Conductive pattern forming method

Abstract

To provide a method for forming a conductive pattern excellent in adhesion to a substrate.SOLUTION: A conductive pattern forming method is a conductive pattern forming method including discharging a liquid body containing conductive fine particles to a porous base material to form a conductive pattern. The conductive fine particles have an average particle diameter of 1 nm or more and 200 nm or less. The porous base material has a plurality of pores formed therein, and has communication holes communicating the pores with each other. The average pore diameter of the communication holes is equal to or less than the average particle diameter of the conductive fine particles.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for forming a conductive pattern. [Background technology]

[0002] A technique has been proposed for forming a conductive pattern by discharging a liquid containing conductive fine particles onto a substrate. Patent Document 1 discloses a technique for forming a conductive pattern by discharging a wiring-forming liquid containing metal nanoparticles onto a substrate provided with a microvoid-type receiving layer. This method allows the conductive pattern to be efficiently formed into a thick film.

[0003] Patent Document 2 discloses a porous film used as a battery separator for lithium batteries and the like. According to this document, the porous film can be used as a battery separator for lithium batteries and the like, a separator for electrolytic capacitors, an electrolyte membrane for fuel cells and the like, a battery electrode material, a gas or liquid separation membrane, a low-dielectric-constant material, and various filters. It also states that the average pore size should preferably be in the range of 0.01 μm (10 nm) to 2.5 μm (2500 nm). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-6578 [Patent Document 2] Japanese Patent Application Publication No. 2017-226777 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of Patent Document 1 sometimes has insufficient adhesion of the conductive pattern printed on the surface of the receiving layer, leaving room for improvement. Also, although it is conceivable to use a substrate having a porous structure instead of a substrate having a receiving layer, Patent Document 2 does not describe or suggest the use of a porous film as a wiring substrate or what type of porosity is suitable for improving the adhesion of the conductive pattern. In other words, there has been a demand for a method for forming a conductive pattern that has excellent adhesion to a substrate. [Means for solving the problem]

[0006] A conductive pattern forming method according to one aspect of the present application is a conductive pattern forming method in which a liquid containing conductive fine particles is discharged onto a porous substrate to form a conductive pattern, wherein the conductive fine particles have an average particle size of 1 nm or more and 200 nm or less, the porous substrate has a plurality of pores formed therein, the pores having interconnecting holes that connect the pores, and the average pore size of the interconnecting holes is equal to or less than the average particle size of the conductive fine particles. [Brief explanation of the drawings]

[0007] [Figure 1] 1A and 1B are views showing one aspect of a method for forming a conductive pattern according to the first embodiment. [Figure 2] FIG. 2 is an enlarged view of the substrate surface at part J in FIG. 1. [Figure 3] A close-up of the droplet after it hits the ground. [Figure 4] A close-up of a droplet landing on a non-porous substrate. [Figure 5] FIG. [Figure 6] FIG. [Figure 7] Enlarged view of area K in Figure 2. [Figure 8] FIG. 2 is a plan view showing a conductive pattern formed by the forming method of the embodiment. [Figure 9] FIG. 10 is a plan view showing a conductive pattern of a comparative example. [Figure 10] FIG. 10 is a plan view showing a conductive pattern of a comparative example. [Figure 11] Appearance of a smartphone. [Figure 12] External view of a laptop computer. [Figure 13] Appearance of the smartwatch. [Figure 14] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Embodiment 1 ***Outline of conductive pattern formation method*** Fig. 1 is a diagram showing one embodiment of a method for forming a conductive pattern, and Fig. 2 is an enlarged view of the surface of the substrate at part J in Fig. 1. Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] As shown in FIG. 1, in the method for forming a conductive pattern according to this embodiment, a droplet discharge head 10 is used to discharge a plurality of droplets 22 onto the surface of a substrate 1 in a desired pattern shape, for example, the shape of a wiring pattern to be formed. Here, as shown in FIG. 2, the substrate 1 is a porous substrate having a porous structure. In a preferred embodiment, the substrate 1 is a polyimide substrate having a porous structure, and has a plurality of pores 7 and communication holes 8 that connect adjacent pores 7. The plurality of pores 7 are approximately spherical and irregularly formed, but their diameters are generally uniform. Such a porous substrate can be manufactured, for example, by the manufacturing method described in Patent Document 2. However, the manufacturing method is not limited to this, and any manufacturing method capable of forming a similar porous structure may be used.

[0010] 1, droplets 22 ejected from a droplet ejection head 10 land on the surface of a substrate 1, and the droplets 22a are ejected so that adjacent droplets 22a come into contact with each other after landing. Note that three or more consecutive droplets 22a may come into contact with each other and partially overlap. In the following description, the ink from which droplets 22 are formed is referred to as a liquid.

[0011] Figure 3 is an enlarged view of a droplet that has landed on a non-porous substrate, and Figure 4 is a comparative view showing an enlarged view of a droplet that has landed on a non-porous substrate. 3 is an enlarged cross-sectional view of droplets 22a that have landed on substrate 1 by the forming method of this embodiment. As shown in FIG. 3, some of the landed droplets 22a penetrate into voids 7a that open on the surface of substrate 1, filling the voids 7a. Note that the voids that open on the surface of substrate 1 will be referred to as voids 7a, the voids that communicate with voids 7a via communicating holes 8 will be referred to as voids 7b, and the voids that communicate with voids 7b via communicating holes 8 will be referred to as voids 7c. In other words, the voids that communicate with voids 7a on the outermost surface inside substrate 1 will be referred to as voids 7b and voids 7c.

[0012] Of the liquid material that has infiltrated into pore 7a, the dispersion medium with high fluidity passes through the communicating holes 8 and enters the adjacent pore 7b. Furthermore, part of the dispersion medium also passes through the communicating holes 8 and enters the adjacent pore 7c. In other words, part of the dispersion medium also enters the multiple pores 7b and pore 7c that are in communication with pore 7a.

[0013] That is, in droplets 22a that land on porous substrate 1, the highly fluid dispersion medium passes through the communicating holes 8 and penetrates into many of the pores 7b and 7c and is quickly absorbed, while most of the solid components, such as the conductive particles and binder, remain on the surface of substrate 1. Here, because much of the highly fluid dispersion medium is absorbed into pores 7, wetting and spreading of the solid components on the surface is suppressed, and the diameter at the time of landing is generally maintained. This makes it possible to obtain a conductive pattern with the desired planar shape. Furthermore, of the liquid material that has entered the pores 7a, most of the conductive particles remain in the pores 7a without being able to pass through the communicating holes 8. After being sintered, the solid component including the conductive particles that remain in the pores 7a exerts an anchor effect, thereby playing a role in increasing the adhesion of the conductive pattern to the substrate 1.

[0014] In contrast, as shown in Fig. 4, droplets 22b that land on a plain substrate 91 without pores hardly penetrate into the substrate 91, and therefore spread on the surface of the substrate 91, becoming wider droplets 22b than droplets 22a in Fig. 3. Note that substrate 91 is a plain polyimide substrate with no surface treatment, and the amount of the ejected liquid (droplets 22) is the same for both droplets 22a and 22b. When a conductive pattern is formed by sintering the droplets 22b shown in Figure 4, the pattern is wider than the desired shape and the edges are blurred. In addition, the adhesive strength of the conductive pattern is insufficient.

[0015] ***Outline of the discharge device*** Fig. 5 is an exploded perspective view of the droplet ejection head, and Fig. 6 is a cross-sectional view of the droplet ejection head. The droplet ejection head 10 is an ejection head of an inkjet device, and is composed of a nozzle plate 12, a partition member 14, a vibration plate 13, and the like.

[0016] As shown in FIG. 5, the nozzle plate 12 is, for example, a stainless steel nozzle plate, and is provided with a plurality of nozzle holes 18 for ejecting a liquid material as ink. The partition member 14 is a partition member having a plurality of walls for partitioning a plurality of pressure chambers 15, and is disposed between the nozzle plate 12 and the vibration plate 13. A nozzle hole 18 is provided for each pressure chamber 15. The partition member 14 also forms a liquid reservoir 16 in which the liquid material pools. The vibration plate 13 is a member that serves as a lid for the multiple pressure chambers 15 and liquid reservoirs 16, and has multiple piezoelectric elements 20 attached to its upper surface. A piezoelectric element 20 is provided for each pressure chamber 15. The pressure chambers 15 and the liquid reservoirs 16 are in communication with each other via supply ports 17, and when filled with liquid, the liquid is supplied from the liquid reservoirs 16 to each pressure chamber 15. The liquid is also supplied to the liquid reservoirs 16 via supply holes 19 provided in the vibration plate 13.

[0017] 6, in the droplet ejection head 10, when a drive voltage is applied to the piezoelectric element 20, the piezoelectric element 20 deforms, and the vibration plate 13 bends in response to the deformation, increasing the pressure in the pressure chamber 15, and the liquid in the pressure chamber 15 is ejected from the nozzle hole 18 in response to this increase in pressure. Note that the ejection is not limited to a liquid jet method using the droplet ejection head 10, and any ejection method that satisfies the following preferred conditions may be used, and known droplet ejection methods may also be used.

[0018] ***Droplet volume, flight speed*** The nozzle diameter of the nozzle holes 18 in the droplet discharge head 10 serving as the discharge unit is preferably 10 μm or more and 25 μm or less. The amount of droplets 22 discharged from the droplet discharge head 10 at one time is preferably 0.2 pL or more and 20 pL or less. The flight speed of the droplets 22 during discharge is preferably 3 m / s or more and 15 m / s or less. These are preferable requirements for suppressing scattering after landing and for efficiently and accurately discharging the desired amount of droplets 22.

[0019] ***Liquid Overview*** The composition of the liquid (ink) in the preferred embodiment will be described below. The liquid is a dispersion in which solid components including conductive particles and a binder are dispersed in a dispersion medium. The liquid is also called an ink or an ink composition. The liquid may further contain a surfactant.

[0020] The conductive fine particles are preferably metal nanoparticles composed of one or more elements selected from the group consisting of a simple metal element, an alloy or compound containing a metal element, or a mixture thereof. Specific examples include simple elements, alloys, compounds, or mixtures of elements selected from the group consisting of Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, and At. Examples of compounds containing metal elements include TiO2, ZnO, SnO2, ITO, ZrO2, and SiO X , MgO, Al2O3, CeO2, Bi2O3, Mn3O4, Y2O3, WO3, Ta2O5, Nb2O5, and La2O3, etc. However, the present invention is not limited to these, and may be, for example, an oxide of a metal selected from the group consisting of silver, copper, nickel, palladium, iron, aluminum, tin, and zinc.

[0021] The conductive fine particles may be used singly or in combination of two or more. In a preferred example, the material of the conductive fine particles is preferably a noble metal such as gold, silver, platinum, copper, palladium, iridium, rhodium, osmium, or ruthenium, a transition metal such as nickel, or an amphoteric metal such as tin, with silver being more preferred. The shape of the conductive fine particles may be, for example, spherical, approximately spherical, etc. However, the shape is not limited to these, and any shape may be used as long as the particles are metal nanoparticles.

[0022] ***Average particle size of conductive particles*** From the viewpoint of dispersion stability, the average particle size of the conductive fine particles is preferably 500 nm or less, more preferably 250 nm or less, even more preferably 200 nm or less, and even more preferably 50 nm or less, while from the viewpoint of ease of production, the average particle size is preferably 1 nm or more. Among the above, from the viewpoint of ensuring that the layer formed using the liquid exhibits excellent conductivity, the conductive fine particles are preferably metal nanoparticles having an average particle size of 1 nm or more and 500 nm or less, and more preferably silver nanoparticles having an average particle size of 1 nm or more and 200 nm or less.

[0023] Furthermore, the content of the conductive microparticles in the liquid is, for example, 0.01 mass% or more, 0.05 mass% or more, 0.5 mass% or more, 5 mass% or more, 10 mass% or more, 20 mass% or more, 30 mass% or more, or 50 mass% or more relative to the total mass (100 mass%) of the liquid, and is preferably 95 mass% or less, 90 mass% or less, 80 mass% or less, 70 mass% or less, or 50 mass% or less.

[0024] The binder functions to improve the adhesion of the layer formed using the liquid to the substrate. It can also improve the strength of the layer formed using the liquid. The binder may be used alone or in combination of two or more. Examples of binders include acrylic resin, polyester, polyurethane, polyethylene resin, polypropylene, polystyrene, polyvinylpyrrolidone, polyethylene glycol, polyamide (e.g., water-soluble nylon), polyepoxy, polyvinyl alcohol, polysaccharides, proteins, polyethyleneimine, polystyrene sulfonic acid, aromatic polyamide, carboxymethyl cellulose, cellulose nanofiber, and chitin nanofiber.

[0025] The amount of binder is, for example, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of conductive fine particles, and is preferably 50 parts by mass or less, and more preferably 25 parts by mass or less.

[0026] The dispersion medium has the function of adjusting the coating properties of the liquid material. The dispersion medium may be used alone or in combination of two or more. The dispersion medium may be, for example, water alone or a mixture of water and a polar organic solvent, etc. In other words, the liquid contains water in its composition. In these polar solvents containing water, electrostatic repulsion between conductive particles tends to ensure dispersibility. Examples of polar organic solvents include those with an SP value, known as the solubility parameter, of 9.5 or greater. More specific examples include water-miscible polar organic solvents such as methanol, ethanol, propanol, acetone, acetonitrile, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, dioxane, phenol, cresol, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, and glycerin, as well as 2-ethylhexanol.

[0027] The surfactant is preferably a fluorosurfactant. Adding a fluorosurfactant to the liquid can improve the coatability of the liquid to various substrates, such as substrates made of cyclic olefin resins. Furthermore, compared to silicone surfactants and the like, fluorosurfactants are less likely to contaminate surrounding equipment when the liquid dries. Furthermore, the use of fluorosurfactants can also increase the conductivity of layers formed using the liquid compared to when silicone surfactants and the like are used. Furthermore, the use of fluorosurfactants can increase the Y value in the Yxy color system (i.e., enhance the metallic feel) of layers formed using the liquid compared to when silicone surfactants and the like are used.

[0028] Examples of the fluorosurfactant include anionic fluorosurfactants, cationic fluorosurfactants, amphoteric fluorosurfactants, and nonionic fluorosurfactants. Among these, nonionic fluorosurfactants are preferred from the viewpoint of sufficiently improving the coatability of the liquid while sufficiently ensuring the dispersibility of the conductive fine particles in the dispersion medium.

[0029] Furthermore, the fluorosurfactant preferably has a perfluoroalkenyl group or a perfluoroalkyl group, and more preferably has a perfluoroalkenyl group. Use of a fluorosurfactant having the above-mentioned groups can sufficiently improve the coatability of the liquid. Furthermore, the conductivity of a layer formed using the liquid can also be sufficiently increased. Furthermore, the fluorosurfactant is preferably a polyoxyethylene ether having an ethylene oxide chain. Use of a fluorosurfactant having the above-mentioned structure can sufficiently improve the coatability of the liquid. Furthermore, the conductivity of a layer formed using the liquid can also be sufficiently increased. The average number of moles of ethylene oxide (EO) added is preferably 25 or less, more preferably 12 or less, even more preferably 10 or less, and particularly preferably 8 or less.

[0030] Examples of fluorine-based surfactants that can be used include the Ftergent M series, such as Ftergent 251, Ftergent 208M, Ftergent 212M, Ftergent 215M, and Ftergent 250, manufactured by Neos Corporation; and the Surflon series, such as Surflon S-211, Surflon S-221, Surflon S-231, Surflon S-232, Surflon S-233, Surflon S-241, Surflon S-242, Surflon S-243, and Surflon S-386, manufactured by AGC Seimi Chemical Co., Ltd.

[0031] The amount of fluorosurfactant in the liquid is, for example, preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.08 parts by mass or more, and preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, and even more preferably 0.12 parts by mass or less, per 100 parts by mass of the dispersion medium. When the content of fluorosurfactant is equal to or greater than the above-mentioned lower limit, the coatability of the liquid can be sufficiently improved, and the layer formed using the liquid can fully exhibit the desired properties. Therefore, the conductivity of the layer formed using the liquid can be sufficiently increased. Furthermore, when the content of fluorosurfactant is equal to or less than the above-mentioned upper limit, the adhesion between the layer formed using the liquid and the substrate 1 can be improved.

[0032] ***Viscosity and surface tension of liquids*** Furthermore, the viscosity of the liquid is preferably 1 mPa·s or more and 10 mPa·s or less. This is because, when discharging by the droplet discharging method, if the viscosity is less than 1 mPa·s, the area around the nozzle is likely to be contaminated by the outflow of the liquid, and if the viscosity is more than 10 mPa·s, the nozzle holes 18 become clogged more frequently, making it difficult to discharge droplets smoothly.

[0033] Furthermore, the surface tension of the liquid is preferably in the range of 20 mN / m to 40 mN / m, because when the liquid is discharged by the droplet discharge method, if the surface tension is less than 20 mN / m, the wettability of the liquid composition to the nozzle surface increases, making flight deflection more likely to occur, and if the surface tension is more than 40 mN / m, the shape of the meniscus at the tip of the nozzle hole 18 becomes unstable, making it difficult to control the discharge amount and discharge timing. The surface tension can be adjusted by adding a small amount of a surface tension modifier, such as a fluorine-based, silicone-based, or nonionic-based one, to the liquid. Nonionic surface tension modifiers improve the wettability of the liquid to the substrate 1, improve the leveling properties of the film, and help prevent the occurrence of bumps and orange peel on the coating film. The liquid may also contain organic compounds such as alcohols, ethers, esters, and ketones, as needed.

[0034] ***Substrate Overview*** FIG. 7 is an enlarged view of the portion K in FIG. As described above, the base material 1 is a polyimide substrate having a porous structure, and has a plurality of pores 7 and communication holes 8 that connect adjacent pores 7 to each other. As mentioned above, Patent Document 2 states that the average pore diameter d1 of the pores 7 should be 10 nm or more and 2500 nm or less. However, when the porous substrate is used as a wiring substrate, the average pore diameter d1 of the pores 7 is preferably 10 nm or more and 150 nm or less. Furthermore, it is more preferably 30 nm or more and 100 nm or less. This is because if the pore diameter is too large, too much liquid will penetrate (absorb) into the substrate 1, resulting in less solid components remaining on the surface. Furthermore, if the pore diameter is too small, too little liquid will penetrate into the substrate 1, resulting in weak adhesion strength.

[0035] Furthermore, it is preferable that the average pore diameter d2 of the communicating pores 8 is smaller than the average pore diameter d1 of the pores 7 and is equal to or smaller than the average particle size of the conductive fine particles. In other words, the substrate 1 has a plurality of pores 7 formed therein, and the communicating pores 8 are communicating with each other, and the average pore diameter d2 of the communicating pores 8 is equal to or smaller than the average particle size of the conductive fine particles. This is because the dispersion medium easily penetrates the communicating pores 8 but the solid components have difficulty passing through them, and therefore it is necessary to achieve an optimal balance between the amount of dispersion medium absorbed by the substrate 1, the solid components that penetrate the substrate 1 and exert an anchoring effect, and the solid components that remain on the surface of the substrate 1 and become the main body of the conductive pattern. The thickness of the substrate 1 is preferably 30 μm or more and 100 μm or less. This is to ensure the strength required for the wiring substrate. The substrate 1 may be layered on a rigid substrate such as a silicon substrate. In other words, the substrate 1 may be reinforced by backing it with a hard substrate. If the substrate 1 is not reinforced, it can be made flexible while maintaining the strength required for the wiring substrate, and can be used by bending or deforming it.

[0036] ***Example*** Fig. 8 is a plan view showing a conductive pattern formed by the method of the example, and Figs. 9 and 10 are plan views showing conductive patterns of comparative examples.

[0037] The conductive pattern 31 shown in FIG. 8 was formed as follows. First, the composition of the liquid will be described. The conductive fine particles used were silver particles with an average particle size of 25 nm, and the content of the conductive fine particles was about 20 mass % relative to the total mass (100 mass %) of the liquid. The binder used was a polyester resin. The dispersion medium was mainly composed of about 50% by mass of water and about 28% by mass of glycol relative to the total mass of the liquid, with polyol, alcohol, surfactant, etc. further added. The viscosity of the liquid with the above composition was approximately 4 mPa·s, and the surface tension was approximately 30 mN / m.

[0038] Return to Figure 2. The thickness of the substrate 1 was 50 μm, and the average pore diameter d1 (FIG. 7) of the pores 7 was about 30 nm. The porosity, which is the proportion of the pores 7 in the substrate 1, was about 70%. Then, droplets 22 were continuously discharged onto the substrate 1 using the droplet discharge head 10 of Fig. 6, as shown in Fig. 1. The nozzle diameter of the nozzle holes 18 (Fig. 6) in the droplet discharge head 10 was set to about 20 µm. The amount of droplets 22 discharged from the droplet discharge head 10 at one time was about 2 pL, and the flight speed of the droplets 22 during discharge was about 10 m / s.

[0039] As shown in FIG. 8, three linear conductive patterns 31 were printed on the surface of the substrate 1 by discharging droplets 22 from the droplet discharging head 10. Then, the substrate 1 on which the conductive pattern 31 was printed was subjected to a heat treatment. The heat treatment conditions were approximately 120°C x 1 hour. The heat treatment was performed by placing the substrate 1 on a hot plate set to 120°C. The width W1 of the conductive pattern 31 thus formed is about 27 μm, and the gap G1 between adjacent conductive patterns 31 is about 30 μm.

[0040] 9 is a comparative diagram in which a conductive pattern 36 is formed under the same conditions as above on a plain substrate 91 without voids. The substrate 91 is a plain polyimide substrate with a thickness of 50 μm. When droplets are ejected onto a plain substrate 91, as explained in FIG. 4, the liquid hardly penetrates into the substrate 91, and the impacted droplets spread on the surface of the substrate 91, resulting in a wide pattern. As a result, the width W2 of the conductive pattern 36 is 40 μm or more. Furthermore, short-circuit areas 41 occur between adjacent conductive patterns 36 separated by a gap G1 of approximately 30 μm. In addition, bulges 42, where the pattern width is locally increased, occur in the central conductive pattern 36 and the lower conductive pattern 36. The bulges 42 are liquid pools, and the short-circuit areas 41 occur when the bulges 42 grow.

[0041] Fig. 10 shows a different failure mode from that shown in Fig. 9, where the conditions for forming conductive pattern 36 are the same as those described above. In conductive pattern 37 shown in Fig. 10, a disconnection 43 occurs due to a bulge. When a bulge occurs, there is a risk of fatal defects such as a short circuit or disconnection occurring. In contrast, the conductive pattern 31 formed on the porous substrate 1 of Fig. 8 in this embodiment was a fine pattern, but had clear edges and no bulging occurred. It was confirmed that the adhesion strength of the conductive pattern 31 was higher than that of the conductive pattern 36 provided on the plain substrate 91. Furthermore, the resistivity of the conductive pattern 31 was equivalent to that of the conductive pattern 36 provided on the plain substrate 91, confirming that it can be used as electrical wiring.

[0042] Furthermore, although not shown in the figures, it has been confirmed that the porous substrate 1 of this example is superior to the substrate having a receiving layer of Patent Document 1. Specifically, when the substrate having a receiving layer is used, bulging and bleeding are observed, although to a better degree than the plain substrate 91. This is thought to be because the substrate having a receiving layer does not have interconnecting pores and absorbs less dispersion medium than the porous substrate 1, causing the solid components on the surface to spread.

[0043] ***Variations*** In the above description, the heat treatment is performed at approximately 120°C for 1 hour, but the conditions are not limited to these and any temperature and time conditions may be used as long as they are within the heat resistance temperature range of the substrate 1 and allow the conductive particles to sinter together and become one body. Even under these conditions, the heat treatment volatilizes the dispersion medium, sintering the conductive particles to form a conductive pattern. Alternatively, the heat treatment may be performed using an electric furnace or lamp annealing.

[0044] The surface of the substrate 1 may also be subjected to a liquid-repellent treatment. For example, the liquid-repellent treatment is performed by subjecting the surface of the substrate 1 to plasma treatment using a fluorine-containing gas, thereby modifying the surface to a liquid-repellent state. This liquid-repellent treatment on the surface of the substrate 1 further suppresses the wetting and spreading of droplets after landing, allowing for the formation of finer conductive patterns. Alternatively, the substrate 1 may be treated by a coating method such as dipping or spraying using a coating agent containing a fluorinated silane material. The inner surfaces of the internal holes 7b and 7c are also subjected to the liquid-repellent treatment, thereby suppressing the wetting and spreading of solid components on the surface. Alternatively, the surface of the substrate 1 may be subjected to a hydrophilic treatment. The hydrophilic treatment involves, for example, oxygen plasma treatment to form highly hydrophilic functional groups (OH groups) on the surface of the substrate 1. Alternatively, a hydrophilic film may be formed by chemical reactions such as UV irradiation, heat curing, or moisture curing. This hydrophilic treatment on the surface of the substrate 1 increases the spreading of droplets after landing, increasing the amount of liquid that penetrates into the substrate 1, thereby improving the adhesion of the conductive pattern after sintering.

[0045] As described above, according to the conductive pattern forming method of this embodiment, the following effects can be obtained. The conductive pattern forming method is a conductive pattern forming method in which a liquid containing conductive fine particles is discharged onto a porous substrate 1 to form a conductive pattern, the conductive fine particles having an average particle size of 1 nm or more and 200 nm or less, the substrate 1 having a plurality of pores 7 formed therein and having communicating holes 8 that connect the pores 7 to each other, and the average pore size d2 of the communicating holes 8 being equal to or less than the average particle size of the conductive fine particles.

[0046] According to this formation method, in droplets 22a that land on porous substrate 1, the highly fluid dispersion medium passes through communicating holes 8 and penetrates into internal pores 7b and 7c and is quickly absorbed, while most of the solid components, such as the conductive particles and binder, remain on the surface of substrate 1. Here, because much of the highly fluid dispersion medium is absorbed into pores 7, wetting and spreading of the solid components on the surface is suppressed, and the diameter at the time of landing is generally maintained. This makes it possible to obtain conductive pattern 31 with the desired planar shape. Furthermore, of the liquid material that has entered pores 7a, most of the conductive particles are unable to pass through communicating holes 8 and remain in pores 7a facing the surface of substrate 1. The solid component containing the conductive particles that remains in pores 7a is sintered by heat treatment, and then exhibits an anchor effect, playing a role in increasing the adhesion of conductive pattern 31 to substrate 1. Therefore, it is possible to provide a method for forming a conductive pattern with excellent adhesion to a substrate. Such a substrate 1 can be suitably used as a flexible substrate. This is because the adhesion of the conductive pattern is ensured even at bent portions, thereby satisfying the mechanical and electrical reliability required for a flexible substrate.

[0047] The viscosity of the liquid is preferably 1 mPa·s or more and 10 mPa·s or less. This allows the droplets 22 to flow easily even after landing on the substrate 1, so that the dispersion medium is quickly absorbed into the plurality of pores 7. This prevents the solid components on the surface from wetting and spreading, making it possible to obtain a conductive pattern 31 with a desired planar shape.

[0048] The surface tension of the liquid is preferably 20 mN / m or more and 40 mN / m or less. This stabilizes the shape of the meniscus at the tip of the nozzle hole 18, making it easier to control the amount and timing of ejection of the droplets 22, and enabling the droplets 22 to be ejected along a desired trajectory.

[0049] The liquid preferably contains water in its composition. According to this, by adjusting the amount of water, it is possible to optimize the viscosity and surface tension of the liquid.

[0050] In addition, the substrate 1 is preferably subjected to a liquid-repellent treatment. According to this, the liquid-repellent treatment on the surface of the substrate 1 further suppresses the wetting and spreading of the droplets after landing, so that a finer conductive pattern can be formed.

[0051] The amount of liquid droplets ejected at one time is preferably 0.2 pl or more and 20 pl or less. According to this, by adjusting the amount of droplets according to the shape of the conductive pattern, it is possible to efficiently form a desired conductive pattern.

[0052] Furthermore, the nozzle diameter of the nozzle holes 18 in the droplet discharge head 10, which serves as a discharge section for discharging the liquid material, is preferably 10 μm or more and 25 μm or less. Furthermore, the flying speed of the droplets 22 when the liquid is discharged is preferably 3 m / s or more and 15 m / s or less. This makes it possible to efficiently and accurately eject a desired amount of droplets 22, and also to prevent the droplets from scattering after landing.

[0053] Embodiment 2 ***Application to electronic devices*** Fig. 11 is an external view of a smartphone, Fig. 12 is an external view of a laptop computer, and Fig. 13 is an external view of a smartwatch. The base material 1 having the conductive pattern described in the above embodiment can be applied as the substrate 1 or substrate 86 to various electronic devices.

[0054] FIG. 11 is an external view of a smartphone 100 as an electronic device. The smartphone 100 is composed of a main board 51 on which a processor and memory are mounted, a display unit 52 equipped with a touch panel, and the like. The main substrate 51 and the display unit 52 are electrically connected by a substrate 1, which is a flexible wiring substrate. The substrate 1 is a flexible substrate that uses the base material 1 having the conductive pattern described in the above embodiment.

[0055] FIG. 12 is an external view of a notebook computer 110 as an electronic device. The notebook computer 110 is composed of a main board 61 on which a processor and memory are mounted, a display unit 62 made up of a liquid crystal panel, and the like. The main substrate 61 and the display unit 62 are electrically connected by a substrate 1, which is a flexible wiring substrate. The substrate 1 is a flexible substrate that uses the base material 1 having the conductive pattern described in the above embodiment.

[0056] FIG. 13 is an external view of a smart watch 120 as an electronic device. The smart watch 120 is composed of a main board 71 equipped with a processor and memory, a display unit 72 made up of an organic EL (Electro Luminescence) panel, and the like. The main substrate 71 and the display unit 72 are electrically connected by a substrate 1, which is a flexible wiring substrate. The substrate 1 is a flexible substrate that uses the base material 1 having the conductive pattern described in the above embodiment. These electronic devices are equipped with the substrate 1 of the above embodiment, which has excellent mechanical and electrical reliability, and therefore can perform stable display operations.

[0057] FIG. 14 is an exploded perspective view of the non-contact card medium. The contactless card medium 130 as an electronic device is a card medium that performs at least one of power supply and data transmission / reception with an external transceiver (not shown) by at least one of electromagnetic waves and electrostatic capacitive coupling. The contactless card medium 130 includes a semiconductor integrated circuit chip 85 and a substrate 86 that functions as an antenna, housed within a housing made up of a card base 81 and a card cover 82. The substrate 86 is formed by providing a square annular antenna wiring 87 on the substrate 1 having the conductive pattern described in the above embodiment, and applying it as a sheet-like loop antenna. The non-contact card medium 130 has the substrate 86 of the above embodiment, which has excellent mechanical and electrical reliability, and therefore functions stably as an antenna. [Explanation of symbols]

[0058] 1...base material (substrate), 7...hole, 7a to 7c...hole, 8...communicating hole, 10...droplet ejection head, 12...nozzle plate, 13...vibration plate, 14...partition member, 15...pressure chamber, 17...supply port, 18...nozzle hole, 19...supply hole, 20...piezoelectric element, 22...droplet, 22a...droplet, 22b...droplet, 31...conductive pattern, 36...conductive pattern, 37...conductive pattern, 41...short circuit portion, 42...bulge, 43...disconnection portion, 51...metal In-board, 52...display section, 61...main board, 62...display section, 71...main board, 72...display section, 81...card base, 82...card cover, 85...semiconductor integrated circuit chip, 86...substrate, 87...antenna wiring, 91...base material, 100...smartphone, 110...notebook computer, 120...smartwatch, 130...contactless card medium, d1...average hole diameter, d2...average hole diameter, G1...gap, W1...width, W2...width.

Claims

1. A conductive pattern forming method for forming a conductive pattern by discharging a liquid containing conductive fine particles onto a porous substrate, the method comprising: the conductive fine particles have an average particle size of 1 nm or more and 200 nm or less, The porous substrate has a plurality of pores formed therein, the pores being interconnected through holes, and the average pore size of the interconnected pores is equal to or smaller than the average particle size of the conductive fine particles. A method for forming a conductive pattern.

2. The viscosity of the liquid is 1 mPa·s or more and 10 mPa·s or less. The conductive pattern forming method according to claim 1 .

3. The surface tension of the liquid is 20 mN / m or more and 40 mN / m or less. The method for forming a conductive pattern according to claim 1 or 2.

4. The liquid contains water in its composition. The method for forming a conductive pattern according to any one of claims 1 to 3.

5. The porous substrate is subjected to a liquid-repellent treatment. The method for forming a conductive pattern according to any one of claims 1 to 4.

6. the amount of droplets of the liquid material ejected at one time is 0.2 pl or more and 20 pl or less; The method for forming a conductive pattern according to any one of claims 1 to 5.

7. a nozzle diameter of the ejection portion that ejects the liquid material is 10 μm or more and 25 μm or less; The method for forming a conductive pattern according to any one of claims 1 to 6.

8. The droplet flight speed when the liquid material is discharged is 3 m / s or more and 15 m / s or less. The method for forming a conductive pattern according to any one of claims 1 to 7.

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