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

Abstract

In the inkjet method, the landing position of inkjet droplets is controlled to further miniaturize the wiring. The circuit forming substrate having a wiring pattern comprises an insulating substrate, a resin layer formed on the insulating substrate and containing epoxy resin, an inkjet droplet landing layer formed by the landing of a plurality of inkjet droplets containing metal particles formed on the resin layer, and a plating layer formed on the inkjet droplet landing layer, wherein the storage modulus (Pa) of the resin layer at 25°C is 4.0711 × 10⁻⁶. 8 The following is true, and the loss modulus of elasticity (Pa) is 6.4825 × 10⁻⁶. 7 The following applies:

Description

[Technical Field]

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

[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. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-76538 [Overview of the Initiative] [Problems that the invention aims to solve]

[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. [Means for solving the problem]

[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 storage modulus (Pa) of the resin layer at 25°C is 4.0711 × 10⁻⁶. 8 The following is true, and the loss modulus of elasticity (Pa) is 6.4825 × 10⁻⁶. 7 The following applies:

[0008] Furthermore, in order to achieve the above-mentioned objectives, the method for manufacturing a circuit-forming substrate of the present disclosure is a method for manufacturing a circuit-forming substrate having a wiring pattern in 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 formed on the resin layer by deposition of a plurality of inkjet droplets containing metal particles and an alcohol-based solvent or a derivative thereof; and forming a plating layer on the inkjet droplet deposition layer, wherein the storage modulus (Pa) of the resin layer at 25°C is 4.0711 × 10⁻⁶. 8 The following is true, and the loss modulus of elasticity (Pa) is 6.4825 × 10⁻⁶. 7 The following applies: [Effects of the Invention]

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

Brief Description of the Drawings

[0010] [Figure 1] It is a diagram schematically showing the layer structure of the circuit formation substrate of the present disclosure. [Figure 2] It is a flowchart showing the basic processing flow of the manufacturing method of the circuit formation substrate of the present disclosure. [Figure 3] It is a micrograph showing an example where fine line drawing was not appropriately performed. [Figure 4] It is a schematic diagram showing the state where droplets interfere with each other after ink droplets land. [Figure 5] It is a photograph showing the states before and after plating treatment when a resin layer is formed using a plating-resistant ink receiving layer forming material. [Figure 6] It is a table showing the relationship between the success or failure of pattern drawing when the storage elastic modulus and the loss elastic modulus are changed. [Figure 7] It is a plot diagram including the success or failure of pattern drawing when the storage elastic modulus and the loss elastic modulus are changed. [Figure 8] It is a table showing the relationship between the degree of swelling and the success or failure of pattern drawing. [Figure 9] It is a micrograph showing the appearance of a wiring pattern formed after inkjet landing. [Figure 10] It is a photograph showing the appearance after plating treatment is performed on the drawn circuit formation substrate. [Figure 11] It is a table showing the relationship between the evaluation of the elastic modulus using an atomic force microscope and the success or failure of pattern drawing. [Figure 12] It is a table showing the relationship between the evaluation of the dissipated energy using an atomic force microscope and the success or failure of pattern drawing.

Embodiments for Carrying Out the Invention

[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 material, a sheet material, a roll 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 (registered trademark) specified as nylon 6, 10, nylon 4, 6, etc., 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 a material with a hardness of, for example, a tensile modulus of 10 GPa or more. Since the tensile modulus is expressed using the same physical quantity as Young's modulus, it may also be defined by Young's modulus. In general, for resins and their composite materials, even those with a relatively high tensile modulus, known as semi-flexible, are only a few GPa, so a rigid substrate is defined as a material with a hardness of 10 GPa or more in tensile modulus. 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 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 device 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 is 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 not be enough nanoparticles to form a conductive layer with 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] For the inkjet droplet layer 3, in addition to removing components other than metal nanoparticles from the ink composition, it is necessary to cause bonding, melting, and contact between the metal nanoparticles. The state in which metal nanoparticles are close together and bonded while maintaining their shape is called necking, and the phenomenon in which the nanoparticles melt from the necking state and become one with a change in shape is called fusion. Sometimes, interparticle bonding is simply called necking. Through this sintering, the nanoparticles melt and become bulk, improving conductivity and allowing them to adhere closely to the resin layer 2 on the insulating substrate 1.

[0035] For example, photosintering using a flash lamp can be used to sinter and bond copper nanoparticles together. The instantaneous heating of a flash discharge lamp applies heat only to the surface of the substrate, suppressing heating of the substrate's interior, which is advantageous in terms of shortening production time and reducing the load on the substrate. The irradiation conditions of the flash lamp can be appropriately adjusted by those skilled in the art using parameters such as input power, Joule heat corresponding to the input power, and charge voltage per shot.

[0036] In addition to sintering using flash lamps, heating methods utilizing infrared light, such as ovens and infrared furnaces, can also be employed from the standpoint of not applying a steep thermal load, and these heating methods can also form a sintered layer of copper nanoparticles.

[0037] Furthermore, a metal layer similar to the sintered layer described above can also be formed by reducing materials such as metal oxide nanoparticles dropped using an inkjet printer with a reducing agent.

[0038] Next, in step S104, a metal plating layer 4, which is suitable for the type of metal nanoparticles, is formed on the inkjet droplet layer 3. If the metal nanoparticles are copper, copper may be plated. The plating method is the same as known plating treatments using known plating solutions, and specifically may include electroless copper plating, electrolytic copper plating, etc. This deposits the plating metal on the surface and inside the inkjet droplet layer 3.

[0039] Through the above process, a circuit forming substrate in which a desired wiring pattern is formed on an insulating substrate 1 can be manufactured.

[0040] Incidentally, with the miniaturization of wiring, ink droplets interfere with each other after landing, making it difficult to draw fine lines. Figure 3 is a micrograph showing an example where fine lines were not drawn properly, and Figure 4 is a schematic diagram illustrating how ink droplets interfere with each other after landing.

[0041] In circuit boards, line width is often indicated by the L / S (line and space) ratio, which is a well-known and commonly used indicator of thinness. For example, an L / S of 1000 μm indicates the ability and quality to form wiring patterns with a line width of 1000 μm or less. In the L / S region of 1000 μm or less, as shown in Figure 3, multiple inkjet droplets form lines L, and there is space S between the lines L where no metal wires are placed. However, if the droplet behavior cannot be controlled and a shift in the droplet position occurs, the desired position and pattern shape of the wiring may not be achieved. As a result, the inkjet droplets are shifted and unevenly distributed, and the space S becomes narrower in some areas.

[0042] The wiring patterns formed by the inkjet method are aggregates of multiple inkjet droplets that land on surfaces. As mentioned above, the diameter of a single ink droplet is, for example, in the range of 1 μm to 100 μm. Therefore, even if a 50 μm droplet is used, more than 20 droplets are needed to draw a line width of 1000 μm. In reality, even more droplets are needed to ensure conductivity between the metals contained in the ink droplets, and these droplets are landed in multiple stages.

[0043] Figure 4 is a schematic diagram illustrating this phenomenon, 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 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 has a storage modulus of 4.0711 × 10 at 25°C. 8 The following is true, and the loss modulus is 6.4825 × 10⁻⁶. 7 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 revealed that such resin layer 2 has a swelling degree of 128 or higher relative to 2-ethoxyethanol.

[0049] To explain how we arrived at these results, we first focused on epoxy primer as a material for forming 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] Regarding the viscoelastic physical properties of the epoxy resin for controlling the landing of inkjet droplets, attention was paid to the storage elastic modulus and the loss elastic modulus. The storage elastic modulus is an index representing the elastic properties of a material. Briefly speaking, it indicates the ability to store and recover deformation energy, and represents the properties like a spring. The closer it is to a perfect elastic body, the higher the storage elastic modulus. On the other hand, the loss elastic modulus is an index representing the viscous properties of a material. Briefly speaking, it indicates the degree to which energy dissipates as heat during deformation, and represents the properties like a damper. The closer it is to a perfect viscous body, the higher the loss elastic modulus.

[0052] Figure 6 is a table showing the results of forming a resin layer 2 containing an epoxy resin with the storage elastic modulus and the loss elastic modulus changed and verifying the success or failure of pattern drawing by controlling the landing of inkjet droplets. Figure 7 is a plot diagram thereof. In Figure 7, the vertical axis represents the storage elastic modulus (Pa) and the horizontal axis represents the loss elastic modulus (Pa) on a logarithmic scale. Those with appropriate desired pattern drawing (Examples 1 to 8) are plotted as ○, and those without appropriate pattern drawing (Comparative Examples 1 to 2) are plotted as ×. Note that the success or failure of such pattern drawing is determined from the appearance of the pattern on the manufactured circuit formation substrate.

[0053] Regarding Examples 1 to 8, as a result of calculating an approximate formula by power approximation from the relationship between the measurement results of the storage elastic modulus and the loss elastic modulus of each example, y = 0.0001x 1.6142 was derived, and the result was R 2 = 0.9484. However, since the positions of Comparative Examples 1 to 2 generally follow this approximate formula, the following properties of this approximate formula are inferred. That is, it can be inferred that even if the absolute values of the loss elastic modulus and the storage elastic modulus of the material are different, they have similar elastic characteristics and viscous characteristics. Comparative Examples 1 to 2 and Examples 1 to 8 are all resin layers containing epoxy resin. Therefore, the above approximate formula may indicate the viscoelastic measurement of the resin layer containing epoxy resin. As a result of calculating the residual band for predicting future values and setting the confidence interval from the values of the examples scattered above and below the approximate formula, for the storage elastic modulus (Pa) Y and the loss elastic modulus (Pa) X, 3.0×10 -5 X1.6142 ≤Y ≤ 4.0 × 10 -4 X 1.6142 It was statistically estimated that 95% would fall within this range. Therefore, resin layers within this range are more likely to have viscoelastic properties similar to those of the embodiments of this disclosure.

[0054] Furthermore, after examining the boundary between the examples and comparative examples, we concluded that the vertical line corresponding to the upper limit of the 95% confidence interval for the loss modulus (Pa) values ​​of Examples 1 to 8 is appropriate. As can be seen in Figure 7, this vertical line is located between the examples and comparative examples in terms of loss modulus (Pa). The loss modulus (Pa) X1 that yields this value is 6.4825 × 10⁻⁶. 7 This is Pa. This vertical line indicates the upper limit of the 95% confidence interval for the population mean of the data, assuming a log-normal distribution. Although there are constraints on the sample size and the assumption that the data follows a log-normal distribution, there is considered to be some validity in setting such an upper limit for the loss modulus.

[0055] Furthermore, when the intersection point of the vertical line X1 and the approximate formula of the embodiment was found, as shown in Figure 7, the horizontal line passing through this intersection point is the storage modulus of elasticity (Pa) Y1: 4.0711 × 10 8 A horizontal line was obtained where (Pa) was obtained. This horizontal line also clearly separated the region of the example from the region of the comparative example. From the above results, in the manufacturing of the circuit forming substrate of this disclosure, the range in which the desired pattern can be formed is defined as the storage modulus (Pa) of the resin layer 2 at 25°C being 4.0711 × 10 8 The following is true, and the loss modulus of elasticity (Pa) is 6.4825 × 10⁻⁶. 7 The following was assumed:

[0056] It should be noted that these results are summarized for a measurement temperature of 25°C. Although the specific values ​​of the storage modulus (Pa) and loss modulus (Pa) change with temperature, it was confirmed that the relationship between the magnitudes of the storage modulus (Pa) and loss modulus (Pa) between the examples and comparative examples was maintained similarly when the temperature was varied from -50°C to 300°C.

[0057] From the above results, it can be concluded that resin layer 2 contains epoxy resin and has a storage modulus (Pa) of 4.0711 × 10⁻¹⁰ at 25°C. 8 The following is true, and the loss modulus of elasticity (Pa) is 6.4825 × 10⁻⁶. 7 The following factors have revealed that in the inkjet method, the landing position of inkjet droplets can be controlled, enabling further miniaturization of wiring. The reason for this is speculated below. While higher viscosity of resin layer 2 improves shock absorption, excessively high viscosity slows down the transmission of impact energy. This may cause the inkjet droplets to remain in contact with the surface of resin layer 2 for a longer period, potentially increasing lateral movement. On the other hand, moderate elasticity allows for temporary storage of collision energy, potentially making it easier to control the behavior of the inkjet droplets.

[0058] Furthermore, as a range of more preferable viscoelastic properties for resin layer 2, the storage modulus (Pa) Y and loss modulus (Pa) X of the same resin layer at 25°C are set to 3.0 × 10⁻⁶. -5 X 1.6142 ≤Y ≤ 4.0 × 10 -4 X 1.6142 This may be assumed. This is a range that is statistically estimated to contain 95% of the results of calculating the residual band from the values ​​of the examples scattered above and below the above approximation formula. Therefore, resin layers included in this range are more likely to have viscoelastic properties similar to those of the examples of this disclosure.

[0059] Furthermore, regarding the loss modulus of elasticity (Pa), it is clear that 0 is excluded, but if you want to set a lower limit, then X2: 2.3765 × 10 6The above may also be used. This value is set slightly wider than the lower limit of the 95% confidence interval for X based on Examples 1-8, since there are no failures on the lower limit of the loss modulus (Pa). It is a robust estimate representing the lower end of the data distribution assuming a log-normal distribution, based on the median of Examples 1-8. Specifically, the median absolute deviation (MAD) was used instead of the standard deviation. Based on Examples 1-8, the MAD of the loss modulus (Pa) was scaled by multiplying it by a scale factor (1.4826: a statistically derived value widely used for adjusting MAD), and the median of the loss modulus (Pa) of Examples 1-8 - 1.4826 × MAD was set as the lower limit. This was used purely to practically grasp the lower trend of the data in situations with small sample sizes and the possibility of potential outliers.

[0060] A more preferable range is the interval defined by the values ​​of the storage modulus (Pa) Y and loss modulus (Pa) X measured in Examples 1 to 8, specifically the ranges of 4,464,500 ≤ X ≤ 3,220,5200 and 9,071,680 ≤ Y ≤ 1,710,9200, as can be seen from the values ​​shown in the table in Figure 6. The above values ​​may be used as the most preferable upper and lower limits for X and Y, respectively.

[0061] The storage modulus and loss modulus of the resin layer 2 described above can be evaluated by dynamic viscoelasticity measurement (DMA). In DMA, there are modes for fixed-frequency measurement and mode for evaluating frequency dependence by sweeping the frequency, and evaluation is possible with fixed-frequency measurement. The measurement frequency in the fixed-frequency case is, for example, 10 Hz.

[0062] Furthermore, the relationship between the storage modulus, loss modulus, and degree of swelling was also examined. The degree of swelling is, Q(%) = 100 × (W - Wa) / Wa This is expressed as follows: W represents the weight of the sample after swelling, and Wa represents the weight of the sample before swelling.

[0063] Figure 8 is a table comparing the results of penetration tests conducted with 2-ethoxyethanol, an alcohol-based solvent that can be simulated as an example of a solvent in an ink composition, for materials constituting multiple types of resin layers, with the success or failure of pattern formation.

[0064] From this table, it was confirmed that the preferred requirements for the material constituting the resin layer 2 can also be defined by the condition that the degree of swelling of the resin layer 2 with respect to 2-ethoxyethanol is 128 or higher. More preferably, it is preferable that all requirements for storage modulus, loss modulus, and degree of swelling are met. Thus, the influence of the degree of swelling on inkjet droplet reception may be related to the fact that an appropriate degree of swelling allows the solvent of the ink composition to be absorbed at an appropriate rate.

[0065] <Examples> Examples of circuit formation substrates manufactured using the above-mentioned resin layer are shown below.

[0066] <Example of ink composition> The following describes 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 additive-containing copper ink composition. A circuit board was then fabricated using the obtained ink composition.

[0067] <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 ranged from 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.

[0068] <Examples of storage modulus and loss modulus of resin layers containing epoxy resin> A mixed solution was prepared by diluting a general-purpose epoxy resin and curing agent with 2-ethoxyethanol 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 performed at 180°C for 60 minutes. The resulting cured material was cut into 3 mm wide and 20 mm long pieces to prepare DMA measurement samples. These samples were measured using a DMA measuring device under conditions of 0.1% strain and 1 Hz frequency from -50 to 300°C to measure their elastic modulus. Based on the obtained elastic modulus measurement results, an epoxy resin with ink-receiving layer function was defined based on the loss modulus (Pa) and storage modulus (Pa) at 25°C.

[0069] <Microscopic image of inkjet-printed projectile after impact> Figure 9 is a microscopic photograph showing the appearance of the wiring pattern formed after inkjet printing. This figure clearly shows that fine lines with an L / S ratio of 50 μm are being drawn.

[0070] <Appearance after plating> Figure 10 is a photograph showing the appearance of the circuit board after plating, as depicted in Figure 9. Even after the plating process, no problems such as peeling due to the plating have occurred. Note that since this is a test pattern, some areas may not be drawn correctly, but this does not pose a problem.

[0071] <Adhesion strength> To confirm the adhesion strength of the plating layer to the substrate, a peel test was performed at a 90-degree angle according to the US UL standard, more specifically, UL796F. The peel test was performed multiple times on multiple test specimen widths. This confirmed an adhesion strength of 0.8 N / mm.

[0072] • Supplementary evaluation methods (Evaluation by dynamic viscoelasticity measurement using an atomic force microscope) Furthermore, using the same resin layers as in Comparative Examples 1-2 and Examples 1-8, Comparative Examples 3-4 and Examples 9-16 were prepared as samples for evaluation using an atomic force microscope (AFM), and evaluation was also performed using AFM-QNM (Quantitative Nanomechanical Mapping). The QNM mode is a method that simultaneously measures surface shape and mechanical properties non-destructively by scanning the sample surface while contacting it with a cantilever at a constant pressure and controlling it with high-speed feedback. The measurement principle is to consider the cantilever as a spring and calculate the force from the amount of indentation based on Hooke's law. From the obtained force, the elastic modulus of the sample is determined using a contact mechanics model such as DMT theory. The measurement temperature was also 25°C.

[0073] Figure 11 is a table showing the elastic modulus (Pa) of each sample measured by AFM-QNM and the success or failure of pattern formation. In this table, Comparative Examples 3 and 4 are circuit formation substrates with the same resin layers as Comparative Examples 1 and 2 shown in the table in Figure 6, and similarly, Examples 10 to 16 are circuit formation substrates with the same resin layers as Examples 1 to 8. 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 any measurement location, or it may be an average value over a surface.

[0074] The modulus of elasticity (Pa) measured by AFM-QNM is not the same physical quantity as the storage modulus and loss modulus measured by DMA as described above. In principle, due to the influence of the interaction between the cantilever and the sample, the measured values ​​do not always have a high correlation with the storage modulus and loss modulus measured by DMA, although there is a certain relationship. For example, DMA is suitable for macro-scale evaluation of bulk samples, while AFM is suitable for measuring nanoscale local properties. Therefore, depending on the morphology of the sample, evaluation using AFM may be appropriate. According to the table in Figure 11, the modulus of elasticity (Pa) measured using an atomic force microscope at 25°C on the surface of the resin layer is 4.60 × 10⁻⁶. 8 The above is 2.18 × 10 9 It can be seen that a good pattern can be formed under the following conditions.

[0075] 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 obtained as a single point, such as the center position of any measurement location, or as an average value over a surface.

[0076] Figure 12 is a table showing the dissipation 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. This table shows that a good pattern can be formed when the dissipation energy (eV) of the resin layer surface at 25°C, measured using an atomic force microscope, is between 65 and 307.

[0077] As described above, the inkjet method of this disclosure allows for control of the landing position of inkjet droplets, enabling further miniaturization of wiring.

[0078] 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 will 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.

[0079] Several embodiments included in this disclosure are described below. [1] A circuit forming substrate having a wiring pattern in at least a portion of it, Insulating substrate and A resin layer containing epoxy resin is formed on the insulating substrate, An inkjet droplet placement layer formed by the impact of multiple inkjet droplets containing metal particles formed on the resin layer, The system comprises a plating layer formed on the aforementioned inkjet droplet layer, The resin layer at 25°C, The storage modulus is 4.0711 × 10⁻⁶. 8 The following: Loss modulus is 6.4825 × 10⁻⁶ 7 The following is a circuit formation substrate. [2] Regarding the storage modulus (Pa) Y and loss modulus (Pa) X of the aforementioned resin layer at 25°C, 3.0×10 -5 X 1.6142 ≤Y ≤ 4.0 × 10 -4 X 1.6142 The circuit formation substrate described in [1]. [3] The circuit forming substrate according to [2], wherein the degree of swelling of the resin layer with respect to 2-ethoxyethanol is 128 or more. [4] The resin layer at 25°C, Loss modulus (Pa) is 6.4825 × 10 7 The circuit formation substrate described in [2] is as follows: [5] A circuit forming substrate having wiring patterns with a line width of 1000 μm or less in at least part of it, The average particle size of the aforementioned metal particles is between 1 nm and 200 nm. The circuit forming substrate according to any one of [1] to [4], wherein the diameter of the inkjet droplets is 1 μm to 100 μm. [6] A method for manufacturing a circuit forming substrate having a wiring pattern in at least a portion thereof, The steps include forming a resin layer containing epoxy resin on an insulating substrate, The steps include forming an inkjet droplet deposition layer on the resin layer by depositing a plurality of inkjet droplets containing metal particles and an alcohol solvent, The step of forming a plating layer on the inkjet droplet layer is included. The resin layer at 25°C, The storage modulus is 4.0711 × 10⁻⁶. 8 The following: Loss modulus is 6.4825 × 10⁻⁶ 7 The following is a method for manufacturing a circuit board. [7] Regarding the storage modulus (Pa) Y and loss modulus (Pa) X of the aforementioned resin layer at 25°C, 3.0×10 -5 X 1.6142 ≤Y ≤ 4.0 × 10 -4 X 1.6142 The method for manufacturing a circuit-forming substrate as described in [6]. [8] The method for manufacturing a circuit-forming substrate according to [7], wherein the degree of swelling of the resin layer with respect to 2-ethoxyethanol is 128 or more. [9] The resin layer at 25°C, Loss modulus (Pa) is 2.3765 × 10 6 The method for manufacturing a circuit-forming substrate as described in [8] above.

[10] A circuit forming substrate having wiring patterns with a line width of 1000 μm or less in at least part of it, The average particle size of the aforementioned metal particles is between 1 nm and 200 nm. The method for manufacturing a circuit-forming substrate according to any one of [6] to [9], wherein the diameter of the inkjet droplet is 1 μm to 100 μm.

[11] A circuit forming substrate having a wiring pattern in at least a portion of it, Insulating substrate and A resin layer containing epoxy resin is formed on the insulating substrate, An inkjet droplet placement layer formed by the impact of multiple inkjet droplets containing metal particles formed on the resin layer, The system comprises a plating layer formed on the aforementioned inkjet droplet layer, Measurements of the surface of the resin layer at 25°C using an atomic force microscope, The modulus of elasticity (Pa) is 4.60 × 10⁻⁶ 8 The above is 2.18 × 10 9 The following is a circuit formation substrate.

[12] Measurements of the surface of the resin layer at 25°C using an atomic force microscope, The circuit forming substrate according to

[11] , wherein the dissipated energy (eV) is 65 or more and 307 or less.

[13] A method for manufacturing a circuit forming substrate having a wiring pattern in at least a portion thereof, The steps include forming a resin layer containing epoxy resin on an insulating substrate, The steps include forming an inkjet droplet deposition layer on the resin layer by depositing a plurality of inkjet droplets containing metal particles and an alcohol solvent, The step of forming a plating layer on the inkjet droplet layer is included. Measurements of the surface of the resin layer at 25°C using an atomic force microscope, The modulus of elasticity (Pa) is 4.60 × 10⁻⁶ 8 The above is 2.18 × 10 9 The following is a method for manufacturing a circuit board.

[14] Measurements of the surface of the resin layer at 25°C using an atomic force microscope, A method for manufacturing a circuit-forming substrate as described in

[13] , wherein the dissipated energy (eV) is 65 or more and 307 or less. [Explanation of Symbols]

[0080] 1. Insulating substrate 2 resin layers 3. Inkjet droplet layer 4 Plating layer 31 Inkjet Drops 32 inkjet droplets

Claims

1. A circuit forming substrate having a wiring pattern in at least a portion of it, Insulating substrate and A resin layer containing epoxy resin is formed on the insulating substrate, An inkjet droplet placement layer formed by the impact of multiple inkjet droplets containing metal particles formed on the resin layer, The system comprises a plating layer formed on the aforementioned inkjet droplet layer, The resin layer at 25°C, The storage modulus (Pa) is 4.0711 × 10⁻⁶. ８ The following: Loss modulus (Pa) is 6.4825 × 10 ７ The following is a circuit formation substrate.

2. Regarding the storage modulus (Pa) Y and loss modulus (Pa) X of the aforementioned resin layer at 25°C, 3.0 x 10 －５ X １．６１４２ ≤Y ≤ 4.0 × 10 －４ X １．６１４２ The circuit forming substrate according to claim 1.

3. The circuit forming substrate according to claim 2, wherein the degree of swelling of the resin layer with respect to 2-ethoxyethanol is 128 or more.

4. The resin layer at 25°C, Loss modulus (Pa) is 2.3765 × 10 ６ The circuit forming substrate according to claim 2.

5. A circuit forming substrate having a wiring pattern with a line width of 1000 μm or less in at least part of it, The average particle size of the aforementioned metal particles is between 1 nm and 200 nm. The circuit forming substrate according to any one of claims 1 to 4, wherein the diameter of the inkjet droplets is 1 μm to 100 μm.

6. A method for manufacturing a circuit forming substrate having a wiring pattern in at least a portion thereof, The steps include forming a resin layer containing epoxy resin on an insulating substrate, The steps include forming an inkjet droplet deposition layer on the resin layer by depositing a plurality of inkjet droplets containing metal particles and an alcohol solvent, The step of forming a plating layer on the inkjet droplet layer is included. The resin layer at 25°C, The storage modulus (Pa) is 4.0711 × 10⁻⁶. ８ The following: A method for manufacturing a circuit formation substrate, wherein the loss elastic modulus (Pa) is 6.4825×10 ７ or less.

7. Regarding the storage modulus (Pa) Y and loss modulus (Pa) X of the aforementioned resin layer at 25°C, 3.0 x 10 －５ X １．６１４２ ≤Y ≤ 4.0 × 10 －４ X １．６１４２ The method for manufacturing a circuit-forming substrate according to claim 6.

8. The method for manufacturing a circuit-forming substrate according to claim 7, wherein the degree of swelling of the resin layer with respect to 2-ethoxyethanol is 128 or more.

9. The resin layer at 25°C, Loss modulus (Pa) is 2.3765 × 10 ６ The method for manufacturing a circuit-forming substrate according to claim 8.

10. A circuit forming substrate having a wiring pattern with a line width of 1000 μm or less in at least part of it, The average particle size of the aforementioned metal particles is between 1 nm and 200 nm. The method for manufacturing a circuit-forming substrate according to any one of claims 6 to 9, wherein the diameter of the inkjet droplet is 1 μm to 100 μm.

Images