Porous laminate and flexible multilayer circuit board

Abstract

A porous laminate (1) is provided with a conductor layer (2) and an insulating layer (3) in this order toward one side in the thickness direction. The insulating layer (3) is provided with a base resin layer (4), a porous resin layer (5), and a bonding layer (6) in this order toward one side in the thickness direction. The thickness of the porous resin layer (5) is 50 [mu] m or less, and the maximum height (Rz) of one surface of the porous resin layer (5) in the thickness direction is 16 [mu] m or less. The maximum height (Rz) of one surface of the porous resin layer (5) in the thickness direction is greater than the maximum height (Rz) of one surface of the base resin layer (4) in the thickness direction.

Description

Technical Field

[0001] The present invention relates to a porous laminate and a flexible multilayer circuit board. Background Art

[0002] In recent years, the development of wireless communication for the so-called "fifth generation (5G)" standard has been promoted. In the case of wireless communication based on the "fifth generation (5G)" standard, it is possible to transmit a large amount of data at high speed. In the wireless communication based on the "fifth generation (5G)" standard, high frequencies including millimeter waves are used. As a substrate for a high-frequency antenna that emits such millimeter waves, a substrate with a low dielectric constant (low-dielectric substrate) is required. In addition, as an FPC (flexible printed circuit board), a high-speed transmission FPC that can transmit data at high speed is required, and for the substrate of this high-speed transmission FPC, a low-dielectric substrate is also required.

[0003] As such a low-dielectric substrate, a low-dielectric substrate having a first metal layer, a porous resin layer, an adhesive layer, and a second metal layer has been proposed (for example, refer to Patent Document 1 below). Prior Art Documents Patent Documents

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-053632 Summary of the Invention Problems to be Solved by the Invention

[0005] On the other hand, for the porous laminate used in a flexible multilayer circuit board, excellent interlayer adhesion is required. In addition, when the flexible multilayer circuit board is used in a small electronic device or the like, it is necessary to connect components to each other in a limited space, and therefore it is desirable that the porous laminate has excellent flexibility.

[0006] However, the low-dielectric substrate of Patent Document 1 has a problem of insufficient interlayer adhesion.

[0007] The present invention provides a porous laminate and a flexible multilayer circuit board having excellent adhesion and excellent flexibility. Technical Means for Solving the Problems

[0008] The present invention [1] includes a porous laminate, in which a conductor layer and an insulating layer are sequentially provided on one side in the thickness direction, and a base resin layer, a porous resin layer, and a bonding layer are sequentially provided on one side in the thickness direction of the insulating layer. The thickness of the porous resin layer is 50 μm or less, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer is 16 μm or less, and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer is greater than the maximum height (Rz) of one surface in the thickness direction of the base resin layer.

[0009] The present invention [2] includes the porous laminated body described in [1], wherein the maximum height (Rz) of one surface in the thickness direction of the base resin layer is 5 μm or less.

[0010] The present invention [3] includes the porous laminated body described in [1] or [2], wherein the maximum height (Rz) of one surface in the thickness direction of the porous resin layer exceeds 5 μm and is 10 μm or less.

[0011] The present invention [4] includes a flexible multilayer circuit board, wherein the flexible multilayer circuit board includes two porous laminated bodies described in any one of [1] to [3]. One porous laminated body and the other porous laminated body are sequentially laminated toward the other side in the thickness direction with the bonding layer of one porous laminated body facing the bonding layer of the other porous laminated body. The flexible multilayer circuit board includes a wiring portion, and the wiring portion is buried in any one of the bonding layers of the bonding layer of one porous laminated body and the bonding layer of the other porous laminated body.

[0012] The present invention [5] includes the flexible multilayer circuit board described in [4], wherein the insulating layers of one porous laminated body and the other porous laminated body have a plurality of first through holes. The first through holes penetrate between the conductor layers of one porous laminated body and the conductor layers of the other porous laminated body in the thickness direction. The flexible multilayer circuit board includes a plurality of first via connection portions, and the plurality of first via connection portions are filled in the plurality of first through holes and are in contact with the conductor layers of one porous laminated body and the conductor layers of the other porous laminated body in a manner of electrically connecting the conductor layers of one porous laminated body and the conductor layers of the other porous laminated body. The wiring portion is arranged between the plurality of first via connection portions.

[0013] The present invention [6] includes the flexible multilayer circuit board described in [5], wherein either the conductor layer of one porous laminated body or the conductor layer of the other porous laminated body has terminal portions at both ends in the long side direction. Either the insulating layer of one porous laminated body or the insulating layer of the other porous laminated body has second through holes at both ends in the long side direction. The second through holes penetrate between the terminal portions and the wiring portion in the thickness direction. The flexible multilayer circuit board includes second via connection portions, and the second via connection portions are filled in the second through holes and are in contact with the terminal portions and the wiring portion in a manner of electrically connecting the terminal portions and the wiring portion.

[0014] The present invention [7] includes the flexible multilayer circuit board described in [6], wherein the flexible multilayer circuit board further includes reinforcing substrates at both ends in the long side direction, and the reinforcing substrates are disposed on the thickness direction side of the conductor layer of the one porous laminate that does not have the terminal portion, or on the thickness direction side of the conductor layer of the other porous laminate that does not have the terminal portion. Effect of the invention

[0015] The thickness of the porous resin layer of the porous laminate of the present invention is 50 μm or less. Therefore, the stress applied to the end of the porous laminate can be alleviated, and the flexibility is excellent. In addition, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer of the porous laminate of the present invention is 16 μm or less, and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer is greater than the maximum height (Rz) of one surface in the thickness direction of the base resin layer. Therefore, the adhesion between the layers is excellent.

[0016] Since the flexible multilayer circuit board of the present invention includes the above-mentioned porous laminate, the adhesion and flexibility are excellent. Description of the drawings

[0017] Figure 1 A cross-sectional view in the width direction in one embodiment of the porous laminate of the present invention is shown. Figure 2 A cross-sectional view in the long side direction in one embodiment of the flexible multilayer circuit board of the present invention is shown. Figure 3 Shown Figure 2 A cross-sectional view taken along line A-A' in the width direction of the flexible multilayer circuit board shown. Figure 4 Shown Figure 2 A cross-sectional view taken along line B-B' in the width direction of the flexible multilayer circuit board shown. Figures 5A - 5D Shown Figure 1 The manufacturing method of the porous laminate shown. Figure 5A The process of preparing the conductor layer is shown, Figure 5B The process of forming the first coating film is shown, Figure 5C The process of forming the second coating film is shown, Figure 5D The process of forming the laminate with the flow path-containing sheet is shown. Figures 6A - 6B Following Figure 5D After that, shown Figure 1 The manufacturing method of the porous laminate shown. Figure 6A The process of forming a roll is shown, Figure 6B The process of making the second coating film porous is shown. Figures 7A - 7B Following Figure 6BAfter that, it represents Figure 1 The manufacturing method of the porous laminate shown. Figure 7A It represents the process of removing the sheet with flow paths. Figure 7B It represents the process of heating the first coating film and the second coating film. Figure 7C It represents the process of forming the bonding layer and the wiring layer. Detailed implementation mode

[0018] 1. Porous laminate Refer to Figure 1 and explain the porous laminate 1 of one embodiment of the present invention.

[0019] In Figure 1 , the up-and-down direction of the paper surface represents the thickness direction of the porous laminate 1. The left-and-right direction of the paper surface represents the width direction (short side direction) of the porous laminate 1. The depth direction of the paper surface represents the long side direction of the porous laminate 1.

[0020] The porous laminate 1 has a thickness. The porous laminate 1 extends in the plane direction orthogonal to the thickness direction. The porous laminate 1 has a substantially flat plate shape. The porous laminate 1 has flexibility.

[0021] The thickness of the porous laminate 1 is, for example, 5 μm to 2000 μm.

[0022] As Figure 1 shown, the porous laminate 1 sequentially includes a conductor layer 2 and an insulating layer 3 toward one side in the thickness direction, and preferably includes a conductor layer 2 and an insulating layer 3 disposed on one surface in the thickness direction of the conductor layer 2. In addition, the porous laminate 1 preferably further includes a wiring layer 7 disposed on one side in the thickness direction of the insulating layer 3.

[0023] <Conductor layer> As Figure 1 shown, the conductor layer 2 is the lowermost layer in the thickness direction of the porous laminate 1.

[0024] The conductor layer 2 has a thickness. The conductor layer 2 has a substantially flat plate shape.

[0025] Examples of the material of the conductor layer 2 include metals. As the metal, for example, copper, iron, silver, gold, aluminum, nickel, and their alloys (such as stainless steel and bronze) can be cited. Copper is preferably cited.

[0026] The thickness of the conductor layer 2 is, for example, 0.1 μm to 100 μm, and preferably 1 μm to 50 μm.

[0027] The thickness of the conductor layer 2 is, for example, 0.1 μm or more, preferably 1 μm or more, and in addition, for example, 100 μm or less, preferably 50 μm or less.

[0028] <Insulating layer> As Figure 1 shown, the insulating layer 3 is disposed on one side in the thickness direction of the conductor layer 2. The insulating layer 3 preferably contacts one surface of the conductor layer 2 in the thickness direction.

[0029] The insulating layer 3 sequentially includes a base resin layer 4, a porous resin layer 5, and a bonding layer 6 toward one side in the thickness direction. The insulating layer 3 preferably includes a base resin layer 4, a porous resin layer 5 disposed on one surface of the base resin layer 4 in the thickness direction, and a bonding layer 6 disposed on one surface of the porous resin layer 5 in the thickness direction.

[0030] [Base resin layer] As Figure 1 shown, the base resin layer 4 is disposed on one side in the thickness direction of the conductor layer 2 and on the other side in the thickness direction of the porous resin layer 5. That is, the base resin layer 4 is disposed between the conductor layer 2 and the porous resin layer 5. The base resin layer 4 preferably contacts one surface of the conductor layer in the thickness direction and contacts the other surface of the porous resin layer 5 in the thickness direction.

[0031] The base resin layer 4 has a thickness. The base resin layer 4 has a substantially flat plate shape. The base resin layer 4 is a layer that improves the adhesion between the porous resin layer 5 and the conductor layer 2. That is, if the base resin layer 4 is provided, the adhesion between the porous resin layer 5 and the conductor layer 2 is excellent.

[0032] As the material (or raw material) of the base resin layer 4, a resin can be cited. The resin is not particularly limited as long as it can be used as an insulating material in a wiring circuit board. As the resin, for example, polycarbonate resin, polyimide resin, fluorinated polyimide resin, epoxy resin, phenolic resin, urea resin, melamine resin, diallyl phthalate resin, silicone resin, thermosetting polyurethane resin, fluororesin, and liquid crystal polymer can be cited. Preferably, polyimide resin and liquid crystal polymer can be cited, and more preferably, polyimide resin can be cited.

[0033] From the aspect of improving the adhesion between layers, the base resin layer 4 is preferably non-porous and a solid dense film. That is, the base resin layer 4 is preferably a non-porous polyimide resin layer.

[0034] The porosity in the base resin layer 4 is, for example, 0.5% or less, preferably 0.1% or less, and more preferably 0%.

[0035] The thickness of the base resin layer 4 is, for example, 0.1 μm to 50 μm, preferably 0.5 μm to 20 μm, more preferably 1.0 μm to 10 μm, further preferably 1.5 μm to 7.0 μm, and particularly preferably 2.0 μm to 5.0 μm.

[0036] The maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.1 μm to 5.0 μm, preferably 0.5 μm to 4.0 μm, more preferably 1.0 μm to 3.5 μm, further preferably 1.5 μm to 3.2 μm, and particularly preferably 2.0 μm to 3.0 μm.

[0037] The maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.1 μm or more, preferably 0.5 μm or more, more preferably 1.0 μm or more, further preferably 1.5 μm or more, and particularly preferably 2.0 μm or more. Further, it is, for example, 5.0 μm or less, preferably 4.0 μm or less, more preferably 3.5 μm or less, further preferably 3.2 μm or less, and particularly preferably 3.0 μm or less.

[0038] If the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is within the above range, the adhesion to the porous resin layer 5 is excellent. Specifically, if the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is equal to or higher than the above lower limit value, the adhesion to the porous resin layer 5 is excellent due to the anchoring effect. Further, if the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is equal to or lower than the above upper limit value, the contact area with the porous resin layer 5 can be increased, the adhesion to the porous resin layer 5 is improved, and moreover, the unevenness of the thickness of the porous resin layer 5 can be suppressed.

[0039] It should be noted that the maximum height (Rz) represents the maximum height according to JIS B 0601 - 2001. (The same shall apply hereinafter)

[0040] The surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.10 μm to 3.0 μm, preferably 0.20 μm to 2.0 μm, more preferably 0.25 μm to 1.5 μm, further preferably 0.30 μm to 1.2 μm, particularly preferably 0.35 μm to 1.0 μm, and most preferably 0.40 μm to 0.80 μm.

[0041] The surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.10 μm or more, preferably 0.20 μm or more, more preferably 0.25 μm or more, further preferably 0.30 μm or more, particularly preferably 0.35 μm or more, and most preferably 0.40 μm or more. Additionally, for example, it is 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.5 μm or less, further preferably 1.2 μm or less, particularly preferably 1.0 μm or less, and most preferably 0.8 μm or less.

[0042] If the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is within the above range, the adhesion to the porous resin layer 5 is excellent. Specifically, if the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is equal to or greater than the above lower limit value, the adhesion to the porous resin layer 5 is excellent due to the anchoring effect. Additionally, if the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is equal to or less than the above upper limit value, the contact area with the porous resin layer 5 can be increased, the adhesion to the porous resin layer 5 is improved, and moreover, the unevenness of the thickness of the porous resin layer 5 can be suppressed.

[0043] It should be noted that the surface roughness (Ra) represents the arithmetic mean surface roughness in accordance with JIS B 0601 - 2001. (The same applies hereinafter)

[0044] In addition, the maximum height (Rz) and the surface roughness (Ra) are measured using a non - contact surface roughness measuring device. (The same applies hereinafter)

[0045] It should be noted that the maximum height (Rz) and the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) are the same as those of one surface in the thickness direction of the first coating film 104' after drying (the contact surface with the porous resin layer 5) described later. Therefore, in the present embodiment, as the maximum height (Rz) and the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5), the maximum height (Rz) and the surface roughness (Ra) of one surface in the thickness direction of the first coating film 104' after drying (the contact surface with the porous resin layer 5) are adopted. It should be noted that the first coating film 104' after drying means the state before imidization if its material is a polyimide resin. The detailed situation is described in the examples described later.

[0046] The dielectric constant of the base resin layer 4 at a frequency of 100 GHz is, for example, 1.0 to 4.5, preferably 1.0 to 4.0, more preferably 1.0 to 3.5, and still more preferably 1.0 to 3.3.

[0047] The dielectric constant of the base resin layer 4 at a frequency of 100 GHz is, for example, more than 1.0, and further, for example, 4.5 or less, preferably 4.0 or less, more preferably 3.5 or less, and still more preferably 3.3 or less.

[0048] The dielectric constant of the base resin layer 4 is actually measured by using a resonator method at a frequency of 100 GHz.

[0049] The tangent of the dielectric loss angle of the base resin layer 4 at a frequency of 100 GHz is, for example, 0 to 0.0050, preferably 0 to 0.0040, more preferably 0 to 0.0030, still more preferably 0 to 0.0025, and particularly preferably 0 to 0.0020.

[0050] The tangent of the dielectric loss angle of the base resin layer 4 at a frequency of 100 GHz is, for example, more than 0, and further, for example, 0.0050 or less, preferably 0.0040 or less, more preferably 0.0030 or less, still more preferably 0.0025 or less, and particularly preferably 0.0020 or less.

[0051] The tangent of the dielectric loss angle of the base resin layer 4 is actually measured by using a resonator method at a frequency of 100 GHz.

[0052] [Porous resin layer] The porous resin layer 5 has a thickness. The porous resin layer 5 has a substantially flat plate shape. Further, the porous resin layer 5 is a layer that reduces the dielectric constant of the porous laminate 1. That is, if the porous resin layer 5 is provided, the dielectric constant can be reduced.

[0053] As Figure 1 shown, the porous resin layer 5 is disposed on one side in the thickness direction of the base resin layer 4 and on the other side in the thickness direction of the bonding layer 6. That is, the porous resin layer 5 is disposed between the base resin layer 4 and the bonding layer 6. Specifically, the porous resin layer 5 is in contact with one surface in the thickness direction of the base resin layer 4 and is in contact with the other surface in the thickness direction of the bonding layer 6.

[0054] As the material (or raw material) of the porous resin layer 5, a resin can be cited. The resin is not particularly limited as long as it can be used as an insulating material in a wiring circuit board. Examples of the resin include polycarbonate resin, polyimide resin, fluorinated polyimide resin, epoxy resin, phenolic resin, urea-formaldehyde resin, melamine resin, diallyl phthalate resin, silicone resin, thermosetting polyurethane resin, fluororesin, and liquid crystal polymer. Polyimide resin and liquid crystal polymer are preferably cited, and polyimide resin is more preferably cited.

[0055] In order to reduce the dielectric constant, the porous resin layer 5 is porous. The porous resin layer 5 has, for example, closed cells and / or continuous cells. That is, as the porous resin layer 5, a porous polyimide resin layer is preferably used.

[0056] The porosity in the porous resin layer 5 is, for example, 50% to 100%, preferably 60% to 99%, more preferably 70% to 99%, and further preferably 80% to 99%.

[0057] The porosity in the porous resin layer 5 is, for example, 50% or more, preferably 60% or more, more preferably 70% or more, and further preferably 80% or more. In addition, for example, it is less than 100%, preferably 99% or less.

[0058] If the porosity in the porous resin layer 5 is equal to or higher than the above lower limit value, the dielectric constant can be reduced. In addition, if the porosity in the porous resin layer 5 is equal to or lower than the above upper limit value, the strength of the porous resin layer 5 can be ensured.

[0059] It should be noted that the porosity of the porous resin layer 5 is obtained by calculation based on the following formula in the case where the material of the porous resin layer 5 is a polyimide resin, that is, in the case of a porous polyimide resin layer. Dielectric constant of porous polyimide resin layer = Dielectric constant of air × Porosity + Dielectric constant of polyimide × (1 - Porosity)

[0060] Here, the dielectric constant of air is 1 and the dielectric constant of polyimide resin is 3.5. Therefore, if substituted into the above formula, it can be expressed as follows. Dielectric constant of porous polyimide resin layer = Porosity + 3.5(1 - Porosity) Porosity (%) = [(3.5 - Dielectric constant of porous polyimide resin layer) / 2.5] × 100

[0061] The thickness of the porous resin layer 5 is, for example, 1 μm to 50 μm, preferably 5 μm to 45 μm, more preferably 10 μm to 40 μm, further preferably 15 μm to 35 μm, and particularly preferably 20 μm to 30 μm.

[0062] If the thickness of the porous resin layer 5 is equal to or greater than the above lower limit value, the dielectric constant can be reduced. Further, if the thickness of the porous resin layer 5 is equal to or less than the above upper limit value, the folding resistance is excellent.

[0063] The maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is, for example, 1.0 μm to 16.0 μm, preferably 3.0 μm to 12.0 μm, more preferably 5.0 μm to 10.0 μm, still more preferably 5.5 μm to 8.5 μm, and particularly preferably 6.0 μm to 7.0 μm.

[0064] The maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is, for example, 1.0 μm or more, preferably 3.0 μm or more, more preferably 5.0 μm or more, still more preferably more than 5.0 μm, particularly preferably 5.5 μm or more, and most preferably 6.0 μm or more. Further, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is 16.0 μm or less, preferably 12.0 μm or less, more preferably 10.0 μm or less, still more preferably 8.5 μm or less, and particularly preferably 7.0 μm or less.

[0065] If the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is within the above range, the adhesiveness with the bonding layer 6 is excellent. Specifically, if the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is equal to or greater than the above lower limit value, the adhesiveness with the bonding layer 6 is excellent due to the anchoring effect. Further, if the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is equal to or less than the above upper limit value, the contact area with the bonding layer 6 can be increased, the adhesiveness with the bonding layer 6 is improved, and the thickness unevenness is small, so that the dielectric constant unevenness can be reduced.

[0066] The surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is, for example, 0.10 μm to 3.0 μm, preferably 0.20 μm to 2.0 μm, more preferably 0.25 μm to 1.5 μm, still more preferably 0.30 μm to 1.2 μm, particularly preferably 0.35 μm to 1.0 μm, and most preferably 0.38 μm to 0.70 μm.

[0067] The surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is, for example, 0.10 μm or more, preferably 0.20 μm or more, more preferably 0.25 μm or more, further preferably 0.30 μm or more, particularly preferably 0.35 μm or more, and most preferably 0.40 μm or more. Additionally, it is, for example, 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.5 μm or less, further preferably 1.2 μm or less, particularly preferably 1.0 μm or less, and most preferably 0.8 μm or less.

[0068] If the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is within the above range, the adhesion to the bonding layer 6 is excellent. Specifically, if the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is at least the above lower limit value, the adhesion to the bonding layer 6 is excellent due to the anchoring effect. Additionally, if the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is at most the above upper limit value, the contact area with the bonding layer 6 can be increased, the adhesion to the bonding layer 6 is improved, and moreover, the thickness unevenness is small, so the unevenness of the dielectric constant can be reduced.

[0069] The difference between the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) and the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) (the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) is, for example, 1.0 μm to 15.0 μm, preferably 2.0 μm to 12.0 μm, more preferably 2.5 μm to 10.0 μm, further preferably 3.0 μm to 8.0 μm, and particularly preferably 3.5 μm to 6.0 μm.

[0070] The difference (the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) is, for example, 1.0 μm or more, preferably 2.0 μm or more, more preferably 2.5 μm or more, further preferably 3.0 μm or more, particularly preferably 3.5 μm or more. Additionally, for example, it is 15.0 μm or less, preferably 12.0 μm or less, more preferably 10.0 μm or less, further preferably 8.0 μm or less, particularly preferably 6.0 μm or less.

[0071] That is, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is greater than the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5).

[0072] If the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is greater than the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5), then due to the anchoring effect, the adhesion between the porous resin layer 5 and the bonding layer 6 is excellent.

[0073] If the difference (the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) is equal to or greater than the above lower limit value, then due to the anchoring effect, the adhesion between the porous resin layer 5 and the bonding layer 6 is excellent. Additionally, if the difference (the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) is equal to or less than the above upper limit value, then the flatness of the exposed surface (one surface in the thickness direction) of the porous laminate 1 can be ensured, and moreover, the adhesion between the base resin layer 4 and the porous resin layer 5 based on the anchoring effect can be ensured.

[0074] The difference (the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) of the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) and the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, -3.0 μm to 3.0 μm, preferably -2.0 μm to 2.0 μm, more preferably -1.0 μm to 1.0 μm, further preferably -0.8 μm to 0.8 μm, particularly preferably -0.5 μm to 0.5 μm, and most preferably -0.3 μm to 0.3 μm.

[0075] The difference (the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) - the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5)) of the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) and the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is, for example, -3.0 μm or more, preferably -2.0 μm or more, more preferably -1.0 μm or more, further preferably -0.8 μm or more, particularly preferably -0.5 μm or more, and most preferably -0.3 μm or more. Additionally, it is, for example, 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.0 μm or less, further preferably 0.8 μm or less, particularly preferably 0.5 μm or less, and most preferably 0.3 μm or less.

[0076] That is, the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is substantially the same as the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6). In other words, the absolute value of the difference between the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) and the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the contact surface with the porous resin layer 5) is small.

[0077] The dielectric constant of the porous resin layer 5 at a frequency of 100 GHz is, for example, 1.0 to 3.0, preferably 1.0 to 2.5, more preferably 1.0 to 2.2, and further preferably 1.0 to 2.0.

[0078] The dielectric constant of the porous resin layer 5 at a frequency of 100 GHz is, for example, more than 1.0, and additionally, for example, 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and further preferably 2.0 or less.

[0079] The dielectric constant of the porous resin layer 5 is actually measured by the resonator method at a frequency of 100 GHz.

[0080] The tangent of the dielectric loss angle of the porous resin layer 5 at a frequency of 100 GHz is, for example, 0 to 0.0050, preferably 0 to 0.0040, more preferably 0 to 0.0030, further preferably 0 to 0.0025, and particularly preferably 0 to 0.0020.

[0081] The tangent of the dielectric loss angle of the porous resin layer 5 at a frequency of 100 GHz is, for example, more than 0, and further, for example, 0.0050 or less, preferably 0.0040 or less, more preferably 0.0030 or less, further preferably 0.0025 or less, and particularly preferably 0.0020 or less.

[0082] The tangent of the dielectric loss angle of the porous resin layer 5 is actually measured by the resonator method at a frequency of 100 GHz.

[0083] The ratio of the thickness of the base resin layer 4 to the thickness of the porous resin layer 5 is, for example, 0.01 to 0.5, preferably 0.05 to 0.3, and more preferably 0.08 to 0.2.

[0084] The ratio of the thickness of the base resin layer 4 to the thickness of the porous resin layer 5 is, for example, 0.01 or more, preferably 0.05 or more, more preferably 0.08 or more, and further, for example, 0.5 or less, preferably 0.3 or less, and more preferably 0.2 or less.

[0085] That is, the base resin layer 4 is thinner than the porous resin layer 5.

[0086] If the ratio of the thickness of the base resin layer 4 to the thickness of the porous resin layer 5 is equal to or greater than the above lower limit value, the adhesion between the porous resin layer 5 and the conductor layer 2 can be sufficiently ensured. In addition, if the ratio of the thickness of the base resin layer 4 to the thickness of the porous resin layer 5 is equal to or less than the above upper limit value, the total thickness of the porous laminate 1 can be reduced, and the dielectric constant can be decreased.

[0087] [Bonding layer] The bonding layer 6 has a thickness. The bonding layer 6 has a substantially flat plate shape. In addition, the bonding layer 6 is an adhesive layer for bonding between layers.

[0088] As Figure 1 shown, the bonding layer 6 is disposed on one side in the thickness direction of the porous resin layer 5. The bonding layer 6 can be the uppermost layer of the porous laminate 1. Specifically, the bonding layer 6 is in contact with one surface of the porous resin layer 5 in the thickness direction.

[0089] The material (or raw material) of the bonding layer 6 is not particularly limited as long as it can be used as an insulating material in a wiring circuit board. As the material of the bonding layer 6, a low dielectric material is preferably cited. As the material of the bonding layer 6, for example, a resin can be cited. As the resin, for example, an acrylic resin, a polycarbonate resin, a polyimide resin, a fluorinated polyimide resin, an epoxy resin, a phenolic resin, a urea resin, a melamine resin, a diallyl phthalate resin, a silicone resin, a thermosetting polyurethane resin, a fluororesin, and a liquid crystal polymer can be cited. A polyimide resin is preferably cited.

[0090] From the aspect of improving the adhesion between layers, the bonding layer 6 is preferably non-porous and a solid dense film. That is, the bonding layer 6 is preferably a non-porous polyimide resin layer.

[0091] The porosity in the bonding layer 6 is, for example, 0.5% or less, preferably 0.1% or less, more preferably 0%.

[0092] The dielectric constant of the bonding layer 6 at a frequency of 100 GHz is, for example, 1.0 to 3.5, preferably 1.0 to 3.2, more preferably 1.0 to 3.0, further preferably 1.0 to 2.7, and particularly preferably 1.0 to 2.5.

[0093] The dielectric constant of the bonding layer 6 at a frequency of 100 GHz is, for example, more than 1.0, and further, for example, 3.5 or less, preferably 3.2 or less, more preferably 3.0 or less, further preferably 2.7 or less, and particularly preferably 2.5 or less.

[0094] The dielectric constant of the bonding layer 6 is actually measured by using a resonator method at a frequency of 100 GHz.

[0095] The dielectric loss tangent of the bonding layer 6 at a frequency of 100 GHz is, for example, 0 to 0.005, preferably 0 to 0.004, more preferably 0 to 0.003, and further preferably 0 to 0.002.

[0096] The dielectric loss tangent of the bonding layer 6 at a frequency of 100 GHz is, for example, more than 0, and further, for example, 0.005 or less, preferably 0.004 or less, more preferably 0.003 or less, further preferably 0.002 or less, and particularly preferably less than 0.002.

[0097] The dielectric loss tangent of the bonding layer 6 is actually measured by using a resonator method at a frequency of 100 GHz.

[0098] The thickness of the bonding layer 6 is, for example, 5 μm to 200 μm, preferably 10 μm to 100 μm, more preferably 15 μm to 70 μm, further preferably 18 μm to 50 μm, and particularly preferably 20 μm to 40 μm.

[0099] <Wiring layer> The wiring layer 7 has a thickness. The wiring layer 7 has a substantially flat plate shape.

[0100] The wiring layer 7 is disposed on one side in the thickness direction of the insulating layer 3. That is, the wiring layer 7 is the uppermost layer of the porous laminate 1. Specifically, the wiring layer 7 is in contact with one surface in the thickness direction of the bonding layer 6.

[0101] Examples of the material of the wiring layer 7 include the same materials as those of the conductor layer 2.

[0102] The thickness of the wiring layer 7 is, for example, 1 μm to 100 μm, preferably 5 μm to 70 μm, more preferably 10 μm to 50 μm, still more preferably 13 μm to 30 μm, and particularly preferably 15 μm to 20 μm.

[0103] <Physical properties of the porous laminate> The peel strength of the porous laminate 1 is, for example, 0.5 N / mm or more, preferably 0.6 N / mm or more, more preferably 0.8 N / mm or more, still more preferably 1.0 N / mm or more, and particularly preferably 1.2 N / mm or more. In addition, the upper limit value of the peel strength of the porous laminate is not particularly limited.

[0104] If the peel strength of the porous laminate 1 is equal to or higher than the above lower limit value, the adhesion is excellent.

[0105] It should be noted that the peel strength of the porous laminate 1 can be measured by the method described in the following examples.

[0106] The number of bending times of the porous laminate 1 in the bending test is, for example, 50 times or more, preferably 100 times or more, more preferably 120 times or more, still more preferably 140 times or more, particularly preferably 150 times or more, and most preferably 175 times or more. In addition, the upper limit value of the number of bending times of the porous laminate 1 is not particularly limited.

[0107] If the number of bending times of the porous laminate 1 is equal to or higher than the above lower limit value, the fold resistance is excellent.

[0108] It should be noted that the number of bending times of the porous laminate 1 can be measured by the method described in the following examples.

[0109] 2. Flexible multilayer circuit board Refer to Figures 2 - 4 A flexible multilayer circuit board 10 according to an embodiment of the present invention will be described.

[0110] In Figure 2In this case, the up-down direction of the paper surface represents the thickness direction of the flexible multi-layer circuit board 10. The left-right direction of the paper surface represents the long side direction of the flexible multi-layer circuit board 10. The depth direction of the paper surface represents the width direction (short side direction) of the flexible multi-layer circuit board 10.

[0111] In Figure 3 and Figure 4 In this case, the up-down direction of the paper surface represents the thickness direction of the flexible multi-layer circuit board 10. The left-right direction of the paper surface represents the width direction (short side direction) of the flexible multi-layer circuit board 10. The depth direction of the paper surface represents the long side direction of the flexible multi-layer circuit board 10.

[0112] The flexible multi-layer circuit board 10 has a thickness. The flexible multi-layer circuit board 10 extends in a plane direction orthogonal to the thickness direction. The flexible multi-layer circuit board 10 has a substantially flat plate shape that is long in the long side direction. It should be noted that the long side direction is orthogonal to both the thickness direction and the width direction.

[0113] As Figure 2 shown, the flexible multi-layer circuit board 10 includes two of the above-mentioned porous laminates 1. One porous laminate (first porous laminate 11) and the other porous laminate (second porous laminate 12) are sequentially laminated toward the other side in the thickness direction with the bonding layer (first bonding layer 61) of the first porous laminate 11 facing the bonding layer (second bonding layer 62) of the second porous laminate 12. In addition, the flexible multi-layer circuit board 10 includes a wiring portion 70, and the wiring portion 70 is buried in either the first bonding layer 61 or the second bonding layer 62.

[0114] Specifically, the flexible multi-layer circuit board 10 sequentially laminates the first porous laminate 11 and the second porous laminate 12 toward the other side in the thickness direction with the first bonding layer 61 facing the second bonding layer 62, and includes a wiring portion 70, and the wiring portion 70 is buried in either the first bonding layer 61 or the second bonding layer 62. It should be noted that, although the details will be described later, the first bonding layer 61 and the second bonding layer 62 may be formed integrally to form a single bonding layer 60.

[0115] That is, either the first porous laminate 11 or the second porous laminate 12 has a wiring layer 7, and the other does not have a wiring layer 7. It should be noted that, although the details will be described later, by patterning the wiring layer 7, the wiring portion 70 can be obtained.

[0116] The flexible multi-layer circuit board 10 may also include a first via connection portion 81, a second via connection portion 82, a covering insulating layer 90, and a reinforcing substrate 95 as needed.

[0117] Figure 2 and Figure 3Shows a part of each cross-sectional view of the flexible multilayer circuit board 10. Specifically, the flexible multilayer circuit board 10 has a plurality of Figure 2 and Figure 3 structures shown.

[0118] <First porous laminate> The first porous laminate 11 has the same structure as the above-mentioned porous laminate 1. Specifically, as Figure 2 shown, the first porous laminate 11 sequentially includes a first conductor layer 21, a first insulating layer 31, and a wiring portion 70 (wiring layer 7) toward the other side in the thickness direction. It is preferably provided with a first conductor layer 21, a first insulating layer 31 disposed on the other surface in the thickness direction of the first conductor layer 21, and a wiring portion 70 disposed on the other surface in the thickness direction of the first insulating layer.

[0119] It should be noted that in the following description, the same structures as those of the above-mentioned porous laminate 1 are omitted.

[0120] In addition, there are cases where the first terminal portion 21b and the second terminal portion 22b described later are collectively referred to as terminal portions.

[0121] [First conductor layer] The first conductor layer 21 has a thickness. The first conductor layer 21 extends in the long side direction.

[0122] As Figure 2 shown, the first conductor layer 21 is disposed on one side in the thickness direction of the first base resin layer 41. Specifically, the first conductor layer 21 is disposed on one surface in the thickness direction of the first base resin layer 41. That is, the first conductor layer 21 is in contact with one surface in the thickness direction of the first base resin layer 41.

[0123] The first conductor layer 21 is disposed opposite to the second conductor layer 22 described later in such a manner that it overlaps with the wiring portion 70 when projected along the thickness direction. That is, the first conductor layer 21 and the second conductor layer 22 are disposed opposite to each other in such a manner that they overlap with the wiring portion 70 when projected along the thickness direction.

[0124] The first conductor layer 21 has, for example, a first ground conductor portion 21a and a first terminal portion 21b. Specifically, as Figure 2 shown, the first conductor layer 21 has a first ground conductor portion 21a and has a first terminal portion 21b at one end in the long side direction.

[0125] {First ground conductor portion} The first ground conductor portion 21a grounds the weak current that affects the first terminal portion 21b. The weak current includes, for example, a current of less than 1 A.

[0126] As Figure 2As shown, the first ground conductor portion 21a is disposed on one side in the thickness direction of the first base resin layer 41. Specifically, the first ground conductor portion 21a is disposed on one surface in the thickness direction of the first base resin layer 41. That is, the first ground conductor portion 21a is in contact with one surface in the thickness direction of the first base resin layer 41.

[0127] The first ground conductor portion 21a extends throughout the entire width direction of the flexible multilayer circuit board 10.

[0128] As Figure 4 shown, at one end in the long side direction, the center in the width direction of the first ground conductor portion 21a is cut toward the other end side in the long side direction so as to be able to dispose the first terminal portion 21b. Specifically, although not shown, at one end in the long side direction, the first ground conductor portion 21a has a plurality of the above-mentioned cuts at intervals in the width direction.

[0129] Although not shown, a ground member is connected to the first ground conductor portion 21a.

[0130] The thickness of the first ground conductor portion 21a is, for example, 1 μm to 300 μm, preferably 5 μm to 200 μm, more preferably 10 μm to 100 μm, further preferably 15 μm to 70 μm, particularly preferably 20 μm to 50 μm, and most preferably 25 μm to 35 μm.

[0131] {First terminal portion} Although not shown, the first terminal portion 21b receives and transmits signals, etc. via signal terminals. As the signal, for example, a differential signal can be cited. The signal includes, for example, a small current of less than 1 A.

[0132] As Figure 2 shown, the first terminal portion 21b is disposed on one side in the thickness direction of the first base resin layer 41. Specifically, the first terminal portion 21b is disposed on one surface in the thickness direction of the first base resin layer 41. That is, the first terminal portion 21b is in contact with one surface in the thickness direction of the first base resin layer 41.

[0133] The first terminal portion 21b is disposed, for example, at one end in the long side direction. It should be noted that the first terminal portion 21b may not be disposed at the other end in the long side direction where the second terminal portion 22b described later is disposed.

[0134] As Figure 4 shown, the first terminal portion 21b is disposed opposite to the wiring portion 70.

[0135] The first terminal portion 21b is disposed in the cutout portion of the first ground conductor portion 21a in the width direction. That is, the first terminal portion 21b is disposed at intervals in the width direction between two first ground conductor portions 21a.

[0136] In addition, although not shown, a plurality of first terminal portions 21b are arranged at intervals in the width direction. Specifically, the first ground conductor portion 21a and the first terminal portions 21b are alternately arranged at intervals in the width direction.

[0137] The thickness of the first terminal portion 21b is the same as the thickness of the first ground conductor portion 21a.

[0138] [First insulating layer] As Figure 2 shown, the first insulating layer 31 includes a first base resin layer 41, a first porous resin layer 51 disposed on the other side in the thickness direction of the first base resin layer 41, and a first bonding layer 61 disposed on the other side in the thickness direction of the first porous resin layer 51. Specifically, the first insulating layer 31 includes a first base resin layer 41, a first porous resin layer 51 disposed on the other surface in the thickness direction of the first base resin layer 41, and a first bonding layer 61 disposed on the other surface in the thickness direction of the first porous resin layer 51.

[0139] As Figure 3 and Figure 4 shown, the first insulating layer 31 and the second insulating layer 32 described later have a plurality of first through holes that penetrate between the first ground conductor portion 21a and the second ground conductor portion 22a described later in the thickness direction.

[0140] In addition, either the first insulating layer 31 or the second insulating layer 32 has a second through hole at one end in the long side direction, and either the first insulating layer 31 or the second insulating layer 32 has a second through hole at the other end in the long side direction. The second through hole penetrates between the terminal portion and the wiring portion 70 described later in the thickness direction.

[0141] {First base resin layer} The first base resin layer 41 has a thickness. The first base resin layer 41 has a substantially flat plate shape. The first base resin layer 41 is a layer that improves the adhesion between the first porous resin layer 51 and the first conductor layer 21.

[0142] As Figure 2 shown, the first base resin layer 41 is disposed on one side in the thickness direction of the first porous resin layer 51 and on the other side in the thickness direction of the first conductor layer 21. That is, the first base resin layer 41 is disposed between the first porous resin layer 51 and the first conductor layer 21. Specifically, the first base resin layer 41 contacts one surface in the thickness direction of the first porous resin layer 51 and contacts the other surface in the thickness direction of the first conductor layer 21.

[0143] {First porous resin layer} The first porous resin layer 51 has a thickness. The first porous resin layer 51 has a substantially flat plate shape. The first porous resin layer 51 is a layer that reduces the dielectric constant of the flexible multilayer circuit board 10.

[0144] As Figure 2 shown, the first porous resin layer 51 is disposed on one side in the thickness direction of the first bonding layer 61 and on the other side in the thickness direction of the first base resin layer 41. That is, the first porous resin layer 51 is disposed between the first bonding layer 61 and the first base resin layer 41. Specifically, the first porous resin layer 51 is in surface contact with one surface in the thickness direction of the first bonding layer 61 and in surface contact with the other surface in the thickness direction of the first base resin layer 41.

[0145] {The first bonding layer} The first bonding layer 61 has a thickness. The first bonding layer 61 has a substantially flat plate shape. In addition, the first bonding layer 61 is an adhesive layer for bonding between layers. Specifically, the first porous laminate 11 and the second porous laminate 12 are bonded by the first bonding layer 61 and the second bonding layer 62 described later.

[0146] As Figure 2 shown, the first bonding layer 61 is disposed on the other side in the thickness direction of the first porous resin layer 51. Specifically, the first bonding layer 61 is in surface contact with the other surface in the thickness direction of the first porous resin layer 51. In addition, the first bonding layer 61 is disposed on one side in the thickness direction of the second bonding layer 62 described later. Specifically, the first bonding layer 61 is in surface contact with one surface in the thickness direction of the second bonding layer 62.

[0147] The first bonding layer 61 has a wiring portion 70 on the other side in the thickness direction.

[0148] <Wiring portion> The wiring portion 70 is formed by patterning the above-described wiring layer 7.

[0149] The wiring portion 70 is electrically connected to the terminal portion and transmits signals from the terminal portion.

[0150] The wiring portion 70 has a thickness. The wiring portion 70 extends in the long side direction.

[0151] Although not shown, a plurality of wiring portions 70 are arranged at intervals in the width direction.

[0152] The wiring portion 70 is disposed on the other side in the thickness direction of the first bonding layer 61. Specifically, the wiring portion 70 is disposed on the other side in the thickness direction of the first bonding layer 61. In addition, the wiring portion 70 is in surface contact with the other surface in the thickness direction of the first bonding layer 61.

[0153] The wiring portion 70 is embedded in the bonding layer 60. Specifically, the wiring portion 70 is disposed between the first bonding layer 61 and the second bonding layer 62. One surface in the thickness direction of the wiring portion 70 is in contact with the first bonding layer 61. In addition, the other surface and the peripheral side surface in the thickness direction of the wiring portion 70 are covered by the second bonding layer 62. That is, the entire outer peripheral surface of the wiring portion 70 is in contact with the bonding layer 60.

[0154] Regarding the material of the wiring portion 70, a material same as that of the first conductor layer 21 can be cited.

[0155] The thickness of the wiring portion 70 may be the same as or different from the thickness of the wiring layer 7. It is preferably the same.

[0156] <Second porous laminate> The second porous laminate 12 has the same structure as the above-mentioned porous laminate 1. Specifically, as Figure 2 shown, the second porous laminate 12 sequentially includes a second conductor layer 22 and a second insulating layer 32 toward one side in the thickness direction. It preferably includes a second conductor layer 22 and a second insulating layer 32 disposed on one surface in the thickness direction of the second conductor layer 22. It should be noted that the second porous laminate 12 does not include the wiring portion 70.

[0157] It should be noted that in the following description, the same structures as those of the above-mentioned porous laminate 1 are omitted.

[0158] [Second conductor layer] The second conductor layer 22 has a thickness. The second conductor layer 22 extends in the long side direction.

[0159] As Figure 2 shown, the second conductor layer 22 is disposed on the other side in the thickness direction of the second base resin layer 42. Specifically, the second conductor layer 22 is disposed on the other surface in the thickness direction of the second base resin layer 42. That is, the second conductor layer 22 is in contact with the other surface in the thickness direction of the second base resin layer 42.

[0160] The second conductor layer 22 is disposed opposite to the first conductor layer 21 so as to overlap the wiring portion 70 when projected in the thickness direction. That is, the first conductor layer 21 and the second conductor layer 22 are disposed opposite to each other so as to overlap the wiring portion 70 when projected in the thickness direction.

[0161] The second conductor layer 22 has a second ground conductor portion 22a and may have a second terminal portion 22b as needed. It preferably has a second ground conductor portion 22a and a second terminal portion 22b. Specifically, as Figure 2 shown, the second conductor layer 22 has a second ground conductor portion 22a and has a second terminal portion 22b at the other end in the long side direction.

[0162] {Second ground conductor part} The second ground conductor part 22a grounds the weak current that affects the second terminal part 22b. The weak current includes, for example, a current of less than 1 A.

[0163] As Figure 2 shown, the second ground conductor part 22a is disposed on the other side in the thickness direction of the second base resin layer 42. Specifically, the second ground conductor part 22a is disposed on the other surface in the thickness direction of the second base resin layer 42. That is, the second ground conductor part 22a is in contact with the other surface in the thickness direction of the second base resin layer 42.

[0164] The second ground conductor part 22a extends throughout the entire width direction of the flexible multilayer circuit board 10.

[0165] Although not shown, at the other end in the long side direction, the center in the width direction of the second ground conductor part 22a is cut out toward the one end side in the long side direction so as to be able to dispose the second terminal part 22b. Specifically, at the other end in the long side direction, the second ground conductor part 22a has a plurality of the above-mentioned cutouts at intervals in the width direction.

[0166] Although not shown, a ground member is connected to the second ground conductor part 22a.

[0167] The thickness of the second ground conductor part 22a is the same as the thickness of the first ground conductor part 21a.

[0168] {Second terminal part} Although not shown, the second terminal part 22b receives and transmits signals, etc. via signal terminals. As the signal, for example, a differential signal can be cited. The signal includes, for example, a small current of less than 1 A.

[0169] As Figure 2 shown, the second terminal part 22b is disposed on the other side in the thickness direction of the second base resin layer 42. Specifically, the second terminal part 22b is disposed on the other surface in the thickness direction of the second base resin layer 42. That is, the second terminal part 22b is in contact with the other surface in the thickness direction of the second base resin layer 42.

[0170] The second terminal part 22b is disposed, for example, at the other end in the long side direction. It should be noted that the second terminal part 22b may not be disposed at the one end in the long side direction where the first terminal part 21b is disposed.

[0171] Although not shown, the second terminal part 22b is disposed opposite to the wiring part 70.

[0172] The second terminal portion 22b is disposed in the width direction at the cutout portion of the second ground conductor portion 22a. That is, the second terminal portions 22b are disposed at intervals in the width direction between the two second ground conductor portions 22a.

[0173] In addition, although not shown, a plurality of second terminal portions 22b are disposed at intervals in the width direction. Specifically, the second ground conductor portions 22a and the second terminal portions 22b are alternately disposed at intervals in the width direction.

[0174] The thickness of the second terminal portion 22b is the same as the thickness of the second ground conductor portion 22a.

[0175] [Second insulating layer] As Figure 2 shown, the second insulating layer 32 includes a second base resin layer 42, a second porous resin layer 52 disposed on one side in the thickness direction of the second base resin layer 42, and a second bonding layer 62 disposed on one side in the thickness direction of the second porous resin layer 52. Specifically, the second insulating layer 32 includes a second base resin layer 42, a second porous resin layer 52 disposed on one surface in the thickness direction of the second base resin layer 42, and a second bonding layer 62 disposed on one surface in the thickness direction of the second porous resin layer 52.

[0176] As Figure 3 and Figure 4 shown, the first insulating layer 31 and the second insulating layer 32 have a plurality of first through holes that penetrate between the first ground conductor portion 21a and the second ground conductor portion 22a in the thickness direction.

[0177] In addition, either the first insulating layer 31 or the second insulating layer 32 has second through holes at both ends in the long side direction, and the second through holes penetrate between the terminal portion and the wiring portion 70 in the thickness direction.

[0178] {Second base resin layer} The second base resin layer 42 has a thickness. The second base resin layer 42 has a substantially flat plate shape. The second base resin layer 42 is a layer that improves the adhesion between the second porous resin layer 52 and the second conductor layer 22.

[0179] As Figure 2 shown, the second base resin layer 42 is disposed on the other side in the thickness direction of the second porous resin layer 52 and on one side in the thickness direction of the second conductor layer 22. That is, the second base resin layer 42 is disposed between the second porous resin layer 52 and the second conductor layer 22. Specifically, the second base resin layer 42 contacts the other surface in the thickness direction of the second porous resin layer 52 and contacts one surface in the thickness direction of the second conductor layer 22.

[0180] {Second Porous Resin Layer} The second porous resin layer 52 has a thickness. The second porous resin layer 52 has a substantially flat plate shape. The second porous resin layer 52 is a layer that reduces the dielectric constant of the flexible multilayer circuit board 10.

[0181] As Figure 2 shown, the second porous resin layer 52 is disposed on the other side in the thickness direction of the second bonding layer 62 and on one side in the thickness direction of the second base resin layer 42. That is, the second porous resin layer 52 is disposed between the second bonding layer 62 and the second base resin layer 42. Specifically, the second porous resin layer 52 contacts the other surface in the thickness direction of the second bonding layer 62 and contacts one surface in the thickness direction of the second base resin layer 42.

[0182] {Second Bonding Layer} The second bonding layer 62 has a thickness. The second bonding layer 62 has a substantially flat plate shape. In addition, the second bonding layer 62 is an adhesive layer for interlayer bonding. Specifically, the first porous laminate 11 and the second porous laminate 12 are bonded by the first bonding layer 61 and the second bonding layer 62.

[0183] As Figure 2 shown, the second bonding layer 62 is disposed on one side in the thickness direction of the second porous resin layer 52. Specifically, the second bonding layer 62 contacts one surface in the thickness direction of the second porous resin layer 52.

[0184] The second bonding layer 62 covers the other surface and the side surface in the thickness direction of the wiring portion 70.

[0185] <Bonding Layer> The bonding layer 60 is a layer in which the first bonding layer 61 and the second bonding layer 62 are integrated. That is, the interface between the first bonding layer 61 and the second bonding layer 62 may not be observable.

[0186] It should be noted that the first bonding layer 61 is disposed on one side in the thickness direction of the second bonding layer 62. Specifically, the first bonding layer 61 contacts one surface in the thickness direction of the second bonding layer 62 except for the portion in contact with the wiring portion 70. Moreover, the first bonding layer 61 and the second bonding layer 62 form a single bonding layer 60.

[0187] That is, the bonding layer 60 buries the wiring portion 70.

[0188] The thickness of the bonding layer 60 is, for example, 1 μm to 300 μm, preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, further preferably 30 μm to 100 μm, and particularly preferably 40 μm to 80 μm.

[0189] The thickness of the above-mentioned bonding layer 60 is the total thickness including the thickness of the embedded wiring portion 70. In addition, the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 and the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 are not particularly limited and may be the same or different. Considering the manufacturing method, it is preferable that the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is different from the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70. It should be noted that the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is the distance from one surface in the thickness direction of the wiring portion 70 to one surface in the thickness direction of the bonding layer 60, and the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 is the distance from the other surface in the thickness direction of the wiring portion 70 to the other surface in the thickness direction of the bonding layer 60.

[0190] The thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is, for example, 1 μm to 100 μm, preferably 3 μm to 70 μm, more preferably 5 μm to 50 μm, further preferably 7 μm to 30 μm, and particularly preferably 8 μm to 20 μm.

[0191] The thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 is, for example, 5 μm to 200 μm, preferably 10 μm to 100 μm, more preferably 15 μm to 70 μm, further preferably 18 μm to 50 μm, and particularly preferably 20 μm to 40 μm.

[0192] The ratio of the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 to the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is, for example, 1.0 to 10, preferably 1.3 to 8.0, more preferably 1.5 to 6.0, further preferably 1.8 to 4.0, and particularly preferably 2.0 to 3.0.

[0193] That is, the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is preferably thinner than the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70.

[0194] <First via connection portion> The first via connection portion 81 is filled in a plurality of first through holes. That is, a plurality of first via connection portions 81 are provided.

[0195] A plurality of first via connection portions 81 are in contact with the first conductor layer 21 and the second conductor layer 22 in a manner of electrically connecting the first conductor layer 21 and the second conductor layer 22. Specifically, one end in the thickness direction of the plurality of first via connection portions 81 is in contact with the other surface in the thickness direction of the first ground conductor portion 21a, and the other end in the thickness direction of the plurality of first via connection portions 81 is in contact with one surface in the thickness direction of the second ground conductor portion 22a. In addition, the peripheral side surfaces of the plurality of first via connection portions 81 are in contact with the first insulating layer 31 and the second insulating layer 32. Thus, the first ground conductor portion 21a and the second ground conductor portion 22a are electrically connected via the plurality of first via connection portions 81.

[0196] In addition, as Figure 3 and Figure 4 shown, a pair of first via connection portions 81 are arranged such that the wiring portion 70 is located therebetween in the width direction.

[0197] That is, as Figure 3 shown, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portions 81 form a substantially square-shaped ground path except at both ends in the long side direction.

[0198] The first conductor layer 21 and the second conductor layer 22 are arranged opposite to each other in a manner of overlapping the wiring portion 70 when projected in the thickness direction, and a pair of first via connection portions 81 are arranged such that the wiring portion 70 is located therebetween. Therefore, dielectric loss generated at the wiring portion 70 can be suppressed.

[0199] In addition, as Figure 4 shown, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portions 81 form a substantially U-shaped ground path at one end in the long side direction. The ground path is open toward the thickness direction side when viewed in cross-section from the width direction. On the other hand, although not shown, at the other end in the long side direction, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portions 81 form a substantially inverted U-shaped ground path. In this case, the ground path is open toward the other side in the thickness direction when viewed in cross-section from the width direction.

[0200] Although not shown, a plurality of pairs of first via connection portions 81 are arranged at intervals in the long side direction. Specifically, the plurality of wiring portions 70 and the plurality of first via connection portions 81 are alternately arranged at intervals in the width direction.

[0201] Although not shown, a plurality of pairs of first via connection portions 81 are arranged at intervals in the long side direction.

[0202] The first via connection portion 81 is formed by filling a first through hole with the material of the first via connection portion 81.

[0203] Examples of the material of the first via connection portion 81 include the same material as that of the first conductor layer 21.

[0204] <Second via connection portion> The second via connection portion 82 is filled in the second through hole.

[0205] The second via connection portion 82 contacts the terminal portion and the wiring portion 70 so as to electrically connect the terminal portion and the wiring portion 70. Specifically, as Figure 2 shown, the second via connection portion 82 contacts the first terminal portion 21b and the wiring portion 70 at one end in the long side direction, and contacts the second terminal portion 22b and the wiring portion 70 at the other end in the long side direction. More specifically, at one end in the long side direction, one end in the thickness direction of the second via connection portion 82 contacts the other surface in the thickness direction of the first terminal portion 21b, and the other end in the thickness direction of the second via connection portion 82 contacts one surface in the thickness direction of the wiring portion 70. In addition, at the other end in the long side direction, the other end in the thickness direction of the second via connection portion 82 contacts one surface in the thickness direction of the second terminal portion 22b, and one end in the thickness direction of the second via connection portion 82 contacts the other surface in the thickness direction of the wiring portion 70. Moreover, the peripheral side surface of the second via connection portion 82 contacts either the first insulating layer 31 or the second insulating layer 32. Thus, either the first terminal portion 21b or the second terminal portion 22b is electrically connected to the wiring portion 70 via the second via connection portion 82.

[0206] The second via connection portions 82 are respectively arranged at both ends in the long side direction. In addition, they are not arranged except at both ends in the long side direction.

[0207] As Figure 4 shown, one second via connection portion 82 is arranged between a pair of first via connection portions 81 in the width direction.

[0208] That is, the terminal portion, the wiring portion 70, and the second via connection portion 82 respectively form a substantially I-shaped signal path at both ends in the long side direction.

[0209] In addition, although not shown, a plurality of second via connection portions 82 are arranged at intervals in the width direction. Specifically, one second via connection portion 82 is arranged corresponding to one wiring portion 70.

[0210] The second via connection portion 82 is formed by filling the second through hole with the material of the second via connection portion 82.

[0211] Examples of the material of the second via connection portion 82 include the same material as that of the first conductor layer 21.

[0212] <Covering insulating layer> The covering insulating layer 90 is a layer for protecting the surface of the flexible multilayer circuit substrate 10.

[0213] As Figure 2 shown, the covering insulating layer 90 is disposed on one side in the thickness direction of the first conductor layer 21 and on the other side in the thickness direction of the second conductor layer 22, respectively. That is, the covering insulating layer has a first covering insulating layer 91 disposed on one side in the thickness direction of the first conductor layer 21 and a second covering insulating layer 92 disposed on the other side in the thickness direction of the second conductor layer 22.

[0214] The first covering insulating layer 91 is in contact with one surface of the first conductor layer 21 in the thickness direction. In addition, the second covering insulating layer 92 is in contact with the other surface of the second conductor layer 22 in the thickness direction.

[0215] It should be noted that at least a part of the terminal portion is exposed from the covering insulating layer 90. That is, the covering insulating layer 90 covers at least the first conductor layer 21 and the second conductor layer 22 except for the terminal portion.

[0216] As the material of the covering insulating layer 90, for example, the same resin as the material of the first porous resin layer 51 can be cited.

[0217] The thickness of the covering insulating layer 90 is, for example, 1 μm to 100 μm, preferably 3 μm to 70 μm, more preferably 5 μm to 50 μm, further preferably 7 μm to 40 μm, and particularly preferably 9 μm to 30 μm.

[0218] <Reinforcing substrate> The reinforcing substrate 95 is a substrate for reinforcing the flexible multilayer circuit substrate 10. The reinforcing substrate 95 has a flat plate shape. The reinforcing substrates 95 are disposed at both ends in the long side direction, respectively.

[0219] By providing the reinforcing substrate 95, breakage of the flexible multilayer circuit substrate 10 can be suppressed at the terminal portion.

[0220] The reinforcing substrate 95 is disposed on one side in the thickness direction of the first conductor layer 21 that does not have the first terminal portion 21b or on the other side in the thickness direction of the second conductor layer 22 that does not have the second terminal portion 22b at both ends in the long side direction, respectively. Specifically, as Figure 2 shown, the reinforcing substrate 95 has a first reinforcing substrate 96 disposed on one side in the thickness direction of the first covering insulating layer 91 at the other end in the long side direction and a second reinforcing substrate 97 disposed on the other side in the thickness direction of the second covering insulating layer 92 at one end in the long side direction.

[0221] The first reinforcing substrate 96 is in contact with one surface of the first covering insulating layer 91 in the thickness direction at the other end in the long side direction. In addition, the second reinforcing substrate 97 is in contact with the other surface of the second covering insulating layer 92 in the thickness direction at one end in the long side direction.

[0222] The material of the reinforcing substrate 95 is not particularly limited. As the material of the reinforcing substrate 95, for example, metals and hard resins can be cited. Preferably, metals can be cited. As the metal, for example, stainless steel, copper, iron, and aluminum can be cited.

[0223] The thickness of the reinforcing substrate 95 is not particularly limited.

[0224] <Adhesive layer> Although not shown, the flexible multilayer circuit board 10 may also have an adhesive layer between the above-mentioned layers. Specifically, an adhesive layer may also be provided between the first conductor layer 21 and the first covering insulating layer 91, between the second conductor layer 22 and the second covering insulating layer 92, between the first covering insulating layer 91 and the first reinforcing substrate 96, and between the second covering insulating layer 92 and the second reinforcing substrate 97.

[0225] The material (or raw material) of the adhesive layer is not particularly limited as long as it is a material of an adhesive layer that can be generally used in a wiring circuit board. As the material (or raw material) of the adhesive layer, for example, resins can be cited.

[0226] The thickness of the adhesive layer is not particularly limited.

[0227] 3. Manufacturing method of the porous laminate With reference to FIGS. 5 to 7, the manufacturing method of the porous laminate 100 will be described.

[0228] (Conductor layer preparation process) First, as Figure 5A shown, a conductor layer 102 is prepared.

[0229] (First coating film formation process) As Figure 5B shown, a first coating film 104' is formed on one surface in the thickness direction of the conductor layer 102. Specifically, a varnish containing a resin (for example, a polyimide resin) that is a material of the above-mentioned base resin layer, a porogen, a nucleating agent, and a solvent is prepared, and the varnish is coated on one surface in the thickness direction of the conductor layer 102 to form the first coating film 104'.

[0230] In the above-mentioned porogen, nucleating agent, and solvent, their types and mixing ratios are described in, for example, WO2018 / 186486.

[0231] Hereinafter, the case where the resin is a polyimide resin will be specifically described.

[0232] The precursor of the polyimide resin is, for example, a reaction product of a diamine component and an acid dianhydride component.

[0233] As the diamine component, for example, aromatic diamines and aliphatic diamines can be cited. Aromatic diamines are preferably cited.

[0234] As the aromatic diamine, for example, a first diamine, a second diamine, and a third diamine can be cited.

[0235] The first diamine contains a single aromatic ring. As the first diamine, for example, phenylenediamine, dimethylphenylenediamine, and ethylmethylphenylenediamine can be cited. Phenylenediamine is preferably cited. As phenylenediamine, for example, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine can be cited. As phenylenediamine, p-phenylenediamine is preferably cited. p-Phenylenediamine is sometimes abbreviated as PDA.

[0236] The second diamine contains multiple aromatic rings and an ether bond disposed between them. As the second diamine, for example, diphenylamine oxide can be cited. As diphenylamine oxide, for example, 3,4'-diphenylamine oxide and 4,4'-diphenylamine oxide can be cited. 4,4'-diphenylamine oxide (alias: 4,4-diaminodiphenyl ether) is preferably cited. 4,4'-diphenylamine oxide is sometimes abbreviated as ODA.

[0237] The third diamine contains multiple aromatic rings and an ester bond disposed between them. As the third diamine, for example, p-aminophenyl p-aminobenzoate can be cited. 4-aminobenzoic acid-4-aminophenyl ester is preferably cited. 4-aminobenzoic acid-4-aminophenyl ester is sometimes abbreviated as APAB.

[0238] It should be noted that as the aromatic diamine, in addition to the first diamine to the third diamine, for example, 4,4'-methylenedianiline, 4,4'-dimethylene dianiline, 4,4'-trimethylene dianiline, and bis(4-aminophenyl) sulfone can also be cited.

[0239] The diamine component can be used alone or in combination of two or more. As the diamine component, a combination of the first diamine, the second diamine, and the third diamine is preferably cited. A combination of p-phenylenediamine (PDA), 4,4'-diphenylamine oxide (ODA), and 4-aminobenzoic acid-4-aminophenyl ester (APAB) is more preferably cited.

[0240] The molar fraction of the first diamine in the diamine component is, for example, 10 mol% to 70 mol%, preferably 20 mol% to 65 mol%. The molar fraction of the second diamine in the diamine component is, for example, 5 mol% to 40 mol%, preferably 10 mol% to 30 mol%. The molar fraction of the third diamine in the diamine component is, for example, 5 mol% to 40 mol%, preferably 10 mol% to 30 mol%.

[0241] In addition, with respect to a total of 100 mol parts of the first diamine and the second diamine, the mol part of the third diamine is, for example, 5 mol parts to 100 mol parts, preferably 10 mol parts to 50 mol parts, and more preferably 20 mol parts to 30 mol parts.

[0242] The acid dianhydride component is not particularly limited. The acid dianhydride component contains, for example, an acid dianhydride containing an aromatic ring. As the acid dianhydride containing an aromatic ring, an aromatic tetracarboxylic dianhydride can be cited, for example.

[0243] As the aromatic tetracarboxylic dianhydride, examples include pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, biphenyl sulfone tetracarboxylic dianhydride, and naphthalene tetracarboxylic dianhydride. They can be used alone or in combination. As the acid dianhydride containing an aromatic ring, biphenyl tetracarboxylic dianhydride is preferably cited. As biphenyl tetracarboxylic dianhydride, examples include 3,3'-4,4'-biphenyl tetracarboxylic dianhydride, 2,2'-3,3'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, and 3,3',4,4'-diphenylether tetracarboxylic dianhydride. As biphenyl tetracarboxylic dianhydride, 3,3'-4,4'-biphenyl tetracarboxylic dianhydride is preferably cited. It should be noted that 3,3'-4,4'-biphenyl tetracarboxylic dianhydride is sometimes abbreviated as BPDA.

[0244] The acid dianhydride component can be used alone or two or more kinds can be used in combination.

[0245] The ratio of the diamine component to the acid dianhydride component is adjusted so that the molar amount of the amino group (-NH 2 ) of the diamine component and the molar amount of the acid anhydride group (-CO-O-CO-) of the acid dianhydride component become, for example, equimolar amounts.

[0246] To prepare a precursor of the polyimide resin, the above diamine component, the above acid dianhydride component, and a solvent are mixed to prepare a solution, and the prepared solution is heated to prepare a precursor solution. Then, a nucleating agent and a porogen are mixed in the precursor solution to prepare a varnish. The concentration (solid content concentration) of the polyimide precursor in the varnish in the first coating film 104' is, for example, 5% by mass to 40% by mass, preferably 10% by mass to 25% by mass.

[0247] Then, the varnish is coated on one surface in the thickness direction of the conductor layer 102 to form the first coating film 104'.

[0248] Then, the first coating film 104' is dried by heating. By heating, the solvent is removed. The heating temperature is, for example, 130°C to 300°C. The heating time is, for example, 15 seconds to 30 minutes.

[0249] If the above heating is insufficient, there is a case where the first coating film 104' is integrated with the second coating film 105' formed below, and the base resin layer 104 described later cannot be formed.

[0250] (Second coating film forming step) As Figure 5C shown, a second coating film 105' is formed on one surface in the thickness direction of the first coating film 104'. Specifically, a varnish containing a precursor of a resin (such as a polyimide resin) as the material of the above-mentioned porous resin layer, a porogen, a nucleating agent, and a solvent is prepared, and the varnish is coated on one surface in the thickness direction of the first coating film 104' to form the second coating film 105'. It should be noted that as the varnish for forming the second coating film 105', it is preferably the same as the varnish for forming the above-mentioned first coating film 104' except for the solid content concentration. The concentration (solid content concentration) of the polyimide precursor in the varnish is, for example, 10% by mass to 95% by mass, preferably 40% by mass to 75% by mass.

[0251] The varnish is coated on one surface in the thickness direction of the first coating film 104' to form the second coating film 105', and it is dried by heating. By heating, the solvent is removed. The heating temperature is, for example, 130°C to 300°C. The heating time is, for example, 10 minutes to 30 minutes. In addition, the above heating can also be carried out in multiple times.

[0252] Through the above, a precursor laminate 108 having a conductor layer 102, a first coating film 104', and a second coating film 105' in this order toward one side in the thickness direction can be obtained.

[0253] (Laminated body forming step of the flow path-containing sheet) As Figure 5D shown, a flow path-containing sheet 110 is disposed on one surface in the thickness direction of the second coating film 105' to form a precursor laminated body 111 of the flow path-containing sheet.

[0254] The flow path-containing sheet 110 has a given thickness and has a long and narrow substantially flat plate shape.

[0255] Specifically, the flow path-containing sheet 110 is formed of, for example, fibers and / or a screen. The fibers are a mesh-like sheet that is not fused or woven. In contrast, the screen is a mesh-like sheet that is fused or woven. Thus, voids (gaps) separated by the fibers and / or the screen are present in the flow path-containing sheet 110. That is, the flow path-containing sheet 110 is also a void-containing sheet. Moreover, the voids form flow paths for supercritical fluids flowing in the flow path-containing sheet 110. The flow path-containing sheet 110 is preferably formed of fibers.

[0256] It should be noted that the presence or absence of fibers and the presence or absence of weaving in the flow path-containing sheet 110 can be confirmed by optical microscope observation.

[0257] The material of the flow path-containing sheet 110 is not particularly limited as long as it is substantially insoluble in the supercritical fluid. Examples of the material of the flow path-containing sheet 110 include organic materials, inorganic materials, and their composite materials. Examples of organic materials include cellulose, polyesters (such as PET and PBT), polyolefins (such as polyethylene and polypropylene), polyacetals, polyamides, polycarbonates, polyimides, polyether ether ketones, polyether sulfones, and polyphenylene ethers. Examples of inorganic materials include metals such as copper, iron, aluminum, and stainless steel. As the material of the flow path-containing sheet 110, organic materials are preferably used, and cellulose is more preferably used from the viewpoint of reducing the dissolution amount of supercritical carbon dioxide in the flow path-containing sheet 110.

[0258] The flow path-containing sheet 110 may be a single layer or a multi-layer. In addition, when the flow path-containing sheet 110 is a multi-layer, each layer may be formed of a different material.

[0259] The thickness of the flow path-containing sheet 110 is, for example, 10 μm to 800 μm, preferably 20 μm to 400 μm, and more preferably 100 μm to 200 μm.

[0260] If the thickness of the flow path-containing sheet 110 is equal to or greater than the above lower limit value, a sufficient amount of supercritical fluid can flow smoothly in the flow path-containing sheet 110. If the thickness of the flow path-containing sheet 110 is equal to or less than the above upper limit value, the thickness of the flow path-containing sheet 110 per unit thickness of the roll body 112 can be reduced. Therefore, the production efficiency of the roll body 112 can be improved.

[0261] The shape of the voids is not particularly limited, but has a shape that is continuous at least in the long side direction and the thickness direction.

[0262] When the flow path-containing sheet 110 has continuous pores, the average pore diameter of each pore is, for example, 1 μm to 50 μm, preferably 1 μm to 30 μm, and more preferably 2 μm to 20 μm.

[0263] The pore diameter of the flow path-containing sheet 110 may be uniform or different in the thickness direction. The pore diameter of the flow path-containing sheet 110 may be, for example, a form in which the pore diameter increases from one side to the other side in the thickness direction, the opposite form, or a form in which the size changes irregularly or regularly. The change in the pore diameter of the flow path-containing sheet 110 (the change in the pore diameter from one side to the other side in the thickness direction) may change continuously, discontinuously, or a combination of them.

[0264] The porosity of the flow path-containing sheet 110 is, for example, 30% or more, preferably 35% or more, more preferably 40% or more, and, for example, less than 100%.

[0265] The shape of the voids in the flow channel-containing sheet 110 is not particularly limited, and may be an amorphous shape, a linear shape, a curved shape, a void shape when fibers are entangled, a flat plate shape, an ellipsoid shape, a spherical shape, or the like.

[0266] From the viewpoint of protecting the surface of the precursor laminate 108 , the surface roughness Ra of the flow path-containing sheet 110 is, for example, 0.01 μm to 5 μm, preferably 0.05 μm to 3 μm, and more preferably 0.1 μm to 2 μm.

[0267] The solubility S of carbon dioxide in the flow channel-containing sheet 110 (temperature: 200° C., pressure: 30 MPa) is, for example, 0.3 or less, preferably 0.2 or less, and more preferably 0.1 or less. The lower limit of the solubility S of carbon dioxide is not particularly limited.

[0268] If the solubility S of carbon dioxide in the flow path-containing sheet 110 is below the upper limit, the amount of carbon dioxide in a supercritical state (supercritical carbon dioxide) dissolved in the flow path-containing sheet 110 is small, and it can be fully circulated in the flow path-containing sheet 110. Therefore, the pore-forming agent in the sheet of the porous body precursor can be extracted more efficiently.

[0269] The solubility S of carbon dioxide in the flow path-containing sheet 110 can be determined by the following method: after the flow path-containing sheet 110 is fully dried, a molding machine (for example, a desktop molding press (Japanese: tabletop molding press) manufactured by Imoto Manufacturing Co., Ltd.) is used to pressurize and release the pressurization at a given temperature (for example, 180°C to 280°C) to prepare a test piece without bubbles (for example, 20 mmφ, 1 mm to 3 mm in thickness), and a magnetic levitation balance measuring device (BELP / O152 manufactured by RUBOTHERM Co., Ltd.) is used to measure the mass change when carbon dioxide is contained in the sample in a carbon dioxide atmosphere at a temperature of 200°C and a pressure of 30 MPa, thereby determining the solubility S of carbon dioxide.

[0270] The channel-containing sheet 110 may be a commercially available product. For example, the Bemliese series (manufactured by Asahi Kasei Corporation) may be used as the channel-containing sheet 110 containing fibers. Also, for example, the mesh #2500 series (manufactured by KBSEIREN) may be used as the channel-containing sheet 110 containing a mesh.

[0271] (Roll Forming Process) like Figure 6AAs shown, the precursor laminate 111 with the flow path-containing sheet is wound to form a roll body 112. Specifically, one end in the long side direction of the precursor laminate 111 with the flow path-containing sheet is fixed to the surface of the core 150, and then the middle and the other end in the long side direction of the precursor laminate 111 with the flow path-containing sheet are wound around the core 150. The core 150 is a winding core and has a substantially cylindrical or substantially columnar shape.

[0272] For example, the precursor laminate 111 with the flow path-containing sheet is wound around the core 150 such that one end in the long side direction of the conductor layer 102 contacts the surface of the core 150.

[0273] Thereby, a layer structure in which the conductor layer 102, the first coating film 104', the second coating film 105', and the flow path-containing sheet 110 are repeatedly arranged is formed on the radially outer side of the core 150. That is, a roll body 112 is produced, and the roll body 112 has the core 150, and the conductor layer 102, the first coating film 104', the second coating film 105', and the flow path-containing sheet 110 that are repeatedly arranged toward the radially outer side of the core 150.

[0274] The outer diameter of the roll body 112 is a value obtained by adding twice the total thickness of the conductor layer 102, the first coating film 104', the second coating film 105', and the flow path-containing sheet 110 to the outer diameter of the core 150. In addition, the outer diameter of the roll body 112 is substantially the same as the inner diameter of the extraction tank 161 of the supercritical fluid extraction device 160 described later.

[0275] As the tension when winding the precursor laminate 111 with the flow path-containing sheet around the core 150, for example, it is 10 N to 85 N, preferably 15 N to 80 N, more preferably 20 N to 60 N, further preferably 25 N to 50 N, and particularly preferably 30 N to 40 N.

[0276] As the tension when winding the precursor laminate 111 with the flow path-containing sheet around the core 150, for example, it is 10 N or more, preferably 15 N or more, more preferably 20 N or more, further preferably 25 N or more, and particularly preferably 30 N or more. In addition, for example, it is less than 90 N, preferably 85 N or less, more preferably 80 N or less, further preferably 60 N or less, particularly preferably 50 N or less, and most preferably 40 N or less.

[0277] If the tension when winding the precursor laminate 111 with the flow path-containing sheet around the core 150 is below the above upper limit value (less than the above upper limit value), the surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 105 (the contact surface with the bonding layer 106) can be reduced, and further, the interlayer adhesion can be improved.

[0278] (Porous chemical process) As Figure 6BAs shown in the figure, the second coating film 105' is made porous by using a supercritical fluid extraction device 160. Specifically, the roll body 112 is placed in the supercritical fluid extraction device 160, and then the supercritical fluid is circulated through the roll body 112, whereby the pore-forming agent is extracted from the second coating film 105' to make it porous.

[0279] Examples of the supercritical fluid include supercritical carbon dioxide, supercritical nitrogen, etc., and supercritical carbon dioxide is preferably cited.

[0280] As Figure 6B shown in the figure, the supercritical fluid extraction device 160 includes, for example, an extraction tank 161. The roll body 112 is introduced into the extraction tank 161 of the supercritical fluid extraction device 160.

[0281] It should be noted that various commercially available supercritical extraction devices (for example, manufactured by Mitsubishi Chemical Corporation, ITECH Corporation, Toyo Koatsu Co., Ltd., Shinko AirTech Co., Ltd.) can be used as the supercritical fluid extraction device 160.

[0282] After the roll body 112 is introduced, the supercritical fluid extraction device 160 is driven. Specifically, the supercritical fluid flows into the extraction tank 161 and then circulates in the flow path-containing sheet 110. In the flow path-containing sheet 110, the supercritical fluid advances upward along the axial direction of the core 150 while contacting the second coating film 105' to extract the pore-forming agent in the second coating film 105'.

[0283] Thus, the pore-forming agent in the second coating film 105' is extracted by the supercritical fluid via the flow path-containing sheet 110. That is, the pore-forming agent is removed from the second coating film 105' to make it porous.

[0284] The extraction rate of the pore-forming agent is the ratio ([M1 - M2] / M1) of the value (M1 - M2) obtained by subtracting the mass (M2) of the pore-forming agent remaining in the second coating film 105' from the mass (M1) of the pore-forming agent contained in the second coating film 105', for example, 35% to 90%, preferably 45% to 90%, and more preferably 50% to 90%.

[0285] Thus, in the roll body 112, a porous roll body in which the second coating film 105' is made porous can be obtained.

[0286] (Flow path-containing sheet removal process) As Figure 7A shown in the figure, the flow path-containing sheet 110 is removed from the precursor laminate 111 with the flow path-containing sheet in which the second coating film 105' is made porous. Specifically, the precursor laminate 111 with the flow path-containing sheet in which the second coating film 105' is made porous is sent out from the porous roll body, and the flow path-containing sheet 110 is removed.

[0287] Thus, the porous precursor laminate 109 can be obtained.

[0288] (Heating step) As Figure 7B shown, the porous precursor laminate 109 is heated. Specifically, when the first coating film 104' and the second coating film 105' contain a precursor of a polyimide resin, by heating the porous precursor laminate 109, the first coating film 104' and the second coating film 105' are imidized thereby.

[0289] The heating temperature is, for example, 340°C to 420°C. The heating time is, for example, 120 minutes to 400 minutes.

[0290] Thus, the first coating film 104' and the second coating film 105' are imidized respectively, and the base resin layer 104 and the porous resin layer 105 are formed.

[0291] (Bonding layer and wiring layer formation step) As Figure 7C shown, the bonding layer 106 and the wiring layer 107 are formed.

[0292] Specifically, a resin composition containing a resin as the material of the above bonding layer is coated on one surface in the thickness direction of the porous resin layer 105. Then, the wiring layer 107 is disposed on one surface in the thickness direction of the bonding layer 106.

[0293] Through the above steps, the porous laminate 100 can be manufactured.

[0294] (Function and effect) The thickness of the porous resin layer 5 of the porous laminate 1 of the present invention is 50 μm or less. Therefore, the flexibility is excellent. In addition, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 of the porous laminate 1 of the present invention is 16 μm or less, and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 is greater than the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4. Therefore, the adhesion between the layers is excellent. Since the flexible multi-layer circuit board 10 of the present invention includes the porous laminate 1, the adhesion is excellent and the flexibility is excellent.

[0295] 4. Modification examples In the following modification examples, the same reference numerals are given to the same components and steps as those in the above-described embodiment, and the detailed description thereof is omitted. In addition, each modification example can achieve the same function and effect as the embodiment unless otherwise specified. Moreover, the embodiment and the modification examples can be appropriately combined.

[0296] (Modification example of flexible multi-layer circuit board) In Figure 2 In the flexible multilayer circuit board 10 shown, at one end in the long side direction, the first conductor layer 21 has a first terminal portion 21b, and the second conductor layer 22 has a second terminal portion 22b. At the other end in the long side direction, the first conductor layer 21 does not have the first terminal portion 21b, and the second conductor layer 22 has the second terminal portion 22b. However, it is not limited thereto.

[0297] That is, as long as either the first conductor layer 21 or the second conductor layer 22 has a terminal portion at one end in the long side direction, and either the first conductor layer 21 or the second conductor layer 22 has a terminal portion at the other end in the long side direction. Specifically, although not shown, the first conductor layer 21 may have first terminal portions 21b at both ends in the long side direction, and the second conductor layer 22 may not have second terminal portions 22b at both ends in the long side direction. In addition, the first conductor layer 21 may not have first terminal portions 21b at both ends in the long side direction, and the second conductor layer 22 may have second terminal portions 22b at both ends in the long side direction. Moreover, the first conductor layer 21 may not have the first terminal portion 21b at one end in the long side direction, the second conductor layer 22 may have the second terminal portion 22b at one end in the long side direction, the first conductor layer 21 may have the first terminal portion 21b at the other end in the long side direction, and the second conductor layer 22 may not have the second terminal portion 22b at the other end in the long side direction.

[0298] In the flexible multilayer circuit board 10, the position of the terminal portion can be selected according to the electronic device to which it is applied.

[0299] In addition, the second via connection portion 82 changes its configuration in order to electrically connect the terminal portion and the wiring portion 70 according to the configuration of the above-mentioned first terminal portion 21b and second terminal portion 22b. Moreover, regarding the reinforcing base material 95, its configuration is also changed according to the configuration of the above-mentioned first terminal portion 21b and second terminal portion 22b. [Embodiment]

[0300] Examples and comparative examples are shown below to further specifically illustrate the present invention. It should be noted that the present invention is not limited to any examples and comparative examples. In addition, the specific numerical values such as the mixing ratio (including ratio), physical property values, parameters, etc. used in the following description can replace the upper limit (defined as "below", "less than" values) or lower limit (defined as "above", "exceeding" values) of the corresponding mixing ratio (including ratio), physical property values, parameters, etc. described in the above-mentioned "Detailed Description".

[0301] Example 1 First, a conductor layer 102 with a thickness of 30 μm containing copper is prepared.

[0302] Next, prepare the polyimide precursor solution in the following order.

[0303] Dissolve 0.66 moles of p-phenylenediamine (PDA) (the first diamine), 0.22 moles of 4,4'-oxydianiline (ODA) (the second diamine), and 0.22 moles of 4-aminophenyl 4-aminobenzoate (APAB) (the third diamine) using N-methyl-2-pyrrolidone (NMP) to prepare a diamine component solution. Next, add 1.00 mole of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) to the diamine component solution and stir at 80°C. Stop stirring and allow it to cool naturally to prepare a polyimide precursor solution. The solid component concentration of the polyimide precursor solution is 13% by mass.

[0304] Furthermore, relative to 100 parts by mass of the polyimide precursor solution, add 150 parts by mass of polyoxyethylene dimethyl ether with a weight average molecular weight of 400 (grade: MM400, manufactured by NOF Corporation) as a porogen, and 3 parts by mass of PTFE powder with a particle size of 1 μm or less as a nucleating agent, and stir them to obtain a transparent and uniform solution. Add 4 parts by mass of 2-methylimidazole as an imidization catalyst to the obtained solution to prepare a varnish.

[0305] Coat one surface in the thickness direction of the conductor layer 102 with the prepared varnish, and heat it to dry to form the first coating film 104'. It should be noted that the first coating film is dried by heating at 140°C for 50 seconds, thereby removing NMP. Thus, a first coating film 104' with a thickness of about 3 μm is formed on one surface in the thickness direction of the conductor layer 102.

[0306] Furthermore, in the same polyimide precursor solution, prepare a polyimide precursor solution with a solid component concentration of 50% by mass. After preparation, coat one surface in the thickness direction of the first coating film 104' with the varnish obtained by adding the porogen, nucleating agent, and imidization solvent in the same manner as above, and heat it to dry to form the second coating film 105'. It should be noted that the second coating film is dried by heating at 150°C for 20 minutes, thereby removing NMP. Thus, a second coating film 105' with a thickness of about 25 μm is formed on one surface in the thickness direction of the first coating film 104'.

[0307] Next, as the flow path-containing sheet 110, prepare TA30B (thickness: 0.26 mm, manufactured by Asahi Kasei Corporation). Bring the flow path-containing sheet 110 into contact with one surface in the thickness direction of the second coating film 105' to prepare a precursor laminate 111 with a flow path-containing sheet, which sequentially includes a conductor layer 102, a first coating film 104', a second coating film 105', and a flow path-containing sheet 110 in the thickness direction.

[0308] The prepared precursor laminate 111 with the flow path-containing sheet was wound around a core 150 with an outer diameter of 85 mm in such a manner that the flow path-containing sheet 110 was on the inside, and a roll body 112 with an outer diameter of 170 mm was produced. It should be noted that the tension during winding around the core 150 was 35 N.

[0309] Next, the produced roll body 112 was inserted into the extraction tank 161 of the supercritical fluid extraction device 160. The inner diameter of the extraction tank 161 of the supercritical fluid extraction device 160 was 170 mm. Then, the temperature was set to 40°C, and carbon dioxide (supercritical carbon dioxide) pressurized to 30 MPa was allowed to flow at a flow rate of 30 kg / h for 8 hours, thereby extracting and removing the porogen and promoting the phase separation and pore formation of the remaining NMP.

[0310] Then, after decompressing carbon dioxide for 5 hours and opening it to the atmosphere, the roll body 112 was recovered. Here, after the carbon dioxide circulating in the extraction tank 161 came out of the extraction tank, it was decompressed to 4.5 MPa at once and became a gas state, thereby separating from the porogen. The separated porogen was accumulated in the porogen accumulation part. Thus, a porous roll body with the second coating film 105' being porous was obtained.

[0311] Next, the porous precursor laminate 109 with the second coating film 105' being porous was sent out from the porous roll body, and the flow path-containing sheet 110 was removed. After removal, it was heated with a heating device at 380°C for 2 hours to imidize the first coating film 104' and the second coating film 105'. Thereby, a base resin layer 104 (non-porous polyimide layer) with a thickness of 3 μm and a porous resin layer 105 (porous polyimide layer) with a thickness of 25 μm were formed.

[0312] Next, a bonding layer 106 with a thickness of 25 μm containing an acrylic adhesive was formed on one surface in the thickness direction of the porous resin layer 105.

[0313] Next, a wiring layer 107 with a thickness of 18 μm containing copper was bonded to one surface in the thickness direction of the bonding layer 106.

[0314] Through the above method, as Figure 1 shown, a porous laminate 100 was manufactured, and the porous laminate 100 sequentially included a conductor layer 102, a base resin layer 104, a porous resin layer 105, a bonding layer 106, and a wiring layer 107 on one side in the thickness direction.

[0315] Examples 2 and 3 and Comparative Examples 1 and 2 As described in Table 1, the porous laminate 100 of Example 2, Example 3, and Comparative Example 1 and 2 was manufactured in the same manner as in Example 1, except for changing the tension when winding around the core 150.

[0316] Comparative Example 3 The porous laminate 100 of Comparative Example 3 was manufactured in the same manner as in Example 1, except that the thickness of the porous resin layer 105 was changed to 80 μm.

[0317] <Evaluation> [Surface roughness - maximum height] In the porous laminate 100 of each example and each comparative example, using a digital microscope (manufactured by KEYENCE Corporation), the surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 105 before bonding the bonding layer 106 were measured. The results are shown in Table 1. In addition, in the porous laminate 100 of each example and each comparative example, the surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the first coating film 104' before forming the second coating film 105' were measured. The surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the first coating film 104' were regarded as the surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the base resin layer 104, and the results are shown in Table 1.

[0318] [Peel strength] The porous laminate 100 of each example and each comparative example was cut into a length of 5 cm × a width of 1 mm to produce a sample for measuring the peel strength. Then, in accordance with JIS C6471, the peel strength (Peel strength) was measured when the wiring layer 107 was continuously peeled from the end in the long side direction of each produced sample for measuring the peel strength at a 90° angle to the peeling surface. It should be noted that the peeling speed was set to 50 mm / min. Evaluation was carried out according to the criteria shown below. The results are shown in Table 1. [Criteria] A: The peel strength is 1.2 N / mm or more B: The peel strength is 0.8 N / mm or more and less than 1.2 N / mm C: The peel strength is 0.5 N / mm or more and less than 0.8 N / mm D: The peel strength is less than 0.5 N / mm

[0319] [Flex resistance] The porous laminate 100 of each example and each comparative example was cut into a length of 100 mm × a width of 10 mm to produce a sample for the MIT test. It should be noted that the fold resistance in the MD direction and the TD direction of each porous laminate 100 was evaluated. Therefore, for the samples of each example and each comparative example, samples with the MD direction corresponding to the length direction and samples with the TD direction corresponding to the length direction were respectively produced. For the produced samples, a bending test was carried out in accordance with JIS C 6471 using an MIT testing machine (trade name: BE-204, manufactured by TESTER SANGYO Co., Ltd.). In the bending test, a load was applied in such a way as to apply a tensile force of 4.9 N to the sample. In addition, in both directions, the bending was carried out at a bending angle of 135° (since it is in two directions, it is -135° to +135°) and at a speed of approximately 175 times / min. The number of times until the sample broke was measured, and the averaged value was taken as the number of fold resistance times. The evaluation was carried out according to the criteria shown below. The results are shown in Table 1. {Criteria} A: 150 times or more in both the MD direction and the TD direction B: 50 times or more and less than 150 times in both the MD direction and the TD direction C: Less than 50 times in any one of the MD direction and the TD direction

[0320] [Table 1]

[0321] It should be noted that the above invention is provided as an illustrative embodiment of the present invention, but this is merely illustrative and should not be construed in a limiting sense. Modification examples of the present invention that are obvious to those skilled in the art are included within the scope of protection of the technical solutions described below. Industrial Applicability

[0322] The porous laminate 1 of the present invention is, for example, suitable for use as a substrate for high-frequency antennas and a high-speed transmission flexible printed circuit board. In addition, the flexible multilayer circuit board 10 of the present invention is, for example, suitable for use in small electronic devices used in wireless communication conforming to the "fifth generation (5G)" standard. Symbol Explanation

[0323] 1: Porous laminate 2: Conductor layer 3: Insulating layer 4: Base resin layer 5: Porous resin layer 6: Bonding layer 7: Wiring layer.

Claims

1. A porous laminate comprising a conductor layer and an insulating layer in this order toward one side in a thickness direction, The insulating layer includes a base resin layer, a porous resin layer, and a bonding layer in order toward one side in the thickness direction. The thickness of the porous resin layer is 50 μm or less. The maximum height Rz of one surface of the porous resin layer in the thickness direction is 16 μm or less, A maximum height Rz of one surface in the thickness direction of the porous resin layer is larger than a maximum height Rz of one surface in the thickness direction of the base resin layer.

2. The porous laminate according to claim 1, wherein The maximum height Rz of one surface in the thickness direction of the base resin layer is 5 μm or less.

3. The porous laminate according to claim 1, wherein The maximum height Rz of one surface in the thickness direction of the porous resin layer is more than 5 μm and less than or equal to 10 μm.

4. A flexible multilayer circuit substrate comprising two porous laminates according to any one of claims 1 to 3, A porous laminate and another porous laminate are sequentially stacked toward the other side in the thickness direction so that the bonding layer of the one porous laminate faces the bonding layer of the other porous laminate. The flexible multilayer circuit board includes a wiring portion embedded in one of the bonding layers of the one porous laminate and the other porous laminate.

5. The flexible multi-layer circuit substrate according to claim 4, wherein: The insulating layer of the one porous laminate and the insulating layer of the other porous laminate have a plurality of first through holes, and the first through holes penetrate between the conductive layer of the one porous laminate and the conductive layer of the other porous laminate in the thickness direction. The flexible multilayer circuit substrate includes a plurality of first via-hole connecting portions, the plurality of first via-hole connecting portions are filled in the plurality of first through holes, and are in contact with the conductor layer of the one porous laminate and the conductor layer of the other porous laminate in a manner that the conductor layer of the one porous laminate and the conductor layer of the other porous laminate are electrically connected. The wiring portion is configured to be located between the plurality of first via connection portions.

6. The flexible multi-layer circuit substrate according to claim 5, wherein: One of the conductive layers of the porous laminate and the conductive layers of the other porous laminate has a terminal portion at one end in the longitudinal direction, and one of the conductive layers of the porous laminate and the conductive layers of the other porous laminate has a terminal portion at the other end in the longitudinal direction. One of the insulating layer of the one porous laminate and the insulating layer of the other porous laminate has a second through hole at both ends in the longitudinal direction, and the second through hole penetrates between the terminal portion and the wiring portion in the thickness direction. The flexible multilayer circuit substrate includes a second via connection portion that is filled in the second through hole and is in contact with the terminal portion and the wiring portion so as to electrically connect the terminal portion and the wiring portion.

7. The flexible multi-layer circuit substrate according to claim 6, wherein: The flexible multilayer circuit substrate further comprises reinforcing substrates at both ends in the long side direction. The reinforcing substrate is disposed on one side of the conductive layer of the one porous laminate in the thickness direction where the terminal portion is not provided, or on the other side of the conductive layer of the other porous laminate in the thickness direction where the terminal portion is not provided.

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