Fired conductive paste

Abstract

To create a flat and smooth plate-like conductive film which has a large film thickness and a large size, by using a fired conductive paste containing a binder resin.SOLUTION: The fired conductive paste includes: conductive powders mainly formed of nickel and having an average particle diameter (D50) in the range of 0.05 μm to 1 μm; an acrylic resin having an acid value in the range of 0 to 10; and an organic solvent which dissolves the acrylic resin, the organic solvent being an alcohol-based solvent having a carbon number of at least 3 and a boiling point of not higher than 300°C, and the moisture content in the paste being less than 0.5 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a sintered conductive paste using conductive powder mainly composed of metallic nickel, and particularly to a sintered conductive paste suitable for forming a flat conductor film having a thickness of 0.5 μm or more, which was difficult to form conventionally, and capable of accommodating a square shape with at least one side being 5.0 cm.

Background Art

[0002] In the field of electronics, sintered conductive paste is used for manufacturing components such as electronic circuits, resistors, capacitors, and IC packages. The sintered conductive paste is obtained by uniformly mixing and dispersing conductive powder such as metal, alloy, or metal oxide in an organic vehicle together with a glassy binder or other additives as necessary to form a paste. After being applied on a substrate and fired at a high temperature, only inorganic components such as metal components and glass components remain as the organic components contained in the paste decompose and scatter, forming a conductor film such as wiring or electrodes on the circuit board.

[0003] The above-mentioned organic vehicle contains a resin component called a binder resin. Therefore, even after applying the sintered conductive paste on an object for forming a conductor film such as a substrate, it does not flow immediately to the surroundings and can maintain the shape at the time of application with a certain thickness. After the binder resin decomposes and scatters by subsequent firing, the conductive powder dispersed at a high concentration in the organic vehicle sinters with each other to maintain the initial coating shape, so that a conductor film shaped into a desired pattern can be obtained by a screen printing method, a gravure printing method, or the like.

[0004] As described above, since the sintered conductive paste can obtain a relatively thick thick-film conductor, it is used for the above-mentioned applications. In recent years, because it enables pattern printing, it is also widely used for forming electrodes of small electronic components such as multilayer capacitors and multilayer inductors with a side length of less than 1 mm.

[0005] On the one hand, depending on the application, a flat conductor film with a large area (size) may be required. Conventionally, the conductor film has generally been formed by sputtering, vapor deposition, plating, or the like. However, since these manufacturing methods increase the size of the production equipment, they are disadvantageous in terms of cost. In addition, since the obtained conductor film is a thin film, it has been difficult to obtain a conductor film with high conductivity compared to a thick film conductor. Although a conductor film with high conductivity can be obtained by stacking several layers of the thin films obtained by these manufacturing methods, in that case, an increase in manufacturing cost is inevitable.

[0006] In addition, it is known to create a flat conductor film with a large area using conductive ink. Different from the sintered conductive paste, the conductive ink does not contain a binder resin and is in a low-viscosity liquid state, so it is suitable for forming a flat and smooth flat conductor film. Moreover, it can be manufactured with simpler production equipment compared to sputtering methods and the like. For example, Patent Document 1 describes that nickel ink in which nickel particles with an average primary particle size of 10 to 30 nm are dispersed in a dispersion medium is applied onto a glass substrate using a spin coater to form a conductor film with a film thickness of 400 nm and an average surface roughness of Ra ≦ 10 nm. However, since the conductor film obtained by Patent Document 1 is still a thin film, high conductivity cannot be expected.

[0007] Patent Document 2 also discloses a conductive ink that uses nickel formate as a conductive component and disperses it with ethylenediamine. Since ethylenediamine is viscous and sticky, it is described that a conductor film with a film thickness of 3.66 μm was obtained despite not containing a binder resin. However, since this conductive ink contains a large amount of organic components compared to the blending amount of metallic nickel, in order to obtain a film thickness of 3.66 μm, a coating film with a thickness of nearly 30 times, i.e., 100 μm, must be formed. Therefore, when forming a flat conductor film with a large size using the conductive ink of Patent Document 2, it is difficult to uniformly degrease and volatilize the organic components from the entire coating film, and it is difficult to obtain a flat and smooth conductor film.

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] JP 2007-146117 A [Patent Document 2] JP 2015-151512 A Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present inventors have been considering forming a large-sized flat conductive film in terms of thickness using a sinterable conductive paste containing a binder resin, but when a large-sized flat conductive film, for example a film with a side length of 5.0 cm, is formed using a conventionally known sinterable conductive paste, the surface of the conductor film after sintering becomes wavy, making it difficult to obtain a flat and smooth flat conductive film. The present inventors have investigated various reasons for this, whether it is due to the sintering furnace or the conductive paste, but have not been able to identify the cause. In any case, however, the present inventors speculate that this is due to a difference in local thermal contraction occurring in the coating film during the sintering process.

[0010] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to make it possible to fabricate a flat, smooth, and large-sized plate-shaped conductor film using a baked conductive paste containing a binder resin. [Means for solving the problem]

[0011] The above objectives are achieved by the following: (1) A conductive powder containing nickel as a main component and having an average particle size D50 in the range of 0.05 to 1 μm; An acrylic resin having an acid value in the range of 0 to 10; an organic solvent that dissolves the acrylic resin; Including, The organic solvent is an alcohol-based solvent having a carbon content of 3 or more and a boiling point of 300° C. or less, A fired conductive paste characterized in that the water content contained in the paste is less than 0.5% by mass. (2) The fired conductive paste according to (1), wherein the blending amount of the acrylic resin is 1 to 10 parts by mass with respect to 100 parts by mass of the conductive powder. (3) The fired conductive paste according to (1) or (2), wherein the blending amount of the alcohol-based solvent is 10 to 100 parts by mass with respect to 100 parts by mass of the conductive powder. (4) The fired conductive paste according to (1), which is used to form a flat conductor film having a shape capable of accommodating a square with at least one side of 5.0 cm and a thickness of 0.5 μm or more. [[Effect of the Invention]]

[0012] While using a fired conductive paste containing a binder resin, a flat conductor film that is large in size in terms of film thickness and flat and smooth can be created. [[Modes for Carrying Out the Invention]]

[0013] (Conductive Powder) The conductive powder used in the present invention may be any powder having nickel as a main component. In addition to 100% pure nickel powder, nickel may be an alloy powder with copper, iron, cobalt, gold, silver, palladium, rhenium, platinum, etc. Also, composite powders in which nickel is coated on inorganic powders such as glass and ceramics can be used. Further, those having a thin oxide film on the surface of the nickel powder, or those having a glassy substance or various oxides adhered to the surface for the purpose of suppressing over-sintering may be used. Furthermore, nickel powder surface-treated with an organometallic compound, a surfactant, fatty acids, etc. may be used as necessary, and two or more of these conductive powders may be mixed and used. In any case, the conductive powder of the present invention has nickel as a main component.

[0014] In this specification, the "main component" refers to a component that is more than 50% by mass of the whole. Also, in this specification, a numerical range represented by the symbol "~" includes the numerical values unless otherwise specified. For example, the description "10~20" means a numerical range of 10 or more and 20 or less.

[0015] The particle size of the conductive powder is the number average particle size D obtained by analyzing an image acquired with a scanning electron microscope (SEM) in order to form a dense, flat, and highly smooth conductor film. 50 Fine powder in the range of 0.05 to 1.0 μm is used. The particle size of the conductive powder is particularly the average particle size D 50 is preferably in the range of 0.1 to 0.5 μm. (Binder resin) As the binder resin, an acrylic resin having an acid value in the range of 0 to 10 is used. The acrylic resin having an acid value in the range of 0 to 10 has particularly high thermal decomposability and is likely to thermally decompose and scatter uniformly even when the coating film area is large. Therefore, it is considered to contribute to making the surface of the flat conductor film flat and smooth. When a resin other than the acrylic resin is used or when an acrylic resin having an acid value greater than 10 is used, defects such as cracks, delamination, undulations on the surface of the conductor film, and minute irregularities are likely to occur in the conductor film obtained by firing, and the flat conductor film required by the present invention cannot be obtained.

[0016] Note that as long as the acid value of the acrylic resin is within the range, a partially modified one may be used.

[0017] Also, as the binder resin, as long as the effects of the present invention are not inhibited, the above-mentioned acrylic resin can be mixed with cellulose-based resins such as ethyl cellulose and hydroxyethyl cellulose, methacrylic resin, butyral resin, epoxy resin, phenolic resin, rosin, and other resins and used. As is well known in the art, by appropriately mixing a plurality of types of binder resins, various properties of the conductive paste may be improved.

[0018] The blending amount of the acrylic resin is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the conductive powder. By the blending amount of the acrylic resin being 1 to 10 parts by mass with respect to 100 parts by mass of the conductive powder, the strength of the coating film after printing can be increased, and it is possible to avoid damage during handling of the coating film and impairing the smoothness of the conductive film. In addition, since the amount of carbon remaining in the coating film after degreasing is small, the occurrence of defects such as cracks and delamination can also be suppressed. (organic solvent) In the present invention, as the organic solvent blended in the sintered conductive paste, an alcohol-based solvent that dissolves the acrylic resin and has a carbon content of 3 or more and a boiling point of 300°C or less is used. By using an alcohol-based solvent that satisfies the above conditions, while sufficiently dissolving the acrylic resin, drying during coating is fast and productivity is excellent. In addition, since uniform drying of the entire coating film easily proceeds, a flat and smooth conductor film can be obtained.

[0019] Examples of the alcohol-based solvent that satisfies the above range include octanol, decanol, terpineol, dihydroterpineol, hexanol, 2-ethylhexanol, cyclohexanol, benzyl alcohol, n-butanol, sec-butanol, and the like.

[0020] When an organic solvent other than an alcohol-based solvent is used, the dispersibility of nickel particles deteriorates, and a flat and smooth conductor film cannot be obtained. However, depending on the application, the flat conductor film formed using the conductive paste may be laminated with an inorganic particle film formed using another inorganic particle paste. Examples of other inorganic particle pastes include those obtained by dispersing inorganic particles such as oxide particles such as glass particles, ceramic particles, silica particles, and alumina particles, metal particles such as copper, cobalt, and iron, etc. in an organic vehicle. An inorganic particle paste is used to form a flat coating film similar to the conductive paste, and a coating film using the conductive paste is laminated thereon. Then, both are fired simultaneously to form a laminate. At this time, if the organic solvent in the conductive paste dissolves the binder resin in the laminated inorganic particle paste, problems such as deformation / alteration of the coating film formed using the inorganic particle paste occur. Therefore, as the organic solvent used in the conductive paste, other organic solvents other than alcohol-based solvents may be mixed and used as long as the effects of the present invention are not inhibited. As is well known in the art, by appropriately mixing multiple types of organic solvents in an appropriate amount, the above-mentioned problems can be alleviated. Examples of other organic solvents include hydrocarbon-based solvents such as paraffinic hydrocarbons, olefinic hydrocarbons, naphthenic hydrocarbons, aromatic hydrocarbons, petroleum-based hydrocarbons (mineral spirits), and mixed solvents thereof, as well as ether-based, ester-based, ketone-based, or glycol-based solvents.

[0021] In the fired conductive paste, the blending amount of the alcohol-based solvent is appropriately blended according to the properties of the conductive powder, the type of resin, the coating method, the coating film thickness, etc., but is preferably 10 to 100 parts by mass with respect to 100 parts by mass of the conductive powder. If the blending amount of the alcohol-based solvent is within the above-mentioned range, the printability during coating is good, and problems such as sedimentation of the conductive powder in the paste and compositional non-uniformity can also be suppressed. (Amount of moisture in the paste) As described above, an alcohol-based solvent is used as the organic solvent for the conductive paste, but since alcohol-based solvents have a high affinity for water, they often contain moisture unintentionally. According to the research of the present inventors, if the moisture content in the sintered conductive paste in the present invention is 0.5 mass% or more, undulations will occur on the surface of the conductor film after sintering, making it difficult to obtain a flat and smooth conductor film. Although the reason is unclear, the present inventors speculate that as the moisture content increases, the solubility of the acrylic resin in the paste decreases, and the fluidity of the paste decreases. Therefore, the moisture content in the sintered conductive paste in the present invention must be less than 0.5 mass%.

[0022] There are no particular limitations on the method for controlling the amount of moisture in the conductive paste, and any widely known method can be used. One example of this is to prevent the paste from coming into contact with the air as much as possible by making improvements to the manufacturing process, or to remove moisture in gases that the paste may come into contact with.

[0023] In the present invention, it is desirable for the moisture content in the fired conductive paste to be zero. However, controlling the moisture content to achieve this leads to high costs, so a moisture content of up to 0.5 mass % in the conductive paste is acceptable. (Other added ingredients) In the present invention, in addition to the above-mentioned components, the sintered conductive paste may contain various additives that can be normally added to a conductive paste. For example, in order to improve the dispersibility of inorganic powders such as conductive powders and to ensure the long-term stability of the viscosity of the sintered conductive paste and the appropriate flow characteristics during printing, a surfactant or a chelating agent is preferably added alone or in combination of two or more kinds.

[0024] Examples of surfactants include allyl polyethers such as polyethylene glycol allyl ether and methoxy polyethylene glycol allyl ether and their copolymers, polyalkylene glycol amines such as polyethylene glycol lauryl amine and polyethylene glycol stearyl amine, phosphate esters such as polyethylene glycol alkyl phosphate ester, polyalkylene glycol phenols such as polyethylene glycol nonyl phenyl ether, sorbitan esters such as sorbitan monolaurate, sorbitan monooleate, and sorbitan trioleate, sorbitan ester ethers such as polyethylene glycol sorbitan monolaurate and polyethylene glycol sorbitan monooleate, fatty acids such as oleic acid and lauric acid, amides such as oleic acid amide, stearic acid amide, and polyethylene glycol alkyl amide, etc.

[0025] Examples of chelating agents include, in addition to the above polyalkylene glycol amines and amides, triethanolamine, diethanolamine, alkylamine, 3-butoxypropylamine, 2-aminopropanol, etc.

[0026] In addition, the sintered conductive paste can be appropriately blended with components that can usually be blended in a conductive paste, such as metal oxides such as glass, alumina, silica, copper oxide, manganese oxide, and titanium oxide, inorganic powders such as ceramics and montmorillonite, metal organic compounds, plasticizers, etc., according to the purpose. (Manufacture of Sintered Conductive Paste) The sintered conductive paste is manufactured by uniformly dispersing conductive powder together with other additive components in an organic vehicle containing a binder resin and an organic solvent using a three-roll mill or the like according to a conventional method. (Formation of Conductor Film) In the present invention, the fired conductive paste can be suitably used for forming a flat conductor film having a large size in terms of film thickness. As an example, on a desired object to be printed, a flat coating film is formed by a printing method such as a known screen printing method, an offset printing method, a gravure printing method, spin coating, etc., and then dried at 50 to 200 ° C for about 0.1 to 20 minutes, and then fired at 800 to 1300 ° C to form a flat conductor film.

[0027] The flat conductor film may have any shape according to the application, but if it has a size and shape that can accommodate a square with a side length of 5.0 cm, the effects of the present invention can be enjoyed. That is, if it is larger than a square with a side length of 5.0 cm and has a shape that can accommodate one or more such squares, the outer shape of the flat conductor film can be circular, rectangular, or irregular. Also, in order to obtain a conductor film with high conductivity, the thickness is preferably 0.5 μm or more.

[0028] There is no particular limitation on the upper limit of the thickness and size of the flat conductor film, but according to the findings of the inventors who have conducted many experiments, it is possible to form a conductor film with a side length of about 30 cm and a thickness of about 10 μm for at least one side.

[0029] Note that the fired conductive paste is not used only for forming a flat conductor film having a shape that can accommodate a square with a side length of 5.0 cm and a thickness of 0.5 μm or more. It can also be used for forming circuit wiring and electrodes of multilayer ceramic electronic components where conductive paste is usually used. In addition, it is also possible to form a square conductor film with a thickness of less than 0.5 μm and a side length of less than 5.0 cm.

Examples

[0030] The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[0031] In this example, Resins A to I represent the following respectively. [Resin A] Acrylic resin (oxidation = 0) [manufactured by Mitsubishi Chemical Corporation: BR-105] [Resin B] Acrylic resin (oxidation = 7.8) [manufactured by Mitsubishi Chemical Corporation: BBR-116] [Resin C] Acrylic resin (oxidation = 6.5) [manufactured by Mitsubishi Chemical Corporation: MB-2539] [Resin D] Acrylic resin (oxidation = 0) [manufactured by Mitsubishi Chemical Corporation: BR-107] [Resin E] Acrylic resin (oxidation = 6.5) [manufactured by Mitsubishi Chemical Corporation: MB-8227] [Resin F] Acrylic resin (oxidation = 18) [manufactured by Mitsubishi Chemical Corporation: BR-77] [Resin G] Ethyl cellulose [manufactured by Dow Inc.: STD4] [Resin H] Polyvinyl butyral resin [manufactured by Sekisui Chemical Co., Ltd.: BLS] [Resin I] Polyvinyl butyral resin [manufactured by Sekisui Chemical Co., Ltd.: SV02] <Experiment - 1> (Example 1) Spherical nickel powder with an average particle size D of 0.2 μm in the field of view was prepared by SEM observation. For 100 parts by mass of the nickel powder, 5 parts by mass of Resin A and 50 parts by mass of terpineol were kneaded using a three-roll mill in a dry room to prepare a conductive paste. 50 A ceramic substrate with a flat surface was prepared, and the obtained conductive paste was printed on the substrate using a wire bar so that the fired film had a flat square shape with a thickness of 3 μm and a side length of 5 cm to form a coating film. Then, the formed coating film was heated at 100 °C for 10 minutes to dry it, and then heated at a heating rate of 5 °C and fired at a maximum temperature of 1000 °C for 120 minutes to form a flat conductor film.

[0032] A ceramic substrate with a flat surface was prepared, and the obtained conductive paste was printed on the substrate using a wire bar so that the fired film had a flat square shape with a thickness of 3 μm and a side length of 5 cm to form a coating film. Then, the formed coating film was heated at 100 °C for 10 minutes to dry it, and then heated at a heating rate of 5 °C and fired at a maximum temperature of 1000 °C for 120 minutes to form a flat conductor film. (Examples 2 - 5) A flat conductor film was formed in the same manner as in Example 1, except that the binder resin was changed to those described in Table 1. (Examples 6 - 7) A flat conductor film was formed in the same manner as in Example 1, except that the organic solvent was changed to those described in Table 1. (Comparative Example 1) A flat conductor film was formed in the same manner as in Example 1, except that the water content was not controlled during the preparation of the paste. (Comparative Examples 2 to 5) A flat conductor film was formed in the same manner as in Example 1, except that the binder resin was changed to those described in Table 1. <Analysis and Evaluation> A part of each conductive paste prepared in Examples 1 to 7 and Comparative Examples 1 to 5 was heated at 200 °C, and the recovered water content was measured by the Karl Fischer method. The measurement results are also shown in Table 1.

[0033] Also, the surfaces of the flat conductor films obtained in Examples 1 to 7 and Comparative Examples 1 to 5 were observed with a white interference microscope, and evaluated as ○ if the surface height difference was less than 0.5 μm, △ if the height difference was 0.5 μm or more and less than 1 μm, and × if it was 1 μm or more. The evaluation results are also shown in Table 1.

[0034]

Table 1

[0035]

Table 2

[0036]

Table 3

Claims

1. A conductive powder having nickel as a main component and an average particle diameter D50 in the range of 0.05 to 1 μm, an acrylic resin having an acid value in the range of 0 to 10, an organic solvent for dissolving the acrylic resin, comprising wherein the organic solvent is an alcohol-based solvent having 3 or more carbon atoms and a boiling point of 300°C or lower, A fired conductive paste characterized in that the water content contained in the paste is less than 0.5% by mass.

2. The fired conductive paste according to Claim 1, wherein the blending amount of the acrylic resin is 1 to 10 parts by mass with respect to 100 parts by mass of the conductive powder.

3. The fired conductive paste according to Claim 1 or 2, wherein the blending amount of the alcohol-based solvent is 10 to 100 parts by mass with respect to 100 parts by mass of the conductive powder.

4. The fired conductive paste according to Claim 1, which is used to form a flat conductor film having a shape capable of accommodating a square with at least one side of 5.0 cm and a thickness of 0.5 μm or more.

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