Method for manufacturing cured film, printed wiring board, and electronic apparatus

Abstract

Provided is a method for manufacturing a cured film, with which it is possible to form, on a substrate having a step, a cured film having high hardness, few voids, and excellent step coverage. A method for manufacturing a cured film according to the present invention comprises: an application step for applying, by an inkjet method, an actinic radiation-curable ink to a medium having non-ink absorbency and a step with a height difference of 15 μm to 110 μm inclusive; a first curing step for irradiating the applied actinic radiation-curable ink with actinic radiation to temporarily cure the actinic radiation-curable ink such that a reaction rate on the medium side is 80% or less; and a second curing step for irradiating the temporarily cured actinic radiation-curable ink with actinic radiation to further cure the actinic radiation-curable ink to form a cured film having a film thickness of 15 μm to 60 μm inclusive.

Description

Method for manufacturing a cured film, printed circuit board, and electronic device.

[0001] The present invention relates to a method for manufacturing a cured film, a printed circuit board, and an electronic device.

[0002] Electric vehicles (EVs) and drones require power electronics, which are power supply devices that provide relatively high voltage or high current. Electronic devices that require power electronics use printed circuit boards (PCBs), which are made by etching copper from copper plates or copper-clad laminates to form wiring. Solder resist is then formed on the outermost layer of the PCB as an insulating protective layer.

[0003] For PCBs requiring high current, relatively thick copper wiring is used to reduce wiring resistance and thus the size of the PCB. To insulate and protect such wiring, a thick solder resist film is necessary.

[0004] Traditionally, solder resist formation using liquid ink has been carried out by post-baking after drying, exposure, and development of a coating film formed by spray coating or screen printing. In contrast, in recent years, methods have been investigated in which a coating film formed by inkjet technology is cured by light irradiation to form solder resist, from the viewpoint of reducing environmental impact by eliminating the need for development and lowering manufacturing costs by simplifying the work process. Active-ray curable inks are used for forming the above coating film.

[0005] Regarding the formation of cured films by inkjet printing, methods are known that involve performing preliminary curing and final curing in multiple stages of light irradiation to suppress bleeding and improve pattern accuracy (for example, Patent Documents 1 to 3).

[0006] European Patent No. 4196540, Japanese Unexamined Patent Publication No. 2022-042842, Japanese Unexamined Patent Publication No. 2017-190442

[0007] Solder resist is formed on a non-ink-absorbing medium that has steps or other uneven surfaces, such as those caused by copper wiring. When forming a cured film on such a medium using an inkjet method, it is considered effective to perform light irradiation in multiple stages to suppress bleeding and improve pattern accuracy.

[0008] Incidentally, according to the inventors' findings, when a cured film is formed using an active-ray curable ink on a non-ink-absorbing medium with steps, voids (gaps) sometimes occur in the cured film near the steps. These voids reduce the adhesion of the cured film, and in the case of solder resist, they reduce the insulation between copper wirings, causing migration. If voids can be suppressed by adjusting the conditions of multiple light irradiations, it would be extremely useful to simultaneously achieve improved pattern accuracy and void suppression. However, Patent Documents 1 to 3 do not describe the formation of cured films on substrates with steps using the inkjet method, and therefore, naturally, they do not describe light irradiation conditions that suppress the generation of voids.

[0009] Furthermore, hardened films such as solder resists require high hardness, and high coverage of steps (for example, copper wiring) is also required.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a cured film that can form a cured film with high hardness, few voids, and excellent coverage of steps on a substrate having steps. The present invention also aims to provide a wiring board and electronic equipment having a cured film manufactured by the above method.

[0011] To solve the above problems, one aspect of the present invention relates to a method for manufacturing a cured film, a printed circuit board, and an electronic device as described in [1] to [9] below. [1] A method for manufacturing a cured film, comprising: an application step of applying an active-ray curable ink to a non-ink-absorbing medium having a step difference of 15 μm or more and 110 μm or less by an inkjet method; a first curing step of irradiating the applied active-ray curable ink with an active ray to pre-cure the active-ray curable ink so that the reaction rate on the medium side is 80% or less; and a second curing step of irradiating the pre-cured active-ray curable ink with an active ray to further cure the active-ray curable ink and form a cured film with a film thickness of 15 μm or more and 60 μm or less. [2] The method for manufacturing a cured film according to [1], further comprising a step of heat-treating the cured active-ray curable ink after the second curing step. [3] The method for manufacturing a cured film according to [1] or [2], wherein the active-ray curable ink contains a (meth)acrylate with five or more functionalities. [4] The method for producing a cured film according to any one of [1] to [3], wherein the active-ray curable ink comprises a (meth)acrylate having a carboxyl group or a salt thereof. [5] The method for producing a cured film according to any one of [1] to [4], wherein the active-ray curable ink comprises a gelling agent. [6] The method for producing a cured film according to any one of [1] to [5], wherein the impregnation step, the first curing step, and the second curing step are performed multiple times. [7] The method for producing a cured film according to any one of [1] to [6], used in the manufacture of a printed circuit board. [8] A printed circuit board having a cured film produced by the method according to any one of [1] to [7]. [9] An electronic device having the printed circuit board according to [8].

[0012] The present invention provides a method for manufacturing a cured film that has high hardness, few voids, and excellent coverage of steps, and can be formed on a substrate having steps.

[0013] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments.

[0014] 1. One embodiment of a method for manufacturing a cured film relates to a method for forming a cured film on a non-ink-absorbing medium having steps. In this embodiment, an active-ray curable ink is applied to the medium by an inkjet method. The applied active-ray curable ink is then irradiated with an active ray multiple times.

[0015] As described above, when an active-ray curing ink is used to form a coating on a non-ink-absorbing medium with steps, voids (gaps) may occur in the cured film near the steps. This is thought to be because the degree of curing of the ink differs between the surface and back sides of the ink when irradiated with active rays. In other words, the active rays are irradiated onto the surface side of the ink (opposite the medium), absorbed, and then penetrate through the ink to reach the back side (the medium side). Therefore, the surface side of the ink tends to cure preferentially, resulting in a relatively higher degree of curing, while the back side tends to cure relatively less. Consequently, if curing shrinkage of the ink preferentially occurs on the surface side, the cured material on the back side is pulled towards the surface, making it easier for voids to occur on the back side. In particular, near steps, the surface of the coating film has a three-dimensionally folded shape, so the cured material on the back side is also pulled three-dimensionally, making it easier for voids to occur.

[0016] Furthermore, stress generated by curing shrinkage accumulates in the cured film after light irradiation. Subsequently, if the cured film is subjected to heat treatment or placed in a high-temperature, high-humidity environment, the aforementioned stress makes the cured film more prone to delamination when it deforms further, which in turn makes it more likely to form voids. These voids are also more likely to form near stepped areas.

[0017] In contrast, in this embodiment, during the initial irradiation of multiple light irradiations, the ink is cured so that the curing rate on the back side (medium side) of the cured film is 80% or less. By intentionally lowering the curing rate on the back side, the ink on the back side remains somewhat fluid. As a result, even if the ink is pulled towards the surface due to curing shrinkage on the surface side, the ink remains fluid, making it less likely for voids to form. Furthermore, because the ink on the back side is fluid, stress during curing is less likely to accumulate. Therefore, even if the cured film is subjected to heat treatment or placed in a high-temperature, high-humidity environment, it is considered less likely for voids to form.

[0018] Each step in the method for manufacturing the cured film in this embodiment, based on the above findings, will be described in more detail below.

[0019] 1-1. Application of Active Ray Curable Ink First, an active ray curable ink is applied to a non-ink-absorbing medium with a stepped surface by an inkjet method (application step).

[0020] The medium is a non-ink-absorbing medium. Examples of non-ink-absorbing mediums include metals and plastic films. Non-ink-absorbing mediums are prone to void formation for the reasons mentioned above because the ink hardens on the surface of the medium.

[0021] Furthermore, the medium has steps with a height difference of 15 μm or more and 110 μm or less. If the height difference of the steps is 15 μm or more, voids are likely to occur for the reasons mentioned above. If the height difference of the steps is 110 μm or less, the steps are easily covered by the cured film. The height difference of the steps is preferably 15 μm or more and 70 μm or less, and more preferably 15 μm or more and 40 μm or less. If the medium has multiple steps with different height differences, it is sufficient that the height difference of at least one of the steps in the medium is within the above range.

[0022] The step can be, for example, a copper wire. Alternatively, the step may be formed by processing or molding the medium. The step may be made of the same material as the rest of the medium, or it may be made of a different material. When the step and the rest of the medium are made of different materials (for example, a resin substrate and copper wiring in a printed circuit board), the wettability of the ink differs between the materials, making it easy for voids to form near their boundaries. According to this embodiment, it is possible to make it difficult for voids to form even in such cases.

[0023] The type of substrate is not particularly limited and should be selected according to the application of the cured film. For example, printed circuit boards (PCBs) made by etching copper from a copper plate or copper-clad laminate to form wiring, as well as aluminum substrates, ceramic substrates, and flexible substrates based on plastic film can be used as substrates.

[0024] In this process, an active-ray curing ink is applied to the above-mentioned medium by an inkjet method. Preferably, the ink is applied to the stepped areas and areas other than the stepped areas to form a coating film that covers the stepped areas.

[0025] The inkjet head used for application by the inkjet method may be an on-demand type head or a continuous type head. The on-demand inkjet head may be a piezo type head or a thermal jet type head. The piezo type head may be any type of head, such as single cavity type, double cavity type, bender type, piston type, shear mode type and shared wall type.

[0026] From the viewpoint of improving ejection stability, it is preferable to heat the ink when it is ejected from the head. For example, it is preferable to heat the ejected ink to 40°C to 100°C, and more preferably to 40°C to 90°C.

[0027] When the ink contains a gelling agent and undergoes a sol-gel phase transition due to temperature changes, it is preferable to heat the ejected ink to a temperature 10°C to 30°C higher than the ink's gelation temperature.

[0028] The method for heating the ink is not particularly limited. For example, ink supply systems such as the ink tank constituting the head carriage, the supply pipe, and the front-chamber ink tank immediately before the head, the piped piping with a filter, and the head can be heated. Heating can be performed by a panel heater, a ribbon heater, heat-retaining water, or the like.

[0029] The viscosity of the ink at the time of ejection is preferably 7 mPa·s or more and 15 mPa·s or less, and more preferably 8 mPa·s or more and 13 mPa·s or less. The lower the viscosity at the time of ejection, the easier it is to follow fine irregularities such as the surface of a medium or a curable composition that has already been applied and irradiated with light, and voids caused by the irregularities are less likely to occur in the cured film.

[0030] From the viewpoint of improving both pattern accuracy and recording speed, the droplet volume of the ejected ink is preferably 2 pL or more and 20 pL or less.

[0031] The amount of ink applied to the medium is such that the film thickness of the cured film formed by the first curing step and the second curing step described later is 15 μm or more and 60 μm or less. By setting the film thickness to 15 μm or more, the step can be easily covered with the cured film. By setting the film thickness to 60 μm or less, active radiation can sufficiently reach the medium side in the first curing step and the second curing step to sufficiently cure the ink, and the hardness of the formed cured film can be sufficiently increased.

[0032] The active radiation curable ink will be described later.

[0033] This step may be performed while scanning the head in a direction orthogonal to the moving direction of the medium, or may be performed without scanning using a single-pass head that covers the entire width of the medium. The scanning method is preferable because light sources can be arranged on both sides of the head of the head carriage to eject ink and irradiate active radiation during scanning, and the device configuration can be easily made compact.

[0034] 1-2. Temporary curing of the applied ink Next, the applied ink is temporarily cured by irradiation with active radiation (first curing step).

[0035] Irradiation with active radiation may be performed under conditions where the photopolymerizable compound contained in the active radiation-curable ink undergoes polymerization and crosslinking. The irradiation light is not particularly limited, and ultraviolet rays, electron beams, and the like can be used. Among these, ultraviolet rays, particularly ultraviolet rays having a peak wavelength of 360 nm or more and 410 nm or less, are preferred.

[0036] The illuminance of the irradiation light is 1 W / cm ２ or more and 20 W / cm ２ or less is preferred, and 3 W / cm ２ or more and 15 W / cm ２ or less is more preferred. When the illuminance is 1 W / cm ２ or more, the photopolymerizable compound can be sufficiently polymerized and crosslinked to sufficiently increase the hardness of the cured film. Further, the higher the illuminance, the shorter the irradiation time required to reach the necessary light quantity, which improves productivity.

[0037] The light quantity per single irradiation is 100 mJ / cm ２ or more and 3000 mJ / cm ２ or less is preferred, and 300 mJ / cm ２ or more and 1800 mJ / cm ２ or less is more preferred, and 300 mJ / cm ２ or more and 800 mJ / cm ２ or less is even more preferred. As the light quantity is increased, the photopolymerizable compound can be sufficiently polymerized and crosslinked to sufficiently suppress bleeding. As the light quantity is decreased, it becomes easier to adjust the reaction rate of the ink per irradiation.

[0038] In this step, the active radiation-curable ink is temporarily cured by irradiation with active radiation such that the reaction rate on the medium side is 80% or less. The reaction rate on the medium side can be adjusted by the illuminance of the light, the light quantity per single irradiation, or the like.

[0039] The reaction rate on the medium side can be obtained from an IR spectrum obtained by measuring the surface of the cured film on the medium side by Fourier transform infrared spectroscopy (FT-IR). For the ink before and after irradiation with active radiation, the following two peak areas are respectively obtained from the obtained IR spectrum. • A peak that decreases when an acrylic monomer is photocured, for example, 810 cm－１ Nearby peaks (CH out-of-plane bending vibrations): Peaks that do not decrease even when the acrylic monomer is photocured, e.g., 1725 cm⁻¹. －１ The peak area with the nearby peak (C=O stretching vibration) and the reaction rate after light irradiation are determined by the following formula: Reaction rate = 1 - (A / B) / (C / D) A: 810 cm of the cured film －１ Nearby peak area B: 1725 cm² of the cured film －１ Nearby peak area C: 810 cm² －１ Nearby peak area D: 1725 cm² －１ Nearby peak area

[0040] If the cured film adheres tightly to the medium and cannot be peeled off, making it impossible to measure the surface of the medium, then the cured film should be formed under the same conditions on a medium with low adhesion to the cured film (such as polyethylene terephthalate, polypropylene, polyimide, or polytetrafluoroethylene). The formed cured film should then be peeled off, and the surface of the medium should be measured.

[0041] By setting the reaction rate of the partially cured ink on the media side to 80% or less, the ink on the media side (back side) can be made somewhat fluid, making it less likely for voids to form during curing. In addition, the accumulation of stress corresponding to the curing shrinkage of the ink on the surface side is also reduced, making it less likely for voids to form due to peeling of the cured film caused by the above stress. The reaction rate on the media side in this process is preferably 30% to 80%, more preferably 50% to 80%, and even more preferably 65% ​​to 80%.

[0042] In this embodiment, the ink applied to the medium is irradiated with active light multiple times. After at least the first irradiation, the reaction rate of the ink on the medium side becomes 80% or less. In this step, multiple light irradiations may be performed. In other words, the reaction rate of the ink on the medium side may be 80% or less after multiple irradiations.

[0043] 1-3. Curing of the partially cured ink Next, the partially cured ink is irradiated with an active ray to further cure the ink (second curing step).

[0044] The irradiation with active light may be carried out under the same conditions as the first curing step, or under different conditions. For example, if the ink hardness has increased in the first curing step, the illuminance and light intensity in this step may be lower than in the first curing step. Alternatively, if the ink hardness has not increased sufficiently in the first curing step, the illuminance and light intensity in this step may be higher than in the first curing step.

[0045] This process is carried out so that the ink hardens sufficiently. For example, it is preferable that this process be carried out so that the reaction rate of the ink on the medium side is greater than 80%. The reaction rate of the ink on the medium side after curing by this process is more preferably 85% or more and 100% or less, and even more preferably 90% or more and 100% or less. The irradiation with active rays in this process may be carried out only once or by multiple irradiations so that the reaction rate of the ink on the medium side is approximately as described above.

[0046] 1-4. Heat treatment of cured ink The cured ink may then be heat-treated. Heat treatment can further react unreacted components, thereby increasing the hardness, adhesion, and heat resistance of the cured film.

[0047] When heat treatment is performed, the cured film may peel off due to stress caused by curing shrinkage during irradiation with an active ray, which can result in the formation of voids. In contrast, in this embodiment, the reaction rate of the ink medium is reduced in the first curing step, making it less likely to generate stress during irradiation with an active ray. This also makes it less likely for voids to form due to the residual stress mentioned above to occur.

[0048] The heat treatment conditions are not particularly limited and can be determined according to the ink composition, etc. For example, it can be performed at a temperature of 120°C to 250°C for a period of 10 minutes to 5 hours. Alternatively, pre-baking at a lower temperature (around 80°C) may be performed before the heat treatment.

[0049] 1-5. The ink application step, the first curing step, and the second curing step described above may be performed only once or multiple times. By repeatedly performing each of the above steps multiple times, a cured film of a certain thickness can be formed.

[0050] 1-6. Ink In this embodiment, a cured film is formed using an active-ray curable ink containing a compound that polymerizes and crosslinks upon irradiation with active rays (photopolymerizable compound). The ink may also contain components such as a photopolymerization initiator, a colorant, and a gelling agent.

[0051] 1-6-1. Photopolymerizable Compounds Photopolymerizable compounds may include radical polymerizable compounds, cationic polymerizable compounds, or both. From the viewpoint of reducing the influence of humidity during curing, it is preferable that the photopolymerizable compound includes radical polymerizable compounds. Examples of radical polymerizable compounds include compounds having a (meth)acryloyl group, other compounds having a vinyl group, and compounds having a maleimide group. Examples of cationic polymerizable compounds include compounds having an alicyclic epoxy group and compounds having an oxetane group.

[0052] Of these, radical polymerizable compounds exhibit a large degree of curing shrinkage and are relatively prone to generating voids. Therefore, the void generation suppression effect of this embodiment is particularly pronounced when the photopolymerizable compound includes a radical polymerizable compound.

[0053] In this specification, (meth)acryloyl means acryloyl or methacryloyl, (meth)acrylate means acrylate or methacrylate, and (meth)acrylic means acrylic or methacrylic.

[0054] The photopolymerizable compound may include a monofunctional compound having only one functional group for polymerization or crosslinking within its molecule, a polyfunctional compound having multiple such functional groups within its molecule, or both. From the viewpoint of increasing the flexibility of the cured film, it is preferable that the photopolymerizable compound includes a monofunctional compound. Furthermore, from the viewpoint of increasing the strength of the cured film, it is preferable that the photopolymerizable compound includes a polyfunctional compound.

[0055] The photopolymerizable compound preferably contains a compound having a (meth)acryloyl group (such as (meth)acrylate). The compound having a (meth)acryloyl group further improves the pattern accuracy of the cured film.

[0056] From the viewpoint of increasing the hardness of the cured film, it is preferable that the photopolymerizable compound contains a polyfunctional (meth)acrylate. For example, it is preferable that the photopolymerizable compound contains a (meth)acrylate with two or more photopolymerizable functional groups, more preferably a (meth)acrylate with three or more photopolymerizable functional groups, and even more preferably a (meth)acrylate with five or more photopolymerizable functional groups. While these polyfunctional (meth)acrylates increase the hardness of the cured film, they also increase the degree of curing shrinkage. Therefore, they tend to cause the void generation problem described above. In contrast, with the cured film manufacturing method of this embodiment, it is possible to make it difficult to generate voids even when using a polyfunctional (for example, five or more functional) (meth)acrylate.

[0057] The content of five- or more functional (meth)acrylates is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 12% by mass or less, based on the total mass of the ink.

[0058] Furthermore, from the viewpoint of improving the adhesion of the cured film to the medium, it is preferable that the photopolymerizable compound contains a (meth)acrylate having a carboxyl group or a salt thereof. The (meth)acrylate having a carboxyl group can be, for example, a compound having a structure represented by the following general formula (1).

[0059]

[0060] In general formula (1), X represents a residue of a compound having a (meth)acryloyl group. Q is an oxygen atom or NR ２ This indicates R ２ R represents a hydrogen atom, an optionally substituted alkyl group, or an optionally substituted aryl group. １ Q represents an unsubstituted alkylene group having 1 to 6 carbon atoms. From the viewpoint of further improving the adhesion of the cured film, Q is preferably an oxygen atom. From the viewpoint of further improving the adhesion of the cured film, R １It is preferable that X is a methylene group or an ethylene group. From the viewpoint of reducing the viscosity of the ink and improving the ejection performance, it is preferable that X has 50 carbon atoms or less, more preferably 30 carbon atoms or less, and even more preferably 10 carbon atoms or less.

[0061] Examples of compounds having the structure represented by general formula (1) or their salts include the following compounds A-1 to A-9.

[0062]

[0063]

[0064] The content of (meth)acrylate or a salt having a carboxyl group is preferably 1% by mass or more and 50% by mass or less, and more preferably 3% by mass or more and 20% by mass or less, based on the total mass of the ink.

[0065] Furthermore, monofunctional (meth)acrylates exhibit less curing shrinkage, making them less prone to generating voids. Therefore, voids are more likely to occur when the amount of monofunctional (meth)acrylate is low, and the void-suppressing effect of this embodiment is particularly pronounced in such cases. For example, the content of monofunctional (meth)acrylate is preferably 0% to 50% by mass relative to the total mass of the ink, more preferably 0% to 30% by mass, and even more preferably 0% to 10% by mass. The ink may also not contain substantially any monofunctional (meth)acrylate. Substantially containing none means that the content of this component is 0.1% by mass or less relative to the total mass of the ink.

[0066] The (meth)acrylate may be a modified product such as an ethylene oxide modified product, a propylene oxide modified product, or a caprolactam modified product.

[0067] 1-6-2. Photopolymerization Initiators The photopolymerization initiator may contain a photoradical polymerization initiator, a photocationic polymerization initiator, or both. When the curable composition contains a radical polymerizable compound as the photopolymerizable compound, it is preferable to include a photoradical polymerization initiator as the photopolymerization initiator. When the curable composition contains a cationic polymerizable compound as the photopolymerizable compound, it is preferable to include a photocationic polymerization initiator as the photopolymerization initiator.

[0068] Photo-radical polymerization initiators are compounds that generate radicals upon irradiation with light, thereby initiating the polymerization and crosslinking of radical-polymerizable compounds.

[0069] Examples of photoradical polymerization initiators include benzoin compounds, alkylphenone compounds, acetophenone compounds, aminoacetophenone compounds, anthraquinone compounds, thioxanthone compounds, ketal compounds, acylphosphine oxide compounds, oxime ester compounds, and titanocene compounds.

[0070] Examples of benzoin compounds include benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether.

[0071] Examples of alkylphenone compounds include 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 2-benzyl-2-(dimethylamino)-4′-morpholinobutyrophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropanone, 1-[4-(2-hydroxyethoxyl)-phenyl]-2-hydroxy-methylpropanone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, and 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one.

[0072] Examples of acetophenone compounds include acetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, and 1,1-dichloroacetophenone.

[0073] Examples of aminoacetophenone compounds include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone, and N,N-dimethylaminoacetophenone, among others.

[0074] Examples of anthraquinone compounds include 2-methylanthraquinone, 2-ethylanthraquinone, and 2-t-butylanthraquinone.

[0075] Examples of thioxanthone compounds include 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone.

[0076] Examples of ketal compounds include acetophenone dimethyl ketal and benzyl dimethyl ketal.

[0077] Examples of acylphosphine oxide compounds include 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.

[0078] Examples of oxime ester compounds include 1,2-octanedione and 1-[4-(phenylthio)-2-(o-benzoyl oxime)]. Other examples include ethanone and 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(o-acetyl oxime).

[0079] Examples of titanocene compounds include bis(cyclopentadienyl)-diphenyl-titanium and bis(cyclopentadienyl)-dichloro-titanium. Other examples include bis(cyclopentadienyl)-bis(2,3,4,5,6-pentafluorophenyl)titanium and bis(cyclopentadienyl)-bis(2,6-difluoro-3-(pyrrole-1-yl)phenyl)titanium.

[0080] The content of the photoradical polymerization initiator in the curable composition can be 1% by mass or more and 10% by mass or less, based on the total mass of the radical polymerizable compound.

[0081] 1-6-3. Colorants The colorants may contain pigments or dyes. From the viewpoint of improving the weather resistance of the cured film, it is preferable that the colorants contain pigments. The type of colorant should be selected according to the color tone that the cured film should exhibit. In this case, two or more types of colorants may be combined to adjust the color tone.

[0082] Examples of yellow pigments include C. I. Pigment Yellow (hereinafter also simply referred to as "PY") 1, PY3, PY12, PY13, PY14, PY17, PY34, PY35, PY37, PY55, PY74, PY81, PY83, PY93, PY94, PY95, PY97, PY108, PY109, PY110, PY137, PY138, PY139, PY153, PY154, PY155, PY157, PY166, PY167, PY168, PY180, PY185, and PY193.

[0083] Examples of red or magenta pigments include C. I. Pigment Red (hereinafter also simply referred to as "PR") 3, PR5, PR19, PR22, PR31, PR38, PR43, PR48:1, PR48:2, PR48:3, PR48:4, PR48:5, PR49:1, PR53:1, PR57:1, PR57:2, PR58:4, PR63:1, PR81, PR81:1, PR81:2, PR 81:3, PR81:4, PR88, PR104, PR108, PR112, PR122, PR123, PR144, PR146, PR149, PR166, PR168, PR169, PR170, PR177, PR178, PR179, PR184, PR185, PR208, PR216, PR226, and PR257, C. I. Pigment Violet (hereinafter also simply referred to as "PV") 3, PV19, PV23, PV29, PV30, PV37, PV50, and PV88, and C. I. This includes Pigment Orange (hereinafter also simply referred to as "PO") 13, PO16, PO20, and PO36, among others.

[0084] Examples of blue or cyan pigments include C. I. Pigment Blue (hereinafter also simply referred to as "PB") 1, PB15, PB15:1, PB15:2, PB15:3, PB15:4, PB15:6, PB16, PB17-1, PB22, PB27, PB28, PB29, PB36, and PB60.

[0085] Examples of green pigments include C. I. Pigment Green (hereinafter also simply referred to as "PG") 7, PG26, PG36, and PG50.

[0086] Examples of black pigments include C. I. Pigment Black (hereinafter also simply referred to as "PBk") 7, PBk 26, and PBk 28.

[0087] Examples of white pigments include inorganic pigments such as titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, and aluminum hydroxide. Of these, titanium dioxide is preferred.

[0088] The crystalline form of the titanium dioxide described above may be rutile, anatase, or blue kite. However, from the viewpoint of making it easier to reduce the particle size of the white pigment, the anatase type, which has a lower specific gravity, is preferred, and from the viewpoint of further improving the opacity of the formed image, the rutile type, which has a higher refractive index in the visible light region, is preferred.

[0089] The colorant content is preferably 0.1% by mass or more and 10% by mass relative to the total mass of the ink, and more preferably 0.1% by mass or more and 5% by mass.

[0090] The ink may contain a pigment dispersant for dispersing the pigment. Examples of pigment dispersants include hydroxyl group-containing carboxylic acid esters, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, polymer copolymers, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, naphthalene sulfonic acid formalin condensate salts, aromatic sulfonic acid formalin condensate salts, polyoxyethylene alkyl phosphate esters, polyoxyethylene nonylphenyl ether, and stearylamine acetate.

[0091] The pigment dispersant content is preferably 10% by mass or more and 200% by mass or less relative to the total mass of the pigment, and more preferably 20% by mass or more and 100% by mass or less. When the dispersant content is 10% by mass or more relative to the total mass of the pigment, the dispersion stability of the pigment is enhanced, and when the dispersant content is 200% by mass or less relative to the total mass of the pigment, the ink discharge performance tends to be more stable.

[0092] 1-6-4. Gelling Agents Gelling agents are compounds that enable ink to undergo a sol-gel phase transition due to temperature changes. Ink containing a gelling agent becomes a sol when heated and can be ejected from the print head. On the other hand, ink containing a gelling agent cools and gels upon contact with the medium, suppressing wetting and spreading. In this way, gelling agents improve the pinning properties of the ink and further enhance the pattern accuracy of the cured film.

[0093] Furthermore, the gelling agent suppresses the inhibition of surface hardening of the ink by oxygen. As a result, inks containing a gelling agent tend to harden more easily on the surface when irradiated with active light, which can lead to significant hardening shrinkage on the surface. This large hardening shrinkage on the surface makes voids more likely to form in inks containing a gelling agent, and in such cases, the void formation suppression effect of this embodiment is remarkable.

[0094] The gelling agent is preferably a material that forms a cardhouse structure when crystallized in the ink. When a cardhouse structure is formed, the photopolymerizable compound is encapsulated within the cardhouse structure, thereby improving the pinning properties of the ink. Furthermore, the gelling agent is preferably compatible with the photopolymerizable compound in the ink.

[0095] Examples of gelling agents that form a cardhouse structure include aliphatic ketones, aliphatic esters, petroleum waxes, plant waxes, animal waxes, mineral waxes, hydrogenated castor oil, modified waxes, higher fatty acids, higher alcohols, hydroxystearic acid, fatty acid amides including N-substituted fatty acid amides and special fatty acid amides, higher amines, esters of sucrose fatty acids, synthetic waxes, dibenzylidene sorbitol, dimer acids, and dimer ols.

[0096] Of these, from the viewpoint of improving pinning properties, aliphatic ketones, aliphatic esters, higher fatty acids, and higher alcohols, all of which have hydrocarbon groups with 9 to 25 carbon atoms, are preferred.

[0097] Examples of aliphatic ketones include dilignoseryl ketone, dibehenyl ketone, distearyl ketone, dieicosyl ketone, dipalmityl ketone, dilauryl ketone, dimyristyl ketone, myristylpalmityl ketone, and palmitylstearyl ketone.

[0098] Examples of aliphatic esters include fatty acid esters of monoalcohols such as behenyl behenate, eicosyl eicosanoate, and oleyl palmitate, as well as fatty acid esters of polyhydric alcohols such as glycerol fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, ethylene glycol fatty acid esters, and polyoxyethylene fatty acid esters.

[0099] Examples of higher fatty acids include behenic acid, arachidic acid, stearic acid, palmitic acid, myristic acid, lauric acid, oleic acid, and erucic acid.

[0100] Examples of higher alcohols include stearyl alcohol and behenyl alcohol.

[0101] From the viewpoint of further enhancing pinning properties, the gelling agent is preferably an aliphatic ketone represented by the following general formula (G1) or an aliphatic ester represented by the following general formula (G2).

[0102] General formula (G1): R1-CO-R2 General formula (G2): R3-COO-R4

[0103] In general formula (G1), R1 and R2 each independently represent an alkyl group having a linear chain with 12 to 26 carbon atoms, and which may also be branched. R1 and R2 may be the same or different. In general formula (G2), R3 and R4 each independently represent an alkyl group having a linear chain with 12 to 26 carbon atoms, and which may also be branched. R3 and R4 may be the same or different.

[0104] Examples of aliphatic ketones represented by general formula (G1) include dilignoseryl ketone (23, 24 carbon atoms), dibehenyl ketone (21, 22 carbon atoms), distearyl ketone (17, 18 carbon atoms), dieicosyl ketone (19, 20 carbon atoms), dipalmityl ketone (15, 16 carbon atoms), dimyristyl ketone (13, 14 carbon atoms), dilauryl ketone (11, 12 carbon atoms), and lauryl myristyl ketone (carbon atoms) This includes carbon atoms 11, 14), lauryl palmityl ketone (carbon number: 11, 16), myristyl palmityl ketone (carbon number: 13, 16), myristyl stearyl ketone (carbon number: 13, 18), myristyl behenyl ketone (carbon number: 13, 22), palmityl stearyl ketone (carbon number: 15, 18), palmityl behenyl ketone (carbon number: 15, 22), and stearyl behenyl ketone (carbon number: 17, 22). The carbon numbers in parentheses represent the number of carbon atoms in each of the two hydrocarbon groups separated by the carbonyl group.

[0105] Examples of aliphatic esters represented by general formula (G2) include behenyl behenate (21, 22 carbon atoms), eicosyl eicosanoate (19, 20 carbon atoms), stearyl stearate (17, 18 carbon atoms), palmityl stearate (16, 17 carbon atoms), lauryl stearate (12, 17 carbon atoms), cetyl palmitate (6, 15 carbon atoms), stearyl palmitate (15, 18 carbon atoms), myristyl This includes myristyl myristate (13, 14 carbon atoms), cetyl myristate (13, 16 carbon atoms), octyldodecyl myristate (13, 20 carbon atoms), stearyl oleate (17, 18 carbon atoms), stearyl erucate (18, 21 carbon atoms), stearyl linoleate (17, 18 carbon atoms), behenyl oleate (18, 22 carbon atoms), and arachidyl linoleate (17, 20 carbon atoms). The carbon numbers in parentheses represent the carbon numbers of the two hydrocarbon groups separated by the ester group.

[0106] The gelling agent content is preferably 1% by mass or more and 10% by mass or less relative to the total mass of the ink.

[0107] 1-6-5. Other component inks may contain other components such as surfactants, coupling agents, polymerization inhibitors, and fillers.

[0108] Furthermore, the ink may contain a thermosetting compound that polymerizes or crosslinks upon heating in the presence of a thermosetting agent or thermosetting accelerator. The thermosetting compound enhances the heat resistance and mechanical strength of the cured film. The thermosetting compound can be a known compound, such as a compound having an epoxy group.

[0109] However, thermosetting compounds (for example, monomers having epoxy or oxetane groups) exhibit less curing shrinkage and are relatively less likely to generate voids. Therefore, the void generation suppression effect of this embodiment is particularly pronounced when the amount of thermosetting compound contained in the ink is small. For example, the content of the thermosetting compound is preferably 0% to 20% by mass, more preferably 0% to 10% by mass, and even more preferably 0% to 5% by mass, based on the total mass of the ink. Similarly, the content of monomers having epoxy or oxetane groups is preferably 0% to 20% by mass, more preferably 0% to 10% by mass, and even more preferably 0% to 5% by mass, based on the total mass of the ink.

[0110] Furthermore, the photopolymerizable compounds described above are themselves liquids and can act as reactive diluents. Therefore, the water content in the curable composition is preferably 0% to 1% by mass, more preferably 0% to 0.5% by mass, and even more preferably 0% to 0.2% by mass, based on the total mass of the curable composition. In addition, the water content in the curable composition is preferably 0% to 5% by mass, more preferably 0% to 1% by mass, and even more preferably 0% to 0.5% by mass, based on the total mass of the curable composition.

[0111] 1-6-6. Method of preparing ink Ink can be prepared by mixing the components described above. When the ink contains a pigment, it is preferable to prepare a dispersion by dispersing the pigment and pigment dispersion in a small amount of liquid component (e.g., a photopolymerizable compound), and then mix this with the other components. Heating may be applied during mixing.

[0112] 2. Cured Film The cured film formed by the method described above can be used in insulating materials (especially insulating protective films for printed circuit boards, etc.), electronic components sealed with the cured film, etc. In particular, since the cured film is less prone to cracking and delamination even when formed to a thick film thickness, it can be suitably used as an insulating film between wiring in thick copper PCBs, etc., where a thick cured film is required. The cured film may be used as a planarizing film for the inner layer thick copper circuits of a thick copper PCB, or as an insulating protective film (solder resist) for the outer layer copper wiring.

[0113] The printed circuit board having a cured film according to this embodiment can be used in various electronic devices. Examples of such electronic devices include information devices such as mobile phones, personal computers, and smartphones; household appliances such as refrigerators, washing machines, and microwave ovens; medical devices; and industrial robots.

[0114] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited to the examples.

[0115] 1. Preparation of Active Ray Curable Ink 1-1. Preparation of Pigment Dispersion 1-1-1. Preparation of Yellow Dispersion Dispersant 1, Dispersant 2, and Dispersion Medium were placed in a stainless steel beaker and heated on a 65°C hot plate for 1 hour while stirring to dissolve, and then cooled to room temperature. After that, the pigment listed below was added to this, and the mixture was placed in a glass bottle with 200 g of 0.5 mm diameter zirconia beads and sealed tightly. This was dispersed in a paint shaker until the desired particle size was achieved, and then the zirconia beads were removed to obtain yellow dispersion Y. As the dispersion medium, an active ray curable ink containing 0.2 parts by mass of polymerization inhibitor (BASF, Irgastab UV-10) was used. Dispersant 1: PX4701 (BASF) 6.0 parts by mass Dispersant 2: Solsperse 22000 (Lubrizol Japan) 0.3 parts by mass Dispersant medium: Dipropylene glycol diacrylate 61.5 parts by mass Pigment: PY185 (BASF, Paliotol Yellow D1155) 10.2 parts by mass

[0116] 1-1-2. Preparation of Cyanide Dispersion A cyanide pigment dispersion C was obtained in the same manner as the preparation of dispersion Y, except that the dispersant, dispersion medium, and pigment were changed as shown below. Dispersant: PX4701 (BASF) 7.0 parts by mass Dispersant medium: Dipropylene glycol diacrylate 70 parts by mass Pigment: PB15:4 (Dainichi Seika, Chromofine Blue 6332JC) 23 parts by mass

[0117] 1-2. Preparation of Inks Dispersions Y and C described above were mixed with the following materials in the proportions shown in Table 1, and the mixture was filtered through an ADVATEC Teflon® 3 μm membrane filter to prepare inks A to D. (Actively Polymerizable Compounds) ・Compound 1: Compound A-3 shown in formula (1) (a trifunctional (meth)acrylate having a carboxyl group) ・Compound 2: Dipentaerythritol pentaacrylate (a pentafunctional (meth)acrylate) ・Compound 3: Pentaerythritol triacrylate (a trifunctional (meth)acrylate) ・Compound 4: Trimethylolpropane triacrylate (a trifunctional (meth)acrylate) ・Compound 5: Dipropylene glycol diacrylate (a bifunctional (meth)acrylate) (Gelling Agent) ・Gelling agent: Exepearl SS (aliphatic ester), manufactured by Kao Corporation (Photopolymerization Initiators) ・Initiator 1: Omnirad 907, manufactured by IGM Resins ・Initiator 2: Omnirad 819, manufactured by IGM Resins ・Initiator 3: Lambson Speedcure ITX (polymerization inhibitor) • Polymerization inhibitor: BASF Irgastab UV-10

[0118]

[0119] 2. Experiment 1 2-1. Formation of Cured Film Each prepared ink was loaded into an inkjet recording device having an inkjet head equipped with a piezo-type inkjet nozzle (nozzle diameter 22 μm). A copper-clad laminate for printed circuit boards (FR-4, thickness 1.6 mm, size 150 mm x 95 mm), which is a non-ink-absorbing substrate, was prepared with copper wiring (copper lines with a width of 100 μm and non-copper lines with a width of 100 μm) formed on it, with a height of 35 μm. A cured film was formed on this copper-clad laminate so as to cover both the copper lines and the non-copper lines. Each ink was applied to the copper-clad laminate without wiring so that the thickness of the cured film was 30 μm. The same process was also carried out on the copper-clad laminate without wiring.

[0120] The inkjet recording device used included an ink tank, an ink channel, a sub-ink tank immediately before the inkjet recording head, piping with a metal filter, and an inkjet head. The ink channel from the ink tank to the head was heated to 80°C. A heater was also built into the inkjet head to heat the ink inside the head to 80°C. Heads with a nozzle resolution of 360 dpi were arranged alternately to form a nozzle row with a resolution of 720 dpi.

[0121] A voltage was applied to the print head to eject ink, creating a dot with a droplet volume of 6.0 pL. A coating film with a thickness of 35 μm was formed in contact with the copper wiring on the substrate. Subsequently, a Phoseon Technology LED lamp (395 nm, 8 W / cm²) was used. ２ Using a water-cooled unit, the illuminance was 5 W / cm². ２ , light intensity 666mJ / cm ２ The ink was cured by irradiating it with an active ray under the specified conditions. The ink was cured by irradiating it with an active ray five times under the same conditions.

[0122] Under the heat treatment condition, after five light irradiations, the ink-coated substrate was placed in an oven set to 150°C for 60 minutes.

[0123] 2-2. Evaluation of Cured Films 2-2-1. Reaction Rate After Each Irradiation A cured film was formed on a 100 μm thick polypropylene film under the same conditions. The number of light irradiations was changed, and the cured film (pre-cured film) after each irradiation was peeled off the substrate. The substrate-side surface of the cured film was measured using FT-IR. In addition, ink that had not been ejected or irradiated was also measured using FT-IR under the same conditions. Of the obtained IR spectra, the 810 cm⁻¹ spectrum, which decreases when acrylic monomer is photocured, was used. －１ The peak in the vicinity (CH out-of-plane angular bending vibration) and the 1725 cm⁻¹ peak, which does not decrease even when the acrylic monomer is photocured. －１ The peak area was determined for the nearby peak (C=O stretching vibration). Then, the reaction rate after light irradiation was calculated using the following formula: Reaction rate = 1 - (A / B) / (C / D) A: 810 cm of the cured film －１ Nearby peak area B: 1725 cm² of the cured film －１Nearby peak area C: 810 cm² －１ Nearby peak area D: 1725 cm² －１ Nearby peak area

[0124] 2-2-2. Pencil Hardness The pencil hardness of the hardened film surface on a copper-clad laminate without wiring was measured in accordance with JIS K 5600-5-4:1999. A pencil hardness of 3H or higher was considered acceptable for practical use.

[0125] 2-2-3. Adhesion In accordance with JIS K 5600-5-6:1999, cross-cut incisions were made in the hardened film on a copper-clad laminate without wiring, adhesive tape was applied, and the peeling state of the hardened film was observed. Adhesion was evaluated according to the following criteria, and a rating of B or higher was considered to be practically acceptable. (Criteria) AAAA: Adhesion retention rate is 100% AAA: Adhesion retention rate is 90% or more and less than 100% AA: Adhesion retention rate is 80% or more and less than 90% A: Adhesion retention rate is 60% or more and less than 80% B: Adhesion retention rate is 40% or more and less than 60% C: Adhesion retention rate is less than 40%

[0126] 2-2-4. Transmitted light was shone onto a substrate with a void-cured film formed on it, and the 100 μm line without copper was observed. The area of ​​voids relative to the area of ​​the observed 100 μm line without copper was calculated. The degree of void formation was evaluated according to the following criteria, and 1 to 3 were considered to be without practical problems. 1: No voids were observed at all. 2: Voids were observed, and the void area was 2% or less. 3: Voids were observed, and the void area was greater than 2% and 5% or less. 4: Voids were observed, and the void area was greater than 5% and 20% or less. 5: Voids were observed, and the void area was greater than 20%.

[0127] 2-2-5. The hardened film formed on a copper-clad laminate without stepped covering wiring was observed under a microscope to check for copper exposure. The covering of the steps was evaluated according to the following criteria, and 1 and 2 were deemed to be practically acceptable. 1: No copper wiring exposure was observed. 2: No copper wiring exposure was observed, but there were areas where the copper was visible through the film. 3: Copper wiring exposure was observed.

[0128] Wiring boards 1 to 5 with cured films were fabricated by changing the type of ink and whether or not heating was performed, and were evaluated according to the above criteria.

[0129] Table 2 shows the type of ink used to fabricate wiring boards 1 to 5, the thickness of the wiring and cured film, the amount of light per irradiation, the number of irradiations, the reaction rate after each irradiation, whether or not heat treatment was performed, and the evaluation results of pencil hardness, adhesion, and coverage of voids and steps.

[0130]

[0131] 3. Experiment 2 3-1. Formation of Cured Film Using the prepared ink, a cured film was formed on copper-clad laminates (FR-4, 1.6 mm thick, 150 mm x 95 mm in size) with wiring formed on them and on copper-clad laminates without wiring formed on them, using the same inkjet recording device as in Experiment 1. At this time, cured films 6 to 16 were produced by changing the thickness of the copper wiring and cured film, the amount of light irradiated per irradiation, or the number of irradiations. The produced cured films were evaluated in the same manner as in Experiment 1.

[0132] Tables 3 and 4 show the types of inks used to fabricate wiring boards 6 to 16, the thickness of the wiring and cured films, the amount of light per irradiation, the number of irradiations, the reaction rate after each irradiation, whether or not heat treatment was performed, and the evaluation results of pencil hardness, adhesion, and coverage of voids and steps. The thickness of the cured film is the target thickness on a copper-clad laminate without wiring. For comparison, the fabrication conditions and evaluation results of cured film 2 are also shown in Table 3.

[0133]

[0134]

[0135] 4. Experiment 3 4-1. Formation of Cured Film Using the prepared ink, a cured film was formed on copper-clad laminates (FR-4, 1.6 mm thick, 150 mm x 95 mm in size) with wiring formed on them and on copper-clad laminates without wiring formed on them, using the same inkjet recording device as in Experiment 1. The thickness of the copper wiring was 35 μm, and the target thickness of the cured film on the copper-clad laminate without wiring was 15 μm. The irradiation of the active ray was 5 W / cm². ２ , light intensity 400mJ / cm ２ The procedure was carried out under the following conditions. The ink was cured by irradiating it with active light 10 times under the same conditions. In this way, the first stage of cured film was produced.

[0136] Subsequently, a coating film was formed with a target thickness of 15 μm, and the illuminance was 5 W / cm². ２ , light intensity 400mJ / cm ２ In the following procedure, the active ray was irradiated 10 times to produce the second stage of the cured film.

[0137] After light irradiation, the ink-coated substrate was placed in an oven set to 150°C for 60 minutes.

[0138] Table 5 shows the type of ink used to produce the wiring board 17 obtained in this way, the thickness of the wiring and cured film, the amount of light per irradiation, the number of irradiations, the reaction rate after each irradiation, whether or not heat treatment was performed, and the evaluation results of pencil hardness, adhesion, and coverage of voids and steps. The thickness of the cured film is the target value of the thickness on a copper-clad laminate without wiring. The reaction rates listed in Table 5 are values ​​common to the production of the first and second cured films.

[0139]

[0140] As is clear from Tables 1 to 5, this embodiment made it possible to form a cured film with high hardness, few voids, and excellent coverage of steps.

[0141] This application claims priority to Japanese Patent Application No. 2025-049916, filed on 25 March 2025. All disclosures of the specification, claims, drawings and abstract contained in the above Japanese application are incorporated herein by reference.

[0142] This invention enables the production of a cured film with fewer voids by light irradiation.

Claims

1. A method for manufacturing a cured film, comprising: an application step of applying an active-ray curable ink to a non-ink-absorbing medium having a step difference of 15 μm or more and 110 μm or less by an inkjet method; a first curing step of irradiating the applied active-ray curable ink with an active ray to pre-cure the active-ray curable ink so that the reaction rate on the medium side is 80% or less; and a second curing step of irradiating the pre-cured active-ray curable ink with an active ray to further cure the active-ray curable ink and form a cured film with a film thickness of 15 μm or more and 60 μm or less.

2. A method for producing a cured film according to claim 1, further comprising a step of heat-treating the cured active-ray curable ink after the second curing step.

3. The method for producing a cured film according to claim 1, wherein the active-ray curable ink contains a (meth)acrylate with five or more functionalities.

4. The method for producing a cured film according to claim 1, wherein the active-ray curable ink comprises a (meth)acrylate having a carboxyl group or a salt thereof.

5. The method for producing a cured film according to claim 1, wherein the active-ray curable ink contains a gelling agent.

6. A method for producing a cured film according to claim 1, comprising performing the impregnation step, the first curing step, and the second curing step multiple times.

7. A method for manufacturing a cured film according to claim 1, used in the manufacture of a printed circuit board.

8. A printed circuit board having a cured film manufactured by the manufacturing method described in any one of claims 1 to 7.

9. An electronic device having a printed circuit board as described in claim 8.

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