WO2024057586A1 - Method for producing printed wiring board - Google Patents

Abstract

The present invention provides a method for forming a fine wiring pattern in the production of a printed wiring board having an inter-layer electrically-conductive path.　A method for producing a printed wiring board 1 according to an embodiment of the present invention comprises: a step for preparing a double-sided metal-clad laminated board 2 that includes an insulating substrate 30 having a first main surface and a second main surface opposite to the first main surface, a metal foil 10 provided on the first main surface, and a metal foil 20 provided on the second main surface; a step for forming a wiring pattern WP1 and a conformal mask 12 by patterning the metal foil 10 of the double-sided metal-clad laminated board 2; a step for forming a conduction hole by irradiating the conformal mask 12 with a laser beam and removing the insulating substrate 30 exposed at an opening 12a of the conformal mask 12; a step for forming a plating resist 14 that covers the wiring pattern WP1 and that does not cover the conduction hole; a step for forming a metal plating 40 inside the conduction hole; and a step for removing the plating resist 14.

Description

Manufacturing method of printed wiring board

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 fine wiring patterns in manufacturing a printed wiring board having interlayer conductive paths.

Electronic devices, including information and communication devices such as smartphones, are becoming smaller and lighter, and there is a need for smaller, higher-density circuit boards. Increasing the density of a substrate means forming more wiring lines on a limited outer shape of the substrate. In order to form more wiring, it is necessary to miniaturize and multilayer wiring patterns.

Etching is used to form the wiring pattern. The subtractive method is one of the methods of 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, it is advantageous for the metal foil used for the wiring to be thinner.

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

Japanese Patent Application Publication No. 2006-108270 Japanese Unexamined Patent Publication No. 11-195849 Patent No. 6884333

The button plating method is a method in which plating is applied only to specific parts of the substrate. An example of a method for forming a wiring pattern and an interlayer conductive path in the button plating method will be described with reference to FIGS. 5A to 5D. 5A to 5D are process cross-sectional views illustrating a method for manufacturing a printed wiring board according to a comparative example.

As shown in FIG. 5A(1), a double-sided metal-clad laminate including metal foils 100, 200 and an insulating base material 300 is prepared. Next, as shown in FIG. 5A(1), conduction holes H are formed in the double-sided metal-clad laminate. Next, as shown in FIG. 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. An opening 140a is provided in the plating resist 140 at a portion of the conduction hole H. That is, the plating resist 140 does not cover the conductive holes H.

Next, as shown in FIG. 5B(1), a plating process is performed to form metal plating 400 (button plating) inside the conduction hole H. Metal plating 400 includes button lands 410. Thereafter, as shown in FIG. 5B(2), the plating resists 140 and 240 are removed.

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

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

The button plating method has the following problems when miniaturizing wiring patterns. As shown in FIG. 5B(2), the upper part of the metal plating 400 protrudes from the metal foil 100. In order to prevent the metal plating 400 from being etched in subsequent steps, it is necessary to bury the metal plating 400 protruding from the metal foil 100 when forming the resist film 150, as shown in FIG. 5C(1). For this reason, the resist film 150 is formed thick. However, when the resist film 150 is made thicker, the etching resolution decreases, making it difficult to form fine wiring patterns.

The present invention has been made based on the above technical recognition, and its purpose is to provide a method for manufacturing a printed wiring board for forming a fine wiring pattern in manufacturing a printed wiring board having interlayer conductive paths. It is to be.

The method for manufacturing a printed wiring board according to the present invention includes:
an insulating base material 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; a step of preparing a double-sided metal-clad laminate having a second metal foil provided on the surface;
patterning the first metal foil of the double-sided metal-clad laminate to form a wiring pattern and a conformal mask;
irradiating the conformal mask with laser light to remove the insulating base material exposed in the opening of the conformal mask to form a conductive hole;
forming a plating resist that covers the wiring pattern but does not cover the conduction hole;
forming metal plating inside the conduction hole;
removing the plating resist;
It is characterized by having the following.

Further, in the method for manufacturing the printed wiring board,
The step of forming the wiring pattern includes:
forming a resist film having a thickness of 1.5 times or less than the thickness of the first metal foil on the first metal foil;
exposing and developing the resist film to form an etching resist corresponding to the wiring pattern;
forming the wiring pattern by etching away the first metal foil that is not covered with the etching resist;
The method may further include a step of removing the etching resist.

Further, in the method for manufacturing the printed wiring board,
In the step of forming the wiring pattern and the conformal mask, the wiring pattern and the conformal mask may be formed simultaneously.

Further, in the method for manufacturing the printed wiring board,
Before the step of forming the plating resist, performing a dry plating treatment on the wiring pattern, the insulating base material exposed between the wiring patterns, and the conduction hole;
After the step of removing the plating resist, the method may further include a step of removing a portion of the metal thin film formed by the dry plating process that is not covered with the metal plating.

Further, in the method for manufacturing the printed wiring board,
The dry plating process may be performed using a sputtering method.

In addition, in the method for producing a printed wiring board,
The metal foil is a copper foil,
The sputtering method is a sputtering method using copper,
The metal thin film may be a copper thin film.

Further, in the method for manufacturing the printed wiring board,
The step of forming the conduction hole may be performed such that the second metal foil is exposed at the bottom of the conduction hole.

Further, in the method for manufacturing the printed wiring board,
patterning the second metal foil of the double-sided metal-clad laminate to form a wiring pattern, another opening that includes the 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 the opening and the other opening.

Further, in the method for manufacturing the printed wiring board,
The conformal mask includes a first opening and a second opening as the opening, and the second metal foil of the double-sided metal-clad laminate is patterned to form a third opening. further comprising a step in which the third opening includes the second opening of the conformal mask in a plan view,
In the step of forming the conduction hole, the insulating base material exposed in the first opening and the second opening of the conformal mask is removed to expose the second metal foil on the bottom surface. A second conduction hole may be formed that connects the first conduction hole and the second opening and the third opening.

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

Further, in the method for manufacturing the printed wiring board,
The first and second metal foils may be rolled copper foils.

Further, in the method for manufacturing the printed wiring board,
The metal plating may be electrolytic plating.

Further, in the method for manufacturing the printed wiring board,
At least one of the above steps may be performed in a roll-to-roll manner.

According to the method for manufacturing a printed wiring board according to the present invention, since the wiring pattern is formed before forming the conduction holes, there is no need to bury the interlayer conductive paths formed in the conduction holes with etching resist. Therefore, a thin resist film can be used, and fine wiring patterns can be formed in the manufacture of printed wiring boards having interlayer conductive paths.

1 is a flowchart showing a method for manufacturing a printed wiring board according to an embodiment. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to the first embodiment. 2A is a process cross-sectional view illustrating the method for manufacturing the printed wiring board according to the first embodiment, following FIG. 2A. FIG. FIG. 2B is a process cross-sectional view illustrating the method for manufacturing the printed wiring board according to the first embodiment, following FIG. 2B. FIG. 2C is a process cross-sectional view illustrating the method for manufacturing the printed wiring board according to the first embodiment, following FIG. 2C. FIG. 2D is a process cross-sectional view illustrating the method for manufacturing the printed wiring board according to the first embodiment, following FIG. 2D. FIG. 2E is a process cross-sectional view illustrating the method for manufacturing the printed wiring board according to the first embodiment, following FIG. 2E. FIG. 7 is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a second embodiment. FIG. 3A is a process cross-sectional view illustrating the method for manufacturing a printed wiring board according to the second embodiment, following FIG. 3A. FIG. 3B is a process cross-sectional view illustrating the method for manufacturing a printed wiring board according to the second embodiment, following FIG. 3B. FIG. 3C is a process cross-sectional view illustrating the method for manufacturing a printed wiring board according to the second embodiment, following FIG. 3C. FIG. 3D is a process cross-sectional view illustrating the method for manufacturing a printed wiring board according to the second embodiment, following FIG. 3D. FIG. 7 is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a third embodiment. FIG. 4A is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a third embodiment, following FIG. 4A. FIG. 3 is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a comparative example. 5A is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a comparative example, following FIG. 5A. FIG. FIG. 5B is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a comparative example, following FIG. 5B. FIG. 5C is a process cross-sectional view illustrating a method for manufacturing a printed wiring board according to a comparative example, following FIG. 5C.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. Note that in each figure, the same reference numerals are given to components having the same function. Further, the drawings are schematic and mainly show the characteristic parts of each embodiment, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each layer, etc. are different from the actual drawings.

(First embodiment)
An example of the method for manufacturing a printed wiring board according to the first embodiment will be described with reference to FIG. 1 and FIGS. 2A to 2F. FIG. 1 is a flowchart showing a method for manufacturing a printed wiring board according to this embodiment. 2A to 2F are process cross-sectional views illustrating the method for manufacturing a printed wiring board according to this embodiment.

The printed wiring board manufactured in this embodiment is a flexible printed wiring board. Note that the printed wiring board manufactured in this embodiment is not limited to a flexible printed wiring board, and may be a rigid printed wiring board.

As shown in FIG. 2A(1), a double-sided metal-clad laminate 2 is prepared (step S1). The double-sided metal-clad laminate 2 includes metal foils 10 and 20 and an insulating base material 30. More specifically, the double-sided metal-clad laminate 2 includes an insulating base material 30 having an upper surface (first main surface) and a lower surface (second main surface opposite to the first main surface); It has a metal foil 10 provided on the upper surface and a metal foil 20 provided on the lower surface of the insulating base material 30.

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

Note that 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, 20 is, for example, 5 to 72 μm. Furthermore, the thicknesses of the metal foil 10 and the metal foil 20 may be different from each other. Furthermore, the material of the metal foils 10 and 20 is not limited to copper, and may be a metal other than copper (for example, silver, aluminum, etc.).

Moreover, when using copper foil as the metal foils 10 and 20, it is not limited to electrolytic copper foil, but may be rolled copper foil. When manufacturing flexible printed wiring boards, rolled copper foil is preferred. By using rolled copper foil, a flexible printed wiring board with high flexibility can be provided.

Note that the thickness and material of the insulating base material 30 are not limited to those described above. The thickness of the insulating base material 30 is, for example, 6 to 100 μm. The material of the insulating base material 30 is, for example, a fluorine-based material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), or polyimide such as MPI (modified polyimide) or PI (polyimide). The material may be a type material such as PEEK (polyetheretherketone), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate).

Next, the metal foil 10 of the double-sided metal-clad laminate 2 is patterned to form the wiring pattern WP1 and the conformal mask 12. Further, the metal foil 20 is 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.

First, as shown in FIG. 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, 25 are formed by laminating a 10 μm thick negative dry film onto the metal foils 10, 20.

Note that the thickness and material of the resist films 15 and 25 are not limited to those described above, but in order to form a fine wiring pattern, it is preferable that the resist films 15 and 25 be thin. Specifically, the thickness is preferably 0.1 times or more and 1.5 times or less the thickness of the metal foils 10 and 20. In this embodiment, the thickness of the resist films 15 and 25 is 0.1 of the thickness of the metal foils 10 and 20.
It is more than twice and less than 1 times. Note that the thicknesses of the resist film 15 and the resist film 25 may be different from each other.

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

In this embodiment, a proximity exposure machine is used for exposure. Note that the exposure method is not limited to proximity exposure, and may be projection exposure, direct exposure, or the like.

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

Thereafter, as shown in FIG. 2C (1), the etching resists 15a and 25a are removed (step S5). Thereby, the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22 on the opposite side of the conformal mask 12 are formed. The wiring pattern WP1 includes a plurality of wirings 11 arranged at intervals. Similarly, the wiring pattern WP2 includes a plurality of wirings 21 arranged at intervals. Conformal mask 12 includes openings 12a and lands 12b.

In this embodiment, the width of the wirings 11 and 21 is 20 μm. Further, the width (gap width) between the wirings 11 and 21 is 20 μm. Note that the width of the wirings 11 and 21 may be 10 to 30 μm. Further, the width between the wirings 11 and 21 may be 10 to 30 μm.

Furthermore, in this embodiment, the diameter of the opening 12a is 50 μm, and the diameter (outer diameter) of the land 12b is 90 μm. Note that the diameters of the openings 12a and the lands 12b are not limited to those described above, but in order to form a high-density wiring pattern, they are preferably as small as possible.

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

Preferably, at least the wiring pattern WP1 and the conformal mask 12 are formed at the same time. Thereby, alignment between the wiring pattern WP1 and the conformal mask 12 can be omitted. More specifically, alignment between the wiring pattern WP1 and the conduction hole H1 (described later) formed at the position of the opening 12a of the conformal mask 12 can be omitted. In the conventional button plating method, first, a conductive hole H is formed, and an exposed pattern of a resist film (which becomes a wiring pattern after etching) is aligned with the formed conductive hole H. More specifically, in the step of FIG. 5C (2), the exposure pattern of the resist film 150 is aligned with the metal plating 400. Generally, a shift occurs during the alignment. At this time, in order to prevent the wiring pattern WP10 from overlapping the conduction hole H, the wiring pattern WP10 is designed with a margin to avoid the conduction hole H. Further, in order to form the land 120b around the conduction hole H, the diameter of the land 120b is designed to be large. On the other hand, in this embodiment, since the alignment itself can be omitted, the wiring pattern WP1 can be designed to be placed closer to the conduction hole H1. Further, the diameter of the land 12b, which will be described later, can be designed to be small. Therefore, a finer wiring pattern can be formed. Further, since there is no need to provide a separate process for forming the conformal mask 12, the process can be simplified.

Through the above steps S2 to S5, the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22 on the opposite side of the conformal mask 12 are formed.

Note that the wiring pattern WP2 may not be formed on the lower surface of the double-sided metal-clad laminate 2 in steps S2 to S5, and the lower surface of the double-sided metal-clad laminate 2 may remain the metal foil 20.

Next, as shown in FIG. 2C (2), the conformal mask 12 is irradiated with laser light to form the conductive hole H1 (step S6). More specifically, from the first main surface side of the insulating base material 30 (the side on which the metal foil 10 is provided), a land is formed with a width wider than the diameter of the opening 12a with respect to the opening 12a of the conformal mask 12. A laser beam whose width is narrower than the diameter of the beam 12b is irradiated. Thereby, using the land 12b as a mask, the insulating base material 30 exposed in the opening 12a is removed to form the conduction hole H1. At this time, a conduction hole H1 is formed at the position of the opening 12a of the conformal mask 12. Note that after removing the insulating base material 30, desmear treatment using plasma or the like may be performed.

The type of laser used in this step is a carbon dioxide laser. Note that the type of laser is not limited to a carbon dioxide laser, and may be, for example, a UV-YAG laser.

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 conduction hole H1 in the step of forming the conduction hole H1. Thereby, the conduction hole H1 becomes a hole with a bottom.

Note that by adjusting the laser beam irradiation conditions, the conduction hole H1 may be formed so that the inner diameter becomes smaller as it gets deeper from the opening 12a, as shown in FIG. 2C (2). Thereby, the metal thin film 13 described later can be easily fixed on the side surface of the conduction hole H1.

Next, as shown in FIG. 2D (1), dry plating is performed on the wiring pattern WP1, the conformal mask 12, and the conduction hole H1 to form the metal thin film 13 (step S7). More specifically, dry plating is performed on the first main surface side (the side on which the metal foil 10 is provided) of the insulating base material 30, and the insulating base exposed between the wiring pattern WP1 and the wiring pattern WP1 is removed. A metal thin film 13 is formed on the material 30, the conformal mask 12 (that is, the land 12b), and the inner wall (side surface and bottom surface) of the conduction hole H1. By forming the metal thin film 13, the insulating base material 30 exposed on the side surface of the conduction hole H1 becomes conductive, and the electrical connection of the interlayer conductive path 50 described later can be stabilized. Note that in this step, a copper thin film with a thickness of 0.3 μm is formed as the metal thin film 13 using, for example, copper sputtering.

Furthermore, since the metal thin film 13 is also formed on the insulating base material 30 exposed in the wiring pattern WP1, the plurality of wirings 11 are temporarily electrically connected to each other. However, in the subsequent step S11, the metal thin film 13 between the wirings 11 is removed.

Note that the thickness of the metal thin film 13 is arbitrary, but it must be at least as thick as necessary to make the metal plating 40 (described later) conductive in the conductive hole H1, and that the metal thin film 13 between the wirings 11 In order to minimize the influence on the wiring pattern WP1 when removing the wiring pattern WP1, it is preferable that the thickness is below a certain level (for example, 0.1 times the width of the wirings 11 and 21 or less).

Note that wet plating treatment (electrolytic plating treatment, chemical plating treatment, etc.) may be used instead of dry plating treatment. Preferably, in step S7, dry plating is used as the plating. By using dry plating, the metal thin film 13 can be made thinner than wet plating, and when the metal thin film 13 is removed in a subsequent process, it can be easily removed by a small amount of etching, etc. The influence on WP1 can be minimized. In addition, the dry plating process can form the metal thin film 13 with few impurities, and the electrical resistance of the metal thin film 13 can be reduced. Therefore, even if the metal thin film 13 is formed on the metal foil 10 (particularly the land 12b) and the land 22 exposed on the bottom surface of the conduction hole H1, the conductivity of the metal plating 40 and the land 12b, which will be described later, will be reduced. , and the influence on the conductivity of the metal plating 40 and the land 22 can be minimized. That is, the influence on the conductivity of the interlayer conductive path 50, which will be described later, can be minimized. Further, in the case of wet plating, a catalyst (for example, palladium, etc.) may remain in the wiring pattern WP1 when removing the metal thin film 13, and a separate process for removing the catalyst may be required. On the other hand, in the dry plating process, since no catalyst is used, the process can be simplified.

Furthermore, the dry plating method is not limited to the sputtering method, but may also be a vapor deposition method or the like. More preferably, the dry plating treatment is performed by a sputtering method. Thereby, the adhesive force of the metal thin film 13 can be increased, and the electrical conductivity of the conductive hole H1 can be stabilized.

Note that when using the sputtering method, the same metal as the metal foil 10 may be used. By using the same metal, the physical, electrical, and chemical properties are uniform, which simplifies subsequent processing. In particular, when the metal foil 10 is a copper foil, the sputtering method may be a sputtering method using copper (copper sputtering). At this time, the metal thin film 13 becomes a copper thin film. By forming the 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 a flexible printed wiring board.

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

Hereinafter, an example of the process performed in step S8 will be described. First, a plating resist is formed to cover the entire both sides of the wiring board obtained in FIG. 2D(1). That is, a resist film that covers the wiring pattern WP1 on which the metal thin film 13 is formed, the land 12b, and the conduction hole H1, and a resist film that covers the wiring pattern WP2 and the land 22 are formed.

Next, the formed resist film is exposed 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 a button land 41, which will be described later.

In this embodiment, a direct exposure machine is used for exposure. The exposure method is not limited to this and may be proximity exposure, projection exposure, etc., but direct exposure is preferably used. Even if the wiring board expands or contracts in a process prior to the exposure process, the direct exposure machine can draw an exposure pattern according to the expansion or contraction. Therefore, there is no need to design the diameter of the opening 14a in 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 in the plating resist 14 can be made smaller. This allows the diameter of the button land 41, which will be described later, to be made smaller, and the diameter of the land 12b to be made even smaller.

Note that in FIG. 2D(2), the wiring pattern WP1 is entirely covered with the plating resist 14, but the present invention is not limited to this. For example, only the wiring pattern WP1 existing around at least the conduction hole H1 may be covered with the plating resist 14. In this case, plating treatment (for example, immersion in a plating solution) is performed only on the conduction hole H1 and the wiring pattern WP1 around the conduction hole H1.

After forming the plating resists 14 and 24 as described above, as shown in FIG. 2E(1), a plating process is performed to form metal plating 40 inside the conduction hole H1 (step S9). More specifically, metal plating 40 is formed inside the opening 14a of the plating resist 14 in which the metal thin film 13 is formed. Metal plating 40 includes button lands 41. By forming the metal plating 40, a part of the metal thin film 13 is covered with the metal plating 40. Specifically, a portion of the metal thin film 13 formed on the inner wall (side surface and bottom surface) of the conduction hole H1 is covered with the metal plating 40.

Note that the metal plating 40 may be formed not only inside the conduction hole H1 but also on the land 12b, as shown in FIG. 2E(1). At this time, a part of the land 12b is covered with the button land 41, as shown in FIG. 2E(1). More specifically, a portion of the metal thin film 13 formed on the land 12b is covered with metal plating 40 (button land 41).

Thereafter, as shown in FIG. 2E(2), the plating resists 14 and 24 are removed (step S10). Thereby, an interlayer conductive path 50 that electrically connects the land 12b and the land 22 is formed.

In this embodiment, since the conduction hole H1 is a bottomed hole, the interlayer conductive path 50 is a bottomed via. Note that in FIG. 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.

In this embodiment, the metal plating 40 is electrolytic plating. More specifically, electroplating is performed to form metal plating 40. By using electrolytic plating, the time for plating treatment can be shortened and manufacturing efficiency can be improved compared to the case where electroless plating is used.

Note that the metal plating 40 may be made of the same metal as the metal foil 10. By using the same metal, they have the same physical, electrical, and chemical properties, making handling easier. In particular, when metal foil 10 is copper foil, metal plating 40 may be copper plating. By forming the copper plating, the metal of the metal plating 40 can be the same metal (copper) as the rolled copper foil that is preferable in the case of a flexible printed wiring board.

Next, as shown in FIG. 2F, the exposed portion of the metal thin film 13, that is, the portion of the metal thin film 13 that is not covered with the metal plating 40 is removed (step S11). More specifically, in the metal thin film 13, the metal thin film formed on the portion of the land 12b not covered by the button land 41, the wiring 11, and the insulating base material 30 exposed between the wiring 11 is removed. . However, the portion of the metal thin film 13 covered with the metal plating 40 is not removed. This insulates the wiring 11 of the wiring pattern WP1. Note that this does not apply when the wirings 11 are designed to be electrically connected to each other in a portion other than the cross section shown in FIG. 2F.

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 amount of etching is extremely small, the effect on the wiring width can be minimized.

Note that when removing the metal thin film 13, the wirings 11 and 21 become slightly thinner. Therefore, when forming the etching resists 15a, 25a in step S3, the widths of the etching resists 15a, 25a above the wirings 11, 21 may be made thicker, and the width between them (gap width) may be made narrower.

Through the above steps (steps S1 to S11), printed wiring board 1 shown in FIG. 2F can be manufactured.

According to this embodiment, since the wiring patterns WP1 and WP2 are formed before forming the conduction hole H1 and the metal plating 40, there is no need to form a thick resist film to bury the metal plating 40. Therefore, thin resist films 15 and 25 can be used to form wiring patterns WP1 and WP2.

Furthermore, since the resist films 15 and 25 are formed before forming the conduction hole H1, no resist film is formed on the conduction hole H1. Therefore, problems caused by so-called tenting can be avoided. For example, problems such as unnecessary etching due to tearing of the tenting can be avoided. Further, 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.

As described above, according to the present embodiment, thin resist films 15 and 25 can be used, so the resolution of exposure and development is increased, and etching resists 15a and 25a having fine patterns can be formed. Since the etching resists 15a and 25a become thinner, the etching resolution increases and fine wiring patterns WP1 and WP2 can be formed. That is, fine wiring patterns can be formed in the manufacture of printed wiring boards having interlayer conductive paths.

Furthermore, according to the present embodiment, since the wiring pattern WP1 is formed before forming the conduction hole H1, the formation of the wiring pattern WP1 and the formation of the conformal mask 12 can be performed at the same time. Therefore, the process of aligning the exposed pattern of the resist film (which becomes the wiring pattern after etching) with the conduction hole can be omitted, and the wiring pattern can be designed to be placed closer to the conduction hole. In addition, the diameter of the land 12b can be designed to be small. Therefore, finer wiring patterns can be formed in the manufacture of printed wiring boards having interlayer conductive paths.

Furthermore, like the button plating method, plating can be performed only on specific parts of the substrate, so the parts where electrolytic plating is present can be limited to the metal plating 40. As a result, by applying this embodiment to the manufacture of a flexible printed wiring board using rolled copper foil as the metal foil, the bending portion can be made of a high-density wiring pattern made of rolled copper foil with high flexibility. Flexible printed wiring boards can be manufactured.

Note that when manufacturing a flexible printed wiring board, at least one of the above steps (steps S1 to S11) may be performed using a roll-to-roll method (continuous conveyance). Thereby, the manufacturing efficiency of flexible printed wiring boards can be improved. Alternatively, all steps may be performed in a roll-to-roll manner.

In the above explanation, the number of conductive holes and the conformal mask for forming the conductive holes is one, but the number of conductive holes and the number of conformal masks for forming each conductive hole is one. A formal mask may also be formed. At this time, the main surface of the insulating base material 30 where the opening of each conductive hole exists (that is, the main surface of the insulating base material 30 where the conformal mask is provided) is the first main surface and the second main surface. Either is fine. Further, when the opening of the conduction hole is also present on the second main surface, the metal thin film 13 may be formed on the second main surface as well.

Note that in this embodiment, a double-sided metal-clad laminate having two layers of metal foil was used, but a multilayer printed wiring board having three or more layers of metal foil may be used as the starting material. In this case, the method according to the present embodiment assumes that the outermost layer of the multilayer printed wiring board on which the wiring pattern and the interlayer conductive path are to be formed is the first main surface of the double-sided metal-clad laminate according to the present embodiment. apply.

(Second embodiment)
Next, a method for manufacturing a printed wiring board according to a second embodiment will be described with reference to FIGS. 1, 2A, and 3A to 3E. One of the differences between this embodiment and the first embodiment is the form of the conduction holes. Hereinafter, this embodiment will be described with a focus on differences from the first embodiment, and description of similar parts will be omitted.

As shown in FIG. 2A(1), a double-sided metal-clad laminate 2 is prepared (step S1). In this embodiment, in the double-sided metal-clad laminate 2, the metal foils 10 and 20 are rolled copper foils with a thickness of 12 μm, and the insulating base material is polyimide with a thickness of 25 μm.

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

First, as shown in FIG. 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 dry films with a thickness of 15 μm are used as the resist films 15 and 25.

Next, as shown in FIG. 3A (1), the resist films 15 and 25 are exposed and developed to form etching resists 15a and 25a (step S3). The etching resist 15a includes a portion corresponding to a wiring pattern WP1, which will be described later, and a portion corresponding to the conformal mask 12. Further, the etching resist 25a includes a portion corresponding to a wiring pattern WP2, which will be described later, and a portion corresponding to the land 22b.

In this embodiment, a double-sided simultaneous exposure machine is used for exposure. By using a double-sided simultaneous exposure machine, the opening 12a of the conformal mask 12 and the opening 22a, which will be described later, can be overlapped with high precision. For example, the deviation between the center positions of the opening 12a and the opening 22a is within ±20 μm. Note that the exposure method may be projection exposure, proximity exposure, direct exposure, or the like.

Next, as shown in FIG. 3A (2), etching is performed using the etching resists 15a, 25a as masks to remove the metal foils 10, 20 that are not covered with the etching resists 15a, 25a (step S4). Thereafter, as shown in FIG. 3B(1), the etching resists 15a and 25a are removed (step S5). Thereby, wiring patterns WP1 and WP2, conformal mask 12, and land 22b are formed. 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.

Note that the diameters of the openings 12a and 22a are arbitrary, but preferably they are formed so that the opening 22a includes the opening 12a in a plan view. That is, the diameter of the opening 22a is larger than the diameter of the opening 12a. Thereby, it is possible to easily form the conduction hole H2, which will be described later, as a through hole. Specifically, even if the center positions of the apertures 12a and 22a are misaligned, it is possible to prevent the metal foil 20 (particularly the land 22b) from overlapping the laser beam emission surface and hinder laser processing. can. In other words, the opening 22a is an escape hole for the laser beam.

Through the above steps S2 to S5, the wiring patterns WP1 and WP2, the conformal mask 12, and the land 22b are formed.

Next, as shown in FIG. 3B (2), by irradiating the conformal mask 12 with a laser beam, the insulating base material 30 exposed in the opening 12a of the conformal mask 12 is removed to form a conductive hole H2. (Step S6).

In this embodiment, the type of laser is a UV-YAG laser. Note that the type of laser is not limited to the UV-YAG laser, and may be, for example, a carbon dioxide laser.

In this embodiment, the conduction hole H2 becomes a through hole that communicates the opening 12a and the opening 22a.

Note that, as in this embodiment, by adjusting the laser beam irradiation conditions, the conductive hole H2 may be formed so that the inner diameter becomes smaller as it gets deeper from the opening 12a. Thereby, the metal thin film 13 described later can be easily fixed on the side surface of the conduction hole H2.

Next, as shown in FIG. 3C (1), dry plating is performed on the wiring pattern WP1, the conformal mask 12, and the conduction hole H2 to form the metal thin film 13 (step S7). More specifically, a dry plating process is performed on the first main surface side (the side on which the metal foil 10 is provided) of the insulating base material 30, and the wiring pattern WP1 and the conformal mask 12 (namely, the land 12b) are formed. , and the metal thin film 13 is formed on the side surface of the conduction hole H2. Further, the wiring pattern WP2 and the land 22b are also subjected to dry plating treatment to form the metal thin film 13. More specifically, dry plating is also performed on the second main surface side of the insulating base material 30 (the side on which the metal foil 20 is provided), and the metal thin film 13 is formed on the wiring pattern WP2 and the land 22b. do. Note that the formation of the metal thin film 13 on the first main surface side and the formation of the metal thin film 13 on the second main surface side may be performed either first or at the same time.

In this embodiment, copper sputtering is performed to form a copper thin film with a thickness of 0.3 μm as the metal thin film 13.

Next, as shown in FIG. 3C (2), plating resists 14 and 24 are formed that cover the wiring patterns WP1 and WP2 but do not cover the conduction holes H2 (step S8). An opening 14a is provided in the plating resist 14 at a portion of the conduction hole H2 so as not to cover the conduction hole H2. Similarly, the plating resist 24 is provided with an opening 24a at the conduction hole H2. In this embodiment, the diameter of the opening 14a is 100 μm, and the diameter of the opening 24a is 140 μm.

Note that, as shown in FIG. 3C(2), the opening 14a is located above the land 12b. Further, the opening 24a is located above the land 22b.

Although the wiring pattern WP1 is entirely covered with the plating resist 14 in FIG. 3C(2), the present invention is not limited to this, and at least only the wiring pattern WP1 around the conduction hole H2 may be covered. Moreover, although the wiring pattern WP2 is entirely covered with the plating resist 24, the present invention is not limited to this, and at least only the wiring pattern WP2 around the conduction hole H2 may be covered. In this case, the plating process may be performed only on the conduction hole H2 and the wiring patterns WP1 and WP2 around the conduction hole H2.

Next, as shown in FIG. 3D(1), metal plating 40 is formed inside the conduction hole H2 by performing a plating process (step S9). More specifically, metal plating 40 is formed inside the opening 14a of the plating resist 14 in which the metal thin film 13 is formed and inside the opening 24a of the plating resist 24. Metal plating 40 includes button lands 41 and 42. Thereafter, as shown in FIG. 3D (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 22b.

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

In this embodiment, since the conduction 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 the present invention is not limited to this, and a via may be formed to fill the through hole.

Next, as shown in FIG. 3E, the exposed portion of the metal thin film 13, that is, the portion of the metal thin film 13 that is not covered with the metal plating 40 (or button lands 41, 42) is removed ( Step S11).

Through the above steps (steps S1 to S11), the printed wiring board 1A according to the present embodiment can be manufactured.

According to this embodiment, in addition to the effects of the first embodiment, a printed wiring board having plated through holes can be manufactured.

In the above explanation, the number of conductive holes and the conformal mask for forming the conductive holes is one, but the number of conductive holes and the number of conformal masks for forming each conductive hole is one. A formal mask may also be formed. At this time, the conformal mask for forming each conduction hole may be present on either the first main surface or the second main surface.

(Third embodiment)
A third embodiment will be described with reference to FIGS. 1, 2A, and 4A to 4B. In this embodiment, both the bottomed hole of the first embodiment and the through hole of the second embodiment are formed. That is, the printed wiring board 1B manufactured in this embodiment has both bottomed vias and plated through holes. Hereinafter, this embodiment will be described with a focus on the differences from the first and second embodiments, and descriptions of similar parts will be omitted.

First, as shown in FIG. 2A(1), a double-sided metal-clad laminate 2 is prepared (step S1).

Next, as shown in FIG. 4A(1), the metal foil 10 of the double-sided metal-clad laminate 2 is patterned to form a wiring pattern WP1, a conformal mask 12, and a conformal mask 12A. Further, the metal foil 20 is patterned to form the wiring pattern WP2, the land 22 facing the conformal mask 12 with the insulating base material 30 in between, and the land 22b (steps S2 to S5). Conformal mask 12 includes openings 12a and lands 12b. Conformal mask 12A includes opening 12Aa and land 12Ab. An opening 22a exists inside the land 22b. Although the diameters of the openings 12a, 12Aa, and 22a are arbitrary, they are preferably formed so that the opening 22a includes the opening 12Aa in a plan view.

Note that in this embodiment, in order to form the conduction hole H2, which is a through hole, it is preferable to use a double-sided simultaneous exposure machine for the exposure in step S3.

Next, as shown in FIG. 4A (2), by irradiating the conformal mask 12 with laser light, the insulating base material 30 exposed in the opening 12a of the conformal mask 12 is removed, and the conductor, which is a bottomed hole, is removed. A common hole H1 is formed. Further, by irradiating the conformal mask 12A with a laser beam, the insulating base material 30 exposed in the opening 12Aa of the conformal mask 12A is removed to form a conduction hole H2 which is a through hole (step S6). The types of lasers include, for example, UV-YAG lasers and carbon dioxide lasers. Further, in this embodiment, the conduction hole H2 is a through hole that allows the opening 12Aa and the opening 22a to communicate with each other. Note that either the conduction hole H1 or the conduction hole H2 may be formed first, or they may be formed at the same time.

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

Next, as shown in FIG. 4B(2), an interlayer conductive path (bottomed via) 50 electrically connects land 12b and land 22, and an interlayer conductive path (bottomed via) electrically connects land 12Ab and land 22b. Form a plated through hole) 50A. More specifically, first, a plating resist is formed that covers the wiring patterns WP1 and WP2 but does not cover the conductive holes H1 and H2 (step S8). Next, metal plating 40 is formed inside the conduction hole H1, and metal plating 40A is formed inside the conduction hole H2 (step S9). 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 FIG. 4B(2), the exposed portion of the metal thin film 13, that is, the portion of the metal thin film 13 that is not covered with the metal plating 40, 40A (or button lands 41, 41A, 42). The metal thin film is removed (step S11).

Through the above steps S8 to S11, 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. form.

Through the above steps (steps S1 to S11), the printed wiring board 1B according to the present embodiment can be manufactured.

According to this embodiment, a printed wiring board having both bottomed vias and plated through holes can be manufactured.

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

Note that a plurality of conduction holes H1 and/or a plurality of conduction holes H2 may be formed. In this case, a conformal mask for forming each conduction hole may be formed on either side of the first main surface or the second main surface of the double-sided metal-clad laminate 2. Further, instead of the plated through hole, a via (filled via) may be formed to fill the through hole.

Based on the above description, those skilled in the art may be able to imagine additional effects and various modifications of the present invention, but aspects of the present invention are not limited to the individual embodiments described above. . Various additions, changes, and partial deletions are possible without departing from the conceptual idea and gist of the present invention derived from the content defined in the claims and equivalents thereof.

1, 1A, 1B Printed wiring board 2 Double-sided metal-clad laminate 10, 20, 100, 200 Metal foil 11, 21, 110, 210 Wiring 12, 12A Conformal mask 12a, 12Aa, 22a Opening 12b, 12Ab, 22b, 120b Land 13 Metal thin film 14, 24, 140, 240 Plating resist 14a, 24a, 140a Opening 15, 25, 150, 250 Resist film 15a, 25a, 150a, 250a Etching resist 22, 220 Land 30, 300 Insulating base material 40, 40A , 400 Metal plating 41, 41A, 42, 410 Button land 50, 50A, 500 Interlayer conductive path H1, H2, H Conductive hole WP1, WP2, WP10, WP20 Wiring pattern

Claims (13)

1. an insulating base material 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; a step of preparing a double-sided metal-clad laminate having a second metal foil provided on the surface;
   patterning the first metal foil of the double-sided metal-clad laminate to form a wiring pattern and a conformal mask;
   irradiating the conformal mask with laser light to remove the insulating base material exposed in the opening of the conformal mask to form a conductive hole;
   forming a plating resist that covers the wiring pattern but does not cover the conduction hole;
   forming metal plating inside the conduction hole;
   removing the plating resist;
   A method for manufacturing a printed wiring board, comprising:
2. The step of forming the wiring pattern includes:
   forming a resist film having a thickness of 1.5 times or less than the thickness of the first metal foil on the first metal foil;
   exposing and developing the resist film to form an etching resist corresponding to the wiring pattern;
   forming the wiring pattern by etching away the first metal foil that is not covered with the etching resist;
   The method for manufacturing a printed wiring board according to claim 1, further comprising the step of removing the etching resist.
3. The method for manufacturing a printed wiring board according to claim 1, wherein in the step of forming the wiring pattern and the conformal mask, the formation of the wiring pattern and the conformal mask are formed simultaneously.
4. a step of performing a dry plating process on the wiring patterns, the insulating base material exposed between the wiring patterns, and the holes for conductivity before the step of forming the plating resist;
   2. The method for producing a printed wiring board according to claim 1, further comprising the step of removing a portion of the thin metal film formed by the dry plating process that is not covered with the metal plating, after the step of removing the plating resist.
5. The method for manufacturing a printed wiring board according to claim 4, wherein the dry plating treatment is performed by a sputtering method.
6. The metal foil is copper foil,
   The sputtering method is a sputtering method using copper,
   6. The method for manufacturing a printed wiring board according to claim 5, wherein the metal thin film is a copper thin film.
7. The method for manufacturing a printed wiring board according to claim 1, wherein the step of forming the conduction hole is performed so that the second metal foil is exposed at the bottom of the conduction hole.
8. patterning the second metal foil of the double-sided metal-clad laminate to form a wiring pattern, another opening that includes the opening in plan view, and a land;
   2. The method of manufacturing a printed wiring board according to claim 1, wherein the step of forming the conduction hole is performed so that the conduction hole becomes a through hole that communicates the opening and the other opening.
9. The conformal mask includes a first opening and a second opening as the opening,
   forming a third opening by patterning the second metal foil of the double-sided metal-clad laminate, the third opening forming a second opening of the conformal mask in a plan view; further comprising the step of including;
   In the step of forming the conduction hole, the insulating base material exposed in the first opening and the second opening of the conformal mask is removed to expose the second metal foil on the bottom surface. 2. The method of manufacturing a printed wiring board according to claim 1, further comprising forming one conduction hole and a second conduction hole that communicates the second opening and the third opening.
10. The method for manufacturing a printed wiring board according to any one of claims 1 to 9, wherein the printed wiring board is a flexible printed wiring board.
11. The method for manufacturing a printed wiring board according to claim 10, wherein the first and second metal foils are rolled copper foils.
12. The method for manufacturing a printed wiring board according to any one of claims 1 to 9, wherein the metal plating is electrolytic plating.
13. 11. The method of manufacturing a printed wiring board according to claim 10, wherein at least one step is performed in a roll-to-roll manner.