Conductive film and method for manufacturing the same

Abstract

The present invention provides a method for manufacturing conductive films that have low resistance and suppressed resistance unevenness, with high formation accuracy and high productivity. [Solution] The method for manufacturing the conductive film 23 includes a printing pattern forming step of applying an ink containing copper and copper hydride (CuH) onto a substrate to form a printed pattern, a drying film forming step of heating and blowing air onto the printed pattern to form a dried film, and a laminate forming step of repeating these steps to form a laminate 6, and a sintering step of sintering the laminate.

Description

Technical Field

[0001] The present invention relates to a conductive film and a method for manufacturing the same.

Background Art

[0002] In recent years, printed electronics has attracted attention. Printed electronics can be manufactured without the need for exposure and etching used in conventional printed circuit board manufacturing methods and without discharging harmful chemical substances. A conductive film obtained by drawing a conductive ink as a wiring pattern on a substrate using an existing printing technique (for example, inkjet, etc.) is also an example.

[0003] For example, a method of forming a conductive pattern by sintering an ink formulation containing copper nanoparticles, a copper oxidizing agent, and CuH in an air atmosphere is disclosed (see, for example, Patent Document 1 and Non-Patent Document 1).

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present disclosure is to provide a method for manufacturing a conductive film that can manufacture a conductive film with low resistance and suppressed resistance unevenness with high formation accuracy and high productivity.

Means for Solving the Problems

[0005] The method for manufacturing a conductive film according to the present embodiment as means for solving the problems includes: a printing pattern forming step of applying an ink containing copper and copper hydride (CuH) onto a substrate to form a printing pattern, a drying film forming step of heating and blowing air onto the printing pattern to form a drying film, and repeatedly performing these steps to form a laminate; a sintering step of sintering the laminate.

Effects of the Invention

[0006] According to this embodiment, it is possible to provide a method for manufacturing conductive films that have low resistance and suppressed resistance unevenness, with high formation accuracy and high productivity. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows the relationship between the ratio (mass ratio) of solvent content to the total amount of ink and its conductivity (IACS). [Figure 2] This figure shows the relationship between the solvent penetration drying time T and electrical conductivity (IACS). [Figure 3] This figure shows the relationship between the contact angle θ of the ink with respect to the substrate and its conductivity (IACS). [Figure 4] This figure shows the relationship between measured and predicted values ​​of electrical conductivity (IACS). [Figure 5] This figure shows an apparatus for measuring electrical resistivity. [Figure 6] This is a schematic diagram illustrating an example of the laminate formation process in this embodiment. [Figure 7] This is a schematic diagram illustrating an example of the sintering process in this embodiment. [Modes for carrying out the invention]

[0008] While copper used in conductive inks is low-cost, there are concerns that it is prone to oxidation, leading to increased resistance and hindering sintering. As one way to address these issues, a method has been disclosed in which copper hydride (CuH) is included in the conductive ink to improve the stability of the copper and promote sintering (see, for example, Patent Document 1 and Non-Patent Document 1).

[0009] Generally, the productivity of conductive films can be increased by increasing the amount of ink applied or by heating the ink to a high temperature. However, when the ink is heated to a high temperature, there is a concern that the copper hydride in the ink will decompose, inhibiting sintering and increasing the resistance of the conductive film. In addition, when increasing the coating amount of the ink, there is also a concern that the formed ink on the substrate flows, resulting in a decrease in the formation accuracy of the conductive film and uneven resistance of the conductive film.

[0010] The method for manufacturing a conductive film according to this embodiment can sufficiently eliminate various concerns in the prior art. More specifically, it is possible to realize a method for manufacturing a conductive film that can manufacture a conductive film with low resistance and suppressed resistance unevenness with high formation accuracy and high productivity.

[0011] The details of this embodiment will be described below.

[0012] (Method for manufacturing a conductive film, and conductive film manufacturing apparatus) The method for manufacturing a conductive film according to this embodiment includes a laminate forming step and a sintering step, and may include other steps as necessary.

[0013] The conductive film manufacturing apparatus according to this embodiment has a laminate forming means and a sintering means, and may have other means as necessary.

[0014] The method for manufacturing a conductive film can be preferably implemented by a conductive film manufacturing apparatus.

[0015] <Laminate forming step, and laminate forming means> The laminate forming step is a step of forming a laminate by repeating a printing pattern forming step and a dry film forming step.

[0016] The laminate forming means has a printing pattern forming means and a dry film forming means.

[0017] The laminate forming step can be preferably implemented by a laminate forming means.

[0018] <<Printing pattern forming step, and printing pattern forming means>> The printing pattern forming step is a step of forming a printing pattern by applying an ink containing copper and copper hydride (CuH) onto a substrate.

[0019] The printing pattern forming means is a means for forming a printing pattern by applying an ink containing copper and copper hydride (CuH) onto a substrate.

[0020] The printing pattern forming step can be preferably carried out by the printing pattern forming means.

[0021] <<<substrate>>> The material of the substrate is not particularly limited and can be appropriately selected according to the purpose. For example, paper, glass, heat-resistant synthetic resin, etc. can be mentioned.

[0022] The paper is not particularly limited and can be appropriately selected according to the purpose. For example, coated paper, wrapping paper, etc. can be mentioned.

[0023] "Heat resistance" in this specification preferably means that the glass transition temperature is higher than the firing temperature of the ink. Examples of heat-resistant synthetic resins include polyimide, epoxy resin, polycarbonate, fluororesin, etc.

[0024] The shape of the substrate is not particularly limited and can be appropriately selected according to the purpose. For example, flat plate shape, three-dimensional shape, film shape, etc. can be mentioned. Examples of three-dimensional substrates include semiconductor packages, etc.

[0025] The size, structure, and thickness of the substrate are not particularly limited and can be appropriately selected according to the application.

[0026] From the viewpoint of removing deposits, oils and fats, etc., it is preferable to wash the ink application surface with pure water, neutral detergent, etc. before applying the ink in the printing pattern forming step. The washing method is not particularly limited and can be appropriately selected according to the purpose. For example, an ultrasonic device may be used in combination.

[0027] The substrate may be surface-treated before the ink is applied in the printing pattern formation process, in order to improve adhesion with the ink. Examples of surface treatment methods include UV / O3 treatment and atmospheric pressure plasma treatment.

[0028] The substrate may be permeable.

[0029] Conventionally, when ink is applied to a permeable substrate, there is a concern that sintering will be inhibited and resistance will increase due to the separation of components necessary for the formation of a metal film as the ink penetrates. As will be described in detail later, according to the laminate formation process of this embodiment, a dried film is formed as each layer of the printed pattern is formed. Since the bottom layer of dried film functions as a penetration-preventing layer, the separation of components necessary for the formation of a metal film is suppressed, and a low-resistance conductive film can be manufactured.

[0030] In the method for manufacturing a conductive film according to this embodiment, it is desirable that the relationship between the solvent contained in the ink and the substrate satisfies the following formula I.

[0031]

number

[0032] In the above formula I, Sw is the ratio (mass ratio) of the solvent content to the total amount of ink, T is the penetration drying time (seconds) of the solvent into the substrate, and θ is the contact angle (°) of the solvent with respect to the substrate.

[0033] Here, we will explain how to derive the above equation I.

[0034] (Exams A-L) [Ink preparation] As copper, Cu nanoparticles (NPs) were used. The method for preparing these Cu nanoparticles is described in detail in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0035] The copper NP dispersion was washed with an ultrafiltration membrane (CO=100kDa, PES). A copper-containing composition was prepared using diethylene glycol monomethyl ether as the solvent. This composition was filtered through a 1 μm syringe filter, and an ink was prepared by adding 1.6% by mass of hypophosphorous acid (HPA).

[0036] The inks used in tests A to D were prepared so that the solvent content was 70% by mass of the total ink volume, the inks used in tests E to H were prepared so that the solvent content was 55% by mass of the total ink volume, and the inks used in tests I to L were prepared so that the solvent content was 20% by mass of the total ink volume.

[0037] [Preparation of the substrate] For tests A, E, and I, gloss coat (OK Topcoat, manufactured by Oji Paper Co., Ltd.) and PVA coat (manufactured by Oji Paper Co., Ltd.) were used as the substrate.

[0038] For tests B, F, and J, fluorine-free oil-resistant paper (Daio Paper Corporation, FS Oil-Resistant Paper FF) was used as the substrate.

[0039] For tests C, G, and K, glassine paper (manufactured by PAPER Entrance, model number 55064) was used as the substrate.

[0040] For tests D, H, and L, an oil-resistant agent containing fluorine as a base material (oil-resistant paper, manufactured by Ishizaki Shoji Co., Ltd., oil-resistant paper T-8) was used.

[0041] [Printing using inkjet technology] The ink used in tests A through H was printed using the inkjet method.

[0042] A Ricoh MH5420 inkjet head was used. The print pattern was a solid image with a recording density of 1200 dpi x 1200 dpi and an image size of 30 mm x 30 mm. It was printed in 2-3 layers to achieve a film thickness of 3 μm. The stage was preheated to a substrate surface temperature of 95°C.

[0043] [Printing using the spin coating method] The ink used in tests I-L was in paste form and was printed using the spin-coating method. Printing was performed on the substrate at 7,000 rpm, with a film thickness of 3 μm after drying and sintering.

[0044] [sintering] After drying, a polyimide film (Toray DuPont, 200H) was applied to the surface of the printed material, and it was placed on a hot plate heated to 230°C. Immediately afterward, a 2kg weight was placed on top and it was sintered for 60 seconds to obtain the electronic components for each test.

[0045] The conductivity (IACS: International Annealed Copper Standard) of each obtained electronic component was measured according to the following method. The results are shown in Tables 1 and 2.

[0046] [Method for measuring electrical conductivity (IACS)] The resistivity test was performed in accordance with a part of the four-probe method for conductive plastics specified in JIK719:1994. In the four-probe method, as shown in Figure 1, a current I was passed between A and D using probes A to D placed on the sample electronic component EC, and the potential difference V between B and C was measured. The sheet resistance ρs was then calculated by multiplying the ratio of these values ​​by a correction factor RCF. An RCF of 4.532, which can be obtained even assuming an infinite plane, was used. A simple low-resistivity meter, Loresta MCP-T380 (manufactured by Nitto Seikou Analytech Co., Ltd.), and a PSP probe with a pin spacing of 1.5 mm were used.

[0047] Next, the film thickness t of the electronic component was measured by observing the cross-section of the sample. Three cross-sections were measured, and the average value was defined as the film thickness t.

[0048] The volume resistivity ρv and its reciprocal, conductivity, were calculated using equation II below. Note that the conductivity (IACS) is calculated using the international standard for soft copper (volume resistivity 1.7241 × 10⁻¹⁰). -8 The conductivity was calculated assuming a conductivity of 100% (Ωm).

[0049]

number

[0050] [Table 1]

[0051] [Table 2]

[0052] Based on the results in Tables 1 and 2, Figure 2 shows the relationship between the solvent content ratio (mass ratio) to the total ink volume and IACS. Figure 2 shows a clear negative correlation between the solvent content ratio (mass ratio) to the total ink volume and IACS. From this, we hypothesized that components such as hypophosphorous acid, which should remain in the ink film, migrate to the substrate as the solvent penetrates, thereby inhibiting sintering, increasing resistance, and reducing the conductivity of the resulting electronic components. Based on this hypothesis, we further investigated the relationship between the solvent and the substrate.

[0053] First, the solvent penetration drying time T was investigated. In this specification, "solvent penetration drying time T" refers to the time (in seconds) it takes for the solvent dropped onto the substrate to disappear from the substrate by penetration and drying.

[0054] The solvent penetration drying time T was measured by taking 1000 frames per second using a high-speed microscope camera (Keyence VW-6000) and observing the time it took for a 30 pL solvent droplet placed on a substrate to disappear from the substrate. The results are shown in Tables 1 and 2.

[0055] Based on the results in Tables 1 and 2, Figure 3 shows the relationship between the solvent penetration drying time T and IACS. Figure 3 shows a negative correlation between the solvent penetration drying time T and IACS.

[0056] Next, to confirm the more microscopic interactions between the substrate and the solvent, the contact angle θ of the ink with respect to the substrate was measured using a contact angle meter DMs-301 (Kyowa Interface Science Co., Ltd.). The droplet sizes were 0.5 μL to 0.6 μL. The results are shown in Tables 1 and 2.

[0057] Based on the results in Tables 1 and 2, Figure 4 shows the relationship between the ink contact angle θ with respect to the substrate and IACS. Figure 4 shows a negative correlation between the ink contact angle θ with respect to the substrate and IACS.

[0058] In addition to the above, we also examined the correlation between the solvent and the surface roughness of the substrate, and the correlation between the solvent and the thickness of the substrate, but we could not confirm a correlation with IACS. Here, using the measurement results obtained in tests A to L, we performed multiple regression analysis with the solvent content ratio Sw (mass ratio) in the total amount of ink, the solvent penetration drying time T (seconds), and the contact angle θ (°) as explanatory variables X. The results are shown in Table 3. The multiple regression analysis shown in Table 3 satisfies the following conditions, indicating that the analysis is statistically correct. • The corrected R² is 0.6 or greater. • The significance level F is 0.05 or less. • The absolute value of the t-value excluding the intercept is 2 or greater. • The p-value is 0.05 or less.

[0059] [Table 3]

[0060] In Table 3, X value 1 is the ratio of solvent content to the total amount of ink (mass ratio) Sw, X value 2 is the logarithm of the penetration drying time T (seconds) of 1 / solvent, and X value 3 is the contact angle θ (°).

[0061] From the results in Table 3, we obtained Equation III, a predictive formula that can predict conductivity from the solvent content ratio Sw (mass ratio) in the total amount of ink, the solvent penetration drying time T (seconds), and the contact angle θ (°).

[0062]

number

[0063] Figure 5 shows the relationship between the measured values ​​obtained in the above tests A to L and the predicted values ​​calculated by Equation III. From Figure 5, it can be seen that the conductivity can be predicted with almost accuracy using the prediction formula Equation III.

[0064] For typical electronic components, an IACS of 10% or more is considered sufficient for proper functioning. Therefore, by setting the left-hand side of equation III above to 10% or more and rearranging the equation, we derive equation I below.

[0065]

number

[0066] In the printing pattern formation process, it is preferable to heat the printed pattern in conjunction with the printing pattern. In other words, when applying ink to the substrate, the substrate may be preheated. Doing so promotes the drying of the ink applied to the substrate, thereby suppressing ink flow and, as a result, improving the accuracy of conductive film formation.

[0067] There are no particular restrictions on the heating means, and they can be appropriately selected according to the purpose. For example, a heating mechanism for the stage in a printing pattern forming means can be used.

[0068] There are no particular restrictions on the heating temperature of the substrate, and it can be appropriately selected according to the purpose, but a temperature of 40°C to 100°C is preferred, and a temperature of 55°C to 75°C is more preferred.

[0069] If the heating temperature of the substrate is within these ranges, the oxidizing and reducing agents contained in the ink will evaporate, which can eliminate problems such as the sintering reaction not proceeding efficiently in the subsequent sintering process.

[0070] As the substrate, you may use one that you have synthesized as appropriate, or you may use a commercially available product.

[0071] Examples of substrates include alkali-free glass substrates (Corning Eagle XG, 40mm x 40mm x t0.7mm), polyimide (Toray DuPont Kapton H ("Kapton" is a registered trademark)), FS oil-resistant paper (Daio Paper Corporation FS Oil-Resistant Paper FF), oil-resistant paper (Ishizaki Shoji Co., Ltd. T-8), glassine paper (PAPER Entrance, model number 55064), and coated paper (Daio Paper Corporation Utrillo Coat L).

[0072] A permeable media is preferred as the substrate. Paper is preferred as the permeable media, and glassine paper is more preferred among them. Glassine paper is a type of paper that is smooth and translucent, and is mainly manufactured by mechanically compressing pulp for a long period of time and then ultra-rolling it. This manufacturing process results in a very dense arrangement of paper fibers, making the paper surface smooth and giving it a certain degree of water and oil resistance. These properties are expected to improve the accuracy of conductive film formation and prevent a decrease in conductive function by preventing the penetration of ink components.

[0073] <<<Ink>>> The ink contains copper and copper hydride (CuH), and may optionally contain reducing agents, oxidizing agents, and other components.

[0074] -copper- There are no particular restrictions on the shape of the copper; it can be appropriately selected according to the purpose, and it may be fixed in shape or irregular in shape. Among these, a fixed shape is preferred. If the copper is fixed in shape, it is preferably spherical. If the shape of the copper is spherical, it is preferably granular.

[0075] There are no particular restrictions on the particle size (volume-average median diameter) of particulate copper (hereinafter sometimes referred to as "copper particles"), and it can be appropriately selected according to the purpose, but it is preferably 10 nm to 1000 nm, and more preferably 10 nm to 200 nm.

[0076] There are no particular restrictions on the method for measuring particle size, and it can be appropriately selected depending on the purpose. For example, it can be measured using a particle size distribution analyzer that uses light scattering or a centrifugal sedimentation type particle size distribution analyzer.

[0077] There are no particular restrictions on the copper content, and it can be appropriately selected depending on the purpose, but it is preferable that it be between 10% and 90% by mass relative to the total amount of ink.

[0078] There are no particular restrictions on the method for measuring copper content, and it can be appropriately selected depending on the purpose. For example, it can be measured by simultaneous thermogravimetric-differential thermal analysis (TG-DTA).

[0079] Copper may be synthesized as appropriate, or commercially available copper may be used. There are no particular restrictions on the method of copper synthesis, and it can be selected as appropriate depending on the purpose. For example, it may be synthesized according to the description in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0080] -Copper hydride (CuH)- Copper hydride (CuH) reduces copper oxide contained in the ink and copper oxide generated during the sintering process. Specifically, during the sintering process, copper oxide contained in the dried film is reduced by the decomposition of copper hydride (CuH), which facilitates copper sintering and allows for the creation of a low-resistance conductive film. Although copper hydride (CuH) is also generated during the sintering process by hypophosphorous acid, its pre-inclusion in the ink promotes the reduction reaction of copper oxide.

[0081] There are no particular restrictions on the copper hydride (CuH) content, and it can be appropriately selected depending on the purpose. However, from the viewpoint of reducing copper oxide and promoting copper sintering in the subsequent sintering process, it is preferable that the content be 0.1% by mass or more and 1% by mass or less of the total amount of ink.

[0082] There are no particular restrictions on the method for measuring the copper hydride (CuH) content, and it can be appropriately selected depending on the purpose. For example, it can be measured by temperature-controlled desorption gas analysis.

[0083] As the copper hydride (CuH), commercially available products may be used as appropriate. Alternatively, the copper hydride (CuH) may be synthesized with reference to Non-Patent Document 1, etc.

[0084] -Reducing agent- The ink may contain reducing agents other than copper hydride (CuH) as needed.

[0085] There are no particular restrictions on the reducing agent, and it can be appropriately selected depending on the purpose. Examples include amine compounds.

[0086] Examples of amine compounds 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, and 2-aminoethanol.

[0087] These can be used individually or in combination of two or more.

[0088] -Oxidizing agent- The ink may contain an oxidizing agent, if necessary.

[0089] There are no particular restrictions on the oxidizing agent, and it can be appropriately selected depending on the purpose. Examples include phosphorus-containing compounds. Examples of phosphorus-containing compounds include phosphorous acid, phosphoric acid, hypophosphorous acid, pyrophosphate, tripolyphosphate, tetrapolyphosphate, trimetaphosphate, phosphoric anhydride, and polyphosphate. Among these, hypophosphorous acid is preferred.

[0090] These can be used individually or in combination of two or more.

[0091] Hypophosphorous acid oxidizes the copper in the ink, producing copper hydride. When hypophosphorous acid is present in the ink, the copper hydride decomposes during the sintering process, generating hydrogen, which accelerates the reduction reaction of copper oxide.

[0092] There are no particular restrictions on the amount of hypophosphorous acid, and it can be appropriately selected depending on the purpose, but it is preferable that the weight ratio of hypophosphorous acid to copper is 0.5% by mass or more and 80% by mass or less.

[0093] As hypophosphorous acid, you may use one that has been synthesized as appropriate, or you may use a commercially available product.

[0094] Examples of commercially available hypophosphorous acid include hypophosphorous acid solutions (manufactured by Sigma-Aldrich and Nippon Chemical Industrial Co., Ltd.).

[0095] -Other ingredients- Other components are not particularly limited and can be selected as appropriate depending on the purpose; for example, solvents can be used.

[0096] There are no particular restrictions on the solvent, and it can be appropriately selected depending on the purpose. For example, 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 mono-n-butyl ether, diethylene glycol monohexyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, Examples include 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, and tripropylene glycol methyl ether.

[0097] These can be used individually or in combination of two or more.

[0098] There are no particular restrictions on the solvent content, and it can be appropriately selected according to the purpose, the printing pattern forming means, and the application.

[0099] There are no particular limitations on the method or means of forming the printed pattern, and they can be appropriately selected depending on the purpose. Examples include spin coating, screen printing, spray coating, roll coating, dispensing, and inkjet. Among these, the inkjet method is preferred.

[0100] When using an inkjet method as a method or means for forming a printed pattern, there are no particular restrictions on the viscosity of the ink, and it can be appropriately selected depending on the inkjet head, but a viscosity of 5 mPa·s or more and 30 mPa·s or less is preferred.

[0101] There are no particular restrictions on the printing patterns, and they can be selected as appropriate depending on the application. Examples include solid films, electrode patterns, geometric patterns, lines, letters, numbers, symbols, and electrical circuits.

[0102] <<Drying film formation process and drying film formation means>> The drying film formation process involves heating and blowing air onto the printed pattern to form a dried film.

[0103] The drying film forming means is a means for heating and blowing air onto the printed pattern. The means for heating the printed pattern is sometimes referred to as the "heating means," and the means for blowing air onto the printed pattern is sometimes referred to as the "blowing means."

[0104] The drying film formation process can be suitably carried out by a drying film formation means.

[0105] The conductive film manufacturing method of this embodiment involves a drying film formation process that combines a heating means and a blowing means. This allows for uniform evaporation or drying of the solvent contained in the printed pattern without raising the drying temperature too high, thereby suppressing resistance unevenness and enabling temperature control that does not decompose copper hydride (CuH). As a result, a low-resistance conductive film can be obtained without reducing productivity.

[0106] There are no particular restrictions on the heating means, and they can be appropriately selected according to the purpose. For example, a heating mechanism for the stage in a printing pattern forming means can be used.

[0107] The heating temperature by the heating means is not particularly limited and can be appropriately selected according to the purpose, but from the viewpoint of promoting the drying of the printed pattern, it is preferable to adjust the temperature of the substrate to be between 40°C and 100°C, and more preferably between 55°C and 75°C.

[0108] There are no particular restrictions on the heating time by the heating means, and it can be appropriately selected according to the purpose, but it is preferably between 10 seconds and 30 minutes, and more preferably between 1 minute and 5 minutes.

[0109] There are no particular restrictions on the means of airflow; it can be selected appropriately depending on the purpose, for example, a hair dryer.

[0110] From the viewpoint of promoting the drying of the printed pattern, it is preferable to blow air using a blower at a wind speed of 3 m / s or more, and more preferably 9 m / s or more. When the wind speed of the blower is within this range, unevenness in solvent vapor pressure is suppressed, reducing uneven drying, and consequently reducing uneven resistance. The upper limit of the wind speed is preferably 36 m / s or less.

[0111] From the viewpoint of promoting the drying of the printed pattern, the air temperature of the blower is preferably between room temperature (25°C) and 200°C, and more preferably between 65°C and 165°C. When the air temperature of the blower is within this range, evaporation is promoted by heating of the printed pattern due to heat transfer from the hot air, which shortens the drying time and consequently improves productivity.

[0112] These heating temperatures, airflow temperatures, heating times, and airflow speeds can be appropriately set according to the film thickness of the printed pattern, the solvents contained in the ink, and other factors.

[0113] In the drying film formation process, it is preferable to blow air onto the surface on which the printed pattern is formed and heat the opposite surface on which the printed pattern is formed. For example, in a conductive film manufacturing apparatus equipped with a substrate transport mechanism, where printing is performed simultaneously with the transport of the substrate, this can be achieved by heating the printed pattern with a stage heating mechanism provided in the substrate transport mechanism, and by blowing air onto the printed pattern with an air blowing means installed downstream of the substrate transport.

[0114] This configuration allows for uniform evaporation (drying) of the solvent contained in the printed pattern without raising the drying temperature too high, thereby suppressing resistance unevenness and enabling temperature control that does not decompose copper hydride (CuH). As a result, a low-resistance conductive film can be obtained without reducing productivity.

[0115] Furthermore, by making the substrate transport speed in the printing pattern formation process the same as the substrate transport speed in the drying film formation process, it is also possible to apply this to a roll-to-roll system.

[0116] In the drying film formation process, it is preferable to perform heating and drying simultaneously. This configuration can suppress the flow of ink applied to the substrate, and as a result, improve the accuracy of conductive film formation.

[0117] The printing pattern formation process and the drying film formation process may be performed simultaneously. This configuration can suppress the flow of ink applied to the substrate, resulting in improved accuracy in the formation of the conductive film.

[0118] As described above, the laminate formation process involves repeatedly performing the printing pattern formation process and the drying film formation process to form a laminate. In other words, the process of forming a printed pattern layer, drying it, and then forming a dried film is repeated to form a laminate.

[0119] If ink is applied while the underlying dry film is insufficiently formed, the flow of the coating film can cause uneven film thickness, resulting in resistance inconsistencies. On the other hand, in the conductive film manufacturing method according to this embodiment, the printing pattern formation step and the drying film formation step are repeated for each layer, so the copper particles in the dried film become dense and homogeneous, which is thought to suppress resistance inconsistencies.

[0120] <Sintering process, sintering equipment> The sintering process is the process of sintering the laminate obtained in the laminate formation process.

[0121] A sintering apparatus is a means for sintering a laminate obtained by a laminate formation process.

[0122] The sintering process can preferably be carried out using a sintering apparatus.

[0123] In the sintering process, heating at a temperature higher than the heating temperature in the drying film formation process alters the crystal structure of the conductive metal contained in the ink, causing it to sinter and exhibit conductivity.

[0124] As for the sintering means, there are no particular restrictions as long as it can sinter the laminate, and it can be appropriately selected according to the purpose. For example, the same apparatus as the drying film forming means can be used.

[0125] For example, when using a hot plate as a sintering method, the laminate can be sintered by placing it on a hot plate heated to a predetermined temperature.

[0126] There are no particular restrictions on the firing temperature in the sintering process, and it can be appropriately selected according to the purpose, but a temperature of 200°C to 300°C is preferred, and a temperature of 200°C to 250°C is more preferred.

[0127] There are no particular restrictions on the firing time in the sintering process, and it can be appropriately selected according to the purpose, but it is preferably between 1 minute and 30 minutes, and more preferably between 1 minute and 5 minutes.

[0128] The sintering process may be carried out in a sealed and confined space.

[0129] When a laminate is sintered in a sealed state, the reducing agent contained in the laminate evaporates and fills the sealed container, while also remaining on the substrate surface, allowing the reduction reaction to proceed efficiently. Due to the efficient progress of the reduction reaction, sintering can be completed at low temperatures (e.g., 200°C to 250°C) and in a short time (e.g., 10 minutes or less).

[0130] In the sintering process, it is preferable to sinter a sealed container containing the laminate in a chamber where the internal space is under an inert gas atmosphere. By using such a configuration, unwanted oxidation that occurs during the sintering process can be suppressed.

[0131] There are no particular restrictions on the inert gas used; it can be appropriately selected depending on the purpose. Examples include N2 gas and Ar gas.

[0132] Here, a method for manufacturing a conductive film according to this embodiment will be described with reference to the drawings. However, this embodiment is not limited in any way to these embodiments.

[0133] In addition, the same reference numeral is used for identical components in each drawing, and redundant explanations may be omitted. Furthermore, the number, position, shape, etc. of the components are not limited to this embodiment, and can be set to a number, position, shape, etc. that is preferable for carrying out this embodiment.

[0134] Figure 6 is a schematic diagram illustrating an example of the laminate formation process in this embodiment. Figure 7 is a schematic diagram illustrating an example of the sintering process in this embodiment.

[0135] The laminate forming means 100 in Figure 6 includes a heater 3, an inkjet head 4, and a blower 5.

[0136] As shown in Figure 6, an inkjet head 4, acting as a printing pattern forming means, applies ink 20 containing copper particles 21 to the substrate 1 to form a printed pattern. At the same time, a heater 3, acting as a heating means, heats the substrate from the opposite side of the surface to which the printed pattern is applied. Note that the substrate 1 may be heated before the ink 20 is applied to it (Figure 6(A), (B)).

[0137] Next, air is blown onto the printing pattern from a blower 5 installed downstream of the conveyor. The printed pattern is dried by heating by a heating means and blowing air by a blowing means, forming the first layer of dried film 22 (Figure 6(C)).

[0138] The above series of operations are repeated to form a laminate 6 having the desired thickness (Figures 6(D), (E)).

[0139] As shown in Figures 7(A) to (C), the laminate 6 is sintered by the heater 3, which is also a sintering means, to form a conductive film 23 (Figures 7(A) to (C)).

[0140] As described above, the method for manufacturing a conductive film according to this embodiment includes a laminate formation step in which a laminate is formed by repeatedly performing a printing pattern formation step and a drying film formation step, and a sintering step in which the laminate is sintered. This makes it possible to manufacture a conductive film with low resistance and suppressed resistance unevenness with high formation accuracy and high productivity.

[0141] [Application] The conductive film obtained by the manufacturing method of the conductive film according to this embodiment can be suitably used as an electromagnetic wave shielding layer, electrode pattern, wiring pattern, and antenna pattern.

[0142] When forming an electromagnetic shielding layer on a semiconductor package, a conductive film is formed on the top and sides of the semiconductor package, and the electromagnetic shielding layer is formed by connecting the conductive film to the ground (earthing) wiring of the semiconductor package with low impedance.

[0143] The electrode pattern is printed onto the desired substrate. [Examples]

[0144] The embodiment will be specifically described below with reference to examples and comparative examples, but the embodiment is not limited to these examples. In the following examples and comparative examples, unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "percentage by mass".

[0145] (Example 1) <Ink Preparation> As copper, Cu nanoparticles (NPs) were used. The method for preparing these Cu nanoparticles is described in detail in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0146] The copper NP dispersion was washed with an ultrafiltration membrane (CO=100kDa, PES). Using diethylene glycol monobutyl ether as the solvent, a composition containing 80% by mass of copper was prepared. This composition was filtered through a 1 μm syringe filter, 1.6% by mass of hypophosphorous acid (HPA) was added, and diethylene glycol monomethyl ether was added to prepare an ink containing 36% by mass of copper.

[0147] The viscosity of the ink was 11.7 mP·s, measured using a rotational viscometer.

[0148] <Preparation of the substrate> An alkali-free glass substrate (Corning Eagle XG, 40mm x 40mm x t0.7mm) was used as the substrate. This substrate was ultrasonically cleaned in a neutral detergent solution, then rinsed with pure water and dried. Furthermore, surface treatment was performed using O2 plasma treatment to improve wettability.

[0149] <apply> Ink was applied to the substrate using an inkjet method. A Ricoh MH5420 inkjet printer was used. The printed pattern was a solid image with a recording density of 600 dpi x 600 dpi and an image size of 30 mm x 30 mm. The stage was preheated, and the temperature conditions are shown in Table 4.

[0150] <Drying> A dryer was installed downstream of the stage transport, and drying was performed by blowing air continuously from the stage movement during printing. The conditions such as air temperature and air velocity are shown in Table 4.

[0151] Furthermore, the linear speed was set so that the print pattern from one scan would dry by the time of the next scan, using heating by the stage and airflow from the dryer. A higher linear speed V reduces printing time and increases productivity. The productivity evaluation criteria are as follows: -Evaluation Criteria- A (Excellent): Linear velocity V is 100 mm / s or more. B (Good): Linear velocity V is 50 mm / s or more and less than 100 mm / s. C (Acceptable): Line speed V is less than 50 mm / s D (Not possible): Printing will take time.

[0152] These steps were repeated four times to obtain the laminate of Example 1.

[0153] Analysis of the laminate using ion chromatography and X-ray diffraction revealed a peak for hypophosphorous acid in ion chromatography and a broad peak for CuH in X-ray diffraction.

[0154] <Sintering> A polyimide film was attached to the surface of the laminate, and the laminate was placed on a hot plate heated to 250°C and fired to obtain the conductive film of Example 1. The firing was carried out in a chamber in an N2 atmosphere, and the firing time was 90 seconds.

[0155] [Evaluation of low resistivity] The conductivity of the obtained conductive film was evaluated using a four-terminal sheet resistance meter (Nitto Seiko Analytech, Loresta MCP-T370 ("Loresta" is a registered trademark)) with volume resistivity as the indicator. The evaluation criteria for volume resistivity are as follows: -Evaluation Criteria- A (Excellent): Volume resistivity ρ is 10 μΩcm or less. B (Good): Volume resistivity ρ is greater than 10 μΩcm and less than or equal to 30 μΩcm. C (Acceptable): Volume resistivity ρ is greater than 30 μΩcm and less than or equal to 100 μΩcm. D (Not acceptable): Volume resistivity ρ exceeds 100 μΩcm.

[0156] (Examples 2-15) Except for the changes in conditions shown in Table 4, the conductive film was fabricated and its volume resistivity evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0157] (Examples 16-19) Except for the changes in the conditions shown in Table 4 and the changes in the substrate as described below, a conductive film was fabricated and its volume resistivity was evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0158] In Example 16, oil-resistant paper FS (manufactured by Daio Paper Corporation) was used as the base material.

[0159] In Example 17, oil-resistant paper T-8 (manufactured by Ishizaki Shoji Co., Ltd.) was used as the base material.

[0160] In Example 18, glassine paper (manufactured by PAPER Entrance, model number 55064) was used as the substrate.

[0161] In Example 19, coated paper (Utrillocoat L, manufactured by Daio Paper Corporation) was used as the substrate.

[0162] (Examples 20-25) Except for the following changes to the ink preparation, a conductive film was prepared and its volume resistivity evaluated in the same manner as in Example 1. The results are shown in Table 4. <Ink preparation> As copper, Cu nanoparticles (NPs) were used. The method for preparing these Cu nanoparticles is described in detail in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0163] The copper NP dispersion was washed with an ultrafiltration membrane (CO=100kDa, PES). Using diethylene glycol monobutyl ether as the solvent, a composition containing 80% by mass of copper was prepared. This composition was filtered through a 1 μm syringe filter, 1.6% by mass of hypophosphorous acid (HPA) was added, and diethylene glycol monomethyl ether was added to prepare an ink containing 24% by mass of copper.

[0164] The viscosity of the ink was 7.1 mP·s, measured using a rotational viscometer.

[0165] (Comparative Examples 1-16) Except for the changes in the conditions shown in Table 5, the conductive film was fabricated and its volume resistivity evaluated in the same manner as in Example 1.

[0166] Furthermore, without airflow using a blower, it is difficult to dry the printed pattern in accordance with the stage linear speed. Therefore, in Comparative Examples 1-4, 10, and 16, the laminate was formed by waiting for the printed pattern to dry after the first scan before forming the second and subsequent layers of printed patterns. In Comparative Examples 5-7 and 11-15, the second and subsequent layers of printed patterns were formed without waiting for the printed pattern to dry after the first scan. The results are shown in Table 5.

[0167] [Table 4]

[0168] [Table 5]

[0169] The results from Examples 1 to 25 show that by drying the printed pattern using a combination of heating and blowing methods, conductive films with low resistance and suppressed resistance unevenness can be manufactured with high formation accuracy and high productivity.

[0170] The results from Comparative Examples 1-7 and 10-16 show that drying printed patterns using only heating methods results in decreased productivity and increased resistance due to high-temperature heating.

[0171] The results from Comparative Examples 5-7 and 11-12 showed that because the second and subsequent printing patterns were formed without waiting for the first printing pattern to dry, the coating film flowed, making it impossible to measure the volume resistivity.

[0172] The results from Comparative Examples 8-9 showed that when the printed pattern was dried using only an air blower without stage heating, the coating did not dry completely, making it impossible to measure the volume resistivity.

[0173] In Comparative Example 14, variations in volume resistivity were observed.

[0174] Comparative Example 15 had an extremely high volume resistivity at a single point, making measurement impossible.

[0175] (Example 26 and Comparative Example 17) The conductive film was fabricated in the same manner as in Example 1, except that the conditions shown in Table 6 were changed.

[0176] [Evaluation of low resistivity] The surface resistance of the conductive film was measured at five locations: the center and the four corners, using a four-terminal sheet resistance meter (Nittō Seikō Analytech, Loresta MCP-T370). The results are shown in Tables 6 and 7.

[0177] [Table 6]

[0178] [Table 7]

[0179] The results from Example 26 show that when the printed pattern is dried using a combination of heating and blowing methods, the variation in surface resistance within the conductive film surface is small, and resistance unevenness is suppressed.

[0180] The results from Comparative Example 17 show that drying the printed pattern using only a heating method results in a large variation in surface resistance within the conductive film surface.

[0181] (Examples 27, 28) <Ink preparation> As copper, Cu nanoparticles (NPs) were used. The method for preparing these Cu nanoparticles is described in detail in Venkata Abhinav et al., RCS Advances 2015, 5, 63985-64030.

[0182] The copper NP dispersion was washed with an ultrafiltration membrane (CO=100kDa, PES). A composition containing 28.4% by mass of copper was prepared using diethylene glycol monomethyl ether as the solvent. This composition was filtered through a 1 μm syringe filter, and an ink was prepared by adding 1.6% by mass of hypophosphorous acid (HPA).

[0183] The viscosity of the ink with a solvent content of 0.7 parts was 10.2 mP·s, and was measured using a rotational viscometer.

[0184] <Preparation of the substrate> As the substrate, FS oil-resistant paper (manufactured by Daio Paper Corporation) was used in Example 27, and glassine paper (manufactured by PAPER Entrance, model number 55064) was used in Example 28.

[0185] <apply> Ink was applied to the substrate using an inkjet method. A Ricoh MH5420 inkjet printer was used. The printed pattern was a solid image with a recording density of 600 dpi x 600 dpi and an image size of 30 mm x 30 mm. The stage was preheated, and the temperature conditions are shown in Table 8.

[0186] <Drying> A dryer was installed downstream of the stage transport, and drying was performed by blowing air continuously from the stage movement during printing. The conditions such as air temperature and air velocity are shown in Table 8.

[0187] Furthermore, the linear speed was set so that the print pattern from one scan would dry by the time of the next scan, using heating by the stage and airflow from the dryer. A higher linear speed V reduces printing time and improves productivity. The evaluation criteria for high productivity are as follows: -Evaluation Criteria- A (Excellent): Linear velocity V is 100 mm / s or more. B (Good): Linear velocity V is 50 mm / s or more and less than 100 mm / s. C (Acceptable): Line speed V is less than 50 mm / s D (Not possible): Printing will take time.

[0188] These steps were repeated four times to obtain the laminates of Examples 27 and 28.

[0189] <Sintering> A polyimide film was attached to the surface of the laminate, and the laminate was placed on a hot plate heated to 250°C and fired to obtain the conductive film of Example 1. The firing was carried out in a chamber in an N2 atmosphere, and the firing time was 90 seconds.

[0190] [Evaluation of low resistivity] The conductivity of the obtained conductive film was evaluated using a four-terminal sheet resistance meter (Nitto Seiko Analytech, Loresta MCP-T370) with volume resistivity as the indicator. The evaluation criteria for volume resistivity are as follows: -Evaluation Criteria- A (Excellent): Volume resistivity ρ is 10 μΩcm or less. B (Good): Volume resistivity ρ is greater than 10 μΩcm and less than or equal to 30 μΩcm. C (Acceptable): Volume resistivity ρ is greater than 30 μΩcm and less than or equal to 100 μΩcm. D (Not acceptable): Volume resistivity ρ exceeds 100 μΩcm.

[0191] [Method for measuring solvent permeation drying time T] The solvent penetration drying time T was measured by taking 1000 frames per second using a high-speed microscope camera (Keyence VW-6000) and observing the time it took for a 30 pL solvent droplet placed on the substrate to disappear from the substrate. The results are shown in Table 8.

[0192] [Method for measuring the contact angle θ of ink with respect to the substrate] The contact angle θ of the ink with respect to the substrate was measured using a contact angle meter DMs-301 (manufactured by Kyowa Interface Science Co., Ltd.). The droplet size was 0.5 μL to 0.6 μL. The results are shown in Table 8.

[0193] [Method for measuring electrical conductivity (IACS)] The resistivity test was performed in part according to the four-probe resistivity test method for conductive plastics specified in JIK719:1994. As shown in Table 8, a current I was passed between A and D at probes A to D placed on the electronic component, and the potential difference V between B and C was measured. The sheet resistance ρs was determined by multiplying the ratio by the correction factor RCF. An RCF of 4.532, which can be obtained even assuming an infinite plane, was used. A simple low-resistivity meter, Loresta MCP-T380 (manufactured by Nitto Seikou Analytech Co., Ltd.), and a PSP probe with a pin spacing of 1.5 mm were used.

[0194] Next, the film thickness t of the electronic component was measured by observing the cross-section of the sample. Three cross-sections were measured, and the average value was defined as the film thickness t.

[0195] The volume resistivity ρv and its reciprocal, conductivity, were calculated using equation II below. Note that the conductivity (IACS) is calculated using the international standard for soft copper (volume resistivity 1.7241 × 10⁻¹⁰). -8 The conductivity was calculated assuming a conductivity of 100% (Ωm). The results are shown in Table 8.

[0196]

number

[0197] [Formula I applicability] We checked whether the combination of solvent and substrate satisfied the conditions of Formula I above. The evaluation criteria for suitability of Formula I are as follows: -Evaluation Criteria- ○: Satisfies the conditions of Equation I. ×: Does not satisfy the conditions of Equation I.

[0198] [Table 8]

[0199] The results from Examples 27-28 show that by drying the printed pattern using a combination of heating and blowing means, a conductive film with low resistance and suppressed resistance unevenness can be manufactured with high formation accuracy and high productivity. Furthermore, all of Examples 27-28 satisfy the conditions of Formula I, and it is clear that a low-resistance conductive film can be manufactured by using a combination of solvent and substrate that satisfies Formula I. Glassine paper is particularly preferred.

[0200] Examples of embodiments of this model are as follows: <1> A laminate formation step involves repeatedly applying an ink containing copper and copper hydride (CuH) to a substrate to form a printed pattern, and a drying film formation step involves heating and blowing air onto the printed pattern to form a dried film, thereby forming a laminate. A sintering step of sintering the laminated body, This is a method for producing a conductive film, characterized by including [a specific ingredient]. <2> The drying film formation step involves blowing air onto the surface on which the print pattern is formed and heating the surface opposite to the surface on which the print pattern is formed. <1> This is a method for manufacturing a conductive film as described above. <3> The printing pattern formation step involves heating the printing pattern. <1> or <2> This is a method for manufacturing a conductive film as described above. <4> The aforementioned drying film formation step involves blowing air at a wind speed of 3 m / s or more. <1> from <3> This is a method for manufacturing a conductive film as described in any of the above. <5> The aforementioned drying film formation step involves blowing air at a blowing temperature of room temperature or higher and 200°C or lower. <1> from <4> This is a method for manufacturing a conductive film as described in any of the above. <6> The drying film formation step involves heating the substrate to 55°C or higher. <1> from <5> This is a method for manufacturing a conductive film as described in any of the above. <7> The aforementioned substrate is paper. <1> from <6> This is a method for manufacturing a conductive film as described in any of the above. <8> The substrate is glassine paper. <1> from <6> This is a method for manufacturing a conductive film as described in any of the above. <9> The aforementioned ink contains hypophosphorous acid, <1> from <7> This is a method for manufacturing a conductive film as described in any of the above. <10> <1> from <9> This conductive film is characterized by being manufactured by a method for manufacturing a conductive film described in any of the above.

[0201] <1> from <9> A method for manufacturing a conductive film as described in any of the following, and <9> The conductive film described herein can solve the problems of the conventional method and achieve the objectives of this embodiment. [Explanation of Symbols]

[0202] 1 Base 20 ink 21 Copper particles 22 Dry membrane 23 Conductive film 3 Heaters 4. Inkjet head 5. Blower means 6 Laminate [Prior art documents] [Patent Documents]

[0203] [Patent Document 1] Special Announcement No. 2019-529587

Non-licensed literature

[0204] [Non-licensed 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 laminate formation step involves repeatedly performing a printing pattern formation step, in which an ink containing copper and copper hydride (CuH) is applied to a substrate to form a printed pattern, and a drying film formation step, in which a dried film is formed by heating and blowing air onto the printed pattern, to form a laminate. A sintering step of sintering the laminated body, A method for producing a conductive film, characterized by including the following:

2. The method for manufacturing a conductive film according to claim 1, wherein the drying film formation step involves blowing air onto the surface on which the print pattern is formed and heating the surface opposite to the surface on which the print pattern is formed.

3. The method for manufacturing a conductive film according to claim 1 or 2, wherein the printing pattern formation step is performed in conjunction with heating the printing pattern.

4. The method for manufacturing a conductive film according to claim 1 or 2, wherein the drying film formation step is performed by blowing air at a wind speed of 3 m / s or more.

5. The method for manufacturing a conductive film according to claim 1 or 2, wherein the drying film formation step is performed by blowing air at an air blowing temperature of room temperature or higher and 200°C or lower.

6. The method for producing a conductive film according to claim 1 or 2, wherein the drying film formation step involves heating the substrate to 55°C or higher.

7. The method for manufacturing a conductive film according to claim 1 or 2, wherein the substrate is paper.

8. The method for manufacturing a conductive film according to claim 1 or 2, wherein the substrate is glassine paper.

9. The method for producing a conductive film according to claim 1 or 2, wherein the ink contains hypophosphorous acid.

10. A conductive film characterized by being manufactured by the method for manufacturing a conductive film described in claim 1 or 2.

Images