Porous laminate and flexible multilayer circuit board

Abstract

To provide a porous laminate with an excellent adhesion and flexibility, and provide a flexible multilayer circuit board.SOLUTION: A porous laminate 1 comprises: a conductor layer 2; an insulation layer 3 to one side in a thickness direction, sequentially. The insulation layer 3 comprises: a base resin layer 4; a porous resin layer 5; and a bonding layer 6 to the one side in the thickness direction, sequentially. Also, the thickness of the porous resin layer 5 is 50 μm or less, and the maximum height (Rz) of one surface of the porous resin layer 5 in the thickness direction is 16 μm or less. In addition, the maximum height (Rz) of the one surface of the porous resin layer 5 in the thickness direction is larger than the maximum height (Rz) of one surface of the base resin layer 4 in the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, development of the so-called "fifth generation (5G)" standard for wireless communication has been progressing. "5th generation (5G)" standard wireless communication will enable the transmission of large volumes of data at high speeds. "5th generation (5G)" standard wireless communication will use high frequencies, including millimeter waves. Substrates with a low dielectric constant (low-dielectric substrates) are required as substrates for high-frequency antennas that emit these millimeter waves. In addition, there is a demand for high-speed transmission FPCs (flexible printed circuit boards) that can transmit data at high speeds, and low-dielectric substrates are also required as substrates for these high-speed transmission FPCs.

[0003] As such a low dielectric substrate, a low dielectric substrate including a first metal layer, a porous resin layer, an adhesive layer, and a second metal layer has been proposed (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-053632 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, porous laminates used in flexible multilayer circuit boards are required to have excellent interlayer adhesion. Furthermore, when flexible multilayer circuit boards are used in small electronic devices, etc., it is necessary to connect components together in a limited space, so the porous laminate is desirably excellent in flexibility.

[0006] However, the low dielectric substrate of Patent Document 1 has the drawback of insufficient adhesion between layers.

[0007] The present invention aims to provide a porous laminate and a flexible multilayer circuit board that are excellent in adhesion and flexibility. [Means for solving the problem]

[0008] The present invention [1] includes a porous laminate comprising a conductor layer and an insulating layer, in that order, toward one side in the thickness direction, and the insulating layer comprises a base resin layer, a porous resin layer, and a bonding layer, in that order, toward one side in the thickness direction, and the thickness of the porous resin layer is 50 μm or less, the maximum height (Rz) of one side in the thickness direction of the porous resin layer is 16 μm or less, and the maximum height (Rz) of one side in the thickness direction of the porous resin layer is greater than the maximum height (Rz) of one side in the thickness direction of the base resin layer.

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

[0010] The present invention [3] includes the porous laminate according to [1] or [2], wherein the maximum height (Rz) of one surface in the thickness direction of the porous resin layer is more than 5 μm and 10 μm or less.

[0011] The present invention [4] includes a flexible multilayer circuit board comprising two porous laminates according to any one of [1] to [3], wherein one porous laminate and the other porous laminate are stacked in order 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, and the flexible multilayer circuit board comprises a wiring portion embedded in either the bonding layer of the one porous laminate or the bonding layer of the other porous laminate.

[0012] The present invention [5] includes a flexible multilayer circuit board as described in [4], in which the insulating layer of the one porous laminate and the insulating layer of the other porous laminate have a plurality of first through holes that penetrate in the thickness direction between the conductor layer of the one porous laminate and the conductor layer of the other porous laminate, and a plurality of first via connection portions filled in the plurality of first through holes, which contact the conductor layer of the one porous laminate and the conductor layer of the other porous laminate so as to electrically connect the conductor layer of the one porous laminate and the conductor layer of the other porous laminate, and the plurality of first via connection portions are arranged so that the wiring portion is located therebetween.

[0013] The present invention [6] includes a flexible multilayer circuit board as described in [5], in which, at each of both longitudinal ends, either the conductor layer of the one porous laminate or the conductor layer of the other porous laminate has a terminal portion, and either the insulating layer of the one porous laminate or the insulating layer of the other porous laminate has a second through hole that penetrates in the thickness direction between the terminal portion and the wiring portion, and a second via connection portion that is filled in the second through hole and contacts the terminal portion and the wiring portion so as to electrically connect the terminal portion and the wiring portion.

[0014] The present invention [7] includes a flexible multilayer circuit board according to [6], further comprising a reinforcing substrate at each of both longitudinal ends, the reinforcing substrate being arranged on one thickness-wise side of the conductor layer of one of the porous laminates that does not have the terminal portion, or on the other thickness-wise side of the conductor layer of the other porous laminate that does not have the terminal portion. [Effects of the Invention]

[0015] In the porous laminate of the present invention, the thickness of the porous resin layer is 50 μm or less. toThe porous laminate of the present invention can relieve such stress and has excellent flexibility. Furthermore, 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. Therefore, the adhesion between the layers is excellent.

[0016] The flexible multilayer circuit board of the present invention has excellent adhesion and flexibility because it includes the porous laminate described above. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows a cross-sectional view in the width direction of one embodiment of the porous laminate of the present invention. [Figure 2] FIG. 2 shows a longitudinal cross-sectional view of one embodiment of the flexible multilayer circuit board of the present invention. [Figure 3] FIG. 3 shows a cross-sectional view of the flexible multilayer circuit board shown in FIG. 2 taken along line AA' in the width direction. [Figure 4] FIG. 4 shows a cross-sectional view of the flexible multilayer circuit board shown in FIG. 2 taken along line BB' in the width direction. [Figure 5] Figures 5A to 5D show a method for producing the porous laminate shown in Figure 1. Figure 5A shows a step of preparing a conductor layer, Figure 5B shows a step of forming a first coating film, Figure 5C shows a step of forming a second coating film, and Figure 5D shows a step of forming a laminate with a flow path-containing sheet. [Figure 6] 6A and 6B, following on from Fig. 5D, show a method for producing the porous laminate shown in Fig. 1. Fig. 6A shows the step of forming a roll body, and Fig. 6B shows the step of making the second coating film porous. [Figure 7] Figures 7A and 7B, following on from Figure 6B, show the method for producing the porous laminate shown in Figure 1. Figure 7A shows the step of removing the flow path-containing sheet, Figure 7B shows the step of heating the first coating film and the second coating film, and Figure 7C shows the step of forming the bonding layer and the wiring layer. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1.Porous laminate A porous laminate 1 according to one embodiment of the present invention will be described with reference to FIG.

[0019] 1, the vertical direction of the paper surface indicates the thickness direction of the porous laminate 1. The horizontal direction of the paper surface indicates the width direction (short side direction) of the porous laminate 1. The depth direction of the paper surface indicates the longitudinal direction of the porous laminate 1.

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

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

[0022] 1, the porous laminate 1 includes a conductor layer 2 and an insulating layer 3 in this order toward one side in the thickness direction, and preferably includes the conductor layer 2 and the insulating layer 3 disposed on one surface in the thickness direction of the conductor layer 2. The porous laminate 1 also preferably further includes a wiring layer 7 disposed on one side in the thickness direction of the insulating layer 3.

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

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

[0025] Examples of materials for the conductor layer 2 include metals. Examples of metals include copper, iron, silver, gold, aluminum, nickel, and alloys thereof (stainless steel, bronze). Copper is preferred.

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

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

[0028] <Insulating layer> 1, 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 includes, in order toward one side in the thickness direction, a base resin layer 4, a porous resin layer 5, and a bonding layer 6. 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] 1, the base resin layer 4 is disposed on one thickness-wise side of the conductor layer 2 and on the other thickness-wise side of the porous resin layer 5. In other words, 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 thickness-wise surface of the conductor layer and the other thickness-wise surface of the porous resin layer 5.

[0031] The base resin layer 4 has a certain thickness. The base resin layer 4 has a generally 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. In other words, the presence of the base resin layer 4 results in excellent adhesion between the porous resin layer 5 and the conductor layer 2.

[0032] Examples of materials (or raw materials) for the resin base layer 4 include resins. There are no particular limitations on the resins, as long as they are used as insulating materials in wiring circuit boards. Examples of resins include polycarbonate resins, polyimide resins, fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting urethane resins, fluororesins, and liquid crystal polymers, preferably polyimide resins and liquid crystal polymers, and more preferably polyimide resins.

[0033] The base resin layer 4 is preferably a non-porous, solid, dense film in order to improve adhesion between layers, that is, the base resin layer 4 is preferably a non-porous polyimide resin layer.

[0034] The porosity of 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 resin base 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, still more 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 surface in contact 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, even more 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 thickness-wise surface 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, even more preferably 1.5 μm or more, particularly preferably 2.0 μm or more, and for example, 5.0 μm or less, preferably 4.0 μm or less, more preferably 3.5 μm or less, even more preferably 3.2 μm or less, particularly preferably 3.0 μm or less.

[0038] When the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is within the above range, the base resin layer 4 has excellent adhesion to the porous resin layer 5. Specifically, when the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is equal to or greater than the above lower limit, the base resin layer 4 has excellent adhesion to the porous resin layer 5 due to the anchor effect. Furthermore, when the maximum height (Rz) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is equal to or less than the above upper limit, the contact area with the porous resin layer 5 can be increased, the adhesion to the porous resin layer 5 can be improved, and further, variations in the thickness of the porous resin layer 5 can be suppressed.

[0039] The maximum height (Rz) is the maximum height in accordance with JIS B 0601-2001. (The same applies below.)

[0040] The surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the surface in contact 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, even more 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 thickness-wise surface of the base resin layer 4 (the surface in contact 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, even more preferably 0.30 μm or more, particularly preferably 0.35 μm or more, and most preferably 0.40 μm or more, and is, for example, 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.5 μm or less, even more preferably 1.2 μm or less, particularly preferably 1.0 μm or less, and most preferably 0.8 μm or less.

[0042] When the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is within the above range, the base resin layer 4 has excellent adhesion to the porous resin layer 5. Specifically, when the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is equal to or greater than the above lower limit, the base resin layer 4 has excellent adhesion to the porous resin layer 5 due to the anchor effect. Furthermore, when the surface roughness (Ra) of one surface in the thickness direction of the base resin layer 4 (the surface in contact with the porous resin layer 5) is equal to or less than the above upper limit, the contact area with the porous resin layer 5 can be increased, the adhesion to the porous resin layer 5 can be improved, and further, variations in the thickness of the porous resin layer 5 can be suppressed.

[0043] The surface roughness (Ra) refers to the arithmetic mean surface roughness in accordance with JIS B 0601-2001 (the same applies hereinafter).

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

[0045] The maximum height (Rz) and surface roughness (Ra) of one thickness direction surface (contact surface with the porous resin layer 5) of the base resin layer 4 are the same as the maximum height (Rz) and surface roughness (Ra) of one thickness direction surface (contact surface with the porous resin layer 5) of the first coating film 104' after drying, which will be described later. Therefore, in this embodiment, the maximum height (Rz) and surface roughness (Ra) of one thickness direction surface (contact surface with the porous resin layer 5) of the first coating film 104' after drying are used as the maximum height (Rz) and surface roughness (Ra) of one thickness direction surface (contact surface with the porous resin layer 5) of the base resin layer 4. Note that, if the material of the first coating film 104' after drying is a polyimide resin, this refers to the state before imidization. Details will be described in the examples below.

[0046] The dielectric constant of the base resin layer 4 at a frequency of 100 GHz is in the range of, 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, for example, 4.5 or less, preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.3 or less.

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

[0049] The dielectric loss tangent of the resin base 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 dielectric loss tangent of the base resin layer 4 at a frequency of 100 GHz is, for example, more than 0 and, for example, 0.0050 or less, preferably 0.0040 or less, more preferably 0.0030 or less, even more preferably 0.0025 or less, and particularly preferably 0.002 or less.

[0051] The dielectric loss tangent of the base resin layer 4 is actually measured by a resonator method using 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. The porous resin layer 5 is a layer that lowers the dielectric constant of the porous laminate 1. In other words, the presence of the porous resin layer 5 can lower the dielectric constant.

[0053] 1, the porous resin layer 5 is disposed on one thickness-wise side of the base resin layer 4 and on the other thickness-wise side of the bonding layer 6. In other words, 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 thickness-wise surface of the base resin layer 4 and is in contact with the other thickness-wise surface of the bonding layer 6.

[0054] Examples of materials (or raw materials) for the porous resin layer 5 include resins. There are no particular limitations on the resins, as long as they are used as insulating materials in wiring circuit boards. Examples of resins include polycarbonate resins, polyimide resins, fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting urethane resins, fluororesins, and liquid crystal polymers, preferably polyimide resins and liquid crystal polymers, and more preferably polyimide resins.

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

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

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

[0058] If the porosity of the porous resin layer 5 is equal to or greater than the above lower limit, the dielectric constant can be reduced. If the porosity of the porous resin layer 5 is equal to or less than the above upper limit, the strength of the porous resin layer 5 can be ensured.

[0059] When the material of the porous resin layer 5 is a polyimide resin, that is, when the porous resin layer 5 is a porous polyimide resin layer, the porosity of the porous resin layer 5 can be calculated based on the following formula. 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, so by applying the above formula, the following can be expressed. 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, still more 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, the dielectric constant can be reduced. If the thickness of the porous resin layer 5 is equal to or less than the above upper limit, the bending endurance is excellent.

[0063] The maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact 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, even 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 surface in contact 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, even more preferably more than 5.0 μm, particularly preferably 5.5 μm or more, and most preferably 6.0 μm or more. The maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is 16.0 μm or less, preferably 12.0 μm or less, more preferably 10.0 μm or less, even more preferably 8.5 μm or less, and particularly preferably 7.0 μm or less.

[0065] When the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is within the above range, the porous resin layer 5 has excellent adhesion to the bonding layer 6. Specifically, when the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is equal to or greater than the above lower limit, the porous resin layer 5 has excellent adhesion to the bonding layer 6 due to the anchor effect. Furthermore, when the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is equal to or less than the above upper limit, the contact area with the bonding layer 6 can be increased, improving adhesion to the bonding layer 6. Furthermore, since the variation in thickness is small, the variation in dielectric constant can be reduced.

[0066] The surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact 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, even 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 thickness-wise surface of the porous resin layer 5 (the surface in contact 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, even more preferably 0.30 μm or more, particularly preferably 0.35 μm or more, and most preferably 0.40 μm or more, and is, for example, 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.5 μm or less, even more preferably 1.2 μm or less, particularly preferably 1.0 μm or less, and most preferably 0.8 μm or less.

[0068] When the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is within the above range, the porous resin layer 5 has excellent adhesion to the bonding layer 6. Specifically, when the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is equal to or greater than the above lower limit, the porous resin layer 5 has excellent adhesion to the bonding layer 6 due to the anchor effect. Furthermore, when the surface roughness (Ra) of one surface in the thickness direction of the porous resin layer 5 (the surface in contact with the bonding layer 6) is equal to or less than the above upper limit, the contact area with the bonding layer 6 can be increased, improving adhesion to the bonding layer 6. Furthermore, since the variation in thickness is small, the variation in dielectric constant can be reduced.

[0069] The difference between the maximum height (Rz) of one thickness direction surface of the porous resin layer 5 (contact surface with the bonding layer 6) and the maximum height (Rz) of one thickness direction surface of the base resin layer 4 (contact surface with the porous resin layer 5) (maximum height (Rz) of one thickness direction surface of the porous resin layer 5 (contact surface with the bonding layer 6) - maximum height (Rz) of one thickness direction surface of the base resin layer 4 (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, even more preferably 3.0 μm to 8.0 μm, and particularly preferably 3.5 μm to 6.0 μm.

[0070] The difference between the maximum height (Rz) of one thickness direction surface of the porous resin layer 5 (contact surface with the bonding layer 6) and the maximum height (Rz) of one thickness direction surface of the base resin layer 4 (contact surface with the porous resin layer 5) (maximum height (Rz) of one thickness direction surface of the porous resin layer 5 (contact surface with the bonding layer 6) - maximum height (Rz) of one thickness direction surface of the base resin layer 4 (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, even more preferably 3.0 μm or more, particularly preferably 3.5 μm or more, and also, for example, 15.0 μm or less, preferably 12.0 μm or less, more preferably 10.0 μm or less, even more preferably 8.0 μm or less, particularly preferably 6.0 μm or less.

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

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

[0073] If the difference between the maximum height (Rz) of one thickness direction surface (contact surface with bonding layer 6) of porous resin layer 5 and the maximum height (Rz) of one thickness direction surface (contact surface with porous resin layer 5) of base resin layer 4 (maximum height (Rz) of one thickness direction surface (contact surface with bonding layer 6) of porous resin layer 5 - maximum height (Rz) of one thickness direction surface (contact surface with porous resin layer 5) of base resin layer 4) is equal to or greater than the above-mentioned lower limit value, the anchor effect will result in excellent adhesion between the porous resin layer 5 and the bonding layer 6. Furthermore, if the difference between the maximum height (Rz) of one thickness direction surface (contact surface with bonding layer 6) of the porous resin layer 5 and the maximum height (Rz) of one thickness direction surface (contact surface with porous resin layer 5) of the base resin layer 4 (maximum height (Rz) of one thickness direction surface (contact surface with bonding layer 6) of the porous resin layer 5 - maximum height (Rz) of one thickness direction surface (contact surface with porous resin layer 5) of the base resin layer 4) is below the above upper limit value, the flatness of the exposed surface (one thickness direction surface) of the porous laminate 1 can be ensured, and further, adhesion between the base resin layer 4 and the porous resin layer 5 due to the anchor effect can be ensured.

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

[0077] The porous resin layer 5 has a dielectric constant at a frequency of 100 GHz in the range of, for example, 1.0 to 3.0, preferably 1.0 to 2.5, more preferably 1.0 to 2.2, and still more 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, for example, 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 2.0 or less.

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

[0080] The dielectric loss tangent 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, still more preferably 0 to 0.0025, and particularly preferably 0 to 0.0020.

[0081] The dielectric loss tangent of the porous resin layer 5 at a frequency of 100 GHz is, for example, more than 0 and, for example, 0.0050 or less, preferably 0.0040 or less, more preferably 0.0030 or less, even more preferably 0.0025 or less, and particularly preferably 0.002 or less.

[0082] The dielectric loss tangent of the porous resin layer 5 is actually measured by a resonator method using 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 in the range of, for example, 0.01 to 0.5, preferably 0.05 to 0.3, or 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 for example, 0.5 or less, preferably 0.3 or less, more preferably 0.2 or less.

[0085] In other words, the base resin layer 4 is thinner than the porous resin layer 5 .

[0086] When 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, it is possible to ensure sufficient adhesion between the porous resin layer 5 and the conductor layer 2. When 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, it is possible to reduce the dielectric constant while reducing the total thickness of the porous laminate 1.

[0087] [Bonding layer] The bonding layer 6 has a certain thickness. The bonding layer 6 has a substantially flat plate shape. The bonding layer 6 is also an adhesive layer that bonds layers together.

[0088] 1, the bonding layer 6 is disposed on one side in the thickness direction of the porous resin layer 5. The bonding layer 6 may 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 is used as an insulating material in a wired circuit board. A preferred material for the bonding layer 6 is a low-dielectric material. A preferred material for the bonding layer 6 is a resin. Examples of the resin include acrylic resin, polycarbonate resin, polyimide resin, fluorinated polyimide resin, epoxy resin, phenol resin, urea resin, melamine resin, diallyl phthalate resin, silicone resin, thermosetting urethane resin, fluororesin, and liquid crystal polymer. A preferred example is polyimide resin.

[0090] The bonding layer 6 is preferably a non-porous, solid, dense film in order to improve adhesion between layers, that is, the bonding layer 6 is preferably a non-porous polyimide resin layer.

[0091] The porosity of the bonding layer 6 is, for example, 0.5% or less, preferably 0.1% or less, and 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, still more 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, for example, 3.5 or less, preferably 3.2 or less, more preferably 3.0 or less, even more preferably 2.7 or less, and particularly preferably 2.5 or less.

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

[0095] The dielectric loss tangent of the bonding layer 6 at a frequency of 100 GHz is in the range of, for example, 0 to 0.005, preferably 0 to 0.004, more preferably 0 to 0.003, and still more 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, for example, 0.005 or less, preferably 0.004 or less, more preferably 0.003 or less, even more 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 a resonator method using 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, still more preferably 18 μm to 50 μm, and particularly preferably 20 μm to 40 μm.

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

[0100] The wiring layer 7 is disposed on one thickness-wise side of the insulating layer 3. In other words, the wiring layer 7 is the uppermost layer of the porous laminate 1. Specifically, the wiring layer 7 contacts one thickness-wise surface of the bonding layer 6.

[0101] The material of the wiring layer 7 is the same as the material 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 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, even more preferably 1.0 N / mm or more, and particularly preferably 1.2 N / mm or more. The upper limit of the peel strength of the porous laminate is not particularly limited.

[0104] When the peel strength of the porous laminate 1 is equal to or greater than the above lower limit, the adhesiveness is excellent.

[0105] The peel strength of the porous laminate 1 can be measured by the method described in the examples below.

[0106] In the bending test, the number of times the porous laminate 1 is bent is, for example, 50 or more, preferably 100 or more, more preferably 120 or more, even more preferably 140 or more, particularly preferably 150 or more, and most preferably 175 or more. There is no particular upper limit to the number of times the porous laminate 1 can be bent.

[0107] If the number of times the porous laminate 1 is bent is equal to or greater than the above lower limit, the porous laminate 1 will have excellent folding endurance.

[0108] The number of times the porous laminate 1 is bent can be measured by the method described in the examples below.

[0109] 2. Flexible multilayer circuit board A flexible multilayer circuit board 10 according to one embodiment of the present invention will be described with reference to FIGS.

[0110] 2, the vertical direction of the paper surface indicates the thickness direction of the flexible multilayer circuit board 10. The horizontal direction of the paper surface indicates the longitudinal direction of the flexible multilayer circuit board 10. The depth direction of the paper surface indicates the width direction (short side direction) of the flexible multilayer circuit board 10.

[0111] 3 and 4, the vertical direction of the paper indicates the thickness direction of the flexible multilayer circuit board 10. The horizontal direction of the paper indicates the width direction (short side direction) of the flexible multilayer circuit board 10. The depth direction of the paper indicates the longitudinal direction of the flexible multilayer circuit board 10.

[0112] The flexible multilayer circuit board 10 has a thickness. The flexible multilayer circuit board 10 extends in a plane direction perpendicular to the thickness direction. The flexible multilayer circuit board 10 has a generally flat plate shape that is long in the longitudinal direction. The longitudinal direction is perpendicular to both the thickness direction and the width direction.

[0113] As shown in FIG. 2, the flexible multilayer circuit board 10 includes two of the porous laminates 1 described above, with one porous laminate (first porous laminate 11) and the other porous laminate (second porous laminate 12) stacked in order toward the other side in the thickness direction so that the bonding layer (first bonding layer 61) of the first porous laminate 11 faces the bonding layer (second bonding layer 62) of the second porous laminate 12. The flexible multilayer circuit board 10 also includes a wiring portion 70 embedded in either the first bonding layer 61 or the second bonding layer 62.

[0114] Specifically, the flexible multilayer circuit board 10 includes a first porous laminate 11 and a second porous laminate 12 laminated in order toward the other side in the thickness direction so that the first bonding layer 61 and the second bonding layer 62 face each other, and includes a wiring portion 70 embedded in either the first bonding layer 61 or the second bonding layer 62. Note that, as will be described in detail later, the first bonding layer 61 and the second bonding layer 62 may be integrated to form a single bonding layer 60.

[0115] That is, one of the first porous laminate 11 and the second porous laminate 12 has the wiring layer 7, and the other does not have the wiring layer 7. As will be described in detail later, the wiring layer 7 can be patterned to obtain the wiring portion 70.

[0116] The flexible multilayer circuit board 10 may include a first via connection portion 81, a second via connection portion 82, a cover insulating layer 90, and a reinforcing base material 95, as required.

[0117] 2 and 3 show a portion of each cross-sectional view of the flexible multilayer circuit board 10. Specifically, the flexible multilayer circuit board 10 has a plurality of structures shown in Figs. 2 and 3 arranged in the width direction.

[0118] <First porous laminate> The first porous laminate 11 has the same configuration as the porous laminate 1. Specifically, as shown in Fig. 2, the first porous laminate 11 includes, in order toward the other side in the thickness direction, a first conductor layer 21, a first insulating layer 31, and a wiring portion 70 (wiring layer 7). Preferably, the first porous laminate 11 includes the first conductor layer 21, the first insulating layer 31 disposed on the other side in the thickness direction of the first conductor layer 21, and the wiring portion 70 disposed on the other side in the thickness direction of the first insulating layer.

[0119] In the following description, the same configuration as the porous laminate 1 described above will be omitted.

[0120] Furthermore, the first terminal portion 21b and the second terminal portion 22b, which will be described later, may be collectively referred to as the terminal portion.

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

[0122] 2, the first conductor layer 21 is disposed on one thickness-wise side of the first base resin layer 41. Specifically, the first conductor layer 21 is disposed on one thickness-wise surface of the first base resin layer 41. In other words, the first conductor layer 21 is in contact with one thickness-wise surface of the first base resin layer 41.

[0123] The first conductor layer 21 is disposed opposite the second conductor layer 22 described below so as to overlap the wiring portion 70 when projected in the thickness direction. In other words, the first conductor layer 21 and the second conductor layer 22 are disposed opposite each other so as to overlap the wiring portion 70 when projected in the thickness direction.

[0124] The first conductor layer 21 includes, for example, a first ground conductor portion 21a and a first terminal portion 21b. Specifically, as shown in Fig. 2, the first conductor layer 21 includes the first ground conductor portion 21a and further includes the first terminal portion 21b at one end in the longitudinal direction.

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

[0126] 2, the first ground conductor 21a is disposed on one thickness-wise side of the first base resin layer 41. Specifically, the first ground conductor 21a is disposed on one thickness-wise surface of the first base resin layer 41. In other words, the first ground conductor 21a is in contact with one thickness-wise surface of the first base resin layer 41.

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

[0128] 4, at one longitudinal end, the first ground conductor part 21a has a notch cut out in the center in the width direction toward the other longitudinal end so that the first terminal part 21b can be disposed therein. Specifically, although not shown, the first ground conductor part 21a has a plurality of such notches at one longitudinal end, spaced apart 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, even more preferably 15 μm to 70 μm, particularly preferably 20 μm to 50 μm, and most preferably 25 μm to 35 μm.

[0131] {1st terminal section} The first terminal 21b receives and transmits signals via a signal terminal (not shown). The signals include, for example, differential signals. The signals include, for example, a small current of less than 1 A.

[0132] 2, the first terminal 21b is disposed on one side in the thickness direction of the first base resin layer 41. Specifically, the first terminal 21b is disposed on one surface in the thickness direction of the first base resin layer 41. In other words, the first terminal 21b is in contact with one surface in the thickness direction of the first base resin layer 41.

[0133] The first terminal 21b is disposed, for example, at one end in the longitudinal direction. Note that the first terminal 21b does not necessarily have to be disposed at the other end in the longitudinal direction where the second terminal 22b (described later) is disposed.

[0134] As shown in FIG. 4, the first terminal portion 21b is disposed opposite the wiring portion .

[0135] The first terminal portion 21b is disposed in a notched portion of the first ground conductor portion 21a in the width direction. That is, the first terminal portion 21b is disposed between the two first ground conductor portions 21a in the width direction with a gap therebetween.

[0136] Although not shown, the first terminal portions 21b are arranged at intervals in the width direction. Specifically, the first ground conductor portions 21a and the first terminal portions 21b are arranged alternately 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] 2, the first insulating layer 31 includes a first base resin layer 41, a first porous resin layer 51 disposed on the other thickness-wise side of the first base resin layer 41, and a first bonding layer 61 disposed on the other thickness-wise side of the first porous resin layer 51. Specifically, the first insulating layer 31 includes the first base resin layer 41, the first porous resin layer 51 disposed on the other thickness-wise surface of the first base resin layer 41, and the first bonding layer 61 disposed on the other thickness-wise surface of the first porous resin layer 51.

[0139] As shown in Figures 3 and 4, the first insulating layer 31 and a second insulating layer 32 (described later) have a plurality of first through holes 71 that penetrate in the thickness direction between the first ground conductor portion 21a and a second ground conductor portion 22a (described later).

[0140] Either the first insulating layer 31 or the second insulating layer 32 has a second through-hole 72 that penetrates in the thickness direction between the terminal portion and a wiring portion 70 described later, at each of both ends in the longitudinal direction.

[0141] {First base resin layer} The first base resin layer 41 has a certain thickness. The first base resin layer 41 has a generally 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] 2, the first base resin layer 41 is disposed on one thickness-wise side of the first porous resin layer 51 and on the other thickness-wise side 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 is in contact with one thickness-wise surface of the first porous resin layer 51 and in contact with the other thickness-wise surface of the first conductor layer 21.

[0143] {First porous resin layer} The first porous resin layer 51 has a certain thickness. The first porous resin layer 51 has a generally 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] 2, the first porous resin layer 51 is disposed on one thickness-wise side of the first bonding layer 61 and on the other thickness-wise side 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 contact with one thickness-wise surface of the first bonding layer 61 and in contact with the other thickness-wise surface of the first base resin layer 41.

[0145] {First bonding layer} The first bonding layer 61 has a thickness. The first bonding layer 61 has a generally flat plate shape. The first bonding layer 61 is an adhesive layer that bonds between layers. Specifically, the first bonding layer 61 and a second bonding layer 62 (described later) bond the first porous laminate 11 and the second porous laminate 12 together.

[0146] 2, the first bonding layer 61 is disposed on the other thickness-wise side of the first porous resin layer 51. Specifically, the first bonding layer 61 contacts the other thickness-wise surface of the first porous resin layer 51. The first bonding layer 61 is also disposed on one thickness-wise side of the second bonding layer 62, which will be described later. Specifically, the first bonding layer 61 contacts one thickness-wise surface of the second bonding layer 62.

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

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

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

[0150] The wiring portion 70 has a thickness and extends in the longitudinal 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 thickness-wise side of the first bonding layer 61. Specifically, the wiring portion 70 is disposed on the other thickness-wise side of the first bonding layer 61. The wiring portion 70 also contacts the other surface of the first bonding layer 61 in the thickness direction.

[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 thickness-wise surface of the wiring portion 70 contacts the first bonding layer 61. The other thickness-wise surface and the peripheral side surface of the wiring portion 70 are covered by the second bonding layer 62. In other words, the entire outer peripheral surface of the wiring portion 70 contacts the bonding layer 60.

[0154] The material of the wiring portion 70 is the same as the material of the first conductor layer 21.

[0155] The thickness of the wiring portion 70 may be the same as or different from the thickness of the wiring layer 7. Preferably, they are the same.

[0156] <Second porous laminate> The second porous laminate 12 has the same configuration as the porous laminate 1. Specifically, as shown in Fig. 2, the second porous laminate 12 includes a second conductor layer 22 and a second insulating layer 32 in this order toward one side in the thickness direction. Preferably, the second conductor layer 22 and the second insulating layer 32 are arranged in this order in the thickness direction of the second conductor layer 22. one side The second porous laminate 12 does not include a wiring portion 70.

[0157] In the following description, the same configuration as the porous laminate 1 described above will be omitted.

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

[0159] 2, the second conductor layer 22 is disposed on the other thickness-wise side of the second base resin layer 42. Specifically, the second conductor layer 22 is disposed on the other thickness-wise surface of the second base resin layer 42. In other words, the second conductor layer 22 is in contact with the other thickness-wise surface of the second base resin layer 42.

[0160] The second conductor layer 22 is disposed opposite the first conductor layer 21 so as to overlap the wiring portion 70 when projected in the thickness direction. In other words, the first conductor layer 21 and the second conductor layer 22 are disposed opposite 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 22a and, if necessary, a second terminal 22b. Preferably, the second conductor layer 22 has both the second ground conductor 22a and the second terminal 22b. Specifically, as shown in FIG. 2, the second conductor layer 22 has the second ground conductor 22a and further has the second terminal 22b at the other end in the longitudinal direction.

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

[0163] 2, the second ground conductor 22a is disposed on the other thickness-wise side of the second base resin layer 42. Specifically, the second ground conductor 22a is disposed on the other thickness-wise surface of the second base resin layer 42. In other words, the second ground conductor 22a is in contact with the other thickness-wise surface of the second base resin layer 42.

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

[0165] Although not shown, at the other longitudinal end, the second ground conductor 22a has a notch cut out in the center in the width direction toward the one longitudinal end so that the second terminal 22b can be disposed therein. Specifically, at the other longitudinal end, the second ground conductor 22a has a plurality of such notches spaced apart in the width direction.

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

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

[0168] {Second terminal section} The second terminal 22b is connected to a connector via a signal terminal (not shown) to receive and transmit signals, such as differential signals. The signals include a small current of less than 1 A.

[0169] 2, the second terminal portion 22b is disposed on the other thickness-wise side of the second base resin layer 42. Specifically, the second terminal portion 22b is disposed on the other thickness-wise surface of the second base resin layer 42. In other words, the second terminal portion 22b is in contact with the other thickness-wise surface of the second base resin layer 42.

[0170] The second terminal 22b is disposed, for example, at the other end in the longitudinal direction. Note that the second terminal 22b does not necessarily have to be disposed at the one end in the longitudinal direction where the first terminal 21b is disposed.

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

[0172] The second terminal 22b is disposed in a notched portion of the second ground conductor 22a in the width direction, i.e., the second terminal 22b is disposed between the two second ground conductors 22a at an interval in the width direction.

[0173] Although not shown, the second terminal portions 22b are arranged at intervals in the width direction. Specifically, the second ground conductor portions 22a and the second terminal portions 22b are arranged alternately 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] 2, the second insulating layer 32 includes a second base resin layer 42, a second porous resin layer 52 disposed on one thickness-wise side of the second base resin layer 42, and a second bonding layer 62 disposed on one thickness-wise side of the second porous resin layer 52. Specifically, the second insulating layer 32 includes the second base resin layer 42, the second porous resin layer 52 disposed on one thickness-wise surface of the second base resin layer 42, and the second bonding layer 62 disposed on one thickness-wise surface of the second porous resin layer 52.

[0176] As shown in FIGS. 3 and 4, the first insulating layer 31 and the second insulating layer 32 have a plurality of first through holes 71 that penetrate between the first ground conductor portion 21a and the second ground conductor portion 22a in the thickness direction.

[0177] The first insulating layer 31 and / or the second insulating layer 32 also have second through holes 72 that penetrate between the terminal portions and the wiring portions 70 in the thickness direction at both ends in the longitudinal direction.

[0178] {Second base resin layer} The second base resin layer 42 has a certain thickness. The second base resin layer 42 has a generally 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] 2, the second base resin layer 42 is disposed on the other thickness-wise side of the second porous resin layer 52 and on one thickness-wise side of the second conductor layer 22. In other words, 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 is in contact with the other thickness-wise surface of the second porous resin layer 52 and is in contact with one thickness-wise surface of the second conductor layer 22.

[0180] {Second porous resin layer} The second porous resin layer 52 has a certain thickness. The second porous resin layer 52 has a generally 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] 2, the second porous resin layer 52 is disposed on the other thickness-wise side of the second bonding layer 62 and on one thickness-wise side of the second base resin layer 42. In other words, 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 is in contact with the other thickness-wise surface of the second bonding layer 62 and is in contact with one thickness-wise surface 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. The second bonding layer 62 is an adhesive layer that bonds layers together. Specifically, First bonding layer 61 The first porous laminate 11 and the second porous laminate 12 are bonded together by the second bonding layer 62 .

[0183] 2, 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 of the second porous resin layer 52 in the thickness direction.

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

[0185] <Bonding layer> The bonding layer 60 is an integrated layer of a first bonding layer 61 and a second bonding layer 62. In other words, the interface between the first bonding layer 61 and the second bonding layer 62 does not need to be observed.

[0186] The first bonding layer 61 is disposed on one thickness-wise side of the second bonding layer 62. Specifically, the first bonding layer 61 contacts one thickness-wise surface of the second bonding layer 62 except for the portion that contacts the wiring portion 70. The first bonding layer 61 and the second bonding layer 62 form one 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, still more preferably 30 μm to 100 μm, and particularly preferably 40 μm to 80 μm.

[0189] The thickness of the bonding layer 60 is the total thickness including the thickness of the embedded wiring portion 70. The thickness of the bonding layer 60 on one thickness-wise side of the wiring portion 70 and the thickness of the bonding layer 60 on the other thickness-wise side of the wiring portion 70 are not particularly limited and may be the same or different. Considering the manufacturing method, the thickness of the bonding layer 60 on one thickness-wise side of the wiring portion 70 is preferably different from the thickness of the bonding layer 60 on the other thickness-wise side of the wiring portion 70. The thickness of the bonding layer 60 on one thickness-wise side of the wiring portion 70 is the distance from one thickness-wise surface of the wiring portion 70 to one thickness-wise surface of the bonding layer 60, and the thickness of the bonding layer 60 on the other thickness-wise side of the wiring portion 70 is the distance from the other thickness-wise surface of the wiring portion 70 to the other thickness-wise surface of the bonding layer 60.

[0190] The thickness of the bonding layer 60 on one side of the wiring portion 70 in the thickness direction is, for example, 1 μm to 100 μm, preferably 3 μm to 70 μm, more preferably 5 μm to 50 μm, even more 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, even more 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 one side of the wiring portion 70 in the thickness direction to the thickness of the bonding layer 60 on the other side of the wiring portion 70 in the thickness direction is, for example, 1.0 to 10, preferably 1.3 to 8.0, more preferably 1.5 to 6.0, even more 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 of the wiring portion 70 in the thickness direction is preferably thinner than the thickness of the bonding layer 60 on the other side of the wiring portion 70 in the thickness direction.

[0194] <First via connection part> The first via connection portion 81 is filled into the plurality of first through holes 71. That is, a plurality of first via connection portions 81 are provided.

[0195] The first via connection portions 81 are in contact with the first conductor layer 21 and the second conductor layer 22 so as to electrically connect the first conductor layer 21 and the second conductor layer 22. Specifically, one thickness direction end of each of the first via connection portions 81 is in contact with the other thickness direction surface of the first ground conductor portion 21a, and the other thickness direction end of each of the first via connection portions 81 is in contact with one thickness direction surface of the second ground conductor portion 22a. Furthermore, peripheral side surfaces of each of the first via connection portions 81 are in contact with the first insulating layer 31 and the second insulating layer 32. As a result, the first ground conductor portion 21a and the second ground conductor portion 22a are electrically connected via the first via connection portions 81.

[0196] As shown in FIGS. 3 and 4, the first via connection portions 81 are arranged in pairs in the width direction, with the wiring portion 70 positioned therebetween.

[0197] That is, as shown in FIG. 3, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portion 81 form a ground path having a substantially square shape.

[0198] The first conductor layer 21 and the second conductor layer 22 are arranged opposite each other so as to overlap with the wiring portion 70 when projected in the thickness direction, and the pair of first via connection portions 81 are arranged so that the wiring portion 70 is located between them, thereby suppressing the occurrence of dielectric loss in the wiring portion 70.

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

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

[0202] The first via connection portion 81 is formed by filling the first through hole 71 with a material for the first via connection portion 81 .

[0203] The material of the first via connection portion 81 is the same as the material of the first conductor layer 21.

[0204] <Second via connection> The second via connection portion 82 fills the second through hole 72 .

[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 shown in FIG. 2 , the second via connection portion 82 contacts the first terminal portion 21b and the wiring portion 70 at one longitudinal end, and contacts the second terminal portion 22b and the wiring portion 70 at the other longitudinal end. More specifically, at one longitudinal end, one thickness direction end of the second via connection portion 82 contacts the other thickness direction surface of the first terminal portion 21b, and the other thickness direction end of the second via connection portion 82 contacts one thickness direction surface of the wiring portion 70. Furthermore, at the other longitudinal end, the other thickness direction end of the second via connection portion 82 contacts one thickness direction surface of the second terminal portion 22b, and the one thickness direction end of the second via connection portion 82 contacts the other thickness direction surface of the wiring portion 70. Furthermore, the peripheral side surface of the second via connection portion 82 contacts either the first insulating layer 31 or the second insulating layer 32. As a result, 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 disposed at both ends in the longitudinal direction, and are not disposed at any other ends than the ends in the longitudinal direction.

[0207] As shown in FIG. 4, one second via connection portion 82 is disposed 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 form a substantially I-shaped signal path at each of both ends in the longitudinal direction.

[0209] 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 72 with the material of the second via connection portion 82 .

[0211] The material of the second via connection portion 82 is the same as the material of the first conductor layer 21.

[0212] <Cover insulating layer> The cover insulating layer 90 is a layer for protecting the surface of the flexible multilayer circuit board 10 .

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

[0214] The first insulating cover layer 91 contacts one surface in the thickness direction of the first conductor layer 21. The second insulating cover layer 92 contacts the other surface in the thickness direction of the second conductor layer 22.

[0215] At least a part of the terminal portion is exposed from the insulating cover layer 90. That is, the insulating cover layer 90 covers at least the first conductor layer 21 and the second conductor layer 22 other than the terminal portion.

[0216] The cover insulating layer 90 may be made of the same resin as the material of the first porous resin layer 51, for example.

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

[0218] <Reinforcing substrate> The reinforcing substrate 95 is a substrate that reinforces the flexible multilayer circuit board 10. The reinforcing substrate 95 has a flat plate shape. The reinforcing substrate 95 is disposed on each of both ends in the longitudinal direction.

[0219] By providing the reinforcing base material 95, damage to the flexible multilayer circuit board 10 at the terminal portion can be suppressed.

[0220] The reinforcing base material 95 is disposed at each of both ends in the longitudinal direction 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. 2 As shown in the figure, the reinforcing substrate 95 has a first reinforcing substrate 96 arranged on one side of the first insulating cover layer 91 in the thickness direction at the other end in the longitudinal direction, and a second reinforcing substrate 97 arranged on the other side of the second insulating cover layer 92 in the thickness direction at one end in the longitudinal direction.

[0221] The other longitudinal end of the first reinforcing base material 96 contacts one thickness direction surface of the first insulating cover layer 91. The other longitudinal end of the second reinforcing base material 97 contacts the other thickness direction surface of the second insulating cover layer 92.

[0222] The material of the reinforcing base material 95 is not particularly limited. Examples of the material of the reinforcing base material 95 include metals and hard resins. Metals are preferred. Examples of metals include stainless steel, copper, iron, and aluminum.

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

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

[0225] The material (or raw material) of the adhesive layer is not particularly limited as long as it is a material that is commonly used for adhesive layers in wired circuit boards. Examples of the material (or raw material) of the adhesive layer include resins.

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

[0227] 3.Method for manufacturing porous laminate A method for producing the porous laminate 100 will be described with reference to FIGS.

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

[0229] (First coating film formation process) 5B, a first coating film 104′ is formed on one surface in the thickness direction of the conductor layer 102. Specifically, a varnish containing a precursor of a resin (e.g., polyimide resin) as the material for the base resin layer, a porosifying agent, a nucleating agent, and a solvent is prepared, and the varnish is applied to one surface in the thickness direction of the conductor layer 102 to form the first coating film 104′.

[0230] The types and blending ratios of the above-mentioned porosifying agent, nucleating agent, and solvent are described in, for example, WO2018 / 186486.

[0231] The case where the resin is a polyimide resin will be specifically described below.

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

[0233] The diamine component may be, for example, an aromatic diamine or an aliphatic diamine. Preferably, an aromatic diamine is used.

[0234] Aromatic diamines include, for example, primary diamines, secondary diamines, and tertiary diamines.

[0235] The first diamine contains a single aromatic ring. Examples of the first diamine include phenylenediamine, dimethylbenzenediamine, and ethylmethylbenzenediamine. Phenylenediamine is preferred. Examples of the phenylenediamine include o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine. Phenylenediamine is preferred. p-phenylenediamine is sometimes abbreviated as PDA.

[0236] The second diamine contains multiple aromatic rings and ether bonds between them. Examples of the second diamine include oxydianiline. Examples of the oxydianiline include 3,4'-oxydianiline and 4,4'-oxydianiline. Preferably, 4,4'-oxydianiline (also known as 4,4-diaminodiphenyl ether) is used. 4,4'-oxydianiline is sometimes abbreviated as ODA.

[0237] The tertiary diamine contains multiple aromatic rings and ester bonds between them. Examples of the tertiary diamine include aminophenylaminobenzoate, preferably 4-aminophenyl-4-aminobenzoate. 4-aminophenyl-4-aminobenzoate is sometimes abbreviated as APAB.

[0238] In addition to the primary to tertiary diamines, examples of the aromatic diamine include 4,4'-methylenedianiline, 4,4'-dimethylenedianiline, 4,4'-trimethylenedianiline, and bis(4-aminophenyl)sulfone.

[0239] The diamine component may be used alone or in combination of two or more. A preferred diamine component is a combination of a primary diamine, a secondary diamine, and a tertiary diamine. A more preferred diamine is a combination of p-phenylenediamine (PDA), 4,4'-oxydianiline (ODA), and 4-aminophenyl-4-aminobenzoate (APAB).

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

[0241] The molar amount of the tertiary diamine relative to 100 parts by mole of the total of the first diamine and the second diamine is, for example, 5 to 100 parts by mole, preferably 10 to 50 parts by mole, and more preferably 20 to 30 parts by mole.

[0242] The acid dianhydride component is not particularly limited. The acid dianhydride component contains, for example, an acid dianhydride containing an aromatic ring. Examples of the acid dianhydride containing an aromatic ring include aromatic tetracarboxylic acid dianhydrides.

[0243] Examples of aromatic tetracarboxylic dianhydrides include benzenetetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, biphenylsulfonetetracarboxylic dianhydride, and naphthalenetetracarboxylic dianhydride. These can be used alone or in combination. Preferred examples of acid dianhydrides containing an aromatic ring include biphenyltetracarboxylic dianhydride. Examples of biphenyltetracarboxylic dianhydrides include 3,3'-4,4'-biphenyltetracarboxylic dianhydride, 2,2'-3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenylethertetracarboxylic dianhydride. Preferred examples of biphenyltetracarboxylic dianhydrides include 3,3'-4,4'-biphenyltetracarboxylic dianhydride. 3,3'-4,4'-biphenyltetracarboxylic dianhydride is sometimes abbreviated as BPDA.

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

[0245] The ratio of the diamine component to the acid dianhydride component is adjusted so that the molar amount of the amino group (-NH2) of the diamine component and the molar amount of the acid anhydride group (-CO-O-CO-) of the acid dianhydride component are, for example, equimolar.

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

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

[0248] Thereafter, the first coating film 104' is dried by heating. Heating promotes removal of the solvent. 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 heating is insufficient, the first coating film 104' may be integrated with the second coating film 105' formed below, making it impossible to form the undercoat resin layer 104 described below.

[0250] (Second coating film formation process) As shown in FIG. 5C, 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 (e.g., polyimide resin) as the material for the porous resin layer, a porosifying agent, a nucleating agent, and a solvent is prepared, and the varnish is applied to one surface in the thickness direction of the first coating film 104' to form the second coating film 105'. The varnish for forming the second coating film 105' preferably has the same composition as the varnish for forming the first coating film 104', differing only in solids concentration. The concentration (solids concentration) of the polyimide precursor in the varnish is, for example, 10% to 95% by mass, preferably 40% to 75% by mass.

[0251] A varnish is applied to one surface in the thickness direction of the first coating film 104' to form a second coating film 105', which is then dried by heating. The heating promotes the removal of the solvent. The heating temperature is, for example, 130°C to 300°C. The heating time is, for example, 10 minutes to 30 minutes. The heating may be performed multiple times.

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

[0253] (Step of forming laminate with flow path-containing sheet) As shown in FIG. 5D, a channel-containing sheet 110 is placed on one surface in the thickness direction of the second coating film 105' to form a precursor laminate 111 with a channel-containing sheet.

[0254] The flow path-containing sheet 110 has a predetermined thickness and is in the shape of a long, substantially flat plate.

[0255] Specifically, the channel-containing sheet 110 is formed, for example, from fibers and / or mesh. Fibers are mesh sheets that are not fused or woven. In contrast, mesh is a mesh sheet that is fused or woven. As a result, the channel-containing sheet 110 has voids (gaps) separated by the fibers and / or mesh. In other words, the channel-containing sheet 110 is also a void-containing sheet. These voids form channels for the supercritical fluid flowing through the channel-containing sheet 110. The channel-containing sheet 110 is preferably formed from fibers.

[0256] The presence or absence of fibers in the flow path-containing sheet 110 and whether or not they are woven can be confirmed by observation with an optical microscope.

[0257] The material of the channel-containing sheet 110 is not particularly limited as long as it is substantially insoluble in the supercritical fluid. Examples of the material of the channel-containing sheet 110 include organic materials, inorganic materials, and hybrid materials thereof. Examples of organic materials include cellulose, polyester (PET, PBT, etc.), polyolefin (polyethylene, polypropylene, etc.), polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, and polyphenylene oxide. Examples of inorganic materials include metals such as copper, iron, aluminum, and stainless steel. The material of the channel-containing sheet 110 is preferably an organic material, and more preferably cellulose, from the viewpoint of reducing the amount of supercritical carbon dioxide dissolved in the channel-containing sheet 110.

[0258] The channel-containing sheet 110 may be a single layer or multiple layers. When the channel-containing sheet 110 is multiple layers, each layer may be made 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 channel-containing sheet 110 is equal to or greater than the above-mentioned lower limit, a sufficient amount of supercritical fluid can smoothly flow through the channel-containing sheet 110. If the thickness of the channel-containing sheet 110 is equal to or less than the above-mentioned upper limit, the thickness of the channel-containing sheet 110 per unit thickness of the roll 112 can be reduced. As a result, the production efficiency of the roll 112 can be improved.

[0261] The shape of the voids is not particularly limited, but they should be continuous at least in the longitudinal direction and thickness direction.

[0262] When the flow path-containing sheet 110 has continuous pores, the average pore size 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 size of the channel-containing sheet 110 may be uniform or may vary in the thickness direction. The pore size of the channel-containing sheet 110 may be, for example, such that the pore size increases from one side to the other in the thickness direction, or vice versa, or may vary irregularly or regularly. The change in pore size of the channel-containing sheet 110 (the change in pore size from one side to the other in the thickness direction) may be continuous, discontinuous, or a combination of these.

[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 is, for example, less than 100%.

[0265] The shape of the voids in the flow path-containing sheet 110 is not particularly limited, and examples thereof include amorphous, linear, curved, void shapes formed when fibers are entangled, flat, ellipsoidal, and spherical.

[0266] From the viewpoint of protecting the surface of the precursor laminate 108, the surface roughness Ra of the flow channel-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 path-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 equal to or less than the upper limit, the amount of carbon dioxide in a supercritical state (supercritical carbon dioxide) that dissolves in the flow path-containing sheet 110 is small, and the carbon dioxide can be sufficiently circulated through the flow path-containing sheet 110. Therefore, the porosifying agent in the porous body precursor sheet can be extracted more efficiently.

[0269] The solubility S of carbon dioxide in the flow path-containing sheet 110 can be determined by thoroughly drying the flow path-containing sheet 110, then using a molding machine (e.g., a benchtop molding press manufactured by Imoto Manufacturing Co., Ltd.) to pressurize and depressurize the sheet at a predetermined temperature (e.g., 180°C to 280°C) to create a bubble-free test piece (e.g., 20 mmφ, 1 mm to 3 mm thick), and using a magnetic levitation balance measuring device (BELP / O152 manufactured by RUBOTHERM) to measure the mass change when carbon dioxide is absorbed into the sample in a carbon dioxide atmosphere at a temperature of 200°C and a pressure of 30 MPa.

[0270] A commercially available product can be used for the channel-containing sheet 110. For example, the Bemliese series (manufactured by Asahi Kasei Corporation) can be used as the channel-containing sheet 110 made of fiber. Also, for example, the Mesh #2500 series (manufactured by KB Seiren) can be used as the channel-containing sheet 110 made of mesh.

[0271] (Roll body forming process) 6A, the precursor laminate 111 with the channel-containing sheet is wound to form a roll 112. Specifically, one end in the longitudinal direction of the precursor laminate 111 with the channel-containing sheet is fixed to the surface of a core 150, and then the middle and the other end in the longitudinal direction of the precursor laminate 111 with the channel-containing sheet are wound around the core 150. The core 150 is a winding core and has a substantially cylindrical or columnar shape.

[0272] For example, the precursor laminate 111 with the flow path-containing sheet is wound around the core 150 so that one end of the conductor layer 102 in the longitudinal direction comes into contact with the surface of the core 150 .

[0273] As a result, a layer configuration 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. In other words, a roll body 112 is produced, which 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 repeatedly arranged toward the radially outer side of the core 150.

[0274] The outer diameter of the roll body 112 is the outer diameter of the core 150 plus 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. The outer diameter of the roll body 112 is substantially the same as the inner diameter of an extraction tank 161 of a supercritical fluid extraction device 160 described below.

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

[0276] The tension when winding the precursor laminate 111 with the flow path-containing sheet around the core 150 is, for example, 10 N or more, preferably 15 N or more, more preferably 20 N or more, even more preferably 25 N or more, particularly preferably 30 N or more, and also, for example, less than 90 N, preferably 85 N or less, more preferably 80 N or less, even more 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 less than the above upper limit value, the surface roughness (Ra) and maximum height (Rz) of one thickness-wise surface of the porous resin layer 105 (the contact surface with the bonding layer 106) can be reduced, and thus the adhesion between the layers can be improved.

[0278] (Porous process) 6B, the second coating film 105' is made porous by a supercritical fluid extraction device 160. Specifically, the roll body 112 is set in the supercritical fluid extraction device 160, and then a supercritical fluid is caused to flow through the roll body 112, thereby extracting the porosifying agent from the second coating film 105' and making it porous.

[0279] Examples of supercritical fluids include supercritical carbon dioxide and supercritical nitrogen, and preferably supercritical carbon dioxide.

[0280] 6B, the supercritical fluid extraction apparatus 160 includes, for example, an extraction tank 161. The roll body 112 is introduced into the extraction tank 161 of the supercritical fluid extraction apparatus 160.

[0281] The supercritical fluid extraction device 160 may be any of various commercially available supercritical fluid extraction devices (for example, manufactured by Mitsubishi Chemical Corporation, ITEC Corporation, Toyo Koatsu Co., Ltd., and Kobe Steel Air Tech Co., Ltd.).

[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 flows through the channel-containing sheet 110. In the channel-containing sheet 110, the supercritical fluid travels upward along the axial direction of the core 150, contacting the second coating film 105′ and extracting the porosifying agent in the second coating film 105′.

[0283] As a result, the porosifying agent in the second coating film 105' is extracted by the supercritical fluid through the flow path-containing sheet 110. In other words, the porosifying agent is removed from the second coating film 105', making it porous.

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

[0285] As a result, a porous roll body 113 can be obtained in which the second coating film 105' on the roll body 112 is made porous.

[0286] (Channel-containing sheet removal step) 7A, 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' has been made porous. Specifically, the precursor laminate 111 with the flow path-containing sheet in which the second coating film 105' has been made porous is unwound from the porous roll body 113, and the flow path-containing sheet 110 is removed.

[0287] In this way, a porous precursor laminate 109 can be obtained.

[0288] (Heating process) 7B, the porous precursor laminate 109 is heated. Specifically, when the first coating film 104′ and the second coating film 105′ are made of a polyimide resin precursor, the porous precursor laminate 109 is heated to imidize the first coating film 104′ and the second coating film 105′.

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

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

[0291] (Bonding layer and wiring layer formation process) As shown in FIG. 7C, a bonding layer 106 and a wiring layer 107 are formed.

[0292] Specifically, a resin composition containing the resin used as the bonding layer material is applied to one thickness-wise surface of the porous resin layer 105. Thereafter, the wiring layer 107 is disposed on one thickness-wise surface of the bonding layer 106.

[0293] In this manner, the porous laminate 100 can be manufactured.

[0294] (Action and effect) In the porous laminate 1 of the present invention, the thickness of the porous resin layer 5 is 50 μm or less. Therefore, the flexibility is excellent. Furthermore, in the porous laminate 1 of the present invention, the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 5 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.

[0295] 4. Variations In the following modifications, the same components and steps as those in the above-described embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, each modification can achieve the same effects as those in the above-described embodiment unless otherwise specified. Furthermore, the embodiment and modifications can be combined as appropriate.

[0296] (Modification of flexible multilayer circuit board) figure 2 In the flexible multilayer circuit board 10 shown in Fig. 1, at one end in the longitudinal direction, the first conductor layer 21 has the first terminal portion 21b and the second conductor layer 22 has the second terminal portion 22b, and at the other end in the longitudinal 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, the present invention is not limited to this.

[0297] That is, it is sufficient that either the first conductor layer 21 or the second conductor layer 22 has a terminal portion at each of both longitudinal ends. Specifically, although not shown, the first conductor layer 21 may have the first terminal portion 21b and the second conductor layer 22 may not have the second terminal portion 22b at each of both longitudinal ends. Alternatively, the first conductor layer 21 may not have the first terminal portion 21b and the second conductor layer 22 may have the second terminal portion 22b at each of both longitudinal ends. Furthermore, it is also possible that 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 at one longitudinal end, and the first conductor layer 21 has the first terminal portion 21b and the second conductor layer 22 does not have the second terminal portion 22b at the other longitudinal end.

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

[0299] In addition, the second via connection portion 82 electrically connects the terminal portion and the wiring portion 70, and therefore its arrangement is changed depending on the arrangement of the first terminal portion 21b and the second terminal portion 22b. Furthermore, the arrangement of the reinforcing base material 95 is also changed depending on the arrangement of the first terminal portion 21b and the second terminal portion 22b. [Example]

[0300] The present invention will be described in more detail below with reference to examples and comparative examples. It should be noted that the present invention is not limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be substituted with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of the Invention" above.

[0301] Example 1 First, a conductor layer 102 made of copper and having a thickness of 30 μm was prepared.

[0302] Next, a polyimide precursor solution was prepared in the following manner.

[0303] A diamine component solution was prepared by dissolving 0.66 mol of p-phenylenediamine (PDA) (primary diamine), 0.22 mol of 4,4'-oxydianiline (ODA) (secondary diamine), and 0.22 mol of 4-aminophenyl-4-aminobenzoate (APAB) (tertiary diamine) in N-methyl-2-pyrrolidone (NMP). Subsequently, 1.00 mol of 3,3'-4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the diamine component solution and stirred at 80°C. The stirring was stopped and the mixture was allowed to cool, preparing a polyimide precursor solution. The solids concentration of the polyimide precursor solution was 13% by mass.

[0304] To 100 parts by mass of the polyimide precursor solution, 150 parts by mass of polyoxyethylene dimethyl ether (grade: MM400, manufactured by NOF Corp.) with a weight-average molecular weight of 400 as a porosifying agent and 3 parts by mass of PTFE powder with a particle size of 1 μm or less as a nucleating agent were added, and the mixture was stirred to obtain a transparent, homogeneous solution. 4 parts by mass of 2-methylimidazole was added as an imidization catalyst to prepare a varnish.

[0305] The prepared varnish was applied to one surface in the thickness direction of the conductor layer 102 and heated and dried to form a first coating film 104'. The first coating film was heated and dried at 140°C for 50 seconds to remove the NMP. In this way, a first coating film 104' having a thickness of approximately 3 μm was formed on one surface in the thickness direction of the conductor layer 102.

[0306] Furthermore, a similar polyimide precursor solution was prepared with a solids concentration of 50% by mass. After preparation, a varnish containing a porosifying agent, a nucleating agent, and an imidization solvent was applied to one side of the thickness direction of the first coating film 104' and heated and dried to form a second coating film 105'. The second coating film was heated and dried at 150°C for 20 minutes to remove the NMP. This resulted in a second coating film 105' with a thickness of approximately 25 μm being formed on one side of the thickness direction of the first coating film 104'.

[0307] Next, TA30B (thickness: 0.26 mm, manufactured by Asahi Kasei Corporation) was prepared as the flow path-containing sheet 110. The flow path-containing sheet 110 was brought 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 having, in order toward one side in the thickness direction, the conductor layer 102, the first coating film 104′, the second coating film 105′, and the flow path-containing sheet 110.

[0308] The prepared precursor laminate 111 with the flow path-containing sheet was wound around a core 150 having an outer diameter of 85 mm with the flow path-containing sheet 110 facing inward to produce a roll body 112 having an outer diameter of 170 mm. The tension when 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 apparatus 160. The inner diameter of the extraction tank 161 of the supercritical fluid extraction apparatus 160 was 170 mm. Then, the temperature was set to 40°C, and carbon dioxide pressurized to 30 MPa (carbon dioxide in a supercritical state) was passed through the tank at a flow rate of 30 kg / h for 8 hours to extract and remove the porosifying agent and promote phase separation of the remaining NMP and pore formation.

[0310] Thereafter, the carbon dioxide was decompressed over 5 hours, and after being opened to the atmosphere, the roll body 112 was recovered. Here, the carbon dioxide circulating in the extraction tank 161 was once decompressed to 4.5 MPa after leaving the extraction tank, becoming gaseous and being separated from the porosifying agent. The separated porosifying agent was accumulated in the porosifying agent accumulation section. In this way, a porous roll body 113 with a porous second coating film 105' was obtained.

[0311] Next, the porous precursor laminate 109 with the second coating film 105' made porous was unwound from the porous roll body 113, and the flow path-containing sheet 110 was removed. After removal, the first coating film 104' and the second coating film 105' were imidized by heating in a heating device at 380°C for 2 hours. This resulted in the formation of a 3 μm-thick base resin layer 104 (non-porous polyimide layer) and a 25 μm-thick porous resin layer 105 (porous polyimide layer).

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

[0313] Next, a wiring layer 107 made of copper and having a thickness of 18 μm was adhered to one surface of the bonding layer 106 in the thickness direction.

[0314] As a result of the above, a porous laminate 100 was produced, which has a conductor layer 102, an undercoat resin layer 104, a porous resin layer 105, a bonding layer 106, and a wiring layer 107 in that order on one side in the thickness direction, as shown in Figure 1.

[0315] Examples 2 and 3 and Comparative Examples 1 and 2 As shown in Table 1, the porous laminates 100 of Examples 2 and 3 and Comparative Examples 1 and 2 were produced in the same manner as in Example 1, except that the tension applied when winding around the core 150 was changed.

[0316] Comparative Example 3 The porous laminate 100 of Comparative Example 3 was produced 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] For the porous laminates 100 of each Example and Comparative Example, a digital microscope (manufactured by KEYENCE Corporation) was used to measure the surface roughness (Ra) and maximum height (Rz) of one surface in the thickness direction of the porous resin layer 105 before the bonding layer 106 was adhered. The results are shown in Table 1. Furthermore, for the porous laminates 100 of each Example and Comparative Example, the surface roughness (Ra) and maximum height (Rz) of one surface in the thickness direction of the first coating film 104' before the formation of the second coating film 105' were measured. The surface roughness (Ra) and maximum height (Rz) of one surface in the thickness direction of the first coating film 104' were taken as the surface roughness (Ra) and 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 and a width of 1 mm to prepare a sample for measuring peel strength. Next, in accordance with JIS C 6471, a cut was made from the end of the long side of each prepared sample for measuring peel strength. Distribution The peel strength was measured when the line layer 107 was peeled off in a direction 90° from the peel surface. The peeling speed was 50 mm / min. Evaluation was performed according to the following criteria. The results are shown in Table 1. {standard} ◎: Peel strength is 1.2N / mm or more ○: Peel strength is 0.8N / mm or more and less than 1.2N / mm △: Peel strength is 0.5N / mm or more and less than 0.8N / mm ×: Peel strength is less than 0.5 N / mm

[0319] [Boldability] The porous laminate 100 of each Example and Comparative Example was cut into a length of 100 mm and a width of 10 mm to prepare samples for MIT testing. The folding endurance of each porous laminate 100 in both the MD and TD directions was evaluated. Therefore, for each Example and Comparative Example, a sample with the MD direction corresponding to the length direction and a sample with the TD direction corresponding to the length direction were prepared. The prepared samples were subjected to a bending test using an MIT testing machine (product name: BE-204, manufactured by Tester Sangyo Co., Ltd.) in accordance with JIS C 6471. In the bending test, a load was applied so that a tension of 4.9 N was applied to the sample. The sample was also bent in both directions at a bending angle of 135° (-135° to +135° in both directions) at a rate of approximately 175 times / min. The number of times until the sample broke was measured, and the average value was taken as the number of times for folding endurance. Evaluation was performed according to the following criteria. The results are shown in Table 1. {standard} ○: 150 times or more in both MD and TD directions △: 50 times or more and less than 150 times in both MD and TD ×: Less than 50 times in either the MD or TD direction

[0320] [Table 1] [Explanation of symbols]

[0321] 1. Porous laminate 2 Conductor layer 3. Insulation layer 4 Base resin layer 5 Porous resin layer 6 Bonding Layer 7 wiring layer

Claims

1. A conductor layer and an insulating layer are provided 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 this order toward one side in a thickness direction; 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, A porous laminate, wherein 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.

2. 2. The porous laminate according to claim 1, wherein the maximum height (Rz) of one surface in the thickness direction of the resin underlayer is 5 [mu]m or less.

3. 2. 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 10 μm or less.

4. A device comprising a first porous laminate, a second porous laminate, and a wiring portion; the first porous laminate includes a first conductor layer and a first insulating layer in this order toward the other side in the thickness direction, the first insulating layer includes a first base resin layer, a first porous resin layer disposed on the other side of the first base resin layer in the thickness direction, and a first bonding layer disposed on the other side of the first porous resin layer in the thickness direction; The thickness of the first porous resin layer is 50 μm or less, the maximum height (Rz) of the surface of the first porous resin layer on the first bonding layer side is 16 μm or less; a maximum height (Rz) of a surface of the first porous resin layer on the first bonding layer side is greater than a maximum height (Rz) of a surface of the first base resin layer on the first porous resin layer side; the second porous laminate includes a second conductor layer and a second insulating layer in this order toward one side in a thickness direction; the second insulating layer includes a second base resin layer, a second porous resin layer disposed on one side of the second base resin layer in a thickness direction, and a second bonding layer disposed on one side of the second porous resin layer in a thickness direction, the thickness of the second porous resin layer is 50 μm or less; the maximum height (Rz) of the surface of the second porous resin layer on the second bonding layer side is 16 μm or less; a maximum height (Rz) of a surface of the second porous resin layer on the second bonding layer side is greater than a maximum height (Rz) of a surface of the second base resin layer on the second porous resin layer side; the first porous laminate and the second porous laminate are laminated in order toward the other side in the thickness direction so that the first bonding layer and the second bonding layer face each other; The wiring portion is embedded in either the first bonding layer or the second bonding layer.

5. the first insulating layer and the second insulating layer have a plurality of first through holes penetrating between the first conductor layer and the second conductor layer in a thickness direction; a plurality of first via connection portions filled in the plurality of first through holes, the first via connection portions being in contact with the first conductor layer and the second conductor layer so as to electrically connect the first conductor layer and the second conductor layer; The flexible multilayer circuit board according to claim 4 , wherein the plurality of first via connection portions are arranged such that the wiring portion is located between the first via connection portions.

6. At both ends in the longitudinal direction, one of the first conductor layer and the second conductor layer has a terminal portion, one of the first insulating layer and the second insulating layer has a second through hole penetrating between the terminal portion and the wiring portion in a thickness direction; 6. The flexible multilayer circuit board according to claim 5, further comprising: a second via connection portion filled in the second through hole, the second via connection portion contacting the terminal portion and the wiring portion so as to electrically connect the terminal portion and the wiring portion.

7. Further, a reinforcing substrate is provided at each end in the longitudinal direction, 7. The flexible multilayer circuit board according to claim 6, wherein the reinforcing base material is disposed on one thickness-wise side of the first conductor layer that does not have the terminal portion, or on the other thickness-wise side of the second conductor layer that does not have the terminal portion.

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