Method for forming sintered film and method for forming electrode wiring pattern

Abstract

To provide a method for forming a sintered film and a method for forming an electrode wiring pattern by which the cost for forming the sintered film by baking can be reduced and danger to eyes caused by a flash lamp and a laser can be avoided because the flash lamp and the laser are not used.SOLUTION: An application step of applying a conductive ink containing a copper complex and a nickel complex to form an application film, a heating and drying step of heating and drying the application film under a gas atmosphere containing an inert gas as a main component or by atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component to form a dried film, and a firing step of firing the dried film by atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component after the heating and drying step to form a sintered film, wherein a copper reduction deposition temperature of the conductive ink is lower than a nickel reduction deposition temperature, and a necking start temperature of copper is lower than the nickel reduction deposition temperature.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for forming a sintered film and a method for forming an electrode wiring pattern, and more particularly to a method for forming a sintered film and a method for forming an electrode wiring pattern that can form a sintered film by firing using atmospheric pressure plasma. [Background technology]

[0002] In recent years, printed electronics has been attracting attention as an environmentally friendly process. While the main focus of printed electronics is the formation of electrode wiring patterns, it is also possible to form insulating layers, semiconductor layers, dielectric layers, etc., and the printing methods used include screen printing, gravure printing, and inkjet printing.

[0003] Conductive inks used in printed electronics to form electrode wiring patterns include inks containing submicron to nanoparticle metal particles and metal complex inks. In addition to metal particles and organic solvents, these inks may also contain reducing agents, resins, dispersants, and other additives.

[0004] The metal particles used in conductive metal powder inks are often silver or copper. For example, when silver powder is mixed in, the electrode wiring pattern can achieve low-resistance conductivity simply by a baking process in which the solvent is evaporated and the ink is heated and dried. However, silver electrode wiring patterns can sometimes suffer from a phenomenon known as migration, in which silver diffuses into the resin substrate, causing problems such as short circuits in the wiring.

[0005] On the other hand, electrode wiring patterns formed from conductive ink mixed with copper powder have very little migration compared to when silver powder is mixed in, and copper powder is also less expensive than silver powder.In the case of conductive ink mixed with copper powder, an electrode wiring pattern with even lower resistance can be obtained by further promoting the firing process by melting the copper powder particles together through a method called photo-firing after the firing process.

[0006] Meanwhile, metal complex inks include copper complex inks made by amminating copper formate powder, and nickel complex inks made by amminating nickel formate to improve oxidation resistance. Metal complex inks undergo a firing process to reduce and precipitate metal, but like metal powder inks, an additional process called photo-firing can be carried out after the firing process to promote necking (fusion) of the precipitated metal powders by melting them together, resulting in an electrode wiring pattern with even lower resistance.

[0007] However, since metal complex ink contains a small amount of metal components, it is difficult to obtain a thick film. However, by adding copper powder, a thick film can be obtained.

[0008] As described in Non-Patent Document 1, a copper-powder-added copper-nickel complex ink is printed on a substrate by screen printing, gravure printing, offset printing, or inkjet printing in the form of an electrode wiring pattern, followed by gradual heating with a heater in an inert gas or reducing gas atmosphere. It is believed that copper is reduced and precipitated from the copper-nickel complex ink, followed by necking of the added copper powder, and finally, nickel is reduced and precipitated. Finally, the precipitated copper, added copper powder, and precipitated nickel are sintered by light sintering, which involves momentary irradiation with a flash lamp or laser. Since printed electronics is expected to be used on resin film substrates, light sintering, which involves momentary light irradiation without damaging the resin film substrate, is more advantageous than prolonged exposure to high temperatures with a heater. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] ACS Appl. Mater. Interfaces 2022, 14, 8146-8156 Summary of the Invention [Problem to be solved by the invention]

[0010] However, photo-sintering requires the most costly equipment in the process of forming electrode wiring patterns using copper powder-added copper-nickel complex ink. Furthermore, there are concerns about the risk to eyes from the use of flash lamps and lasers. Therefore, there is a need for a replacement for photo-sintering that can reduce capital investment and processing floor space while also not endangering the health of the people manufacturing the electrode wiring patterns.

[0011] Therefore, an object of the present invention is to provide a method for forming a sintered film and a method for forming an electrode wiring pattern that can reduce the cost of forming a sintered film by firing and that does not use a flash lamp or laser, thereby avoiding the risk to the eyes that these may pose. [Means for solving the problem]

[0012] In order to solve the above problems, the method for forming a sintered film of the present invention includes: a coating step of applying a conductive ink containing a copper complex and a nickel complex to form a coated film; a heat-drying step of heating and drying the coated film in a gas atmosphere containing an inert gas as a main component, or by heating and drying with atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component, to form a dried film; and a firing step of firing the dried film using atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component, after the heat-drying step, to form a sintered film, wherein the copper reduction precipitation temperature of the conductive ink is lower than the nickel reduction precipitation temperature, and the copper necking onset temperature is lower than the nickel reduction precipitation temperature.

[0013] The conductive ink may further include copper particles.

[0014] The necking initiation temperature of copper may be higher than the copper reduction precipitation temperature.

[0015] The plasma gas may be either hydrogen-enriched nitrogen gas or hydrogen-enriched argon gas, or a mixture thereof.

[0016] The atmospheric pressure plasma may be generated by applying a high frequency pulse voltage to the plasma gas under atmospheric pressure.

[0017] The dry film may be a film formed in an electrode wiring pattern on a substrate, and the baking step may be a step of selectively scanning and irradiating only the dry film in the electrode wiring pattern with the atmospheric pressure plasma to bake the dry film.

[0018] In order to solve the above-mentioned problems, the method for forming an electrode wiring pattern of the present invention is a method for forming an electrode wiring pattern using the method for forming a sintered film of the present invention, in which the coating step is a step of forming a coating film in the shape of an electrode wiring pattern on a substrate using the conductive ink, and the baking step is a step of selectively scanning and irradiating only the dry film in the shape of the electrode wiring pattern with the atmospheric pressure plasma, thereby baking the dry film. [Effects of the Invention]

[0019] The method for forming a sintered film and the method for forming an electrode wiring pattern of the present invention can reduce the cost of forming a sintered film by firing, and since no flash lamp or laser is used, it is possible to avoid the danger to the eyes caused by these. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1(a) is a schematic diagram of a mesh used when screen-printing conductive ink, and FIG. 1(b) is a schematic diagram of a substrate on which a coating film is printed in the form of an electrode wiring pattern. [Figure 2] FIG. 1 is a schematic diagram illustrating a heating and drying step in which a substrate on which a coating film is printed in the form of an electrode wiring pattern is heated by a general-purpose hot plate device to reduce and deposit metal. [Figure 3] FIG. 10 is a diagram showing an example of atmospheric pressure plasma scanning over an electrode wiring pattern in the atmospheric pressure plasma firing step of the present invention. [Figure 4] FIG. 1 is a schematic diagram illustrating a conventional optical baking process using a flash lamp. [Figure 5] FIG. 1 is a schematic diagram illustrating a conventional laser light-curing process. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the method for forming a sintered film and the method for forming an electrode wiring pattern of the present invention will be described in detail with reference to the drawings.

[0022] [Method for forming sintered film] The method for forming a sintered film of the present invention includes a coating step, a heat drying step, and a firing step.

[0023] <Coating process> This step involves applying a conductive ink containing a copper complex and a nickel complex to form a coating film. The conductive ink may further contain copper particles. The conductive ink will be described later.

[0024] The substrate on which the coating film is formed is not particularly limited, but examples thereof include insulating ceramic substrates such as alumina substrates and zirconia substrates, glass substrates, resin substrates such as polyimide film substrates and PET film substrates, and resin film substrates.

[0025] The method for applying the conductive ink is not particularly limited, and known printing pattern formation techniques such as screen printing, gravure printing, offset printing, inkjet printing, etc. can be used. By forming a coating film pattern through the application process, it is possible to form an electrode wiring pattern (wiring electrode, etc.) which is a sintered film of a desired shape.

[0026] <Heat drying process> This step is a step in which the coated film is heated and dried to form a dry film, whereby the copper complex and nickel complex are reduced to precipitate the metals.

[0027] The heat drying method includes a method of heating and drying the coating film in an inert gas / reducing gas atmosphere containing an inert gas as the main component. For example, the coating film can be heated and dried by placing it in a box-type dryer and gradually increasing the temperature inside the dryer using a heater.

[0028] Examples of inert gases include nitrogen gas, argon gas, and mixtures thereof. Since the inert gas is the main component, the ratio of the inert gas in the heating atmosphere can be 50% by volume or more. Examples of reducing gases include hydrogen gas.

[0029] Alternatively, the coating film may be heated and dried using atmospheric pressure plasma generated using a plasma gas in an inert gas / reducing gas atmosphere containing an inert gas as the main component. In this case, the coating film can be heated and dried using a plasma device.

[0030] In this heat-drying step, the same plasma device as that used in the substrate hydrophilization step described below can be used. The sintered film production line may be equipped with a plasma device for hydrophilizing the substrate before the conductive ink is applied. If a plasma device is already present, it can be used to perform the heat-drying step, allowing the hydrophilization step and the heat-drying step to be performed in a single plasma device. This eliminates the need to install new drying equipment for the heat-drying step in the production line, reducing the cost of installing new equipment and eliminating the need to increase the installation area of ​​the production line.

[0031] Examples of inert gases used for heating and drying using atmospheric pressure plasma include nitrogen gas, argon gas, and mixed gases of these. Since the inert gas is the main component, the proportion of the inert gas in the heating atmosphere can be 50% by volume or more. In addition, examples of reducing gases include hydrogen gas.

[0032] Nitrogen gas or oxygen gas can be used as the plasma gas, but in order to prevent oxidation of the film to be dried, it is desirable to use nitrogen gas, nitrogen gas with a trace amount of hydrogen added (for example, 1% to 10% by volume in the atmosphere), argon gas, argon gas with a trace amount of hydrogen added (for example, 1% to 10% by volume in the atmosphere), or a mixed gas atmosphere of any of these gases.

[0033] Intensity parameters for plasma heating and drying using atmospheric pressure plasma include high frequency power, the distance from the plasma head to the coating film, and the plasma scanning speed, and can be adjusted as appropriate.

[0034] For example, the atmospheric pressure plasma may be plasma generated by applying a high frequency pulse voltage to a plasma gas under atmospheric pressure.

[0035] Examples of atmospheric pressure plasma irradiation methods include whole-surface irradiation by scanning linear atmospheric pressure plasma or scanning the coating film, and irradiation methods by scanning only the coating film with spot atmospheric pressure plasma.

[0036] <Firing process> This step is a step in which, after the heating and drying step, the dried film is fired by atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component to form a sintered film.

[0037] In the baking step, the coating film can be baked using a plasma device. The plasma device used in the heat-drying step can be used, and in this case, the heat-drying step and the baking step can be performed as a continuous step without inserting another step between them.

[0038] The baking process can use the same plasma device as that used in the heating and drying process and the substrate hydrophilization process described below. The sintered film production line may be equipped with a plasma device for hydrophilizing the substrate before applying the conductive ink. If a plasma device is already available, it can be used to perform not only the heating and drying process but also the baking process. This allows the hydrophilization process, heating and drying process, and baking process to be performed in a single plasma device, eliminating the need to install new optical baking equipment in the production line, reducing the cost of installing new equipment and eliminating the need to increase the installation area of ​​the production line.

[0039] Examples of atmospheric pressure plasma irradiation methods include whole-surface irradiation by scanning or scanning the dry film with linear atmospheric pressure plasma, and irradiation methods by scanning only the dry film with spot atmospheric pressure plasma.

[0040] In the firing step, the coating film can be fired by atmospheric pressure plasma generated using a plasma gas in an inert gas / reducing gas atmosphere containing an inert gas as the main component.

[0041] Even when firing using atmospheric pressure plasma, examples of inert gases include nitrogen gas, argon gas, and mixed gases thereof. Since the inert gas is the main component, the proportion of the inert gas in the heating atmosphere can be 50% by volume or more. In addition, examples of reducing gases include hydrogen gas.

[0042] Nitrogen gas or oxygen gas can be used as the plasma gas, but in order to prevent oxidation of the film to be dried, it is desirable to use nitrogen gas, nitrogen gas with a trace amount of hydrogen added (for example, 1% to 10% by volume in the atmosphere), argon gas, argon gas with a trace amount of hydrogen added (for example, 1% to 10% by volume in the atmosphere), or a mixed gas atmosphere of any of these gases.

[0043] Intensity parameters for atmospheric pressure plasma baking include high frequency power, the distance from the plasma head to the dried film, and the plasma scanning speed, and can be adjusted as appropriate.

[0044] For example, the atmospheric pressure plasma may be plasma generated by applying a high frequency pulse voltage to a plasma gas under atmospheric pressure.

[0045] In the method for forming a sintered film of the present invention, if the copper reduction precipitation temperature of the conductive ink is lower than the nickel reduction precipitation temperature, the copper complex is first reduced to copper, and then the nickel complex is reduced to nickel, resulting in a structure in which copper is the core and nickel is the shell, with the copper surface being coated with nickel. This structure allows the nickel to suppress oxidation of the copper, and prevents the resistance of the sintered film from increasing over time.

[0046] In the method for forming a sintered film of the present invention, if the copper necking onset temperature is higher than the copper reduction precipitation temperature but lower than the nickel reduction precipitation temperature, the copper complex is first reduced to copper, the reduced copper necks due to melting, and then the nickel complex is reduced to nickel, resulting in a structure in which the copper is the core and the nickel is the shell after necking, and the nickel coats the copper surface. This structure allows for the production of a sintered film with low resistance, and the nickel inhibits the oxidation of the copper, thereby inhibiting an increase in the resistance of the sintered film over time.

[0047] When the conductive ink contains copper particles, the copper complex is reduced to copper, and the reduced copper and copper particles undergo necking. The nickel complex is then reduced to nickel, coating the surface of the necked copper. Even in this case, a low-resistance sintered film can be obtained, and the nickel inhibits copper oxidation, preventing the resistance of the sintered film from increasing over time. Furthermore, fine particles formed by the reduction of the copper complex precipitate on the surface of the copper particles, forming irregularities on the surface of the copper particles. These irregularities lower the necking temperature of the copper particles below the nickel reduction precipitation temperature.

[0048] In the method for forming a sintered film of the present invention, the dry film may be a film formed in the shape of an electrode wiring pattern on a substrate, and the firing step may be a step of firing the dry film by selectively scanning and irradiating atmospheric pressure plasma only onto the dry film in the shape of an electrode wiring pattern.

[0049] The atmospheric pressure plasma irradiation method includes whole irradiation by scanning or scanning the dry film with linear atmospheric pressure plasma, and irradiation method by scanning only the dry film with spot atmospheric pressure plasma. For example, in the case where the dry film is formed on the substrate in the shape of an electrode wiring pattern, the dry film is baked by selectively scanning only the dry film in the shape of the electrode wiring pattern with atmospheric pressure plasma, thereby reducing the cost required for irradiation and suppressing or preventing damage caused by plasma irradiation to parts other than the dry film.

[0050] <Other processes> The method for forming a sintered film of the present invention may include the following steps of preparing a conductive ink, a step of subjecting a substrate to hydrophilic treatment, and the like, in addition to the steps described above.

[0051] (Conductive ink manufacturing process) The conductive ink can be obtained by first preparing a copper complex ink and a nickel complex ink and then mixing them. Alternatively, copper particles may be further mixed to form a conductive ink, and a solvent may be added to adjust the viscosity of the conductive ink.

[0052] Preparation of copper complex ink <Copper complex> The copper complex has the general formula Cu(HCOO)2(L) m In the general formula, m is a natural number of 2 to 6. Furthermore, L is, for example, the same or different amino alcohol having one amino group or aliphatic amine having one amino group.

[0053] The amino alcohol has one primary amino group, at least one hydroxyl group, and may have a saturated or unsaturated, linear, branched, or cyclic hydrocarbon group having 1 to 20 carbon atoms.

[0054] Specific examples of amino alcohols include 2-aminoethanol, 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1-propanol, 1-amino-2-methyl-2-propanol, 2-amino-1-butanol, 1-amino-2-butanol, 2-amino-3,3-dimethyl-1-butanol, 2-amino-3-methyl-1-butanol, 2-amino-4-methyl-1-pentanol, 3-amino-1-propanol, 5-amino-1-pentanol, 6-amino-1-hexanol, Examples include 3-amino-2,2-dimethyl-1-propanol, 4-amino-1-butanol, 8-amino-1-octanol, 10-amino-1-decanol, 12-amino-1-dodecanol, 2-aminocyclohexanol, 4-amino-2-methyl-1-butanol, 2-amino-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-amino-1,2-propanediol, and 2-amino-2-ethyl-1,3-propanediol, and at least one of these may be selected.

[0055] The aliphatic amine has one primary amino group and may have a saturated or unsaturated, linear, branched or cyclic hydrocarbon group having 1 to 20 carbon atoms.

[0056] Specific examples of the aliphatic amine include 2-ethylhexylamine, n-butylamine, tert-butylamine, benzylamine, n-hexylamine, 2-heptylamine, cyclohexylamine, and n-dodecylamine, and at least one of these may be selected.

[0057] <Production of copper complex ink> (Raw material for copper complex ink) The raw materials for the copper complex ink can be selected from powder of Cu(HCOO)2·4H2O and at least one of the amino alcohols or aliphatic amines mentioned above.

[0058] (Mixing process) The copper complex ink can be produced by adding the above raw materials to a container and stirring them. When producing the copper complex ink, the mixing device used in the stirring step and mixing conditions such as temperature and stirring speed can be appropriately set.

[0059] Preparation of nickel complex ink Nickel complex Nickel complexes have the general formula Ni(HCOO)2(L) n In the general formula, n is a natural number of 2 to 6. L is, for example, the same or different amino alcohol having one amino group or aliphatic amine having one amino group.

[0060] The amino alcohol has one primary amino group, at least one hydroxyl group, and may have a saturated or unsaturated, linear, branched, or cyclic hydrocarbon group having 1 to 20 carbon atoms.

[0061] Specific examples of amino alcohols include 2-aminoethanol, 2-amino-2-methyl-1-propanol, 1-amino-2-propanol, 2-amino-1-propanol, 1-amino-2-methyl-2-propanol, 2-amino-1-butanol, 1-amino-2-butanol, 2-amino-3,3-dimethyl-1-butanol, 2-amino-3-methyl-1-butanol, 2-amino-4-methyl-1-pentanol, 3-amino-1-propanol, 5-amino-1-pentanol, 6-amino-1-hexanol, Examples include 3-amino-2,2-dimethyl-1-propanol, 4-amino-1-butanol, 8-amino-1-octanol, 10-amino-1-decanol, 12-amino-1-dodecanol, 2-aminocyclohexanol, 4-amino-2-methyl-1-butanol, 2-amino-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-amino-1,2-propanediol, and 2-amino-2-ethyl-1,3-propanediol, and at least one of these may be selected.

[0062] The aliphatic amine has one primary amino group and may have a saturated or unsaturated, linear, branched or cyclic hydrocarbon group having 1 to 20 carbon atoms.

[0063] Specific examples of the aliphatic amine include 2-ethylhexylamine, n-butylamine, tert-butylamine, benzylamine, n-hexylamine, 2-heptylamine, cyclohexylamine, and n-dodecylamine, and at least one of these may be selected.

[0064] <Production of nickel complex ink> (Raw material for nickel complex ink) The raw materials for the nickel complex ink can be selected from Ni(HCOO)2·2H2O powder and at least one of the amino alcohols or aliphatic amines mentioned above.

[0065] (Mixing process) The nickel complex ink can be produced by adding the above raw materials to a container and stirring them. When producing the nickel complex ink, the mixing device used in the stirring step and mixing conditions such as temperature and stirring speed can be appropriately set.

[0066] Copper particles By including copper particles in the conductive ink, the thickness of the sintered film obtained by firing the conductive ink can be made several micrometers or more, making it possible to form thick metal wiring and electrode wiring patterns.

[0067] When the number average particle diameter of the copper particles is 100 nm to 600 nm, a sufficient thickness of the metal wiring can be ensured, and the metal wiring can have a small surface irregularity and be free of cracks. More preferably, the number average particle diameter of the copper particles is 300 nm to 500 nm.

[0068] ·solvent A solvent may be included to adjust the viscosity of the conductive ink.

[0069] As the solvent, various solvents such as alcohol-based, ketone-based, hydrocarbon-based, glycol-based, terpene-based solvents, and water-based solvents can be used, and may be appropriately selected depending on the substrate to be used. Specifically, alcohol-based solvents such as methanol, ethanol, 1-propanol, isopropanol, butanol, pentanol, benzyl alcohol, diacetone alcohol, ethylene glycol, propylene glycol, and diethylene glycol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester-based solvents such as 3-methyl-methoxy-propionate; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, and diethylene glycol monoethyl ether; Examples of solvents that can be used include glycol derivatives such as terpineol, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol methyl ether acetate, and propylene glycol ethyl ether acetate; terpene solvents such as terpineol, dihydroterpineol, and dihydroterpineol acetate; amides such as formamide, N-methylformamide, dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone; aromatic hydrocarbons such as toluene and xylene; ethylene chloride; and chlorobenzene.

[0070] When a resin substrate or a resin film substrate is used as the substrate to which the conductive ink is applied, it is preferable to use a terpene solvent or a glycol derivative such as diethylene glycol monoethyl ether or diethylene glycol monobutyl ether, since this can avoid problems such as dissolution of the substrate by the solvent. Furthermore, ethylene glycol, diethylene glycol, or the like can be used in combination to adjust the viscosity.

[0071] By using these solvents, a coating film formed by applying (printing) conductive ink to a substrate made of, for example, a polyimide film can be heated to a temperature of 80°C to 150°C, and the solvent can be evaporated from the coating film, drying it out and removing it, thereby forming a dry film.

[0072] <Conductive Ink Production> The produced copper complex ink, nickel complex ink, and solvent are placed in a container and kneaded using a planetary mixer or the like to produce a conductive ink. The amounts of the copper complex, nickel complex, and solvent can be set as appropriate.

[0073] When copper particles are added, the conductive ink can be produced by putting the copper complex ink, the nickel complex ink, the solvent, and the copper particles into a container and kneading them using a planetary mixer, etc. The amounts of the copper particles, the copper complex, the nickel complex, and the solvent can be set as appropriate.

[0074] (Substrate hydrophilization treatment process) The substrates on which the sintered film is formed can be insulating ceramic substrates such as alumina and zirconia, plate glass, as well as resin substrates and resin film substrates. Hydrophilizing these substrates can improve the adhesion between the substrate and copper or nickel. For example, before applying conductive ink to a polyimide film substrate, atmospheric pressure plasma containing 80% nitrogen and 20% oxygen can be used to hydrophilize the surface of the substrate.

[0075] The substrate hydrophilic treatment process can use the same plasma device as the plasma device used in the heating and drying process and the baking process. The production line for sintered films that performs the substrate hydrophilic treatment is equipped with a plasma device used in the substrate hydrophilic treatment process. By using this to perform the substrate hydrophilic treatment process, heating and drying process, and baking process, these processes can be performed in a single plasma device, so there is no need to install new equipment for optical baking in the production line, which reduces the cost of installing new equipment and eliminates the need to increase the installation area of ​​the production line.

[0076] [Method for forming electrode wiring patterns] The method for forming an electrode wiring pattern of the present invention uses the method for forming a sintered film of the present invention. The coating step in the method for forming a sintered film is a step of forming a coating film in the shape of an electrode wiring pattern on a substrate using a conductive ink. This coating step can utilize known printing pattern formation techniques, such as screen printing, gravure printing, offset printing, and inkjet printing. By forming a coating film pattern in the coating step, a sintered film (wiring electrode, etc.) in the shape of the electrode wiring pattern can be formed.

[0077] In addition, the firing step in the method for forming a sintered film is preferably a step of firing the dry film by selectively scanning and irradiating atmospheric pressure plasma only onto the dry film in the shape of an electrode wiring pattern. By firing the dry film in this way, it is possible to reduce the cost required for irradiation and suppress or prevent damage caused by plasma irradiation to areas other than the dry film. [Example]

[0078] EXAMPLES The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0079] [Example 1] In the method for forming the sintered film of Example 1, the heat-drying step involved heating and drying the coated film in a gas atmosphere mainly composed of an inert gas, and the baking step involved baking the dried film with atmospheric pressure plasma generated using a plasma gas mainly composed of an inert gas instead of photo-baking to form a sintered film. Specifically, a conductive ink was prepared and an electrode wiring pattern was formed according to the following steps (1) to (5).

[0080] (1) Preparation of conductive ink (Manufacturing copper complex ink) Raw materials for copper complex ink The raw materials used for the copper complex ink were powder of copper(II) formate tetrahydrate (Cu(HCOO)2·4H2O) (Fujifilm Wako Pure Chemical Industries, Ltd.) and solid of 2-amino-2-methyl-1-propanol ((CH3)2C(NH2)CH2OH) (AMP, Fujifilm Wako Pure Chemical Industries, Ltd.).

[0081] Crushing process Copper (II) formate tetrahydrate was ground in a mortar until it turned whitish in color.

[0082] Mixing process A 30 mL screw cap tube was charged with one 20 mm long stirrer tip and 4.00 g of 2-amino-2-methyl-1-propanol at 40°C, followed by stirring at 500 rpm and 40°C using a hot stirrer. Next, 5.06 g of the ground copper(II) formate tetrahydrate was added to the screw cap tube. After stirring for 24 hours, the stirring conditions were changed to 100 rpm and 25°C, and stirring continued. After a total of 96 hours of stirring, a copper complex ink (sometimes referred to as "Cu-AMP") was obtained, represented by the formula (HCOO)2Cu((CH3)2C(NH2)CH2OH)2.

[0083] (Manufacturing nickel complex ink) Nickel complex ink raw material The raw materials used for the nickel complex ink were powdered nickel(II) formate dihydrate (Ni(HCOO)2·2H2O) (Fujifilm Wako Pure Chemical Industries, Ltd.) and liquid 2-ethylhexylamine (CH3CH2CH2CH2CH2(CH2CH3)CH2NH2) (2EHA Fujifilm Wako Pure Chemical Industries, Ltd.).

[0084] Crushing process Nickel (II) formate dihydrate was ground in a mortar until it turned whitish in color.

[0085] Mixing process A 30 mL screw tube was charged with one 20 mm long stirrer tip and 2-ethylhexylamine, and then stirred using a hot stirrer at 500 rpm and 25°C. The crushed nickel(II) formate dihydrate was then charged into the screw tube. After stirring for 24 hours, a nickel complex ink (sometimes referred to as "Ni-2EHA") was obtained, in which two molecules of 2-ethylhexylamine were coordinated to nickel formate (Ni(HCOO)2), represented by the formula (HCOO)2Ni(CH3CH2CH2CH2CH2(CH2CH3)CH2NH2)2.

[0086] (Conductive ink manufacturing) The manufactured Cu-AMP ink, Ni-2EHA ink, propylene glycol, and copper particles (number average particle diameter 300 nm) were placed in a container and mixed for 6 minutes at 2000 rpm using a planetary centrifugal mixer (THINKY ARE-310, manufactured by THINKY Corporation) to obtain a conductive ink. The mixing ratio of the raw materials was copper complex ink: nickel complex ink: copper powder = 1:1:2 by mass. The propylene glycol content in the conductive ink was 5% by mass.

[0087] (2) Hydrophilic treatment of the substrate (resin film) The substrate was a 50 μm thick, 100 mm square polyimide film. Before screen printing, the surface of the polyimide film was hydrophilized using atmospheric pressure plasma treatment with a mixed gas of 80% by volume of nitrogen and 20% by volume of oxygen in an atmospheric pressure plasma device (Plasmatreat GmbH, Germany).

[0088] (3) Conductive ink is printed onto the substrate (resin film) in the form of an electrode wiring pattern using screen printing. Next, using a mesh 100 capable of forming the four identical electrode wiring patterns shown in Figure 1(a), conductive ink was printed on a polyimide film substrate 200 using a screen printing method in a shape with a line width of 1 mm and a length of 30 mm to form a coating film 300 (Figure 1(b) Coating step). The thickness of the coating film 300 was adjusted to be 3 μm.

[0089] (4) Heat drying by gradually increasing the temperature using a heater in an inert gas / reducing gas atmosphere (reduction precipitation of the complex ink by heat drying) 2, in order to reduce and precipitate copper and nickel from the coating film 300 by heating and drying, nitrogen gas 420 was introduced into a box-type drying chamber 410 of a general-purpose hot plate device 400 to prevent oxidation, creating a nitrogen-purged atmosphere inside the box-type drying chamber 410, and the substrate 200 on which the coating film 300 was printed was heated with a heater in the nitrogen-purged atmosphere. The temperature was increased from room temperature at a rate of 2°C / min, and when the temperature of the coating film reached 160°C, it was held at 160°C for 10 minutes, and then the temperature was increased from 160°C at a rate of 2°C / min. When the temperature of the coating film reached 220°C, it was held at 220°C for 10 minutes to obtain a dried film 500 (heat drying process).

[0090] (5) Atmospheric pressure plasma sintering as an alternative to light sintering For the plasma baking in Example 1, a spot-type atmospheric pressure plasma device using a high-frequency power source, which was used for the hydrophilic treatment of the substrate, was used. Nitrogen with 4 volume % hydrogen added was used as the plasma gas. In the atmospheric pressure plasma device, the dried film 500 can be baked by irradiating plasma 610 while the atmospheric pressure plasma head 600 moves, as shown in the side view of FIG. 3(a). In this baking process, as shown in the plan view of FIG. 3(b), the atmospheric pressure plasma head 600 was scanned in accordance with the electrode wiring pattern shape of the dried film 500, and the plasma 610 was irradiated onto the dried film 500 to perform plasma baking (baking process). The distance from the plasma head to the dried film in the shape of the electrode wiring pattern was 10 mm, and the scanning speed was 10 mm / s to 250 mm / s, and the baking process was performed by scanning 10 times at 5-second intervals.

[0091] [Example 2] A sintered film was formed in the same manner as in Example 1, except that the distance from the plasma head to the dried film in the shape of an electrode wiring pattern was set to 20 mm.

[0092] [Example 3] A sintered film was formed in the same manner as in Example 1, except that the heat-drying step was changed to that of Example 1, and the coating film was heat-dried using atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component. Specifically, a conductive ink was prepared and an electrode wiring pattern was formed according to the following steps (1) to (5).

[0093] (1) Preparation of conductive ink A conductive ink was prepared in the same manner as in Example 1.

[0094] (2) Hydrophilic treatment of the substrate (resin film) The substrate was subjected to hydrophilization treatment in the same manner as in Example 1.

[0095] (3) Conductive ink is printed onto the substrate (resin film) in the form of an electrode wiring pattern using screen printing. As in Example 1, conductive ink was printed on a polyimide film in the form of an electrode wiring pattern.

[0096] (4) Heat drying in an inert gas / reducing gas atmosphere. Instead of baking, heat drying is performed by gradually increasing the temperature using atmospheric pressure plasma with low power control (reduction precipitation of complex ink by heat drying). Unlike Example 1, in the heat-drying process of Example 3, instead of the process of reducing and precipitating copper and nickel from the coating film by heating and drying with a heater, atmospheric pressure plasma was used to reduce and precipitate copper and nickel from the coating film. The device used was a spot-type atmospheric pressure plasma device using a high-frequency power supply, which was also used for hydrophilic treatment of substrates. Nitrogen gas containing 4% hydrogen by volume was used as the plasma gas. Rapid heating of the coating film by atmospheric pressure plasma can cause the solvent in the coating film to boil off all at once, potentially blowing away the electrode wiring pattern. Therefore, it is important to gradually heat and dry the coating film using low-energy atmospheric pressure plasma. As in Figure 3(b), the atmospheric pressure plasma head 600 was scanned to match the shape of the electrode wiring pattern of the coating film, and plasma 610 was irradiated onto the coating film. The distance from the plasma head to the coating film was 40 mm, the scanning speed was 200 mm / s, and the heating and drying process was performed by scanning 10 times at 5-second intervals.

[0097] (5) Atmospheric pressure plasma sintering as an alternative to light sintering Plasma firing was carried out in the same manner as in Example 1.

[0098] [Comparative Example 1] (Formation of sintered film by conventional light sintering) In the method for forming a sintered film in Comparative Example 1, a sintered film was formed by firing a dried film using a conventional method of photo-firing in the firing step. Specifically, a conductive ink was prepared and an electrode wiring pattern was formed according to the following steps (1) to (5).

[0099] (1) Preparation of conductive ink A conductive ink was prepared in the same manner as in Example 1.

[0100] (2) Hydrophilic treatment of the substrate (resin film) The substrate was subjected to hydrophilization treatment in the same manner as in Example 1.

[0101] (3) Conductive ink is printed onto the substrate (resin film) in the shape of an electrode wiring pattern using screen printing. As in Example 1, conductive ink was printed on a polyimide film in the form of an electrode wiring pattern.

[0102] (4) Heat drying by gradually increasing the temperature using a heater in an inert gas / reducing gas atmosphere (reduction precipitation of the complex ink by heat drying) The heat drying step was carried out in the same manner as in Example 1.

[0103] (5) Photo-curing by momentarily irradiating with a flash lamp As an existing light-curing method, light-curing was performed using a xenon flash lamp method shown in Fig. 4. A device manufactured by NovaCentrix, Inc., USA, was used as the flash lamp device 700. In order to prevent oxidation of the dried film 500, nitrogen gas 720 containing 4% hydrogen by volume was introduced into the box-type baking chamber 710 of the flash lamp device 700 to create a hydrogen-nitrogen mixed gas atmosphere inside the box-type baking chamber 710, and in this atmosphere, the dried film 500 was irradiated with a flash lamp from a light source 730.

[0104] [Comparative Example 2] (Formation of sintered film by conventional light sintering) In Comparative Example 2, a sintered film was formed in the same manner as in Comparative Example 1, except that instead of photo-curing using a flash lamp, photo-curing using a laser, which will be described below, was performed as an existing photo-curing method.

[0105] The laser method may involve shaping the beam into a line shape using a cylindrical lens and moving the printed substrate in a direction perpendicular to the line width, or may involve scanning the line-shaped laser beam. In Comparative Example 2, an LD irradiation light source device 800 manufactured by Hamamatsu Photonics K.K. was used as the laser device, and the laser beam was scanned as shown in FIG. 5. To prevent oxidation of the dried film 500, nitrogen gas 820 containing 4% hydrogen by volume was introduced into the box-shaped baking chamber 810 of the LD irradiation light source device 800 to create a hydrogen-nitrogen mixed gas atmosphere inside the box-shaped baking chamber 810. In this atmosphere, the laser beam was scanned at a scanning speed of 200 mm / sec with a laser 830, and the dried film was irradiated through a glass window 840 by scanning once. The second harmonic of an Nd:YAG laser (wavelength 532 nm) was used as the light source, and the laser beam was shaped into a line shape using a cylindrical lens and a mask.

[0106] [Volume resistivity measurement] The volume resistivities of the sintered films obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were measured by a four-terminal method using a Hioki RM3548 resistance meter and pin-type leads as electrode terminals. The resistance value of the sintered film was measured by contacting the electrode terminals with both ends of the sintered film immediately after production, and the volume resistivity R0 was calculated by calculating the obtained "resistance value × width of sintered film × thickness of sintered film ÷ length of sintered film."

[0107] The measurement results of the volume resistivity R0 of the sintered films of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Tables 1 to 5.

[0108] [Table 1]

[0109] [Table 2]

[0110] [Table 3]

[0111] [Table 4]

[0112] [Table 5]

[0113] [Evaluation results] In the conventional light-curing methods (flash lamp / laser) of Comparative Examples 1 and 2, the volume resistivity of the sintered film decreased with increasing irradiation energy. Specifically, in the conventional light-curing method (flash lamp) of Comparative Example 1, the volume resistivity decreased with increasing flash lamp irradiation time. In the conventional light-curing method (laser) of Comparative Example 2, the volume resistivity tended to decrease with slower scanning speed. In both Comparative Examples 1 and 2, it was found that the volume resistivity of the sintered film could be reduced to 30 μΩ·cm by adjusting the light-curing conditions. However, when using a polyimide film as the substrate, it is clear that it is important to balance the curing conditions, taking into account the damage to the polyimide film caused by light-curing.

[0114] On the other hand, in the plasma firing method using atmospheric pressure plasma of the present invention according to Examples 1 to 3, the volume resistivity of the sintered film decreased as the scanning speed of the atmospheric pressure plasma slowed and the irradiation energy increased. In all of Examples 1 to 3, it was found that the volume resistivity of the sintered film could be reduced to 30 μΩ·cm by adjusting the firing conditions using atmospheric pressure plasma. As in Comparative Examples 1 and 2, when using a polyimide film as the substrate, it is clear that it is important to balance the plasma firing conditions taking into account the damage that the polyimide film will sustain due to atmospheric pressure plasma.

[0115] In other words, it can be said that both light sintering and plasma sintering have the same effect on the sintered film. The greatest advantage of adopting atmospheric pressure plasma sintering as a sintered film sintering method as in the present invention is that atmospheric pressure plasma treatment is already provided within the sintered film manufacturing process in order to hydrophilize the substrate (film, glass, ceramic, etc.) on which the electrode wiring pattern is formed, and there is no need to prepare new light sintering equipment such as a flash lamp device or laser device. Furthermore, in the case of laser sintering, consideration must be given to eye safety, and in the case of flash lamp sintering, the equipment inevitably becomes quite large. [Industrial Applicability]

[0116] By adopting the atmospheric pressure plasma baking of the present invention, it becomes possible to achieve the same effect as light baking using atmospheric pressure plasma, which is used for hydrophilic treatment of substrates, thereby reducing capital investment and process floor space, and as a result, it is expected that the cost of forming electrode wiring patterns will be reduced. [Explanation of symbols]

[0117] 100: mesh, 200: substrate, 300: coating film, 400: general-purpose hot plate device, 410: box-type drying chamber, 420: nitrogen gas, 500: dried film, 600: atmospheric pressure plasma head, 610: plasma, 700: flash lamp device, 710: box-type baking chamber, 720: nitrogen gas, 730: light source, 800: LD irradiation light source device, 810: box-type baking chamber, 820: nitrogen gas, 830: laser, 840: glass window

Claims

1. a coating step of coating a conductive ink containing a copper complex and a nickel complex to form a coating film; a heat-drying step of heating and drying the coating film in a gas atmosphere containing an inert gas as a main component, or by heating and drying with atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component, to form a dried film; a firing step of firing the dried film by atmospheric pressure plasma generated using a plasma gas containing an inert gas as a main component to form a sintered film after the heating and drying step, the copper reduction deposition temperature of the conductive ink is lower than the nickel reduction deposition temperature; A method for forming a sintered film, in which the necking initiation temperature of copper is lower than the reduction precipitation temperature of nickel.

2. The method for forming a sintered film according to claim 1 , wherein the conductive ink further contains copper particles.

3. The method for forming a sintered film according to claim 2 , wherein the necking initiation temperature of copper is higher than the copper reduction precipitation temperature.

4. 2. The method for forming a sintered film according to claim 1, wherein the plasma gas is either hydrogen-added nitrogen gas or hydrogen-added argon gas, or a mixture thereof.

5. 2. The method for forming a sintered film according to claim 1, wherein the atmospheric pressure plasma is generated by applying a high frequency pulse voltage to the plasma gas under atmospheric pressure.

6. 2. The method for forming a sintered film according to claim 1, wherein the dry film is a film formed on a substrate in the shape of an electrode wiring pattern, and the firing step is a step of firing the dry film by selectively scanning only the dry film in the shape of an electrode wiring pattern with the atmospheric pressure plasma.

7. A method for forming an electrode wiring pattern using the method for forming a sintered film according to claim 1, the coating step is a step of forming a coating film in the shape of an electrode wiring pattern on a substrate using the conductive ink; The method for forming an electrode wiring pattern, wherein the baking step is a step of selectively irradiating only the dry film in the shape of an electrode wiring pattern with the atmospheric pressure plasma while scanning the dry film, thereby baking the dry film.

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