Flexible multilayer circuit board

Abstract

Insulating layer and, A first conductor layer is disposed on one side in the thickness direction of the insulating layer, A second conductor layer is disposed on the other side in the thickness direction of the insulating layer, A conductive portion that electrically connects the first conductor layer and the second conductor layer, A flexible multilayer circuit board comprising, The insulating layer has a porous insulating region and a non-porous insulating region. A flexible multilayer circuit board in which the non-porous insulating region covers the side surface of the conductive portion.

Description

Technical Field

[0001] The present invention relates to a flexible multilayer printed circuit board.

Background Art

[0002] Since a porous polymer film can obtain a low dielectric constant by porosity, for example, its use as an insulating layer of FPC (Flexible printed circuits) has been promoted.

[0003] For example, a laminate for a wiring board has been proposed which includes a porous film formed of a resin containing at least one of polyamic acid, polyimide, polyamide-imide, polyamide, polyvinylidene fluoride, polybenzoxazole resin, polybenzimidazole resin, polysulfone, polyarylsulfone, and polyethersulfone, and having a plurality of voids in a spherical or interconnected spherical shape, and a conductive film laminated on at least one surface of the porous film (see Patent Document 1). Further, a wiring board has been proposed in which a wiring pattern is formed on at least a part of the conductive film of the laminate for the wiring board (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A flexible multilayer printed circuit board usually has a conductive portion (for example, a conductor via) penetrating through a porous insulating layer for electrical connection between two conductor layers sandwiching the porous insulating layer. A manufacturing example thereof will be described using FIGS. 11A to 11C. First, a laminate having a first conductor layer 102, a porous insulating layer 101, and a second conductor layer 103 in this order is prepared (FIG. 11A). Next, through-holes a are formed in the laminate, penetrating the second conductor layer 103 and the porous insulating layer 101 from the second conductor layer 103 side and reaching the first conductor layer 102 (Figure 11B). The through-holes a can be formed, for example, by laser processing. Next, the through-hole a is plated, and the inside of the through-hole a is filled with copper to form the conductive portion 104 (Figure 11C). In this process, when forming conductive areas, the plating solution may penetrate into the fine pores (pores that constitute the porous structure) on the sides of the through-holes in the porous insulating layer. In particular, in the case of a porous insulating layer with an open-cell structure, the penetration of the plating solution into the pores is greater. If the plating solution remains in the porous insulating layer, there is a risk that the electrical properties of the insulating layer (relative permittivity, dielectric loss tangent, etc.) will deteriorate.

[0006] Therefore, the present invention aims to provide a flexible multilayer circuit board that, when a porous insulator is used for the insulating layer, can prevent liquid from entering the fine pores constituting the porous structure when forming conductive parts, thereby suppressing a decrease in the electrical properties of the insulating layer. [Means for solving the problem]

[0007] The inventors of the present invention conducted diligent research to solve the above problems and, as a result, found that they could solve the above problems, and completed the present invention having the following gist.

[0008] In other words, the present invention encompasses the following: [1] Insulating layer and, A first conductor layer is disposed on one side in the thickness direction of the insulating layer, A second conductor layer is disposed on the other side in the thickness direction of the insulating layer, A conductive portion that electrically connects the first conductor layer and the second conductor layer, A flexible multilayer circuit board comprising, The insulating layer has a porous insulating region and a non-porous insulating region. A flexible multilayer circuit board in which the non-porous insulating region covers the side surface of the conductive portion. [2] The flexible multilayer circuit board according to [1], wherein the width of the nonporous insulating region is 1 μm to 100 μm. [3] Furthermore, it has a wiring section, The aforementioned wiring section is embedded in the porous insulator region. A flexible multilayer circuit board as described in [1] or [2]. [Effects of the Invention]

[0009] According to the present invention, when a porous insulator is used for the insulating layer, it is possible to provide a flexible multilayer circuit board that prevents liquid from entering the fine pores constituting the porous structure when forming conductive parts, thereby suppressing a decrease in the electrical properties of the insulating layer. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view of one embodiment of a flexible multilayer circuit board. [Figure 2] Figure 2 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 3] Figure 3 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 4] Figure 4 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 5A] Figure 5A is a diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 1 (Part 1). [Figure 5B] Figure 5B is a diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 1 (part 2). [Figure 5C] Figure 5C is a diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 1 (part 3). [Figure 5D] Figure 5D is a diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 1 (part 4). [Figure 5E]FIG. 5E is a diagram (part 5) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 1. [Figure 5F] FIG. 5F is a diagram (part 6) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 1. [Figure 6A] FIG. 6A is a diagram (part 1) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6B] FIG. 6B is a diagram (part 2) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6C] FIG. 6C is a diagram (part 3) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6D] FIG. 6D is a diagram (part 4) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6E] FIG. 6E is a diagram (part 5) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6F] FIG. 6F is a diagram (part 6) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 6G] FIG. 6G is a diagram (part 7) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 4. [Figure 7A] FIG. 7A is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 7B] FIG. 7B is a cross-sectional view taken along line A-A' of the flexible multilayer circuit board of FIG. 7A. [Figure 8A] FIG. 8A is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 8B] FIG. 8B is a cross-sectional view taken along line A-A' of the flexible multilayer circuit board of FIG. 8A. [Figure 9] FIG. 9 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 10]Figure 10 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 11A] Figure 11A is a schematic cross-sectional view illustrating a conventional flexible multilayer circuit board (Part 1). [Figure 11B] Figure 11B is a schematic cross-sectional view illustrating a conventional flexible multilayer circuit board (part 2). [Figure 11C] Figure 11C is a schematic cross-sectional view illustrating a conventional flexible multilayer circuit board (part 3). [Modes for carrying out the invention]

[0011] (Flexible multilayer circuit board) The flexible multilayer circuit board of the present invention comprises an insulating layer, a first conductor layer, a second conductor layer, and a conductive portion. The first conductor layer is positioned on one side in the thickness direction of the insulating layer. The second conductor layer is positioned on the other side of the thickness direction of the insulating layer. The conductive portion electrically connects the first conductor layer and the second conductor layer. The insulating layer has a porous insulating region and a non-porous insulating region. The non-porous insulating region covers the sides of the conductive area.

[0012] The non-porous insulating region prevents liquid from entering the fine pores (pores that make up the porous structure) of the porous insulating region when forming conductive areas. As a result, the deterioration of the electrical properties of the insulating layer of the flexible multilayer circuit board can be suppressed.

[0013] In a flexible multilayer circuit board, one non-porous insulating region may cover one side of a conductive portion, or it may cover the sides of two or more conductive portions. For example, if the distance between two adjacent conductive parts is short, one non-porous insulating region may cover the sides of two or more conductive parts. For example, if the distance between two adjacent conductive parts is long, one non-porous insulating region may cover the side of one conductive part. Here, a short distance between two adjacent conductive parts is, for example, when the distance between the two conductive parts is 150 μm or less. The distance between the two conductive parts is the shortest distance between the ends of the two conductive parts. The distance between the two conductive parts may be, for example, 50 μm to 150 μm.

[0014] The width of the non-porous insulator region is not particularly limited, for example, 1 μm to 100 μm, and preferably 1 μm to 50 μm. If the width of the non-porous insulator region is 1 μm or more, the penetration of liquid (e.g., plating solution) into the porous insulator region can be sufficiently suppressed. On the other hand, if the width of the non-porous insulator region is too thick relative to the spacing between adjacent conductive parts, the proportion of the porous insulator region in the insulating layer decreases, and the dielectric constant of the insulating layer increases. In this respect, the width of the non-porous insulator region is preferably 50 μm or less. The width of the non-porous insulator region is the thickness of the non-porous insulator region in a direction perpendicular to the thickness direction of the flexible multilayer circuit board. Note that, as shown in Figure 1 later, if the conductive portion 4 has a tapered shape and the width of the non-porous insulator region 12 varies depending on its position due to this tapered shape, the width (T) of the non-porous insulator region 12 refers to the shortest distance between the conductive portion 4 and the porous insulator region 11. Furthermore, as shown in Figure 8B later, if one non-porous insulator region covers the sides of two or more conductive portions, the width (T) of the non-porous insulator region 12 refers to the shortest distance between the conductive portion 4 and the porous insulator region 11.

[0015] The following describes each component.

[0016] <Insulating layer> Examples of materials for the insulating layer include resin. The type of resin is not limited. Examples of resins include polycarbonate resin, polyimide resin, fluorinated polyimide resin, epoxy resin, phenolic resin, urea resin, melamine resin, diallyl phthalate resin, silicone resin, thermosetting urethane resin, fluororesin, and liquid crystal polymer. Polyimide resin and liquid crystal polymer are preferred.

[0017] The insulating layer has a porous insulating region and a non-porous insulating region. The porous insulating region may be, for example, a porous insulating layer. The insulating layer may, for example, have a non-porous insulating layer and a second non-porous insulating layer. The insulating layer may, for example, have an adhesive insulating layer. The insulating layer may have a second non-porous insulating region.

[0018] Examples of materials for the porous insulating region, non-porous insulating region, second non-porous insulating region, non-porous insulating layer, and second non-porous insulating layer include the resin exemplified as the material for the insulating layer.

[0019] The porous insulator region is porous. The porous insulator region has closed cells and / or open cells. The porosity in the porous insulator region is, for example, 50% or more, preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. Furthermore, the porosity in the porous insulator region is, for example, less than 100%, and even more preferably 99% or less. When the material of the porous insulator region is polyimide resin, the porosity of the porous insulator region can be determined by calculation based on the following formula.

[0020] Relative permittivity of a porous insulator = Relative permittivity of air × porosity + Relative permittivity of polyimide × (1 - porosity) Here, since the relative permittivity of air is 1 and the relative permittivity of polyimide resin is 3.5, the following holds true. Relative permittivity of a porous insulator = porosity + 3.5(1 - porosity) Porosity (%) = [(3.5 - relative permittivity of porous insulator region) / 2.5] × 100

[0021] The relative permittivity in the porous insulator region at a frequency of 10 GHz is, for example, 2.5 or less, preferably 1.9 or less, more preferably 1.6 or less, and also, for example, greater than 1.0. The relative permittivity in the porous insulator region is measured by a resonator method using a frequency of 10 GHz.

[0022] The dielectric loss tangent in the porous insulator region at a frequency of 10 GHz is, for example, 0.006 or less, and also, for example, greater than 0. The dielectric loss tangent in the porous insulator region is measured using a resonator method at a frequency of 10 GHz.

[0023] The material for the adhesive insulating layer is not particularly limited, and various types of adhesives can be used, such as hot-melt adhesives and thermosetting adhesives. Specifically, examples include acrylic adhesives, epoxy adhesives, and silicone adhesives.

[0024] The thickness of the insulating layer is not particularly limited, but is, for example, 5 μm or more, preferably 10 μm or more, and also, for example, 150 μm or less, preferably 100 μm or less.

[0025] <Conductor layer> The material of the conductive layers (first conductive layer, second conductive layer) is not particularly limited and includes, for example, copper, iron, silver, gold, aluminum, nickel, and their alloys (e.g., stainless steel, bronze). Copper is preferred. The conductive layer may be in a patterned form. The thickness of the conductor layer is not particularly limited, but is, for example, 5 μm or more, preferably 10 μm or more, and also, for example, 100 μm or less, preferably 80 μm or less.

[0026] <Conductive section> The material of the conductive part is not particularly limited, and examples include conductors. Examples of conductors include copper, iron, silver, gold, aluminum, nickel, and their alloys (e.g., stainless steel, bronze). Copper is preferred. The size of the conductive portion is not particularly limited, but the diameter is preferably 50 μm or more, more preferably 75 μm or more, and preferably 300 μm or less, and more preferably 200 μm or less.

[0027] <Wiring section> Flexible multilayer circuit boards may have wiring sections. The material of the wiring section is not particularly limited, but examples include copper, iron, silver, gold, aluminum, nickel, and their alloys (e.g., stainless steel, bronze). Copper is preferred. The wiring section is, for example, a signal line.

[0028] Figure 1 shows one embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 1 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive portion 4 has a tapered shape that narrows from the second conductor layer 3 side towards the first conductor layer 2 side. The shape of the conductive portion 4 is not particularly limited and may be cylindrical, for example. Here, "side surface" refers to a surface different from the surface in the thickness direction. The side surface of a conductive portion refers to a surface different from the surface in the thickness direction of the conductive portion. The side surface of a through-hole in a porous insulating layer refers to a surface different from the surface of the opening of the through-hole.

[0029] As shown in Figure 1, the presence of a non-porous insulator region 12 between the conductive portion 4 and the porous insulator region 11 (in other words, the conductive portion 4 and the porous insulator region 11 are not in contact) prevents liquid from entering the fine pores (pores constituting the porous structure) of the porous insulator region 11 when the conductive portion 4 is formed. As a result, the deterioration of the electrical properties of the insulating layer of the flexible multilayer circuit board can be suppressed.

[0030] Flexible multilayer circuit boards may have an adhesive insulating layer. One embodiment of a flexible multilayer circuit board having an adhesive insulating layer is, for example, the same flexible multilayer circuit board as the one shown in Figure 1, except that the adhesive insulating layer is arranged between the porous insulating region 11 and the second conductor layer 3.

[0031] Flexible multilayer circuit boards may have a non-porous insulating layer. One embodiment of a flexible multilayer circuit board having a non-porous insulating layer is, for example, the same flexible multilayer circuit board as the one shown in Figure 1, except that the non-porous insulating layer is arranged between the porous insulating region 11 and the first conductor layer 2.

[0032] A flexible multilayer circuit board may have an adhesive insulating layer and a non-porous insulating layer. One embodiment of a flexible multilayer circuit board having an adhesive insulating layer and a non-porous insulating layer is, for example, the same flexible multilayer circuit board as the one shown in Figure 1, except that the adhesive insulating layer and the non-porous insulating layer are arranged between the porous insulating region 11 and the second conductor layer 3. In this case, for example, the non-porous insulating layer is in contact with the porous insulating region 11 and the adhesive insulating layer. The adhesive insulating layer is in contact with the non-porous insulating layer and the second conductor layer 3.

[0033] Figure 2 shows another embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 2 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive portion 4 has a tapered shape that narrows from the second conductor layer 3 side towards the first conductor layer 2 side. The insulating layer 1 further comprises an adhesive insulating layer 13, a second non-porous insulating layer 14, and a non-porous insulating layer 15. The non-porous insulating layer 15 is located on the second conductor layer 3 side of the porous insulating region 11. The adhesive insulating layer 13 is located on the porous insulating region 11 side of the second conductor layer 3. The non-porous insulating layer 15 is in contact with the porous insulating region 11 and the adhesive insulating layer 13. The adhesive insulating layer 13 is in contact with the non-porous insulating layer 15 and the second conductor layer 3. The second non-porous insulating layer 14 is located on the first conductor layer 2 side of the porous insulating region 11. The second non-porous insulating layer 14 is in contact with the porous insulating region 11 and the first conductor layer 2.

[0034] Figure 3 shows another embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 3 differs from the flexible multilayer circuit board shown in Figure 2 in that it does not have an adhesive insulating layer 13. The flexible multilayer circuit board shown in Figure 3 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive portion 4 has a tapered shape that narrows from the second conductor layer 3 side towards the first conductor layer 2 side. The insulating layer 1 further comprises a second non-porous insulating layer 14 and a non-porous insulating layer 15. The non-porous insulating layer 15 is located on the second conductor layer 3 side of the porous insulating region 11. The non-porous insulating layer 15 is in contact with the porous insulating region 11 and the second conductor layer 3. The second non-porous insulating layer 14 is located on the first conductor layer 2 side of the porous insulating region 11. The second non-porous insulating layer 14 is in contact with the porous insulating region 11 and the first conductor layer 2.

[0035] Figure 4 shows another embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 4 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive part 4 is cylindrical in shape. The insulating layer 1 further comprises a second non-porous insulating layer 14. The second non-porous insulating layer 14 is positioned on the first conductor layer 2 side of the porous insulating region 11. The second non-porous insulating layer 14 is in contact with both the porous insulating region 11 and the first conductor layer 2. The insulating layer 1 further has a second non-porous insulating region 16. The second non-porous insulating region 16 covers the side surface of the porous insulating region 11 at the widthwise edges of the flexible multilayer circuit board. When forming the porous insulating region 11 by coating during the manufacturing of the flexible multilayer circuit board, forming the porous insulating region 11 by coating after providing the second non-porous insulating region 16 prevents the coating liquid from flowing out from the edges and makes the thickness of the porous insulating region 11 uniform.

[0036] Next, we will describe an example of the manufacturing process for a flexible multilayer circuit board. Figures 5A to 5F are diagrams illustrating manufacturing examples of the flexible multilayer circuit board shown in Figure 1. First, a laminate is prepared having the first conductor layer 2, the porous insulating region 11 (porous insulating layer), and the second conductor layer 3 in this order (Figure 5A). Next, through-holes a are formed in the laminate, penetrating the second conductor layer 3 and the porous insulator region 11 from the second conductor layer 3 side and reaching the first conductor layer 2 (Figure 5B). The through-holes a can be formed, for example, by laser processing. Examples of lasers include YAG lasers and carbon dioxide lasers. Next, a non-porous insulator 12a is formed in the through-hole a to fill the through-hole a, and a non-porous insulating layer is formed on the second conductor layer 3 (Figure 5C). The non-porous insulator 12a and the non-porous insulating layer can be formed, for example, by applying a resin-containing solution and drying it. Next, the non-porous insulating layer and a portion of the non-porous insulator 12a filling the through-hole a are removed by etching (Figure 5D). Next, through-holes a are formed in the non-porous insulator 12a, penetrating the non-porous insulator 12a and reaching the first conductor layer 2, such that the outer periphery of the non-porous insulator 12a remains (Figure 5E). The through-holes a can be formed, for example, by laser processing. The remaining outer periphery becomes the non-porous insulator region 12. Next, copper plating is applied to the through-hole a, filling the inside of the through-hole a with copper to form the conductive portion 4 (Figure 5F). The copper plating is, for example, electrolytic copper plating. Before performing electrolytic copper plating, a seed layer may be formed. As a result of the above steps, the flexible multilayer circuit board shown in Figure 1 (Figure 5F) is obtained.

[0037] Next, we will describe another example of the manufacturing of a flexible multilayer circuit board. Figures 6A to 6G are diagrams illustrating manufacturing examples of the flexible multilayer circuit board shown in Figure 4. First, prepare the first conductor layer 2 (Figure 6A). Next, a layered non-porous insulator 14A is formed on the first conductor layer 2 (Figure 6B). The non-porous insulator 14A can be formed, for example, by applying a photosensitive resin solution containing a photosensitive resin and drying it. Next, the nonporous insulator 14A is processed so that a second nonporous insulating layer 14 is formed on the first conductor layer 2, and a cylindrical nonporous insulator 12A for forming a nonporous insulating region 12 and a second nonporous insulating region 16 covering the sides of the porous insulating region 11 at the widthwise end of the flexible multilayer circuit board are formed on the second nonporous insulating layer 14 (Figure 6C). The processing can be carried out, for example, by exposure and development of a photosensitive nonporous insulator 14A to pattern it. Next, a porous insulating region 11 is formed on the second non-porous insulating layer 14 (Figure 6D). Methods for forming the porous insulating region 11 include, for example, applying a solution containing a resin and a porosizing agent onto the second non-porous insulating layer 14, drying it, and then performing porosization. Methods for porosization include, for example, extracting the porosizing agent from the resin film using supercritical carbon dioxide. Another method for forming the porous insulating region 11 is, for example, applying a solution containing a resin and hollow particles onto the second non-porous insulating layer 14 and drying it. Next, a second conductor layer 3 is formed on the porous insulator region 11, the non-porous insulator 14A, and the second non-porous insulator region 16 (Figure 6E). The second conductor layer 3 can be formed, for example, by thermocompressing copper foil as the second conductor layer 3 onto the porous insulator region 11, the non-porous insulator 14A, and the second non-porous insulator region 16. The conditions for thermocompression bonding are not particularly limited. Next, through-holes a are formed in the second conductor layer 3 and the non-porous insulator 12A, penetrating the non-porous insulator 12A and reaching the first conductor layer 2, such that the outer periphery of the non-porous insulator 12A remains (Figure 6F). The through-holes a can be formed, for example, by laser processing. The remaining outer periphery becomes the non-porous insulator region 12. Next, copper plating is applied to the through-hole a, filling the inside of the through-hole a with copper to form the conductive portion 4 (Figure 6G). The copper plating is, for example, electrolytic copper plating. Before performing electrolytic copper plating, a seed layer may be formed. As a result of the above steps, the flexible multilayer circuit board shown in Figure 4 (Figure 6G) is obtained.

[0038] Figures 7A and 7B show another embodiment of the flexible multilayer circuit board. Figure 7A is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. Figure 7B is a cross-sectional view of the flexible multilayer circuit board shown in Figure 7A, taken along line A-A'. The flexible multilayer circuit board shown in Figures 7A and 7B has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive part 4 is cylindrical in shape. The insulating layer 1 further comprises a second non-porous insulating layer 14. The second non-porous insulating layer 14 is positioned on the first conductor layer 2 side of the porous insulating region 11. The second non-porous insulating layer 14 is in contact with both the porous insulating region 11 and the first conductor layer 2.

[0039] In the flexible multilayer circuit board shown in Figures 7A and 7B, as shown in Figure 7B, the two non-porous insulating regions 12 covering the sides of two adjacent conductive portions 4 are separate and independent. The width (T) of the non-porous insulating region 12 covering the sides of the conductive portions 4 is, for example, 1 μm to 100 μm, and preferably 1 μm to 50 μm.

[0040] Figures 8A and 8B show another embodiment of the flexible multilayer circuit board. Figure 8A is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. Figure 8B is a cross-sectional view of the flexible multilayer circuit board shown in Figure 8A, taken along line A-A'. The flexible multilayer circuit board shown in Figures 8A and 8B has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, and a conductive portion 4. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 11 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive part 4 is cylindrical in shape. The insulating layer 1 further comprises a second non-porous insulating layer 14. The second non-porous insulating layer 14 is positioned on the first conductor layer 2 side of the porous insulating region 11. The second non-porous insulating layer 14 is in contact with both the porous insulating region 11 and the first conductor layer 2.

[0041] In the flexible multilayer circuit board shown in Figures 8A and 8B, as shown in Figure 8B, the sides of three adjacent conductive portions 4 are covered by a single non-porous insulating region 12. The distance (L) between two conductive portions 4 covered by a single non-porous insulating region 12 is, for example, 150 μm or less, and between 50 μm and 150 μm. The distance (L) between two conductive portions 4 is the shortest distance between the ends of the two conductive portions 4.

[0042] Figure 9 shows another embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 9 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, a conductive portion 4, and a wiring portion 5. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 comprises a first porous insulating region 21, an adhesive insulating layer 22, a second porous insulating region 23, and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The first porous insulating region 21 and the second porous insulating region 23 are porous insulating layers having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive portion 4 is columnar. The wiring section 5 is embedded in the insulating layer 1. Specifically, the wiring section 5 is embedded in the adhesive insulating layer 22. The wiring section 5 is not in contact with the first conductor layer 2, the second conductor layer 3, or the conductive section 4. The wiring section 5 is, for example, a signal line that transmits electrical signals, and preferably a signal line for high-speed transmission. An example of high-speed transmission is a fifth-generation mobile communication system (5G).

[0043] Examples of methods for manufacturing the flexible multilayer circuit board shown in Figure 9 include the following: First, a first laminate is prepared in which a first conductor layer 2, a porous insulating layer which is the first porous insulating region 21, a first adhesive insulating layer precursor layer, and a conductor layer for wiring section fabrication are stacked in this order. The wiring section 5 and the conductor are formed by patterning the conductor layer for fabricating the wiring section of the first laminate using photolithography (e.g., subtractive method) with a photoresist. A second laminate is prepared in which a second conductor layer 3, a porous insulating layer which is a second porous insulating region 23, and a second adhesive insulating layer precursor layer are stacked in this order. The first laminate on which the wiring section 5 is formed and the second laminate are arranged so that the first adhesive insulating layer precursor layer and the second adhesive insulating layer precursor layer face each other, and then bonded together to obtain a third laminate. In this way, the first adhesive insulating layer precursor layer and the second adhesive insulating layer precursor layer become one to form an adhesive insulating layer 22. In the obtained third laminate, through holes are formed that penetrate the first conductor layer 2, the first porous insulator region 21, the adhesive insulator layer 22, the conductor embedded in the adhesive insulator layer 22, the second porous insulator region 23, and the second conductor layer 3. Then, non-porous insulator regions 12 are formed on the sides of the formed through holes. Finally, the conductive portion 4 is formed. Based on the above, the flexible multilayer circuit board shown in Figure 9 is obtained.

[0044] Figure 10 shows another embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 10 has an insulating layer 1, a first conductor layer 2, a second conductor layer 3, a conductive portion 4, and a wiring portion 5. The first conductor layer 2 is positioned on one side of the thickness direction of the insulating layer 1. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 1. The conductive portion 4 electrically connects the first conductor layer 2 and the second conductor layer 3. The insulating layer 1 has a porous insulating region 31 and a non-porous insulating region 12. The non-porous insulating region 12 covers the side surface of the conductive portion 4. The porous insulating region 31 is a porous insulating layer having through holes that penetrate in the thickness direction. The non-porous insulating region 12 covers the sides of the through holes in the porous insulating layer. The conductive portion 4 is located within the through holes of the porous insulating layer. The conductive part 4 is columnar in shape. The insulating layer 1 further comprises a non-porous insulating layer 32. The non-porous insulating layer 32 is positioned on the second conductor layer 3 side of the porous insulating region 31. The non-porous insulating layer 32 is in contact with the porous insulating region 11 and the second conductor layer 3. The second conductor layer 3 is patterned. The wiring section 5 is arranged on a non-porous insulating layer 32. The wiring section 5 is not in contact with the first conductor layer 2, the second conductor layer 3, and the conductive section 4. The wiring section 5 is, for example, a signal line that transmits electrical signals, and is preferably a signal line for high-speed transmission. An example of high-speed transmission is a fifth-generation mobile communication system (5G). The wiring section 5 and the patterned second conductor layer 3 are located on the same plane. [Explanation of Symbols]

[0045] 1. Insulating layer 2. First Conductor Layer 3. Second Conductor Layer 4. Conductive section 5 Wiring section 11 Porous insulator region 12 Non-porous insulating region 12a Non-porous insulator 12A Non-porous insulator 13 Adhesive insulating layer 14. Second non-porous insulating layer 14A Non-porous insulator 15 Non-porous insulating layer 16. Second non-porous insulating region 21 First porous insulator region 22 Adhesive insulating layer 23. Second porous insulator region 31 Porous insulator region 32 Non-porous insulating layer 101 Porous insulating layer 102 First Conductor Layer 103 Second Conductor Layer 104 Conductive section a Through hole

Claims

1. Insulating layer and, A first conductor layer is disposed on one side in the thickness direction of the insulating layer, A second conductor layer is disposed on the other side in the thickness direction of the insulating layer, A conductive portion that electrically connects the first conductor layer and the second conductor layer, A flexible multilayer circuit board comprising, The insulating layer comprises a porous insulating region, a non-porous insulating region, a second non-porous insulating region, and a non-porous insulating layer. The non-porous insulating region covers the side surface of the conductive portion. The second non-porous insulator region covers the side surface of the porous insulator region at the widthwise end of the flexible multilayer circuit board. The non-porous insulating layer is arranged on the first conductor layer side of the porous insulating region. The non-porous insulating region, the second non-porous insulating region, and the non-porous insulating layer are integrally formed. Flexible multilayer circuit board.

2. The flexible multilayer circuit board according to claim 1, wherein the width of the non-porous insulating region is 1 μm to 100 μm.

3. Furthermore, it has a wiring section, The aforementioned wiring section is embedded in the porous insulator region. The flexible multilayer circuit board according to claim 1.

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