High Frequency Board

Abstract

To provide a high-frequency substrate that can achieve impedance matching in a high frequency range.SOLUTION: A high-frequency substrate includes a first substrate, a second substrate laminated on the surface of the first substrate, a first metal layer that covers the inner surface of a through hole that communicates from the front surface of the second substrate to the back surface of the first substrate, a first strip line provided on the surface of the second substrate, a second strip line provided on the back surface of the first substrate and electrically connected to the first strip line via the first metal layer, and a second metal layer extending between the first substrate and the second substrate and provided apart from the first metal layer. The second substrate includes a first region, a second region, and a third region arranged in a direction along the surface of the first substrate, and the third region is provided between the first region and the second region, and in the second region and the third region, a recess is provided on the surface side of the second substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiment relates to a high frequency substrate. [Background technology]

[0002] High-frequency boards are used in high-frequency circuits such as wireless communication devices and radar devices. High-frequency boards have strip lines that transmit high-frequency signals such as microwaves or millimeter waves, and some have a structure in which a strip line provided on the front side of the board is electrically connected to a strip line provided on the back side via a through hole. However, with such a line connection, it becomes more difficult to maintain impedance matching between the lines as the signal frequency increases. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-204209 A Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiment provides a high frequency substrate capable of achieving impedance matching in a high frequency region. [Means for solving the problem]

[0005] A high-frequency substrate according to an embodiment includes an insulating first substrate, an insulating second substrate laminated on a surface of the first substrate, a first metal layer covering an inner surface of a through hole communicating from the surface of the second substrate to a back surface of the first substrate, a first strip line provided on the surface of the second substrate, a second strip line provided on the back surface of the first substrate and electrically connected to the first strip line via the first metal layer, and a second metal layer extending between the first substrate and the second substrate and spaced apart from the first metal layer, the second metal layer including a portion located between the first substrate and the first strip line and a portion located between the second substrate and the second strip line. The second substrate includes a first region having a first thickness in a first direction from the first substrate to the second substrate, a second region surrounded by the first region and having a second thickness in the first direction thinner than the first thickness, and a third region provided between the first region and the second region, surrounding the second region, and having a third thickness in the first direction thinner than the first thickness and thicker than the second thickness. The first region, the second region, and the third region are aligned in a direction along the surface of the first substrate, and the second region and the third region have a recess on the surface side of the second substrate opposite to the first substrate. The first metal layer covers an inner surface of the through hole provided in the second region of the second substrate. The first strip line extends from the first region through the third region to the second region along the surface of the second substrate. [Brief description of the drawings]

[0006] [Figure 1] 1 is a perspective view showing a schematic diagram of a high-frequency substrate according to an embodiment of the present invention; [Diagram 2] 1 is a schematic diagram showing a high-frequency substrate according to an embodiment of the present invention; [Diagram 3] 5A to 5C are schematic diagrams showing characteristics of the high-frequency substrate according to the embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view showing a strip line according to an embodiment. [Diagram 5] 6 is a graph showing characteristics of a connection portion of a strip line according to the embodiment. [Figure 6]5A to 5C are schematic cross-sectional views showing a manufacturing process of the high-frequency substrate according to the embodiment. [Figure 7] 7A to 7C are schematic cross-sectional views showing the manufacturing process following FIG. 6. [Figure 8] 8A to 8C are schematic cross-sectional views showing the manufacturing process following FIG. 7. [Figure 9] FIG. 13 is a schematic diagram showing a high-frequency substrate according to a modified example of the embodiment. [Figure 10] FIG. 11 is a perspective view illustrating a high-frequency substrate according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments will be described with reference to the drawings. The same parts in the drawings are given the same numbers, and detailed descriptions thereof will be omitted as appropriate, and different parts will be described. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as the actual ones. Even when the same parts are shown, the dimensions and ratios of each part may be different depending on the drawing.

[0008] Furthermore, the arrangement and configuration of each part will be explained using the X-axis, Y-axis, and Z-axis shown in each figure. The X-axis, Y-axis, and Z-axis are mutually perpendicular and represent the X-direction, Y-direction, and Z-direction, respectively. In addition, the Z-direction may be described as upward and the opposite direction as downward.

[0009] 1 is a perspective view that typically illustrates a high-frequency substrate 1 according to an embodiment. The high-frequency substrate 1 has a structure in which, for example, a first substrate 10 and a second substrate 20 are laminated. The first substrate 10 and the second substrate 20 are each an insulating substrate containing resin or ceramics. The high-frequency substrate 1 also includes a first strip line 30, a second strip line 40, a connection portion 50, and a metal layer 60.

[0010] The second substrate 20 is laminated on the first substrate 10 via a metal layer 60. The metal layer 60 contains, for example, copper (Cu) or gold (Au). The metal layer 60 is provided on the front surface of the first substrate 10 or on the back surface of the second substrate 20. In order to connect the first substrate 10 and the second substrate 20, an adhesive layer containing, for example, an insulating resin (see FIG. 8) is provided between the second substrate 20 and the metal layer 60 or between the first substrate 10 and the metal layer 60.

[0011] The second substrate 20 is laminated, for example, so that its back surface faces the first substrate 10 via the metal layer 60. The first stripline 30 is provided on the front surface of the second substrate 20. Meanwhile, the second stripline 40 is provided on the back surface of the first substrate 10. The first stripline 30 and the second stripline 40 are, for example, metal layers containing copper (Cu) or gold (Au).

[0012] The first strip line 30 is electrically connected to the second strip line 40 via a connection portion 50 that penetrates the first substrate 10 and the second substrate 20. The connection portion 50 has a metal layer (see FIG. 2(b)) containing, for example, copper (Cu) or gold (Au).

[0013] As shown in Fig. 1, the second substrate 20 has a recessed RPF provided on its front surface side. The first stripline 30 extends inside the recessed RPF along the front surface of the second substrate 20. The first substrate 10 has a recessed RPB provided on its rear surface side. The second stripline 40 extends inside the recessed RPB along the rear surface of the first substrate 10.

[0014] The connection portion 50 extends from the bottom surface of the recessed portion RPF to the bottom surface of the recessed portion RPB through the second substrate 20 and the first substrate 10. The first strip line 30 is electrically connected to the connection portion 50 at the bottom surface of the recessed portion RPF. The second strip line 40 is electrically connected to the connection portion 50 at the bottom surface of the recessed portion RPB.

[0015] 2(a) and (b) are schematic diagrams showing the high-frequency substrate 1 according to the embodiment. Fig. 2(a) is a schematic plan view showing the surface of the second substrate 20. Fig. 2(b) is a schematic diagram showing a cross section taken along line AA shown in Fig. 2(a).

[0016] As shown in FIG. 2(a), the second substrate 20 has, for example, a first region 20a, a second region 20b, and a third region 20c. The first region 20a is provided so as to surround the second region 20b. The third region 20c is provided between the first region 20a and the second region 20b and surrounds the second region 20b. The second region 20b and the third region 20c form a recessed portion RPF.

[0017] The recess RPF has, for example, a circular outer edge. The boundary between the first region 20a and the third region 20c and the boundary between the second region 20b and the third region 20c are, for example, concentric. The connection portion 50 is, for example, provided in the center of the second region 20b. The metal layer 60 also has an opening 60R located in the second region 20b (see FIG. 2(b)), and the connection portion 50 is provided in the center of the opening 60R.

[0018] The first stripline 30 extends, for example, in the X direction on the surface of the second substrate 20. The first stripline 30 extends from the first region 20a through the third region 20c into the second region 20b.

[0019] The first stripline 30 has a width WLF in the Y direction in the first region 20a. The first stripline 30 has a width WCF in the Y direction in the second region 20b, and a width WSF in the Y direction in the third region 20c. WCF is narrower than WLF. WSF is narrower than WLF and wider than WCF.

[0020] The width WSF of the first stripline 30 in the third region 20c narrows from the first region 20a toward the second region 20b. For example, assuming an arbitrary first position P1 in a part of the third region 20c located below the first stripline 30 and a second position P2 closer to the second region 20b than the first position P1, the width WSF of the first stripline 30 at the second position P2 is narrower than the width WSF of the first stripline 30 at the first position P1.

[0021] The outer edge of the first stripline 30 is continuously connected at the boundary between the first region 20a and the third region 20c and the boundary between the third region 20c and the second region 20b. That is, the first stripline 30 is provided so as to have no steps at the boundary between the first region 20a and the third region 20c and the boundary between the third region 20c and the second region 20b.

[0022] As shown in FIG. 2(b), the first region 20a, the third region 20c, and the second region 20b of the second substrate 20 are aligned in a direction along the surface of the first substrate 10. The first thickness TR1 in the Z direction of the first region 20a is, for example, the same as the thickness TS2 in the Z direction of the second substrate 20. The first thickness TR1 is thicker than the second thickness TR2 in the Z direction of the second region 20b. The depth DRF of the recess RPF is, for example, equal to the difference between the first thickness TR1 and the second thickness TR2. The third region 20c has a third thickness TR3 in the Z direction. The third thickness TR3 is thinner than the first thickness TR1 and thicker than the second thickness TR2.

[0023] The third thickness TR3 of the third region 20c, for example, gradually becomes thinner from the first region 20a toward the second region 20b. For example, assuming an arbitrary first position P1 in the third region 20c and a second position P2 closer to the second region 20b than the first position (see FIG. 2(a)), the third thickness TR3 at the second position P2 is thinner than the third thickness TR3 at the first position P1. At the boundary between the first region 20a and the third region 20c, the third thickness TR3 is equal to the first thickness TR1. Also, at the boundary between the third region 20c and the second region 20b, the third thickness TR3 is equal to the second thickness TR2.

[0024] 2(b), the first substrate 10 includes a fourth region 10a, a fifth region 10b, and a sixth region 10c. The fourth region 10a, the fifth region 10b, and the sixth region 10c are aligned in a direction along the rear surface of the first substrate 20. The sixth region 10c is provided between the fourth region 10a and the fifth region 10b.

[0025] The fourth region 10a is provided so as to surround the sixth region 10c and the fifth region 10b. The sixth region 10c is provided so as to surround the fifth region 10b. The boundary between the fourth region 10a and the sixth region 10c and the boundary between the sixth region 10c and the fifth region 10b are provided, for example, in a concentric shape. The fifth region 10b of the first substrate 10 and the third region 20b of the second substrate 20 are aligned in the Z direction.

[0026] The fourth region 10a has a fourth thickness TR4 in the Z direction, and the fifth region 10b has a fifth thickness TR5 in the Z direction. The sixth region 10c has a sixth thickness TR6 in the Z direction. The fifth thickness TR5 is thinner than the fourth thickness TR4. The sixth thickness TR6 is thicker than the fifth thickness TR5 and thinner than the fourth thickness TR4. That is, the fifth region 10b and the sixth region 10c form a recess RPB on the back side of the first substrate 10. The depth DRB of the recess RPB in the Z direction is, for example, the difference between the fourth thickness TR4 and the fifth thickness TR5.

[0027] The sixth region 10c is provided such that the sixth thickness TR6 gradually becomes thinner in the direction from the fourth region 10a to the fifth region 10b. For example, when an arbitrary first position P1 in the sixth region 10c and a second position P2 closer to the fifth region 10b than the first position P1 are assumed (see FIG. 2(a)), the sixth thickness TR6 at the second position P2 is thinner than the sixth thickness TR6 at the first position P1. At the boundary between the fourth region 10a and the sixth region 10c, the sixth thickness TR6 is equal to the fourth thickness TR4. Also, at the boundary between the sixth region 10c and the fifth region 10b, the sixth thickness TR6 is equal to the fifth thickness TR5.

[0028] The second strip line 40 extends, for example, in the X direction on the rear surface of the first substrate 10. The second strip line 40 extends from the fourth region 10a through the sixth region 10c to the fifth region 10b.

[0029] The second strip line 40 has a Y-direction width WLB in the fourth region 10a, and a Y-direction width WSB in the sixth region 10c (see FIG. 2(a)). The second strip line 40 also has a Y-direction width WCB in the fifth region 10b (see FIG. 2(a)). The width WCB may be the same as or different from the Y-direction width WCF of the first strip line 30, for example. WCB is narrower than WLB. WSB is narrower than WLB and wider than width WCB.

[0030] The width WSB of the second stripline 40 in the sixth region 10c narrows from the fourth region 10a toward the fifth region 10b. For example, assuming an arbitrary third position P3 in a part of the sixth region 10c located below the second stripline 40 and a fourth position P4 closer to the fifth region 10b than the third position P3 (see FIG. 2(a)), the width WSB of the second stripline 40 at the fourth position P4 is narrower than the width WSB of the second stripline 40 at the third position P3.

[0031] The outer edge of the second strip line 40 is continuously connected at the boundary between the fourth region 10a and the sixth region 10c and the boundary between the sixth region 10c and the fifth region 10b (see FIG. 2(a)). That is, the second strip line 40 is provided so as not to have a step at the boundary between the fourth region 10a and the sixth region 10c and the boundary between the sixth region 10c and the fifth region 10b.

[0032] 2(b), the connection portion 50 is provided inside a through hole TH that penetrates the fifth region 10b of the first substrate 10 and the second region 20b of the second substrate 20. The connection portion 50 includes, for example, a metal layer 53 and an insulator 55. The metal layer 53 covers the inner surface of the through hole TH and electrically connects the first strip line 30 and the second strip line 40. The insulator 55 is, for example, a resin filled inside the through hole TH.

[0033] The connection portion 50 is provided, for example, in the center of the opening 60R of the metal layer 60. The connection portion 50 is provided apart from the metal layer 60 and is electrically insulated from the metal layer 60.

[0034] Fig. 3 is a schematic diagram showing the characteristics of the high-frequency substrate 1 according to the embodiment. Fig. 3 is a graph showing the standing wave ratio (VSWR) of the high-frequency substrate 1 according to the embodiment. Fig. 3 also shows the characteristics of a high-frequency substrate 2 according to a comparative example. The horizontal axis is the signal frequency (GHz) and the vertical axis is the VSWR.

[0035] 10 also has a structure in which a first substrate 10 and a second substrate 20 are laminated with a metal layer 60 interposed therebetween. A first stripline 30 is provided on the front surface of the second substrate 20, and a second stripline 40 is provided on the back surface of the first substrate 10. In the high-frequency substrate 2, no recesses are provided on the back surface of the first substrate 10 or on the front surface of the second substrate 20, and the first stripline 30 and the second stripline 40 each extend on the flat substrate surface.

[0036] The first stripline 30 is electrically connected to the second stripline 40 by a connection portion 50 provided in a through hole extending from the front surface of the second substrate 20 to the rear surface of the first substrate 10. Such a configuration is used, for example, when the first stripline 30 extending in the X direction intersects, on the front surface of the second substrate 20, with another stripline extending in the Y direction.

[0037] In the high-frequency substrate 1 according to the embodiment, recesses RPB and RPF are provided on the back surface side of the first substrate 10 and the front surface side of the second substrate 20, respectively. For this reason, the length in the Z direction of the connection portion 50 in the high-frequency substrate 1 is shorter than the length in the Z direction of the connection portion 50 in the high-frequency substrate 2 by the depths of the recesses RPF and RPB.

[0038] The VSWR shown in Fig. 3 is preferably in the range of 1 to 1.5 in the wavelength band of 10 GHz to 40 GHz, and more preferably in the range of 1 to 1.2. In the characteristic S2 of the high-frequency substrate 2 shown in Fig. 3, the VSWR exceeds 1.2 at 10 GHz, for example, and increases monotonically up to 40 GHz as the frequency increases. In contrast, in the characteristic S1 of the high-frequency substrate 1, the VSWR is kept at 1.2 or less from 5 GHz to 40 GHz.

[0039] In this way, in the high-frequency substrate 1 according to the embodiment, by shortening the length of the connection portion 50 in the Z direction, it is possible to suppress reflection of high-frequency signals at the connection portion 50. In other words, it is possible to ensure impedance matching at the connection portion 50 in a wide frequency band up to 40 GHz.

[0040] 4 is a schematic cross-sectional view showing the first stripline 30 according to the embodiment. The characteristic impedance Z0 of the first stripline 30 is calculated by the following equation.

number

[0041] The characteristic impedance Z0 of the second stripline 40 is similarly calculated using the thickness and dielectric constant of the first substrate 10. In the first stripline 30 and the second stripline 40, the width "W" and thickness "T" are set, for example, so that the characteristic impedance Z0 is 50Ω.

[0042] 5(a) and (b) are graphs showing the characteristics of the connection part 50 of the strip line according to the embodiment. Fig. 5(a) is a graph showing the change in inductance L (nH) of the connection part 50. Fig. 5(b) is a graph showing the change in impedance Z (Ω) of the connection part 50. The horizontal axis is the length of the connection part 50 in the Z direction.

[0043] 5(a) and (b) show the inductance L and impedance Z when the through-hole diameter d is 0.15 mm and 0.3 mm. The signal frequency is 40 GHz.

[0044] The inductance L and impedance Z are calculated using the following equations:

number

number

[0045] 5(a), the inductance L increases as the length of the connection portion 50 in the Z direction increases. Also, as the through-hole diameter increases, the inductance L decreases.

[0046] 5(b), the impedance Z increases as the length of the connection portion 50 in the Z direction increases, similar to the inductance L. Furthermore, as the through-hole diameter increases, the impedance Z decreases.

[0047] The VSWR characteristics shown in FIG. 3 are based on the characteristic impedance Z0, the inductance L, and the impedance Z calculated using the dimensions of the high-frequency board 1.

[0048] 2(a) and (b), the thicknesses TS1 and TS2 in the Z direction of the first substrate 10 and the second substrate 20 are 0.4 mm, respectively. The depths DRF and DRB of the recesses RPF and RPB are 0.2 mm, respectively. The widths WLF and WLB of the first and second striplines 30 and 40 in the Y direction are 0.8 mm, respectively. The widths WCF and WCB of the first and second striplines 30 and 40 in the Y direction at the portions connected to the connection portion 50 are 0.4 mm, respectively.

[0049] The diameter of the opening 60R of the metal layer 60 is 0.8 mm. The diameter of the through hole TH in the XY cross section is 0.3 mm. The diameter of the boundary between the first region 20a and the third region 20c of the second substrate 20 is 2 mm, and the diameter of the boundary between the third region 20c and the second region 20b is 1 mm. The dimensions of the fifth region 10b and the sixth region 10c of the first substrate 10 are the same as the dimensions of the second region 20b and the third region 20c of the second substrate 20, for example.

[0050] Next, a method for manufacturing the high-frequency substrate 1 will be described with reference to Fig. 6(a) to Fig. 8(c). Note that the manufacturing process of the high-frequency substrate 1 shown in Fig. 6(a) to Fig. 8(c) is an example, and the embodiment is not limited thereto. Note that the top and bottom of Fig. 6(a) to Fig. 8(c) are written to match the explanation of Fig. 1 and Fig. 2.

[0051] 6(a), the second substrate 20 is prepared. A metal layer 60 is provided on the rear surface of the second substrate 20. The second substrate 20 is, for example, an insulating resin substrate. The metal layer 60 is, for example, a copper foil.

[0052] Subsequently, an opening 60R is formed in the metal layer 60. The opening 60R is formed by selectively removing the metal layer 60 using an etching mask (not shown) formed by, for example, photolithography. The metal layer 60 is removed by, for example, wet etching.

[0053] 6(b), the first substrate 10 is bonded onto the rear surface of the second substrate 20 via a metal layer 60. The first substrate 10 is bonded, for example, via an adhesive layer 13. The adhesive layer 13 includes, for example, a thermosetting resin.

[0054] The metal layer 60 may be provided on the surface of the first substrate 10. In that case, the second substrate 20 is bonded onto the metal layer 60 via an adhesive layer 13.

[0055] 6(c), a recess RPB is formed on the rear surface side of the first substrate 10. The recess RPB is formed, for example, by cutting using a tapered rotating jig.

[0056] As shown in Fig. 6(d), a through hole TH is formed. The through hole TH is formed so as to communicate from the rear surface of the first substrate 10 to the front surface side of the second substrate 20. The through hole TH is formed, for example, by drilling or laser processing. The through hole TH is formed so as to pass through the center of the opening 60R of the metal layer 60.

[0057] 7(a), a metal layer 40g is formed so as to cover the rear surface of the first substrate 10 and the inner surface of the through hole TH. The metal layer 40g includes, for example, copper (Cu) or gold (Au). The metal layer 40g is formed by, for example, sputtering and plating.

[0058] 7(b), the metal layer 40g is selectively removed to form the second strip line 40 and a metal layer 53. The metal layer 53 covers the inner surface of the through hole TH.

[0059] As shown in Fig. 7(c), the through hole TH and the recess RPB are filled with a resin layer 15. The resin layer 15 is, for example, an epoxy resin. Then, as shown in Fig. 7(d), the resin layer 15 covering the rear surface of the first substrate 10 is ground to expose the second strip line 40.

[0060] 8(a), a recess RPF is formed on the front surface side of the second substrate 20. The recess RPF is formed, for example, by cutting using a tapered rotating jig.

[0061] As shown in FIG. 8(b), a metal layer 30g is formed to cover the surface of the second substrate 20. The metal layer 30g includes, for example, copper (Cu) or gold (Au). The metal layer 30g is formed by, for example, sputtering or plating. Then, as shown in FIG. 8(c), the metal layer 30g is selectively removed to form the first strip line 30.

[0062] In this example, the resin layer 15 is filled inside the recess RPB on the back surface side of the first substrate 10, but the embodiment is not limited to this. For example, the resin layer 15 may be filled inside the through hole TH and not provided in the recess RPB. Also, the resin layer 15 may not be provided.

[0063] 9 is a schematic diagram showing a high-frequency substrate 3 according to a modified example of the embodiment. In this example, a recess RPF is provided on the front surface side of the second substrate 20. On the other hand, no recess RPB is provided on the back surface side of the first substrate 10.

[0064] In this case, the thickness TS1 in the Z direction of the first substrate 10 is smaller than the thickness TS2 in the Z direction of the second substrate 20. For example, the thickness TS1 is 0.2 mm, and the thickness TS2 is 0.4 mm.

[0065] The depth of the recess RPF is deeper than the depth of the recess RPF of the high-frequency substrate 1. The depth DRF of the recess RPF is, for example, 0.4 mm. As a result, the length of the connection portion 50 in the Z direction is the same as the length of the connection portion 50 of the high-frequency substrate 1 in the Z direction, and for example, characteristics equivalent to the VSWR shown in FIG. 3 can be realized.

[0066] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0067] REFERENCE SIGNS LIST 1, 2, 3...high frequency substrate, 10...first substrate, 20...second substrate, 20a...first region, 20b...second region, 20c...third region, 10a...fourth region, 10b...fifth region, 10c...sixth region, 13...adhesive layer, 15...resin layer, 30...first strip line, 40...second strip line, 30g, 40g, 53, 60...metal layer, 50...connection portion, 55...insulator, 60R...opening, RPB, RPF...recess, TH...through hole

Claims

1. An insulating first substrate; an insulating second substrate laminated on a surface of the first substrate, a first region having a first thickness in a first direction from the first substrate to the second substrate; a second region surrounded by the first region and having a second thickness in the first direction that is less than the first thickness; a third region disposed between the first region and the second region, surrounding the second region, and having a third thickness in the first direction that is thinner than the first thickness and thicker than the second thickness; Including, a second substrate, the first region, the second region, and the third region being aligned in a direction along the surface of the first substrate, and the second region and the third region being provided with recesses on a surface side opposite to the first substrate; a first metal layer provided in the second region of the second substrate and covering an inner surface of a through hole that communicates from the front surface of the second substrate to a rear surface of the first substrate; a first stripline extending along the surface of the second substrate from the first region through the third region to the second region; a second stripline provided on a rear surface of the first substrate and electrically connected to the first stripline via the first metal layer; a second metal layer extending between the first substrate and the second substrate and spaced apart from the first metal layer, the second metal layer including a portion located between the first substrate and the first stripline and a portion located between the second substrate and the second stripline; Equipped with the first substrate includes a fourth region having a fourth thickness in the first direction, the fourth region being surrounded by the fourth region; a fifth region having a fifth thickness in the first direction that is thinner than the fourth thickness; and a sixth region provided between the fourth region and the fifth region, surrounding the fifth region, and having a sixth thickness in the first direction that is thinner than the fourth thickness and thicker than the fifth thickness, the fourth region, the fifth region, and the sixth region are aligned in a direction along the back surface of the second substrate, and the fifth region and the sixth region provide recesses on the back surface side of the first substrate; the fifth region is aligned with the second region of the second substrate in the first direction; the through hole is provided in the second region of the second substrate and the fifth region of the first substrate, The second strip line extends from the fourth region through the sixth region to the fifth region. A high-frequency board.

2. The high frequency substrate according to claim 1 , wherein the third thickness at a first position in the third region of the second substrate is greater than the third thickness at a second position in the third region that is closer to the second region than the first position.

3. the first stripline extends in a second direction along the surface of the second substrate; In a third direction along a surface of the second substrate and perpendicular to the second direction, a first width of the first stripline in the first region of the second substrate is wider than a second width of the first stripline in the second region of the second substrate, and a third width of the first stripline in the third region of the second substrate is narrower than the first width, The high frequency board according to claim 1 , wherein the width is greater than the second width.

4. the first stripline extends over a first location in the third region of the second substrate and a second location in the third region that is closer to the second region than the first location; The high-frequency substrate according to claim 3 , wherein the third width of the first stripline at the first position in the third region of the second substrate is wider than the third width of the first stripline at the second position in the third region.

5. A high-frequency substrate according to any one of claims 1 to 4, wherein an outer edge of the first strip line is continuously connected at the boundary between the first region and the third region of the second substrate and at the boundary between the second region and the third region.

6. 6. The high frequency substrate according to claim 1, further comprising an insulator filled inside the through hole.

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