Conductive film manufacturing method

Abstract

To provide a conductive film manufacturing method capable of manufacturing a conductive film having a uniform film thickness at a low temperature.SOLUTION: A conductive film manufacturing method includes a discharging step of discharging an ink containing a conductive metal onto a substrate by an ink jet, a drying step of drying the ink discharged onto the substrate by irradiating the ink with light from a light source, and a firing step of firing a dried film obtained in the drying step, in which the light has a maximum peak in an emission spectrum in a half-value width region of a maximum peak in a light absorption spectrum of the conductive metal.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a conductive film. [Background technology]

[0002] Printed electronics has been attracting attention in recent years. Unlike conventional methods for manufacturing printed circuit boards, which require exposure and etching, printed electronics can be manufactured without emitting harmful chemicals. Printed electronics are electronic devices that can be obtained by, for example, using existing printing technology to print a predetermined wiring pattern using conductive ink containing metal particles. Printed electronics are widely used in shielding films, battery current collectors, solar cells, electrodes, RFID antennas, and more. To develop conductivity, conductive inks used in printed electronics are typically formed into films using existing printing techniques, and then dried and baked using heating and drying equipment such as heaters or hot plates.

[0003] For example, Patent Document 1 discloses a technology for forming a conductive layer that covers the surface of an electronic component by ejecting a liquid composition containing a metal such as silver by inkjet and irradiating it with light, with the aim of providing high-quality EMI shielding for electronic components that are sensitive to EMI within an electronic module (see, for example, Patent Document 1). For example, Patent Document 2 discloses a method comprising the steps of depositing a pattern of conductive ink having clusters of conductive copper nanoparticles, drying the conductive ink, and photosintering the conductive ink, in which copper oxide is reduced to metallic copper during photosintering, and the drying is performed in a vacuum chamber (see, for example, Patent Document 2). Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a method for producing a conductive film that can produce a conductive film with a uniform thickness at a low temperature. [Means for solving the problem]

[0005] The conductive film manufacturing method of the present invention as a means for solving the problems includes: a discharge step of discharging an ink containing a conductive metal onto a substrate by inkjet; a drying step of irradiating the ink ejected onto the substrate with light from a light source to dry it; A baking step of baking the dried film obtained in the drying step, The light has a maximum peak in the emission spectrum in the half width region of the maximum peak in the optical absorption spectrum of the conductive metal. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a method for producing a conductive film that can produce a conductive film with a uniform thickness at a low temperature. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a conductive film manufacturing apparatus according to the present invention. [Figure 2] FIG. 2 is a schematic diagram of the inkjet printer in the embodiment as viewed from above. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the invention described in Patent Document 1, during the process of forming a conductive layer on an electronic component, the conductive ink applied to the side surface of the electronic component drips, causing the thickness of the conductive film on the side surface of the electronic component to become uneven. This causes the drying speed to differ depending on the location where the conductive ink is applied, resulting in uneven drying, which creates a problem of differences in the resistance values ​​of the resulting electronic components. Furthermore, in the invention described in Patent Document 2, the high temperature of the heat source used increases the evaporation rate of the solvent contained in the conductive ink, causing the conductive metal inside the coating to shrink and resulting in cracks in the coating.

[0009] The conductive film manufacturing method of the present invention can sufficiently resolve various concerns in the prior art. More specifically, it is possible to realize a conductive film manufacturing method that can manufacture a conductive film with a uniform thickness at a low temperature.

[0010] The present invention will be described in detail below.

[0011] (Conductive film manufacturing method and conductive film manufacturing device) The conductive film manufacturing method of the present invention includes a discharging step, a drying step, and a baking step, and may include other steps as necessary. The conductive film manufacturing apparatus according to the present invention includes a discharge means, a drying means, and a baking means, and may include other means as necessary. The conductive film manufacturing method can be suitably carried out by a conductive film manufacturing apparatus.

[0012] <Discharge step and discharge means> The ejection step is a step of ejecting ink containing a conductive metal onto a substrate by inkjet. The ejection means is an ink jet. The ejection step can be suitably carried out by an ejection means.

[0013] The inkjet as a discharging means is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a continuous jet type, an on-demand type, etc. On-demand types include a piezo type, a thermal type, an electrostatic type, etc.

[0014] <<Base>> The material of the substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples include electronic components, cardboard, building materials such as wallpaper and flooring, concrete, cloth for clothing such as T-shirts, textiles, leather, etc.

[0015] The shape of the substrate is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a flat plate, a three-dimensional shape, a film shape, etc. Examples of three-dimensional substrates include semiconductor packages.

[0016] The size, structure, and thickness of the substrate are not particularly limited and can be appropriately selected depending on the application.

[0017] From the viewpoint of removing deposits, oils, etc., it is preferable to wash the ink-coated surface of the substrate using pure water, a neutral detergent, etc. before applying the ink in the ejection step. The washing method is not particularly limited and can be appropriately selected depending on the purpose, and for example, an ultrasonic device may be used in combination.

[0018] To improve adhesion to the ink, the substrate may be surface-treated before the ink is applied in the ejection step. Examples of surface treatment methods include UV / O3 and atmospheric pressure plasma treatment.

[0019] In the ejection and drying steps, the substrate may be preheated. This can accelerate the drying of the ink (ink film) applied to the substrate, thereby shortening or eliminating the subsequent drying step. The substrate temperature is preferably 60°C or higher and 100°C or lower.

[0020] The substrate may be suitably synthesized or may be a commercially available product. An example of a commercially available substrate is a product called Package (20 mm x 20 mm x 2.0 mm, manufactured by Denken Co., Ltd.).

[0021] <<Ink>> The ink contains a conductive metal and may contain other ingredients as needed.

[0022] -Conductive metal- In this specification, "electrically conductive" means that the resistance is 100 mΩ / □ or less. The resistance is preferably 50 mΩ / □ or less, and more preferably 10 mΩ / □ or less. The method for measuring the resistance is not particularly limited and can be appropriately selected depending on the purpose. For example, the resistance can be measured by the four-probe method or the eddy current method.

[0023] The conductive metal is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include copper, silver, and gold.

[0024] The conductive metal preferably has a maximum peak in the range of 550 nm to 650 nm in the absorption spectrum, and specifically, copper is preferred as the conductive metal.

[0025] The shape of the conductive metal is not particularly limited and can be appropriately selected depending on the purpose, and may be regular or irregular. Among these, regular shapes are preferred. When the conductive metal has a regular shape, it is preferably spherical. When the conductive metal has a spherical shape, it is preferably in the form of particles.

[0026] The particle diameter (volume-average median diameter) of the particulate conductive metal (hereinafter sometimes referred to as "conductive metal particles") is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 10 nm or more and 1,000 nm or less, and more preferably 10 nm or more and 200 nm or less.

[0027] When copper is used as the conductive metal, it is preferably copper nanoparticles. In this specification, copper nanoparticles refer to copper particles having a particle diameter of 10 nm to 200 nm. By using copper nanoparticles as a conductive metal, the surface energy is increased compared to bulk copper, which lowers the melting point and allows for a lower firing temperature.

[0028] The method for measuring particle size is not particularly limited and can be appropriately selected depending on the purpose. For example, the particle size can be measured using a particle size distribution measuring device that uses light scattering or a centrifugal sedimentation particle size distribution measuring device.

[0029] When copper is used as the conductive metal, the copper may be in the form of a copper complex. Copper complexes can be prepared, for example, by reacting a cyclic amine, imine, or primary amine with a copper precursor compound, which may, for example, contain one or more coordinating leaving groups (e.g., water, ammonia, etc.) that are displaced by the cyclic amine, imine, or primary amine during the reaction. The reaction may be carried out in a solvent, preferably one that does not outcompete the cyclic amine, imine, or primary amine for coordination to copper and that promotes displacement of the leaving group, such as, for example, acetonitrile, dimethyl sulfoxide (DMSO), tetrahydrofuran, and the like. In some cases, the reaction can be carried out at a higher temperature to assist in the displacement of the leaving group. The amount of cyclic amine, imine, or primary amine depends on the number of molecules coordinated to copper. For example, if two molar equivalents of cyclic amine, imine, or primary amine and one molar equivalent of copper precursor compound are used, two molecules of the cyclic amine, imine, or primary amine will be coordinated to copper.

[0030] The copper complex may be obtained from a copper precursor composition comprising a copper complex, for example, a cuprous complex comprising an imine or a primary cyclic amine coordinated to a cuprous precursor compound, and a cupric complex comprising a primary amine or a secondary cyclic amine coordinated to a cupric precursor compound.

[0031] The amounts of the cuprous complex and the cupric complex in the copper precursor composition can be adjusted depending on the properties of the cuprous complex and the cupric complex. The amount (w / w) of the cuprous complex relative to the cupric complex may be in the range of about 1 to 99% of the total amount of the cuprous complex and the cupric complex, preferably in the range of about 5 to 95%, more preferably in the range of about 10 to 75%, about 20 to 75%, about 40 to 75%, about 50 to 75%, or about 60 to 66%.

[0032] The copper precursor composition may be contained in an amount of about 1 to 99 wt %, preferably about 5 to 95 wt %, about 10 to 90 wt %, or about 20 to 80 wt %, based on the total amount of the ink. After considering all other components, including the copper precursor composition, any binders present, and any other ingredients, the solvent generally constitutes the balance of the ink, which may comprise about 1-99 wt% of the total ink, and preferably about 5-95 wt%, about 15-95 wt%, about 20-75 wt%, or about 20-40 wt%.

[0033] The content of the conductive metal is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 10% by mass or more and 90% by mass or less based on the total amount of the ink.

[0034] The method for measuring the content of the conductive metal is not particularly limited and can be appropriately selected depending on the purpose. For example, the content can be measured by simultaneous thermogravimetry-differential thermal analysis (TG-DTA).

[0035] The conductive metal may be suitably synthesized or may be a commercially available product. The method for synthesizing copper as a conductive metal is not particularly limited and can be appropriately selected depending on the purpose. For example, copper may be synthesized based on the description in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0036] -Other ingredients- The other components are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include solvents, reducing agents, copper oxide, dispersants, rust inhibitors, antifoaming agents, wetting agents, and antioxidants.

[0037] --solvent-- The solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the solvent include water, terpineol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol monohexyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monomethyl ether, di ... glycol monoethyl ether acetate, ethylene glycol monopropyl ether acetate, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol monophenyl ether acetate, ethylene glycol monobenzyl ether acetate, ethylene glycol monohexyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, diethylene glycol monohexyl ether acetate, diethylene glycol n-butyl ether acetate, propylene glycol, dipropylene glycol methyl ether, tripropylene glycol methyl ether, and the like. Among these, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, and dipropylene glycol monomethyl ether are preferred as diluent solvents. These may be used alone or in combination of two or more.

[0038] The content of the solvent is not particularly limited as long as it can be ejected by the inkjet ejection means, and can be appropriately selected depending on the purpose.

[0039] --Reducing agent-- When the conductive metal comprises copper, the ink preferably comprises a reducing agent. The reducing agent reduces copper oxide contained in the ink and copper oxide produced during the firing process. The reducing agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include amine compounds, copper hydride (CuH), etc. Examples of the amine compound include 2-amino-1-butanol, 1-amino-2-propanol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-hydroxymethyl-1,3-propanediol, 1,3-diamino-2-propanol, 1-amino-2-butanol, 2-aminoethanol, etc. Among these, copper hydride (CuH) is preferred. Copper hydride (CuH) is also produced during the baking process by an oxidizing agent (e.g., hypophosphorous acid), but by including CuH in the ink in advance, the reduction reaction of copper oxide is promoted.

[0040] The reducing agent may be one that has been appropriately synthesized, or copper hydride may be produced by referring to Non-Patent Document 1.

[0041] --Oxidizing agent-- When the conductive metal comprises copper, the ink preferably comprises an oxidizer. The oxidizing agent oxidizes the copper contained in the ink. The oxidizing agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include phosphorus-containing compounds. Examples of phosphorus-containing compounds include hypophosphorous acid, phosphorous acid, phosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, phosphoric anhydride, and polyphosphoric acid. Among these, hypophosphorous acid is preferred. When hypophosphorous acid is contained in the ink, copper hydride (CuH) is generated during the baking process, which promotes the reduction reaction of copper oxide. These may be used alone or in combination of two or more.

[0042] The content of the oxidizing agent is not particularly limited and can be appropriately selected depending on the purpose, but the weight ratio of hypophosphorous acid to copper is preferably 0.5% by mass or more and 80% by mass or less.

[0043] The oxidizing agent may be an appropriately synthesized one or a commercially available product. Examples of commercially available oxidizing agents include hypophosphorous acid solution (manufactured by Sigma-Aldrich and Nippon Chemical Industry Co., Ltd.).

[0044] [Ink properties] The viscosity of the ink is not particularly limited as long as it can be jetted by inkjet and can be appropriately selected depending on the purpose, but from the viewpoint of jetting stability, the viscosity at 25°C to 60°C is preferably 3 mPa·s to 40 mPa·s, more preferably 5 mPa·s to 15 mPa·s, and even more preferably 6 mPa·s to 12 mPa·s. Furthermore, the viscosity at 25°C is preferably 3 mPa·s to 40 mPa·s, more preferably 5 mPa·s to 15 mPa·s, and even more preferably 6 mPa·s to 12 mPa·s.

[0045] There are no particular limitations on the method for measuring the viscosity of the ink and it can be selected appropriately depending on the purpose. For example, the viscosity can be measured using a cone-plate rotational viscometer VISCOMETER TVE-22L manufactured by Toki Sangyo Co., Ltd., using a cone rotor (1°34' x R24) at a rotation speed of 50 rpm and setting the temperature of the constant temperature circulating water appropriately in the range of 20°C to 65°C. A VISCOMATE VM-150III can be used to adjust the temperature of the circulating water.

[0046] The ink may be an appropriately synthesized ink or a commercially available ink. Examples of commercially available inks include IJ02 (manufactured by Ishihara Chemical Co., Ltd.) and Metalon CI-005 (manufactured by NovaCentrix).

[0047] The ink of the present invention may be contained in a container. The containers containing the ink can be used as ink cartridges or ink bottles. This eliminates the need to directly touch the ink when transporting or replacing it, preventing hands and clothing from getting dirty. It also prevents foreign matter such as dust from getting mixed into the ink. The shape and size of the ink container are not particularly limited and can be selected appropriately depending on the application. The material of the ink container is not particularly limited and can be selected appropriately depending on the purpose, but is preferably a light-blocking material that does not transmit light. The ink container itself may be covered with a light-blocking sheet or the like.

[0048] <Drying process and drying means> The drying step is a step in which the ink ejected onto the substrate is dried by irradiating it with light from a light source. The drying means is a light source, preferably an LED light source. The drying step can be suitably carried out by a drying means.

[0049] The drying step is a step of drying the solvent contained in the ink. When the ink contains an oxidizing agent and a reducing agent, it is preferable to dry the ink to a degree that does not evaporate the oxidizing agent and the reducing agent. By going through the drying step, it becomes easier to prevent the ink applied to the side surface of the substrate from dripping.

[0050] The drying temperature in the drying step and the temperature at which the oxidizing agent and reducing agent are dried to a degree that does not evaporate are not particularly limited and can be appropriately selected depending on the purpose, but it is preferable to set the temperature of the coating film during light irradiation to 50° C. or higher and 100° C. or lower, and more preferably to set it to 60° C. or higher and 80° C. If the drying temperature is within this range, it is possible to eliminate the problem that the conductivity of conductive metals (particularly copper) is not expressed when drying at high temperatures.

[0051] In this specification, "light having a maximum peak in its emission spectrum in the half width region of the maximum peak in the optical absorption spectrum of the conductive metal" may be referred to as "specific light." In the drying step of the present invention, the ink can be dried efficiently by irradiating the ink with specific light. That is, when the specific light is used in the drying step, the ink dries faster, which makes it possible to prevent the ink applied to the side surface of the substrate from dripping, thereby obtaining a high-quality conductive film with a uniform film thickness.

[0052] The light irradiation time in the drying step is not particularly limited and can be selected appropriately depending on the purpose, but from the viewpoint of making the conductive film have a uniform thickness and obtaining a good resistance value, it is preferably 2 minutes or more and 4 minutes or less.

[0053] In the conductive film manufacturing method of the present invention, the time from when the ink is ejected until when light is irradiated is not particularly limited and can be selected appropriately depending on the purpose. However, from the viewpoint of effectively suppressing dripping of the ink applied to the side surface of the substrate, it is preferably 0.01 seconds or more and 1 second or less.

[0054] The drying step in the present invention can be carried out under an atmospheric environment.

[0055] In the drying process, the angle of incidence of light on the substrate is not particularly limited and can be selected appropriately depending on the purpose, but it is preferably 45° or more from the viewpoint of effectively suppressing dripping of the ink applied to the side surface of the substrate.

[0056] From the viewpoint of improving the efficiency of energy absorption for ink, it is preferable that the peak in the absorption spectrum of the substrate is different from the peak in the light absorption spectrum of the conductive metal. In this specification, "different peaks" means that the difference in maximum peaks is at least 50 nm or more. The method for determining the absorption spectrum of the substrate is not particularly limited and can be appropriately selected depending on the purpose. For example, the absorption spectrum can be analyzed by the ATR method of infrared spectroscopy.

[0057] There are no particular restrictions on the LED light source, and it can be selected appropriately depending on the purpose, as long as it can irradiate light having a maximum peak in the emission spectrum in the half-width region of the maximum peak in the light absorption spectrum of the conductive metal. With conventional drying methods, the high temperature of the heat source (IR heater, etc.) used accelerates the evaporation of the solvent contained in the ink, causing the conductive metal inside the coating to shrink and resulting in cracks in the resulting conductive film.Using an LED light source as the light source in the drying process reduces power consumption during drying and enables drying at low temperatures, making it possible to produce a high-quality, uniform conductive film.

[0058] As the LED light source, a commercially available product may be used as appropriate. Commercially available LED light sources include, for example, NIR-LED lamps (maximum peak wavelength: 800 nm or more, manufactured by Phoseon Technology), high-power spot lighting (maximum peak wavelength: approximately 625 nm, manufactured by MBJ Imaging), LS-60RD (maximum peak wavelength: 620 nm, manufactured by CCS Inc.), and IDBC-LSR200R-S (maximum peak wavelength: 634 nm, manufactured by Raymac Co., Ltd.).

[0059] <Firing process and firing means> The firing step is a step of firing the dried film obtained in the drying step. The calcination means is a means for calcining the dried film. The calcination step can be suitably carried out by a calcination means.

[0060] In the baking step, the ink is heated at a temperature equal to or higher than the drying temperature in the drying step, thereby changing the crystal structure of the conductive metal contained in the ink and baking it, thereby developing conductivity. The firing temperature in the firing step is not particularly limited and can be selected appropriately depending on the purpose. It is preferable to set the temperature of the dried film to 200°C or higher and 250°C or lower, and more preferably to set it to 230°C or higher and 250°C or lower.

[0061] The baking means is not particularly limited as long as it can heat the dried film to a temperature equal to or higher than the drying temperature, and can be appropriately selected depending on the purpose, but UV-LED is preferred. When a UV-LED is used as the baking means, the maximum peak in the emission spectrum of the UV-LED is preferably 395 nm.

[0062] As the calcination means, commercially available products may be used as appropriate. Examples of commercially available baking means include a UV-LED lamp (peak wavelength: 395 nm, manufactured by Ushio Inc.).

[0063] Here, a conductive film manufacturing apparatus according to the present invention will be described with reference to the drawings, although the present invention is not limited to these embodiments. In each drawing, the same components are denoted by the same reference numerals, and redundant explanations may be omitted. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. may be any number, position, shape, etc. that is preferable for implementing the present invention.

[0064] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a conductive film manufacturing apparatus according to the present invention. The conductive film manufacturing apparatus 1 of FIG. 1 includes a printing unit 1a, a printing unit 1b, a light source 2a, a light source 2b, a light source 3, and a stage 4.

[0065] The printing unit 1a has an ink cartridge filled with ink and a carriage that holds an ejection head. The carriage is provided with a plurality of ejection heads each having a plurality of nozzles, and forms an image by ejecting ink from the nozzles of the ejection heads. The nozzles are provided at an angle relative to the surface facing the stage. On the surface of the carriage facing the stage 4, there are provided light sources 2a and 2b that emit visible light, and a light source 3 that emits ultraviolet light.

[0066] Ink is ejected onto a substrate 5 on a stage 4 by the printing unit 1a and the printing unit 1b. Then, in order to dry the ink, visible light is irradiated from a light source 2b to dry the ink, thereby forming an image. Similarly, ink is again ejected onto the substrate 5 on the stage 4 by the printing units 1a and 1b. Next, in order to dry the ink, visible light is irradiated from the light source 2a to dry it, thereby forming an image. After this reciprocating printing is completed, the substrate is transported to the light source 3 for curing the ink. The ink is cured by irradiating it with ultraviolet light from the light source 3, forming a conductive film.

[0067] Each printing unit 1a and printing unit 1b may be provided with a heating mechanism to liquefy the ink in the ink ejection section. If necessary, a mechanism for heating the substrate by contact or non-contact may also be provided.

[0068] As the inkjet recording method, either a serial method in which ink is ejected by moving the head onto a substrate that moves intermittently according to the width of the ejection head, or a line method in which ink is ejected from a head held at a fixed position while the substrate moves continuously, can be applied.

[0069] The substrate 5 is not particularly limited, but examples thereof include a package, a PWB, a PCB, and a semiconductor. When the substrate 5 is a film or paper that is transparent or translucent to a specific light, the specific light may be irradiated from the backside of the substrate. This configuration promotes drying of the interface between the substrate and the ink and is also effective in reducing the installation area of ​​the device.

[0070] [Application] The conductive film obtained by the conductive film manufacturing method of the present invention can be suitably used as an electromagnetic wave shielding layer. When forming an electromagnetic wave shielding layer on a semiconductor package, a conductive film is formed on the top and side surfaces of the semiconductor package, and the conductive film is connected to the ground (earth) wiring of the semiconductor package with low impedance, thereby forming the electromagnetic wave shielding layer. [Example]

[0071] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples and comparative examples, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0072] (Examples 1 to 14 and Comparative Examples 1 to 2) <Ink Preparation> Copper nanoparticles (NPs) were used as copper in Examples 1 to 13. The method for preparing the Cu nanoparticles is described in detail in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030. The copper NP dispersion was washed with an ultrafiltration membrane (CO = 100 kDa, PES). A composition containing 30 to 60 mass% copper was prepared using diethylene glycol monomethyl ether (DEGME, manufactured by Kanto Chemical Co., Ltd.), dipropylene glycol monobutyl ether (DPGBE, manufactured by Kanto Chemical Co., Ltd.), and diethylene glycol monobutyl ether (DEGBE, manufactured by Kanto Chemical Co., Ltd.) as solvents. The composition was filtered through a 1 μm syringe filter, and 1.6 mass% hypophosphorous acid (HPA) was added to prepare an ink. In Example 14, copper(II) formate amine complexes were used, which were prepared by coordinating two molar equivalents of different amines with one molar equivalent of copper(II) formate.

[0073] The viscosity of the ink was adjusted to 10 mP·s or more and 20 mP·s or less, preferably 10 mP·s or more and 15 mPa·s or less. The viscosity of the ink was measured using a rotational viscometer. The resulting ink was analyzed by ion chromatography and X-ray diffraction, and a hypophosphorous acid peak was detected by ion chromatography, and a broad CuH peak was detected by X-ray diffraction.

[0074] <Preparation of the substrate> The substrate used was a package (20 mm x 20 mm x 2.0 mm, manufactured by Denken Co., Ltd.) In order to improve the wettability of the substrate, a surface treatment was performed using O2 plasma.

[0075] <Discharge ~ Drying> The inkjet printer used had the structure shown in Figure 2. Figure 2 is a schematic diagram of the inkjet printer in the example when viewed from above. The inkjet printer has printing unit 1a and printing unit 1b, which are equipped with ink cartridges filled with ink and ejection heads, a stage 4, drying lamps 2a to 2d provided on the left and right or front, back, left and right of stage 4, and a baking lamp 3. When using high-power spot lighting (manufactured by MBJ Imaging, wavelength around 625 nm) as the drying lamp, drying lamps 2 a to 2 d are arranged on the front, back, left and right sides of the stage 4 . When an NIR-LED lamp (manufactured by Phoseon Technology, wavelength 800 nm or more) is used as a drying lamp, drying lamps 2 a and 2 b are placed on the left and right of the stage 4 .

[0076] The substrate was placed on stage 4 of the inkjet printer, and ink was ejected onto the top and sides of the substrate from printing units 1a and 1b. The stage was then moved back and forth so as to pass under lamps installed on the front, back, left and right sides of stage 4. The illumination conditions at this time were a high-power spot light with an illuminance of 6 W / cm. 2 The irradiance of the NIR-LED lamp is 20W / cm 2 The distance between the substrate and the lamp was set to 5 mm. The discharge amount was controlled so that the average thickness of the coating film would be 3 μm to 5 μm. Other conditions are shown in Tables 1 to 3. In Comparative Example 1, the stage 4 was dried by moving back and forth so as to pass under a UV-LED lamp (manufactured by Ushio Inc., peak wavelength 395 nm) installed next to the drying lamp.

[0077] <Firing> The stage 4 was moved to a position under a UV-LED lamp (manufactured by Ushio Inc., peak wavelength 395 nm) installed next to the drying lamp, and the dried film was irradiated with light to obtain a conductive film. The irradiation conditions were illuminance: 10 W / cm 2 The irradiation time was set to 2 minutes, the distance between the substrate and the lamp was set to 5 mm, and the baking temperature was set to 230°C.

[0078] The electronic devices obtained in Examples 1 to 14 and Comparative Examples 1 and 2 were subjected to the following measurements and evaluations.

[0079] <Film thickness measurement> The thickness of the resulting conductive film was measured using a stylus-type step gauge (Alphastep D-500, manufactured by KLA-Tencor). The film thickness was measured at two arbitrary points on the conductive film on the upper surface of the substrate, the difference between the two measurements was calculated, and the film was evaluated based on the following evaluation criteria. Similarly, the film thickness was measured at two arbitrary points on the conductive film on the side surface of the substrate, the difference between the two measurements was calculated, and the film was evaluated based on the following evaluation criteria. A rating of "△" or better was considered to be acceptable. The results are shown in Tables 1 to 3. -Evaluation criteria- ◎: Film thickness difference is 1 μm or less ○: Film thickness difference is more than 1 μm and less than 2 μm △: Film thickness difference is more than 2 μm and less than 3 μm ×: Film thickness difference exceeds 3 μm

[0080] <Sheet resistance measurement> The sheet resistance of the obtained conductive film was measured using a four-terminal measuring device (Loresta MCP-T370, manufactured by Nitto Seiko Analytech) and evaluated based on the following evaluation criteria. A rating of "△" or better was considered to be acceptable. The results are shown in Tables 1 to 3. -Evaluation criteria- ◎: Resistance value is 10mΩ / □ or less ○: Resistance value is over 10mΩ / □ and 50mΩ / □ or less △: Resistance value is over 50mΩ / □ and 100mΩ / □ or less ×: Resistance value exceeds 100mΩ / □

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] In Examples 1 and 2, conductive films were obtained in which the difference in film thickness between the upper surface and the side surface of the substrate was good and the sheet resistance value was also good. In Examples 3 to 6, compared to Example 1, it can be seen that as the time from application of the ink to irradiation with light becomes longer, the difference in film thickness between the upper surface and the side surface of the substrate becomes larger. In Examples 7 to 9, it is clear that when the drying time is shorter than in Example 1, the difference in film thickness between the upper surface and the side surface of the substrate increases, and the sheet resistance also increases. In Example 10, it is clear that the sheet resistance increases as the drying time increases compared to Example 1. In Example 11, it can be seen that without heating from the stage, the difference in film thickness between the upper surface and the side surface of the substrate becomes larger than in Example 1, and the sheet resistance also increases. Examples 12 and 13 use inks different from those used in Examples 1 to 11, and it is clear that similar effects can be obtained even with other ink types. Example 14 uses ink different from Examples 1 to 11, which uses a copper complex, and it is clear that similar effects can be obtained with other ink types.

[0085] In Comparative Examples 1 and 2, the light irradiated onto the ink did not have a maximum peak in the emission spectrum in the half-width region of the maximum peak in the optical absorption spectrum of the conductive metal, and therefore the film thickness difference on the top and side surfaces of the substrate and the sheet resistance value deteriorated, making the ink unusable.

[0086] The present invention includes, for example, the following aspects. <1> a discharge step of discharging an ink containing a conductive metal onto a substrate by inkjet; a drying step of drying the ink ejected onto the substrate by irradiating the ink with light from a light source; A firing step of firing the dried film obtained in the drying step, The conductive film manufacturing method is characterized in that the light has a maximum peak in its emission spectrum in a half width region of the maximum peak in the optical absorption spectrum of the conductive metal. <2> The conductive metal has a maximum peak in the range of 550 nm to 650 nm in its absorption spectrum. <1> 1. A method for producing a conductive film according to claim 1. <3> The conductive metal includes copper. <1> or <2> 1. A method for producing a conductive film according to claim 1. <4> The copper is copper nanoparticles. <3> 1. A method for producing a conductive film according to claim 1. <5> a peak in the optical absorption spectrum of the substrate is different from a peak in the optical absorption spectrum of the conductive metal; <1> from <4> The conductive film manufacturing method according to any one of the above items. <6> the time from when the ink is ejected to when the light is irradiated is 0.01 seconds or more and 1 second or less; <1> from <5> The conductive film manufacturing method according to any one of the above items. <7> The light irradiation time in the drying step is 2 minutes or more and 4 minutes or less. <1> from <6> The conductive film manufacturing method according to any one of the above items. <8> the temperature of the substrate in the discharging step and the drying step is 60°C or higher and 100°C or lower; <1> from <7> The conductive film manufacturing method according to any one of the above items. <9> The incident angle of the light to the substrate is 45° or more. <1> from <8> The conductive film manufacturing method according to any one of the above items. <10> The baking step is performed by UV-LED, The maximum peak in the emission spectrum of the UV-LED is 395 nm. <1> from <9> The conductive film manufacturing method according to any one of the above items. <11> The light source is an LED light source. <1> from <10> The conductive film manufacturing method according to any one of the above items.

[0087] <1> from <11> According to any one of the conductive film manufacturing methods described above, the conventional problems can be solved and the object of the present invention can be achieved. [Explanation of symbols]

[0088] 1 Conductive film manufacturing equipment 1a Printing unit 1b Printing unit 2a Drying lamp 2b Drying lamp 2c Drying Lamp 2d Drying Lamp 3 Firing lamp 4 Stages 5 Base [Prior art documents] [Patent documents]

[0089] [Patent Document 1] Patent Publication No. 2021-072438 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-128068 [Non-patent literature]

[0090] [Non-Patent Document 1] Lousada CM, Fernandes RMF, Tarakina NV, Soroka IL. Synthesis of copper hydride (CuH) from CuCO3 Cu(OH)2 a path to electrically conductive thin films of Cu. Dalton Trans. 2017 May 23;46(20):6533-6543. doi: 10.1039 / c7dt00511c. PMID: 28379275.

Claims

1. a discharge step of discharging an ink containing a conductive metal onto a substrate by inkjet; a drying step of drying the ink ejected onto the substrate by irradiating the ink with light from a light source; A firing step of firing the dried film obtained in the drying step, The conductive film manufacturing method, wherein the light has a maximum peak in its emission spectrum in a half width region of a maximum peak in the optical absorption spectrum of the conductive metal.

2. 2. The conductive film manufacturing method according to claim 1, wherein the conductive metal has a maximum peak in the range of 550 nm to 650 nm in the absorption spectrum.

3. The conductive film manufacturing method according to claim 1 , wherein the conductive metal includes copper.

4. The conductive film manufacturing method according to claim 3 , wherein the copper is copper nanoparticles.

5. 3. The conductive film manufacturing method according to claim 1, wherein a peak in the optical absorption spectrum of the substrate is different from a peak in the optical absorption spectrum of the conductive metal.

6. 3. The conductive film manufacturing method according to claim 1, wherein the time from when the ink is ejected to when the light is irradiated is 0.01 seconds or more and 1 second or less.

7. 3. The conductive film manufacturing method according to claim 1, wherein the light irradiation time in the drying step is from 2 minutes to 4 minutes.

8. 3. The conductive film manufacturing method according to claim 1, wherein the temperature of the substrate in the discharging step and the drying step is 60° C. or higher and 100° C. or lower.

9. 3. The conductive film manufacturing method according to claim 1, wherein the incident angle of the light on the substrate is 45 degrees or more.

10. The baking step is performed by UV-LED, 3. The conductive film manufacturing method according to claim 1, wherein the UV-LED has an emission spectrum with a maximum peak at 395 nm.

11. The conductive film manufacturing method according to claim 1 , wherein the light source is an LED light source.

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