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 Art

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

[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

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, a porous laminate used for a flexible multilayer circuit board is required to have excellent adhesion between layers. Further, when a flexible multilayer circuit board is used in a small electronic device or the like, it is necessary to connect components in a limited space, so the porous laminate is desired to have excellent flexibility.

[0006] However, the low dielectric substrate of Patent Document 1 has a problem that the adhesion between layers is insufficient.

[0007] An object of the present invention is to provide a porous laminate and a flexible multilayer circuit board that are excellent in adhesion and flexibility.

Means for Solving the Problems

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

[0009] The present invention [2] includes the porous laminate according to [1], wherein the maximum height (Rz) on one side in the thickness direction of the base 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) on one side in the thickness direction of the porous resin layer exceeds 5 μm and is 10 μm or less.

[0011] The present invention [4] includes two porous laminates according to any one of [1] to [3], and one porous laminate and the other porous laminate are laminated in order toward the other side in the thickness direction such that the bonding layer of the one porous laminate faces the bonding layer of the other porous laminate. It includes a flexible multilayer circuit board including a wiring portion embedded in either the bonding layer of 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 according to [4], wherein the insulating layer of the one porous laminate and the insulating layer of the other porous laminate have a plurality of first through-holes penetrating in the thickness direction between the conductor layer of the one porous laminate and the conductor layer of the other porous laminate, and a first via connection portion filled in the plurality of first through-holes, and includes a plurality of first via connection portions that 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 such that the wiring portion is positioned therebetween.

[0013] The present invention [6] includes a flexible multilayer circuit board according to [5], wherein at each of both ends in the longitudinal direction, 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 penetrating in the thickness direction between the terminal portion and the wiring portion, and a second via connection portion filled in the second through-hole, and includes a second via connection portion that 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], wherein at each of both ends in the longitudinal direction, a reinforcing base material is further provided, and the reinforcing base material is disposed on one side in the thickness direction of the conductor layer of the one porous laminate having no terminal portion or on the other side in the thickness direction of the conductor layer of the other porous laminate having no terminal portion.

Advantages of the Invention

[0015] In the porous laminate of the present invention, the thickness of the porous resin layer is 50 μm or less. Therefore, the stress applied to the end of the porous laminate can be relaxed, and it has excellent flexibility. Further, in the porous laminate of the present invention, the maximum height (Rz) on one side in the thickness direction of the porous resin layer is 16 μm or less, and the maximum height (Rz) on one side in the thickness direction of the porous resin layer is larger than the maximum height (Rz) on one side in the thickness direction of the base resin layer. Therefore, the adhesion between the layers is excellent.

[0016] Since the flexible multilayer circuit board of the present invention includes the above-described porous laminate, it has excellent adhesion and excellent flexibility.

Brief Description of Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0018] 1. Porous laminate Referring to FIG. 1, a porous laminate 1 according to an embodiment of the present invention will be described.

[0019] In FIG. 1, the vertical direction of the paper surface indicates the thickness direction of the porous laminate 1. The left - right 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 orthogonal to the thickness direction. The porous laminate 1 has a substantially flat plate shape. The porous laminate 1 has flexibility.

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

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

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

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

[0025] Examples of the material of the conductor layer 2 include metals. Examples of the metals include copper, iron, silver, gold, aluminum, nickel, and their alloys (stainless steel, bronze). Preferably, copper is included.

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

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

[0028] <Insulating layer> As shown in FIG. 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 in the thickness direction of the conductor layer 2.

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

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

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

[0032] Examples of the material (or raw material) of the underlayer resin layer 4 include resins. The resin is not particularly limited as long as it can be used as an insulating material in a wiring circuit board. Examples of the resin include polycarbonate resin, polyimide resin, fluorinated polyimide resin, epoxy resin, phenol resin, urea resin, melamine resin, diallyl phthalate resin, silicone resin, thermosetting urethane resin, fluororesin, and liquid crystal polymer. Preferably, polyimide resin and liquid crystal polymer are mentioned, and more preferably, polyimide resin is mentioned.

[0033] Since the underlayer resin layer 4 improves the adhesion between layers, it is preferably non-porous and a solid dense film. That is, the underlayer resin layer 4 is preferably a non-porous polyimide resin layer.

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

[0035] The thickness of the underlayer resin layer 4 is, for example, 0.1 μm to 50 μm, preferably 0.5 μm to 20 μm, more preferably 1.0 μm to 10 μm, 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) in one aspect (contact surface with the porous resin layer 5) in the thickness direction of the underlayer resin layer 4 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, still 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 surface in the thickness direction of the underlayer 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, still 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, still more preferably 3.2 μm or less, particularly preferably 3.0 μm or less.

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

[0039] Note that the maximum height (Rz) indicates the maximum height conforming to JIS B 0601-2001. (The same applies hereinafter.)

[0040] The surface roughness (Ra) of one surface in the thickness direction of the underlayer resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.10 μm to 3.0 μm, preferably 0.20 μm to 2.0 μm, more preferably 0.25 μm to 1.5 μm, still 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 surface in the thickness direction of the underlying resin layer 4 (the contact surface with the porous resin layer 5) is, for example, 0.10 μm or more, preferably 0.20 μm or more, more preferably 0.25 μm or more, still more preferably 0.30 μm or more, particularly preferably 0.35 μm or more, most preferably 0.40 μm or more. Also, for example, it is 3.0 μm or less, preferably 2.0 μm or less, more preferably 1.5 μm or less, still more preferably 1.2 μm or less, particularly preferably 1.0 μm or less, most preferably 0.8 μm or less.

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

[0043] Note that the surface roughness (Ra) indicates the arithmetic mean surface roughness conforming to JIS B 0601 - 2001. (The same shall apply hereinafter.)

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

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

[0046] The dielectric constant of the base resin layer 4 at a frequency of 100 GHz is, for example, 1.0 to 4.5, preferably 1.0 to 4.0, more preferably 1.0 to 3.5, and even 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 measured by the resonator method using a frequency of 100 GHz.

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

[0050] The dielectric 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 tangent of the underlying resin layer 4 is 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. Further, the porous resin layer 5 is a layer that lowers the dielectric constant of the porous laminate 1. That is, if the porous resin layer 5 is provided, the dielectric constant can be lowered.

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

[0054] Examples of the material (or raw material) of the porous resin layer 5 include resins. The resin is not particularly limited as long as it is used as an insulating material in a wiring circuit board. Examples of the resin include 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. Preferably, polyimide resin and liquid crystal polymer are mentioned, and more preferably, polyimide resin is mentioned.

[0055] The porous resin layer 5 is porous in order to lower 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 in 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 in the porous resin layer 5 is, for example, 50% or more, preferably 60% or more, more preferably 70% or more, still more preferably 80% or more, and, for example, less than 100%, preferably 99% or less.

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

[0059] Note that the porosity of the porous resin layer 5 is obtained by calculation based on the following formula when the material of the porous resin layer 5 is a polyimide resin, that is, when it is a porous polyimide resin layer. Dielectric constant of porous polyimide resin layer = Dielectric constant of air × Porosity + Dielectric constant of polyimide × (1 - Porosity)

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

[0061] The thickness of the porous resin layer 5 is, for example, 1 μm to 50 μm, preferably 5 μm to 45 μm, more preferably 10 μm to 40 μm, 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 higher than the above lower limit value, the dielectric constant can be lowered. Also, if the thickness of the porous resin layer 5 is equal to or lower than the above upper limit value, it has excellent folding resistance.

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

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

[0065] If the maximum height (Rz) in one direction in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is within the above range, the adhesion to the bonding layer 6 is excellent. Specifically, if the maximum height (Rz) in one direction in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is equal to or greater than the above lower limit value, the adhesion to the bonding layer 6 is excellent due to the anchor effect. Further, if the maximum height (Rz) in one direction in the thickness direction of the porous resin layer 5 (the contact surface with the bonding layer 6) is equal to or less than the above upper limit value, the contact area with the bonding layer 6 can be increased, the adhesion to the bonding layer 6 is improved, and furthermore, since the thickness variation 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 contact surface with the bonding layer 6) is, for example, 0.10 μm to 3.0 μm, preferably 0.20 μm to 2.0 μm, more preferably 0.25 μm to 1.5 μm, still more preferably 0.30 μm to 1.2 μm, particularly preferably 0.35 μm to 1.0 μm, most preferably 0.38 μm to 0.70 μm.

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

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

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

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

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

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

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

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

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

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

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

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

[0084] The ratio of the thickness of the underlying 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, and more preferably 0.2 or less.

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

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

[0087] [Bonding layer] The bonding layer 6 has a thickness. The bonding layer 6 has a substantially flat plate shape. Also, the bonding layer 6 is an adhesive layer that bonds between layers.

[0088] As shown in FIG. 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 contacts one surface in the thickness direction of the porous resin layer 5.

[0089] The material (or raw material) of the bonding layer 6 is not particularly limited as long as it can be used as an insulating material in a wiring circuit board. Examples of the material of the bonding layer 6 preferably include low-dielectric materials. Examples of the material of the bonding layer 6 include resins. 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. Preferably, polyimide resin is mentioned.

[0090] Since the bonding layer 6 improves the adhesion between layers, it is preferably non-porous and a solid dense film. That is, the bonding layer 6 is preferably a non-porous polyimide resin layer.

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

[0092] The dielectric constant of the bonding layer 6 at a frequency of 100 GHz is, for example, 1.0 to 3.5, preferably 1.0 to 3.2, more preferably 1.0 to 3.0, 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, still 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 tangent of the bonding layer 6 at a frequency of 100 GHz is, for example, 0 to 0.005, preferably 0 to 0.004, more preferably 0 to 0.003, still more preferably 0 to 0.002.

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

[0097] The dielectric tangent of the bonding layer 6 is 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, particularly preferably 20 μm to 40 μm.

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

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

[0101] 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, particularly preferably 15 μm to 20 μm.

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

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

[0105] Note that 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 bending times of the porous laminate 1 is, for example, 50 times or more, preferably 100 times or more, more preferably 120 times or more, still more preferably 140 times or more, particularly preferably 150 times or more, and most preferably 175 times or more. The upper limit value of the number of bending times of the porous laminate 1 is not particularly limited.

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

[0108] Note that the number of bending times of the porous laminate 1 can be measured by the method described in the examples below.

[0109] 2. Flexible Multilayer Circuit Board The flexible multilayer circuit board 10 according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4.

[0110] In FIG. 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] In FIGS. 3 and 4, 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 width direction (short side direction) of the flexible multilayer circuit board 10. The depth direction of the paper surface 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 orthogonal to the thickness direction. The flexible multilayer circuit board 10 has a substantially flat plate shape that is long in the longitudinal direction. Note that the longitudinal direction is orthogonal 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 above-mentioned porous laminates 1. One porous laminate (first porous laminate 11) and the other porous laminate (second porous laminate 12) are laminated 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 and the bonding layer (second bonding layer 62) of the second porous laminate 12 face each other. Further, the flexible multilayer circuit board 10 includes a wiring portion 70 embedded in one of the bonding layers of the first bonding layer 61 and 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 one of the bonding layers of the first bonding layer 61 and the second bonding layer 62. Note that, although details will be described later, the first bonding layer 61 and the second bonding layer 62 may be integrated to form one bonding layer 60.

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

[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] FIGS. 2 and 3 show a part of each cross-sectional view of the flexible multilayer circuit board 10. Specifically, the flexible multilayer circuit board 10 includes a plurality of the configurations shown in FIGS. 2 and 3 in the width direction.

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

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

[0120] In addition, the first terminal portion 21b and the second terminal portion 22b described later may be collectively referred to as a 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] As shown in FIG. 2, the first conductor layer 21 is disposed on one side in the thickness direction of the first base resin layer 41. Specifically, the first conductor layer 21 is disposed on one surface of the first base resin layer 41 in the thickness direction. That is, the first conductor layer 21 is in contact with one surface of the first base resin layer 41 in the thickness direction.

[0123] When projected in the thickness direction, the first conductor layer 21 is disposed opposite to the second conductor layer 22, which will be described later, so as to overlap with the wiring portion 70. That is, the first conductor layer 21 and the second conductor layer 22 are disposed opposite to each other so as to overlap with the wiring portion 70 when projected in the thickness direction.

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

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

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

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

[0128] As shown in FIG. 4, at one end in the longitudinal direction, the center in the width direction of the first ground conductor portion 21a is cut out toward the other end side in the longitudinal direction so that the first terminal portion 21b can be disposed. Specifically, although not shown, at one end in the longitudinal direction, the first ground conductor portion 21a has a plurality of the above-mentioned cutouts at intervals in the width direction.

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

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

[0131] {The first terminal portion} Although not shown, the first terminal portion 21b receives and transmits signals such as signals via signal terminals. Examples of the signal include a differential signal. The signal includes, for example, a small current of less than 1 A.

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

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

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

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

[0136] Although not shown, a plurality of first terminal portions 21b are disposed at intervals in the width direction. Specifically, the first ground conductor portions 21a and the first terminal portions 21b are alternately disposed at intervals in the width direction.

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

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

[0139] As shown in FIGS. 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 a first ground conductor portion 21a and a second ground conductor portion 22a described later.

[0140] Further, either one of the first insulating layer 31 and 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 both ends in the longitudinal direction.

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

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

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

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

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

[0146] As shown in FIG. 2, the first bonding layer 61 is disposed on the other side in the thickness direction of the first porous resin layer 51. Specifically, the first bonding layer 61 contacts the other surface in the thickness direction of the first porous resin layer 51. Further, the first bonding layer 61 is disposed on one side in the thickness direction of the second bonding layer 62 described later. Specifically, the first bonding layer 61 contacts one surface in the thickness direction 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 portion> The wiring portion 70 is formed by patterning the above-described wiring layer 7.

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

[0150] The wiring portion 70 has a thickness. The wiring portion 70 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 arranged on the other side in the thickness direction of the first bonding layer 61. Specifically, the wiring portion 70 is arranged on the other side in the thickness direction of the first bonding layer 61. Further, the wiring portion 70 is in contact with the other surface in the thickness direction of the first bonding layer 61.

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

[0154] The material of the wiring portion 70 is the same as that 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 above-described 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 porous laminate 12 includes a second conductor layer 22 and a second insulating layer 32 arranged on the other surface in the thickness direction of the second conductor layer 22. Note that the second porous laminate 12 does not include the wiring portion 70.

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

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

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

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

[0161] The second conductor layer 22 has a second ground conductor portion 22a and, if necessary, a second terminal portion 22b. Preferably, it has the second ground conductor portion 22a and the second terminal portion 22b. Specifically, as shown in FIG. 2, the second conductor layer 22 has the second ground conductor portion 22a and further has the second terminal portion 22b at the other end in the longitudinal direction.

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

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

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

[0165] Although not shown, at the other longitudinal end, the center in the width direction of the second ground conductor portion 22a is notched toward one longitudinal end side so that the second terminal portion 22b can be arranged. Specifically, at the other longitudinal end, the second ground conductor portion 22a includes a plurality of the notches at intervals in the width direction.

[0166] Although not shown, an earth 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 portion} Although not shown, the second terminal portion 22b is connected to a connector via a signal terminal and receives and transmits signals and the like. Examples of the signal include a differential signal. The signal includes, for example, a small current of less than 1 A.

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

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

[0171] Although not shown, the second terminal portion 22b is arranged to face the wiring portion 70.

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

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

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

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

[0176] As 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] Further, the first insulating layer 31 and / or the second insulating layer 32 have second through holes 72 that penetrate between the terminal portion and the wiring portion 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 thickness. The second base resin layer 42 has a substantially flat plate shape. The second base resin layer 42 is a layer that enhances the adhesion between the second porous resin layer 52 and the second conductor layer 22.

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

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

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

[0182] {Second bonding layer} The second bonding layer 62 has a thickness. The second bonding layer 62 has a substantially flat plate shape. Also, the second bonding layer 62 is an adhesive layer that bonds between layers. Specifically, the first porous laminate 11 and the second porous laminate 12 are bonded by the second bonding layer 62 and the second bonding layer 62.

[0183] As shown in FIG. 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 in the thickness direction of the second porous resin layer 52.

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

[0185] <Bonding layer> The bonding layer 60 is a layer formed by integrating the first bonding layer 61 and the second bonding layer 62. That is, the interface between the first bonding layer 61 and the second bonding layer 62 may not be observed.

[0186] Note that the first bonding layer 61 is disposed on one side in the thickness direction of the second bonding layer 62. Specifically, the first bonding layer 61 contacts one surface in the thickness direction of the second bonding layer 62 except for the portion that contacts the wiring portion 70. Then, the first bonding layer 61 and the second bonding layer 62 form a single bonding layer 60.

[0187] That is, the bonding layer 60 embeds 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 above thickness of the bonding layer 60 is the total thickness including the thickness of the wiring portion 70 to be embedded. Also, the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 and the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 are not particularly limited and may be the same or different. Considering the manufacturing method, the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 and the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 are preferably different. Note that the thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is the distance from one surface in the thickness direction of the wiring portion 70 to one surface in the thickness direction of the bonding layer 60, and the thickness of the bonding layer 60 on the other side in the thickness direction of the wiring portion 70 is the distance from the other surface in the thickness direction of the wiring portion 70 to the other surface in the thickness direction of the bonding layer 60.

[0190] The thickness of the bonding layer 60 on one side in the thickness direction of the wiring portion 70 is, for example, 1 μm to 100 μm, preferably 3 μm to 70 μm, more preferably 5 μm to 50 μm, still more preferably 7 μm to 30 μm, 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, still more preferably 18 μm to 50 μm, particularly preferably 20 μm to 40 μm.

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

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

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

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

[0196] Also, as shown in FIGS. 3 and 4, two first via connection portions 81 are arranged in a pair so that the wiring portion 70 is positioned therebetween in the width direction.

[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 portions 81 form a substantially square-shaped ground path.

[0198] The first conductor layer 21 and the second conductor layer 22 are arranged to face each other so as to overlap 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 positioned therebetween. Therefore, the generation of dielectric loss in the wiring portion 70 can be suppressed.

[0199] Also, as shown in FIG. 4, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portions 81 form a substantially U-shaped ground path at one end in the longitudinal direction. The ground path is open toward one side in the thickness direction in a cross-sectional view from the width direction. On the other hand, although not shown, at the other end in the longitudinal direction, the first ground conductor portion 21a, the second ground conductor portion 22a, and the first via connection portions 81 form a substantially inverted U-shaped ground path. In that case, the ground path is open toward the other side in the thickness direction in a cross-sectional view from the width 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 alternately arranged at intervals in the width direction.

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

[0202] The first via connection portion 81 is formed by filling the material of the first via connection portion 81 into the first through hole 71.

[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 portion> The second via connection portion 82 is filled in 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 end in the longitudinal direction, and contacts the second terminal portion 22b and the wiring portion 70 at the other end in the longitudinal direction. More specifically, at one end in the longitudinal direction, one end in the thickness direction of the second via connection portion 82 contacts the other surface in the thickness direction of the first terminal portion 21b, and the other end in the thickness direction of the second via connection portion 82 contacts one surface in the thickness direction of the wiring portion 70. Also, at the other end in the longitudinal direction, the other end in the thickness direction of the second via connection portion 82 contacts one surface in the thickness direction of the second terminal portion 22b, and one end in the thickness direction of the second via connection portion 82 contacts the other surface in the thickness direction of the wiring portion 70. Further, the circumferential side surface of the second via connection portion 82 contacts either the first insulating layer 31 or the second insulating layer 32. Thereby, either the first terminal portion 21b or the second terminal portion 22b and the wiring portion 70 are electrically connected via the second via connection portion 82.

[0206] The second via connection portion 82 is arranged at each of both ends in the longitudinal direction. Also, it is not arranged other than both ends in the longitudinal direction.

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

[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 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] As shown in FIG. 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, respectively. 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 cover insulating layer 91 is in contact with one surface in the thickness direction of the first conductor layer 21. Also, the second cover insulating layer 92 is in contact with the other surface in the thickness direction of the second conductor layer 22.

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

[0216] Examples of the material of the cover insulating layer 90 include the same resin as the material of the first porous resin layer 51.

[0217] The thickness of the cover insulating 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 base material> The reinforcing base material 95 is a base material for reinforcing the flexible multilayer circuit board 10. The reinforcing base material 95 has a flat plate shape. The reinforcing base material 95 is disposed at both ends in the longitudinal direction.

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

[0220] The reinforcing base material 95 is disposed on one side in the thickness direction of the first conductor layer 21 having no first terminal portion 21b or on the other side in the thickness direction of the second conductor layer 22 having no second terminal portion 22b at both ends in the longitudinal direction. Specifically, as shown in FIG. 1, the reinforcing base material 95 includes a first reinforcing base material 96 disposed on one side in the thickness direction of the first cover insulating layer 91 at the other end in the longitudinal direction, and a second reinforcing base material 97 disposed on the other side in the thickness direction of the second cover insulating layer 92 at one end in the longitudinal direction.

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

[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. Preferably, metals are included. Examples of the metal 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 be provided with an adhesive layer between each of the above-described layers. Specifically, an adhesive layer may be provided between the first conductor layer 21 and the first cover insulating layer 91, between the second conductor layer 22 and the second cover insulating layer 92, between the first cover insulating layer 91 and the first reinforcing base material 96, and between the second cover insulating 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 of an adhesive layer commonly used in a wiring circuit board. 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 a porous laminate With reference to FIGS. 5 to 7, a method for manufacturing the porous laminate 100 will be described.

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

[0229] (First coating film formation step) As shown in FIG. 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 (for example, a polyimide resin) as the material of the above-described base resin layer, a porogen, 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] In the above porogen, nucleating agent, and solvent, their types and blending ratios, etc. are described, for example, in WO2018 / 186486.

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

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

[0233] Examples of the diamine component include aromatic diamines and aliphatic diamines. Preferably, aromatic diamines are included.

[0234] Examples of the aromatic diamine include a first diamine, a second diamine, and a third diamine.

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

[0236] The second diamine contains a plurality of aromatic rings and an ether bond disposed therebetween. Examples of the second diamine include oxydianiline. Examples of oxydianiline include 3,4'-oxydianiline and 4,4'-oxydianiline. Preferably, 4,4'-oxydianiline (also known as 4,4-diaminodiphenyl ether) is included. 4,4'-oxydianiline may be abbreviated as ODA.

[0237] The third diamine contains a plurality of aromatic rings and an ester bond disposed therebetween. Examples of the third diamine include aminophenylaminobenzoate, and preferably 4-aminophenyl-4-aminobenzoate is included. 4-aminophenyl-4-aminobenzoate may be abbreviated as APAB.

[0238] In addition to the first to third 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. As the diamine component, preferably, a combination of the first diamine, the second diamine, and the third diamine is exemplified. More preferably, a combination of p-phenylenediamine (PDA), 4,4'-oxydianiline (ODA), and 4-aminophenyl-4-aminobenzoate (APAB) is exemplified.

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

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

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

[0243] Examples of the aromatic tetracarboxylic dianhydrides include benzene tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, biphenyl sulfone tetracarboxylic dianhydride, and naphthalene tetracarboxylic dianhydride. These can be used alone or in combination. As the acid dianhydride containing an aromatic ring, preferably biphenyl tetracarboxylic dianhydride can be mentioned. Examples of the biphenyl tetracarboxylic dianhydride include 3,3'-4,4'-biphenyl tetracarboxylic dianhydride, 2,2'-3,3'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride. As the biphenyl tetracarboxylic dianhydride, preferably 3,3'-4,4'-biphenyl tetracarboxylic dianhydride can be mentioned. Note that 3,3'-4,4'-biphenyl tetracarboxylic dianhydride may be abbreviated as BPDA.

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

[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 amounts.

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

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

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

[0249] If the above heating is insufficient, the first coating film 104' may integrate with the second coating film 105' formed below, and the base resin layer 104 described later may not be formed.

[0250] (Second Coating Film Forming Step) As shown in FIG. 5C, the second coating film 105' is formed on one side in the thickness direction of the first coating film 104'. Specifically, a varnish containing a precursor of the resin (for example, a polyimide resin) as the material of the porous resin layer described above, a porogen, a nucleating agent, and a solvent is prepared, and the varnish is applied on one side in the thickness direction of the first coating film 104' to form the second coating film 105'. Note that the varnish for forming the second coating film 105' preferably has the same composition as the varnish for forming the above first coating film 104', and only the solid content concentration is different. The concentration (solid content concentration) of the polyimide precursor in the varnish is, for example, 10% by mass to 95% by mass, preferably 40% by mass to 75% by mass.

[0251] The varnish is applied on one side in the thickness direction of the first coating film 104' to form the second coating film 105', and is dried by heating. By heating, the removal of the solvent proceeds. The heating temperature is, for example, 130°C to 300°C. The heating time is, for example, 10 minutes to 30 minutes. Also, the above heating may be performed in multiple times.

[0252] Thus, a precursor laminate 108 including 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 can be obtained.

[0253] (Forming Step of Laminate with Channel-Containing Sheet) As shown in FIG. 5D, the channel-containing sheet 110 is disposed on one side 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 has a long and substantially flat plate shape.

[0255] Specifically, the flow path-containing sheet 110 is formed of, for example, fibers and / or a mesh. The fibers are a non-fused or non-woven mesh sheet. In contrast, the mesh is a fused or woven mesh sheet. As a result, the flow path-containing sheet 110 has voids (gaps) partitioned by the fibers and / or the mesh. That is, the flow path-containing sheet 110 is also a void-containing sheet. And these voids form a flow path for the supercritical fluid flowing through the flow path-containing sheet 110. The flow path-containing sheet 110 is preferably formed of fibers.

[0256] Note that the presence or absence of fibers and the presence or absence of being woven in the flow path-containing sheet 110 are confirmed by optical microscope observation.

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

[0258] The flow path-containing sheet 110 may be a single layer or a plurality of layers. Further, when the flow path-containing sheet 110 is a plurality of layers, each layer may be formed of different materials.

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

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

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

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

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

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

[0265] Note that the shape of the void portion of the flow path-containing sheet 110 is not particularly limited, and examples include an amorphous shape, a linear shape, a curved shape, a void shape when fibers are intertwined, a flat plate shape, an ellipsoidal shape, and a spherical shape.

[0266] The surface roughness Ra of the flow path-containing sheet 110 is, from the viewpoint of protecting the surface of the precursor laminate 108, for example, 0.01 μm to 5 μm, preferably 0.05 μm to 3 μm, 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, more preferably 0.1 or less. The lower limit value 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 above upper limit value, the amount of supercritical carbon dioxide (supercritical CO₂) dissolved in the flow path-containing sheet 110 is small, and it can flow sufficiently through the flow path-containing sheet 110. Therefore, the porogen in the sheet of the precursor for the porous body can be extracted more efficiently.

[0269] The solubility S of carbon dioxide in the flow path-containing sheet 110 is measured by using a magnetic suspension balance measuring device (manufactured by RUBOTHERM, BELP / O152) after sufficiently drying the flow path-containing sheet 110, and then using a molding machine (for example, a tabletop molding press manufactured by Imoto Seisakusho) to apply pressure and depressurize at a predetermined temperature (for example, 180 °C to 280 °C) to produce a bubble-free test piece (for example, 20 mmφ, thickness 1 mm to 3 mm), and measuring the mass change when the sample contains carbon dioxide in a carbon dioxide atmosphere at a temperature of 200 °C and a pressure of 30 MPa.

[0270] Commercially available products can be used for the flow path-containing sheet 110. For example, as the flow path-containing sheet 110 made of fibers, the Benrize series (manufactured by Asahi Kasei Corporation) can be used. Also, for example, as the flow path-containing sheet 110 made of a mesh, the Mesh #2500 series (manufactured by KB Seiren) can be used.

[0271] (Roll body forming step) As shown in FIG. 6A, the precursor laminate 111 with the channel-containing sheet is wound to form a roll body 112. Specifically, one end in the longitudinal direction of the precursor laminate 111 with the channel-containing sheet is fixed to the surface of the 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 substantially columnar shape.

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

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

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

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

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

[0277] When winding the precursor laminate 111 with a flow path-containing sheet around the core 150, if the tension is less than or equal to (less than) the above upper limit value, the surface roughness (Ra) and the maximum height (Rz) of one surface in the thickness direction of the porous resin layer 105 (the contact surface with the bonding layer 106) can be reduced, and thus the adhesion between layers can be improved.

[0278] (Porousization process) As shown in FIG. 6B, the second coating film 105' is porousized by a supercritical fluid extraction device 160. Specifically, the roll body 112 is set in the supercritical fluid extraction device 160, and then, by flowing a supercritical fluid through the roll body 112, a porogen is extracted from the second coating film 105' to make it porous.

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

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

[0281] Note that as the supercritical fluid extraction device 160, various commercially available supercritical extraction devices (for example, manufactured by Mitsubishi Chemical Corporation, Itech Corporation, Toyo Koatsu Co., Ltd., and Kobe Steel Airtec Co., Ltd.) can be used.

[0282] After introducing the roll body 112, the supercritical fluid extraction device 160 is driven. Specifically, the supercritical fluid flows into the extraction tank 161 and then circulates through the channel-containing sheet 110. In the channel-containing sheet 110, the supercritical fluid advances upward along the axial direction of the core 150 while contacting the second coating film 105' and extracting the porogen in the second coating film 105'.

[0283] As a result, the porogen in the second coating film 105' is extracted by the supercritical fluid through the channel-containing sheet 110. That is, the porogen is removed from the second coating film 105' and becomes porous.

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

[0285] As a result, in the roll body 112, a porous roll body 113 with the second coating film 105' being porous can be obtained.

[0286] (Channel-containing sheet removal step) As shown in FIG. 7A, the channel-containing sheet 110 is removed from the precursor laminate 111 with the channel-containing sheet having the second coating film 105' being porous. Specifically, the precursor laminate 111 with the channel-containing sheet having the second coating film 105' being porous is drawn out from the porous roll body 113, and the channel-containing sheet 110 is removed.

[0287] As a result, a porous precursor laminate 109 can be obtained.

[0288] (Heating step) As shown in Fig. 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 precursor of a polyimide resin, heating the porous precursor laminate 109 imidizes 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] Thereby, each of the first coating film 104' and the second coating film 105' is 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 as the material of the bonding layer described above is applied to one side in the thickness direction of the porous resin layer 105. Then, the wiring layer 107 is disposed on one side in the thickness direction of the bonding layer 106.

[0293] Thus, the porous laminate 100 can be manufactured.

[0294] (Function 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, it has excellent flexibility. Further, in the porous laminate 1 of the present invention, the maximum height (Rz) on one side in the thickness direction of the porous resin layer 5 is 16 μm or less, and the maximum height (Rz) on one side in the thickness direction of the porous resin layer 5 is larger than the maximum height (Rz) on one side in the thickness direction of the base resin layer 4. Therefore, the adhesion between the layers is excellent.

[0295] 4. Modification example In each of the following modified examples, members and processes similar to those in the above-described embodiment are denoted by the same reference numerals, and detailed descriptions thereof are omitted. Further, each modified example can achieve the same operational effects as the embodiment unless otherwise specified. Furthermore, the embodiment and the modified examples can be combined as appropriate.

[0296] (Modified Example of Flexible Multilayer Circuit Board) 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. 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, it is not limited thereto.

[0297] That is, at each of both ends in the longitudinal direction, either one of the first conductor layer 21 and the second conductor layer 22 may have a terminal portion. Specifically, although not shown, at each of both ends in the longitudinal direction, 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. Also, at each of both ends in the longitudinal direction, 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. Further, at one end in the longitudinal direction, 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 the other end in the longitudinal direction, 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.

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

[0299] Also, since the second via connection portion 82 electrically connects the terminal portion and the wiring portion 70, its arrangement is changed according to the arrangements of the above-described first terminal portion 21b and second terminal portion 22b. Further, the arrangement of the reinforcing base material 95 is also changed according to the arrangements of the above-described first terminal portion 21b and second terminal portion 22b.

Example

[0300] Examples and comparative examples are shown below to explain the present invention more specifically. Note that the present invention is not limited to any examples and comparative examples. Also, specific numerical values such as the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (numerical values defined as "below" or "less than") or lower limit (numerical values defined as "above" or "exceeding") of the corresponding blending ratio (content ratio), physical property values, parameters, etc. described in the above "Mode for Carrying Out the Invention".

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

[0302] Next, a polyimide precursor solution was prepared by the following procedure.

[0303] 0.66 mol of p-phenylenediamine (PDA) (the first diamine), 0.22 mol of 4,4'-oxydianiline (ODA) (the second diamine), and 0.22 mol of 4-aminophenyl-4-aminobenzoate (APAB) (the third diamine) were dissolved in N-methyl-2-pyrrolidone (NMP) to prepare a diamine component solution. Subsequently, 1.00 mol of 3,3'-4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added to the diamine component solution, and the mixture was stirred at 80°C. The stirring was stopped, and the mixture was allowed to cool to prepare a polyimide precursor solution. The solid content concentration of the polyimide precursor solution was 13% by mass.

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

[0305] The prepared varnish was applied to one side in the thickness direction of the conductor layer 102, 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 NMP. Thereby, a first coating film 104' with a thickness of about 3 μm was produced on one side in the thickness direction of the conductor layer 102.

[0306] Furthermore, in the same polyimide precursor solution, a solution with a solid content concentration of 50% by mass was prepared. After preparation, the varnish added with a porogen, a nucleating agent, and an imidization solvent in the same manner as above was applied to one side in the thickness direction of the first coating film 104', 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 NMP. Thereby, a second coating film 105' with a thickness of about 25 μm was produced on one side in the thickness direction of the first coating film 104'.

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

[0308] The prepared precursor laminate 111 with a flow path-containing sheet was wound around a core 150 with an outer diameter of 85 mm so that the flow path-containing sheet 110 was on the inside to produce a roll body 112 with an outer diameter of 170 mm. The tension during winding around the core 150 was 35 N.

[0309] Next, the produced roll body 112 was inserted into the extraction tank 161 of the supercritical fluid extraction device 160. The inner diameter of the extraction tank 161 of the supercritical fluid extraction device 160 was 170 mm. Then, by flowing carbon dioxide (supercritical carbon dioxide) with a temperature of 40 °C and a pressure increased to 30 MPa at a flow rate of 30 kg / h for 8 hours, the porogen was extracted and removed, and the phase separation of the remaining NMP and the formation of pores were promoted.

[0310] Thereafter, carbon dioxide was depressurized over 5 hours and released to the atmosphere, and then the roll body 112 was recovered. Here, the carbon dioxide circulating in the extraction tank 161 was depressurized to 4.5 MPa once after coming out of the extraction tank and became gaseous, thus being separated from the porogen. The separated porogen was accumulated in the porogen accumulation part. In this way, a porous roll body 113 with the second coating film 105' being porous was obtained.

[0311] Next, from the porous roll body 113, a porous precursor laminate 109 with the second coating film 105' being porous was drawn out, and the channel-containing sheet 110 was removed. After the removal, it was heated with a heating device at 380 °C for 2 hours to imidize the first coating film 104' and the second coating film 105'. As a result, a base resin layer 104 (non-porous polyimide layer) with a thickness of 3 μm and a porous resin layer 105 (porous polyimide layer) with a thickness of 25 μm were formed.

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

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

[0314] As described above, as shown in FIG. 1, a porous laminate 100 including a conductor layer 102, a base resin layer 104, a porous resin layer 105, a bonding layer 106, and a wiring layer 107 in this order on one side in the thickness direction was manufactured.

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

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

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

[0318] [Peel strength] The porous laminate 100 of each example and each comparative example was cut into a length of 5 cm × a width of 1 mm to prepare a sample for measuring the peel strength. Then, in accordance with JIS C 6471, from the end in the long side direction of each prepared sample for measuring the peel strength, the peeling strength (peel strength) when the wiring layer 107 was peeled off from the wiring layer 107 in a 90° direction with respect to the peeling surface was measured. The peeling speed was set to 50 mm / min. Evaluation was made according to the following criteria. The results are shown in Table 1. [Criteria] ◎: Peel strength is 1.2 N / mm or more ○: Peel strength is 0.8 N / mm or more and less than 1.2 N / mm △: Peel strength is 0.5 N / mm or more and less than 0.8 N / mm ×: Peel strength is less than 0.5 N / mm

[0319] [Flex resistance] The porous laminates 100 of each example and each comparative example were cut into a length of 100 mm × a width of 10 mm to prepare samples for the MIT test. Note that the folding resistance in the MD direction and the TD direction of each porous laminate 100 was evaluated. Therefore, samples in which the MD direction corresponded to the length direction and samples in which the TD direction corresponded to the length direction were prepared for each example and each comparative example. For the prepared samples, a folding test was performed using an MIT tester (product name: BE-204, manufactured by Tester Sangyo Co., Ltd.) in accordance with JIS C 6471. In the folding test, a load was applied so that a tensile force of 4.9 N was applied to the sample. Also, the sample was folded at a folding angle of 135° in both directions (since it is both directions, -135° to +135°) at a speed of approximately 175 times / min. The number of times until the sample broke was measured, and the averaged value was taken as the number of folding resistance times. Evaluation was performed according to the following criteria. The results are shown in Table 1. {Criteria} ○: In both the MD direction and the TD direction, 150 times or more △: In both the MD direction and the TD direction, 50 times or more and less than 150 times ×: Either the MD direction or the TD direction is less than 50 times

[0320]

Table 1

Explanation of symbols

[0321] 1 Porous laminate 2 Conductor layer 3 Insulating layer 4 Base resin layer 5 Porous resin layer 6 Bonding layer 7 Wiring layer

Claims

1. A porous laminate comprising a conductor layer and an insulating layer provided in this order toward one side in the thickness direction, wherein the insulating layer comprises a base resin layer, a porous resin layer, and a bonding layer provided in this order toward one side in the thickness direction, wherein the thickness of the porous resin layer is 50 µm or less, wherein the maximum height (Rz) on one surface in the thickness direction of the porous resin layer is 16 µm or less, wherein the maximum height (Rz) on one surface in the thickness direction of the porous resin layer is greater than the maximum height (Rz) on one surface in the thickness direction of the base resin layer.

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

3. The porous laminate according to Claim 1, wherein the maximum height (Rz) on one surface in the thickness direction of the porous resin layer exceeds 5 µm and is 10 µm or less.

4. A flexible multilayer circuit board comprising two porous laminates according to any one of Claims 1 to 3, wherein one porous laminate and the other porous laminate are laminated in this order toward the other side in the thickness direction such that the bonding layer of one porous laminate faces the bonding layer of the other porous laminate, and comprising a wiring portion embedded in either one of the bonding layer of one porous laminate and the bonding layer of the other porous laminate.

5. The insulating layer of one porous laminate and the insulating layer of the other porous laminate have a plurality of first through holes penetrating in the thickness direction between the conductor layer of one porous laminate and the conductor layer of the other porous laminate, wherein the plurality of first via connection portions are filled in the plurality of first through holes, and the plurality of first via connection portions are in contact with the conductor layer of one porous laminate and the conductor layer of the other porous laminate so as to electrically connect the conductor layer of one porous laminate and the conductor layer of the other porous laminate, wherein the plurality of first via connection portions are arranged such that the wiring portion is positioned therebetween. The flexible multilayer circuit board according to Claim 4.

6. At each of both ends in the longitudinal direction, either one of the conductor layer of one porous laminate and the conductor layer of the other porous laminate has a terminal portion, and either one of the insulating layer of one porous laminate and the insulating layer of the other porous laminate has a second through hole penetrating in the thickness direction between the terminal portion and the wiring portion. A second via connection portion filled in the second through hole, the second via connection portion including a second via connection portion that contacts the terminal portion and the wiring portion so as to electrically connect the terminal portion and the wiring portion, the flexible multilayer circuit board according to claim 5.

7. At each of both ends in the longitudinal direction, further comprising a reinforcing base material, The reinforcing base material is disposed on one side in the thickness direction of the conductor layer of the one porous laminate having no terminal portion, or on the other side in the thickness direction of the conductor layer of the other porous laminate having no terminal portion, the flexible multilayer circuit board according to claim 6.

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