Circuit formation substrate and method for manufacturing circuit formation substrate

Abstract

The purpose of the present invention is to further miniaturize wiring by controlling the landing position of inkjet droplets in an inkjet method. A circuit formation substrate provided with a wiring pattern in at least a portion thereof comprises: an insulating base material; a resin layer that is formed on the insulating base material and contains an epoxy resin; an inkjet droplet landing layer that is formed on the resin layer and is formed by landing of a plurality of metal-particle-containing inkjet droplets; and a plating layer that is formed on the inkjet droplet landing layer. The elastic modulus (Pa) of the surface of the resin layer measured at 25°C using an atomic force microscope is 7.0 × 106 to 12.0 × 106.

Description

Circuit formation substrate, and method for manufacturing a circuit formation substrate

[0001] This disclosure relates to a circuit-forming substrate and a method for manufacturing a circuit-forming substrate.

[0002] To provide a method for manufacturing an electronic circuit board that can quickly and efficiently coat a uniform nano-ink composition layer under normal temperature and pressure, and an electronic circuit board obtained thereby, a technique is known in which a nano-ink composition containing metal particles is held in a printing plate having an ink-holding portion with a predetermined pattern formed on its surface, the surface of a substrate is brought into close contact with the printing plate, the nano-ink composition held in the ink-holding portion is transferred onto the substrate, and after the transfer, the transferred nano-ink composition is dried and fixed in an environment of 40°C or lower in air to form an electronic circuit with a predetermined pattern (see Patent Document 1 below).

[0003] Furthermore, from the perspective of the prior art mentioned above, the inkjet method is considered inefficient and therefore avoided, while the flexographic printing method is adopted.

[0004] Japanese Patent Publication No. 2016-76538

[0005] However, the manufacturing of circuit boards using the inkjet method offers many advantages that cannot be measured by existing productivity evaluations, such as enabling production with reduced environmental impact through material reduction, and is therefore expected to contribute to a sustainable world. In recent years, as the development of the inkjet method has progressed and line widths have become narrower, a challenge has arisen in controlling the landing position of inkjet droplets. If the landing position of inkjet droplets does not fall to the desired position, miniaturization of circuits becomes difficult.

[0006] Therefore, at least one aspect of the problem addressed in this disclosure is to control the landing position of inkjet droplets in the inkjet method and to further miniaturize wiring. Furthermore, problems that are obvious to a person skilled in the art, as can be inferred from the embodiments and descriptions of the features of this disclosure described in the specification, drawings, etc., may also become problems that the divisional inventions should solve if a divisional application based on this disclosure is filed.

[0007] To achieve the above-mentioned objective, the circuit formation substrate of this disclosure is a circuit formation substrate having a wiring pattern in at least a part thereof, comprising an insulating substrate, a resin layer formed on the insulating substrate and containing an epoxy resin, an inkjet droplet deposition layer formed by the deposition of a plurality of inkjet droplets containing metal particles formed on the resin layer, and a plating layer formed on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, as measured using an atomic force microscope at 25°C, is 7.0 × 10⁻⁶. ６ The above is 12.0 x 10 ６ The following applies:

[0008] Furthermore, in order to achieve the above-mentioned objectives, the present disclosure is a method for manufacturing a circuit-forming substrate having a wiring pattern on at least a part thereof, comprising the steps of: forming a resin layer containing epoxy resin on an insulating substrate; forming an inkjet droplet deposition layer on the resin layer by deposition of a plurality of inkjet droplets containing metal particles and an alcohol solvent; and forming a plating layer on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 7.0 × 10⁻⁶. ６ The above is 12.0 x 10 ６ The following applies:

[0009] According to this disclosure, the landing position of inkjet droplets can be controlled in the inkjet method, enabling further miniaturization of wiring.

[0010] This is a schematic diagram showing the layer structure of the circuit formation substrate of this disclosure. This is a flowchart showing the basic processing flow of the manufacturing method of the circuit formation substrate of this disclosure. This is a micrograph showing an example where fine lines were not drawn properly. This is a schematic diagram showing how ink droplets interfere with each other after droplet placement. This is a photograph showing the state before and after plating when a resin layer is formed using an ink-receiving layer forming material that does not have plating resistance. This is a micrograph showing the appearance of a wiring pattern formed after inkjet placement. This is a photograph showing the appearance of a circuit formation substrate after plating. This is a table showing the relationship between the evaluation of elastic modulus using an atomic force microscope and the success or failure of pattern drawing. This is a table showing the relationship between the evaluation of dissipation energy using an atomic force microscope and the success or failure of pattern drawing.

[0011] Embodiments of this disclosure will be described with reference to the drawings. Figure 1 is a schematic diagram showing the layer structure of the circuit formation substrate of this disclosure. This figure illustrates a single layer of the circuit formation substrate, and the circuit formation substrate may consist of multiple wiring structures in which multiple layers of insulating material such as resin and multiple layers of conductive material such as metal are laminated. For example, it may include single-sided substrates (1-layer substrates), double-sided substrates (2-layer substrates), 4-layer substrates, 6-layer substrates, 8-layer substrates, or laminated substrates of more than 1-layer. Figure 2 is a flowchart showing the basic process flow of the manufacturing method of the circuit formation substrate of this disclosure.

[0012] The circuit formation substrate comprises an insulating substrate 1, a resin layer 2 formed on the insulating substrate 1, an inkjet droplet deposition layer 3 formed by a plurality of nanometal particles deposited on the resin layer 2 as a plurality of inkjet droplets, and a plating layer 4 formed on the inkjet droplet deposition layer 3.

[0013] First, in step S100, an insulating substrate 1 is prepared. This insulating substrate 1 is an insulating substrate such as a flexible printed circuit board or a rigid printed circuit board, and may be supplied in various forms such as a film-like material, a sheet-like material, a roll-like material, or a rigid unclad material.

[0014] Flexible insulating substrates include, for example, polyimide, polyamide, polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide synthetic resins such as nylon 6, 10, nylon 4, 6, etc., resins such as polyether ether ketone, acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA), polyvinyl chloride, epoxy resins, polystyrene, and polyphenylene sulfide (PPS).

[0015] Furthermore, other flexible insulating substrates, such as inorganic substrates, may be used, for example, ceramics. Other organic substrates may include, for example, polyvinylidene chloride, polyvinyl alcohol, styrene-acrylonitrile copolymer, polyethylene, styrene-vinyl acetate copolymer, polyacetal, cellulose acetate, polycarbonate, thermoplastic polyurethane, and polytetrafluoroethylene.

[0016] A rigid insulating substrate may be, for example, a material with a hardness of 10 GPa or more in tensile modulus. Since tensile modulus is expressed using the same physical quantity as Young's modulus, it may also be defined by Young's modulus. Generally, in resins and their composite materials, even in cases where the tensile modulus is relatively high, known as semi-flexible, it is only around a few GPa, so a material with a hardness of 10 GPa or more in tensile modulus is used as a rigid substrate. For example, an insulating rigid substrate containing glass epoxy resin has a tensile modulus of about 20 GPa.

[0017] Next, in step S101, a resin layer 2 is formed on the insulating substrate 1. The resin layer 2 may be formed on the surface of the insulating substrate 1 for various purposes, such as improving the applicability of the ink composition or modifying the surface of the insulating substrate 1. The resin layer 2 may generally be formed by applying a resin or an adhesion enhancer to improve the adhesion of the resin-containing ink, but in this disclosure, it may also be formed for the purpose of controlling the behavior of inkjet droplets upon impact. This will be described later.

[0018] The resin layer 2 can be formed by coating the resin layer 2 material, diluted with a diluent solvent, onto the insulating substrate 1, and curing it by raising the temperature. The diluent solvent may be, for example, ethylene glycol monomethyl ether to prepare a 50% diluted solution. Other diluents can also be used. When using the ratio of curable resin to the total curable resin of the diluent solvent as one of the dilution ratios, it is preferably 1 to 90%, more preferably 10 to 70%, and even more preferably 20 to 60%. If the dilution ratio is too high, it may be difficult to reach the specified film thickness and to exhibit the desired primer properties. The desired properties here mainly relate to controlling the landing position of inkjet droplets in this disclosure. If the dilution ratio is too low, the liquid viscosity may increase, and uniform coating properties tend to be poor.

[0019] The printing film thickness of the coating may be, for example, 1 to 100 μm relative to the insulating substrate 1. More preferably, it is 5 to 70 μm, and even more preferably 10 to 50 μm. If the printing film thickness is too low, it may not reach the specified film thickness, making it difficult to achieve the desired physical properties described above. If the printing film thickness is too high, the material cost tends to be high, and the ratio of the thickness of the resin layer 2 to the thickness of the insulating substrate 1 becomes high, which may result in the substrate properties not being met. For example, the bending resistance may decrease.

[0020] The effect after this printing and coating can be cured by raising the temperature to the curing temperature and holding it for 1 to 120 minutes. While the curing temperature cannot be specified, it is believed that a suitable curing temperature for the resin layer 2 material can be determined by a reasonable number of trials and experiments for those skilled in the art. As an example of a suitable curing temperature, it is preferable to obtain the exothermic peak using TGDTA measurement and set the temperature within ±30°C of that exothermic peak. The primer curing time is preferably 1 to 120 minutes, more preferably 10 to 60 minutes, and even more preferably 30 to 60 minutes. If the curing time is too short, primer curing failure may occur, and if the curing time is too long, productivity may decrease.

[0021] The thickness of the cured resin layer 2 may be 0.5 to 50 μm. More preferably, it is 0.5 μm to 30 μm, and even more preferably, 1 μm to 20 μm. If the thickness is too low, it may be difficult to achieve the desired physical properties described above. If the thickness is too high, the material cost tends to be high, and the ratio of primer to the substrate thickness becomes high, which may result in the substrate properties not being met. For example, the bending resistance may decrease.

[0022] Next, in step S102, an inkjet printing apparatus is used to eject and apply an ink composition containing metal nanoparticles from an inkjet head in a wiring pattern. The application of the ink composition is achieved by the deposition of inkjet droplets of the ink composition containing metal nanoparticles. The metal nanoparticles can be various, such as gold, silver, platinum, copper, or alloys thereof, and are not technically limited to one metal, but copper nanoparticles may be a suitable example considering conductivity, availability, price, and worldwide supply. For this reason, metal nanoparticles and copper nanoparticles may be described together below. A copper nano-ink composition containing copper nanoparticles, a coating material, a dispersant, and a solvent will be described below as an example, but copper nano-inks with other compositions may also be used.

[0023] The copper nanoparticles preferably have an average particle size of 1 nm to 200 nm, and more preferably 10 nm to 100 nm. If the particle size is too small, the reactivity of the particles may increase, potentially reducing the storage and stability of the ink. If the particle size is too large, the uniformity of the thin film may decrease, and precipitation of ink particles may occur more easily.

[0024] The coating material is intended to prevent copper nanoparticles from being easily oxidized, and may be a carboxylic acid, more preferably a monocarboxylic acid having an integer number of carbon atoms from 6 to 10, such as hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, or decanoic acid.

[0025] The dispersant is used to disperse copper nanoparticles coated with a coating material to form an ink. Its purpose is to uniformly disperse the copper nanoparticles, which are the dispersed phase, in the solvent, which is the dispersion medium, and to maintain a stable dispersed state without aggregation. The dispersant may be a carboxylic acid-based, thiol-based, phenol-based, phosphoric acid-based, or amine-based compound. Preferably, it may be a carboxylic acid-based compound that can coordinate with copper.

[0026] Rather than being an exhaustive list, a more preferred example is a polycarboxylic acid as a dispersant when octanoic acid is selected as the coating material. A more preferred polycarboxylic acid is a polycarboxylic acid having a comb-like structure.

[0027] The solvent may be an aqueous solvent or an organic solvent. The organic solvent may be an alcohol-based solvent or a derivative thereof, and more specifically, glycol ethers such as ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, or mixtures thereof can be used, and solvents described later may also be used.

[0028] In addition, stabilizers and other additives may be used.

[0029] The content of copper nanoparticles in the ink composition may be 5% to 60% by weight, or 10% to 30% by weight, by mass ratio. The reason for selecting these ranges is that if the content is too low, there may be insufficient nanoparticles to form a conductive layer made of copper nanoparticles, potentially causing pores such as pinholes. If the content is too high, the particles may aggregate easily within the ink, potentially impairing the stability of the ink.

[0030] The viscosity of the ink composition is preferably 1 to 100 mPa·s at a measurement temperature of 25°C, as measured by an E-type viscometer or rheometer. More preferably, the viscosity is 1 to 100 mPa·s and 1 to 50 mPa·s when the shear rate is 100 (1 / S) or higher. This is because the conditions are suitable for the environment in which the ink is ejected by the inkjet head, and if the viscosity is too high, ejection from the inkjet head becomes difficult.

[0031] The diameter of a single inkjet droplet ejected from an inkjet nozzle of an inkjet printing device is, for example, within the range of 1 μm to 100 μm.

[0032] Thus, in this disclosure, the pattern is pre-formed by inkjet printing, eliminating the need for etching to form the desired shape of the pattern. In other words, the basic wiring pattern is already formed on this circuit-forming substrate at the moment the inkjet droplet lands. This method of additionally forming circuits is superior in terms of reducing environmental impact.

[0033] Next, in step S103, the metal nanoparticles contained in the inkjet droplet layer 3 are fixed onto the resin layer 2. The inkjet droplet layer 3 of metal nanoparticles may be formed by applying an ink composition containing metal nanoparticles and, for example, photosintering. There are various methods for fixing the metal nanoparticles contained in the inkjet droplets, and in addition to photosintering, wet reduction processes using reducing agents such as formalin or hydrazine, various heating processes and drying processes can be used as appropriate. The drying process may be heat treatment, hot air treatment using a nitrogen stream or air stream. As a result, the metal nanoparticles remain on the resin layer 2.

[0034] Regarding the inkjet droplet landing layer 3, in addition to removing components other than the metal nanoparticles in the ink composition, it is necessary to cause bonding, melting, and contact between the metal nanoparticles. The state in which the metal nanoparticles approach and bond while maintaining their shapes is called necking, and the phenomenon in which the nanoparticles melt from the necking state and integrate with a change in shape is also called fusion. Also, the inter-particle bonding is sometimes simply called necking. By sintering in this way, the nanoparticles melt and bulkify, improving the conductivity and adhering to the resin layer 2 on the insulating substrate 1.

[0035] For example, for sintering of metal nanoparticles, by using photosintering by flash lamp irradiation, copper nanoparticles can be photo-sintered and bonded to each other. According to the instantaneous heating of the flash discharge lamp, heat is applied only to the surface of the substrate, and heating of the interior of the substrate can be suppressed, which is suitable in terms of shortening the production time and reducing the load on the substrate. Regarding the irradiation conditions of the flash lamp, those skilled in the art can appropriately adjust parameters such as the input power, Joule heat corresponding to the input power, and charge voltage per shot.

[0036] Not limited to sintering by a flash lamp, heating methods using infrared light such as an oven or an infrared furnace can also be adopted from the viewpoint of not giving a steep thermal load, and a sintered layer of copper nanoparticles can also be formed by these heating methods.

[0037] In addition, a metal layer similar to the above sintered layer can also be formed by a method of reducing materials such as metal oxide nanoparticles dropped by inkjet using a reducing agent.

[0038] Next, in step S104, a plating layer 4 of a metal compatible with the type of metal nanoparticles is formed on the inkjet droplet landing layer 3. When the metal nanoparticles are copper, copper can be plated. The plating method is the same as the known plating process using a known plating solution, and specifically, it can include electroless copper plating, electrolytic copper plating, etc. Thereby, the plated metal is deposited on the surface and inside of the inkjet droplet landing layer 3.

[0039] Through the above steps, a circuit formation substrate with wiring of a desired pattern formed on the insulating substrate 1 can be manufactured.

[0040] By the way, with the miniaturization of wiring, after the ink droplets land, the droplets interfere with each other, making it difficult to draw fine lines. FIG. 3 is a micrograph showing an example where the drawing of a fine line was not properly performed, and FIG. 4 is a schematic diagram showing the state where the ink droplets interfere with each other after landing.

[0041] In a circuit board, the line width, for example, L / S (line and space) is known and used as an index of fineness. For example, when L / S: 1000 μm is mentioned, it indicates the ability and quality to form a wiring pattern with a line width of 1000 μm or less. In the region where L / S is 1000 μm or less, for example, in FIG. 3, a plurality of inkjet droplets form a line L and have a space S, which is a region where no metal wire is arranged, between the lines L. However, if the landing behavior cannot be controlled and a deviation in the landing position occurs, the wiring may not be drawn in the desired position and pattern shape. As a result, the position of the inkjet droplets is displaced and biased, and the space S is narrowed in part.

[0042] The wiring pattern formed by the inkjet method is an aggregate of a plurality of landed inkjet droplets. As described above, the diameter of a single ink droplet is, for example, a value within the range of 1 μm to 100 μm. Therefore, even if a droplet of 50 μm is used as an example, more than 20 droplets are required to draw a line width of 1000 μm. In practice, in order to ensure the conductivity between the metals contained in the ink droplets, it is necessary to land a larger number of droplets in multiple times.

[0043] Figure 4 is a schematic diagram illustrating this situation, but it does not accurately represent the actual dimensions. In this diagram, when an inkjet droplet 31 newly lands on the resin layer 2, if it moves instead of converging to its intended landing position, it interferes with an inkjet droplet 32 ​​that has already landed nearby, causing it to merge as if being drawn in, and thus move from its original position. Note that the above explanation of the phenomenon is a simplified description of the situation for the purpose of understanding the problem. However, due to the accumulation of such interference, a situation may occur where the desired pattern cannot be obtained in fine wiring, as shown in Figure 3.

[0044] To avoid such misalignment of inkjet droplet placement, methods such as increasing the time interval between droplets or raising the stage temperature can be considered. The former involves delaying the placement of the first droplet so that its placement stabilizes before ejecting the second droplet nearby, but this takes extra time. The latter promotes the drying and evaporation of the solvent, but because the distance between the stage and the inkjet head is small, the temperature of the head may rise, potentially causing problems with ejection control.

[0045] Therefore, in order to control the landing position of inkjet droplets, it was considered to impart the function of an ink-receiving layer to the resin layer 2 to control the landing position of the ink. The function of the layer having the ink-receiving layer is either a porous type that absorbs the ink solvent or a swelling type. However, an issue arose with ink-receiving layers that could be formed using readily available materials: they lacked resistance to plating treatments performed after inkjet printing. Specifically, resistance to highly alkaline environments such as electroless copper plating was required.

[0046] Figure 5 is a photograph showing the state before and after plating when a circuit board is manufactured using the above method, with the resin layer 2 formed using an ink-receiving layer-forming material that lacks plating resistance. According to this figure, even if an ink-receiving layer is formed and fine inkjet droplet control becomes possible, it is understood that a circuit board cannot be formed without plating resistance.

[0047] Therefore, after thorough investigation and experimental verification, it was found that the resin layer 2 contains epoxy resin, and the elastic modulus (Pa) of the surface of the resin layer 2, measured using an atomic force microscope at 25°C, is 7.0 × 10⁻⁶. ６ The above is 12.0 x 10 ６ The following factors have revealed that it is possible to control the landing position of inkjet droplets in the inkjet method and further miniaturize the wiring.

[0048] Furthermore, it was also found that, more preferably, such a resin layer 2 has a dissipation energy (eV) of 37 or more and 58 or less, as measured using an atomic force microscope at 25°C on the surface of the resin layer 2.

[0049] To explain how we arrived at these results, we first focused on epoxy primer as a material for forming the resin layer 2, which has high resistance to the electroless copper plating process, and investigated how to achieve inkjet droplet receiving functionality by controlling the viscoelastic properties of the epoxy primer.

[0050] Epoxy resins are thermosetting resins containing epoxy groups in their molecules, and the cured resin is chemically stable against alkalis. A typical example of epoxy resin production is the condensation reaction of bisphenol A [2,2-bis(4-hydroxyphenyl-propane)] and epichlorohydrin. First, the raw material bisphenol A is synthesized from phenol and acetone, and epichlorohydrin is synthesized from propylene. By condensing bisphenol A and epichlorohydrin using these raw materials, a resin containing epoxy groups is produced. Such epoxy resins can be made into materials with desired viscoelastic properties and chemical stability depending on the composition of various components and their reaction with various curing agents.

[0051] To understand the viscoelastic properties of epoxy resin for controlling inkjet droplet placement, we focused on elastic modulus and dissipated energy. Elastic modulus is an indicator of a material's elastic properties. Simply put, it indicates the ability to store and recover deformation energy, representing spring-like properties. The closer a material is to a perfect elastic body, the higher its storage modulus. On the other hand, dissipated energy is an indicator of a material's viscous properties. Simply put, it indicates the degree to which energy is dissipated as heat when a force is applied periodically and the material deforms, resulting in damper-like properties. The closer a material is to a perfect viscous body, the higher its dissipated energy.

[0052] <Examples> The following are examples of circuit formation substrates manufactured using the above resin layer.

[0053] <Example of Ink Composition> Below is an example of an ink used to create a circuit board. 15 parts copper nanoparticles, 1 part polycarboxylic acid dispersant, 10 parts 2-ethoxyethanol (manufactured by Tokyo Chemical Industry Co., Ltd.), 15 parts 2-(2-n-butoxyethoxy)ethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) (diethylene glycol monobutyl ether), 10 parts 3-methoxymethylbutanol (manufactured by Tokyo Chemical Industry Co., Ltd.), and 47 parts 2-(2-methoxyethoxy)ethanol (manufactured by Tokyo Chemical Industry Co., Ltd.) (diethylene glycol monomethyl ether) were mixed in a container and dispersed using a rotary-rotating mixer. 0.2 to 1.0 parts of various additives were then added and dispersed again using the rotary-rotating mixer to obtain a copper-brown copper ink composition containing additives. A circuit board was then made using the obtained ink composition. A rigid FR-4 substrate was used as the substrate.

[0054] <Examples of inkjet droplets or L / S examples> When droplets were ejected onto an epoxy resin in the elastic modulus range shown in this embodiment using a piezo-type inkjet device, the droplet size was in the range of 40 to 80 μm. It was found that with epoxy resins having an ink-receiving layer function, the behavior of the droplets after impact can be controlled, and a line width of 40 to 200 μm can be achieved.

[0055] <Resin layer containing epoxy resin> A mixed solution was prepared by diluting a general-purpose epoxy resin and curing agent with diethylene glycol diethyl ether at a solid content ratio of 40%. After solvent removal, this mixed solution was applied to a total resin thickness of approximately 2 mm, and a drying and curing treatment was carried out at 180°C for 60 minutes. The resulting cured material was cut into pieces 3 mm wide and 20 mm long, and AFM-QNM measurement samples were prepared. Samples for Examples 1, 2, and 3 were prepared, of which Example 3 underwent annealing treatment after plating. Examples 1 and 2 were evaluated with only the resin layer 2 formed, while Example 3 was evaluated with the plating layer 4 formed.

[0056] <Microscopic observation image after inkjet printing> Figure 6 is a microscopic observation image showing the appearance of the wiring pattern formed after inkjet printing. In this figure, it can be seen that fine lines with an L / S ratio of 50 μm have been clearly drawn.

[0057] <Appearance after plating> Figure 7 is a photograph showing the appearance of the circuit board after plating, as depicted in Figure 6. Even after the plating process, no problems such as peeling due to the plating process have occurred. Note that since this is a test pattern, some areas may not be drawn correctly, but this does not pose a problem.

[0058] <Adhesion Strength> For Example 3, a peel test was performed at a 90-degree angle to confirm the adhesion strength of the plating layer to the substrate, in accordance with the US UL standard, more specifically, UL796F. The peel test was performed multiple times on multiple test pieces of different widths. This confirmed an adhesion strength of 0.8 N / mm.

[0059] (Evaluation by Dynamic Viscoelasticity Measurement Using Atomic Force Microscope) Examples 1 to 3 were prepared and evaluated by AFM-QNM (Quantitative Nanomechanical Mapping). The QNM mode is a technique for simultaneously nondestructively measuring the surface shape and mechanical properties by scanning while contacting the cantilever with a constant contact pressure on the sample surface and controlling it with high-speed feedback. The measurement principle is to regard the cantilever as a spring and calculate the force from the indentation amount based on Hooke's law. The elastic modulus of the sample is obtained from the obtained force using a contact mechanics model such as the DMT theory. Also, the measurement temperature is 25 °C in the same manner.

[0060] Figure 8 is a table showing the elastic modulus (Pa) of each sample measured by AFM-QNM and the success or failure of pattern formation. Regarding the elastic modulus, in AFM, it can often be obtained as a two-dimensional map, so it may be a single point such as the center position of an arbitrary measurement location, or it may be the surface average value.

[0061] The elastic modulus (Pa) measured by AFM-QNM is suitable for measuring the local characteristics at the nanoscale. Examples 1 to 3 had elastic modulus (Pa) values of 7.0×10 ６ , 11.0×10 ６ , 12.0×10 ６ , and all succeeded in forming patterns. According to the table in this Figure 8, when the elastic modulus (Pa) measured by using an atomic force microscope at 25 °C on the surface of the resin layer is 7.0×10 ６ or more and 12.00×10 ６ or less, it can be seen that patterns can be formed well. Furthermore, it is more preferable that the elastic modulus (Pa) is 7.0×10 ６ or more and 12.00×10 ６ or less even after annealing after plating.

[0062] Furthermore, when evaluation is performed using AFM-QNM, dissipated energy (eV) (also known as energy dissipation) can also be measured. Dissipated energy is the value of energy lost due to the viscosity of a fluid and converted into thermal energy. This dissipated energy generally indicates the portion of energy that is converted into heat or other forms when a material is subjected to stress. It is useful for understanding the viscous behavior and internal structure of materials and is important when evaluating the viscoelastic properties of thin films and micro-scale samples. Similarly, in AFM, dissipated energy can often be obtained as a two-dimensional map, so it can be measured at a single point, such as the center position of any measurement location, or as an average value over a surface.

[0063] Figure 9 is a table showing the dissipated energy (eV) obtained in conjunction with the measurement of the elastic modulus (Pa) of each sample measured by the AFM-QNM method described above, and the success or failure of pattern formation. Examples 1 to 3 took dissipated energy (eV) values ​​of 37, 58, and 51, respectively, and all successfully formed patterns. This table shows that when the dissipated energy (eV) of the resin layer surface at 25°C, measured using an atomic force microscope, is between 37 and 58, a good pattern can be formed. Furthermore, it is even more preferable that the dissipated energy (eV) remains between 37 and 58 after annealing following the plating treatment.

[0064] As described above, the inkjet method of this disclosure allows for control of the landing position of inkjet droplets, enabling further miniaturization of wiring.

[0065] This concludes the explanation. However, the new technologies described herein can be realized in various other forms, and parts of the content may be omitted, modified, or replaced without departing from the spirit of this disclosure. The embodiments and variations thereof shown in this disclosure are also included in the scope and spirit of this disclosure and shall be treated as equivalent to the technologies protected under the claims. Furthermore, the technical scope of this disclosure may also be defined in a manner that excludes certain parts. For example, if physical quantities from 1 to 100 are disclosed in this disclosure, it may be expressed as 1 to 100 (excluding 20 to 40) to demonstrate superiority over other technologies.

[0066] Several embodiments included in this disclosure are described below. [1] A circuit forming substrate having a wiring pattern in at least part of it, comprising: an insulating substrate; a resin layer formed on the insulating substrate and containing an epoxy resin; an inkjet droplet deposition layer formed by the deposition of a plurality of inkjet droplets containing metal particles formed on the resin layer; and a plating layer formed on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 7.0 × 10 ６ The above is 12.0 x 10 ６ The following are circuit-forming substrates: [2] The circuit-forming substrate according to [1], wherein the dissipation energy (eV) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 37 or more and 58 or less. [3] A method for manufacturing a circuit-forming substrate having a wiring pattern on at least a part thereof, comprising the steps of: forming a resin layer containing epoxy resin on an insulating substrate; forming an inkjet droplet deposition layer on the resin layer by the deposition of a plurality of inkjet droplets containing metal particles and an alcohol solvent; and forming a plating layer on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 7.0 × 10 ６ The above is 12.0 x 10 ６The method for manufacturing a circuit-forming substrate is as follows: [4] The method for manufacturing a circuit-forming substrate according to [3], wherein the dissipation energy (eV) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 37 or more and 58 or less.

[0067] 1. Insulating substrate 2. Resin layer 3. Inkjet droplet layer 4. Plating layer 31. Inkjet droplet 32. Inkjet droplet

Claims

1. A circuit forming substrate having a wiring pattern on at least a portion thereof, comprising: an insulating substrate; a resin layer formed on the insulating substrate and containing epoxy resin; an inkjet droplet deposition layer formed by the deposition of a plurality of inkjet droplets containing metal particles formed on the resin layer; and a plating layer formed on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 7.0 × 10⁻⁶. ６ The above is 12.0 x 10 ６ The following is a circuit formation substrate.

2. The circuit forming substrate according to claim 1, wherein the dissipation energy (eV) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 37 or more and 58 or less.

3. A method for manufacturing a circuit-forming substrate having a wiring pattern on at least a portion thereof, comprising the steps of: forming a resin layer containing epoxy resin on an insulating substrate; forming an inkjet droplet deposition layer on the resin layer by deposition of a plurality of inkjet droplets containing metal particles and an alcohol solvent; and forming a plating layer on the inkjet droplet deposition layer, wherein the elastic modulus (Pa) of the surface of the resin layer, measured using an atomic force microscope at 25°C, is 7.0 × 10⁻⁶. ６ The above is 12.0 x 10 ６ The following is a method for manufacturing a circuit board.

4. The method for manufacturing a circuit-forming substrate according to claim 3, wherein the dissipation energy (eV) of the surface of the resin layer at 25°C, as measured using an atomic force microscope, is 37 or more and 58 or less.

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