting of bismuth-based glass frit, tellurium-based glass frit, and zinc borosilicate-based glass frit.

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

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

7. The conductive paste according to any one of claims 1 to 6, wherein the softening point temperature of the (B) glass frit is lower than the decomposition temperature of the (C) organic vehicle measured by a differential thermal-thermogravimetric simultaneous measurement apparatus in a nitrogen atmosphere.

8. The conductive paste according to any one of claims 1 to 7, wherein the content of the resin solid content in the (C) organic vehicle is in the range of 0.5 part by mass or more and 10 parts by mass or less based on 100 parts by mass of the (A) conductive powder.

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

10. The conductive paste according to any one of claims 1 to 9 for a conductive film, which is used for forming a conductive film obtained by applying and firing the conductive paste on the ceramic substrate.

11. The ceramic substrate includes at least one selected from the group consisting of aluminum oxide (Al ２ O ３ ), aluminum nitride (AlN), and silicon nitride (Si ３ N ４ ), and the conductive paste according to any one of claims 1 to 10.

12. A conductive film obtained by applying the conductive paste according to any one of claims 1 to 11 to a ceramic substrate and firing it.

13. The conductive film according to claim 12, having a film thickness of 100 μm or more.

14. The ceramic substrate is an aluminum oxide (Al ２ O ３ ) substrate, and the conductive paste is applied to the aluminum oxide (Al ２ O ３ ) substrate and fired to form a conductive film with a film thickness of 250 μm. The compressive shear adhesion strength measured in accordance with JIS K6852 is 1.0 N / mm ２ or more. The conductive film according to claim 12 or 13.

15. The ceramic substrate is an aluminum nitride (AlN) substrate, and the conductive paste is applied to the aluminum nitride (AlN) substrate and fired to form a conductive film with a film thickness of 250 μm. The compressive shear adhesion strength measured in accordance with JIS K6852 is 1.0 N / mm ２ or more. The conductive film according to claim 12 or 13.

16. The ceramic substrate is a silicon nitride (Si ３ N ４ ) substrate, and the conductive film having a film thickness of 250 μm formed by applying and baking the conductive paste on the silicon nitride (Si ３ N ４ ) substrate has a compression shear adhesion strength measured in accordance with JIS K6852 of 1.0 N / mm ２ or more mm ２ or more. The conductive film according to claim 15 or 16.

17. A ceramic circuit board comprising a conductive film obtained by applying the conductive paste according to any one of claims 1 to 11 to a ceramic substrate and firing it.

18. An electronic component comprising a conductive film obtained by applying the conductive paste according to any one of claims 1 to 11 to a ceramic substrate and firing it.

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