Method for producing flexible printed boards

Abstract

This method for producing flexible printed boards comprises a step for coating, using a vertical lift roll coater, a liquid photosensitive resin composition (17) on both sides of a board (11) that has a film-shaped support (13) and wiring (14) disposed on both sides of the film-shaped support (13). A hole (15) is provided in the board (11). The liquid photosensitive resin composition (17) comprises a binder polymer, a photoradical polymerization initiator, a multifunctional epoxy compound, an epoxy cure accelerator, and a radically polymerizable compound having at least three radically polymerizable groups in each molecule. During the coating of the liquid photosensitive resin composition (17), the liquid photosensitive resin composition (17) is coated simultaneously on both sides of the board (11).

Description

Flexible printed circuit board manufacturing method

[0001] The present invention relates to a method for manufacturing a flexible printed circuit board.

[0002] As electronic components become smaller, lighter, and more multifunctional, apertures in flexible printed circuit boards incorporated into electronic devices are required to be fine enough to mount components on smaller-diameter lands, etc. (hereinafter, this may be referred to as "fine aperture capability") As a method for forming fine apertures in flexible printed circuit boards, a method is known in which a film made of a liquid photosensitive resin composition is formed on a component mounting portion of a flexible printed circuit board (hereinafter, this may be simply referred to as a "substrate") before a protective film is formed, and this film is patterned by photolithography to form a protective film with fine apertures.

[0003] Furthermore, in recent years, as the screens of mobile devices such as smartphones have become larger and thinner, flexible printed circuit boards used in the mobile devices are required to have low resilience so that they can be easily folded and installed in narrow spaces. One known method for improving the low resilience of flexible printed circuit boards is to partially apply a thermosetting resin composition known as bending ink to the bent portions of the board.

[0004] Furthermore, flexible printed circuit boards usually have through holes (through holes) and non-through holes (blind vias), and when applying a liquid photosensitive resin composition to the board, it is necessary to fill the through holes and non-through holes with the liquid photosensitive resin composition. For this reason, flexible printed circuit boards are also required to be sufficiently filled with the liquid photosensitive resin composition in the through holes and non-through holes (hereinafter, this may be referred to as "fillability"). Note that, hereinafter, through holes and non-through holes may be collectively referred to as "holes." Furthermore, hereinafter, "hole" refers to one hole or multiple holes. Furthermore, a substrate provided with holes includes a substrate provided with only through holes, a substrate provided with only non-through holes, and a substrate provided with both through holes and non-through holes.

[0005] Under these circumstances, various resin compositions for protective films (more specifically, liquid photosensitive resin compositions, etc.) and coating devices for protective film resin compositions have been investigated in order to improve the fine opening properties, low resilience, or embeddability of flexible printed circuit boards (see, for example, Patent Documents 1 to 4).

[0006] JP 2015-161764 A JP 2020-148971 A International Publication No. 2018 / 092330 JP 2015-115602 A

[0007] However, it is difficult to suppress discoloration of the wiring during a heating process (e.g., a heat press process) while suppressing penetration of the plating solution between the protective film (cured film) and the substrate during a plating process (e.g., a gold plating process) using only the techniques described in Patent Documents 1 to 4. Penetration of the plating solution during the plating process and discoloration of the wiring during the heating process lead to a decrease in product yield. Hereinafter, the property that can suppress penetration of the plating solution during the plating process may be referred to as "plating solution resistance." Furthermore, the property that can suppress discoloration of the wiring during the heating process may be referred to as "discoloration resistance of the wiring."

[0008] The present invention has been made in view of these problems, and an object of the present invention is to provide a method for producing a flexible printed circuit board that has excellent resistance to plating solutions and excellent resistance to discoloration of wiring.

[0009] The method for manufacturing a flexible printed circuit board according to the present invention includes a step of applying a liquid photosensitive resin composition to both sides of a substrate having a film support and wiring provided on both sides of the film support using a vertical lifting roll coater. The substrate has holes formed therein. The liquid photosensitive resin composition contains a binder polymer, a photoradical polymerization initiator, a polyfunctional epoxy compound, an epoxy curing accelerator, and a radical polymerizable compound having three or more radically polymerizable groups per molecule. When applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is simultaneously applied to both sides of the substrate.

[0010] In the method for producing a flexible printed circuit board according to one embodiment of the present invention, the film-like support has a width and a length of 200 mm or more and 600 mm or less.

[0011] In the method for producing a flexible printed circuit board according to one embodiment of the present invention, the film-like support has a thickness of 8.0 μm or more and 50.0 μm or less.

[0012] In the method for manufacturing a flexible printed circuit board according to one embodiment of the present invention, the wiring has a thickness of 8 μm or more and 50 μm or less.

[0013] In the method for manufacturing a flexible printed circuit board according to one embodiment of the present invention, the diameter of the hole is 50 μm or more and 250 μm or less.

[0014] In one embodiment of the method for producing a flexible printed circuit board according to the present invention, the film-like support contains one or more polymers selected from the group consisting of polyimide, polyamide, polyester, polycarbonate, polyarylate, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesin, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.

[0015] In the method for producing a flexible printed circuit board according to one embodiment of the present invention, the binder polymer is one or more polymers selected from the group consisting of polymers having a urethane bond in one molecule, polymers having an imide group in one molecule, polymers having a (meth)acryloyl group in one molecule, and polymers having a carboxy group in one molecule.

[0016] In the method for producing a flexible printed circuit board according to one embodiment of the present invention, the content of the epoxy curing accelerator is 0.1 parts by weight or more and 0.5 parts by weight or less with respect to 100 parts by weight of the binder polymer.

[0017] In the method for producing a flexible printed circuit board according to one embodiment of the present invention, the acid value of the binder polymer is 10 mgKOH / g or more.

[0018] In the method for manufacturing a flexible printed circuit board according to one embodiment of the present invention, the vertical lifting roll coater includes a pair of coating rolls, and the roll diameter of the coating rolls is 70 mm or more and 150 mm or less.

[0019] According to the present invention, a method for producing a flexible printed circuit board having excellent resistance to plating solutions and excellent resistance to discoloration of wiring can be provided.

[0020] Fig. 1 is a cross-sectional view of a main part for explaining an example of a manufacturing method for a flexible printed circuit board according to the present invention; Fig. 2 is another cross-sectional view of a main part for explaining an example of a manufacturing method for a flexible printed circuit board according to the present invention; Fig. 3 is another cross-sectional view of a main part for explaining an example of a manufacturing method for a flexible printed circuit board according to the present invention; Fig. 4 is another cross-sectional view of a main part for explaining an example of a manufacturing method for a flexible printed circuit board according to the present invention; Fig. 5 is a cross-sectional view of a coating roll used in an example of a manufacturing method for a flexible printed circuit board according to the present invention, cut along a plane including its axis.

[0021] Preferred embodiments of the present invention will be described in detail below, but the present invention is not limited thereto. In addition, all academic and patent documents described in this specification are incorporated herein by reference.

[0022] First, the terms used in this specification will be explained. A "roll coater" refers to a coating device having a pair of rotatable coating rolls. Roll coater coating methods include a vertical lifting type, in which the liquid photosensitive resin composition is coated on a substrate while the substrate is lifted vertically, and a horizontal conveying type, in which the liquid photosensitive resin composition is coated on the substrate while the substrate is conveyed horizontally. A vertical lifting type roll coater can simplify the coating device and save space compared to a horizontal conveying type roll coater. Furthermore, a vertical lifting type roll coater can dry a substrate coated with the liquid photosensitive resin composition in a suspended state, thereby preventing the adhesion of foreign matter during the drying process of a coating film (hereinafter sometimes simply referred to as a "coating film") made of the liquid photosensitive resin composition.

[0023] "Photoradical polymerization initiator" refers to a compound that generates radicals as active species when irradiated with light. "Epoxy compound" refers to a compound that has one or more epoxy groups in one molecule. "Multifunctional epoxy compound" refers to an epoxy compound that has two or more epoxy groups in one molecule. "Epoxy curing accelerator" refers to a compound that promotes the crosslinking and chain extension reaction of epoxy compounds.

[0024] The "thickness" of the film-like support is the arithmetic mean value of 10 measured values ​​obtained by randomly selecting 10 measurement points from an electron microscope image of a cross section of the film-like support cut in the thickness direction and measuring the thicknesses of the selected 10 measurement points.The "thickness" of the wiring is the arithmetic mean value of 10 measured values ​​obtained by randomly selecting 10 measurement points from an electron microscope image of a cross section of the wiring cut in the thickness direction and measuring the thicknesses of the selected 10 measurement points.

[0025] The "average particle size" is a volume-based median diameter (particle size at 50% of the cumulative distribution value) measured using a laser diffraction / scattering particle size distribution analyzer (for example, "LA-950V2" manufactured by Horiba, Ltd.).

[0026] Hereinafter, the compound and its derivatives may be collectively referred to by adding "based" after the compound name. When the polymer name is represented by adding "based" after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative. Furthermore, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". Furthermore, acrylate and methacrylate may be collectively referred to as "(meth)acrylate". Furthermore, acryloyl groups and methacryloyl groups may be collectively referred to as "(meth)acryloyl groups". Unless otherwise specified, the components and functional groups exemplified in this specification may be used alone or in combination of two or more types.

[0027] The drawings referred to in the following description mainly show each component in a schematic manner for ease of understanding, and the size, number, shape, etc. of each component shown may differ from the actual size, number, shape, etc. of each component due to the convenience of creating the drawings. Furthermore, for convenience of explanation, in drawings described later, the same components as those in previously described drawings may be assigned the same reference numerals, and their explanation may be omitted.

[0028] <Method for manufacturing a flexible printed circuit board> The method for manufacturing a flexible printed circuit board according to this embodiment includes a step of applying a liquid photosensitive resin composition to both sides of a substrate having a film support and wiring provided on both sides of the film support using a vertical lifting roll coater. The substrate has holes. The liquid photosensitive resin composition contains a binder polymer, a photoradical polymerization initiator, a polyfunctional epoxy compound, an epoxy curing accelerator, and a radical polymerizable compound having three or more radically polymerizable groups per molecule. When applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is simultaneously applied to both sides of the substrate.

[0029] In the method for manufacturing a flexible printed circuit board according to this embodiment, when the liquid photosensitive resin composition is applied, the liquid photosensitive resin composition is simultaneously applied to both sides of the substrate, so that the liquid photosensitive resin composition can be applied while filling holes provided in the substrate.

[0030] According to the present embodiment, a method for manufacturing a flexible printed circuit board having excellent resistance to plating solutions and resistance to discoloration of wiring can be provided. The reason for this is presumed to be as follows.

[0031] The liquid photosensitive resin composition used in this embodiment contains a polyfunctional epoxy compound, an epoxy curing accelerator, and a radically polymerizable compound having three or more radically polymerizable groups per molecule. Therefore, the crosslink density of a cured film (hereinafter, simply referred to as a "cured film of the liquid photosensitive resin composition" or "cured film") obtained by curing a coating film made of the liquid photosensitive resin composition tends to be high. Therefore, this embodiment can suppress the penetration of plating solution between the cured film and the substrate during the plating process, while suppressing the permeation of oxygen, which causes discoloration of the wiring, through the cured film during the heating process. Furthermore, in this embodiment, by simultaneously applying the liquid photosensitive resin composition to both sides of the substrate, uniform roll pressure can be transmitted to the substrate, making it easier to obtain a cured film with a uniform thickness. For these reasons, this embodiment can produce a flexible printed circuit board with excellent resistance to plating solutions and excellent resistance to discoloration of the wiring.

[0032] In the present embodiment, in order to obtain a flexible printed circuit board that is excellent in flexibility, resistance to plating solutions, and resistance to discoloration of wiring, it is preferable that the liquid photosensitive resin composition contains a radically polymerizable compound having 3 to 6 radically polymerizable groups in one molecule.

[0033] In this embodiment, in order to prevent the occurrence of poor appearance of the substrate on which the coating film is formed (more specifically, deformation, tearing, etc. of the substrate), the width and length of the film support are preferably both 150 mm or more and 650 mm or less, more preferably both 200 mm or more and 600 mm or less, and even more preferably both 250 mm or more and 550 mm or less. The term "width of the film support" refers to the width of the film support in a direction parallel to the axial direction of the applicator roll when applying the liquid photosensitive resin composition to the substrate. The term "length of the film support" refers to the width of the film support in a direction perpendicular to the axial direction of the applicator roll when applying the liquid photosensitive resin composition to the substrate.

[0034] In this embodiment, in order to suppress the occurrence of defective appearance of the substrate on which the coating film is formed, the thickness of the film-like support is preferably 8.0 μm or more, more preferably 10.0 μm or more, and even more preferably 12.0 μm or more. Furthermore, in this embodiment, in order to suppress the occurrence of defective appearance of the coating film (specifically, pinholes, uneven coverage of the coating film covering the wiring, groove marks of the coating roll, streaks, etc.), the thickness of the film-like support is preferably 50.0 μm or less.

[0035] In this embodiment, in order to suppress the occurrence of poor appearance of the coating film, the thickness of the wiring is preferably 8 μm or more and 50 μm or less, more preferably 10 μm or more and 50 μm or less, and even more preferably 15 μm or more and 50 μm or less.

[0036] In this embodiment, in order to obtain a flexible printed circuit board with excellent embeddability while ensuring electrical continuity between the wiring provided on both sides of the film-like support, the diameter (opening diameter) of the hole provided in the board is preferably 50 μm or more and 250 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0037] In the present embodiment, in order to obtain a flexible printed circuit board that can suppress the occurrence of poor appearance of the coating film and the substrate on which the coating film is formed while ensuring the flexibility of the obtained cured film and that has excellent plating solution resistance and wiring discoloration resistance, it is preferable to satisfy the following condition 1, more preferably to satisfy the following condition 2, and even more preferably to satisfy the following condition 3. Condition 1: The liquid photosensitive resin composition contains a radically polymerizable compound having 3 to 6 radically polymerizable groups per molecule, and the width and length of the film-like support are both 200 mm to 600 mm. Condition 2: The above condition 1 is satisfied, and the thickness of the film-like support is 8.0 μm to 50.0 μm. Condition 3: The above condition 2 is satisfied, and the thickness of the wiring is 8 μm to 50 μm.

[0038] This embodiment will be described below with reference to the drawings as appropriate. Figures 1 to 5 are cross-sectional views of essential parts for explaining an example of a manufacturing method for a flexible printed circuit board according to this embodiment (particularly, the coating process). In each of Figures 1 to 5, the left side of the drawing will be the upstream side of the manufacturing process, and the right side of the drawing will be the downstream side of the manufacturing process.

[0039] In the coating process of this embodiment, first, a substrate 11 suspended by a hanging jig 10 is transferred from the upstream side of the manufacturing process to above a pair of coating rolls 12a and 12b ( FIG. 1 ). In FIG. 1 , the coating roll 12a is located upstream in the manufacturing process, and the coating roll 12b is located downstream in the manufacturing process. It is preferable that the diameters of both the coating rolls 12a and 12b be 70 mm or more and 150 mm or less.

[0040] The substrate 11 also has a film-like support 13 and wiring 14 provided on both sides of the film-like support 13. Holes 15 are provided in the substrate 11. The width of the wiring 14 is, for example, 10 μm or more and 200 μm or less. The spacing (pitch) between the wiring 14 is, for example, 10 μm or more and 200 μm or less.

[0041] In the state shown in FIG. 1, a gap is provided between the application rolls 12a and 12b that allows the substrate 11 to pass through. The application roll 12a is in contact with the doctor bar 16a located upstream in the manufacturing process, and is subjected to a predetermined pressure (e.g., 0.5 kgf / cm) from the doctor bar 16a. ２ Over 3.0 kgf / cm ２ The application roll 12b is in contact with the doctor bar 16b on the downstream side of the manufacturing process, and a predetermined pressure (for example, 0.5 kgf / cm or less) is applied from the doctor bar 16b. ２ Over 3.0 kgf / cm ２ (See below) is applied.

[0042] The applicator roll 12a and the applicator roll 12b each rotate at a predetermined rotational speed (for example, 1 m / min to 10 m / min). A liquid photosensitive resin composition 17 is stored between the applicator roll 12a and the doctor bar 16a, and between the applicator roll 12b and the doctor bar 16b. The liquid photosensitive resin composition 17 is transferred to the surfaces of the applicator roll 12a and the applicator roll 12b.

[0043] 1, the hanging jig 10 is lowered, and the hanging substrate 11 passes between the coating rolls 12a and 12b and is transferred to a location (see FIG. 2) where the upper end of the substrate 11 is located between the coating rolls 12a and 12b. Then, as shown in FIG. 2, the hanging jig 10 releases the substrate 11, and the fixing jig 18 grips the lower end of the substrate 11.

[0044] Next, the rotating applicator rolls 12a and 12b sandwich the substrate 11 and press it in so as to apply pressure to the substrate 11, while the fixing jig 18 releases the lower end of the substrate 11 ( FIG. 3 ). When the substrate 11 is released from the fixing jig 18, the rotating applicator rolls 12a and 12b simultaneously apply the liquid photosensitive resin composition 17 to both sides of the substrate 11, while the substrate 11 is lifted upward. In the state shown in FIG. 3 , the amount of press-in by the applicator rolls 12a and 12b is, for example, in the range of 100 μm to 200 μm.

[0045] Next, the upper end of the substrate 11, which has been lifted upward while both sides are simultaneously coated with the liquid photosensitive resin composition 17, is gripped by a hanging jig 10 ( FIG. 4 ). As the substrate 11 is lifted, the liquid photosensitive resin composition 17 fills the holes 15 formed in the substrate 11, and a coating film 19 made of the liquid photosensitive resin composition 17 is formed on both sides of the substrate 11. To obtain a flexible printed circuit board that is superior in plating solution resistance and wiring discoloration resistance, it is preferable to adjust the composition of the liquid photosensitive resin composition 17 and the coating conditions so that the thickness of the film (cured film) obtained by curing the coating film 19 around the holes 15 is 10 μm or more. Furthermore, by gripping the upper end of the substrate 11 with the hanging jig 10 while bringing the hanging jig 10 as close as possible to the coating rolls 12 a and 12 b, it is possible to prevent the substrate 11 from wrapping around the coating rolls 12 a and 12 b.

[0046] Next, the substrate 11 having the coating films 19 formed on both sides is transferred downstream in the manufacturing process while being suspended by the suspension jig 10 (FIG. 5). The substrate 11 transferred downstream in the manufacturing process is then placed in a drying furnace (not shown) and dried. For example, the substrate 11 is transported to the drying furnace while being suspended. The substrate 11 is then dried as it passes through the drying furnace.

[0047] Inside the drying oven, for example, hot air from which environmental foreign matter has been removed by a filter is applied to the coating film 19 formed on the substrate 11. Because the substrate 11 has a film-like support, when drying multiple substrates 11 simultaneously, if the distance between the substrates 11 is narrow, the substrates 11 will be fanned by the hot air circulation inside the drying oven, making it easier for the substrates 11 to stick together. Therefore, when drying multiple substrates 11 simultaneously, it is preferable to set the distance between the substrates 11 greater than the vertical width of the substrates 11.

[0048] The drying temperature for the substrate 11 is preferably 60°C or higher and 130°C or lower, and more preferably 70°C or higher and 120°C or lower. By setting the drying temperature for the substrate 11 to 60°C or higher, the organic solvent contained in the liquid photosensitive resin composition 17 can be sufficiently removed, thereby preventing foreign matter from adhering to the coating film 19 after drying. Furthermore, by setting the drying temperature for the substrate 11 to 130°C or lower, the curing reaction of the liquid photosensitive resin composition 17 can be suppressed, thereby preventing an increase in development time in the subsequent photolithography process. The drying temperature can be set appropriately depending on the number of substrates 11 to be put into the drying furnace and the coating speed.

[0049] The drying time for the substrate 11 is preferably 1 minute or more and 60 minutes or less, and more preferably 3 minutes or more and 40 minutes or less. By setting the drying time to 1 minute or more, the organic solvent contained in the liquid photosensitive resin composition 17 can be sufficiently removed, thereby preventing foreign matter from adhering to the coating film 19 after drying. Furthermore, by setting the drying time to 60 minutes or less, the curing reaction of the liquid photosensitive resin composition 17 can be suppressed, thereby preventing an increase in development time in the subsequent photolithography process. The drying time can be set appropriately depending on the number of substrates 11 to be put into the drying furnace and the coating speed.

[0050] Next, an example of the applicator roll 12a and the applicator roll 12b will be described. Fig. 6 is a cross-sectional view of an applicator roll 100, which is an example of the applicator roll 12a and the applicator roll 12b, cut along a plane including its axis. The applicator roll 100 shown in Fig. 6 has a metallic core 110 having a cylindrical hollow portion, and a surface layer roll 120 arranged on the outer peripheral surface of the core 110.

[0051] The surface roll 120 is a roll onto which the liquid photosensitive resin composition 17 (see FIG. 1) is transferred, and is made of rubber that is elastic in an atmosphere at a temperature of 25° C. The rubber that makes up the surface roll 120 is not particularly limited, but is preferably a rubber that has chemical resistance and abrasion resistance, such as butyl rubber, ethylene propylene rubber, urethane rubber, or nitrile rubber.

[0052] The surface roll 120 also has a plurality of ring-shaped grooves 120a. The plurality of ring-shaped grooves 120a are independent of each other. The cross-sectional shape of the ring-shaped grooves 120a is not particularly limited, and shapes such as a V-shape and a U-shape can be adopted. In order to further suppress poor appearance of the coating film 19 (see FIG. 5) and the substrate 11 (see FIG. 5) on which the coating film 19 is formed, it is preferable that the cross-sectional shape of the ring-shaped grooves 120a be V-shaped. The pitch P of the ring-shaped grooves 120a is, for example, 500 μm or more and 1000 μm or less. The opening width of the ring-shaped grooves 120a is, for example, 500 μm or more and 1000 μm or less. The depth of the ring-shaped grooves 120a is, for example, 200 μm or more and 900 μm or less. 6 has a plurality of independent ring-shaped grooves 120a, the coating roll that can be used in the present invention is not limited to this, and a coating roll provided with a single spiral groove may also be used. However, in order to suppress deformation of the substrate 11 by uniformly transmitting roll pressure to the substrate 11, it is preferable that both of the pair of coating rolls have a plurality of independent ring-shaped grooves.

[0053] The width W of the surface layer roll 120 may be appropriately selected depending on the method for hanging the substrate 11 (see FIG. 1 ). For example, as shown in FIG. 1 , when only the upper end of the substrate 11 is gripped by the hanging jig 10, it is preferable to make the width W of the surface layer roll 120 wider than the lateral width of the substrate 11, because this allows for a wider coating area of ​​the liquid photosensitive resin composition 17 on the substrate 11. On the other hand, when both left and right ends of the substrate 11 are gripped by the hanging jig (not shown), it is preferable to make the width W of the surface layer roll 120 narrower than the lateral width of the substrate 11, because this allows for an easier gripping margin for the substrate 11.

[0054] The roll diameter D of the applicator roll 100 is preferably 70 mm or more and 150 mm or less, more preferably 80 mm or more and 140 mm or less, even more preferably 90 mm or more and 130 mm or less, and particularly preferably 100 mm or more and 120 mm or less. By setting the roll diameter D to 70 mm or more, the phenomenon of excessive retention (liquid pooling) of the liquid photosensitive resin composition 17 between the applicator roll 100 and the substrate 11 tends to be less likely to occur. Therefore, by setting the roll diameter D to 70 mm or more, the occurrence of traces of grooves or streaks in the coating film 19 from the applicator roll 100 tends to be suppressed. Furthermore, by setting the roll diameter D to 150 mm or less, damage (more specifically, tearing, etc.) to the substrate 11 caused by the pressure of the applicator roll 100 can be suppressed when the liquid photosensitive resin composition 17 is applied to the substrate 11.

[0055] Next, elements of the method for manufacturing a flexible printed circuit board according to this embodiment will be described in detail.

[0056] [Film-like support] The film-like support is not particularly limited, but from the viewpoint of heat resistance, chemical resistance and dimensional stability, a film-like support containing one or more polymers selected from the group consisting of polyimide, polyamide, polyester, polycarbonate, polyarylate, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesin, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer and ethylene-chlorotrifluoroethylene copolymer is preferred, and a film-like support containing polyimide is more preferred. The film-like support may contain additives such as fillers as components other than the polymer. However, in order to obtain a film-like support with excellent flexibility, the content of the polymer in the film-like support is preferably 70 wt% or more, more preferably 80 wt% or more, even more preferably 90 wt% or more, based on the total amount of the film-like support, and may even be 100 wt%.

[0057] [Wiring] The wiring provided on the film-like support is not particularly limited, but from the viewpoint of wiring shape stability and fine wiring, wiring formed by etching electrolytic copper foil or rolled copper foil by a subtractive method, or wiring formed by screen printing a copper paste or a silver paste on the film-like support is preferred.

[0058] [Hole] The hole to be provided in the substrate is not particularly limited, but from the viewpoint of hole shape stability and interlayer connection reliability, it is preferable to form a hole in a flexible copper-clad laminate having a film-like support using a laser processing machine (more specifically, a processing machine using a carbon dioxide laser, a UV laser, a YAG laser, an excimer laser, or the like) or an NC drill processing machine, and then subject the inside of the hole to a cleaning treatment (desmear treatment) and a carbon treatment, followed by a copper plating treatment (electroless copper plating treatment, electrolytic copper plating treatment, or the like).

[0059] [Liquid Photosensitive Resin Composition] The liquid photosensitive resin composition contains a binder polymer (hereinafter sometimes referred to as "component (A)"), a photoradical polymerization initiator (hereinafter sometimes referred to as "component (B)"), a polyfunctional epoxy compound (hereinafter sometimes referred to as "component (C)"), an epoxy curing accelerator (hereinafter sometimes referred to as "component (D)"), and a radically polymerizable compound having three or more radically polymerizable groups per molecule (hereinafter sometimes referred to as "component (E)"). The liquid photosensitive resin composition may also contain, as optional components, particles having an average particle size of 0.01 μm to 100 μm (hereinafter sometimes referred to as "component (F)") and an organic solvent (hereinafter sometimes referred to as "component (G)"). The liquid photosensitive resin composition may also contain other components described below.

[0060] {Component (A)} As component (A), for example, a polymer that is soluble in component (G) and has a weight-average molecular weight of 1,000 to 1,000,000 in terms of polyethylene glycol can be used. The weight-average molecular weight in terms of polyethylene glycol can be measured by the same method as in the examples described below or a method equivalent thereto. Note that "component (A) is soluble in component (G)" means that when 5 parts by weight of component (A) are added to 100 parts by weight of component (G), the mixture is stirred at 40°C for 1 hour, cooled to 25°C, and left to stand for 24 hours, the resulting solution is free of insoluble matter and precipitates.

[0061] By setting the weight-average molecular weight of component (A) to 1,000 or more, the flexibility and chemical resistance of the resulting cured film can be improved, while by setting the weight-average molecular weight of component (A) to 1,000,000 or less, the viscosity of the liquid photosensitive resin composition can be prevented from becoming excessively high.

[0062] Specific examples of the component (A) include polyurethane-based resins, (meth)acrylic-based resins, polyvinyl-based resins, polystyrene-based resins, polyethylene-based resins, polypropylene-based resins, polyimide-based resins, polyamide-based resins, polyacetal-based resins, polycarbonate-based resins, polyester-based resins, polyphenylene ether-based resins, polyphenylene sulfide-based resins, polyether sulfone-based resins, and polyether ether ketone-based resins, and these can be used alone or in combination of two or more.

[0063] Among these, it is preferable to use, as component (A), one or more polymers selected from the group consisting of polymers having a urethane bond in one molecule, polymers having an imide group in one molecule, polymers having a (meth)acryloyl group in one molecule, and polymers having a carboxy group in one molecule.

[0064] When a polymer having a urethane bond per molecule is used as component (A), the low resilience and fold resistance of the resulting cured film tend to be improved, and the warpage of the cured film tends to be reduced. Furthermore, when a polymer having an imide group per molecule is used as component (A), the heat resistance, flame retardancy, and electrical insulation reliability of the resulting cured film tend to be improved. Furthermore, when a polymer having a (meth)acryloyl group per molecule is used as component (A), the photosensitivity of the liquid photosensitive resin composition tends to be improved, and the chemical resistance of the resulting cured film tends to be improved. Furthermore, when a polymer having a carboxy group per molecule is used as component (A), the alkali developability of the liquid photosensitive resin composition tends to be improved, and the adhesion of the resulting cured film to the substrate tends to be improved.

[0065] The component (A) may be a polymer having multiple types of functional groups in one molecule. For example, when a polymer having a urethane bond and an imide group in one molecule is used as the component (A), the low resilience, crease resistance, heat resistance, flame retardancy, and electrical insulation reliability of the resulting cured film tend to be improved, and the warpage of the cured film tends to be reduced. Furthermore, when a polymer having a urethane bond, a carboxy group, and a (meth)acryloyl group in one molecule is used as the component (A), the photosensitivity and alkaline developability of the liquid photosensitive resin composition, the low resilience, crease resistance, and chemical resistance of the resulting cured film, and the adhesion of the resulting cured film to the substrate tend to be improved, and the warpage of the cured film tends to be reduced. Therefore, it is preferable that the polymer having a urethane bond in one molecule further has one or more functional groups selected from the group consisting of an imide group, a carboxy group, and a (meth)acryloyl group.

[0066] (Polymer Having a Urethane Bond in One Molecule) The term "polymer having a urethane bond in one molecule" refers to a polymer having at least one urethane bond in one molecule. Examples of polymers having a urethane bond in one molecule include polymers having a repeating unit represented by the following general formula (3), which is a reaction product of a diol compound represented by the following general formula (1) and a diisocyanate compound represented by the following general formula (2).

[0067]

[0068]

[0069]

[0070] In general formula (1), general formula (2) and general formula (3), R １ and X １ each independently represents a divalent organic group.

[0071] Examples of the diol compound represented by the general formula (1) include alkylene diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol; polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and tetramethylene glycol and neopentyl glycol. polyester diols obtained by reacting a polyhydric alcohol with a polybasic acid; polycarbonate diols having a carbonate skeleton; polycaprolactone diols obtained by ring-opening addition reaction of lactones such as γ-butyrolactone, ε-caprolactone, δ-valerolactone; and bisphenol A compounds such as bisphenol A, ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, hydrogenated bisphenol A, ethylene oxide adducts of hydrogenated bisphenol A, and propylene oxide adducts of hydrogenated bisphenol A, and these can be used alone or in combination of two or more.

[0072] In order to obtain a liquid photosensitive resin composition that has excellent roll pressure dispersibility during coating and to improve the low resilience and crease resistance of the resulting cured film, the diol compound represented by general formula (1) is preferably a long-chain diol such as a polyoxyalkylene diol, a polyester diol, a polycarbonate diol, or a polycaprolactone diol.

[0073] Examples of the diisocyanate compound represented by general formula (2) include diphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'- Diethyldiphenylmethane-2,4'-diisocyanate, 3,2'- or 3,3'- or 4,2'- or 4,3'- or 5,2'- or 5,3'- or 6,2'- or 6,3'-dimethoxydiphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-3,3'-diisocyanate, diphenylmethane-3,4'-diisocyanate, diphenylether-4 , 4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, tolylene-2,4-diisocyanate, tolylene-2,6-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, naphthalene-2,6-diisocyanate, 4,4'-[2,2-bis(4-phenoxyphenyl)propane]diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate and other aromatic diisocyanate compounds; isophorone diisocyanate, norbornene diisocyanate and other alicyclic diisocyanate compounds; hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate and other aliphatic diisocyanate compounds, and the like, can be used alone or in combination of two or more of these.

[0074] In particular, one or more compounds selected from the group consisting of alicyclic diisocyanate compounds and aliphatic diisocyanate compounds are preferred because, when used as the diisocyanate compound represented by general formula (2), a liquid photosensitive resin composition having excellent photosensitivity can be obtained.

[0075] When synthesizing a polymer having a urethane bond in one molecule, it is preferable to blend a diol compound and a diisocyanate compound so that the ratio of the number of hydroxyl groups to the number of isocyanate groups, i.e., isocyanate groups / hydroxyl groups, is 0.5 or more and 2.0 or less.

[0076] Furthermore, when two or more types of diol compounds are used, the reaction with the diisocyanate compound may be carried out after mixing the two or more types of diol compounds, or each diol compound may be reacted separately with the diisocyanate compound. Alternatively, after reacting the diol compound with the diisocyanate compound, the resulting terminal isocyanate compound may be further reacted with another diol compound, and the resulting reaction product may be further reacted with another diisocyanate compound. The same applies when two or more types of diisocyanate compounds are used. In this manner, a desired polymer having a urethane bond per molecule can be synthesized.

[0077] The reaction temperature between the diol compound and the diisocyanate compound is preferably 40°C or higher and 160°C or lower, and more preferably 60°C or higher and 150°C or lower, from the viewpoint of shortening the reaction time and suppressing gelation. The reaction time between the diol compound and the diisocyanate compound can be appropriately selected depending on the amounts of starting materials and the reaction conditions employed. If necessary, the reaction may be carried out in the presence of a catalyst such as a compound containing a metal or semimetal such as an alkali metal, alkaline earth metal, tin, zinc, titanium, or cobalt; or a tertiary amine.

[0078] The diol compound and the diisocyanate compound can be reacted without using a solvent, but in order to control the reaction, it is desirable to react them in an organic solvent. The organic solvent used here is not particularly limited, but for example, the organic solvents listed as specific examples of component (G) described below can be used.

[0079] In order to enhance the reactivity of the polymerization reaction, the amount of organic solvent used in the reaction is preferably such that the weight concentration of the solute in the reaction solution, i.e., the solution concentration, is 5% by weight or more and 90% by weight or less, more preferably 10% by weight or more and 80% by weight or less.

[0080] A polymer having a urethane bond and a (meth)acryloyl group in one molecule can be obtained by carrying out a polymerization reaction using, for example, a diol compound and a diisocyanate compound, as well as one or more monomers selected from the group consisting of a compound represented by the following general formula (4) (hereinafter, sometimes referred to as “compound (4)”) and a compound represented by the following general formula (5) (hereinafter, sometimes referred to as “compound (5)”):

[0081]

[0082] In general formula (4), m represents an integer of 1 or more and 3 or less, R ２ represents an (m+1)-valent organic group, and R ３ represents a hydrogen atom or a methyl group.

[0083]

[0084] In the general formula (5), n represents an integer of 1 or more and 3 or less, and X ２ represents an (n+1)-valent organic group, and X ３ represents a hydrogen atom or a methyl group.

[0085] Examples of compound (4) include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-hydroxy-1-acryloxy-3-methacryloxypropane, o-phenylphenol glycidyl ether (meth)acrylate, polyethylene glycol mono(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, 1,4-cyclohexanedimethanol mono(meth)acrylate, 4-hydroxyphenyl (meth)acrylate, and 2-(4-hydroxyphenyl)ethyl (meth)acrylate, and these may be used alone or in combination of two or more.

[0086] Examples of compound (5) include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate, and 2-(2-methacryloyloxyethyloxy)ethyl isocyanate, and these can be used alone or in combination of two or more.

[0087] A polymer having a urethane bond and a carboxy group in one molecule can be obtained by carrying out a polymerization reaction using, for example, a diol compound, a diisocyanate compound, and a compound represented by the following general formula (6) (hereinafter, sometimes referred to as “compound (6)”) as a monomer.

[0088]

[0089] In general formula (6), R ４ represents a trivalent organic group.

[0090] Examples of compound (6) include 2,2-bis(hydroxymethyl)propionic acid, 2,2-bis(2-hydroxyethyl)propionic acid, 2,2-bis(3-hydroxypropyl)propionic acid, 2,3-dihydroxy-2-methylpropionic acid, 2,2-bis(hydroxymethyl)butanoic acid, 2,2-bis(2-hydroxyethyl)butanoic acid, 2,2-bis(3-hydroxypropyl)butanoic acid, 2,3-dihydroxybutanoic acid, 2,4-dihydroxy-3,3-dimethylbutanoic acid, 2,3-dihydroxyhexadecanoic acid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and 3,5-dihydroxybenzoic acid. These may be used alone or in combination of two or more.

[0091] In order to enhance the photosensitivity of the liquid photosensitive resin composition, it is preferable to use an aliphatic compound (6).

[0092] A polymer having a urethane bond and an imide group in one molecule can be obtained, for example, by carrying out a polymerization reaction using a tetracarboxylic acid dianhydride as a monomer in addition to a diol compound and a diisocyanate compound.

[0093] Examples of tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimellitate anhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, and 9,9-bis(trimellitate anhydride). Examples of the dianhydride include (3,4-dicarboxyphenyl)fluorene dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, and these may be used alone or in combination of two or more.

[0094] (Polymer Having an Imide Group in One Molecule) "Polymer Having an Imide Group in One Molecule" means a polymer having at least one imide group in one molecule. Examples of polymers having an imide group in one molecule include the above-mentioned polymers having a urethane bond and an imide group in one molecule. Furthermore, for example, a polymer having an imide group in one molecule can be obtained by reacting a tetracarboxylic dianhydride (more specifically, the compounds listed above as tetracarboxylic dianhydrides for synthesizing a polymer having a urethane bond and an imide group in one molecule) with a diamine.

[0095] Examples of diamines that can be used as raw materials to obtain polymers having an imide group in one molecule include p-phenylenediamine, 4,4'-diaminobenzanilide, 2,2'-bis(trifluoromethyl)benzidine, 9,9-bis(4-aminophenyl)fluorene, 4-aminophenyl-4-aminobenzoate, 1,4-diaminocyclohexane, m-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, N,N' -bis(4-aminophenyl)terephthalamide, 4,4'-diaminodiphenyl sulfone, m-tolidine, o-tolidine, 4,4'-bis(4-aminophenoxy)biphenyl, 2-(4-aminophenyl)-6-aminobenzoxazole, 3,5-diaminobenzoic acid, 4,4'-diamino-3,3'-dihydroxybiphenyl, 4,4'-methylenebis(cyclohexaneamine), 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and the like can be mentioned, and these can be used alone or in combination of two or more.

[0096] The method for reacting a tetracarboxylic acid anhydride with a diamine is not particularly limited, but examples thereof include the following methods 1 to 3.

[0097] Method 1: A polyamic acid solution is prepared by adding a diamine to a solution in which a tetracarboxylic dianhydride is dispersed or dissolved in an organic solvent and reacting the diamine. The total amount of diamine added is preferably adjusted so that the ratio is 0.50 to 1.50 moles per mole of tetracarboxylic dianhydride. After the reaction between the tetracarboxylic dianhydride and the diamine is complete, the resulting polyamic acid solution is heated to 100°C to 300°C, more preferably 150°C to 250°C, to carry out imidization.

[0098] Method 2: A polyamic acid solution is prepared in the same manner as in Method 1. An imidization catalyst (preferably a tertiary amine such as pyridine, picoline, isoquinoline, trimethylamine, triethylamine, or tributylamine) and a dehydrating agent (acetic anhydride or the like) are added to the prepared polyamic acid solution, and the solution is heated to 60° C. or higher and 180° C. or lower to carry out imidization.

[0099] Method 3: A polyamic acid solution is prepared in the same manner as in Method 1. The prepared polyamic acid solution is placed in a vacuum oven set at 100° C. to 250° C., and heated under reduced pressure to carry out imidization.

[0100] (Polymer Having a (meth)acryloyl Group in One Molecule) "Polymer Having a (meth)acryloyl Group in One Molecule" means a polymer having at least one (meth)acryloyl group in one molecule. Examples of polymers having a (meth)acryloyl group in one molecule include the above-mentioned polymers having a urethane bond and a (meth)acryloyl group in one molecule. Furthermore, for example, a polymer having a (meth)acryloyl group in one molecule can also be obtained by reacting an epoxy resin with (meth)acrylic acid.

[0101] Examples of epoxy resins that can be used as raw materials for obtaining polymers having a (meth)acryloyl group in one molecule include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, hydrogenated bisphenol A type epoxy resins, biphenyl type epoxy resins, phenoxy type epoxy resins, naphthalene type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, trisphenolmethane type epoxy resins, dicyclopentadiene type epoxy resins, amine type epoxy resins, flexible epoxy resins, urethane-modified epoxy resins, rubber-modified epoxy resins, chelate-modified epoxy resins, and heterocycle-containing epoxy resins, and these can be used alone or in combination of two or more.

[0102] Specific examples of bisphenol A type epoxy resins include jER (registered trademark) 828, jER (registered trademark) 1001, and jER (registered trademark) 1002, both of which are trade names manufactured by Mitsubishi Chemical Corporation; ADEKA RESIN (registered trademark) EP-4100E and ADEKA RESIN (registered trademark) EP-4300E, both of which are trade names manufactured by ADEKA Corporation; RE-310S and RE-410S, both of which are trade names manufactured by Nippon Kayaku Co., Ltd.; Epicron 840S, Epicron 850S, Epicron 1050, and Epicron 7050, both of which are trade names manufactured by DIC Corporation; and Epotohto (registered trademark) YD-115, Epotohto (registered trademark) YD-127, and Epotohto (registered trademark) YD-128, both of which are trade names manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.

[0103] Specific examples of bisphenol F type epoxy resins include jER (registered trademark) 806 and jER (registered trademark) 807, both manufactured by Mitsubishi Chemical Corporation; ADEKA RESIN (registered trademark) EP-4901E, ADEKA RESIN (registered trademark) EP-4930, and ADEKA RESIN (registered trademark) EP-4950, both manufactured by ADEKA Corporation; RE-303S, RE-304S, RE-403S, and RE-404S, both manufactured by Nippon Kayaku Co., Ltd.; Epicron 830 and Epicron 835, both manufactured by DIC Corporation; and Epotohto (registered trademark) YDF-170, Epotohto (registered trademark) YDF-175S, and Epotohto (registered trademark) YDF-2001, both manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.

[0104] A specific example of the bisphenol S type epoxy resin is Epiclon EXA-1514, a product name of DIC Corporation.

[0105] Specific examples of hydrogenated bisphenol A epoxy resins include jER (registered trademark) YX8000, jER (registered trademark) YX8034, and jER (registered trademark) YL7170, both of which are manufactured by Mitsubishi Chemical Corporation; ADEKA Resin (registered trademark) EP-4080E, both of which are manufactured by ADEKA Corporation; Epiclon EXA-7015, both of which are manufactured by DIC Corporation; and Epotohto (registered trademark) YD-3000 and Epotohto (registered trademark) YD-4000D, both of which are manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.

[0106] Specific examples of biphenyl-type epoxy resins include jER (registered trademark) YX4000, jER (registered trademark) YL6121H, jER (registered trademark) YL6640, and jER (registered trademark) YL6677, both of which are trade names manufactured by Mitsubishi Chemical Corporation, and NC-3000 and NC-3000H, both of which are trade names manufactured by Nippon Kayaku Co., Ltd.

[0107] Specific examples of phenoxy type epoxy resins include jER (registered trademark) 1256, jER (registered trademark) 4250, and jER (registered trademark) 4275, both of which are trade names manufactured by Mitsubishi Chemical Corporation.

[0108] Specific examples of naphthalene-type epoxy resins include Epiclon HP-4032, Epiclon HP-4700, and Epiclon HP-4200, both of which are trade names manufactured by DIC Corporation, and NC-7000L, which is a trade name manufactured by Nippon Kayaku Co., Ltd.

[0109] Specific examples of phenol novolac epoxy resins include jER (registered trademark) 152 and jER (registered trademark) 154, both manufactured by Mitsubishi Chemical Corporation, EPPN (registered trademark)-201-L, both manufactured by Nippon Kayaku Co., Ltd., Epiclon N-740 and Epiclon N-770, both manufactured by DIC Corporation, and Epotohto (registered trademark) YDPN-638, both manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.

[0110] Specific examples of cresol novolac epoxy resins include those manufactured by Nippon Kayaku Co., Ltd. under the trade names EOCN (registered trademark)-1020, EOCN (registered trademark)-102S, EOCN (registered trademark)-103S, and EOCN (registered trademark)-104S, and those manufactured by DIC Corporation under the trade names Epiclon N-660, Epiclon N-670, Epiclon N-680, and Epiclon N-695.

[0111] Specific examples of trisphenolmethane type epoxy resins include those available from Nippon Kayaku Co., Ltd. under the trade names EPPN (registered trademark)-501H, EPPN (registered trademark)-501HY, and EPPN (registered trademark)-502H.

[0112] Specific examples of dicyclopentadiene type epoxy resins include XD-1000 (trade name) manufactured by Nippon Kayaku Co., Ltd., and Epiclon HP-7200 (trade name) manufactured by DIC Corporation.

[0113] Specific examples of amine-type epoxy resins include jER (registered trademark) 604 and jER (registered trademark) 630, both of which are trade names manufactured by Mitsubishi Chemical Corporation; Epotohto (registered trademark) YH-434 and Epotohto (registered trademark) YH-434L, both of which are trade names manufactured by Nippon Steel Epoxy Manufacturing Co., Ltd.; and TETRAD (registered trademark)-X and TERRAD (registered trademark)-C, both of which are trade names manufactured by Mitsubishi Gas Chemical Company, Inc.

[0114] Specific examples of flexible epoxy resins include jER (registered trademark) 871, jER (registered trademark) 872, jER (registered trademark) YL7175, and jER (registered trademark) YL7217, both of which are trade names manufactured by Mitsubishi Chemical Corporation, and Epiclon EXA-4850, which is a trade name manufactured by DIC Corporation.

[0115] Specific examples of urethane-modified epoxy resins include ADEKA RESIN (registered trademark) EPU-6, ADEKA RESIN (registered trademark) EPU-73, and ADEKA RESIN (registered trademark) EPU-78-11, both of which are trade names manufactured by ADEKA Corporation.

[0116] Specific examples of rubber-modified epoxy resins include ADEKA RESIN (registered trademark) EPR-4023, ADEKA RESIN (registered trademark) EPR-4026, and ADEKA RESIN (registered trademark) EPR-1309, both of which are trade names manufactured by ADEKA Corporation.

[0117] Specific examples of chelate-modified epoxy resins include ADEKA RESIN (registered trademark) EP-49-10 and ADEKA RESIN (registered trademark) EP-49-20, both of which are trade names manufactured by ADEKA Corporation.

[0118] Specific examples of heterocycle-containing epoxy resins include TEPIC (registered trademark) manufactured by Nissan Chemical Industries, Ltd.

[0119] The method for reacting an epoxy resin with (meth)acrylic acid is not particularly limited, but examples include a method in which (meth)acrylic acid and an esterification catalyst (for example, a tertiary amine such as trimethylamine or triethylamine; a phosphorus compound such as triphenylphosphine; or an imidazole compound such as 2-ethyl-4-methylimidazole) are added to a solution in which an epoxy resin is dispersed or dissolved in an organic solvent, and the resulting mixture is heated to 40° C. or higher and 120° C. or lower. The total amount of (meth)acrylic acid added is preferably adjusted so that the ratio is 0.1 mol or higher and 1.0 mol or lower per mol of epoxy groups in the epoxy resin.

[0120] (Polymer having a carboxy group in one molecule) "Polymer having a carboxy group in one molecule" means a polymer having at least one carboxy group in one molecule. Examples of polymers having a carboxy group in one molecule include the above-mentioned polymers having a urethane bond and a carboxy group in one molecule. Furthermore, for example, a polymer having a carboxy group in one molecule can also be obtained by reacting an epoxy resin with (meth)acrylic acid and then further reacting with a polybasic acid anhydride.

[0121] As a method for obtaining a polymer having a carboxy group in one molecule by reacting an epoxy resin with (meth)acrylic acid and then further reacting with a polybasic acid anhydride, for example, a method can be mentioned in which an epoxy resin is reacted with (meth)acrylic acid by the above-mentioned method, and then a polybasic acid anhydride is added and the reaction is carried out by heating at 60° C. or more and 150° C. or less. The total amount of polybasic acid anhydride added is preferably adjusted so that the acid value of the resulting solid content is 10 mgKOH / g or more and 160 mgKOH / g or less.

[0122] In addition to the above-mentioned methods, a polymer having a carboxy group in one molecule can also be obtained by reacting (meth)acrylic acid with a (meth)acrylic acid ester. The method for reacting (meth)acrylic acid with a (meth)acrylic acid ester is not particularly limited, but examples thereof include a method in which (meth)acrylic acid and a (meth)acrylic acid ester are subjected to a radical polymerization reaction in a solvent in the presence of a radical polymerization initiator.

[0123] The (meth)acrylic acid ester is not particularly limited, but examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate (n-butyl (meth)acrylate), isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and benzyl (meth)acrylate, and these can be used alone or in combination of two or more. In order to improve the flexibility and chemical resistance of the cured film of the liquid photosensitive resin composition, the (meth)acrylic acid ester is preferably one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and benzyl (meth)acrylate.

[0124] Examples of the radical polymerization initiator include azo compounds such as azobisisobutyronitrile, azobis(2-methylbutyronitrile), and 2,2′-azobis-2,4-dimethylvaleronitrile; organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide; persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; and hydrogen peroxide, and these can be used alone or in combination of two or more.

[0125] In order to increase the reactivity of the polymerization reaction while suppressing a decrease in the molecular weight of the resulting polymer, the amount of the radical polymerization initiator used is preferably 0.001 parts by weight or more and 5 parts by weight or less, and more preferably 0.01 parts by weight or more and 1 part by weight or less, relative to 100 parts by weight of the monomer used.

[0126] In order to enhance the reactivity of the polymerization reaction, the amount of solvent used in the radical polymerization reaction is preferably such that the weight concentration of the solute in the reaction solution, i.e., the solution concentration, is 5% by weight or more and 90% by weight or less, more preferably 20% by weight or more and 70% by weight or less.

[0127] From the viewpoint of shortening the reaction time and suppressing gelation, the reaction temperature of the radical polymerization reaction is preferably 20° C. or higher and 120° C. or lower, and more preferably 50° C. or higher and 100° C. or lower. The reaction time of the radical polymerization reaction can be appropriately selected depending on the amounts of starting materials and the reaction conditions employed.

[0128] In order to suppress the occurrence of poor appearance of the coating film and the substrate on which the coating film is formed, the content of component (A) is preferably 10% by weight or more and 50% by weight or less, and more preferably 20% by weight or more and 40% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0129] {Component (B)} The component (B) is not particularly limited, and examples thereof include Michler's ketone, 4,4'-bis(diethylamino)benzophenone, 4,4',4''-tris(dimethylamino)triphenylmethane, 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-diimidazole, acetophenone, benzoin, 2-methylbenzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-t-butylanthraquinone, 1,2-benzo-9,10-anthraquinone, methylanthraquinone, thioxanthone, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, 1-hydroxycyclohexyl phenyl ketone, diacetylbenzyl, benzil dimethyl ketal, benzil diethyl ketal, 4,4'-diazidochalcone, 2,2 -dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, ethyl-4-dimethylaminobenzoate, 2-ethylhexyl-4-dimethylaminobenzoate, and the like, can be used alone or in combination of two or more.

[0130] In order to enhance the reactivity and resolution of the photoradical polymerization, the content of component (B) is preferably 0.5% by weight or more and 5% by weight or less, and more preferably 0.8% by weight or more and 4% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0131] {Component (C)} The component (C) is not particularly limited as long as it is an epoxy compound having two or more epoxy groups in one molecule. For example, the compounds listed above as specific examples of "epoxy resins that serve as raw materials for obtaining polymers having (meth)acryloyl groups in one molecule" can be used.

[0132] The liquid photosensitive resin composition may contain a curing agent as component (C). Note that, when a polymer having an acid value of 10 mgKOH / g or more (preferably a polymer having an acid value of 10 mgKOH / g or more and 160 mgKOH / g or less) is used as component (A), the curing agent as component (C) does not need to be blended into the liquid photosensitive resin composition. The acid value of component (A) can be adjusted, for example, by changing the amount of a monomer having one or more groups selected from the group consisting of a carboxy group and a carboxylic anhydride group added when synthesizing component (A).

[0133] In order to improve the flexibility and chemical resistance of the resulting cured film, the content of the component (C) is preferably from 1 to 10% by weight, and more preferably from 3 to 8% by weight, based on the total amount of the liquid photosensitive resin composition.

[0134] {Component (D)} The component (D) is not particularly limited, and examples thereof include phosphine compounds such as triphenylphosphine; amine compounds such as trimethanolamine, triethanolamine, and melamine; borate compounds such as 1,8-diazabicyclo[5,4,0]-7-undecenium tetraphenylborate; imidazole compounds such as imidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, and 2-phenyl-4-methylimidazole; Examples thereof include imidazoline compounds such as imidazoline, 2-ethylimidazoline, 2-isopropylimidazoline, 2-phenylimidazoline, 2-undecylimidazoline, 2,4-dimethylimidazoline, and 2-phenyl-4-methylimidazoline; and triazine compounds such as 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine, 2,4-diamino-6-[2-(2-undecyl-1-imidazolyl)ethyl]-1,3,5-triazine and 2,4-diamino-6-(2'-ethyl-4'-methylimidazolyl)ethyl-1,3,5-triazine, and these can be used alone or in combination of two or more.

[0135] In order to obtain a flexible printed circuit board that is superior in resistance to plating solutions and resistance to discoloration of wiring, the component (D) is preferably an amine-based compound, and more preferably melamine.

[0136] In order to obtain a flexible printed circuit board that is superior in plating solution resistance and wiring discoloration resistance, the content of component (D) is preferably 0.01 part by weight or more and 1.0 part by weight or less, more preferably 0.01 part by weight or more and 0.5 part by weight or less, even more preferably 0.1 part by weight or more and 0.5 part by weight or less, and particularly preferably 0.2 part by weight or more and 0.4 part by weight or less, relative to 100 parts by weight of component (A).

[0137] {Component (E)} Component (E) is a photoradical polymerizable component incorporated into the liquid photosensitive resin composition. Component (E) is not particularly limited as long as it is a radically polymerizable compound having three or more radically polymerizable groups (functional groups that undergo polymerization in the presence of a radical polymerization initiator) per molecule. However, to obtain a flexible printed circuit board that exhibits excellent plating solution resistance and wiring discoloration resistance while maintaining the flexibility of the cured film, component (E) is preferably a radically polymerizable compound having three to six radically polymerizable groups per molecule. Component (E) is also preferably a compound with a molecular weight (weight average molecular weight in the case of a polymer) of less than 1,000. Examples of the radically polymerizable group contained in component (E) include a group having an unsaturated double bond. To enhance radical polymerizability, the radically polymerizable group is preferably a (meth)acryloyl group or a vinyl group.

[0138] Specific examples of the component (E) include trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, tetramethylolpropane tetraacrylate, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, dipentaerythritol hexamethacrylate, tetramethylolpropane tetramethacrylate, tetramethylolmethane triacrylate, tetramethylolmethane tetraacrylate, isocyanuric acid tri(ethane acrylate), pentasritol tetraacrylate, ditrimethylolpropane tetraacrylate, caprolactone-modified dipentaerythritol hexaacrylate, ethoxylated dipentaerythritol hexaacrylate, triallyl isocyanurate, and 1,3,5-triacryloylhexahydro-s-triazine. These may be used alone or in combination of two or more.

[0139] In order to obtain a flexible printed circuit board having excellent plating solution resistance and wiring resistance to discoloration, the content of the component (E) is preferably from 1 to 10% by weight, and more preferably from 3 to 8% by weight, based on the total amount of the liquid photosensitive resin composition.

[0140] {Component (F)} The component (F) is not particularly limited as long as it is a particle having an average particle diameter of 0.01 μm or more and 100 μm or less, and for example, one or more types of particles selected from the group consisting of inorganic particles and organic particles can be used. By blending component (F) into the liquid photosensitive resin composition, the viscosity and thixotropy of the liquid photosensitive resin composition can be adjusted.

[0141] In order to improve the flexibility and chemical resistance of the resulting cured film while increasing the resolution of the liquid photosensitive resin composition, the average particle size of component (F) is preferably 0.01 μm or more and 50 μm or less, and more preferably 0.01 μm or more and 10 μm or less.

[0142] Specific examples of component (F) include inorganic particles such as silica, mica, talc, clay, barium titanate, barium sulfate, wollastonite, calcium carbonate, magnesium carbonate, aluminum oxide, titanium oxide, silicon nitride, and aluminum nitride; and organic particles such as core-shell rubber and crosslinked polymers. These may be used alone or in combination of two or more.

[0143] As the inorganic particles, silica particles are preferred from the viewpoint of suppressing cure shrinkage of the resulting cured film while increasing the hardness and adhesion of the resulting cured film. Examples of silica particles include fused silica particles, crushed silica particles, spherical silica particles, crystalline silica particles, and fumed silica particles.

[0144] As the organic particles, from the viewpoint of improving the dispersibility of roll pressure during coating while also improving the flexibility and chemical resistance of the resulting cured film, crosslinked polymer particles are preferred, and crosslinked polymer particles having an average particle size of 1 μm or more and 10 μm or less are more preferred. Specific examples of crosslinked polymer particles include Dainichiseika Color & Chemicals Mfg. Co., Ltd. products under the trade names Dimic Beads (registered trademark) UCN-8070CM Clear, UCN-8150CM Clear, UCN-5070D Clear, and UCN-5150D Clear, and Negami Chemical Industrial Co., Ltd. products under the trade names Art Pearl (registered trademark) C-100 Clear, C-200 Clear, C-300 Clear, C-300WA, C-400 Clear, C-400WA, C-600 Clear, C-800 Clear, C-800WA, C-1000T, P-400T, P-800T, U-600T, CF-600T, JB-400T, JB-800T, CE-400T, CE-800T, and MM-120T, which can be used alone or in combination of two or more.

[0145] In order to further increase the flexibility of the resulting cured film, it is preferable to use polyurethane particles as component (F).Furthermore, in order to further increase the flexibility of the resulting cured film while improving the dispersibility of roll pressure during coating, it is preferable to use crosslinked polyurethane particles, which are crosslinked polymer particles, as component (F).

[0146] In order to further suppress the occurrence of poor appearance of the coating film and the substrate on which the coating film is formed, the content of component (F) is preferably 5 parts by weight or more and 100 parts by weight or less, more preferably 5 parts by weight or more and 80 parts by weight or less, even more preferably 10 parts by weight or more and 80 parts by weight or less, and even more preferably 20 parts by weight or more and 80 parts by weight or less, per 100 parts by weight of component (A).

[0147] {Component (G)} Component (G) is a component used to adjust the viscosity of the liquid photosensitive resin composition. Examples of component (G) include sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide; formamide solvents such as N,N-dimethylformamide and N,N-diethylformamide; acetamide solvents such as N,N-dimethylacetamide and N,N-diethylacetamide; pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone; hexamethylphosphoramide; and γ-butyrolactone. Furthermore, if necessary, these organic solvents can be used in combination with aromatic hydrocarbons (more specifically, xylene, toluene, etc.).

[0148] Examples of the component (G) include symmetric glycol diether solvents such as 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, bis[2-(2-methoxyethoxyethyl)]ether, 1,2-diethoxyethane, bis(2-ethoxyethyl) ether, and bis(2-butoxyethyl) ether; methyl acetate, ethyl acetate, isopropyl acetate, n-propyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 3-methoxybutyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, propanediol, propylene glycol methyl ether acetate, propylene glycol methyl ether acetate, propanediol ... Acetate-based solvents such as propylene glycol diacetate and 1,3-butylene glycol diacetate; and ether-based solvents such as dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, tripropylene glycol n-propyl ether, propylene glycol phenyl ether, dipropylene glycol dimethyl ether, 1,3-dioxolane, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monoethyl ether, and triethylene glycol dimethyl ether can also be used.

[0149] In order to easily adjust the viscosity of the liquid photosensitive resin composition to a range suitable for coating, the content of the component (G) is preferably 10% by weight or more and 80% by weight or less, and more preferably 20% by weight or more and 70% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0150] {Other Components} The liquid photosensitive resin composition may contain, as necessary, various additives such as a radically polymerizable compound having two radically polymerizable groups per molecule, a flame retardant, an antifoaming agent, a leveling agent, a colorant, an adhesion aid, a polymerization inhibitor, etc. as other components (components different from the components (A) to (G)). The total content of the other components is, for example, 20% by weight or less, and preferably 10% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0151] The radical polymerizable compound having two radical polymerizable groups per molecule (hereinafter sometimes referred to as "specific radical polymerizable compound") is preferably a compound having a molecular weight (weight average molecular weight in the case of a polymer) of less than 1,000. Examples of the radical polymerizable group possessed by the specific radical polymerizable compound include a group having an unsaturated double bond. In order to enhance radical polymerizability, the radical polymerizable group is preferably a (meth)acryloyl group or a vinyl group.

[0152] Specific examples of the specific radical polymerizable compound are listed below. In the following, ethylene oxide is referred to as "EO." The average number of moles of EO added is referred to as "n." Specific examples of the specific radical polymerizable compound include EO-modified bisphenol F diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol A diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol S diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol F dimethacrylate (n: 2 or more and 50 or less), EO-modified bisphenol A dimethacrylate (n: 2 or more and 50 or less), EO-modified bisphenol S dimethacrylate (n: 2 or more and 50 or less), 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, pentaerythritol diacrylate, tetraethylene glycol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, pentaerythritol dimethacrylate, tetraethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol Examples of suitable dimethacrylates include glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polypropylene glycol dimethacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol dimethacrylate, 3-methyl-1,5-pentanediol dimethacrylate, 2,4-diethyl-1,5-pentanediol dimethacrylate, 2,4-diethyl-1,5-pentanediol diacrylate, diallylamine, diallyldimethylsilane, diallyl disulfide, diallyl ether, diallyl isophthalate, and diallyl terephthalate. These may be used alone or in combination of two or more.

[0153] In order to obtain a flexible printed circuit board having excellent resistance to plating solutions and resistance to discoloration of wiring, the specific radical polymerizable compound is preferably at least one selected from the group consisting of EO-modified bisphenol F diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol A diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol S diacrylate (n: 2 or more and 50 or less), EO-modified bisphenol F dimethacrylate (n: 2 or more and 50 or less), EO-modified bisphenol A dimethacrylate (n: 2 or more and 50 or less), and EO-modified bisphenol S dimethacrylate (n: 2 or more and 50 or less).

[0154] In order to obtain a flexible printed circuit board having excellent plating solution resistance and wiring discoloration resistance, the content of the specific radical polymerizable compound is preferably 1% by weight or more and 10% by weight or less based on the total amount of the liquid photosensitive resin composition.

[0155] Examples of the flame retardant include halogen-based flame retardants, phosphorus-based flame retardants, metal hydroxides, and antimony-based flame retardants.

[0156] A halogen-based flame retardant refers to a compound that contains at least one halogen atom in one molecule and inhibits the combustion of organic matter. Examples of halogen-based flame retardants include bromine-based compounds and chlorine-based compounds, which can be used alone or in combination of two or more.

[0157] Phosphorus-based flame retardants refer to compounds that contain at least one phosphorus atom per molecule and inhibit the combustion of organic matter. Examples of phosphorus-based flame retardants include red phosphorus, condensed phosphate ester compounds, cyclic organic phosphorus compounds, phosphazene compounds, phosphorus-containing polyol compounds, phosphorus-containing amine compounds, ammonium polyphosphate, melamine phosphate, and phosphinate, which can be used alone or in combination of two or more.

[0158] Examples of metal hydroxides that function as flame retardants include aluminum hydroxide and magnesium hydroxide, which can be used alone or in combination of two or more.

[0159] Antimony-based flame retardants are compounds that contain at least one antimony atom per molecule and inhibit the combustion of organic matter, such as antimony trioxide.

[0160] Examples of the antifoaming agent include acrylic compounds, vinyl compounds, and butadiene compounds.

[0161] Examples of the leveling agent include acrylic compounds and vinyl compounds.

[0162] Examples of colorants include phthalocyanine compounds, azo compounds, and carbon black.

[0163] Examples of the adhesion aid (also called an adhesion promoter) include silane coupling agents, triazole-based compounds, tetrazole-based compounds, and triazine-based compounds.

[0164] Examples of the polymerization inhibitor include hydroquinone and hydroquinone monomethyl ether.

[0165] [Method for Preparing Liquid Photosensitive Resin Composition] The liquid photosensitive resin composition can be prepared by grinding, dispersing, and mixing the above-mentioned components (A) to (E), and any optional components used as needed (such as component (F), component (G), and the other components described above). The grinding and dispersion method is not particularly limited, and examples include methods using kneading devices such as a bead mill, a ball mill, and a three-roll mill. Among these, the method of grinding, dispersing, and mixing using a three-roll mill is preferred because it results in a uniform particle size distribution.

[0166] [Optional Steps] In this embodiment, the steps other than the step of applying the liquid photosensitive resin composition are optional steps, including the step of drying the substrate (drying step) described above. In addition to the drying step, the optional steps include, for example, the micro-aperture forming step, curing step, gold plating step, heat pressing step, and baking step described below.

[0167] (Micro-aperture formation process) After the drying process, the coating film is irradiated with active energy rays (more specifically, ultraviolet rays, visible light, electron beams, etc.) through a negative photomask to expose a portion of the coating film. This causes photo-radical polymerizable components to polymerize in the exposed portions of the coating film. Next, the unexposed portions are washed away with a developer using a development method such as spraying, puddling, immersion, or ultrasonic waves, thereby patterning the coating film and forming micro-apertures. Note that the time until opening varies depending on the spray pressure and flow rate of the developing device and the temperature of the developer, so it is desirable to find the optimal device conditions as appropriate.

[0168] The developer is preferably an alkaline aqueous solution. The developer may contain a water-soluble organic solvent such as methanol, ethanol, 1-propanol, 2-propanol, or N-methyl-2-pyrrolidone. Examples of alkaline compounds contained in the alkaline aqueous solution include hydroxides, carbonates, or bicarbonates of alkali metals, alkaline earth metals, or ammonium ions, and amine compounds. Specific examples include sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammonium bicarbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetraisopropylammonium hydroxide, N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylethanolamine, triethanolamine, and triisopropylamine. Compounds other than these can also be used as long as they produce a basic aqueous solution. The concentration of the alkaline compound in the alkaline aqueous solution is preferably 0.01% by weight or more and 20% by weight or less, more preferably 0.02% by weight or more and 10% by weight or less. The temperature of the developer depends on the composition of the liquid photosensitive resin composition and the composition of the alkaline developer, but is generally from 0°C to 80°C, preferably from 10°C to 60°C.

[0169] The inside of the fine openings formed by development is preferably washed to remove unnecessary residues. Examples of the washing liquid include water and an acidic aqueous solution.

[0170] (Curing Step) Next, the coating film with microapertures formed therein (patterned coating film) is subjected to a heat treatment. By carrying out the heat treatment, reactive groups (e.g., reactive groups of component (C)) remaining in the molecular structure constituting the coating film are reacted, thereby obtaining a cured film with excellent heat resistance. The thickness of the cured film is determined taking into consideration the thickness of the wiring, etc., but is preferably 2 μm or more and 50 μm or less. The final curing temperature in the curing step is preferably low in order to prevent oxidation of the wiring, etc., and to avoid reducing the adhesion between the wiring and the film-like support. The final curing temperature is preferably 100°C or more and 250°C or less, more preferably 120°C or more and 200°C or less, and even more preferably 130°C or more and 180°C or less. The curing time at the final curing temperature is, for example, 1 minute or more and 120 minutes or less. The cured film formed according to this embodiment has excellent flexibility, flame retardancy, and electrical insulation reliability, and tends to have little warping after the curing step. Therefore, the cured film formed according to this embodiment is particularly suitable as an insulating material for flexible printed circuit boards.

[0171] (Gold Plating Step) Next, the substrate on which the cured film has been formed (hereinafter, may be referred to as a "cured film-coated substrate") is subjected to a gold plating step. The gold plating step includes, for example, a degreasing treatment step, an etching treatment step, a catalyzing treatment step, an electroless nickel plating treatment step, and an electroless gold plating treatment step.

[0172] Electroless gold plating solutions that can be used in the electroless gold plating process contain, for example, gold salts such as potassium gold cyanide, potassium gold cyanide, and sodium gold sulfite; buffers such as organic acid salts, sulfates, boric acid, phosphates, and sulfamic acid; metal masking agents such as ethylenediaminetetraacetic acid, N'-(2-hydroxyethyl)ethylenediamine-N,N,N'-triacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid; and crystal adjusters such as cobalt, nickel, silver, iron, palladium, copper, thallium, lead, and arsenic. Examples of such electroless gold plating solutions include those available under the trade names Flash Gold 2000, Flash Gold VT, Flash Gold 330, Flash Gold NC, Wireless Noble AU, and Self Gold OTK-IT, all manufactured by Okuno Chemical Industries, Ltd.; and those available under the trade names Cobright TMX-22, Cobright TMX-23, Cobright TMX-40, Cobright TSB-71, Cobright TSB-72, Cobright TCU-37, Cobright TUC-38, Cobright TAM-LC, Cobright TCL-61, Cobright TIG-10, Cobright TAW-66, and Aurical (registered trademark) TKK-51, all manufactured by Uemura Kogyo Co., Ltd.

[0173] (Heat Pressing Step) Next, the substrate with the cured film after the gold plating step and a plate-like or film-like member (specifically, a reinforcing plate, an electromagnetic wave shielding film, etc.) are laminated by heat pressing. The heat pressing method that can be used in the heat pressing step is not particularly limited, and examples include general heat pressing methods used in processing flexible printed circuit boards, such as multi-layer laminate heat pressing and quick pressing. In order to further suppress discoloration of the wiring, the heat pressing temperature in the heat pressing step is preferably 120°C or higher and 200°C or lower, and more preferably 150°C or higher and 180°C or lower. The heat pressing time in the heat pressing step is, for example, 30 minutes or higher and 90 minutes or lower.

[0174] (Baking Step) Next, the laminate obtained in the heat pressing step is baked. Baking methods that can be used in the baking step include common baking methods used in the processing of flexible printed circuit boards, such as heating methods using a box oven or a tunnel oven. In order to further suppress discoloration of the wiring, the baking temperature in the baking step is preferably 120°C or higher and 200°C or lower, more preferably 140°C or higher and 180°C or lower. The baking time in the baking step is, for example, 60 minutes or higher and 120 minutes or lower. A flexible printed circuit board is obtained through the above steps.

[0175] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0176] First, methods for measuring the weight average molecular weights and acid values ​​of binder polymers P1 to P3, and the solid content concentrations of resin solutions SP1 to SP3 containing binder polymers P1 to P3, respectively, will be described.

[0177] <Method for measuring weight-average molecular weight> The weight-average molecular weight of binder polymers P1 to P3 was measured under the following conditions: Apparatus used: "HLC-8220GPC" manufactured by Tosoh Corporation Column: "TSKgel Super AWM-H" (6.0 mm I.D. x 15 cm) x 2 manufactured by Tosoh Corporation Guard column: "TSKguard column Super AW-H" x 1 manufactured by Tosoh Corporation Eluent: LiBr (concentration: 30 mmol / L) and H ３ P.O. ４ (concentration: 20 mmol / L) dissolved in N,N-dimethylformamide. Flow rate: 0.6 mL / min. Column temperature: 40°C. Detector: RI (differential refractometer). RI detection conditions: polarity (+), response (0.5 seconds). Sample concentration: 5 mg / mL. Standard: PEG (polyethylene glycol).

[0178] <Method for Measuring Acid Value> The acid values ​​of the binder polymers P1 to P3 were measured by the method described in JIS K 5601-2-1 (1999).

[0179] <Method for measuring solid content concentration of resin solution> The solid content concentrations of resin solutions SP1 to SP3 were measured by the method described in JIS K 5601-1-2 (2008). The drying conditions for the measurement were 170°C x 1 hour.

[0180] <Preparation of Resin Solutions> Hereinafter, methods for preparing resin solutions SP1 to SP3 containing binder polymers P1 to P3, respectively, as component (A) will be described. Note that, unless otherwise specified, the reaction (stirring) was carried out under a nitrogen stream.

[0181] [Preparation of resin solution SP1 containing binder polymer P1] A reaction vessel equipped with a stirrer, a thermometer, and a nitrogen inlet tube was charged with 35.00 g of triethylene glycol dimethyl ether (hereinafter sometimes referred to as "TEGDM") as a polymerization solvent and 10.31 g (0.050 mol) of norbornene diisocyanate, and the contents of the vessel were heated to 80 ° C. while stirring under a nitrogen stream, and norbornene diisocyanate was dissolved in TEGDM. Next, a TEGDM solution of polycarbonate diol (manufactured by Asahi Kasei Corporation, "PCDL T5652", weight average molecular weight: 2,000) was added to the contents of the vessel over 1 hour, and the resulting solution was stirred for 2 hours while being heated to 80 ° C. The polycarbonate diol TEGDM solution was prepared by dissolving 50.00 g (0.025 mol) of polycarbonate diol in 35.00 g of TEGDM. Next, 15.51 g (0.050 mol) of 4,4'-oxydiphthalic anhydride was added to the contents of the vessel, and the contents were heated to 190°C while stirring for 1 hour. The contents of the vessel were then cooled to 80°C, and 3.60 g (0.200 mol) of pure water was added to the contents of the vessel. The contents of the vessel were then heated to 110°C and refluxed for 5 hours to obtain a resin solution SP1 containing a binder polymer P1 having a urethane bond and an imide group per molecule. The solids concentration of the resulting resin solution SP1 was 53 wt%. The weight average molecular weight and acid value of the binder polymer P1 were 9,200 and 86 mgKOH / g, respectively.

[0182] [Preparation of resin solution SP2 containing binder polymer P2] A reaction vessel equipped with a stirrer, thermometer, and nitrogen inlet tube was charged with 40.00 g of TEGDM as a polymerization solvent and 20.62 g (0.100 mol) of norbornene diisocyanate. The contents of the vessel were heated to 80 ° C. while stirring under a nitrogen stream, and norbornene diisocyanate was dissolved in TEGDM. Next, to the contents of the vessel, polycarbonate diol (Asahi Kasei Corporation "PCDL T5652", weight average molecular weight: 2,000), 2,2-bis (hydroxymethyl) butanoic acid, and a TEGDM solution of 2-hydroxyethyl methacrylate were added over 1 hour. The resulting solution was stirred for 5 hours while heating to 80 ° C. to obtain a resin solution SP2 containing binder polymer P2 having a urethane bond, a carboxy group, and a methacryloyl group in one molecule. The TEGDM solution of polycarbonate diol, 2,2-bis(hydroxymethyl)butanoic acid, and 2-hydroxyethyl methacrylate was prepared by dissolving 50.00 g (0.025 mol) of polycarbonate diol, 3.70 g (0.025 mol) of 2,2-bis(hydroxymethyl)butanoic acid, and 13.02 g (0.100 mol) of 2-hydroxyethyl methacrylate in 40.00 g of TEGDM. The solids concentration of the resulting resin solution SP2 was 52 wt%. The weight average molecular weight and acid value of binder polymer P2 were 8,600 and 18 mg KOH / g, respectively.

[0183] [Preparation of resin solution SP3 containing binder polymer P3] A reaction vessel equipped with a stirrer, thermometer, and nitrogen inlet tube was charged with 100.00 g of TEGDM as a polymerization solvent, and the contents of the vessel were heated to 80 ° C. while stirring under a nitrogen stream. Next, while maintaining the temperature of the contents of the vessel at 80 ° C., a mixture containing a methacrylic acid compound was added dropwise to the reaction vessel using a dropping funnel over 3 hours. The mixture containing the methacrylic acid compound was a mixture of 12.0 g (0.14 mol) of methacrylic acid, 28.0 g (0.16 mol) of benzyl methacrylate, 60.0 g (0.42 mol) of butyl methacrylate, and 0.5 g of azobisisobutyronitrile as a radical polymerization initiator, which had been mixed in advance under an atmosphere of 25 ° C. After the dropwise addition was completed, the contents of the vessel were heated to 90 ° C. while stirring. The contents of the vessel were then stirred for 2 hours while maintaining the temperature at 90°C to obtain a resin solution SP3 containing a binder polymer P3 having a carboxyl group per molecule. The solids concentration of the resulting resin solution SP3 was 50 wt%. The weight average molecular weight and acid value of the binder polymer P3 were 48,000 and 78 mgKOH / g, respectively.

[0184] <Preparation of Liquid Photosensitive Resin Compositions> Any of the resin solutions SP1 to SP3 obtained by the above-described preparation method was mixed with each of the components (specifically, components other than component (A)) listed in Tables 1 to 4 below using a stirrer equipped with a stirring blade. The resulting mixture was then passed through a three-roll mill twice and degassed using a degassing device to obtain the liquid photosensitive resin compositions used in Examples 1 to 14 and Comparative Examples 1 to 3. The average particle size of the particles in the resulting liquid photosensitive resin compositions was measured and found to be 10 μm or less in all of Examples 1 to 14 and Comparative Examples 1 to 3.

[0185] <Method for measuring physical properties of liquid photosensitive resin composition, and method for evaluating liquid photosensitive resin composition> [Method for evaluating micro-opening property] Each liquid photosensitive resin composition was applied to a portion (area 200 mm x 200 mm) of a 25 μm thick polyimide film ("Apical (registered trademark) 25NPI" manufactured by Kaneka Corporation) using a Baker-type applicator. At this time, the amount of liquid photosensitive resin composition applied was adjusted so that the thickness of the cured film was 20 μm. Next, the coating film made of the liquid photosensitive resin composition was dried under conditions of a drying temperature of 80°C and a drying time of 20 minutes, and then exposed to an accumulated exposure dose of 300 mJ / cm through a negative photomask having circular light-shielding regions with diameters of 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, and 200 μm. ２ The coating film was exposed by irradiating it with ultraviolet light under the conditions of: Then, a 1.0 wt % aqueous solution of sodium carbonate (temperature: 30°C) was used as a developer, and the exposed coating film was exposed to ultraviolet light under the conditions of: ２ Spray development was carried out for 90 seconds under the conditions of . The developed coating film was then washed with pure water and heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on the polyimide film. The resulting cured film was observed under an optical microscope, and the smallest diameter of the formed holes was used as an evaluation value for micro-opening property.

[0186] [Method for Measuring Repulsion Force] First, a flexible copper-clad laminate was prepared by laminating electrolytic copper foil (thickness: 12 μm) to both sides of a polyimide film ("Pixio (registered trademark) BP FRS-522#SW" manufactured by Kaneka Corporation, thickness: 12.5 μm) as a film support. The copper foil on one side of this flexible copper-clad laminate was patterned to form a comb-shaped pattern with a line width / space width of 100 μm / 100 μm on the film support. Next, the laminate with the comb-shaped pattern formed was immersed in a 10% by volume aqueous sulfuric acid solution for 1 minute and then washed with pure water. Next, each liquid photosensitive resin composition was applied onto the comb-shaped pattern using a Baker-type applicator. At this time, the amount of liquid photosensitive resin composition applied was adjusted so that the thickness of the cured film on the comb-shaped pattern was 20 μm. Next, the coating film made of the liquid photosensitive resin composition was dried under conditions of a drying temperature of 80°C and a drying time of 20 minutes, and then subjected to an integrated exposure dose of 300 mJ / cm ２ Then, a 1.0 wt % aqueous solution of sodium carbonate (temperature: 30°C) was used as a developer, and the exposed coating was exposed to ultraviolet light under the conditions of: ２ Spray development was performed for 90 seconds under the conditions of . The developed coating film was then washed with pure water and heated in an oven at 150 ° C. for 60 minutes to form a cured film of the liquid photosensitive resin composition on the comb pattern. The resulting laminate including the cured film was then cut into a size of 15 mm wide x 200 mm long to obtain a test piece. This test piece was rolled into a loop with a circumference of 50 mm and fixed to a resilience measuring device ("Loop Stiffness Tester (registered trademark)" manufactured by Toyo Seiki Seisaku-sho, Ltd.), and the looped test piece was pressed until the shortest loop diameter was 10 mm, and the resilience from the looped test piece was measured. The smaller the resilience, the more excellent the cured film's low resilience.

[0187] [Method for evaluating solder heat resistance] Each liquid photosensitive resin composition was applied to an electrolytic copper foil having a thickness of 35 μm using a Baker-type applicator. At this time, the amount of the liquid photosensitive resin composition applied was adjusted so that the thickness of the cured film would be 20 μm. Next, the coating film made of the liquid photosensitive resin composition was dried under conditions of a drying temperature of 80° C. and a drying time of 20 minutes, and then subjected to an integrated exposure dose of 300 mJ / cm.２ Then, a 1.0 wt % aqueous solution of sodium carbonate (temperature: 30°C) was used as a developer, and the exposed coating was exposed to ultraviolet light under the conditions of: ２ Spray development was performed for 90 seconds under the conditions of . The developed coating film was then washed with pure water and heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on the electrolytic copper foil, thereby obtaining a test piece. The obtained test piece was immersed in a solder bath at 260°C and then pulled out after 10 seconds, which was considered as one operation, and this operation was performed three times consecutively. Next, the condition of the cured film surface was visually observed, and when no blistering or peeling was observed on the cured film surface, it was evaluated as "A (excellent solder heat resistance)". On the other hand, when blistering or peeling was observed on the cured film surface, it was evaluated as "B (not excellent solder heat resistance)".

[0188] [Method for evaluating electrical insulation reliability] First, a flexible copper-clad laminate was prepared by laminating electrolytic copper foil (thickness: 12 μm) to both sides of a polyimide film ("Pixio (registered trademark) BP FRS-142#SW" manufactured by Kaneka Corporation, thickness: 25 μm) as a film support. The copper foil on one side of this flexible copper-clad laminate was patterned to form a comb-shaped pattern with a line width / space width of 100 μm / 100 μm on the film support. Next, the laminate with the comb-shaped pattern formed was immersed in a 10% by volume aqueous sulfuric acid solution for 1 minute and then washed with pure water. Next, each liquid photosensitive resin composition was applied onto the comb-shaped pattern using a Baker-type applicator. At this time, the amount of the liquid photosensitive resin composition applied was adjusted so that the thickness of the cured film on the comb-shaped pattern was 20 μm. Next, the coating film made of the liquid photosensitive resin composition was dried under conditions of a drying temperature of 80°C and a drying time of 20 minutes, and then subjected to an integrated exposure dose of 300 mJ / cm ２ Then, a 1.0 wt % aqueous solution of sodium carbonate (temperature: 30°C) was used as a developer, and the exposed coating was exposed to ultraviolet light under the conditions of: ２Spray development was carried out for 90 seconds under the conditions of 1.0×10. The developed coating film was then washed with pure water and heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on the comb-shaped pattern, thereby obtaining a test piece. Next, a DC voltage of 100 V was applied to both terminals of the test piece in an environment of 85°C and 85% relative humidity, and the change in resistance value between the two terminals was observed. Then, after 1000 hours had passed since the start of application, a DC voltage of 1.0×10 ８ When the resistance value was 1.0×10 Ω or more, it was evaluated as "A (excellent electrical insulation reliability)." ８ When the resistance value was less than Ω, it was evaluated as "B (not excellent in electrical insulation reliability)."

[0189] <Preparation of Substrate> First, a flexible copper-clad laminate was prepared by laminating electrolytic copper foil to both sides of a polyimide film ("Pixio (registered trademark) BP FRS#SW" manufactured by Kaneka Corporation) as a film-like support. Six hundred through-holes each having diameters (opening diameters) of 30 μm, 50 μm, 80 μm, 100 μm, 130 μm, 190 μm, 240 μm, and 290 μm were provided in this flexible copper-clad laminate. Next, a cleaning treatment (desmear treatment) and a carbon treatment were performed inside the through-holes. Next, the insides of the through-holes were electrolytically copper plated, and then the electrolytic copper foil on both sides was patterned to form wiring, thereby obtaining a substrate having a film-like support, wiring provided on both sides of the film-like support, and through-holes. For each of Examples 1 to 14 and Comparative Examples 1 to 3, the longitudinal and lateral widths of the substrates used, the thickness of the film-like support used, and the thickness of the wiring on the substrates used are shown in Tables 1 to 4 described below.

[0190] <Coating of Liquid Photosensitive Resin Composition onto Substrate and Formation of Coating Film> A liquid photosensitive resin composition (any of the liquid photosensitive resin compositions listed in Tables 1 to 4 described below) was coated onto both sides of the substrate prepared by the procedure described above using a vertically lifted roll coater equipped with a pair of coating rolls. The liquid photosensitive resin composition was simultaneously coated onto both sides of the substrate. The coating conditions were as follows. In the following coating conditions, "coating roll" means "each of the pair of coating rolls." - Material of surface layer (surface layer roll) of coating roll: ethylene propylene rubber - Width of surface layer roll: 680 mm - Roll diameter of coating roll: as listed in Tables 1 to 4 described below - Type of groove in coating roll: multiple independent ring-shaped grooves - Pitch of coating roll groove: 700 μm - Opening width of coating roll groove: 700 μm - Cross-sectional shape of coating roll groove: V-shaped - Depth of coating roll groove: 350 μm - Doctor bar pressure: 1.5 kgf / cm ２ Pressing depth of application roll: 150 μm Rotation speed of application roll: 5 m / min

[0191] The substrate coated with the liquid photosensitive resin composition was then dried in a hanging state at a drying temperature of 80°C for 20 minutes to obtain a substrate having a coating film made of the dried liquid photosensitive resin composition (hereinafter, this may be referred to as a "substrate with a coating film"). The thickness of the coating film made of the liquid photosensitive resin composition after drying (specifically, the thickness of the coating film on the wiring other than around the holes) was 20 μm on both sides.

[0192] <Method for Evaluating Coated Substrates> [Embeddability] The through holes of each coated substrate (specifically, 600 through holes each with diameters of 30 μm, 50 μm, 80 μm, 100 μm, 130 μm, 190 μm, 240 μm, and 290 μm) were observed with an optical microscope, and the largest diameter of the through holes when the filling rate was 100% (when all 600 through holes were filled) was used as the evaluation value for embeddability. For example, an "evaluation value for embeddability of 50 μm" means that all 600 through holes with diameters of 30 μm and 50 μm were filled, but some or all of the 600 through holes with diameter of 80 μm were not filled. Therefore, the higher this evaluation value, the better the embeddability can be evaluated.

[0193] [Appearance of Coating Film] The coating film of each coated substrate was visually observed to check for the presence or absence of pinholes, uneven coating of the coating film covering the wiring, traces of the coating roll grooves, and streaks. The appearance of the coating film was then judged according to the following criteria. A rating of A or B was evaluated as "the occurrence of poor appearance of the coating film was suppressed." On the other hand, a rating of C was evaluated as "the occurrence of poor appearance of the coating film was not suppressed."

[0194] (Criteria for judging the appearance of the coating film) A: None of the following was observed: pinholes, uneven coating, groove marks, or streaks. B: At least one of the following defects was observed in one or two places in total: pinholes, uneven coating, groove marks, or streaks. C: At least one of the following defects was observed in three or more places in total: pinholes, uneven coating, groove marks, or streaks.

[0195] [Appearance of coated substrate] The appearance of each coated substrate was visually observed to check for the presence or absence of substrate breakage and deformation. The appearance of the coated substrate was then judged according to the following criteria. A rating of A or B was evaluated as "the occurrence of defective appearance of the coated substrate was suppressed." On the other hand, a rating of C was evaluated as "the occurrence of defective appearance of the coated substrate was not suppressed."

[0196] (Evaluation criteria for the appearance of the coated substrate) A: Neither breakage nor deformation of the substrate was observed. B: No breakage of the substrate was observed, but deformation of the substrate was observed. C: Both breakage and deformation of the substrate were observed.

[0197] <Formation of Cured Film> The substrate with the coating film obtained by the above procedure was exposed to a cumulative exposure dose of 300 mJ / cm through a negative photomask having 100 circular light-shielding regions with a diameter of 150 μm. ２ The coating film was exposed to ultraviolet light under the following conditions: Then, a 1.0 wt % aqueous solution of sodium carbonate (temperature: 30°C) was used as a developer, and the exposed coating film was exposed to ultraviolet light under the following conditions: ２ Spray development was performed for 90 seconds under the conditions of . The developed coating film was then washed with pure water and heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition, thereby obtaining a substrate provided with a cured film that protects the wiring (hereinafter, sometimes referred to as a "cured film-coated substrate"). 100 circular openings were formed in the cured film of the obtained cured film-coated substrate. Furthermore, a portion of the wiring was exposed from each circular opening.

[0198] <Evaluation method for cured film-coated substrates> [Thickness of cured film around holes] Each cured film-coated substrate obtained by the method described above in <Formation of cured film> was cut in the thickness direction, and the resulting small pieces were embedded in an epoxy-based embedding resin. The cross section of the embedded small piece was polished with a cross section polishing device to obtain a sample for cross section observation. The cross section of the obtained sample was observed with an electron microscope, and the thickness of the cured film around the hole (through hole) was measured.

[0199] [Resistance to plating solution] Each of the substrates with a cured film obtained by the method described above in <Formation of cured film> was subjected to electroless gold plating treatment according to the standard process using an electroless gold plating solution (product name: Flash Gold 330) manufactured by Okuno Chemical Industries Co., Ltd. The detailed procedure is shown below.

[0200] First, the cured film-coated substrate was immersed in a degreasing treatment solution ("ICP Clean S-135K" manufactured by Okuno Chemical Industries, Ltd.) at a temperature of 40°C for 4 minutes to degrease the cured film-coated substrate. Next, the degreased cured film-coated substrate was immersed in an etching solution at a temperature of 30°C for 1 minute to etch the cured film-coated substrate. The etching solution used was an aqueous solution prepared by dissolving sulfuric acid (10 mL / L), sodium persulfate (100 g / L), and copper sulfate pentahydrate (8 g / L) in ion-exchanged water. Next, the cured film-coated substrate after the etching treatment was immersed in a catalysis treatment solution ("ICP Accela" manufactured by Okuno Chemical Industries, Ltd., Pd concentration: 0.04 wt%) at a temperature of 30°C for 1 minute to catalyze the cured film-coated substrate. Next, the cured film-coated substrate after the catalysis treatment was immersed in an electroless nickel plating solution ("ICP Nicoron FPF" manufactured by Okuno Pharmaceutical Industries, Ltd.) at a temperature of 84°C for 30 minutes, thereby subjecting the cured film-coated substrate to electroless nickel plating. The electroless nickel-plated cured film-coated substrate was then immersed in an electroless gold plating solution ("Flash Gold 330" manufactured by Okuno Pharmaceutical Industries, Ltd.) at a temperature of 80°C for 8 minutes, thereby subjecting the cured film-coated substrate to electroless gold plating, and then washed with water at a temperature of 25°C. The washed cured film-coated substrate was then heated at a temperature of 150°C for 30 minutes to obtain a test piece for evaluating plating solution resistance. The periphery of the circular opening formed in the cured film of the obtained test piece was observed with an optical microscope, and the plating solution resistance was evaluated according to the following criteria. A rating of A was evaluated as "excellent plating solution resistance." On the other hand, a rating of B or C was evaluated as "not excellent plating solution resistance."

[0201] (Evaluation criteria for plating solution resistance) A: For all openings (100 openings), penetration of plating solution between the cured film and the substrate (penetration of plating solution through the openings) was not observed. B: For some openings, penetration of plating solution between the cured film and the substrate was observed. C: For all openings, penetration of plating solution between the cured film and the substrate was observed.

[0202] [Discoloration Resistance of Wiring] After evaluation using the method described above in [Resistance to Plating Solution], the test piece was subjected to a heat press treatment at a temperature of 160°C for 60 minutes using a heat press device, and then baked at a temperature of 150°C for 90 minutes using a box oven. The wiring of the test piece after the baking treatment (more specifically, the wiring covered with the cured film) was visually observed, and the discoloration resistance of the wiring was evaluated according to the following criteria. When the evaluation was A, the wiring was evaluated as having excellent discoloration resistance. On the other hand, when the evaluation was B or C, the wiring was evaluated as having poor discoloration resistance.

[0203] (Criteria for evaluation of discoloration resistance of wiring) A: No discoloration of the wiring was observed. B: Discoloration was observed in part of the wiring. C: Discoloration was observed in the entire wiring.

[0204] <Evaluation Results> For Examples 1 to 14 and Comparative Examples 1 to 3, the components and amounts of the liquid photosensitive resin composition used, the longitudinal and lateral widths of the substrate used, the thickness of the film-like support used, the thickness of the wiring on the substrate used, the roll diameter of the applicator roll used, the physical properties and evaluation results of the liquid photosensitive resin composition used, the evaluation results of the coated substrate, and the evaluation results of the cured film-bearing substrate are shown in Tables 1 to 4. In Tables 1 to 4, the numerical values ​​in the column for the composition of the liquid photosensitive resin composition indicate the amount of the component (unit: parts by weight). In Tables 1 to 4, the amount of component (G) (organic solvent) also includes the amount of organic solvent in Resin Solution SP1, Resin Solution SP2, or Resin Solution SP3. In Tables 1 to 4, "-" indicates that the component was not included. In Tables 1 to 4, "component (C)" also includes epoxy compounds having only one epoxy group. In Tables 1 to 4, "Component (E)" also includes radically polymerizable compounds having two radically polymerizable groups in one molecule.

[0205] In addition, in Tables 1 to 4, "369", "828", "1032", "PGE", "DPEHA", "PETA", "321", "8070", "TEGDM", and "2000" are as follows. 369: 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 as a photoradical polymerization initiator (IGM Resins' "Omnirad (registered trademark) 369") 828: Epoxy compound having two epoxy groups in one molecule (Mitsubishi Chemical's "jER (registered trademark) 828") 1032: Epoxy compound having three epoxy groups in one molecule (Mitsubishi Chemical's "jER (registered trademark) 1032H60") PGE: Phenyl glycidyl ether DPEHA: Dipentaerythritol hexaacrylate PETA: Pentaerythritol triacrylate 321: EO-modified bisphenol A dimethacrylate (Showa Denko Materials' "Fancryl (registered trademark) FA-321M", average number of moles of EO added: 10) 8070: Crosslinked polyurethane particles (Daimic Beads (registered trademark) UCN-8070CM Clear, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., average particle size: 7 μm) TEGDM: Triethylene glycol dimethyl ether 2000: Butadiene-based defoamer (Florene AC-2000, manufactured by Kyoeisha Chemical Co., Ltd.)

[0206]

[0207]

[0208]

[0209]

[0210] In Examples 1 to 14, the liquid photosensitive resin compositions used contained a binder polymer, a photoradical polymerization initiator, a polyfunctional epoxy compound, an epoxy curing accelerator, and a radically polymerizable compound having three or more radically polymerizable groups in one molecule.

[0211] In Examples 1 to 14, the plating solution resistance was evaluated as A. Therefore, the flexible printed circuit boards obtained by the manufacturing methods of Examples 1 to 14 were excellent in plating solution resistance. In Examples 1 to 14, the discoloration resistance of the wiring was evaluated as A. Therefore, the flexible printed circuit boards obtained by the manufacturing methods of Examples 1 to 14 were excellent in discoloration resistance of the wiring.

[0212] In Comparative Examples 1 to 3, the liquid photosensitive resin compositions used did not contain a polyfunctional epoxy compound. In Comparative Examples 2 and 3, the liquid photosensitive resin compositions used did not contain an epoxy curing accelerator. In Comparative Example 3, the liquid photosensitive resin composition used did not contain a radically polymerizable compound having three or more radically polymerizable groups in one molecule.

[0213] In Comparative Examples 1 to 3, the plating solution resistance was evaluated as B or C. Therefore, the flexible printed circuit boards obtained by the manufacturing methods of Comparative Examples 1 to 3 did not have excellent plating solution resistance. In Comparative Examples 1 to 3, the discoloration resistance of the wiring was evaluated as C. Therefore, the flexible printed circuit boards obtained by the manufacturing methods of Comparative Examples 1 to 3 did not have excellent discoloration resistance of the wiring.

[0214] The above results demonstrate that the present invention can provide a method for producing a flexible printed circuit board that is excellent in plating solution resistance and wiring discoloration resistance.

[0215] REFERENCE SIGNS LIST 11 Substrate 12a, 12b, 100 Coating roll 13 Film-like support 14 Wiring 15 Hole 17 Liquid photosensitive resin composition

Claims

1. A method for producing a flexible printed circuit board, comprising applying a liquid photosensitive resin composition to both sides of a substrate having a film-like support and wiring provided on both sides of the film-like support by using a vertically suspended roll coater, The substrate has a hole therein, The liquid photosensitive resin composition contains a binder polymer, a photoradical polymerization initiator, a polyfunctional epoxy compound, an epoxy curing accelerator, and a radical polymerizable compound having three or more radical polymerizable groups in one molecule, The thickness of the film-like support is 8.0 μm or more and 50.0 μm or less, In applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is applied simultaneously to both sides of the substrate.

2. The method for producing a flexible printed circuit board according to claim 1 , wherein the width and length of the film-like support are both 200 mm or more and 600 mm or less.

3. The method for producing a flexible printed circuit board according to claim 1 or 2, wherein the wiring has a thickness of 8 μm or more and 50 μm or less.

4. The method for manufacturing a flexible printed circuit board according to any one of claims 1 to 3, wherein the hole has a diameter of 50 µm or more and 250 µm or less.

5. The method for producing a flexible printed circuit board according to any one of claims 1 to 4, wherein the film-like support contains one or more polymers selected from the group consisting of polyimide, polyamide, polyester, polycarbonate, polyarylate, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluorine resin, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer.

6. The method for producing a flexible printed circuit board according to any one of claims 1 to 5, wherein the binder polymer is one or more polymers selected from the group consisting of a polymer having a urethane bond in one molecule, a polymer having an imide group in one molecule, a polymer having a (meth)acryloyl group in one molecule, and a polymer having a carboxy group in one molecule.

7. The method for producing a flexible printed circuit board according to any one of claims 1 to 6, wherein the content of the epoxy curing accelerator is 0.1 parts by weight or more and 0.5 parts by weight or less with respect to 100 parts by weight of the binder polymer.

8. The method for producing a flexible printed circuit board according to any one of claims 1 to 7, wherein the binder polymer has an acid value of 10 mgKOH / g or more.

9. The vertical lift roll coater includes a pair of coating rolls, The method for producing a flexible printed circuit board according to any one of claims 1 to 8, wherein the roll diameter of the coating roll is 70 mm or more and 150 mm or less.

10. A method for manufacturing a flexible printed circuit board as described in Claim 9, wherein the coating roll has a plurality of independent ring-shaped grooves.