Printed wiring board and method for manufacturing printed wiring board

Abstract

A printed wiring board comprises an insulating part and a first wiring part. The insulating part has a bottom surface, a first side wall surface, and a second side wall surface. The first wiring part has a seed layer and a plating layer. In a cross section perpendicular to the direction in which the first wiring part extends, a third thickness is less than each of a first thickness and a second thickness, where the first thickness is the first-direction thickness of the seed layer in contact with the first side wall surface, the first direction being the depth direction of a first groove, the second thickness is the first-direction thickness of the seed layer in contact with the second side wall surface, and the third thickness is the first-direction thickness of the seed layer at an intermediate position between the first side wall surface and the second side wall surface.

Description

Printed wiring board and method for manufacturing printed wiring board

[0001] The present disclosure relates to a printed wiring board and a method for manufacturing a printed wiring board. This application claims priority from Japanese Patent Application No. 2024-148390, filed on August 30, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[0002] Japanese Patent Laid-Open Publication No. 2014-027265 (Patent Document 1) describes an example of a method for forming a circuit on a printed wiring board. According to this circuit forming method, an insulating resin layer is removed to form a recessed structure. A dispersion liquid containing metal nanoparticles is applied to the inside of the recessed structure by an inkjet method.

[0003] JP 2014-027265 A

[0004] A printed wiring board according to the present disclosure includes an insulating portion and a first wiring portion. A first groove is provided in the insulating portion. The first wiring portion is provided within the first groove. The insulating portion includes a bottom surface, a first sidewall surface, and a second sidewall surface. The first sidewall surface is continuous with the bottom surface. The second sidewall surface is continuous with the bottom surface. The second sidewall surface faces the first sidewall surface. The bottom surface, the first sidewall surface, and the second sidewall surface form a first groove. The first wiring portion includes a seed layer and a plating layer. The plating layer is provided on the seed layer. In a cross section perpendicular to the extension direction of the first wiring portion, if the depth direction of the first groove is defined as the first direction, the thickness in the first direction of the seed layer in contact with the first side wall surface is defined as the first thickness, the thickness in the first direction of the seed layer in contact with the second side wall surface is defined as the second thickness, and the thickness in the first direction of the seed layer at an intermediate position between the first side wall surface and the second side wall surface is defined as the third thickness, the third thickness is thinner than both the first thickness and the second thickness.

[0005] FIG. 1 is a schematic diagram showing the configuration of a printed wiring board according to the first embodiment. FIG. 2 is a schematic plan view showing the configuration of a printed wiring board according to the first embodiment. FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. 2. FIG. 4 is a schematic cross-sectional view taken along line IV-IV in FIG. 2. FIG. 5 is a schematic cross-sectional view taken along line V-V in FIG. 2. FIG. 6 is a schematic plan view showing the configuration of a second layer as viewed in a first direction. FIG. 7 is a flow chart outlining a method for manufacturing a printed wiring board according to the first embodiment. FIG. 8 is a schematic perspective view showing the step of preparing a second insulating section. FIG. 9 is a schematic perspective view showing the step of supplying a dispersion liquid to a groove in the second insulating section. FIG. 10 is a schematic view illustrating the process of supplying a dispersion liquid from a second dispersion liquid supply section to a fourth groove. FIG. 11 is a schematic perspective view showing the step of preparing a first insulating section. FIG. 12 is a schematic perspective view showing the step of supplying a dispersion liquid to a groove in the first insulating section. FIG. 13 is a schematic diagram illustrating a process in which a dispersion is supplied from a first dispersion supply unit to a first groove. FIG. 14 is a schematic diagram illustrating a step of supplying a dispersion to a groove in an insulating unit in a comparative example. FIG. 15 is a schematic diagram illustrating a step of forming a seed layer in a comparative example. FIG. 16 is a schematic perspective view illustrating a configuration of a printed wiring board in a comparative example. FIG. 17 is a schematic cross-sectional view illustrating a configuration of a printed wiring board in a comparative example. FIG. 18 is a first schematic cross-sectional view illustrating a configuration of a printed wiring board in a first modified example of the first embodiment. FIG. 19 is a second schematic cross-sectional view illustrating a configuration of a printed wiring board in a first modified example of the first embodiment. FIG. 20 is a schematic cross-sectional view illustrating a configuration of a printed wiring board in a second modified example of the first embodiment. FIG. 21 is a schematic plan view illustrating a method for manufacturing a printed wiring board in a third modified example of the first embodiment. FIG. 22 is a schematic plan view illustrating a configuration of a printed wiring board according to the second embodiment. FIG. 23 is a schematic cross-sectional view taken along line XXIII-XXIII in FIG. 22. Fig. 24 is a schematic cross-sectional view taken along line XXIV-XXIV in Fig. 23. Fig. 25 is a schematic cross-sectional view showing a step of supplying a dispersion liquid to the groove of the first insulating part in the method for manufacturing a printed wiring board according to the second embodiment. Fig. 26 is a schematic perspective view showing the configuration of a printed wiring board according to a modified example of the second embodiment.

[0006] When a dispersion liquid is applied to the inside of a recessed structure by an inkjet method, metal nanoparticles may adhere to the sidewalls of the recessed structure. In this case, when wiring is formed by plating the metal nanoparticles, voids (cavities) may occur in the wiring. If voids occur in the wiring, the electrical resistance of the wiring increases.

[0007] According to the present disclosure, it is possible to provide a printed wiring board capable of reducing the electrical resistance of a wiring portion and a method for manufacturing the printed wiring board.

[0008] First, embodiments of the present disclosure will be listed and described. (1) A printed wiring board according to the present disclosure has an insulating portion and a first wiring portion. A first groove is provided in the insulating portion. The first wiring portion is provided in the first groove. The insulating portion has a bottom surface, a first sidewall surface, and a second sidewall surface. The first sidewall surface is continuous with the bottom surface. The second sidewall surface is continuous with the bottom surface. The second sidewall surface faces the first sidewall surface. The bottom surface, the first sidewall surface, and the second sidewall surface form a first groove. The first wiring portion has a seed layer and a plating layer. The plating layer is provided on the seed layer. In a cross section perpendicular to the extension direction of the first wiring portion, the depth direction of the first groove is defined as a first direction, the thickness in the first direction of the seed layer in contact with the first sidewall surface is defined as a first thickness, the thickness in the first direction of the seed layer in contact with the second sidewall surface is defined as a second thickness, and the thickness in the first direction of the seed layer at a midpoint between the first sidewall surface and the second sidewall surface is defined as a third thickness, the third thickness is thinner than both the first thickness and the second thickness, thereby reducing the electrical resistance of the first wiring portion.

[0009] (2) In the printed wiring board according to (1), in a cross section perpendicular to the direction in which the first wiring portion extends, the thickness of the seed layer in the first direction may decrease from the first sidewall surface toward the intermediate position. In a cross section perpendicular to the direction in which the first wiring portion extends, the thickness of the seed layer in the first direction may decrease from the second sidewall surface toward the intermediate position. This can effectively reduce the electrical resistance of the first wiring portion.

[0010] (3) The printed wiring board according to (1) or (2) above may have a first layer, a second layer, and an adhesive layer. The first layer may have an insulating portion and a first wiring portion. The second layer may have a second wiring portion. The adhesive layer may bond the first layer and the second layer. A through hole may be provided in the insulating portion and the adhesive layer. The first wiring portion may have an interlayer connection portion. The interlayer connection portion may be located within the through hole. The interlayer connection portion may electrically connect the first wiring portion and the second wiring portion. A crack may be provided in a portion of the seed layer forming at least a portion of the interlayer connection portion. A portion of the plating layer may be located within the crack. This can reduce the electrical resistance between the layers.

[0011] (4) In the printed wiring board according to any one of (1) to (3), a recess may be provided in at least one of the bottom surface, the first sidewall surface, and the second sidewall surface. A part of the seed layer may be located in the recess. This can prevent the first wiring portion from peeling off from the insulating portion.

[0012] (5) According to the printed wiring board according to any one of (1) to (4), a second groove and a hole may be provided in the insulating portion. The second groove may be continuous with the first groove. The hole may be continuous with the second groove. The width of the second groove may be larger than the width of the first groove. The first wiring portion may have a first wiring member, a second wiring member, and a third wiring member. The first wiring member may be located in the first groove. The second wiring member may be located in the second groove. The second wiring member may be continuous with the first wiring member. The third wiring member may be located in the hole. The third wiring member may be continuous with the second wiring member. The thickness of the third wiring member may be thinner than the thickness of the first wiring member. This effectively prevents the generation of burrs and the like when cutting the first wiring portion.

[0013] (6) In the printed wiring board according to any one of (1) to (5), the first wiring portion may have a maximum thickness in the first direction of 100 μm or more. In this way, even if the first wiring portion is relatively thick, the electrical resistance of the first wiring portion can be reduced.

[0014] (7) In the printed wiring board according to any one of (1) to (6), the first thickness may be smaller than the height of the first side wall surface. The second thickness may be smaller than the height of the second side wall surface. This can effectively reduce the electrical resistance of the first wiring portion.

[0015] (8) In the printed wiring board according to any one of (1) to (7), the insulating portion may be composed of a base film and a photosensitive resin. The photosensitive resin may be laminated on the base film.

[0016] (9) A method for manufacturing a printed wiring board according to the present disclosure includes the following steps: An insulating section is prepared, the insulating section having a groove and a dispersion supply section connected to the groove; A dispersion containing metal particles is supplied into the groove; A seed layer is formed by sintering the metal particles; A wiring section is formed by plating the seed layer; In the step of supplying a dispersion containing metal particles into the groove, the dispersion is supplied to the dispersion supply section, and then the dispersion is supplied from the dispersion supply section to the groove; This reduces the electrical resistance of the wiring section.

[0017] (10) In the method for manufacturing a printed wiring board according to (9), in the step of supplying a dispersion containing metal particles into the groove, the dispersion may be supplied to the dispersion supply unit, and then the dispersion may be supplied from the dispersion supply unit to the groove using capillary action, thereby effectively reducing the electrical resistance of the wiring portion.

[0018] (11) In the method for manufacturing a printed wiring board according to (9) or (10), the width of the dispersion supply portion may be five times or more the width of the groove, which makes it easier to supply the dispersion to the dispersion supply portion.

[0019] Hereinafter, an embodiment of the present disclosure (also referred to as the present embodiment) will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0020] First Embodiment <Configuration of Printed Wiring Board> First, the configuration of a printed wiring board 100 according to a first embodiment will be described.

[0021] 1, the printed wiring board 100 mainly includes a first layer 10a, a second layer 10b, and an adhesive layer 9. The printed wiring board 100 is, but is not limited to, a coil device, for example.

[0022] The first layer 10a is located above the second layer 10b. The adhesive layer 9 bonds the first layer 10a and the second layer 10b together. The adhesive layer 9 is located between the first layer 10a and the second layer 10b. The adhesive layer 9 is formed of, for example, a thermosetting adhesive. The adhesive layer 9 is formed of an electrically insulating material.

[0023] The first layer 10a has a first insulating portion 1a and a first wiring portion 2a. The first insulating portion 1a has a first groove 91, a second groove 92, and a third groove 93. The depth direction of the first groove 91 is a first direction 101.

[0024] The first insulating portion 1a is composed of a first base film 5a and a first photosensitive resin 6a. The first base film 5a is made of an electrically insulating material and may be flexible. The first base film 5a is made of, for example, polyimide.

[0025] The first photosensitive resin 6a is laminated on the first base film 5a. The first photosensitive resin 6a is formed from an electrically insulating material and may be flexible. The first photosensitive resin 6a is formed from, for example, a liquid or film type photosensitive resin. The first photosensitive resin 6a is a permanent resist. The first photosensitive resin 6a is formed from, for example, "SU-8" (trademark) or "KMPR-1000" (trademark) manufactured by Nippon Kayaku Co., Ltd., or "TMMR S2000" (trademark) or "TMMF S2000" (trademark) manufactured by Tokyo Ohka Kogyo Co., Ltd.

[0026] The first photosensitive resin 6a has a first top surface 39 and an outer wall surface 38. The first top surface 39 faces in a direction from the first base film 5a toward the first photosensitive resin 6a. The outer wall surface 38 is continuous with the first top surface 39. The outer wall surface 38 forms a part of the outer peripheral side surface of the printed wiring board 100.

[0027] The first wiring unit 2a has a first seed layer 3a and a first plating layer 4a. The first seed layer 3a is provided on, for example, a first base film 5a. The first plating layer 4a is provided on the first seed layer 3a. The first plating layer 4a covers the first seed layer 3a. The thickness direction of the first wiring unit 2a is parallel to the first direction 101. The direction from the first wiring unit 2a toward the first base film 5a is the same as the first direction 101.

[0028] The second layer 10b includes a second insulating portion 1b and a second wiring portion 2b. The second insulating portion 1b is composed of a second base film 5b and a second photosensitive resin 6b.

[0029] The second base film 5b is formed of an electrically insulating material and may be flexible. The second base film 5b is formed of, for example, polyimide. The second photosensitive resin 6b is laminated on the second base film 5b. The second photosensitive resin 6b is formed of, for example, an electrically insulating material and may be flexible. The second photosensitive resin 6b is formed of, for example, a liquid type or dry film type photosensitive resin.

[0030] The second wiring portion 2b has a second seed layer 3b and a second plating layer 4b. The second seed layer 3b is provided on, for example, a second base film 5b. The second plating layer 4b is provided on the second seed layer 3b. The second plating layer 4b covers the second seed layer 3b. An adhesive layer 9 is located on each of the second wiring portion 2b and the second photosensitive resin 6b.

[0031] 2 shows the configuration of printed wiring board 100 as viewed in first direction 101. As shown in FIG. 2, first wiring portion 2a has first wiring member 21, second wiring member 22, and fourth wiring member 24.

[0032] When viewed in a first direction 101 (hereinafter referred to as a plan view), the first wiring member 21 is wound. In a plan view, the first wiring member 21 has, for example, a spiral shape. The first wiring portion 2a forms a coil. The first wiring member 21 has a first end 61 and a second end 62. In the extension direction of the first wiring member 21, the second end 62 is opposite the first end 61. The extension direction of the first wiring member 21 will be described later.

[0033] The second wiring member 22 is continuous with the first wiring member 21. Specifically, the second wiring member 22 is continuous with a first end 61 of the first wiring member 21. From another perspective, the first end 61 is the interface between the first wiring member 21 and the second wiring member 22. The second wiring member 22 may be used, for example, as a portion electrically connected to an external component (not shown). In other words, the second wiring member 22 may be used as an external connection terminal. The second wiring member 22 may also be used as a land when a circuit board is further stacked on the first wiring portion 2a.

[0034] The second wiring member 22 has a third end 63. In Figures 1 and 2, the third end 63 forms part of the outer peripheral side surface of the printed wiring board 100, but the first photosensitive resin 6a may be arranged adjacent to the third end 63. The third end 63 faces in a direction perpendicular to the first direction 101. The third end 63 is an end of the first wiring portion 2a.

[0035] The fourth wiring member 24 is continuous with the first wiring member 21. The fourth wiring member 24 is continuous with the second end 62 of the first wiring member 21. From another perspective, the first wiring member 21 connects the second wiring member 22 and the fourth wiring member 24. The fourth wiring member 24 is a portion that comes into contact with the second wiring portion 2b (see FIG. 1) of the second layer 10b.

[0036] 1 and 2 , the first wiring member 21 is located in the first groove 91. From another perspective, a part of the first wiring portion 2a is provided in the first groove 91. In the first groove 91, the first photosensitive resin 6a may be open in the direction opposite to the first direction 101.

[0037] The second groove 92 is continuous with the first groove 91. A second wiring member 22 is located in the second groove 92. In the second groove 92, the first photosensitive resin 6a may be open in the direction opposite to the first direction 101. The third groove 93 is continuous with the first groove 91. The third groove 93 is continuous with the second groove 92 via the first groove 91. A fourth wiring member 24 is provided in the third groove 93. In the third groove 93, the first photosensitive resin 6a may be open in the direction opposite to the first direction 101.

[0038] 3 shows a cross section (first cross section CS1) perpendicular to the extension direction of the first wiring portion 2a and intersecting with the first wiring member 21. For ease of explanation, the second layer 10b and the adhesive layer 9 are not shown in FIG. 3. As shown in FIG. 3, the first insulating portion 1a has a bottom surface 30, a first side wall surface 31, and a second side wall surface 32. The bottom surface 30 may be perpendicular to the first direction 101.

[0039] The first side wall surface 31 is continuous with each of the bottom surface 30 and the first top surface 39. In the first cross section CS1, the first side wall surface 31 extends along a first direction 101. The second side wall surface 32 is continuous with each of the bottom surface 30 and the first top surface 39. The second side wall surface 32 faces the first side wall surface 31. In the first cross section CS1, the second side wall surface 32 extends along the first direction 101. The bottom surface 30, the first side wall surface 31, and the second side wall surface 32 form a first groove 91. The first top surface 39 may be perpendicular to the first direction 101.

[0040] 2, the first wiring member 21 is located between the first side wall surface 31 and the second side wall surface 32. In a plan view, an imaginary line equidistant from each of the first side wall surface 31 and the second side wall surface 32 is defined as a center line C of the first wiring member 21. The extension direction of the center line C is defined as the extension direction of the first wiring member 21. The extension direction of the first wiring member 21 is defined as the extension direction of the first wiring portion 2a.

[0041] In a plan view, the width of the first groove 91 in a direction perpendicular to the extension direction of the first wiring member 21 (the width direction of the first wiring member 21) is defined as a first width W1. The first width W1 is equal to the width of the first wiring member 21 in the width direction of the first wiring member 21. The first width W1 is, for example, not less than 10 μm and not more than 200 μm. The first width W1 may be the same regardless of the position at which the first width W1 is measured.

[0042] The maximum width of the second groove 92 in the width direction of the first wiring member 21 at the first end 61 is the width (second width W2) of the second groove 92. The second width W2 may be equal to the maximum width of the second wiring member 22 in the width direction of the first wiring member 21 at the first end 61.

[0043] The second width W2 is larger than the first width W1. The second width W2 is, for example, five times or more the first width W1. The second width W2 is, for example, 1 mm or more. Hereinafter, the width direction of the first wiring member 21 at the first end 61 will also be referred to as the width direction of the second wiring member 22.

[0044] As shown in FIG. 2 , the first insulating portion 1a has a winding portion 35. The winding portion 35 is in contact with the first wiring member 21. In a plan view, the winding portion 35 is wound. The minimum width of the winding portion 35 is, for example, 60 μm. The width of the winding portion 35 may be, for example, 10 μm or more and 200 μm or less. Note that in FIG. 2 , the winding portion 35 is wound one turn, but the winding portion 35 may be wound two or more turns. Similarly, the first wiring member 21 may be wound two or more turns.

[0045] 3, the first base film 5a has a first main surface 51 and a second main surface 52. A first photosensitive resin 6a and a first wiring portion 2a are provided on the first main surface 51. The bottom surface 30 is formed by, for example, a part of the first main surface 51. The first main surface 51 is planar. A first direction 101 is a direction perpendicular to the first main surface 51.

[0046] The second main surface 52 is opposite to the first main surface 51. The second main surface 52 is flat. At the second main surface 52, the first base film 5a is in contact with the adhesive layer 9 (see FIG. 1).

[0047] The first seed layer 3 a is provided on the bottom surface 30. The first seed layer 3 a is formed of a sintered body of metal particles. The metal particles are mainly composed of copper, for example. The metal particles may be mainly composed of gold, silver, or the like. Note that a "main component" refers to a component contained in an amount of 50 mass% or more.

[0048] The first seed layer 3a has a first surface 36 and a second surface 37. The first surface 36 is in contact with the bottom surface 30. The first surface 36 is planar. The second surface 37 is opposite the first surface 36. At the second surface 37, the first seed layer 3a is in contact with the first plating layer 4a. From another perspective, the second surface 37 is the interface between the first seed layer 3a and the first plating layer 4a. At the first cross section CS1, the second surface 37 is concave in the first direction 101.

[0049] In the first cross section CS1, a position equidistant from each of the first side wall surface 31 and the second side wall surface 32 in the width direction of the first wiring member 21 is defined as an intermediate position 90. In a plan view, the intermediate position 90 overlaps with the center line C (see FIG. 2 ).

[0050] At the first cross section CS1, the thickness of the first seed layer 3a in the first direction 101 decreases from the first side wall surface 31 toward the intermediate position 90. From another perspective, the second surface 37 approaches the bottom surface 30 from the first side wall surface 31 toward the intermediate position 90. At the first cross section CS1, the thickness of the first seed layer 3a in the first direction 101 decreases from the second side wall surface 32 toward the intermediate position 90. From another perspective, the second surface 37 approaches the bottom surface 30 from the second side wall surface 32 toward the intermediate position 90.

[0051] The first plating layer 4 a is in contact with each of the first side wall surface 31 and the second side wall surface 32. The first plating layer 4 a is separated from the bottom surface 30 by, for example, a first seed layer 3 a. The first plating layer 4 a is positioned in a first direction 101 relative to the first top surface 39.

[0052] The first plating layer 4a is, for example, electroplated. The first plating layer 4a may also be electroless plated. When the first plating layer 4a is primarily composed of copper, the cost reduction effect is high and the flexibility of the first wiring portion 2a can be improved. The first plating layer 4a may also be primarily composed of either nickel or gold.

[0053] The thickness (fourth thickness T4) of the first wiring member 21 in the first direction 101 is smaller than each of the height (first height H1) of the first side wall surface 31 and the height (second height H2) of the second side wall surface 32. The fourth thickness T4 is, for example, 100 μm or more. The fourth thickness T4 may be, for example, 150 μm or more, or 200 μm or more. The fourth thickness T4 is, for example, 500 μm or less. The value obtained by dividing the fourth thickness T4 by the first width W1 (see FIG. 1 ) may be, for example, 5 or more, or 10 or more. The value obtained by dividing the fourth thickness T4 by the first width W1 is, for example, 30 or less.

[0054] At the first cross section CS1, the thickness of the first seed layer 3 a in contact with the first side wall surface 31 in the first direction 101 is defined as a first thickness T1. In other words, the first thickness T1 is the thickness from the bottom surface 30 of the first seed layer 3 a in contact with the first side wall surface 31. At the first cross section CS1, the thickness of the first seed layer 3 a in contact with the second side wall surface 32 in the first direction 101 is defined as a second thickness T2. At the first cross section CS1, the thickness of the first seed layer 3 a in the first direction 101 at an intermediate position 90 between the first side wall surface 31 and the second side wall surface 32 is defined as a third thickness T3.

[0055] The third thickness T3 is thinner than both the first thickness T1 and the second thickness T2. The first thickness T1 and the second thickness T2 may be the same or different. The third thickness T3 may be 0.5 times or less, 0.2 times or less, 0.1 times or less, or 0.01 times or less of the first thickness T1. The third thickness T3 is, for example, 0.001 times or more of the first thickness T1. Similarly, the third thickness T3 may be 0.5 times or less, 0.2 times or less, 0.1 times or less, or 0.01 times or less of the second thickness T2. The third thickness T3 is, for example, 0.001 times or more of the second thickness T2.

[0056] The first thickness T1 is smaller than the height (first height H1) of the first side wall surface 31. The first thickness T1 may be, for example, 0.9 times or less, 0.75 times or less, or 0.5 times or less of the first height H1. The first thickness T1 may be, for example, 0.1 times or more, or 0.25 times or more of the first height H1.

[0057] The second thickness T2 is smaller than the height (second height H2) of the second side wall surface 32. The second thickness T2 may be, for example, 0.9 times or less, 0.75 times or less, or 0.5 times or less of the second height H2. The second thickness T2 may be, for example, 0.1 times or more, or 0.25 times or more of the second height H2.

[0058] 4 shows a cross section (second cross section CS2) that is parallel to the width direction of second wiring member 22 and intersects with second wiring member 22. For ease of explanation, second layer 10b and adhesive layer 9 are not shown in FIG.

[0059] 4, at the second cross section CS2, the second surface 37 is concave in the first direction 101. At the second cross section CS2, the thickness of the first seed layer 3a in the first direction 101 decreases with increasing distance from the first insulating portion 1a along the width direction of the second wiring member 22.

[0060] The thickness of the second wiring member 22 in the first direction 101 (fifth thickness T5) is thinner than, for example, the thickness of the first wiring member 21 (fourth thickness T4, see FIG. 3 ). The fifth thickness T5 may be substantially the same as the fourth thickness T4. The portion of the first seed layer 3 a that forms the second wiring member 22 is continuous with the portion of the first seed layer 3 a that forms the first wiring member 21 (see FIG. 3 ).

[0061] 5 shows a cross section (third cross section CS3) that is parallel to the thickness direction of the first wiring portion 2a and intersects with the fourth wiring member 24. As shown in FIG. 5, a through hole 99 is provided in the first base film 5a and the adhesive layer 9.

[0062] The through hole 99 extends along the first direction 101. When viewed in the first direction 101, the through hole 99 is, for example, circular. The diameter of the through hole 99 is, for example, 25 μm. A part of the first wiring portion 2 a is located inside the through hole 99. The part of the fourth wiring member 24 located inside the through hole 99 is also referred to as the interlayer connection portion 73. In other words, the first wiring portion 2 a has the interlayer connection portion 73.

[0063] The interlayer connection portion 73 is in contact with the second wiring portion 2 b. The interlayer connection portion 73 electrically connects the first wiring portion 2 a and the second wiring portion 2 b. The thickness of the interlayer connection portion 73 in the first direction 101 (eighth thickness T8) is, for example, 30 μm.

[0064] The first seed layer 3 a has a first convex portion 71. The first convex portion 71 is a portion of the first seed layer 3 a located inside the through hole 99. The first convex portion 71 is in contact with each of the second wiring portion 2 b and the adhesive layer 9.

[0065] The first convex portion 71 has a convex shape in the first direction 101. The first convex portion 71 protrudes in the first direction 101 relative to the first surface 36 of the first seed layer 3 a. A depression 79 is provided in the second surface 37 of the first seed layer 3 a.

[0066] The first plating layer 4a has a second convex portion 72. The second convex portion 72 is a portion of the first plating layer 4a located within the through hole 99. The second convex portion 72 is located within the depression 79. The second convex portion 72 has a convex shape in the first direction 101. The second convex portion 72 is separated from the second wiring portion 2b by, for example, the first convex portion 71. The first convex portion 71 and the second convex portion 72 form an interlayer connection portion 73. Note that the interlayer connection portion 73 may be formed by only the first convex portion 71.

[0067] In the third cross section CS3, the second surface 37 has a convex shape in the first direction 101. The portion of the first seed layer 3 a that forms the fourth wiring member 24 is continuous with the portion of the first seed layer 3 a that forms the first wiring member 21 (see FIG. 3 ).

[0068] The maximum thickness of the first wiring portion 2a in the first direction 101 is 100 μm or more. The maximum thickness of the first wiring portion 2a is, for example, the thickness of the first wiring member 21 (fourth thickness T4, see FIG. 3 ). The maximum thickness of the first wiring portion 2a may be the thickness of the second wiring member 22 (fifth thickness T5, see FIG. 4 ) or the thickness of the fourth wiring member 24 (sixth thickness T6, see FIG. 5 ). The maximum thickness of the first wiring portion 2a may be, for example, 110 μm or more, or 120 μm or more. The maximum thickness of the first wiring portion 2a is, for example, 500 μm or less.

[0069] Next, the configuration of the second layer 10b will be described. The second layer 10b differs from the first layer 10a in that the winding direction of the second wiring portion 2b is opposite to the winding direction of the first wiring portion 2a (see FIG. 2) and that the second wiring portion 2b does not have portions corresponding to the first convex portion 71 and the second convex portion 72 (see FIG. 5) of the first wiring portion 2a. In other respects, the second layer 10b is substantially identical to the first layer 10a.

[0070] 6, the second wiring portion 2b has a fifth wiring member 25, a sixth wiring member 26, and a seventh wiring member 27. The second insulating portion 1b is provided with a fourth groove 94, a fifth groove 95, and a sixth groove 96.

[0071] 2 and 6 , the fifth wiring member 25, the sixth wiring member 26, and the seventh wiring member 27 correspond to the first wiring member 21, the second wiring member 22, and the fourth wiring member 24, respectively. In a plan view, the winding direction of the fifth wiring member 25 is opposite to the winding direction of the first wiring member 21. The second insulating portion 1b corresponds to the first insulating portion 1a. The fourth groove 94, the fifth groove 95, and the sixth groove 96 correspond to the first groove 91, the second groove 92, and the third groove 93, respectively.

[0072] The seventh wiring member 27 is in contact with the interlayer connection portion 73 (see FIG. 5 ) of the first wiring portion 2 a. The second wiring portion 2 b is covered with the adhesive layer 9 and the first wiring portion 2 a. The second insulating portion 1 b is covered with the adhesive layer 9.

[0073] <Method for Manufacturing Printed Wiring Board> Next, a method for manufacturing the printed wiring board 100 according to the first embodiment will be described.

[0074] As shown in FIG. 7 , the method for manufacturing the printed wiring board 100 according to the first embodiment includes a step of preparing a second insulating portion (S10), a step of supplying a dispersion liquid into the grooves of the second insulating portion (S20), a step of forming a second seed layer (S30), a step of forming a second wiring portion (S40), a step of preparing a first insulating portion (S50), a step of supplying a dispersion liquid into the grooves of the first insulating portion (S60), a step of forming a first seed layer (S70), and a step of forming a first wiring portion (S80).

[0075] First, a step (S10) of preparing a second insulating portion is performed. As shown in FIG. 8, a second base film 5b is prepared. A second photosensitive resin 6b is disposed on the second base film 5b. For example, "SU-8" (trademark) or "KMPR-1000" (trademark) manufactured by Nippon Kayaku Co., Ltd., or "TMMR S2000" (trademark) or "TMMF S2000" (trademark) manufactured by Tokyo Ohka Kogyo Co., Ltd., is used as the second photosensitive resin 6b.

[0076] The thickness of the second photosensitive resin 6b is, for example, 150 μm. The second photosensitive resin 6b is exposed and developed. A descum process is performed. This forms a resist pattern. Specifically, a fourth groove 94, a fifth groove 95, and a sixth groove 96 are formed in the second photosensitive resin 6b. This completes the preparation of the second insulating portion 1b.

[0077] In this specification, the fifth groove 95 is also referred to as the second dispersion liquid supply portion 95. After the step (S10) of preparing the second insulating portion, the width of the second dispersion liquid supply portion 95 (fourth width W4) is five times or more the width of the fourth groove 94 (third width W3). The fourth width W4 is, for example, 300 μm or more. The third width W3 is, for example, 10 μm or more and 200 μm or less.

[0078] Next, a step (S20) of supplying the dispersion liquid to the groove of the second insulating part is performed. As shown in Fig. 9 , the dispersion liquid 80 is supplied to the second dispersion liquid supply part 95. Specifically, the dispersion liquid 80 is dropped into the second dispersion liquid supply part 95 using a dispenser. As a result, the bottom part of the second dispersion liquid supply part 95 is filled with the dispersion liquid 80.

[0079] The dispersion liquid 80 contains metal particles and a solvent. The metal particles are dispersed in the solvent. The metal particles are primarily composed of, for example, copper. The metal particles may also be primarily composed of, for example, gold or silver. The solvent is, for example, a mixture of water and isopropyl alcohol. The concentration of the metal particles in the dispersion liquid 80 is, for example, 1% by mass or more and 40% by mass or less.

[0080] The contact angle of the dispersion liquid 80 with the first base film 5a and the second base film 5b (hereinafter also simply referred to as the base films) is used as an indicator of the wettability of the dispersion liquid 80. The contact angle of the dispersion liquid 80 with the base films is, for example, 45 degrees or less. The contact angle of the dispersion liquid 80 with the base films may be 30 degrees or less. When the contact angle of the dispersion liquid 80 with the base films is 45 degrees or less, the dispersion liquid 80 can easily flow inside the grooves.

[0081] The average particle diameter of the metal particles is, for example, 25 nm. The average particle diameter of the metal particles may be, for example, 1 nm or more and 200 nm or less. "Average particle diameter" refers to the value at 50% of the volume integrated value (D50) in the particle size distribution. The particle size distribution is measured, for example, by a laser diffraction method. The average particle diameter can be measured, for example, using a particle size distribution analyzer "UPA-EX150" manufactured by Nikkiso Co., Ltd.

[0082] 10 , after the dispersion liquid 80 is supplied to the second dispersion liquid supply unit 95, the dispersion liquid 80 is supplied from the second dispersion liquid supply unit 95 to the fourth groove 94 along the arrow A1. From another perspective, the dispersion liquid 80 is supplied from the second dispersion liquid supply unit 95 to the fourth groove 94 by a flow of the dispersion liquid 80 along a direction perpendicular to the first direction 101. The dispersion liquid 80 filled in the second dispersion liquid supply unit 95 flows toward the fourth groove 94 so as to permeate into the fourth groove 94.

[0083] The dispersion liquid 80 is supplied from the second dispersion liquid supply unit 95 to the fourth groove 94 by, for example, capillary action. The dispersion liquid 80 that has flowed into the fourth groove 94 spreads over the sidewall and bottom surfaces of the fourth groove 94. The surface tension acting on the portion of the dispersion liquid 80 that has spread out causes the portion of the dispersion liquid 80 filling the second dispersion liquid supply unit 95 to be pulled.

[0084] The dispersion liquid 80 is supplied from the fourth groove 94 to the sixth groove 96. Specifically, the dispersion liquid 80 is supplied from the fourth groove 94 to the sixth groove 96 by the flow of the dispersion liquid 80 along the direction perpendicular to the first direction 101. In this way, the dispersion liquid 80 is supplied to the grooves of the second insulating part 1b.

[0085] Next, a step (S30) of forming a second seed layer is performed. The dispersion liquid 80 supplied to the groove of the second insulating portion 1b is dried at a temperature equal to or higher than room temperature (25°C), for example. The dried dispersion liquid 80 is then subjected to a heat treatment. The heat treatment temperature is set to, for example, 200°C or higher and 300°C or lower. The heat treatment is performed using, for example, nitrogen (N ２ The heat treatment is carried out in a 0.1% to 1.5% atmosphere. The heat treatment time is, for example, 10 minutes to 2 hours. The metal particles contained in the dispersion liquid 80 are sintered by the heat treatment. As a result, the second seed layer 3b is formed.

[0086] The sintering of metal particles is carried out by heat treatment in a vacuum atmosphere or by adding hydrogen (H ２ The sintering of the metal particles may be carried out by a light sintering method using a flash lamp and a laser, or by sintering using plasma.

[0087] Next, a step (S40) of forming a second wiring portion is performed. For example, electroplating is performed on the second seed layer 3b. Specifically, electroplating is performed by supplying electricity to the second seed layer 3b from a portion of the second seed layer 3b located within the second dispersion liquid supply unit 95. By plating the second seed layer 3b, a second plating layer 4b is formed. The second plating layer 4b grows mainly along the direction opposite to the first direction 101. In this manner, the second wiring portion 2b is formed.

[0088] Next, a step (S50) of preparing a first insulating portion is performed. A composite formed by applying adhesive to the first base film 5a is superimposed on the second wiring portion 2b and the second insulating portion 1b. Heating is performed while the first base film 5a and the second layer 10b are pressed in a direction parallel to the first direction 101. This bonds the second layer 10b to the first base film 5a. An adhesive layer 9 is formed. Next, a through-hole 99 (see FIG. 5 ) is formed in the first base film 5a and the adhesive layer 9.

[0089] A first photosensitive resin 6a is disposed on the first base film 5a by a process substantially identical to the process (S10) of preparing the second insulating portion. As shown in Fig. 11, a first groove 91, a second groove 92, and a third groove 93 are formed in the first photosensitive resin 6a. In this manner, the first insulating portion 1a is prepared.

[0090] In this specification, the second groove 92 is also referred to as a first dispersion liquid supply portion 92. After the step (S50) of preparing a first insulating portion, the width of the first dispersion liquid supply portion 92 (second width W2) is five times or more the width of the first groove 91 (first width W1). The second width W2 is, for example, 1 mm or more. The first width W1 is, for example, 10 μm or more and 200 μm or less.

[0091] Next, a step (S60) of supplying the dispersion liquid to the grooves of the first insulating part is performed. In the step (S60) of supplying the dispersion liquid to the grooves of the first insulating part, substantially the same step as the step (S20) of supplying the dispersion liquid to the grooves of the second insulating part is performed. Specifically, as shown in FIG. 12 , dispersion liquid 80 is dropped into a first dispersion liquid supply unit 92 using a dispenser.

[0092] 13 , after the dispersion liquid 80 is supplied to the first dispersion liquid supply unit 92, the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first groove 91 along the arrow A2. From another perspective, the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first groove 91 by a flow of the dispersion liquid 80 along a direction perpendicular to the first direction 101. The dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first groove 91 using, for example, capillary action. The dispersion liquid 80 spreads over the bottom surface 30, a portion of the first side wall surface 31, and a portion of the second side wall surface 32.

[0093] The dispersion liquid 80 is supplied from the first groove 91 to the third groove 93. Specifically, the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first groove 91 by the flow of the dispersion liquid 80 along a direction perpendicular to the first direction 101. In this way, the dispersion liquid 80 is supplied to the groove of the first insulating part 1 a.

[0094] Next, a step (S70) of forming a first seed layer is performed. In the step (S70) of forming the first seed layer, substantially the same steps as the step (S30) of forming the second seed layer are performed. Specifically, the metal particles contained in the dispersion liquid 80 are sintered to form the first seed layer 3 a.

[0095] Next, a step (S80) of forming a first wiring portion is performed. In the step (S80) of forming the first wiring portion, substantially the same step as the step (S40) of forming the second wiring portion is performed. Specifically, for example, electricity is supplied to the first seed layer 3 a from a portion of the first seed layer 3 a located in the first dispersion liquid supply unit 92, thereby performing electroplating.

[0096] The first seed layer 3a is plated to form a first plating layer 4a. The first plating layer 4a grows mainly in the direction opposite to the first direction 101. This forms the first wiring portion 2a. In this manner, the printed wiring board 100 is manufactured. Note that the first wiring portion 2a may be cut to remove the power supply circuit for electroplating used in the step (S80) of forming the first wiring portion.

[0097] Next, the effects of printed wiring board 100 and the method for manufacturing printed wiring board 100 according to the first embodiment will be described.

[0098] There are three methods for forming circuits on printed wiring boards: the subtractive method, the semi-additive method, and the full-additive method. In the subtractive method, a patterned resist is formed on a copper-clad substrate made by laminating copper foil and an insulating layer. The circuit is then formed by removing part of the copper foil by etching. However, when using the subtractive method, there is a problem in that the cross-sectional shape of the circuit becomes trapezoidal.

[0099] In the semi-additive method, a thin seed layer is formed on an insulating layer. A patterned resist is formed on the seed layer. After the seed layer is electroplated, the resist is removed. A circuit is then formed by etching to remove unnecessary parts of the seed layer. When using the semi-additive method, the circuit is also etched when removing unnecessary parts of the seed layer. This makes it difficult to create finer circuits. With the aim of creating finer circuits, research is being conducted on circuit formation methods using the full-additive method.

[0100] 14 to 17 , an example of the full additive process (comparative example) will be described. As shown in FIG. 14 , in the method for manufacturing a printed wiring board 100 according to the comparative example, a dispersion liquid 80 containing metal particles is directly dripped into a groove 91c formed in an insulating portion 1c. In this case, the dispersion liquid 80 adheres to the sidewall surface of the groove 91c due to variations in the size of the droplets of the dispersion liquid 80 and variations in the position where the dispersion liquid 80 is dripped.

[0101] As shown in Fig. 15, the seed layer 3c is formed by sintering the metal particles contained in the dispersion liquid 80. The dispersion liquid 80 attached to the sidewall surfaces of the grooves 91c and the top surface of the insulating portion 1c is sintered, so that the seed layer 3c spreads from the bottom surface of the grooves 91c to the top surface of the insulating portion 1c. As shown in Figs. 16 and 17, the seed layer 3c is plated to form a plating layer 4c on the seed layer 3c. In this way, the wiring portion 2c is formed.

[0102] In the comparative example, the seed layer 3c extends from the bottom surface of the groove 91c to the top surface of the insulating portion 1c, which is thought to result in a faster plating growth rate in the upper portion of the groove 91c than in the center portion of the groove 91c. Therefore, as shown in FIG. 17, voids 78 are formed in the wiring portion 2c. When voids 78 are formed in the wiring portion 2c, the electrical resistance of the wiring portion 2c increases. Furthermore, as the width of the groove 91c narrows, the dispersion liquid 80 is more likely to adhere to the shoulder portion of the top surface of the insulating portion 1c. This makes it more likely that short-circuit defects will occur due to the dispersion liquid 80 adhering to the top surface being sintered on the top surface.

[0103] According to the printed wiring board 100 according to the first embodiment, a first groove 91 is provided in the first insulating portion 1a. The first groove 91 is formed by a bottom surface 30, a first side wall surface 31, and a second side wall surface 32. The thickness (third thickness T3) of the first seed layer 3a in the first direction 101 at an intermediate position 90 between the first side wall surface 31 and the second side wall surface 32 is smaller than the thickness (first thickness T1) of the first seed layer 3a in contact with the first side wall surface 31 in the first direction 101 and the thickness (second thickness T2) of the first seed layer 3a in contact with the second side wall surface 32 in the first direction 101.

[0104] Therefore, the first plating layer 4a grows mainly from the bottom surface 30. This prevents the occurrence of voids 78 in the first plating layer 4a, thereby reducing the electrical resistance of the first wiring portion 2a.

[0105] According to the printed wiring board 100 of the first embodiment, in a cross section (first cross section CS1) perpendicular to the extension direction of the first wiring portion 2a, the thickness of the first seed layer 3a in the first direction 101 decreases from the first side wall surface 31 toward the intermediate position 90. In the first cross section CS1, the thickness of the first seed layer 3a in the first direction 101 decreases from the second side wall surface 32 toward the intermediate position 90. Therefore, the first plating layer 4a grows mainly from the bottom surface 30. This prevents the generation of voids 78 in the first plating layer 4a. Therefore, the electrical resistance of the first wiring portion 2a can be effectively reduced.

[0106] According to the printed wiring board 100 according to the first embodiment, the maximum thickness of the first wiring portion 2 a in the first direction 101 is 100 μm or more. In this way, even if the first wiring portion 2 a is relatively thick, the electrical resistance of the first wiring portion 2 a can be reduced.

[0107] In the printed wiring board 100 according to the first embodiment, the thickness (first thickness T1) in the first direction 101 of the first seed layer 3a in contact with the first side wall surface 31 is smaller than the height (first height H1) of the first side wall surface 31. The thickness (second thickness T2) in the first direction 101 of the first seed layer 3a in contact with the second side wall surface 32 is smaller than the height (second height H2) of the second side wall surface 32. This effectively reduces the electrical resistance of the first wiring portion 2a.

[0108] According to the method for manufacturing the printed wiring board 100 according to the first embodiment, in the step (S60) of supplying the dispersion liquid to the grooves of the first insulating portion, the dispersion liquid 80 is supplied to the first dispersion liquid supply unit 92, and then the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first grooves 91. This prevents the dispersion liquid 80 from adhering to the upper portions of the sidewall surfaces (first sidewall surface 31 and second sidewall surface 32) of the first grooves 91. This prevents the first seed layer 3a from being formed on the upper portions of the sidewall surfaces of the first grooves 91. This allows the first plating layer 4a to grow mainly from the bottom surface 30. This prevents the generation of voids 78 in the first plating layer 4a. As a result, the electrical resistance of the first wiring portion 2a can be reduced.

[0109] According to the method for manufacturing the printed wiring board 100 of the first embodiment, the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the first groove 91, thereby preventing the dispersion liquid 80 from adhering to the first top surface 39 of the first insulating portion 1a. This prevents a sintered body of metal particles from being formed on the first top surface 39 of the first insulating portion 1a. As a result, short-circuit defects can be prevented.

[0110] According to the method for manufacturing the printed wiring board 100 of the first embodiment, the dispersion 80 is supplied from the first dispersion supply unit 92 to the first groove 91 by capillary action. Therefore, clogging of the first groove 91 with the dispersion 80 can be prevented when the dispersion 80 flows through the first groove 91. This more reliably prevents the dispersion 80 from adhering to the upper portions of the sidewall surfaces (first sidewall surface 31 and second sidewall surface 32) of the first groove 91. Therefore, the generation of voids 78 in the first plating layer 4a can be more reliably prevented. As a result, the electrical resistance of the first wiring portion 2a can be effectively reduced.

[0111] By supplying the dispersion 80 from the first dispersion supply unit 92 to the first groove 91 using capillary action, adhesion of the dispersion 80 to a portion (shoulder portion) of the top surface (first top surface 39) of the first insulating portion 1a that is close to the first groove 91 can be suppressed. In addition, the speed of the dispersion 80 flowing through the first groove 91 can be increased. This reduces the time required to fill the first groove 91 with the dispersion 80. As a result, the time required to manufacture the printed wiring board 100 can be reduced.

[0112] According to the method for manufacturing the printed wiring board 100 according to the first embodiment, the width of the first dispersion supply portion 92 is five times or more the width of the first groove 91. This makes it easier to supply the dispersion 80 to the first dispersion supply portion 92.

[0113] 18 and 19 , one or more cracks 97 may be provided in the first seed layer 3 a. From another perspective, each of the first seed layer 3 a and the second seed layer 3 b may have a portion where the metal grains constituting the sintered body are discontinuous. Specifically, the crack 97 is provided in the second surface 37 of the first seed layer 3 a. Similarly, the crack 97 may be provided in the second seed layer 3 b. The crack 97 is a groove extending in the extension direction of the first wiring member 21.

[0114] A portion of the first plating layer 4a is located in the crack 97. Within the crack 97, the first plating layer 4a is in contact with the first seed layer 3a. Similarly, a portion of the second plating layer 4b is located in the crack 97. Within the crack 97, the second plating layer 4b is in contact with the second seed layer 3b.

[0115] In the first cross section CS1, the crack 97 extends from the second surface 37 toward the first insulating portion 1a. The crack 97 may reach the first insulating portion 1a. Specifically, the crack 97 may reach any one of the first side wall surface 31, the second side wall surface 32, and the bottom surface 30. From another perspective, the portion of the first plating layer 4a located within the crack 97 may be in contact with the first insulating portion 1a.

[0116] 19 , a crack 97 may be provided in the depression 79 of the first protrusion 71. From another perspective, the crack 97 may be provided in a portion of the first seed layer 3a that forms at least a part of the interlayer connection 73. A part of the first plating layer 4a may be located within the crack 97 provided in the interlayer connection 73. Specifically, the second protrusion 72 may be located within the crack 97 provided in the interlayer connection 73. The second protrusion 72 may be in contact with the second plating layer 4b. The second protrusion 72 may be in contact with the adhesive layer 9.

[0117] In the step (S70) of forming the first seed layer, the sintered body shrinks when the metal particles are sintered, thereby forming cracks 97 in the first seed layer 3 a. Similarly, in the step (S30) of forming the second seed layer, the sintered body shrinks when the metal particles are sintered, thereby forming cracks 97 in the second seed layer 3 b.

[0118] Metal sintered bodies have a higher electrical resistivity than plated metals. In particular, in the interlayer connection portion 73, the ratio of the volume of the first seed layer 3a to the total volume of the interlayer connection portion 73 is relatively large, so the electrical resistivity of the interlayer connection portion 73 is likely to increase. According to the printed wiring board 100 according to the first modification of the first embodiment, a crack 97 is provided in the first seed layer 3a that forms at least a portion of the interlayer connection portion 73. A portion of the first plating layer 4a is located within the crack 97. This reduces the electrical resistance between the layers. Specifically, the electrical resistance between the first wiring portion 2a and the second wiring portion 2b can be reduced. As a result, the power consumption of the printed wiring board 100 can be reduced. Furthermore, a larger current can be passed through the printed wiring board 100.

[0119] 20 , one or more recesses 98 may be provided in the first insulating portion 1a. Specifically, the recesses 98 may be provided in at least one of the bottom surface 30, the first sidewall surface 31, or the second sidewall surface 32. The recesses 98 are provided in a portion of the first insulating portion 1a with which the first seed layer 3a is in contact. A portion of the first seed layer 3a is located within the recess 98. Within the recess 98, the first seed layer 3a is in contact with the first insulating portion 1a.

[0120] The recess 98 is open in a direction perpendicular to the surface on which the recess 98 is provided. When viewed perpendicular to the surface on which the recess 98 is provided, the recess 98 has, for example, a circular shape. The recess 98 is formed when the metal particles bite into the surface of the first insulating portion 1 a when the metal particles are sintered.

[0121] When the printed wiring board 100 is heated, the first wiring portion 2a may peel off from the first insulating portion 1a due to the difference in thermal expansion coefficient between the first insulating portion 1a and the first wiring portion 2a. According to the second modification of the first embodiment, a portion of the first seed layer 3a is located within the recess 98, thereby improving the adhesion between the first seed layer 3a and the first plating layer 4a. This prevents the first wiring portion 2a from peeling off from the first insulating portion 1a.

[0122] <Third Modification of First Embodiment> In the above, a configuration has been described in which, in the step (S40) of forming the second wiring portion, electroplating is performed by supplying electricity to the second seed layer 3 b from a portion of the second seed layer 3 b located in the second dispersion liquid supply unit 95. However, as shown in Fig. 21 , a plurality of second insulating portions 1 b, a plurality of second seed layers 3 b, and a second connection seed layer 3 d may be prepared before the step (S40) of forming the second wiring portion.

[0123] Each of the second seed layers 3 b is continuous with a second connection seed layer 3 d. In plan view, the second connection seed layer 3 d surrounds each of the second insulating portions 1 b. The second insulating portions 1 b are aligned in a direction perpendicular to the first direction 101.

[0124] In the step (S40) of forming the second wiring portion, electricity may be supplied from the second connection seed layer 3d to each of the plurality of second seed layers 3b. This reduces the cost required to form the second plating layer 4b. Note that in the step (S20) of supplying the dispersion liquid to the grooves of the second insulating portion, the dispersion liquid 80 may be dropped onto each of the plurality of second dispersion liquid supply units 95 using a dispenser. The dispersion liquid 80 may be supplied from the outside of each of the plurality of second insulating portions 1b.

[0125] Similarly, before the step (S80) of forming the first wiring portion, a plurality of first insulating portions 1 a, a plurality of first seed layers 3 a, and a first connection seed layer (not shown) may be prepared. In the step (S80) of forming the first wiring portion, electricity may be supplied from the first connection seed layer to each of the plurality of first seed layers 3 a.

[0126] <Other Modifications of First Embodiment> In the above, printed wiring board 100 is formed of two layers (first layer 10 a and second layer 10 b), but there is no particular limitation on the number of layers of printed wiring board 100. The number of layers of printed wiring board 100 may be three or more.

[0127] In the method for manufacturing printed wiring board 100 according to the first embodiment, descumming may not be performed after the resist pattern is formed. In this case, bottom surface 30 may be formed of first photosensitive resin 6 a. From another perspective, first main surface 51 of first base film 5 a may be entirely covered with first photosensitive resin 6 a.

[0128] A third base film may be provided on the first layer 10a. Each of the first insulating portion 1a and the first wiring portion 2a may be covered with the third base film.

[0129] At the first cross section CS1, the first seed layer 3 a may be divided into a portion in contact with the first side wall surface 31 and a portion in contact with the second side wall surface 32. From another perspective, the first seed layer 3 a may not be provided at the intermediate position 90. From yet another perspective, the third thickness T3 may be 0 μm.

[0130] In the step (S20) of supplying the dispersion liquid to the grooves of the second insulating section, the dispersion liquid 80 may be supplied to the sixth grooves 96 by dripping the dispersion liquid 80 into the sixth grooves 96. Similarly, in the step (S60) of supplying the dispersion liquid to the grooves of the first insulating section, the dispersion liquid 80 may be supplied to the third grooves 93 by dripping the dispersion liquid 80 into the third grooves 93.

[0131] Second Embodiment Next, the configuration of a printed wiring board 100 according to a second embodiment will be described. The printed wiring board 100 according to the second embodiment differs from the printed wiring board 100 according to the first embodiment mainly in that it has a third wiring member 23 that is continuous with the second wiring member 22, but is otherwise substantially identical to the printed wiring board 100 according to the first embodiment. The following description will focus on the differences from the printed wiring board 100 according to the first embodiment.

[0132] 22 , the first photosensitive resin 6a has a main portion 11 and a bridging portion 12. The configuration of the main portion 11 is substantially the same as the configuration of the first photosensitive resin 6a of the printed wiring board 100 according to the first embodiment. The bridging portion 12 is continuous with the main portion 11. An outer peripheral space 88 is provided around the first photosensitive resin 6a.

[0133] The first wiring portion 2a has a peripheral wiring portion 28. The peripheral wiring portion 28 is located in a peripheral space 88. In a plan view, the peripheral wiring portion 28 is located outside the first photosensitive resin 6a.

[0134] Figure 23 shows a cross section (fourth cross section CS4) parallel to the first direction 101 and passing through the bridging portion 12. As shown in Figure 23, a hole 89 is provided in the first insulating portion 1a. The hole 89 is connected to each of the second groove 92 and the outer circumferential space 88. The hole 89 connects the second groove 92 and the outer circumferential space 88. The hole 89 is tunnel-shaped. The hole 89 is provided at a position in the first direction 101 with respect to the bridging portion 12. The hole 89 extends along a direction perpendicular to the first direction 101.

[0135] The first wiring portion 2a has a third wiring member 23. The third wiring member 23 is located in the hole 89. From another perspective, the third wiring member 23 is provided between the bridging portion 12 and the first base film 5a.

[0136] The third wiring member 23 is continuous with the second wiring member 22 and the peripheral wiring portion 28. The third wiring member 23 connects the second wiring member 22 and the peripheral wiring portion 28. At a third end 63 (see FIG. 22 ), the third wiring member 23 is continuous with the second wiring member 22. From another perspective, the third end 63 is the interface between the second wiring member 22 and the third wiring member 23.

[0137] The thickness of the third wiring member 23 (seventh thickness T7) is thinner than the thickness of the first wiring member 21 (fourth thickness T4, see FIG. 3 ). The seventh thickness T7 is, for example, 0.1 to 0.5 times the fourth thickness T4. The seventh thickness T7 may be thinner than the thickness of the second wiring member 22 (fifth thickness T5). The seventh thickness T7 is, for example, 20 μm. The seventh thickness T7 is the same as the height of the hole 89 in the first direction 101.

[0138] The bridging portion 12 is in contact with each of the second wiring member 22 and the peripheral wiring portion 28. The bridging portion 12 is provided between the peripheral wiring portion 28 and the second wiring member 22. The bridging portion 12 is spaced apart from the first base film 5a.

[0139] 24 shows a cross section (fifth cross section CS5) parallel to the first direction 101 and perpendicular to the fourth cross section CS4. The fifth cross section CS5 passes through the bridging portion 12. As shown in FIG. 24, the first seed layer 3a is in contact with the bridging portion 12. In the fifth cross section CS5, the first seed layer 3a may surround the first plating layer 4a. In the fifth cross section CS5, the first seed layer 3a may be annular. In the width direction of the first wiring member 21 at the first end 61, the width (fifth width W5) of the hole 89 may be the same as or smaller than the second width W2.

[0140] Fig. 25 shows a cross section corresponding to the cross section shown in Fig. 23. As shown in Fig. 25, the dispersion liquid 80 supplied to the first dispersion liquid supply unit 92 flows through the hole 89 into the outer circumferential space 88. In this way, the dispersion liquid 80 is supplied from the first dispersion liquid supply unit 92 to the outer circumferential space 88. After the step (S60) of supplying the dispersion liquid into the groove of the first insulating part, the entire inside of the hole 89 may be filled with the dispersion liquid 80, or only a portion of the hole 89 may be filled with the dispersion liquid 80.

[0141] According to the printed wiring board 100 of the second embodiment, a hole 89 communicating with the second groove 92 is provided in the first insulating portion 1a. The first wiring portion 2a has a third wiring member 23 positioned in the hole 89. The thickness of the third wiring member 23 is thinner than the thickness of the first wiring member 21. Therefore, the first wiring portion 2a can be easily cut by cutting the third wiring member 23. This makes it possible to prevent burrs and the like from being generated when cutting the first wiring portion 2a.

[0142] When the manufacturing method according to the third modification of the first embodiment described above (see FIG. 21 ) is used, a plurality of first wiring portions 2 a are formed. Each of the plurality of first wiring portions 2 a is connected by the peripheral wiring portion 28. According to the printed wiring board 100 according to the second embodiment, by cutting the third wiring member 23 when each of the plurality of first wiring portions 2 a is separated from the peripheral wiring portion 28, it is possible to prevent the occurrence of burrs and the like on the first wiring portions 2 a.

[0143] 26 , a part of the third wiring member 23 and the peripheral wiring portion 28 (see FIG. 22 ) may be removed by cutting the third wiring member 23. From another perspective, the first wiring portion 2 a may not have the peripheral wiring portion 28.

[0144] The third wiring member 23 may be exposed from the outer wall surface 38. The third wiring member 23 may form part of the outer peripheral side surface of the printed wiring board 100. According to the printed wiring board 100 according to the modified example of the second embodiment, even if the third wiring member 23 is cut, the generation of burrs and the like is prevented.

[0145] (Sample Preparation) First, printed wiring boards 100 according to Samples 1 to 6 were prepared. Samples 1, 3, and 5 are comparative examples, and Samples 2, 4, and 6 are examples.

[0146] Samples 1, 3, and 5 were manufactured using the method for manufacturing printed wiring board 100 according to the comparative example described above (see FIGS. 14 to 17 ). Samples 2, 4, and 6 were manufactured using the method for manufacturing printed wiring board 100 according to the first embodiment.

[0147] In Samples 1, 2, 5, and 6, the circuit width (first width W1) was 50 μm. In Samples 3 and 4, the circuit width was 30 μm. In Samples 1 to 4, the circuit height (thickness of the first wiring member 21, fourth thickness T4) was 150 μm. In Samples 5 and 6, the circuit height was 100 μm. In Samples 1 to 6, the circuit length was 3.7 mm. The circuit length is the length of the center line C (see FIG. 2 ).

[0148] (Evaluation Method) The average void fraction and circuit resistance were measured for Samples 1 to 6. In measuring the average void fraction, the area of ​​the voids and the area of ​​the first wiring portion 2a were measured in a cross section (first cross section CS1) perpendicular to the extension direction of the first wiring portion 2a and intersecting with the first wiring member 21. The void fraction was determined as the value obtained by dividing the void area by the sum of the area of ​​the voids and the area of ​​the first wiring portion 2a. In each sample, the void fraction was measured in five cross sections at different positions. The average value of the five void fractions was determined as the average void fraction. In measuring the circuit resistance, the electrical resistance between the second wiring member 22 and the fourth wiring member 24 of the first wiring portion 2a was measured.

[0149] (Evaluation results)

[0150]

[0151] Table 1 shows the evaluation results for Samples 1 to 6. As shown in Table 1, the average void fraction was 19% or more in Samples 1, 3, and 5. The average void fraction was 0% in Samples 2, 4, and 6. When comparing samples with the same circuit width and circuit height, the samples with a lower average void fraction (Samples 2, 4, and 6) had lower circuit resistance than the samples with a higher average void fraction (Samples 1, 3, and 5).

[0152] From the above results, it was confirmed that the manufacturing method of the printed wiring board 100 according to the first embodiment can suppress the occurrence of voids in the first wiring portion 2a and can reduce the electrical resistance of the first wiring portion 2a.

[0153] (Sample Preparation) Next, the influence of the presence or absence of cracks 97 in interlayer connection portion 73 on the interlayer electrical resistance was investigated. First, printed wiring boards 100 according to samples 7 to 10 were prepared. The printed wiring boards 100 according to samples 7 to 10 are examples.

[0154] The printed wiring boards 100 of Samples 7 to 10 had the same configuration as the printed wiring board 100 of Sample 2, except for the crack area ratios shown below. In Samples 7 to 10, the thickness of the interlayer connection 73 (eighth thickness T8) was 30 μm. The diameter of the through hole 99 was 25 μm. The average thickness of the portion of the first seed layer 3 a forming the interlayer connection 73 was 5 μm.

[0155] The crack area ratio was varied between 0% and 35% in Samples 7 to 10. The crack area ratio is the value obtained by dividing the area of ​​the crack 97 in a cross section (third cross section CS3) that is parallel to the thickness direction of the first wiring portion 2a and intersects with the fourth wiring member 24 by the total area of ​​the crack 97 and the area of ​​the portion of the first seed layer 3a that forms the interlayer connection portion 73 (first convex portion 71).

[0156] (Evaluation Method) The circuit resistance including the interlayer connection portion 73 was measured for Samples 7 to 10. Specifically, the electrical resistance between the first wiring portion 2a and the second wiring portion 2b was measured.

[0157] (Evaluation results)

[0158]

[0159] Table 2 shows the measurement results of the circuit resistance of Samples 7 to 10. As shown in Table 2, the circuit resistance decreased as the crack area ratio increased. The above results confirmed that the electrical resistance between layers can be reduced by providing cracks 97 in the portion of the first seed layer 3a (first convex portion 71) that forms the interlayer connection portion 73.

[0160] It should be understood that at least one of the configurations and features described in each embodiment and example can be combined with other embodiments and examples or modified in various ways.

[0161] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0162] DESCRIPTION OF SYMBOLS 1a First insulating portion, 1b Second insulating portion, 1c Insulating portion, 2a First wiring portion, 2b Second wiring portion, 2c Wiring portion, 3a First seed layer, 3b Second seed layer, 3c Seed layer, 3d Second connection seed layer, 4a First plating layer, 4b Second plating layer, 4c Plating layer, 5a First base film, 5b Second base film, 6a First photosensitive resin, 6b Second photosensitive resin, 9 Adhesive layer, 10a First layer, 10b Second layer, 11 Main portion, 12 Bridging portion, 21 First wiring member, 22 Second wiring member, 23 Third wiring member, 24 Fourth wiring member, 25 Fifth wiring member, 26 Sixth wiring member, 27 Seventh wiring member, 30 Bottom surface, 31 First side wall surface, 32 Second side wall surface, 35 Winding portion, 36 First surface, 37 Second surface, 38 Outer wall surface, 39 First top surface, 51 First main surface, 52 Second main surface, 61 First end, 62 Second end, 63 Third end, 71 First convex portion, 72 Second convex portion, 73 Interlayer connection portion, 78 Void, 79 Depression, 80 Dispersion, 88 Peripheral space, 89 Hole, 90 Intermediate position, 91 First groove, 91c Groove, 92 Second groove (first dispersion supply portion), 93 Third groove, 94 Fourth groove, 95 Fifth groove (second dispersion supply portion), 96 Sixth groove, 97 Crack, 98 Recess, 99 Through hole, 100 Printed wiring board, 101 First direction, A1, A2 Arrow, C Center line, CS1 First cross section, CS2 Second cross section, CS3 Third cross section, CS4 Fourth cross section, CS5 Fifth cross section, H1 First height, H2 Second height, T1 first thickness, T2 second thickness, T3 third thickness, T4 fourth thickness, T5 fifth thickness, T6 sixth thickness, T7 seventh thickness, T8 eighth thickness, W1 first width, W2 second width, W3 third width, W4 fourth width, W5 fifth width.

Claims

1. A printed wiring board comprising: an insulating portion having a first groove provided therein; and a first wiring portion provided in the first groove, wherein the insulating portion includes a bottom surface, a first sidewall surface continuous with the bottom surface, and a second sidewall surface continuous with the bottom surface and facing the first sidewall surface, wherein the bottom surface, the first sidewall surface, and the second sidewall surface form the first groove, and the first wiring portion includes a seed layer and a plating layer provided on the seed layer, wherein, in a cross section perpendicular to the direction in which the first wiring portion extends, a depth direction of the first groove is defined as a first direction, a thickness in the first direction of the seed layer in contact with the first sidewall surface is defined as a first thickness, a thickness in the first direction of the seed layer in contact with the second sidewall surface is defined as a second thickness, and a thickness in the first direction of the seed layer at a midpoint between the first sidewall surface and the second sidewall surface is defined as a third thickness, wherein the third thickness is thinner than both the first thickness and the second thickness.

2. A printed wiring board as described in claim 1, wherein, in a cross section perpendicular to the direction in which the first wiring portion extends, the thickness of the seed layer in the first direction becomes thinner as it moves from the first side wall surface toward the intermediate position, and the thickness of the seed layer in the first direction becomes thinner as it moves from the second side wall surface toward the intermediate position.

3. A printed wiring board as described in claim 1 or claim 2, comprising: a first layer having the insulating portion and the first wiring portion; a second layer having a second wiring portion; and an adhesive layer bonding the first layer and the second layer together, wherein a through hole is provided in the insulating portion and the adhesive layer, and the first wiring portion has an interlayer connection portion located within the through hole and electrically connecting the first wiring portion and the second wiring portion, and a crack is provided in a portion of the seed layer forming at least a part of the interlayer connection portion, and a part of the plating layer is located within the crack.

4. A printed wiring board according to any one of claims 1 to 3, wherein a recess is provided in at least one of the bottom surface, the first side wall surface, or the second side wall surface, and a portion of the seed layer is located within the recess.

5. A printed wiring board as claimed in any one of claims 1 to 4, wherein the insulating section is provided with a second groove communicating with the first groove and a hole communicating with the second groove, the width of the second groove being greater than the width of the first groove, the first wiring section includes: a first wiring member located in the first groove; a second wiring member located in the second groove and communicating with the first wiring member; and a third wiring member located in the hole and communicating with the second wiring member, and the thickness of the third wiring member is thinner than the thickness of the first wiring member.

6. A printed wiring board according to any one of claims 1 to 5, wherein the maximum thickness of the first wiring portion in the first direction is 100 μm or more.

7. A printed wiring board according to any one of claims 1 to 6, wherein the first thickness is smaller than the height of the first side wall surface, and the second thickness is smaller than the height of the second side wall surface.

8. A printed wiring board according to any one of claims 1 to 7, wherein the insulating portion is composed of a base film and a photosensitive resin laminated on the base film.

9. A method for manufacturing a printed wiring board, comprising: a step of preparing an insulating section having a groove and a dispersion liquid supply section connected to the groove; a step of supplying a dispersion liquid containing metal particles into the groove; a step of forming a seed layer by sintering the metal particles; and a step of forming a wiring section by plating the seed layer, wherein in the step of supplying the dispersion liquid containing the metal particles into the groove, the dispersion liquid is supplied to the dispersion liquid supply section and then the dispersion liquid is supplied from the dispersion liquid supply section to the groove.

10. A method for manufacturing a printed wiring board as described in claim 9, wherein, in the step of supplying the dispersion liquid containing the metal particles into the groove, the dispersion liquid is supplied to the dispersion liquid supply section, and then the dispersion liquid is supplied from the dispersion liquid supply section to the groove using capillary action.

11. The method for manufacturing a printed wiring board according to claim 9 or 10, wherein the width of the dispersion liquid supply portion is at least five times the width of the groove.

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