wiring board

Abstract

To provide a wiring board that improves the transmission characteristics of radio waves in a built-in post wall waveguide.SOLUTION: A wiring board 1 has a built-in post wall waveguide 1W in which an area surrounded by two opposing conductors 16p, 17p and a first post wall 31 and a second post wall 32 connecting the two conductors serves as a transmission path for electromagnetic waves. The second post wall 32 has a configuration in which a second columnar portion 32p in which via wirings 13v, 16v, 17v penetrating a plurality of insulating layers 12, 14, 15 are stacked is arranged at a predetermined interval in a direction of electromagnetic wave transmission. In a cross-sectional view taken in a direction perpendicular to the direction of electromagnetic wave transmission, the via wirings 13v, 16v, 17v constituting a first columnar portion 31p and the second columnar portion 32p are stacked in a stepped manner, and the interval between the opposing via wirings 13v in the insulating layer 12 that is not in contact with the conductors 16p, 17p is wider than the interval between the opposing via wirings 16v, 17v in the two insulating layers 14, 15 that are in contact with the conductors.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wiring board. [Background technology]

[0002] A technology called a post-wall waveguide has been proposed. The post-wall waveguide has, for example, side post walls and a rear post wall formed by a plurality of metal pillars that vertically penetrate a first region of a dielectric block. The waveguide also has conductor foils formed on the upper and lower surfaces of the first region of the dielectric block corresponding to at least the side post walls and the rear post wall, and the region surrounded by the side post walls and the rear post wall (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5669043 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the post-wall waveguide has a shape similar to that of a rectangular waveguide, there is room for improvement in the transmission characteristics of radio waves.

[0005] The present invention has been made in view of the above points, and has as its object to improve the transmission characteristics of radio waves in a post-wall waveguide built into a wiring board. [Means for solving the problem]

[0006] The present wiring board has a built-in post wall waveguide, in which an area surrounded by two opposing conductors and a first post wall and a second post wall connecting the two conductors serves as a transmission path for electromagnetic waves, the two conductors are arranged facing each other with three or more insulating layers sandwiched between them, the first post wall has a configuration in which first columnar portions each having via wirings that penetrate each of the insulating layers stacked thereon are arranged at predetermined intervals in the direction of transmission of the electromagnetic waves, the second post wall has a configuration in which second columnar portions each having via wirings that penetrate each of the insulating layers stacked thereon are arranged at predetermined intervals in the direction of transmission of the electromagnetic waves, and in a cross-sectional view taken in a direction perpendicular to the direction of transmission of the electromagnetic waves, the via wirings that constitute the first columnar portion and the second columnar portion are stacked in a stepped manner, and the interval between the via wirings that face each other in the insulating layer that does not contact the conductors is wider than the interval between the via wirings that face each other in the two insulating layers that contact the conductors. Ku , In the cross-sectional view, the via wiring located in any of the insulating layers not in contact with the conductor has a width that gradually narrows from a wide portion located on both surfaces of the insulating layer toward a narrow portion located at the center in the thickness direction. . [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to improve the transmission characteristics of radio waves in a post-wall waveguide built into a wiring board. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram (part 1) illustrating a wiring board according to a first embodiment. [Figure 2] FIG. 2 is a diagram (part 2) illustrating the wiring board according to the first embodiment. [Figure 3] 1A to 1C are diagrams illustrating a manufacturing process of a wiring board according to the first embodiment (part 1); [Figure 4] 5A to 5C are diagrams illustrating the manufacturing process of the wiring board according to the first embodiment (part 2). [Figure 5] 5A to 5C are views (part 3) illustrating the manufacturing process of the wiring board according to the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating a simulation. [Figure 7] FIG. 10 is a diagram showing the results of a simulation. [Figure 8] 1 is a cross-sectional view (part 1) illustrating a wiring board according to Modification 1 of the first embodiment. [Figure 9] 10 is a cross-sectional view (part 2) illustrating the wiring board according to the first modification of the first embodiment. FIG. [Figure 10] FIG. 10 is a diagram (part 1) illustrating a via receiving pad formed larger than usual. [Figure 11] FIG. 2 is a diagram (part 2) illustrating a via receiving pad formed larger than usual. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment [Overall structure of wiring board] 1A and 1B are diagrams (part 1) illustrating a wiring board according to a first embodiment. Fig. 1A is a cross-sectional view showing the entire wiring board 1, and Fig. 1B is a vertical cross-sectional view of the post-wall waveguide 1w and its vicinity in Fig. 1A.

[0011] 1, wiring board 1 has wiring layer 11, insulating layer 12, wiring layer 13, insulating layer 14, insulating layer 15, wiring layer 16, wiring layer 17, insulating layer 18, insulating layer 19, wiring layer 20, and wiring layer 21. Wiring board 1 may have a solder resist layer on insulating layer 18 that selectively exposes wiring layer 20. Wiring board 1 may also have a solder resist layer on insulating layer 19 that selectively exposes wiring layer 21. Wiring board 1 has a built-in post-wall waveguide 1w. The post-wall waveguide 1w will be described later.

[0012] In this embodiment, for convenience, the wiring layer 20 side of the wiring board 1 in FIG. 1 is referred to as the upper side or one side, and the wiring layer 21 side is referred to as the lower side or the other side. The surface of each part facing the wiring layer 20 is referred to as the one side or upper side, and the surface facing the wiring layer 21 is referred to as the other side or lower side. However, the wiring board 1 can be used upside down or positioned at any angle. Furthermore, a planar view refers to viewing an object from the normal direction of one side of the insulating layer 18, and a planar shape refers to the shape of the object viewed from the normal direction of one side of the insulating layer 18. When the wiring board 1 is shown upside down compared to FIG. 1, the definitions of the upper and lower sides are reversed to match the illustration in the drawing.

[0013] In the wiring board 1, the wiring layer 11 is embedded in the upper surface side of the insulating layer 12. The upper surface of the wiring layer 11 is exposed from the upper surface of the insulating layer 12, and the lower surface and side surfaces of the wiring layer 11 are covered with the insulating layer 12. The wiring layer 11 includes a wiring pattern and a pad for receiving a via. The planar shape of the pad is, for example, a circle with a diameter of about 60 μm to 120 μm. The material of the wiring layer 11 can be, for example, copper (Cu). The wiring layer 11 may have a laminated structure of multiple metal layers. The thickness of the wiring layer 11 can be, for example, about 10 to 30 μm.

[0014] The insulating layer 12 is formed so as to cover the side and lower surfaces of the wiring layer 11. The upper surface of the insulating layer 12 can be flush with the upper surface of the wiring layer 11, for example. The insulating layer 12 can be made of an insulating resin whose main component is, for example, an epoxy resin or a polyimide resin. The thickness of the insulating layer 12 can be, for example, about 20 to 30 μm. The thickness of the insulating layer 12 here refers to the distance from the lower surface of the wiring layer 11 to the lower surface of the insulating layer 12. The same applies to the thicknesses of the subsequent insulating layers, etc. The insulating layer 12 can contain a filler such as silica (SiO2).

[0015] The wiring layer 13 includes via wirings 13v filled in via holes 12x that penetrate the insulating layer 12 and expose the underside of the wiring layer 11, and a wiring pattern 13p formed on the underside of the insulating layer 12. The wiring pattern 13p may include a via-receiving pad. In the vertical cross-sectional view shown in FIG. 1 , the via wirings 13v may have an hourglass shape that gradually narrows from wide portions 13a located on both sides of the insulating layer 12 toward narrow portions 13b located toward the center in the thickness direction. The wiring layer 13 is electrically connected to the wiring layer 11 exposed at the bottom of the via holes 12x. The material of the wiring layer 13 and the thickness of the wiring pattern that constitutes the wiring layer 13 may be the same as those of the wiring layer 11, for example.

[0016] Insulating layer 14 is disposed on the upper surface of insulating layer 12 and covers the upper surface of wiring layer 11. The material and thickness of insulating layer 14 may be, for example, the same as those of insulating layer 12. Insulating layer 14 may contain a filler such as silica (SiO2).

[0017] Insulating layer 15 is disposed on the lower surface of insulating layer 12 and covers the lower surface and side surfaces of wiring layer 13. The material and thickness of insulating layer 15 may be, for example, the same as those of insulating layer 12. Insulating layer 15 may contain a filler such as silica (SiO2).

[0018] The wiring layer 16 includes via wirings 16v filled in via holes 14x that penetrate the insulating layer 14 and expose the upper surface of the wiring layer 11, and a wiring pattern formed on the upper surface of the insulating layer 14. The wiring pattern includes conductors 16p. The wiring pattern may also include via-receiving pads. The via wirings 16v may have a shape that narrows with increasing distance from the conductors 16p. For example, the via wirings 16v may have an inverted truncated cone shape whose diameter on the insulating layer 18 side is larger than the diameter on the upper surface side of the wiring layer 11. The wiring layer 16 is electrically connected to the wiring layer 11 exposed at the bottom of the via holes 14x. The material of the wiring layer 16 and the thickness of the wiring pattern that constitutes the wiring layer 16 may be the same as those of the wiring layer 11, for example.

[0019] The wiring layer 17 includes via wirings 17v filled in via holes 15x that penetrate the insulating layer 15 and expose the lower surface of the wiring layer 13, and a wiring pattern formed on the lower surface of the insulating layer 15. The wiring pattern includes conductors 17p. The wiring pattern may also include via-receiving pads. The via wirings 17v may have a shape that narrows with increasing distance from the conductors 17p. For example, the via wirings 17v may have a truncated cone shape whose diameter on the insulating layer 19 side is larger than the diameter on the lower surface side of the wiring layer 13. The wiring layer 17 is electrically connected to the wiring layer 13 exposed at the bottom of the via holes 15x. The material of the wiring layer 17 and the thickness of the wiring pattern that constitutes the wiring layer 17 may be the same as those of the wiring layer 11, for example.

[0020] The insulating layer 18 is disposed on the upper surface of the insulating layer 14 and covers the upper and side surfaces of the wiring layer 16. The material and thickness of the insulating layer 18 may be the same as those of the insulating layer 12. The insulating layer 18 may contain a filler such as silica (SiO2).

[0021] Insulating layer 19 is disposed on the lower surface of insulating layer 15, and covers the lower surface and side surfaces of wiring layer 17. The material and thickness of insulating layer 19 may be, for example, the same as those of insulating layer 12. Insulating layer 19 may contain a filler such as silica (SiO2).

[0022] The wiring layer 20 is configured to include via wiring filled in via holes 18x that penetrate the insulating layer 18 and expose the upper surface of the wiring layer 16, and a wiring pattern formed on the upper surface of the insulating layer 18. The via wiring of the wiring layer 20 may be shaped like an inverted truncated cone, with the diameter on the wiring layer 20 side being larger than the diameter on the upper surface side of the wiring layer 16. The wiring layer 20 is electrically connected to the wiring layer 16 exposed at the bottom of the via hole 18x. The material of the wiring layer 20 and the thickness of the wiring pattern that constitutes the wiring layer 20 may be the same as those of the wiring layer 11, for example.

[0023] The wiring layer 21 is configured to include via wiring filled in via holes 19x that penetrate the insulating layer 19 and expose the lower surface of the wiring layer 17, and a wiring pattern formed on the lower surface of the insulating layer 19. The via wiring of the wiring layer 21 may be shaped like a truncated cone with a diameter on the wiring layer 21 side larger than the diameter on the lower surface side of the wiring layer 17. The wiring layer 21 is electrically connected to the wiring layer 17 exposed at the bottom of the via hole 19x. The material of the wiring layer 20 and the thickness of the wiring pattern that constitutes the wiring layer 20 may be the same as those of the wiring layer 11, for example.

[0024] [Post-wall waveguide] 2A and 2B are diagrams illustrating a wiring board according to the first embodiment (part 2). Fig. 2A is a perspective view of the post-wall waveguide 1w in Fig. 1A, and Fig. 2B is a longitudinal cross-sectional view taken along line AA in Fig. 2A. The post-wall waveguide 1w will be described with reference to Figs. 1 and 2.

[0025] 1 and 2, the wiring board 1 includes a post-wall waveguide 1w, which is an electromagnetic wave transmission path 1t, surrounded by two conductors 16p and 17p facing each other in the Z direction and a first post wall 31 and a second post wall 32 connecting the conductors 16p and 17p. In the example of FIGS. 1 and 2, the electromagnetic wave is transmitted in the Y direction. The transmission path 1t is not limited to a straight line, but may be a curved line, or may have a mixture of straight and curved lines.

[0026] The conductor 16p is part of the wiring pattern of the wiring layer 16, and the conductor 17p is part of the wiring pattern of the wiring layer 17. The conductors 16p and 17p are arranged opposite each other in the Z direction with the insulating layers 15, 12, and 14 sandwiched therebetween. The shapes of the conductors 16p and 17p are, for example, rectangular solid patterns facing each other, as shown in FIG. 2(a).

[0027] The first post wall 31 has a configuration in which first columnar portions 31p each having a stack of via wirings 17v penetrating the insulating layer 15, via wirings 13v penetrating the insulating layer 12, and via wirings 16v penetrating the insulating layer 14 are arranged at predetermined intervals in the Y direction in which electromagnetic waves are transmitted, as shown in Fig. 2. The second post wall 32 has a configuration in which second columnar portions 32p each having a stack of via wirings 17v penetrating the insulating layer 15, via wirings 13v penetrating the insulating layer 12, and via wirings 16v penetrating the insulating layer 14 are arranged at predetermined intervals in the Y direction in which electromagnetic waves are transmitted, similar to the first columnar portions 31p. The length L1 in the Y direction of each of the first post wall 31 and the second post wall 32 can be, for example, 5 mm.

[0028] The first post wall 31 and the second post wall 32 face each other at a predetermined distance in the X direction. The distance L2 in the X direction between the first post wall 31 and the second post wall 32 may be, for example, 0.82 mm. The distance L2 in the X direction between the first post wall 31 and the second post wall 32 is determined at the position in the thickness direction where the distance in the X direction is widest.

[0029] In the longitudinal cross section shown in Figure 2(b), the central axes of the via wirings 17v, 13v, and 16v that make up the first columnar section 31p are substantially aligned. Similarly, the central axes of the via wirings 17v, 13v, and 16v that make up the second columnar section 32p are substantially aligned. The pitch L3 in the Y direction between the first columnar section 31p and the second columnar section 32p can be, for example, 0.125 mm. The frequency of the electromagnetic waves that can be transmitted through the transmission line 1t can be, for example, 150 GHz to 160 GHz.

[0030] In a vertical cross section taken perpendicular to the direction of electromagnetic wave transmission, i.e., in the vertical cross section shown in FIG. 1(b), the via wirings constituting the first columnar section 31p and the second columnar section 32p are stacked in a stepped manner. Here, "stepped" means that the central axes of adjacent via wirings above and below do not coincide. In other words, the stacked structure of the via wirings constituting the first columnar section 31p and the second columnar section 32p employs a staggered method in which adjacent via wirings above and below do not overlap at the same position in a plan view.

[0031] The interval between the via wirings 13v facing each other in the X direction in the insulating layer 12 that is not in contact with the conductors 16p and 17p is wider than the interval between the via wirings 16v facing each other in the X direction in the insulating layer 14 that is in contact with the conductor 16p. Also, the interval between the via wirings 13v facing each other in the X direction in the insulating layer 12 that is not in contact with the conductors 16p and 17p is wider than the interval between the via wirings 17v facing each other in the X direction in the insulating layer 15 that is in contact with the conductor 17p. The interval between the via wirings 16v facing each other in the X direction in the insulating layer 14 that is in contact with the conductor 16p may be the same as the interval between the via wirings 17v facing each other in the X direction in the insulating layer 15 that is in contact with the conductor 17p.

[0032] Here, the spacing between via wirings 16v facing each other in the X direction is determined by the widest spacing in the X direction. For example, the spacing between via wirings 16v facing each other in the X direction is determined by the spacing between the lower ends of the via wirings 16v that contact the upper surface of the insulating layer 12. Furthermore, the spacing between via wirings 13v facing each other in the X direction is determined by the spacing between the narrow portions 13b.

[0033] In the vertical cross section shown in Fig. 1(b), the first columnar section 31p and the second columnar section 32p have, for example, a bilaterally symmetrical structure. Also, in the vertical cross section shown in Fig. 1(b), the first columnar section 31p and the second columnar section 32p have, for example, a vertically symmetrical structure.

[0034] In this way, the distance in the X direction between the first columnar section 31p and the second columnar section 32p that make up the post-wall waveguide 1w is widest near the center in the thickness direction and becomes narrower as it approaches the conductors 16p and 17p. This gives the transmission line 1t a shape similar to that of a circular waveguide, which can improve the radio wave transmission characteristics compared to a shape similar to that of a rectangular waveguide in which the distance in the X direction between the first columnar section 31p and the second columnar section 32p is constant in the thickness direction.

[0035] 1(b), from the end of the via wiring 16v on the conductor 16p side to the narrow portion 13b, the sides of the via wirings 16v and 13v facing the transmission line 1t are preferably inclined in the same direction. Also, from the end of the via wiring 17v on the conductor 17p side to the narrow portion 13b, the sides of the via wirings 17v and 13v facing the transmission line 1t are preferably inclined in the same direction. This makes the transmission line 1t more similar in shape to a circular waveguide, thereby further improving the radio wave transmission characteristics.

[0036] In the longitudinal cross section shown in FIG. 1(b), the lower ends of the via wirings 16v constituting the first columnar section 31p and the second columnar section 32p are preferably connected to a region close to the transmission line 1t on the upper surface of the via receiving pad of the wiring layer 11. Furthermore, the upper ends of the via wirings 17v constituting the first columnar section 31p and the second columnar section 32p are preferably connected to a region close to the transmission line 1t on the surface of the via receiving pad of the wiring layer 13. Furthermore, the upper ends of the via wirings 13v constituting the first columnar section 31p and the second columnar section 32p are preferably connected to a region close to the transmission line 1t on the lower surface of the via receiving pad of the wiring layer 11. This causes the via receiving pad to protrude toward the transmission line 1t, resulting in a shape that is closer to a circular waveguide, thereby further improving the radio wave transmission characteristics.

[0037] In the wiring board 1, the number of insulating layers can be any number equal to or greater than three.

[0038] Furthermore, the wiring board 1 does not need to have any insulating layers or wiring layers other than those constituting the post-wall waveguide 1w, that is, the wiring board 1 itself may be the post-wall waveguide 1w.

[0039] A semiconductor chip may be mounted or built into the wiring board 1. This semiconductor chip is capable of transmitting and / or receiving electromagnetic waves transmitted through the transmission line 1t, for example.

[0040] [Method of manufacturing wiring board] Next, a method for manufacturing a wiring board according to the first embodiment will be described. Figures 3 to 5 are diagrams illustrating the manufacturing process of a wiring board according to the first embodiment. Here, an example of a process for forming a layer structure only on one side of the support is shown, but a process for forming layer structures on both sides of the support may also be used. Note that dashed lines C in each figure indicate the positions at which the wiring board is cut when it is divided into individual pieces. The regions located between adjacent dashed lines C in a cross-sectional view are ultimately divided into individual pieces to form one wiring board.

[0041] First, in the step shown in FIG. 3(a), a support 300 is prepared. The support 300 has a structure in which, for example, a carrier-attached copper foil 304 is laminated on one side of a core substrate 301. The core substrate 301 is, for example, a resin substrate having a thickness of about 0.7 mm, and may have a reinforcing member such as glass fiber. The carrier-attached copper foil 304 has a structure in which, for example, a thin copper foil 304a having a thickness of about 1.5 to 5 μm is peelably attached to a thick copper foil (carrier foil) 304b having a thickness of about 10 to 50 μm via a release layer (not shown). The thick foil 304b is provided as a support material to facilitate handling of the thin foil 304a.

[0042] The above-described structure of the support 300 is an example, and the present invention is not limited to this. For example, in the support 300, a laminate in which a plurality of prepregs are stacked may be used instead of the core substrate 301. Furthermore, the support 300 may have a structure in which a carrier-attached copper foil 304 is disposed on one side of a glass substrate, a metal substrate, or the like, via a release layer.

[0043] Next, in the step shown in FIG. 3(b), the wiring layer 11 is formed on the support 300. Specifically, a resist layer having openings where the wiring layer 11 is to be formed is formed on the upper surface of the carrier-attached copper foil 304 (upper surface of the thin foil 304a) using a dry film resist or the like. Then, by electrolytic plating using the carrier-attached copper foil 304, which is a metal layer, as a power supply layer, the wiring layer 11, which is an electrolytic plating layer, is formed on the upper surface of the carrier-attached copper foil 304 exposed in the openings. The material and thickness of the wiring layer 11 are as described above. Thereafter, the resist layer is peeled off and removed.

[0044] Next, in the step shown in FIG. 3(c), an insulating layer 12 is formed on the support 300 to cover the surface of the wiring layer 11 that is not in contact with the support 300. Specifically, the insulating layer 12 is formed on the upper surface of the carrier-attached copper foil 304 to cover the wiring layer 11. First, for example, a semi-cured film-like insulating resin containing a thermosetting resin as its main component is prepared. Then, this insulating resin is laminated on the upper surface of the carrier-attached copper foil 304 and cured under heat and pressure to form the insulating layer 12. Alternatively, instead of laminating a film-like insulating resin, a liquid or paste-like insulating resin may be applied and then cured to form the insulating layer 12. The material and thickness of the insulating layer 12 are as described above.

[0045] 3(d), via holes 12x are formed in the insulating layer 12, penetrating the insulating layer 12 and exposing the upper surface of the wiring layer 11. The via holes 12x can be formed by a laser processing method using, for example, a CO2 laser, a YAG laser, an excimer laser, or the like. After the via holes 12x are formed, it is preferable to perform a desmearing process to remove resin residues adhering to the surfaces of the wiring layer 11 exposed at the bottoms of the via holes 12x.

[0046] The via hole 12x can be formed, for example, in an hourglass shape. The hourglass shape can be formed by adjusting the power of the laser light irradiated onto the insulating layer 12. By adjusting the power of the laser light, a portion of the laser light is reflected by the upper surface of the wiring layer 11 toward the insulating layer 12, resulting in an hourglass shape as shown in FIG. 3(d).

[0047] Next, in the step shown in FIG. 4( a), the wiring layer 13 is formed on the insulating layer 12. The wiring layer 13 can be formed by, for example, a semi-additive method. Specifically, for example, a seed layer that continuously covers the upper surface of the insulating layer 12, the inner surfaces of the via holes 12x, and the upper surface of the wiring layer 11 exposed in the via holes 12x is formed by electroless copper plating or copper sputtering. Next, a resist layer having openings matching the shape of the wiring layer 13 is formed on the seed layer. Then, an electrolytic plating layer is formed on the seed layer exposed in the openings by electrolytic plating using the seed layer as a power supply layer. Next, after removing the resist layer, the seed layer exposed from the electrolytic plating layer is removed by etching, thereby forming the wiring layer 13 in which the electrolytic plating layer is laminated on the seed layer.

[0048] Next, in the steps shown in Figures 4(b) and 4(c), the support 300 shown in Figure 4(a) is removed. To remove the support 300, first, as shown in Figure 4(b), the core substrate 301 and the thick foil 304b are mechanically peeled off from the thin foil 304a. Then, as shown in Figure 4(c), the thin foil 304a is removed by wet etching using, for example, a ferric chloride aqueous solution, a cupric chloride aqueous solution, or an ammonium persulfate aqueous solution.

[0049] Next, in the step shown in FIG. 4(d), an insulating layer 14 is formed on one side of the insulating layer 12 so as to cover the surface of the wiring layer 11 that was in contact with the support 300. An insulating layer 15 is also formed on the other side of the insulating layer 12 so as to cover the wiring layer 13. Specifically, for example, two semi-cured film-like insulating resins, each containing a thermosetting resin as a main component, are prepared. These insulating resins are then laminated on one side and the other side of the insulating layer 12 and cured under heat and pressure to form the insulating layers 14 and 15. Alternatively, instead of laminating the film-like insulating resin, a liquid or paste-like insulating resin may be applied and cured to form the insulating layers 14 and 15. The material and thickness of the insulating layers 14 and 15 may be the same as, for example, the insulating layer 12. Note that FIG. 4(d) is depicted upside down compared to FIG. 4(c). The same applies to FIG. 5, described below.

[0050] 5(a), a via hole 14x is formed in the insulating layer 14, penetrating the insulating layer 14 and exposing the upper surface of the wiring layer 11. Also, a via hole 15x is formed in the insulating layer 15, penetrating the insulating layer 15 and exposing the lower surface of the wiring layer 13. The via holes 14x and 15x can be formed by, for example, a laser processing method using a CO2 laser or the like. After the via holes 14x and 15x are formed, it is preferable to perform a desmear process as necessary to remove resin residues adhering to the surface of the wiring layer 11 exposed at the bottom of the via hole 14x and the surface of the wiring layer 13 exposed at the bottom of the via hole 15x.

[0051] 5(b), a wiring layer 16 is formed on the insulating layer 14. Also, a wiring layer 17 is formed under the insulating layer 15. The wiring layers 16 and 17 can be formed by, for example, a semi-additive method, similar to the wiring layer 13.

[0052] 5(c), the same steps as those shown in FIGS. 4(d) to 5(b) are repeated to form insulating layers 18 and 19, via holes 18x and 19x, and wiring layers 20 and 21. Thereafter, cutting is performed along the dashed lines C to obtain individual wiring substrates 1.

[0053] [simulation] S-parameter simulations were performed on a wiring board 1 incorporating a post-wall waveguide 1w and a wiring board incorporating post-wall waveguides 2w to 5w as comparative examples. The post-wall waveguides 1w to 5w are designed to be capable of transmitting radio waves in the 150 GHz to 160 GHz range. As shown in FIG. 6, the post-wall waveguides 2w to 5w have a shape similar to a rectangular waveguide. The post-wall waveguide 2w has a columnar portion formed by a through-hole. The post-wall waveguide 3w has a columnar portion formed by stacking rectangular via wires with a uniform width in a vertical cross section. The post-wall waveguide 4w has a columnar portion formed by stacking trapezoidal via wires facing the same direction in a vertical cross section. The post-wall waveguide 5w has a columnar portion formed by stacking hourglass-shaped via wires whose width narrows at the center in the thickness direction in a vertical cross section. In the post-wall waveguides 3w to 5w, the central axes of the stacked via wires are aligned.

[0054] Figure 7 shows the high-frequency signal transmission characteristics of each post-wall waveguide shown in Figure 6, and shows the simulation results of S-parameters normalized to 120 Ω. Figure 7(a) shows the reflection characteristics, and Figure 7(b) shows the transmission characteristics. Figure 7(a) shows that the post-wall waveguide 2w has slightly better reflection characteristics in the 150 GHz to 160 GHz range, but there is no significant difference between the post-wall waveguides 1w and 3w to 5w. On the other hand, Figure 7(b) shows that the post-wall waveguide 1w has the best transmission characteristics in the 150 GHz to 160 GHz range.

[0055] Thus, the simulations revealed that a shape similar to a circular waveguide, such as the post-wall waveguide 1w, has improved transmission characteristics compared to shapes similar to a rectangular waveguide, such as the post-wall waveguides 2w to 5w.

[0056] <Modification of the first embodiment> In the modified example of the first embodiment, an example is shown in which the laminated structure of the via wiring in the columnar portion of the post wall waveguide built into the wiring substrate is different from that of the first embodiment. Note that in the modified example of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0057] 8A and 8B are cross-sectional views illustrating a wiring board according to a first modification of the first embodiment, and are longitudinal cross-sectional views of a post-wall waveguide and its vicinity similar to those in FIG. 1B. In FIG. 8A, the shape of the via wiring 13v is different from that in FIG. 1B. In FIG. 8A, the via wiring 13v has a truncated cone shape in which the diameter on the insulating layer 15 side is larger than the diameter on the underside of the wiring layer 11. Even in the case of a structure such as that in FIG. 8A, a post-wall waveguide shaped like a circular waveguide can be realized, thereby improving the transmission characteristics of radio waves.

[0058] 8(b), three insulating layers are added to FIG. 1(b). Specifically, insulating layer 51 is inserted between insulating layer 12 and insulating layer 15. A wiring pattern 52p including a via receiving pad and via wiring 52v are formed on insulating layer 51. Via wiring 52v has a truncated cone shape with a diameter on the insulating layer 15 side larger than the diameter on the bottom surface side of wiring pattern 13p.

[0059] Insulating layers 53 and 55 are inserted between insulating layer 12 and insulating layer 14. A wiring pattern 54p including a via receiving pad and a via wiring 54v are formed in insulating layer 53. The via wiring 54v has an inverted truncated cone shape with a diameter on the insulating layer 55 side larger than the diameter on the top surface of wiring layer 11. A wiring pattern 56p including a via receiving pad and a via wiring 56v are formed in insulating layer 55. The via wiring 56v has an inverted truncated cone shape with a diameter on the insulating layer 14 side larger than the diameter on the top surface of wiring pattern 54p. The structure shown in FIG. 8(b) also realizes a post-wall waveguide with a shape similar to a circular waveguide, thereby improving the radio wave transmission characteristics. Furthermore, increasing the number of insulating layers stacked is advantageous in that a post-wall waveguide with a shape even closer to a circular waveguide can be realized.

[0060] FIG. 9 is a cross-sectional view illustrating a wiring board according to Modification 2 of the first embodiment, and is a longitudinal cross-sectional view of a post-wall waveguide and its vicinity similar to FIG. 1(a). In FIG. 9(a), the shapes of via wirings 13v and 17v are different from those in FIG. 8(a). In FIG. 9(a), the via wiring 13v has an inverted truncated cone shape in which the diameter on the insulating layer 14 side is larger than the diameter on the upper surface of the wiring pattern 13p. The via wiring 17v has an inverted truncated cone shape in which the diameter on the insulating layer 12 side is larger than the diameter on the upper surface of the conductor 17p. Even with the structure shown in FIG. 9(a), a post-wall waveguide shaped similar to a circular waveguide can be realized, thereby improving the radio wave transmission characteristics.

[0061] FIG. 9(b) differs from FIG. 8(b) in that the insulating layer 51 has been removed. In FIG. 9(b), the via wiring 13v has an inverted truncated cone shape with a diameter on the insulating layer 53 side larger than the diameter on the upper surface of the wiring pattern 13p. Also, the via wiring 17v has an inverted truncated cone shape with a diameter on the insulating layer 12 side larger than the diameter on the upper surface of the conductor 17p. The structure shown in FIG. 9(b) also realizes a post-wall waveguide with a shape similar to a circular waveguide, thereby improving the transmission characteristics of radio waves. In addition, increasing the number of stacked insulating layers is advantageous in that a post-wall waveguide with a shape even closer to a circular waveguide can be realized.

[0062] As shown in Figures 9(a) and 9(b), even if all the via wirings have approximately the same shape, by stacking the via wirings in a stepped manner, a post-wall waveguide with a shape similar to a circular waveguide can be realized.

[0063] Although the preferred embodiments have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0064] For example, in the above-described embodiment, an example was introduced in which the ends of the via wirings are connected unevenly to a region on the surface of the via receiving pad that is close to the transmission path, but this may also be the case as shown in Figure 10. Figure 10(a) is a cross-sectional view, and Figure 10(b) is a partial plan view illustrating the via receiving pad of the wiring pattern 13p. In Figure 10(b), the region on the upper surface of the via receiving pad that is connected to the lower end of the via wiring 13v is indicated by a dashed line, and the region on the lower surface of the via receiving pad that is connected to the upper end of the via wiring 17v is indicated by a dashed line.

[0065] As shown in Figure 10, by connecting via wiring to a via receiving pad that is larger than usual, it is possible to obtain the same effect without intentionally distributing the end of the via wiring unevenly. This eliminates the need for delicate alignment and allows for stable production of wiring boards.

[0066] Examples of larger-than-normal via receiving pads include circular and elliptical shapes. Furthermore, larger-than-normal via receiving pads can be of various shapes, such as a dumbbell shape as shown in Fig. 11(a), a gourd shape as shown in Fig. 11(b), or a square shape as shown in Fig. 11(c). Furthermore, instead of forming a larger-than-normal via receiving pad, two normal-sized via receiving pads connected by wiring may be used. [Explanation of symbols]

[0067] 1. Wiring board 1t transmission line 1W Post-wall Waveguide 11,13,16,17,20,21 wiring layer 12,14,15,18,19,51,53,55 Insulation layer 12x, 14x, 18x, 19x via holes 13a wide part 13b Narrow part 13p, 52p, 54p, 56p wiring pattern 13v, 16v, 17v, 52v, 54v, 56v via wiring 16p,17p conductor 31 First Post Wall 31p 1st columnar part 32 Second Post Wall 32p 2nd columnar part 300 Support 301 Core Board 304 Copper foil with carrier 304a thin foil 304b thick foil

Claims

1. A wiring board incorporating a post wall waveguide, in which an area surrounded by two opposing conductors and a first post wall and a second post wall connecting the two conductors serves as a transmission path for electromagnetic waves, The two conductors are arranged opposite each other with three or more insulating layers interposed therebetween, the first post wall is configured such that first columnar portions, each having a stack of via wirings penetrating the insulating layers, are arranged at predetermined intervals in the direction of transmission of the electromagnetic waves; the second post wall is configured such that second columnar portions, each having a stack of via wirings penetrating the insulating layers, are arranged at predetermined intervals in the direction of transmission of the electromagnetic waves, In a cross-sectional view taken in a direction perpendicular to the direction of transmission of the electromagnetic waves, the via wirings constituting the first columnar section and the second columnar section are stacked in a step-like manner, and the interval between the via wirings facing each other in the insulating layer that is not in contact with the conductor is wider than the interval between the via wirings facing each other in the two insulating layers that are in contact with the conductor; A wiring board, wherein, in the cross-sectional view, the via wiring located in any of the insulating layers that is not in contact with the conductor gradually narrows in width from a wide portion located on both sides of the insulating layer to a narrow portion located in the center in the thickness direction.

2. The wiring board according to claim 1 , wherein, in the cross-sectional view, the via wirings located in the two insulating layers in contact with the conductor have widths that narrow with increasing distance from the conductor.

3. 3. The wiring board according to claim 2, wherein, in the cross-sectional view, the side of the via wiring facing the transmission path is inclined in the same direction from the conductor-side end of the via wiring located in the two insulating layers in contact with the conductor to the narrow portion.

4. 4. The wiring substrate according to claim 1, wherein, in the cross-sectional view, the ends of the via wiring constituting the first columnar portion and the second columnar portion are connected in a concentrated manner in an area close to the transmission path on the surface of the via receiving pad.

5. The wiring substrate according to claim 1 , wherein the first columnar section and the second columnar section have a bilaterally symmetrical structure in the cross-sectional view.

6. The wiring board according to claim 5 , wherein the first columnar section and the second columnar section have a vertically symmetrical structure in the cross-sectional view.

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