Manufacturing method for flexible printed circuit 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

[Technical Field]

[0001] This invention relates to a method for manufacturing a flexible printed circuit board. [Background technology]

[0002] With the miniaturization, weight reduction, and increased functionality of electronic components, the openings in flexible printed circuit boards incorporated into electronic devices require miniaturization (hereinafter sometimes referred to as "micro-aperture") that allows components to be mounted on reduced-diameter lands, etc. One known method for forming micro-apertures in flexible printed circuit boards is to form a film made of a liquid photosensitive resin composition on the component mounting area of ​​the flexible printed circuit board (hereinafter sometimes simply referred to as "board") before the protective film is formed, and then pattern this film by photolithography to form a protective film with micro-apertures.

[0003] Furthermore, in recent years, with the increasing size and thinning of mobile devices such as smartphones, flexible printed circuit boards used in these devices are required to have low rebound properties that allow them to easily maintain their folded shape in order to be folded and incorporated into narrow spaces. One known method for improving the low rebound properties of flexible printed circuit boards is to partially apply a thermosetting resin composition called bending ink to the bent portion of the board.

[0004] Flexible printed circuit boards typically have through-holes and blind vias, and when applying a liquid photosensitive resin composition to the board, it is necessary to fill the through-holes and blind vias with the liquid photosensitive resin composition. For this reason, flexible printed circuit boards are required to have sufficient filling of the liquid photosensitive resin composition in the through-holes and blind vias (hereinafter sometimes referred to as "fillability"). In the following, through-holes and blind vias may be collectively referred to as "holes." Also, in the following, "hole" means one hole or multiple holes. Furthermore, boards with holes include boards with only through-holes, boards with only blind vias, and boards with both through-holes and blind vias.

[0005] Under these circumstances, various protective resin compositions (specifically, liquid photosensitive resin compositions, etc.) and coating apparatuses for protective resin compositions have been investigated to improve the fine aperture properties, low rebound properties, or embedding properties of flexible printed circuit boards (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-161764 [Patent Document 2] Japanese Patent Publication No. 2020-148971 [Patent Document 3] International Publication No. 2018 / 092330 [Patent Document 4] Japanese Patent Publication No. 2015-115602 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the technologies described in Patent Documents 1 to 4 alone are insufficient to suppress the penetration of the plating solution between the protective film (cured film) and the substrate during the plating process (e.g., gold plating process) while simultaneously suppressing the discoloration of the wiring during the heating process (e.g., hot pressing process). The penetration of the plating solution during the plating process and the discoloration of the wiring during the heating process lead to a decrease in product yield. Hereinafter, the characteristic that can suppress the penetration of the plating solution during the plating process may be referred to as "plating solution resistance." Similarly, the characteristic that can suppress the discoloration of the wiring during the heating process may be referred to as "wiring discoloration resistance."

[0008] The present invention has been made in view of these problems, and its objective is to provide a method for manufacturing a flexible printed circuit board that is excellent in resistance to plating solutions and resistance to discoloration of wiring. [Means for solving the problem]

[0009] A method for manufacturing a flexible printed circuit board according to the present invention comprises the step of 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 using a vertical lifting roll coater. The substrate is provided with 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 radical polymerizable groups in one molecule. When applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is applied simultaneously to both sides of the substrate.

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

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

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

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

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

[0015] In the method for manufacturing a flexible printed circuit board according to an embodiment of the present invention, 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.

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

[0017] In the method for manufacturing a flexible printed circuit board according to an 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 an embodiment of the present invention, the vertical lifting type roll coater includes a pair of coating rolls, and the roll diameter of the coating roll is 70 mm or more and 150 mm or less.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a method for manufacturing a flexible printed circuit board that has excellent resistance to plating solutions and resistance to discoloration of wiring. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view of a key part illustrating an example of a method for manufacturing a flexible printed circuit board according to the present invention. [Figure 2] This is another cross-sectional view illustrating an example of a method for manufacturing a flexible printed circuit board according to the present invention. [Figure 3] This is another cross-sectional view illustrating an example of a method for manufacturing a flexible printed circuit board according to the present invention. [Figure 4] This is another cross-sectional view illustrating an example of a method for manufacturing a flexible printed circuit board according to the present invention. [Figure 5] This is another cross-sectional view illustrating an example of a method for manufacturing a flexible printed circuit board according to the present invention. [Figure 6] This is a cross-sectional view of a coating roll used in an example of a flexible printed circuit board manufacturing method according to the present invention, when cut along a plane containing its axis. [Modes for carrying out the invention]

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

[0022] First, let's explain the terms used in this specification. "Roll coater" refers to a coating device having a pair of rotatable coating rolls. There are two coating methods for roll coaters: the vertical lifting type, which coats the substrate with a liquid photosensitive resin composition while lifting the substrate vertically, and the horizontal transport type, which coats the substrate with a liquid photosensitive resin composition while transporting the substrate horizontally. Compared to the horizontal transport type roll coater, the vertical lifting type roll coater allows for a simpler and more space-saving coating device. Furthermore, because the substrate coated with the liquid photosensitive resin composition can be dried while suspended, the vertical lifting type roll coater can suppress the adhesion of foreign matter during the drying process of the coating film made of the liquid photosensitive resin composition (hereinafter sometimes simply referred to as "coating film").

[0023] A "photoradical polymerization initiator" refers to a compound that generates radicals as active species upon light irradiation. An "epoxy compound" refers to a compound that has one or more epoxy groups in one molecule. A "polyfunctional epoxy compound" refers to an epoxy compound that has two or more epoxy groups in one molecule. An "epoxy curing accelerator" refers to a compound that promotes the crosslinking and chain extension reactions of epoxy compounds.

[0024] The "thickness" of the film-like support is the arithmetic mean of 10 measurements obtained by randomly selecting 10 measurement points from electron microscope images of cross-sections obtained by cutting the film-like support in the thickness direction and measuring the thickness of those 10 selected measurement points. The "thickness" of the wiring is the arithmetic mean of 10 measurements obtained by randomly selecting 10 measurement points from electron microscope images of cross-sections obtained by cutting the wiring in the thickness direction and measuring the thickness of those 10 selected measurement points.

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

[0026] Hereinafter, the compound name may be followed by "system" to refer to the compound and its derivatives collectively. When "system" is followed by a compound name to represent a polymer name, it means that the repeating unit of the polymer originates 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 group and methacryloyl group may be collectively referred to as "(meth)acryloyl group." Unless otherwise specified, the components and functional groups exemplified herein may be used individually or in combination of two or more.

[0027] The diagrams referenced in the following explanation are schematic representations of each component for ease of understanding, and the size, number, shape, etc., of each component shown may differ from the actual dimensions due to the limitations of drawing creation. Furthermore, for the sake of explanation, components identical to those described earlier may be denoted by the same reference numerals in later diagrams, and their explanations may be omitted.

[0028] <Manufacturing method for flexible printed circuit boards> The method for manufacturing a flexible printed circuit board according to this embodiment comprises a step of 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 using a vertical lifting roll coater. Holes are provided in the substrate. 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. When applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is applied to both sides of the substrate simultaneously.

[0029] In the manufacturing method of a flexible printed circuit board according to this embodiment, when applying the liquid photosensitive resin composition, the liquid photosensitive resin composition is applied simultaneously 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 this embodiment, a method for manufacturing a flexible printed circuit board with 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 radical polymerizable compound having three or more radical polymerizable groups in one molecule. As a result, the crosslinking density of the cured film (hereinafter sometimes simply referred to as "cured film of 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, according to this embodiment, it is possible to suppress the penetration of the plating solution between the cured film and the substrate during the plating process, and to suppress the permeation of oxygen, which causes discoloration of 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, roll pressure can be uniformly transmitted to the substrate, making it easier to obtain a cured film with uniform thickness. For these reasons, according to this embodiment, it is possible to manufacture a flexible printed circuit board with excellent resistance to plating solutions and resistance to wiring discoloration.

[0032] In this 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 radical polymerizable compound having 3 to 6 radical polymerizable groups in one molecule.

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

[0034] In this embodiment, in order to suppress the occurrence of defects in the 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 defects in the appearance of the coating film (specifically, pinholes, uneven coating of the coating film covering the wiring, groove marks from 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 defects in the 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 embedding properties while ensuring electrical conductivity between wirings provided on both sides of the film-like support, the diameter of the holes (opening diameter) provided in the substrate 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 this embodiment, in order to obtain a flexible printed circuit board that ensures the flexibility of the resulting cured film, suppresses the occurrence of defects in the appearance of the coating film and the substrate on which the coating film is formed, and has excellent resistance to plating solutions and resistance to discoloration of wiring, it is preferable to satisfy the following condition 1, more preferably the following condition 2, and even more preferably the following condition 3. Condition 1: The liquid photosensitive resin composition contains a radical polymerizable compound having 3 to 6 radical polymerizable groups in one molecule, and the width and height of the film-like support are both 200 mm to 600 mm. Condition 2: The above condition 1 is met, and the thickness of the film-like support is 8.0 μm or more and 50.0 μm or less. Condition 3: The above condition 2 is met, and the thickness of the wiring is 8 μm or more and 50 μm or less.

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

[0039] In the coating process of this embodiment, first, the substrate 11 suspended by the suspension jig 10 is transferred from the upstream side of the manufacturing process to the upper side of a pair of coating rolls 12a and 12b (Figure 1). In Figure 1, coating roll 12a is a coating roll located on the upstream side of the manufacturing process, and coating roll 12b is a coating roll located on the downstream side of the manufacturing process. Preferably, both coating rolls 12a and 12b have a roll diameter of 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) of the wiring 14 is, for example, 10 μm or more and 200 μm or less.

[0041] In the state shown in Figure 1, a gap sufficient to allow the substrate 11 to pass through is provided between the coating roll 12a and the coating roll 12b. The coating roll 12a is in contact with the doctor bar 16a on the upstream side of the manufacturing process, and is subjected to a predetermined pressure (for example, 0.5 kgf / cm²) from the doctor bar 16a. 2 The above is 3.0 kgf / cm². 2 The following pressure is applied: The coating 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 / cm²) is applied from the doctor bar 16b. 2 The above is 3.0 kgf / cm². 2 The following is applied:

[0042] Furthermore, the coating rolls 12a and 12b are each rotating at a predetermined rotational speed (for example, 1 m / min or more and 10 m / min or less). The liquid photosensitive resin composition 17 is stored between the coating roll 12a and the doctor bar 16a, and between the coating roll 12b and the doctor bar 16b. The liquid photosensitive resin composition 17 is transferred to the surface of the coating roll 12a and the surface of the coating roll 12b.

[0043] From the state shown in Figure 1, the suspension jig 10 descends, and the suspended substrate 11 is moved through the space between the coating rolls 12a and 12b until the upper end of the substrate 11 is positioned between the coating rolls 12a and 12b (see Figure 2). Then, as shown in Figure 2, the suspension jig 10 releases the substrate 11, and the fixing jig 18 grasps the lower end of the substrate 11.

[0044] Next, the rotating coating rolls 12a and 12b press down on the substrate 11, applying pressure to it, while the fixing jig 18 releases the lower end of the substrate 11 (Figure 3). As the substrate 11 is released from the fixing jig 18, the coating rolls 12a and 12b are still rotating, so the liquid photosensitive resin composition 17 is applied to both sides of the substrate 11 simultaneously, while the substrate 11 is lifted upward. In the state shown in Figure 3, the amount of pressure applied by the coating 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 is lifted upward while the liquid photosensitive resin composition 17 is applied to both sides simultaneously, is grasped by the suspension jig 10 (Figure 4). When the substrate 11 is lifted, the liquid photosensitive resin composition 17 is embedded in the holes 15 provided 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. In order to obtain a flexible printed circuit board with superior resistance to plating solutions and resistance to discoloration of wiring, it is preferable to adjust the composition of the liquid photosensitive resin composition 17 and the coating conditions so that the thickness around the holes 15 in the cured film (cured film) of the coating film 19 is 10 μm or more. Furthermore, by grasping the upper end of the substrate 11 with the suspension jig 10 while the suspension jig 10 is as close as possible to the coating rolls 12a and 12b, it is possible to prevent the substrate 11 from getting tangled in the coating rolls 12a or 12b.

[0046] Next, the substrate 11, with the coating 19 formed on both sides, is suspended by a suspension jig 10 and transported to the downstream side of the manufacturing process (Figure 5). The substrate 11 that has been transported to the downstream side of the manufacturing process is then placed in a drying oven (not shown) and dried. For example, the substrate 11 is transported to the drying oven while suspended. The substrate 11 is dried as it passes through the inside of the drying oven.

[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. Since 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 tossed around by the circulation of hot air inside the drying oven, making them more likely to stick together. Therefore, when drying multiple substrates 11 simultaneously, it is preferable to make the distance between the substrates 11 greater than the vertical width of the substrates 11.

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

[0050] Next, an example of coating rolls 12a and 12b will be described. Figure 6 is a cross-sectional view of a coating roll 100, which is an example of coating rolls 12a and 12b, when cut in a plane containing its axis. The coating roll 100 shown in Figure 6 has a metal core 110 with a cylindrical hollow section and a surface roll 120 arranged on the outer circumferential surface of the core 110.

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

[0052] Furthermore, the surface roll 120 has multiple ring-shaped grooves 120a. Each of the multiple ring-shaped grooves 120a is independent of the others. The cross-sectional shape of the ring-shaped grooves 120a is not particularly limited, and shapes such as V-shape and U-shape can be adopted. In order to further suppress defects in the appearance of the coating film 19 (see Figure 5) and the substrate 11 (see Figure 5) on which the coating film 19 is formed, it is preferable that the cross-sectional shape of the ring-shaped grooves 120a is 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. Although the coating roll 100 shown in Figure 6 has multiple independent ring-shaped grooves 120a, the coating rolls that can be used in the present invention are not limited to this, and a coating roll with a single helical 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 each of the pair of coating rolls is a coating roll that has multiple independent ring-shaped grooves.

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

[0054] The roll diameter D of the coating 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 accumulation of the liquid photosensitive resin composition 17 between the coating roll 100 and the substrate 11 (liquid pooling) tends to be less likely to occur. Therefore, by setting the roll diameter D to 70 mm or more, the occurrence of groove marks and streaks from the coating roll 100 in the coating film 19 tends to be suppressed. In addition, by setting the roll diameter D to 150 mm or less, damage to the substrate 11 (specifically, tearing, etc.) caused by the pressure of the coating roll 100 can be suppressed when applying the liquid photosensitive resin composition 17 to the substrate 11.

[0055] Next, the elements of the manufacturing method for the 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 also contain additives other than polymers, such as fillers. However, in order to obtain a film-like support with excellent flexibility, the polymer content in the film-like support is preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and may be 100% by weight, based on the total amount of the film-like support.

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

[0058] [hole] While there are no particular limitations on the holes provided in the substrate, from the viewpoint of hole shape stability and interlayer connection reliability, it is preferable to form holes 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, UV laser, YAG laser, excimer laser, etc.) or an NC drilling machine, and then perform a cleaning treatment (desmear treatment) and carbon treatment inside the holes, followed by a copper plating treatment (electroless copper plating treatment, electrolytic copper plating treatment, etc.).

[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 radical polymerizable compound having three or more radical polymerizable groups in one molecule (hereinafter sometimes referred to as "component (E)"). The liquid photosensitive resin composition may also contain, as optional components, particles with an average particle size of 0.01 μm or more and 100 μm or less (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 later.

[0060] {(A) component} For 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 method for measuring the weight-average molecular weight in terms of polyethylene glycol is the same as or similar to the method used in the examples described later. 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, and then cooled to 25°C and left 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. Furthermore, by setting the weight-average molecular weight of component (A) to 1,000,000 or less, it is possible to suppress the viscosity of the liquid photosensitive resin composition from becoming excessively high.

[0062] (A) Specific examples of component include polyurethane resins, (meth)acrylic resins, polyvinyl resins, polystyrene resins, polyethylene resins, polypropylene resins, polyimide resins, polyamide resins, polyacetal resins, polycarbonate resins, polyester resins, polyphenylene ether resins, polyphenylene sulfide resins, polyethersulfone resins, polyetheretherketone resins, etc., which can be used individually or in combination of two or more types.

[0063] In particular, it is preferable to use 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 carboxyl group in one molecule as component (A).

[0064] When a polymer containing a urethane bond in one molecule is used as component (A), the low rebound and bending resistance of the resulting cured film tend to improve, and the curing of the cured film tends to decrease. Furthermore, when a polymer containing an imide group in one molecule is used as component (A), the heat resistance, flame retardancy, and electrical insulation reliability of the resulting cured film tend to improve. Furthermore, when a polymer containing a (meth)acryloyl group in one molecule is used as component (A), the photosensitivity of the liquid photosensitive resin composition tends to improve, and the chemical resistance of the resulting cured film tends to improve. Furthermore, when a polymer containing a carboxyl group in one molecule is used as component (A), the alkali developability of the liquid photosensitive resin composition tends to improve, and the adhesion between the resulting cured film and the substrate tends to improve.

[0065] Furthermore, component (A) may be a polymer having multiple functional groups in one molecule. For example, if a polymer having a urethane bond and an imide group in one molecule is used as component (A), the low resilience, flexure resistance, heat resistance, flame retardancy, and electrical insulation reliability of the resulting cured film are improved, and the curing of the cured film tends to be reduced. Also, if a polymer having a urethane bond, a carboxyl group, and a (meth)acryloyl group in one molecule is used as component (A), the photosensitivity and alkali developability of the liquid photosensitive resin composition, the low resilience, flexure resistance, and chemical resistance of the resulting cured film, and the adhesion between the resulting cured film and the substrate are improved, and the curing 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 carboxyl group, and a (meth)acryloyl group.

[0066] (A polymer containing urethane bonds in one molecule) A polymer having a urethane bond in one molecule means a polymer having at least one urethane bond in one molecule. Examples of polymers having a urethane bond in one molecule include polymers having repeating units represented by the general formula (3) below, which are reaction products of a diol compound represented by the general formula (1) below and a diisocyanate compound represented by the general formula (2) below.

[0067] [ka]

[0068] [ka]

[0069] [ka]

[0070] In general formulas (1), (2), and (3), R 1 and X 1Each of these independently represents a divalent organic group.

[0071] Examples of diol compounds represented by general formula (1) include alkylenediols 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, tetramethylene glycol, and neopentyl glycol. Examples include polyoxyalkylenediols such as random copolymers of polyoxyalkylene diols; polyester diols obtained by reacting polyhydric alcohols with polybasic acids; polycarbonate diols having a carbonate skeleton; polycaprolactone diols obtained by ring-opening addition reactions of lactones such as γ-butyrolactone, ε-caprolactone, and 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. These can be used individually or in combination of two or more types.

[0072] In order to obtain a liquid photosensitive resin composition with excellent roll pressure dispersion during coating, and to improve the low rebound and flexure resistance of the resulting cured film, long-chain diols such as polyoxyalkylenediol, polyester diol, polycarbonate diol, and polycaprolactone diol are preferred as the diol compound represented by general formula (1).

[0073] Examples of diisocyanate compounds 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, diphenyl ether-4 Examples include aromatic diisocyanate compounds such as ,4'-diisocyanate, benzophenone-4,4'-diisocyanate, diphenylsulfone-4,4'-diisocyanate, torylene-2,4-diisocyanate, torylene-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, and hydrogenated xylylene diisocyanate; alicyclic diisocyanate compounds such as isophorone diisocyanate and norbornene diisocyanate; and aliphatic diisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and lysine diisocyanate. These can be used individually or in combination of two or more types.

[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 a diisocyanate compound represented by general formula (2), a liquid photosensitive resin composition with excellent photosensitivity can be obtained.

[0075] When synthesizing a polymer having a urethane bond in one molecule, it is preferable to blend the diol compound and the diisocyanate compound such that the ratio of hydroxyl groups to isocyanate groups is between 0.5 and 2.0.

[0076] Furthermore, when using two or more diol compounds, the reaction with the diisocyanate compound may be carried out after mixing the two or more 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 reaction product may be further reacted with another diisocyanate compound. The same applies when using two or more diisocyanate compounds. In this way, a desired polymer having a urethane bond in one molecule can be synthesized.

[0077] The reaction temperature between the diol compound and the diisocyanate compound is preferably 40°C to 160°C, and more preferably 60°C to 150°C, 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 amount of starting material and the reaction conditions adopted. In addition, if necessary, the reaction may be carried out in the presence of catalysts such as compounds containing metals or metalloids such as alkali metals, alkaline earth metals, tin, zinc, titanium, and cobalt; or tertiary amines.

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

[0079] In order to enhance the reactivity of the polymerization reaction, the amount of the 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, the weight concentration of the solute in the reaction solution is 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, for example, by conducting a polymerization reaction using, as monomers, one or more 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)") in addition to a diol compound and a diisocyanate compound.

[0081] [Chemical formula]

[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] [Chemical formula]

[0084] In general formula (5), n represents an integer of 1 or more and 3 or less, 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, which can be used individually 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, which can be used individually or in combination of two or more.

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

[0088] [ka]

[0089] In general formula (6), R 4 This 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, 3,5-dihydroxybenzoic acid, etc., which can be used individually or in combination of two or more.

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

[0092] Polymers having urethane bonds and imide groups in a single molecule can be obtained, for example, by carrying out a polymerization reaction using tetracarboxylic dianhydride as a monomer in addition to diol compounds and diisocyanate compounds.

[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 Examples include (3,4-dicarboxyphenyl)fluorene dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic acid anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, which can be used individually or in combination of two or more.

[0094] (A polymer containing an imide group in one molecule) A 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 polymers having a urethane bond and an imide group in one molecule as described above. In addition, polymers having an imide group in one molecule can also be obtained by reacting a tetracarboxylic dianhydride (more specifically, the compounds listed as tetracarboxylic dianhydrides for synthesizing the polymers having a urethane bond and an imide group in one molecule as described above) with a diamine.

[0095] Examples of diamines used as raw materials for obtaining 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, and N,N' Examples include -bis(4-aminophenyl)terephthalamide, 4,4'-diaminodiphenylsulfone, 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, etc., which can be used individually or in combination of two or more.

[0096] The method for reacting the tetracarboxylic anhydride with the diamine is not particularly limited, but examples include the methods shown in methods 1 to 3 below.

[0097] Method 1: A polyamic acid solution is prepared by adding a diamine to a solution in which tetracarboxylic dianhydride is dispersed or dissolved in an organic solvent and reacting the mixture. Preferably, the total amount of diamine added is adjusted to a ratio of 0.50 moles to 1.50 moles per mole of tetracarboxylic dianhydride. After the reaction between tetracarboxylic dianhydride and 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 imidation.

[0098] Method 2: Prepare a polyamic acid solution using the same method as in Method 1 above. Add an imidation catalyst (preferably a tertiary amine such as pyridine, picoline, isoquinoline, trimethylamine, triethylamine, or tributylamine) and a dehydrating agent (such as acetic anhydride) to the prepared polyamic acid solution, and heat to 60°C or higher and 180°C or lower to carry out imidation.

[0099] Method 3: Prepare a polyamic acid solution using the same method as in Method 1 above. Place the prepared polyamic acid solution in a vacuum oven set to 100°C or higher and 250°C or lower, and heat under reduced pressure to perform imidation.

[0100] (A polymer containing a (meth)acryloyl group in one molecule) A 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 polymers having a urethane bond and a (meth)acryloyl group in one molecule, as mentioned above. Alternatively, a polymer having a (meth)acryloyl group in one molecule can be obtained by reacting an epoxy resin with (meth)acrylic acid, for example.

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

[0102] Specific examples of bisphenol A type epoxy resins include the product names jER(registered trademark) 828, jER(registered trademark) 1001, and jER(registered trademark) 1002 from Mitsubishi Chemical Corporation; the product names Adeka Resin(registered trademark) EP-4100E and Adeka Resin(registered trademark) EP-4300E from ADEKA Corporation; the product names RE-310S and RE-410S from Nippon Kayaku Co., Ltd.; the product names Epiclon 840S, Epiclon 850S, Epiclon 1050, and Epiclon 7050 from DIC Corporation; and the product names Epotote(registered trademark) YD-115, Epotote(registered trademark) YD-127, and Epotote(registered trademark) YD-128 from Nippon Steel Epoxy Manufacturing Co., Ltd.

[0103] Specific examples of bisphenol F type epoxy resins include the product names jER(registered trademark) 806 and jER(registered trademark) 807 from Mitsubishi Chemical Corporation, Adeka Resin(registered trademark) EP-4901E, Adeka Resin(registered trademark) EP-4930, and Adeka Resin(registered trademark) EP-4950 from ADEKA Corporation, RE-303S, RE-304S, RE-403S, and RE-404S from Nippon Kayaku Co., Ltd., Epiclon 830 and Epiclon 835 from DIC Corporation, and Epotote(registered trademark) YDF-170, Epotote(registered trademark) YDF-175S, and Epotote(registered trademark) YDF-2001 from Nippon Steel Epoxy Manufacturing Co., Ltd.

[0104] Specific examples of bisphenol S type epoxy resins include Epiclon EXA-1514, manufactured by DIC Corporation.

[0105] Specific examples of hydrogenated bisphenol A type epoxy resins include the product names jER(registered trademark) YX8000, jER(registered trademark) YX8034, and jER(registered trademark) YL7170 from Mitsubishi Chemical Corporation; ADEKA Corporation's product name Adeka Resin(registered trademark) EP-4080E; DIC Corporation's product name Epiclon EXA-7015; and Nippon Steel Epoxy Manufacturing Co., Ltd.'s product names Epotote(registered trademark) YD-3000 and Epotote(registered trademark) YD-4000D.

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

[0107] Specific examples of phenoxy epoxy resins include the product names jER(registered trademark) 1256, jER(registered trademark) 4250, and jER(registered trademark) 4275, all manufactured by Mitsubishi Chemical Corporation.

[0108] Specific examples of naphthalene-type epoxy resins include DIC Corporation's product names Epiclon HP-4032, Epiclon HP-4700, and Epiclon HP-4200, and Nippon Kayaku Co., Ltd.'s product name NC-7000L.

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

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

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

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

[0113] Specific examples of amine-type epoxy resins include the product names jER(registered trademark) 604 and jER(registered trademark) 630 from Mitsubishi Chemical Corporation, the product names Epotote(registered trademark) YH-434 and Epotote(registered trademark) YH-434L from Nippon Steel Epoxy Manufacturing Co., Ltd., and the product names TETRAD(registered trademark)-X and TERRAD(registered trademark)-C from Mitsubishi Gas Chemical Company.

[0114] Specific examples of flexible epoxy resins include the product names jER(registered trademark)871, jER(registered trademark)872, jER(registered trademark)YL7175, and jER(registered trademark)YL7217 from Mitsubishi Chemical Corporation, and the product name Epiclon EXA-4850 from DIC Corporation.

[0115] Specific examples of urethane-modified epoxy resins include ADEKA Corporation's product names ADEKA Resin® EPU-6, ADEKA Resin® EPU-73, and ADEKA Resin® EPU-78-11.

[0116] Specific examples of rubber-modified epoxy resins include ADEKA Corporation's product names ADEKA Resin® EPR-4023, ADEKA Resin® EPR-4026, and ADEKA Resin® EPR-1309.

[0117] Specific examples of chelate-modified epoxy resins include ADEKA's product names ADEKA Resin® EP-49-10 and ADEKA Resin® EP-49-20.

[0118] Specific examples of heterocyclic epoxy resins include TEPIC (registered trademark), manufactured by Nissan Chemical Corporation.

[0119] The method for reacting epoxy resin with (meth)acrylic acid is not particularly limited, but for example, one method involves adding (meth)acrylic acid and an esterification catalyst (e.g., tertiary amines such as trimethylamine and triethylamine; phosphorus compounds such as triphenylphosphine; imidazole compounds such as 2-ethyl-4-methylimidazole) to a solution in which the epoxy resin has been dispersed or dissolved in an organic solvent, and then heating the mixture to a temperature of 40°C to 120°C to carry out the reaction. It is preferable to adjust the total amount of (meth)acrylic acid added to a ratio of 0.1 moles to 1.0 mole per mole of epoxy groups in the epoxy resin.

[0120] (A polymer containing a carboxyl group in one molecule) A polymer having a carboxyl group in one molecule means a polymer having at least one carboxyl group in one molecule. Examples of polymers having a carboxyl group in one molecule include the polymers having a urethane bond and a carboxyl group in one molecule, as mentioned above. Alternatively, a polymer having a carboxyl group in one molecule can be obtained by reacting an epoxy resin with (meth)acrylic acid and then further reacting it with a polybasic acid anhydride.

[0121] One method for obtaining a polymer having a carboxyl group in one molecule by reacting an epoxy resin with (meth)acrylic acid and then further reacting it with a polybasic acid anhydride is to react the epoxy resin with (meth)acrylic acid in the manner described above, then add the polybasic acid anhydride and heat the mixture to a temperature of 60°C to 150°C. The total amount of polybasic acid anhydride added is preferably adjusted so that the acid value of the resulting solid content is between 10 mg KOH / g and 160 mg KOH / g.

[0122] In addition to the methods described above, polymers having a carboxyl group in one molecule can also be obtained by reacting (meth)acrylic acid with (meth)acrylic acid esters. The method for reacting (meth)acrylic acid with (meth)acrylic acid esters is not particularly limited, but one example is a method in which (meth)acrylic acid and (meth)acrylic acid esters 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 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 individually 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, it is preferable to use one or more (meth)acrylic acid esters selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and benzyl (meth)acrylate.

[0124] Examples of radical polymerization initiators 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. These can be used individually or in combination of two or more.

[0125] In order to enhance the reactivity of the polymerization reaction while suppressing a decrease in the molecular weight of the resulting polymer, it is preferable that the amount of radical polymerization initiator used be 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, per 100 parts by weight of monomer used.

[0126] To enhance the reactivity of the polymerization reaction, it is preferable that the amount of solvent used in the radical polymerization reaction is such that the weight concentration of the solute in the reaction solution, i.e., the solution concentration, is between 5% and 90% by weight. More preferably, the weight concentration of the solute in the reaction solution is between 20% and 70% by weight.

[0127] The reaction temperature for the radical polymerization reaction described above is preferably 20°C to 120°C, and more preferably 50°C to 100°C, from the viewpoint of shortening the reaction time and suppressing gelation. The reaction time for the radical polymerization reaction described above can be appropriately selected depending on the amount of starting material and the reaction conditions adopted.

[0128] In order to suppress the occurrence of defects in the appearance of the coating film and defects in the appearance of 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] {(B) component} (B) The components are not particularly limited, but include, for example, Michla'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-hydroxycyclohexylphenyl ketone, diacetylbenzyl, benzyldimethylketal, benzyldiethylketal, 4,4'-diazidochalcone, 2,2 Examples include dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-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, etc., which can be used individually or in combination of two or more.

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

[0131] {(C) component} Component (C) is not particularly limited as long as it is an epoxy compound having two or more epoxy groups in one molecule, but for example, those listed as specific examples of "epoxy resins used 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 of component (C). However, if a polymer with an acid value of 10 mg KOH / g or more (preferably a polymer with an acid value of 10 mg KOH / g or more and 160 mg KOH / g or less) is used as component (A), the curing agent of component (C) does not need to be incorporated into the liquid photosensitive resin composition. The acid value of component (A) can be adjusted, for example, by changing the amount of monomer having one or more groups selected from the group consisting of carboxyl groups and carboxylic acid anhydride groups when synthesizing component (A).

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

[0134] {(D) component} (D) The component is not particularly limited, but examples 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-undeceniumtetraphenylborate; 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; 2-methyl Examples include imidazoline compounds such as ruimidazoline, 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, which can be used individually or in combination of two or more.

[0135] To obtain a flexible printed circuit board with superior resistance to plating solutions and wiring discoloration, an amine-based compound is preferred as component (D), and melamine is more preferred.

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

[0137] {(E) component} Component (E) is incorporated into the liquid photosensitive resin composition as a photopolymerizable component. Component (E) is not particularly limited as long as it is a radical polymerizable compound having three or more radical polymerizable groups (functional groups that undergo polymerization reactions by radical polymerization initiators) per molecule. However, in order to obtain a flexible printed circuit board that ensures the flexibility of the cured film while exhibiting excellent resistance to plating solutions and wiring discoloration, component (E) is preferably a radical polymerizable compound having three to six radical polymerizable groups per molecule. Furthermore, component (E) is preferably a compound with a molecular weight (weight-average molecular weight in the case of a polymer) of less than 1,000. Examples of radical polymerizable groups in component (E) include groups having unsaturated double bonds. To enhance radical polymerizability, (meth)acryloyl groups or vinyl groups are preferred as radical polymerizable groups.

[0138] Specific examples of component (E) include trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol hexaacrylate, tetramethylolpropane tetraacrylate, trimethylolpropane trimethacrylate, pentaerythritol trimethacrylate, dipentaerythritol hexamethacrylate, tetramethylolpropane tetramethacrylate, tetramethylolmethane triacrylate, tetramethylolmethane tetraacrylate, isocyanurate tri(ethaneacrylate), pentasritol tetraacrylate, ditrimethylolpropane tetraacrylate, caprolactone-modified dipentaerythritol hexaacrylate, ethoxylated dipentaerythritol hexaacrylate, isocyanurate trialyl, 1,3,5-triacryloylhexahydro-s-triazine, etc., which can be used alone or in combination of two or more.

[0139] To obtain a flexible printed circuit board with superior resistance to plating solutions and wiring discoloration, the content of component (E) is preferably 1% by weight or more and 10% by weight or less, and more preferably 3% by weight or more and 8% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0140] {(F) component} Component (F) is not particularly limited as long as it consists of particles with an average particle diameter of 0.01 μm or more and 100 μm or less. For example, one or more particles selected from the group consisting of inorganic particles and organic particles can be used. By incorporating 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 resolution of the liquid photosensitive resin composition while also improving the flexibility and chemical resistance of the resulting cured film, 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] (F) Specific examples of component 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 cross-linked polymers. These can be used individually or in combination of two or more types.

[0143] As inorganic particles, silica particles are preferred from the viewpoint of suppressing curing shrinkage of the resulting cured film while improving 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 for the organic particles, cross-linked polymer particles are preferred from the viewpoint of improving the dispersibility of the roll pressure during coating while also improving the flexibility and chemical resistance of the resulting cured film, and cross-linked polymer particles with an average particle diameter of 1 μm or more and 10 μm or less are more preferred. Specific examples of cross-linked polymer particles include the product names Daimic Beads (registered trademark) UCN-8070CM Clear, UCN-8150CM Clear, UCN-5070D Clear, and UCN-5150D Clear manufactured by Dainichi Seika Kogyo Co., Ltd., and Art Pearl (registered trademark) C-100 Transparent, C-200 Transparent, C-300 Transparent, C-300WA, C-400 Transparent, C-400WA, C-600 Transparent, C-800 Transparent, C-800WA, C-1000T, P-400T, P-800T, U-600T, CF-600T, JB-400T, JB-800T, CE-400T, CE-800T, and MM-120T manufactured by Negami Kogyo Co., Ltd. These can be used individually or in combination of two or more types.

[0145] To further enhance the flexibility of the resulting cured film, it is preferable to use polyurethane particles as component (F). Furthermore, to improve the dispersion of roll pressure during coating while further enhancing the flexibility of the resulting cured film, it is preferable to use cross-linked polyurethane particles, which are cross-linked polymer particles, as component (F).

[0146] In order to further suppress the occurrence of defects in the appearance of the coating film and defects in the appearance of 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] {(G) component} Component (G) is 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, these organic solvents can be used in combination with aromatic hydrocarbons (more specifically, xylene, toluene, etc.) as needed.

[0148] Furthermore, as component (G), 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, 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, pr Acetate solvents such as propylene glycol diacetate and 1,3-butylene glycol diacetate; ether 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 component (G) is preferably 10% to 80% by weight, and more preferably 20% to 70% by weight, based on the total amount of the liquid photosensitive resin composition.

[0150] {Other components} The liquid photosensitive resin composition may optionally contain other components (components different from components (A) to (G)), such as radical polymerizable compounds having two radical polymerizable groups per molecule, flame retardants, defoamers, leveling agents, colorants, adhesive aids, polymerization inhibitors, and other additives. The total content of the other components is preferably 20% by weight or less, and more preferably 10% by weight or less, based on the total amount of the liquid photosensitive resin composition.

[0151] As a radical polymerizable compound having two radical polymerizable groups in one molecule (hereinafter sometimes referred to as "specific radical polymerizable compound"), compounds with a molecular weight (or weight-average molecular weight in the case of polymers) of less than 1,000 are preferred. Examples of radical polymerizable groups in a specific radical polymerizable compound include groups having an unsaturated double bond. To enhance radical polymerizability, (meth)acryloyl groups or vinyl groups are preferred as radical polymerizable groups.

[0152] The following are specific examples of radical polymerizable compounds. In the following, ethylene oxide will be abbreviated as "EO," and the average number of moles of EO added will be denoted as "n." Specific examples of radical polymerizable compounds include EO-modified bisphenol F diacrylate (n: 2 to 50), EO-modified bisphenol A diacrylate (n: 2 to 50), EO-modified bisphenol S diacrylate (n: 2 to 50), EO-modified bisphenol F dimethacrylate (n: 2 to 50), EO-modified bisphenol A dimethacrylate (n: 2 to 50), EO-modified bisphenol S dimethacrylate (n: 2 to 50), 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, and diethylene glycol dimethacrylate. Examples 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, diallyl terephthalate, etc., which can be used individually or in combination of two or more.

[0153] To obtain a flexible printed circuit board with superior resistance to plating solutions and wiring discoloration, it is preferable to use one or more compounds selected from the group consisting of EO-modified bisphenol F diacrylate (n: 2 to 50), EO-modified bisphenol A diacrylate (n: 2 to 50), EO-modified bisphenol S diacrylate (n: 2 to 50), EO-modified bisphenol F dimethacrylate (n: 2 to 50), EO-modified bisphenol A dimethacrylate (n: 2 to 50), and EO-modified bisphenol S dimethacrylate (n: 2 to 50) as the specific radical polymerizable compound.

[0154] To obtain a flexible printed circuit board with superior resistance to plating solutions and wiring discoloration, it is preferable that the content of the specific radical polymerizable compound is 1% by weight or more and 10% by weight or less of the total amount of the liquid photosensitive resin composition.

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

[0156] Halogenated flame retardants are compounds that contain at least one halogen atom in a single molecule and suppress the combustion of organic matter. Examples of halogenated flame retardants include bromine-based compounds and chlorine-based compounds, which can be used individually or in combination of two or more types.

[0157] Phosphorus-based flame retardants refer to compounds that contain at least one phosphorus atom in one molecule and suppress the combustion of organic matter. Examples of phosphorus-based flame retardants include red phosphorus, condensed phosphate ester compounds, cyclic organophosphorus compounds, phosphazene compounds, phosphorus-containing polyol compounds, phosphorus-containing amine compounds, ammonium polyphosphate, melamine phosphates, phosphinates, etc. These can be used individually or in combination of two or more types.

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

[0159] Antimony-based flame retardants are compounds that contain at least one antimony atom in each molecule and suppress the combustion of organic matter. An example of an antimony-based flame retardant is antimony trioxide.

[0160] Examples of defoaming agents include acrylic compounds, vinyl compounds, and butadiene compounds.

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

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

[0163] Examples of adhesion aids (also called adhesion modifiers) include silane coupling agents, triazole compounds, tetrazole compounds, and triazine compounds.

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

[0165] [Method for preparing a liquid photosensitive resin composition] A liquid photosensitive resin composition can be prepared by grinding, dispersing, and mixing the above components (A) to (E) and any optional components used as needed (components (F), (G), and the above-mentioned other components). The grinding and dispersion method is not particularly limited, but examples include using a kneading device such as a bead mill, ball mill, or 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, all steps except the step of applying the liquid photosensitive resin composition are optional, including the step of drying the substrate as described above (drying step). Optional steps other than the drying step include, for example, the following micro-aperture formation step, curing step, gold plating step, hot pressing step, and baking step.

[0167] (Fine opening formation process) After the drying process, the coating film is irradiated with active energy rays (more specifically, ultraviolet light, visible light, electron beams, etc.) through a negative-type photomask to expose a portion of the coating film. This causes photoradical polymerization-capable components to polymerize in the exposed areas of the coating film. Next, the unexposed areas are washed away with a developer using a development method such as spraying, paddle work, immersion, or ultrasonic development, thereby patterning the coating film and forming micro-apertures. Note that the time required to form apertures varies depending on the spray pressure and flow rate of the development equipment and the temperature of the developer, so it is desirable to find the optimal equipment conditions as needed.

[0168] An alkaline aqueous solution is preferred as the developer. 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, as well as amine compounds. Specifically, 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, triisopropylamine, etc. Other compounds can also be used as long as the aqueous solution exhibits basic properties. 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. Furthermore, the temperature of the developer depends on the composition of the liquid photosensitive resin composition and the alkaline developer, but is generally between 0°C and 80°C, and preferably between 10°C and 60°C.

[0169] It is preferable to clean the inside of the micro-apertures formed by development to remove any unwanted residue. Examples of cleaning solutions include water and acidic aqueous solutions.

[0170] (hardening process) Next, the coating film with micro-apertures (patterned coating film) is heat-treated. By performing the heat treatment and reacting the reactive groups remaining in the molecular structure constituting the coating film (for example, the reactive groups of component (C)), a heat-resistant cured film can be obtained. The thickness of the cured film is determined considering the thickness of the wiring, etc., but it is preferably 2 μm to 50 μm. The final curing temperature in the curing process 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 to 250°C, more preferably 120°C to 200°C, and even more preferably 130°C to 180°C. The curing time at the final curing temperature is, for example, 1 minute to 120 minutes. The cured film formed by this embodiment is excellent in flexibility, flame retardancy, and electrical insulation reliability, and tends to have little warping after the curing process. Therefore, the cured film formed by this embodiment is particularly suitable as an insulating material for flexible printed circuit boards.

[0171] (Gold plating process) Next, a gold plating process is performed on the substrate on which the cured film has been formed (hereinafter sometimes referred to as the "substrate with cured film"). The gold plating process includes, for example, a degreasing process, an etching process, a catalytic process, an electroless nickel plating process, and an electroless gold plating process.

[0172] Electroless gold plating solutions usable in the electroless gold plating process include, for example, gold salts such as potassium gold cyanide, potassium gold dicyanide, and sodium gold sulfite; buffering agents such as organic acid salts, sulfates, boric acid, phosphates, and sulfamic acid; metal opacifiers such as ethylenediaminetetraacetic acid, N'-(2-hydroxyethyl)ethylenediamine-N,N,N'-triacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, and triethylenetetraminehexaacetic acid; and crystal modifiers such as cobalt, nickel, silver, iron, palladium, copper, thallium, lead, and arsenic. Examples of such electroless gold plating solutions include the following products manufactured by Okuno Pharmaceutical Co., Ltd.: Flash Gold 2000, Flash Gold VT, Flash Gold 330, Flash Gold NC, Muden Noble AU, Self Gold OTK-IT; and the following products manufactured by Uemura Industries Co., Ltd.: 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.

[0173] (Hot pressing process) Next, the substrate with the hardened film after the gold plating process and a plate-shaped or film-shaped component (specifically, a reinforcing plate, electromagnetic wave shielding film, etc.) are laminated by heat pressing. The heat pressing method that can be used in the heat pressing process is not particularly limited, and examples include general heat pressing methods used in flexible printed circuit board processing such as multi-stage lamination heat pressing and quick pressing. In order to further suppress discoloration of the wiring, the heat pressing temperature in the heat pressing process is preferably 120°C to 200°C, and more preferably 150°C to 180°C. The heat pressing time in the heat pressing process is, for example, 30 minutes to 90 minutes.

[0174] (Baking process) Next, the laminate obtained in the hot pressing process is subjected to a baking process. Suitable baking methods include general baking methods used in flexible printed circuit board processing, such as heating methods using a box oven or tunnel oven. To further suppress discoloration of the wiring, the baking temperature in the baking process is preferably between 120°C and 200°C, and more preferably between 140°C and 180°C. The baking time in the baking process is, for example, between 60 minutes and 120 minutes. Through these steps, a flexible printed circuit board is obtained. [Examples]

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

[0176] First, we will explain the weight-average molecular weight and acid value of the binder polymers P1 to P3, which will be described later, as well as the method for measuring the solid content concentration of the resin solutions SP1 to SP3, each containing binder polymers P1 to P3.

[0177] <Method for measuring weight-average molecular weight> The weight-average molecular weights of binder polymers P1 to P3 were measured under the following conditions. • Equipment used: Tosoh Corporation's "HLC-8220GPC" • Column: Two TSKgel Super AWM-H columns (6.0mm I.D. x 15cm) manufactured by Tosoh Corporation. • Guard column: 1 x "TSKguardcolumn Super AW-H" manufactured by Tosoh Corporation • Eluent: N,N-dimethylformamide solution containing LiBr (concentration: 30 mmol / L) and H3PO4 (concentration: 20 mmol / L) ·Flow rate: 0.6mL / min Column temperature: 40°C • Detector: RI (Differential Refractometer) • RI detection conditions: Polarity (+), Response (0.5 seconds) • Sample concentration: 5 mg / mL • Standard product: PEG (polyethylene glycol)

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

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

[0180] <Preparation of resin solution> The following describes the preparation methods for resin solutions SP1 to SP3, each containing binder polymers P1 to P3 as component (A). Unless otherwise specified, the reaction (stirring) was carried out under a nitrogen atmosphere.

[0181] [Preparation of resin solution SP1 containing binder polymer P1] In a reaction vessel equipped with a stirrer, thermometer, and nitrogen inlet tube, 35.00 g of triethylene glycol dimethyl ether (hereinafter sometimes referred to as "TEGDM") as the polymerization solvent and 10.31 g (0.050 mol) of norbornene diisocyanate were charged. The contents of the vessel were heated to 80°C while stirring under a nitrogen stream to dissolve the norbornene diisocyanate in TEGDM. Next, a TEGDM solution of polycarbonate diol (Asahi Kasei Corporation's "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 TEGDM solution of polycarbonate diol was a solution 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 container, and the contents were stirred for 1 hour while heating to 190°C. Then, after the contents of the container were cooled to 80°C, 3.60 g (0.200 mol) of pure water was added to the contents of the container. Next, the contents of the container were refluxed for 5 hours while heating to 110°C to obtain a resin solution SP1 containing a binder polymer P1 having a urethane bond and an imide group in one molecule. The solid content concentration of the obtained resin solution SP1 was 53% by weight. The weight-average molecular weight and acid value of binder polymer P1 were 9,200 and 86 mgKOH / g, respectively.

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

[0183] [Preparation of resin solution SP3 containing binder polymer P3] 100.00 g of TEGDM as the polymerization solvent was placed in a reaction vessel equipped with a stirrer, thermometer, and nitrogen inlet tube, and the contents of the vessel were heated to 80°C while being stirred under a nitrogen atmosphere. Then, while maintaining the temperature of the contents of the vessel at 80°C, a mixture containing a methacrylic acid-based compound was added dropwise to the reaction vessel using a dropping funnel over a period of 3 hours. The mixture containing the methacrylic acid-based 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 pre-mixed under an atmosphere of 25°C. After the dropwise addition was complete, the contents of the vessel were heated to 90°C while being stirred. Next, the contents of the container were 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 in each molecule. The solid content concentration of the obtained resin solution SP3 was 50% by weight. 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 composition> One of the resin solutions SP1 to SP3 obtained by the preparation method described above was mixed with each of the components listed in Tables 1 to 4 below (specifically, components other than component (A)) using a stirring device equipped with a stirring blade. The resulting mixture was then passed through a three-roll mill twice, followed by degassing with a degasser to obtain the liquid photosensitive resin compositions to be used in Examples 1 to 14 and Comparative Examples 1 to 3. The average particle size of the particles in the obtained liquid photosensitive resin compositions was measured to be 10 μm or less for all of Examples 1 to 14 and Comparative Examples 1 to 3.

[0185] <Method for measuring the physical properties of a liquid photosensitive resin composition, and method for evaluating a liquid photosensitive resin composition> [Method for evaluating micro-aperture properties] Each liquid photosensitive resin composition was applied to a portion (a 200 mm x 200 mm area) of a 25 μm thick polyimide film (Kaneka Corporation's "Apical® 25NPI"). The amount of liquid photosensitive resin composition applied was adjusted so that the cured film thickness was 20 μm. The coating film was then dried at a drying temperature of 80°C for 20 minutes. Afterward, it was exposed to a total exposure of 300 mJ / cm² through a negative-type 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 was exposed to ultraviolet light under the specified conditions. Next, a 1.0 wt% sodium carbonate aqueous solution (temperature: 30°C) was used as a developer, and the exposed coating was exposed to ultraviolet light at a discharge pressure of 1.0 kgf / mm². 2 Spray development was performed for 90 seconds under the specified conditions. Next, the developed coating was washed with pure water and then 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 obtained cured film was observed with an optical microscope, and the smallest diameter of the formed holes was used as the evaluation value for microaperture properties.

[0186] [Method for measuring rebound force] First, a flexible copper-clad laminate was prepared by laminating electrolytic copper foil (thickness: 12 μm) to both sides of a polyimide film (Kaneka Corporation's "PIXIO® BP FRS-522#SW", thickness: 12.5 μm) as a film-like support. The copper foil on one side of this flexible copper-clad laminate was patterned to form a comb-shaped pattern with line width / space width = 100 μm / 100 μm on the film-like support. Next, the laminate with the comb-shaped pattern was immersed in a 10 vol% sulfuric acid aqueous solution for 1 minute, and then washed with pure water. Then, 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. Finally, the coating film made of the liquid photosensitive resin composition was dried at a drying temperature of 80°C for 20 minutes, followed by an integrated exposure of 300 mJ / cm². 2The entire surface of the coating was exposed by irradiating it with ultraviolet light under the specified conditions. Next, a 1.0 wt% sodium carbonate aqueous solution (temperature: 30°C) was used as a developer, and the exposed coating was subjected to a discharge pressure of 1.0 kgf / mm². 2 Spray development was performed for 90 seconds under the specified conditions. Next, the developed coating was washed with pure water and then heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on a comb-shaped pattern. The laminate containing the obtained cured film was then cut to a size of 15 mm wide x 200 mm long to obtain a test piece. This test piece was rolled into a loop shape with an outer circumference of 50 mm and fixed to a repulsion force measuring device (Toyo Seiki Seisakusho Co., Ltd.'s "Loop Stiffness Tester (registered trademark)"). The rolled test piece was pushed in until the shortest loop diameter was 10 mm, and the repulsion force from the rolled test piece was measured. The smaller the repulsion force, the better the cured film can be evaluated as having low repulsion properties.

[0187] [Method for evaluating solder heat resistance] Each liquid photosensitive resin composition was applied to a 35 μm thick electrolytic copper foil using a Baker applicator. The amount of liquid photosensitive resin composition applied was adjusted so that the cured film thickness was 20 μm. Next, the coating film made of the liquid photosensitive resin composition was dried at a drying temperature of 80°C for 20 minutes, followed by an integrated exposure of 300 mJ / cm². 2 The entire surface of the coating was exposed by irradiating it with ultraviolet light under the specified conditions. Next, a 1.0 wt% sodium carbonate aqueous solution (temperature: 30°C) was used as a developer, and the exposed coating was subjected to a discharge pressure of 1.0 kgf / mm². 2 Spray development was performed for 90 seconds under the specified conditions. Next, the developed coating was washed with pure water and then heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on electrolytic copper foil, thereby obtaining a test specimen. The obtained test specimen was immersed in a solder bath at 260°C, and after 10 seconds, it was removed. This operation was performed three times consecutively. Next, the condition of the cured film surface was visually observed, and if no blistering or peeling was observed on the cured film surface, it was evaluated as "A (excellent solder heat resistance)". On the other hand, if blistering or peeling was observed on the cured film surface, it was evaluated as "B (poor solder heat resistance)".

[0188] [Methods 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 (Kaneka Corporation's "PIXIO® BP FRS-142#SW", thickness: 25 μm) as a film-like support. The copper foil on one side of this flexible copper-clad laminate was patterned to form a comb-shaped pattern with line width / space width = 100 μm / 100 μm on the film-like support. Next, the laminate with the comb-shaped pattern was immersed in a 10 vol% sulfuric acid aqueous solution for 1 minute, and then washed with pure water. Then, 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. Finally, the coating film made of the liquid photosensitive resin composition was dried at a drying temperature of 80°C for 20 minutes, followed by an integrated exposure of 300 mJ / cm². 2 The entire surface of the coating was exposed by irradiating it with ultraviolet light under the specified conditions. Next, a 1.0 wt% sodium carbonate aqueous solution (temperature: 30°C) was used as a developer, and the exposed coating was subjected to a discharge pressure of 1.0 kgf / mm². 2 Spray development was performed for 90 seconds under the following conditions. Next, the developed coating was washed with pure water and then heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition on a comb-shaped pattern, and a test specimen was obtained. Next, a DC voltage of 100V was applied to both terminals of the test specimen in an environment of 85°C and 85% relative humidity, and the change in resistance between the two terminals was observed. Then, after 1000 hours from the start of application, 1.0 × 10⁻⁶ was obtained. 8 A resistance value of Ω or more was evaluated as "A (excellent electrical insulation reliability)". On the other hand, after 1000 hours from the start of application, 1.0 × 10 8 A resistance value of less than Ω was evaluated as "B (Poor electrical insulation reliability)".

[0189] <Fabrication of circuit boards> First, a flexible copper-clad laminate was prepared by laminating electrolytic copper foil to both sides of a polyimide film (Kaneka Corporation's "PIXIO® BP FRS#SW") as a film-like support. 600 through-holes with 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, cleaning (desmearing) and carbon treatment were performed inside the through-holes. Then, after electrolytic copper plating of the through-holes, wiring was formed by patterning the electrolytic copper foil on both sides, resulting in a substrate having a film-like support, wiring provided on both sides of the film-like support, and through-holes. For each of Examples 1-14 and Comparative Examples 1-3, Tables 1-4, described later, show the length and width of the substrate used, the thickness of the film-like support used, and the thickness of the wiring on the substrate used.

[0190] <Application of liquid photosensitive resin composition to a substrate and formation of a coating film> A liquid photosensitive resin composition (one of the liquid photosensitive resin compositions listed in Tables 1 to 4 below) was applied to both sides of the substrate prepared using the above procedure, using a vertical lift-type roll coater equipped with a pair of coating rolls. The liquid photosensitive resin composition was applied simultaneously to both sides of the substrate. The coating conditions were as follows. In the following coating conditions, "coating roll" refers to "each of the pair of coating rolls." • Material of the surface layer (surface roll) of the coating roll: Ethylene propylene rubber • Width of surface roll: 680mm • Roll diameter of the coating roll: As described in Tables 1 to 4 below. • Groove type of coating roll: Multiple independent ring-shaped grooves • Groove pitch of coating roll: 700 μm • Groove opening width of coating roll: 700 μm • Cross-sectional shape of the groove in the coating roll: V-shaped • Groove depth of the coating roll: 350 μm • Doctor bar pressure: 1.5 kgf / cm² 2 • Indentation depth of the coating roll: 150 μm • Rotation speed of the coating roll: 5 m / min

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

[0192] <Evaluation method for coated substrates> [Embedding] The through-holes in 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 maximum 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 embedding performance. For example, "an evaluation value for embedding performance of 50 μm" means that all 600 through-holes of diameters 30 μm and 50 μm are filled, but some or all of the 600 through-holes of diameter 80 μm are not filled. Therefore, the larger this evaluation value, the better the embedding performance.

[0193] [Appearance of the coating film] The coating on each coated substrate was visually inspected to check for the presence or absence of pinholes, uneven coating of wiring, groove marks from the coating roll, and streaks. The appearance of the coating was then judged according to the following criteria. A rating of A or B indicated that "the occurrence of coating appearance defects has been suppressed." On the other hand, a rating of C indicated that "the occurrence of coating appearance defects has not been suppressed."

[0194] (Criteria for judging the appearance of the coating film) A: No pinholes, uneven coating, groove marks, or slits were found. B: At least one of the following defects was identified in a total of one or two locations: pinholes, uneven coating, groove marks, and striated lines. C: At least one of the following defects was found in a total of three or more locations: pinholes, uneven coating, groove marks, and striated lines.

[0195] [Appearance of a coated substrate] The appearance of each coated substrate was visually inspected to check for tears and deformation. The appearance of the coated substrates was then judged according to the following criteria. A rating of A or B indicated that "the occurrence of defects in the appearance of the coated substrates has been suppressed." On the other hand, a rating of C indicated that "the occurrence of defects in the appearance of the coated substrates has not been suppressed."

[0196] (Criteria for judging the appearance of coated substrates) A: No tears or deformation of the circuit board were found. B: No tears were found in the circuit board, but deformation was observed. C: Both tearing and deformation of the circuit board were confirmed.

[0197] <Formation of hardened film> The coated substrate obtained by the above procedure is subjected to an integrated exposure of 300 mJ / cm² via a negative-type photomask having 100 circular light-shielding regions with a diameter of 150 μm. 2 The coating was exposed by irradiating it with ultraviolet light under the specified conditions. Next, a 1.0 wt% sodium carbonate aqueous solution (temperature: 30°C) was used as a developer, and the exposed coating was subjected to a discharge pressure of 1.0 kgf / mm². 2 Spray development was performed for 90 seconds under the specified conditions. Next, the developed coating was washed with pure water and then heated in an oven at 150°C for 60 minutes to form a cured film of the liquid photosensitive resin composition, obtaining a substrate with a cured film that protects the wiring (hereinafter sometimes referred to as "substrate with cured film"). The cured film of the obtained substrate with cured film had 100 circular openings formed in it. In addition, a portion of the wiring was exposed through each of the circular openings.

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

[0199] [Plating solution resistance] Each substrate with a cured film obtained by the method described above in <Formation of Cured Film> was subjected to electroless gold plating according to the standard procedure for electroless gold plating solution (product name: Flash Gold 330) manufactured by Okuno Pharmaceutical Co., Ltd. The detailed procedure is shown below.

[0200] First, the substrate with the hardened film was immersed in a degreasing solution ("ICP Clean S-135K" manufactured by Okuno Pharmaceutical Co., Ltd.) at 40°C for 4 minutes to degrease it. Next, the degreased substrate with the hardened film was immersed in an etching solution at 30°C for 1 minute to etch it. 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 deionized water. Next, the etched substrate with the hardened film was immersed in a catalytic treatment solution ("ICP Accelerator" manufactured by Okuno Pharmaceutical Co., Ltd., Pd concentration: 0.04 wt%) at 30°C for 1 minute to catalytically treat it. Next, the substrate with the cured film after catalytic treatment was immersed in an electroless nickel plating solution ("ICP Nicolon FPF" manufactured by Okuno Pharmaceutical Co., Ltd.) at a temperature of 84°C for 30 minutes to electroless nickel plating the substrate with the cured film. Then, the substrate with the cured film that had been electroless nickel plated was immersed in an electroless gold plating solution ("Flash Gold 330" manufactured by Okuno Pharmaceutical Co., Ltd.) at a temperature of 80°C for 8 minutes to electroless gold plating the substrate with the cured film, and then washed with water at a temperature of 25°C. After washing, the substrate with the cured film was heated at a temperature of 150°C for 30 minutes to obtain a test piece for evaluating resistance to plating solutions. The area around the circular opening formed in the cured film of the obtained test piece was observed with an optical microscope, and the resistance to plating solutions was judged according to the following criteria. If the judgment was A, it was evaluated as "excellent resistance to plating solutions". On the other hand, if the judgment was B or C, it was evaluated as "not excellent resistance to plating solutions".

[0201] (Criteria for determining resistance to plating solutions) A: No penetration of the plating solution between the cured film and the substrate (penetration of the plating solution from the openings) was confirmed for any of the openings (100 openings). B: Penetration of the plating solution between the cured film and the substrate was confirmed for some of the openings. C: Penetration of the plating solution between the cured film and the substrate was confirmed for all openings.

[0202] [Discoloration resistance of wiring] After evaluating the test specimens using the method described above for [Plating Solution Resistance], they were subjected to a heat press treatment at 160°C for 60 minutes using a heating press device, and then baked in a box oven at 150°C for 90 minutes. The wiring of the test specimens after baking (specifically, the wiring coated with the cured film) was visually observed, and the discoloration resistance of the wiring was determined according to the following criteria. A rating of A indicated that "the wiring has excellent discoloration resistance." On the other hand, a rating of B or C indicated that "the wiring does not have excellent discoloration resistance."

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

[0204] <Evaluation Results> Tables 1 to 4 show the components and their amounts used in Examples 1 to 14 and Comparative Examples 1 to 3, the length and width of the substrates used, the thickness of the film-like support used, the thickness of the wiring on the substrates used, the roll diameter of the coating rolls used, the physical properties and evaluation results of the liquid photosensitive resin compositions used, the evaluation results of the coated substrates, and the evaluation results of the cured substrates. In Tables 1 to 4, the values ​​in the "Composition of Liquid Photosensitive Resin Composition" column represent the amount of the component (in parts by weight). In Tables 1 to 4, the amount of component (G) (organic solvent) includes the amount of organic solvent in resin solution SP1, resin solution SP2, or resin solution SP3. In Tables 1 to 4, "-" means that the component was not included. In Tables 1 to 4, "(C) component" also includes epoxy compounds having only one epoxy group. In Tables 1 to 4, "(E) component" also includes radical polymerizable compounds that have two radical polymerizable groups in one molecule.

[0205] Furthermore, 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 (Omnirad® 369, manufactured by IGM Resins) as a photoradical polymerization initiator. • 828: An epoxy compound having two epoxy groups in one molecule (Mitsubishi Chemical Corporation's "jER(registered trademark) 828"). • 1032: An epoxy compound having three epoxy groups in one molecule (Mitsubishi Chemical Corporation's "jER(registered trademark)1032H60") PGE: Phenylenglycidyl ether DPEHA: Dipentaerythritol hexaacrylate • PETA: Pentaerythritol triacrylate • 321: EO-modified bisphenol A dimethacrylate (Showa Denko Materials Co., Ltd. "Funcryl (registered trademark) FA-321M", average number of EO added moles: 10) • 8070: Cross-linked polyurethane particles (Dainichi Seika Kogyo Co., Ltd. "Dymic Beads (registered trademark) UCN-8070CM Clear", average particle size: 7μm) TEGDM: Triethylene glycol dimethyl ether • 2000: Butadiene-based defoaming agent (Florence AC-2000, manufactured by Kyoeisha Chemical Co., Ltd.)

[0206] [Table 1]

[0207] [Table 2]

[0208] [Table 3]

[0209] [Table 4]

[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 radical polymerizable compound having three or more radical polymerizable groups in one molecule.

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

[0212] In Comparative Examples 1-3, the liquid photosensitive resin compositions used did not contain polyfunctional epoxy compounds. In Comparative Examples 2 and 3, the liquid photosensitive resin compositions used did not contain epoxy curing accelerators. In Comparative Example 3, the liquid photosensitive resin composition used did not contain radical polymerizable compounds having three or more radical polymerizable groups per molecule.

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

[0214] The results above demonstrate that the present invention provides a method for manufacturing a flexible printed circuit board that is excellent in resistance to plating solutions and resistance to discoloration of wiring. [Explanation of symbols]

[0215] 11 circuit boards 12a, 12b, 100 coating rolls 13 Film-like support 14 Wiring 15 holes 17 Liquid photosensitive resin composition

Claims

1. A method for manufacturing 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 using a vertical lifting type roll coater, The substrate having the film-like support and the wiring is provided with 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 radical polymerizable groups in one molecule. The thickness of the aforementioned film-like support is 8.0 μm or more and 50.0 μm or less. A method for manufacturing a flexible printed circuit board, comprising applying the liquid photosensitive resin composition to both sides of the substrate simultaneously.

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

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

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

5. A method for manufacturing a flexible printed circuit board according to any one of claims 1 to 4, wherein the film-like support comprises 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.

6. The method for manufacturing 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 carboxyl group in one molecule.

7. A method for manufacturing 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 per 100 parts by weight of the binder polymer.

8. A method for manufacturing a flexible printed circuit board according to any one of claims 1 to 7, wherein the acid value of the binder polymer is 10 mg KOH / g or more.

9. The aforementioned vertical lifting type roll coater is equipped with a pair of coating rolls, A method for manufacturing 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. The method for manufacturing a flexible printed circuit board according to claim 9, wherein each of the coating rolls has a plurality of independent ring-shaped grooves.

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