Manufacturing method of printed circuit boards

Abstract

To provide a method of forming a fine wiring pattern in manufacturing of a print circuit board including an inter-layer conductive path.SOLUTION: A manufacturing method of a print circuit board 1 of an embodiment, comprises: a step of preparing a double-surface metal tension lamination plate 2 including an insulation substrate 30 having a first main surface and a second main surface on the side opposite to the first main surface, a metal foil 10 provided to the first main surface, and a metal foil 20 provided to the second main surface; a step of patterning the metal foil 10 of the double-surface metal tension lamination plate 2, and forming a wiring pattern WP1 and a conformal mask 12; a step of forming a conductive hole by removing the insulation substrate 30 exposed to an opening 12a of the conformal mask 12 by irradiating the conformal mask 12 with a laser beam; a step of coating the wiring pattern WP1, and forming a plating resistor 14 to which the conductive hole is not coated; a step of forming a metal plating 40 in an inner part of the conductive hole; and a step of removing the plating resistor 14.SELECTED DRAWING: Figure 1

Description

[[Technical Field]]

[0001] The present invention relates to a method for manufacturing a printed wiring board, and more particularly, to a method for manufacturing a printed wiring board for forming a fine wiring pattern in the manufacture of a printed wiring board having interlayer conductive paths. [[Background Art]]

[0002] Electronic devices including information communication devices such as smartphones tend to be smaller and lighter, so there is a demand for smaller and higher-density substrates. Higher density of a substrate means forming more wirings within a limited substrate outer shape. In order to form more wirings, miniaturization and multilayering of wiring patterns are required.

[0003] Etching is used for forming wiring patterns. The subtractive method is one of the methods for forming wiring patterns by etching, and is generally used particularly in forming wiring patterns of flexible printed wiring boards. In the subtractive method, etching in the depth direction of the wiring and etching in the width direction of the wiring occur isotropically. Therefore, in order to form a fine wiring pattern, a thinner metal foil used for the wiring is more advantageous.

[0004] On the other hand, for multilayering, interlayer conductive paths such as vias and through holes are formed in substrates having metal foil on both sides and multilayer substrates, and wirings of each layer are electrically connected by the interlayer conductive paths. When forming the interlayer conductive path, it is necessary to form metal plating in the conductive hole. Patent Documents 1 to 3 describe a method called button plating as one embodiment of a method for forming metal plating. [[Prior Art Literature]] [[Patent Literature]]

[0005] [[Patent Document 1]] Japanese Unexamined Patent Publication No. 2006-108270 [[Patent Document 2]] Japanese Patent Application Publication No. 11-195849 [Patent Document 3] Patent No. 6884333 [Overview of the project] [Problems that the invention aims to solve]

[0006] The button plating method is a method of applying plating treatment only to specific parts of a substrate. An example of the method for forming wiring patterns and interlayer conductive paths in the button plating method will be explained with reference to Figures 5A to 5D. Figures 5A to 5D are cross-sectional process views illustrating the manufacturing method of a printed circuit board according to a comparative example.

[0007] As shown in Figure 5A(1), a double-sided metal-clad laminate comprising metal foils 100, 200 and an insulating substrate 300 is prepared. Next, as shown in Figure 5A(1), conductive holes H are formed in the double-sided metal-clad laminate. Next, as shown in Figure 5A(2), plating resist 140 and plating resist 240 are formed on the upper and lower surfaces of the double-sided metal-clad laminate, respectively. The plating resist 140 has an opening 140a in the portion of the conductive holes H. That is, the plating resist 140 does not cover the conductive holes H.

[0008] Next, as shown in Figure 5B(1), a plating process is performed to form a metal plating 400 (button plating) inside the conductive holes H. The metal plating 400 includes button lands 410. After that, as shown in Figure 5B(2), the plating resists 140 and 240 are removed.

[0009] Next, as shown in Figure 5C(1), resist films 150 and 250 are formed to cover the upper and lower surfaces of the double-sided metal-clad laminate, respectively. The metal plating 400 is embedded in the resist film 150. Next, as shown in Figure 5C(2), the resist films 150 and 250 are exposed and developed to form etching resists 150a and 250a.

[0010] Next, as shown in Figure 5D(1), etching is performed to remove the metal foil 100 that is not covered by the etching resist 150a and the metal foil 200 that is not covered by the etching resist 250a. Then, as shown in Figure 5D(2), the etching resists 150a and 250a are removed. Through these steps, a wiring pattern WP10 having multiple wirings 110, a land 120b, a WP20 having multiple wirings 210, a land 220 on the opposite side of the land 120b, and an interlayer conductive path 500 are formed.

[0011] The button plating method presents the following challenges when miniaturizing wiring patterns. As shown in Figure 5B(2), the upper part of the metal plating 400 protrudes from the metal foil 100. To prevent the metal plating 400 from being etched in subsequent processes, as shown in Figure 5C(1), it is necessary to embed the metal plating 400 that protrudes from the metal foil 100 when forming the resist film 150. For this reason, the resist film 150 is formed thickly. However, making the resist film 150 thicker reduces the etching resolution, making it difficult to form fine wiring patterns.

[0012] The present invention is based on the above technical understanding and aims to provide a method for manufacturing a printed circuit board for forming a fine wiring pattern in the manufacture of a printed circuit board having interlayer conductive paths. [Means for solving the problem]

[0013] The method for manufacturing a printed circuit board according to the present invention is: A step of preparing a double-sided metal-clad laminate having an insulating substrate having a first main surface and a second main surface opposite to the first main surface, a first metal foil provided on the first main surface, and a second metal foil provided on the second main surface, The process of patterning the first metal foil of the double-sided metal-clad laminate to form a wiring pattern and a conformal mask, The process of irradiating the conformal mask with laser light to remove the insulating substrate exposed at the opening of the conformal mask and form a conductive hole, A step of forming a plating resist that covers the wiring pattern but does not cover the conductive holes, The process of forming a metal plating inside the aforementioned conductive hole, The step of removing the aforementioned plating resist, It is characterized by having the following features.

[0014] Furthermore, in the method for manufacturing the printed circuit board, The step of forming the aforementioned wiring pattern is: A step of forming a resist film on the first metal foil having a thickness of 1.5 times or less the thickness of the first metal foil, A step of exposing and developing the resist film to form an etching resist corresponding to the wiring pattern, The process of forming the wiring pattern by etching away the first metal foil that is not covered with the etching resist, The process may also include a step of removing the etching resist.

[0015] Furthermore, in the method for manufacturing the printed circuit board, In the process of forming the wiring pattern and the conformal mask, the wiring pattern and the conformal mask may be formed simultaneously.

[0016] Furthermore, in the method for manufacturing the printed circuit board, Prior to the step of forming the plating resist, a step of performing a dry plating treatment on the wiring pattern, the insulating substrate exposed between the wiring patterns, and the conductive holes, The process may further include, after the step of removing the plating resist, a step of removing the portion of the metal thin film formed by the dry plating process that is not covered by the metal plating.

[0017] Further, in the method for manufacturing a printed wiring board, the dry plating treatment may be performed by a sputtering method.

[0018] Further, in the method for manufacturing a printed wiring board, the metal foil is a copper foil, the sputtering method is a sputtering method using copper, and the metal thin film may be a copper thin film.

[0019] Further, in the method for manufacturing a printed wiring board, the step of forming the conduction hole may be performed such that the second metal foil is exposed on a bottom surface of the conduction hole.

[0020] Further, in the method for manufacturing a printed wiring board, patterning the second metal foil of the double-sided metal-clad laminate to form a wiring pattern, another opening that includes said opening in plan view, and a land, the step of forming the conduction hole may be performed such that the conduction hole becomes a through hole that communicates said opening and said another opening with each other.

[0021] Further, in the method for manufacturing a printed wiring board, the conformal mask includes a first opening and a second opening as said openings, further comprising a step of patterning the second metal foil of the double-sided metal-clad laminate to form a third opening, wherein the third opening includes the second opening of the conformal mask in plan view,[=END]] in the step of forming the conduction hole, the insulating base material exposed at the first opening and the second opening of the conformal mask may be removed to form a first conduction hole with the second metal foil exposed on a bottom surface thereof, and a second conduction hole that communicates the second opening and the third opening with each other.

[0022] Further, in the method for manufacturing a printed wiring board, The printed circuit board may be a flexible printed circuit board.

[0023] Furthermore, in the method for manufacturing the printed circuit board, The first and second metal foils may be rolled copper foils.

[0024] Furthermore, in the method for manufacturing the printed circuit board, The aforementioned metal plating may be electrolytic plating.

[0025] Furthermore, in the method for manufacturing the printed circuit board, At least one of the above processes may be performed using a roll-to-roll method. [Effects of the Invention]

[0026] According to the method for manufacturing printed circuit boards of the present invention, since the wiring pattern is formed before the conductive holes are formed, it is not necessary to fill the interlayer conductive paths formed in the conductive holes with etching resist. Therefore, a thin resist film can be used, and fine wiring patterns can be formed in the manufacture of printed circuit boards having interlayer conductive paths. [Brief explanation of the drawing]

[0027] [Figure 1] This is a flowchart showing a method for manufacturing a printed circuit board according to an embodiment. [Figure 2A] This is a cross-sectional view illustrating a process for manufacturing a printed circuit board according to the first embodiment. [Figure 2B] This is a cross-sectional view illustrating the manufacturing method of a printed circuit board according to the first embodiment, following Figure 2A. [Figure 2C] Figure 2B is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the first embodiment. [Figure 2D] Figure 2C is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the first embodiment. [Figure 2E] Figure 2D is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the first embodiment. [Figure 2F] Figure 2E is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the first embodiment. [Figure 3A] This is a cross-sectional view illustrating a process for manufacturing a printed circuit board according to a second embodiment. [Figure 3B] This is a cross-sectional view illustrating the manufacturing method of a printed circuit board according to the second embodiment, following Figure 3A. [Figure 3C] Figure 3B is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the second embodiment. [Figure 3D] Figure 3C is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to the second embodiment. [Figure 3E] Figure 3D is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to a second embodiment. [Figure 4A] This is a cross-sectional view illustrating a process for manufacturing a printed circuit board according to a third embodiment. [Figure 4B] This is a cross-sectional view illustrating a process for manufacturing a printed circuit board according to a third embodiment, following Figure 4A. [Figure 5A] This is a cross-sectional view illustrating a process for manufacturing a printed circuit board according to a comparative example. [Figure 5B] Figure 5A is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to a comparative example. [Figure 5C] Figure 5B is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to a comparative example. [Figure 5D] Figure 5C is a cross-sectional view illustrating the process for manufacturing a printed circuit board according to a comparative example. [Modes for carrying out the invention]

[0028] Embodiments of the present invention will be described below with reference to the drawings. In each figure, components having equivalent functions are denoted by the same reference numerals. The drawings are schematic and mainly show characteristic parts of each embodiment, and the relationship between thickness and planar dimensions, the ratio of the thickness of each layer, etc., may differ from reality.

[0029] (First embodiment) An example of a method for manufacturing a printed circuit board according to the first embodiment will be described with reference to Figures 1 and 2A to 2F. Figure 1 is a flowchart illustrating the method for manufacturing a printed circuit board according to this embodiment. Figures 2A to 2F are cross-sectional views illustrating the process for manufacturing a printed circuit board according to this embodiment.

[0030] The printed circuit board manufactured in this embodiment is a flexible printed circuit board. However, the printed circuit board manufactured in this embodiment is not limited to a flexible printed circuit board, and may also be a rigid printed circuit board.

[0031] As shown in Figure 2A(1), a double-sided metal-clad laminate 2 is prepared (step S1). The double-sided metal-clad laminate 2 has metal foils 10 and 20 and an insulating substrate 30. More specifically, the double-sided metal-clad laminate 2 has an insulating substrate 30 having an upper surface (first main surface) and a lower surface (second main surface opposite the first main surface), metal foil 10 provided on the upper surface of the insulating substrate 30, and metal foil 20 provided on the lower surface of the insulating substrate 30.

[0032] For example, the metal foils 10 and 20 are copper foils (electrolytic copper foils) with a thickness of 12 μm, and the insulating substrate 30 is polyimide with a thickness of 25 μm.

[0033] The thickness and material of the metal foils 10 and 20 are not limited to those described above. The thickness of the metal foils 10 and 20 is, for example, 5 to 72 μm. Also, the thicknesses of metal foil 10 and metal foil 20 may be different from each other. Furthermore, the material of the metal foils 10 and 20 is not limited to copper, but may be other metals (for example, silver, aluminum, etc.).

[0034] Furthermore, when copper foil is used as the metal foil 10,20, it is not limited to electrolytic copper foil, but may also be rolled copper foil. When manufacturing flexible printed circuit boards, rolled copper foil is preferred. By using rolled copper foil, a flexible printed circuit board with high flexibility can be provided.

[0035] The thickness and material of the insulating substrate 30 are not limited to those described above. The thickness of the insulating substrate 30 is, for example, 6 to 100 μm. The material of the insulating substrate 30 may be, for example, fluorine-based materials such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) and PTFE (polytetrafluoroethylene), polyimide-based materials such as MPI (modified polyimide) and PI (polyimide), PEEK (polyether ether ketone), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate).

[0036] Next, the metal foil 10 of the double-sided metal-clad laminate 2 is patterned to form the wiring pattern WP1 and conformal mask 12. The metal foil 20 is also patterned to form the wiring pattern WP2 and the land 22 on the opposite side of the conformal mask 12. Specifically, the following steps S2 to S5 are performed.

[0037] First, as shown in Figure 2A(2), a resist film 15 is formed on the metal foil 10, and a resist film 25 is formed on the metal foil 20 (step S2). For example, the resist films 15 and 25 are formed by laminating a 10 μm thick negative-type dry film onto the metal foils 10 and 20.

[0038] The thickness and material of the resist films 15 and 25 are not limited to those described above, but to form fine wiring patterns, it is preferable that the resist films 15 and 25 be thin. Specifically, a thickness of 0.1 times or more and 1.5 times or less the thickness of the metal foils 10 and 20 is preferred. In this embodiment, the thickness of the resist films 15 and 25 is 0.1 times or more and 1 time less than the thickness of the metal foils 10 and 20. The thicknesses of resist film 15 and resist film 25 may be different from each other.

[0039] Next, as shown in Figure 2B(1), the resist films 15 and 25 are exposed and developed to form etching resists 15a and 25a (step S3). Etching resist 15a includes a portion corresponding to the wiring pattern WP1, which will be described later, and a portion corresponding to the conformal mask 12. Etching resist 25a includes a portion corresponding to the wiring pattern WP2, which will be described later, and a portion corresponding to the land 22 on the opposite side of the conformal mask 12.

[0040] In this embodiment, a proximity exposure machine is used for exposure. However, the exposure method is not limited to proximity exposure, and may also be projection exposure, direct exposure, etc.

[0041] Next, as shown in Figure 2B(2), etching is performed using etching resists 15a and 25a as masks. More specifically, the metal foils 10 and 20 that are not covered with etching resists 15a and 25a are removed by etching (step S4). In this step, for example, wet etching using copper chloride is performed.

[0042] Subsequently, etching resists 15a and 25a are removed as shown in Figure 2C(1) (step S5). This forms wiring patterns WP1 and WP2, a conformal mask 12, and lands 22 on the opposite side of the conformal mask 12. Wiring pattern WP1 includes multiple spaced wirings 11. Similarly, wiring pattern WP2 includes multiple spaced wirings 21. The conformal mask 12 includes openings 12a and lands 12b.

[0043] In this embodiment, the width of the wiring 11 and 21 is 20 μm. The width between the wiring 11 and 21 (gap width) is also 20 μm. However, the width of the wiring 11 and 21 may be 10 to 30 μm. The width between the wiring 11 and 21 may also be 10 to 30 μm.

[0044] In this embodiment, the diameter of the opening 12a is 50 μm, and the diameter (outer diameter) of the land 12b is 90 μm. While the diameters of the opening 12a and land 12b are not limited to those described above, it is preferable that they be as small as possible in order to form a high-density wiring pattern.

[0045] Note that the wiring pattern WP1, wiring pattern WP2, conformal mask 12, and land 22 may each be formed in separate processes. Specifically, the same process as described above may be repeated each time the wiring pattern WP1, wiring pattern WP2, conformal mask 12, and land 22 are formed. In this case, the order in which the wiring pattern WP1, wiring pattern WP2, conformal mask 12, and land 22 are formed is arbitrary.

[0046] Preferably, at least the wiring pattern WP1 and the conformal mask 12 are formed simultaneously. This eliminates the need to align the wiring pattern WP1 and the conformal mask 12. More specifically, it eliminates the need to align the wiring pattern WP1 with the conductive holes H1 (described later) formed at the opening 12a of the conformal mask 12. In conventional button plating methods, conductive holes H are formed first, and the exposure pattern of the resist film (which becomes the wiring pattern after etching) is aligned with the formed conductive holes H. More specifically, in the process shown in Figure 5C(2), the exposure pattern of the resist film 150 is aligned with the metal plating 400. Generally, misalignment occurs during this alignment. In this case, to prevent the wiring pattern WP10 from overlapping the conductive holes H, the wiring pattern WP10 is designed with a margin to avoid the conductive holes H. Also, to ensure that the land 120b is formed around the conductive holes H, the diameter of the land 120b is designed to be large. On the other hand, in this embodiment, the alignment process itself can be omitted, allowing the wiring pattern WP1 to be designed to be positioned closer to the conductive hole H1. Furthermore, the diameter of the land 12b, which will be described later, can be designed to be smaller. As a result, a finer wiring pattern can be formed. In addition, since there is no need to provide a separate step for forming the conformal mask 12, the process can be simplified.

[0047] Steps S2 to S5 described above form the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22 on the opposite side of the conformal mask 12.

[0048] In addition, in steps S2 to S5, the wiring pattern WP2 may not be formed on the lower surface of the double-sided metal-clad laminate 2, and the lower surface of the double-sided metal-clad laminate 2 may remain as metal foil 20.

[0049] Next, as shown in Figure 2C(2), a conductive hole H1 is formed by irradiating the conformal mask 12 with laser light (step S6). More specifically, a laser beam wider than the diameter of the opening 12a and narrower than the diameter of the land 12b is irradiated onto the opening 12a of the conformal mask 12 from the first main surface side of the insulating substrate 30 (the side on which the metal foil 10 is provided). This removes the insulating substrate 30 exposed at the opening 12a using the land 12b as a mask, thereby forming a conductive hole H1. At this time, a conductive hole H1 is formed at the position of the opening 12a of the conformal mask 12. After removing the insulating substrate 30, desmearing treatment using plasma or the like may be performed.

[0050] The type of laser used in this step is a carbon dioxide laser. However, the type of laser is not limited to a carbon dioxide laser; for example, a UV-YAG laser may also be used.

[0051] In this embodiment, since there is no opening in the land 22, the metal foil 20 (land 22) is exposed on the bottom surface of the conductive hole H1 during the process of forming the conductive hole H1. As a result, the conductive hole H1 becomes a bottomed hole.

[0052] Furthermore, by adjusting the laser irradiation conditions, the conductive hole H1 may be formed such that its inner diameter decreases as it deepens from the opening 12a, as shown in Figure 2C(2). This makes it easier to fix the metal thin film 13, which will be described later, to the side surface of the conductive hole H1.

[0053] Next, as shown in Figure 2D(1), dry plating is performed on the wiring pattern WP1, conformal mask 12, and conductive holes H1 to form a thin metal film 13 (step S7). More specifically, dry plating is performed on the first main surface side of the insulating substrate 30 (the side on which the metal foil 10 is provided) to form a thin metal film 13 on the wiring pattern WP1, the insulating substrate 30 exposed between the wiring patterns WP1, the conformal mask 12 (i.e., the land 12b), and the inner walls (sides and bottoms) of the conductive holes H1. By forming the thin metal film 13, the insulating substrate 30 exposed on the side of the conductive holes H1 becomes conductive, and the electrical connection of the interlayer conductive path 50, which will be described later, can be stabilized. In this step, for example, copper sputtering is used to form a thin copper film with a thickness of 0.3 μm as the thin metal film 13.

[0054] Furthermore, since a thin metal film 13 is formed on the insulating substrate 30 exposed to the wiring pattern WP1, multiple wirings 11 are temporarily electrically connected to each other. However, in the later step S11, the thin metal film 13 between the wirings 11 is removed.

[0055] The thickness of the metal thin film 13 is arbitrary, but it is preferable that it is at least thick enough to provide the necessary conductivity for depositing the metal plating 40 described later into the conductive holes H1, and is below a certain thickness (for example, 0.1 times or less the width of the wirings 11, 21) in order to minimize the impact on the wiring pattern WP1 when removing the metal thin film 13 between the wirings 11.

[0056] Alternatively, wet plating (such as electrolytic plating and chemical plating) may be used instead of dry plating. Preferably, in step S7, dry plating is used as the plating process. By using dry plating, the metal thin film 13 can be made thinner compared to wet plating, and when removing the metal thin film 13 in a subsequent process, it can be easily removed with a small amount of etching, thus minimizing the impact on the wiring pattern WP1. In addition, dry plating allows for the formation of a metal thin film 13 with fewer impurities, thereby reducing the electrical resistance of the metal thin film 13. Therefore, even when the metal thin film 13 is formed on the metal foil 10 (especially the land 12b) and the land 22 exposed on the bottom surface of the conductive hole H1, the impact on the conductivity of the metal plating 40 and land 12b, and the conductivity of the metal plating 40 and land 22, can be minimized. In other words, the impact on the conductivity of the interlayer conductive path 50, which will be described later, can be minimized. Furthermore, in the case of wet plating, when the thin metal film 13 is removed, a catalyst (for example, palladium, etc.) may remain on the wiring pattern WP1, and a separate step to remove the catalyst may be required. On the other hand, in dry plating, no catalyst is used, so the process can be simplified.

[0057] Furthermore, the dry plating method is not limited to sputtering, but may also be vapor deposition or the like. More preferably, the dry plating is performed by sputtering. This increases the adhesion of the metal thin film 13 and stabilizes the conductivity of the conductive holes H1.

[0058] Furthermore, when using the sputtering method, the same metal as the metal foil 10 may be used. Using the same metal ensures that the physical, electrical, and chemical properties are consistent, simplifying subsequent processing. In particular, if the metal foil 10 is copper foil, the sputtering method may be a copper sputtering method (copper sputtering). In this case, the metal thin film 13 will be a copper thin film. By forming a copper thin film, the metal of the metal thin film 13 can be the same metal (copper) as the rolled copper foil which is preferable in the case of flexible printed circuit boards.

[0059] After forming the metal thin film 13 as described above, plating resists 14 and 24 are formed as shown in Figure 2D(2) (step S8). The plating resist 14 is provided with an opening 14a in which the conductive holes H1 are exposed. As shown in Figure 2D(2), the opening 14a is provided on the land 12b. In this way, the plating resist 14 is formed to cover the wiring pattern WP1 but not the conductive holes H1.

[0060] The following describes an example of the process performed in step S8. First, a plating resist is formed to cover the entire surface of both sides of the wiring board obtained in Figure 2D(1). That is, a resist film is formed to cover the wiring pattern WP1, land 12b, and conductive holes H1 on which the metal thin film 13 is formed, and a resist film is formed to cover the wiring pattern WP2 and land 22.

[0061] Next, the formed resist film is exposed to light and developed to form plating resists 14 and 24. In this embodiment, the diameter of the opening 14a provided in the plating resist 14 is 70 μm. The diameter of the opening 14a is equal to the diameter of the button land 41, which will be described later.

[0062] In this embodiment, a direct-writing exposure machine is used for exposure. The exposure method is not limited to this, and may also be proximity exposure, projection exposure, etc., but direct-writing exposure is preferred. Even if the wiring board expands or contracts in a process prior to the exposure process, the direct-writing exposure machine can draw an exposure pattern corresponding to that expansion or contraction. Therefore, it is not necessary to design the diameter of the opening 14a of the plating resist 14 to be large in anticipation of the expansion or contraction of the wiring board, and as a result, the diameter of the opening 14a of the plating resist 14 can be reduced. Thus, the diameter of the button land 41, which will be described later, can be reduced, and the diameter of the land 12b can be reduced even further.

[0063] In Figure 2D(2), the wiring pattern WP1 is completely covered with the plating resist 14, but this is not the only option. For example, only the wiring pattern WP1 surrounding at least the conductive hole H1 may be covered with the plating resist 14. In this case, only the conductive hole H1 and the wiring pattern WP1 surrounding the conductive hole H1 are plated (for example, by immersion in a plating solution).

[0064] After forming the plating resists 14 and 24 as described above, a plating process is performed as shown in Figure 2E(1) to form a metal plating 40 inside the conductive hole H1 (step S9). More specifically, the metal plating 40 is formed inside the opening 14a of the plating resist 14 on which the metal thin film 13 is formed. The metal plating 40 includes button lands 41. As a result of the formation of the metal plating 40, a portion of the metal thin film 13 is covered by the metal plating 40. Specifically, the portion of the metal thin film 13 formed on the inner wall (side and bottom) of the conductive hole H1 is covered by the metal plating 40.

[0065] Furthermore, as shown in Figure 2E(1), the metal plating 40 may be formed not only inside the conductive hole H1 but also on the land 12b. In this case, as shown in Figure 2E(1), a portion of the land 12b is covered by the button land 41. More specifically, the portion of the metal thin film 13 formed on the land 12b is covered by the metal plating 40 (button land 41).

[0066] Subsequently, as shown in Figure 2E(2), the plating resists 14 and 24 are removed (step S10). This forms an interlayer conductive path 50 that electrically connects land 12b and land 22.

[0067] In this embodiment, since the conductive hole H1 is a bottomed hole, the interlayer conductive path 50 is a bottomed via. In Figure 2E(2), the upper surface of the metal plating 40 is flat, but the upper surface of the metal plating 40 may have a recess.

[0068] In this embodiment, the metal plating 40 is electroplated. More specifically, the metal plating 40 is formed by performing an electroplating process. By using electroplating, the plating process time can be shortened compared to using electroless plating, and manufacturing efficiency can be improved.

[0069] Furthermore, the metal plating 40 may be made of the same metal as the metal foil 10. Using the same metal ensures that the physical, electrical, and chemical properties are consistent, making handling easier. In particular, if the metal foil 10 is copper foil, the metal plating 40 may be copper plating. By forming a copper plating, the metal of the metal plating 40 can be made of the same metal (copper) as the rolled copper foil which is preferable in the case of flexible printed circuit boards.

[0070] Next, as shown in Figure 2F, the exposed portion of the metal thin film 13, that is, the portion of the metal thin film 13 not covered by the metal plating 40, is removed (step S11). More specifically, the portion of the metal thin film 13 not covered by the button land 41 of the land 12b, the wiring 11, and the metal thin film formed on the insulating substrate 30 exposed between the wiring 11 are removed. However, the portion of the metal thin film 13 covered by the metal plating 40 is not removed. This insulates the wiring 11 of the wiring pattern WP1. This does not apply if the wiring 11 are electrically connected to each other in a portion other than the cross-section shown in Figure 2F.

[0071] Specifically, in this embodiment, the metal thin film 13 is removed by flash etching. The etching amount is, for example, 0.5 μm in terms of electrolytic copper foil. Since the etching amount is very small, the impact on the wiring width can be minimized.

[0072] When the thin metal film 13 is removed, the wirings 11 and 21 become slightly thinner. Therefore, when forming the etching resists 15a and 25a in step S3, the width of the etching resists 15a and 25a on the wirings 11 and 21 may be increased, and the width between them (gap width) may be narrowed.

[0073] By following the above steps (steps S1 to S11), the printed circuit board 1 shown in Figure 2F can be manufactured.

[0074] According to this embodiment, since the wiring patterns WP1 and WP2 are formed before the conductive holes H1 and metal plating 40 are formed, there is no need to form a thick resist film to embed the metal plating 40. Therefore, thin resist films 15 and 25 can be used to form the wiring patterns WP1 and WP2.

[0075] Furthermore, since the resist films 15 and 25 are formed before the conductive holes H1 are formed, no resist film is formed on top of the conductive holes H1. Therefore, problems caused by so-called tenting can be avoided. For example, problems such as etching of unnecessary areas due to tenting failure can be avoided. Also, since it is not necessary to form a thick resist film to avoid problems caused by tenting, thinner resist films 15 and 25 can be used.

[0076] As described above, according to this embodiment, since thin resist films 15 and 25 can be used, the resolution of exposure and development is increased, and etching resists 15a and 25a with fine patterns can be formed. Furthermore, because the etching resists 15a and 25a are thin, the etching resolution is increased, and fine wiring patterns WP1 and WP2 can be formed. In other words, fine wiring patterns can be formed in the manufacture of printed circuit boards having interlayer conductive paths.

[0077] Furthermore, according to this embodiment, since the wiring pattern WP1 is formed before the conductive holes H1 are formed, the formation of the wiring pattern WP1 and the conformal mask 12 can be performed simultaneously. Therefore, the step of aligning the exposure pattern of the resist film (which becomes the wiring pattern after etching) with respect to the conductive holes can be omitted, the wiring pattern can be designed to be placed closer to the conductive holes, and the diameter of the land 12b can be designed to be smaller. Consequently, finer wiring patterns can be formed in the manufacture of printed circuit boards with interlayer conductive paths.

[0078] Furthermore, similar to the button plating method, the plating process can be applied only to specific parts of the substrate, thus limiting the area where electrolytic plating is present to the metallic plating 40. As a result, by applying this embodiment to the manufacture of flexible printed circuit boards using rolled copper foil as the metal foil, it is possible to manufacture flexible printed circuit boards in which the bent parts are composed of a high-density wiring pattern made of highly flexible rolled copper foil.

[0079] Furthermore, when manufacturing flexible printed circuit boards, at least one of the above processes (steps S1 to S11) may be carried out using a roll-to-roll method (continuous transport). This can improve the manufacturing efficiency of flexible printed circuit boards. Alternatively, all processes may be carried out using a roll-to-roll method.

[0080] In the above description, the number of conductive holes and conformal masks for forming said conductive holes was assumed to be one, but multiple conductive holes and multiple conformal masks for forming each conductive hole may be formed. In this case, the main surface of the insulating substrate 30 on which the openings of each conductive hole exist (i.e., the main surface of the insulating substrate 30 on which the conformal mask is provided) may be either the first main surface or the second main surface. Furthermore, if the openings of the conductive holes also exist on the second main surface, the thin metal film 13 may also be formed on the second main surface.

[0081] In this embodiment, a double-sided metal-clad laminate having two layers of metal foil was used, but a multilayer printed circuit board having three or more layers of metal foil may also be used as the starting material. In this case, the outermost layer of the multilayer printed circuit board, which is the target for forming the wiring pattern and interlayer conductive paths, is considered to be the first main surface of the double-sided metal-clad laminate in this embodiment, and the method according to this embodiment is applied.

[0082] (Second embodiment) Next, a method for manufacturing a printed circuit board according to the second embodiment will be described with reference to Figures 1, 2A, and 3A to 3E. One of the differences between this embodiment and the first embodiment is the shape of the conductive holes. Hereafter, this embodiment will be described focusing on the differences from the first embodiment, and descriptions of similar parts will be omitted.

[0083] As shown in Figure 2A(1), a double-sided metal-clad laminate 2 is prepared (step S1). In this embodiment, the double-sided metal-clad laminate 2 consists of metal foils 10 and 20 which are rolled copper foils with a thickness of 12 μm, and an insulating substrate which is polyimide with a thickness of 25 μm.

[0084] Next, the metal foil 10 of the double-sided metal-clad laminate 2 is patterned to form the wiring pattern WP1 and conformal mask 12. The metal foil 20 is also patterned to form the wiring pattern WP2 and land 22b. Specifically, the following steps S2 to S5 are performed.

[0085] First, as shown in Figure 2A(2), a resist film 15 is formed on the metal foil 10, and a resist film 25 is formed on the metal foil 20 (step S2). In this embodiment, negative-type dry films with a thickness of 15 μm are used as the resist films 15 and 25.

[0086] Next, as shown in Figure 3A(1), the resist films 15 and 25 are exposed and developed to form etching resists 15a and 25a (step S3). Etching resist 15a includes portions corresponding to the wiring pattern WP1 (described later) and the conformal mask 12. Etching resist 25a includes portions corresponding to the wiring pattern WP2 (described later) and the land 22b.

[0087] In this embodiment, a double-sided simultaneous exposure machine is used for exposure. By using a double-sided simultaneous exposure machine, the aperture 12a of the conformal mask 12 and the aperture 22a, described later, can be superimposed with high precision. For example, the misalignment of the centers of aperture 12a and aperture 22a is within ±20 μm. The exposure method may be projection exposure, proximity exposure, or direct exposure.

[0088] Next, as shown in Figure 3A(2), etching is performed using the etching resists 15a and 25a as masks to remove the metal foils 10 and 20 that are not covered by the etching resists 15a and 25a (step S4). Then, as shown in Figure 3B(1), the etching resists 15a and 25a are removed (step S5). This forms the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22b. An opening 22a exists inside the land 22b. In this embodiment, the diameter of the opening 12a is 50 μm, and the diameter of the opening 22a is 90 μm.

[0089] The diameters of the openings 12a and 22a are arbitrary, but preferably, the opening 22a is formed so that it encloses the opening 12a in a plan view. That is, the diameter of the opening 22a is larger than the diameter of the opening 12a. This makes it easier to form the conductive hole H2, which will be described later, as a through hole. Specifically, even if the center positions of the openings 12a and 22a are misaligned, it is possible to suppress the obstruction of laser processing by the metal foil 20 (especially the land 22b) overlapping the laser beam emission surface. In other words, the opening 22a is a relief hole for the laser beam.

[0090] Steps S2 to S5 described above form the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22b.

[0091] Next, as shown in Figure 3B(2), the conformal mask 12 is irradiated with laser light to remove the insulating substrate 30 exposed in the opening 12a of the conformal mask 12 and form a conductive hole H2 (step S6).

[0092] In this embodiment, the type of laser is a UV-YAG laser. However, the type of laser is not limited to a UV-YAG laser; for example, a carbon dioxide laser may also be used.

[0093] In this embodiment, the conductive hole H2 is a through hole that connects opening 12a and opening 22a.

[0094] Furthermore, as in this embodiment, the conductive hole H2 may be formed such that its inner diameter decreases as it deepens from the opening 12a by adjusting the laser light irradiation conditions. This makes it easier to fix the metal thin film 13, which will be described later, to the side surface of the conductive hole H2.

[0095] Next, as shown in Figure 3C(1), dry plating is performed on the wiring pattern WP1, conformal mask 12, and conductive holes H2 to form a thin metal film 13 (step S7). More specifically, dry plating is performed on the first main surface side of the insulating substrate 30 (the side on which the metal foil 10 is provided) to form a thin metal film 13 on the wiring pattern WP1, conformal mask 12 (i.e., land 12b), and the side surface of the conductive holes H2. Dry plating is also performed on the wiring pattern WP2 and land 22b to form a thin metal film 13. More specifically, dry plating is also performed on the second main surface side of the insulating substrate 30 (the side on which the metal foil 20 is provided) to form a thin metal film 13 on the wiring pattern WP2 and land 22b. Note that the formation of the thin metal film 13 on the first main surface side and the formation of the thin metal film 13 on the second main surface side may be performed first or simultaneously.

[0096] In this embodiment, copper sputtering is performed to form a copper thin film 13 with a thickness of 0.3 μm.

[0097] Next, as shown in Figure 3C(2), plating resists 14 and 24 are formed that cover the wiring patterns WP1 and WP2 but do not cover the conductive holes H2 (step S8). The plating resist 14 has an opening 14a in the portion of the conductive holes H2 so as not to cover them. Similarly, the plating resist 24 has an opening 24a in the portion of the conductive holes H2. In this embodiment, the diameter of the opening 14a is 100 μm, and the diameter of the opening 24a is 140 μm.

[0098] As shown in Figure 3C(2), opening 14a is located above land 12b. Also, opening 24a is located above land 22b.

[0099] In Figure 3C(2), the wiring pattern WP1 is completely covered with the plating resist 14, but this is not limited to this; at least the wiring pattern WP1 around the conductive hole H2 may be covered. Similarly, the wiring pattern WP2 is completely covered with the plating resist 24, but this is not limited to this; at least the wiring pattern WP2 around the conductive hole H2 may be covered. In this case, the plating treatment may be performed only on the conductive hole H2 and the wiring patterns WP1 and WP2 around the conductive hole H2.

[0100] Next, as shown in Figure 3D(1), a metal plating 40 is formed inside the conductive holes H2 by plating (step S9). More specifically, the metal plating 40 is formed inside the opening 14a of the plating resist 14 on which the metal thin film 13 is formed, and inside the opening 24a of the plating resist 24. The metal plating 40 includes button lands 41 and 42. Then, as shown in Figure 3D(2), the plating resists 14 and 24 are removed (step S10). This forms an interlayer conductive path 50 that electrically connects lands 12b and 22b.

[0101] In this embodiment, the metal plating 40 is electrolytic copper plating.

[0102] In this embodiment, since the conductive hole H2 is a through hole, the interlayer conductive path 50 is a plated through hole. In this embodiment, a plated through hole is formed as the interlayer conductive path 50, but it is not limited to this, and vias that fill the through hole may also be formed.

[0103] Next, as shown in Figure 3E, the exposed portion of the metal thin film 13, that is, the portion of the metal thin film 13 that is not covered by the metal plating 40 (or button lands 41, 42), is removed (step S11).

[0104] The printed circuit board 1A according to this embodiment can be manufactured by the above steps (steps S1 to S11).

[0105] According to this embodiment, in addition to the effects of the first embodiment, it is possible to manufacture printed circuit boards having plated through-holes.

[0106] In the above explanation, the number of conductive holes and conformal masks for forming said conductive holes was assumed to be one, but multiple conductive holes and multiple conformal masks for forming each conductive hole may be formed. In this case, the conformal mask for forming each conductive hole may be located on either the first main surface or the second main surface.

[0107] (Third embodiment) A third embodiment will be described with reference to Figures 1, 2A, and 4A to 4B. In this embodiment, both the bottomed holes of the first embodiment and the through-holes of the second embodiment are formed. That is, the printed circuit board 1B manufactured in this embodiment has both bottomed vias and plated through-holes. Hereafter, this embodiment will be described focusing on the differences from the first and second embodiments, and descriptions of similar parts will be omitted.

[0108] First, prepare a double-sided metal-clad laminate 2 as shown in Figure 2A(1) (Step S1).

[0109] Next, as shown in Figure 4A(1), the metal foil 10 of the double-sided metal-clad laminate 2 is patterned to form the wiring pattern WP1, conformal mask 12, and conformal mask 12A. The metal foil 20 is also patterned to form the wiring pattern WP2, lands 22 and lands 22b that face the conformal mask 12 with the insulating substrate 30 in between (steps S2 to S5). The conformal mask 12 includes an opening 12a and lands 12b. The conformal mask 12A includes an opening 12Aa and lands 12Ab. An opening 22a exists inside the land 22b. The diameters of the openings 12a, 12Aa, and 22a are arbitrary, but preferably, the opening 22a is formed to encompass the opening 12Aa in a plan view.

[0110] In this embodiment, it is preferable to use a double-sided simultaneous exposure machine for exposure in step S3 in order to form the conductive hole H2, which is a through hole.

[0111] Next, as shown in Figure 4A(2), the conformal mask 12 is irradiated with laser light to remove the insulating substrate 30 exposed at the opening 12a of the conformal mask 12, thereby forming a closed-ended conductive hole H1. Furthermore, the conformal mask 12A is irradiated with laser light to remove the insulating substrate 30 exposed at the opening 12Aa of the conformal mask 12A, thereby forming a through-hole conductive hole H2 (step S6). The type of laser can be, for example, a UV-YAG laser or a carbon dioxide laser. In this embodiment, the conductive hole H2 is a through-hole connecting the opening 12Aa and the opening 22a. Note that the conductive holes H1 and H2 may be formed either first or simultaneously.

[0112] Next, as shown in Figure 4B(1), dry plating is performed on the wiring patterns WP1, WP2, conformal masks 12, 12A, and conductive holes H1, H2 to form a thin metal film 13 (step S7). In this embodiment, since the conductive hole H2 is a through hole, the thin metal film 13 is formed on both the first main surface and the second main surface of the insulating substrate 30.

[0113] Next, as shown in Figure 4B(2), interlayer conductive paths (bottomed vias) 50 that electrically connect land 12b and land 22, and interlayer conductive paths (plated through-holes) 50A that electrically connect land 12Ab and land 22b are formed. More specifically, first, a plating resist is formed that covers the wiring patterns WP1 and WP2 but does not cover the conduction holes H1 and H2 (step S8). Next, a metal plating 40 is formed inside the conduction hole H1, and a metal plating 40A is formed inside the conduction hole H2 (step S9). The metal plating 40 includes button lands 41. The metal plating 40A includes button lands 41A and 42. After that, the plating resist is removed (step S10). Next, as shown in Figure 4B(2), the exposed portion of the metal thin film 13, i.e., the portion of the metal thin film 13 that is not covered by the metal plating 40, 40A (or button lands 41, 41A, 42), is removed (step S11).

[0114] Steps S8 to S11 above form an interlayer conductive path (bottomed via) 50 that electrically connects land 12b and land 22, and an interlayer conductive path (plated through-hole) 50A that electrically connects land 12Ab and land 22b.

[0115] The printed circuit board 1B according to this embodiment can be manufactured by the above steps (steps S1 to S11).

[0116] According to this embodiment, it is possible to manufacture printed circuit boards having both bottomed vias and plated through-holes.

[0117] In this embodiment, the conformal mask 12 and conformal mask 12A are formed on the same main surface (first main surface) of the double-sided metal-clad laminate 2, but the embodiment is not limited to this, and the conformal mask 12 and conformal mask 12A may be formed on different main surfaces of the double-sided metal-clad laminate 2, respectively.

[0118] Multiple conductive holes H1 and / or conductive holes H2 may be formed. In this case, the conformal mask for forming each conductive hole may be formed on either the first main surface or the second main surface of the double-sided metal-clad laminate 2. Alternatively, vias (filled vias) may be formed to fill the through holes instead of plated through holes.

[0119] Based on the above description, those skilled in the art may conceive of additional effects and various modifications of the present invention, but the embodiments of the present invention are not limited to the individual embodiments described above. Various additions, modifications, and partial deletions are possible without departing from the conceptual idea and spirit of the present invention derived from the claims and their equivalents. [Explanation of Symbols]

[0120] 1,1A,1B Printed Circuit Board 2. Double-sided metal-clad laminate 10, 20, 100, 200 metal foils 11,21,110,210 wiring 12,12A Conformal Mask 12a,12Aa,22a opening 12b, 12Ab, 22b, 120b Land 13 Metal Thin Films 14, 24, 140, 240 Plating resist 14a,24a,140a opening 15, 25, 150, 250 resist film 15a, 25a, 150a, 250a etching resist 22,220 rand 30,300 Insulating substrate 40, 40A, 400 Metal Plating 41,41A,42,410 Buttonland 50, 50A, 500 Interlayer Conductive Path H1,H2,H Conduction hole WP1, WP2, WP10, WP20 Wiring Pattern

Claims

1. A step of preparing a double-sided metal-clad laminate having an insulating substrate having a first main surface and a second main surface opposite to the first main surface, a first metal foil provided on the first main surface, and a second metal foil provided on the second main surface, The process of patterning the first metal foil of the double-sided metal-clad laminate to form a wiring pattern and a conformal mask, The process of irradiating the conformal mask with laser light to remove the insulating substrate exposed at the opening of the conformal mask and form a conductive hole, A step of forming a plating resist that covers the wiring pattern but does not cover the conductive holes, The process of forming a metal plating inside the aforementioned conductive hole, The process includes removing the aforementioned plating resist, Prior to the step of forming the plating resist, a step of performing a dry plating treatment on the wiring pattern, the insulating substrate exposed between the wiring patterns, and the conductive holes, A method for manufacturing a printed circuit board, further comprising the step of removing the plating resist, followed by the step of removing the portion of the metal thin film formed by the dry plating process that is not covered by the metal plating.

2. The step of forming the aforementioned wiring pattern is: A step of forming a resist film on the first metal foil having a thickness of 1.5 times or less the thickness of the first metal foil, A step of exposing and developing the resist film to form an etching resist corresponding to the wiring pattern, The process of forming the wiring pattern by etching away the first metal foil that is not covered with the etching resist, A method for manufacturing a printed circuit board according to claim 1, comprising the step of removing the etching resist.

3. The method for manufacturing a printed circuit board according to claim 1, wherein in the step of forming the wiring pattern and the conformal mask, the wiring pattern and the conformal mask are formed simultaneously.

4. The method for manufacturing a printed circuit board according to claim 1, wherein the dry plating process is performed by sputtering.

5. The first and second metal foils are copper foils. The aforementioned sputtering method is a sputtering method using copper, The method for manufacturing a printed circuit board according to claim 4, wherein the metal thin film is a copper thin film.

6. The method for manufacturing a printed circuit board according to claim 1, wherein the step of forming the conductive hole is performed such that the second metal foil is exposed on the bottom surface of the conductive hole.

7. A step of preparing a double-sided metal-clad laminate having an insulating substrate having a first main surface and a second main surface opposite to the first main surface, a first metal foil provided on the first main surface, and a second metal foil provided on the second main surface, The process of patterning the first metal foil of the double-sided metal-clad laminate to form a wiring pattern and a conformal mask, The process of patterning the second metal foil of the double-sided metal-clad laminate to form a wiring pattern, another opening that encloses the opening of the conformal mask in a plan view, and a land, A step of irradiating the conformal mask with laser light to remove the insulating substrate exposed in the opening of the conformal mask and to form a conductive hole that becomes a through hole connecting the opening and the other opening, A step of forming a plating resist that covers the wiring pattern but does not cover the conductive holes, The process of forming a metal plating inside the aforementioned conductive hole, A method for manufacturing a printed circuit board, comprising the step of removing the aforementioned plating resist.

8. The conformal mask includes a first opening and a second opening as the openings. A step of patterning the second metal foil of the double-sided metal-clad laminate to form a third opening, further comprising the step of ensuring that the third opening encloses the second opening of the conformal mask in a plan view, A method for manufacturing a printed circuit board according to claim 1, wherein in the step of forming the conductive holes, the insulating substrate exposed to the first opening and the second opening of the conformal mask is removed to form a first conductive hole on the bottom surface in which the second metal foil is exposed, and a second conductive hole that connects the second opening and the third opening.

9. The method for manufacturing a printed circuit board according to any one of claims 1 to 8, wherein the printed circuit board is a flexible printed circuit board.

10. The method for manufacturing a printed circuit board according to claim 9, wherein the first and second metal foils are rolled copper foils.

11. The method for manufacturing a printed circuit board according to any one of claims 1 to 8, wherein the metal plating is electrolytic plating.

12. A method for manufacturing a printed circuit board, wherein at least one step is performed in a roll-to-roll manner, according to the manufacturing method described in claim 9.

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