Laminates for circuit boards, and flexible multilayer circuit boards

Abstract

To provide a laminate for circuit boards that can be used in flexible multilayer circuit boards that have excellent flexibility when bent and arranged. [Solution] The solution comprises a metal layer and an insulating layer disposed on one side of the metal layer in the thickness direction, The insulating layer has a porous insulating region and a non-porous insulating region. The insulating layer, in a cross-section of the insulating layer perpendicular to the thickness direction, has a portion in which the porous insulating region, the non-porous insulating region, and the porous insulating region are arranged in this order in the longitudinal direction. Laminate for circuit boards.

Description

Technical Field

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

Background Art

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

[0003] For example, a porous film formed of a resin containing at least one of polyamic acid, polyimide, polyamideimide, polyamide, polyvinylidene fluoride, polybenzoxazole resin, polybenzimidazole resin, polysulfone, polyarylsulfone, and polyethersulfone, and having a plurality of voids in a spherical shape or a shape in which spheres are connected, and a conductive film laminated on at least one surface of the porous film, have been proposed for a laminate for a circuit board (see Patent Document 1). Further, a wiring board in which a wiring pattern is formed on at least a part of the conductive film of the laminate for a circuit board has been proposed (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] Although a porous insulating layer has excellent dielectric properties, on the other hand, the porous insulating layer may have inferior mechanical properties. For example, the porous insulating layer may have inferior flexibility. Therefore, when a flexible multilayer circuit board including a porous insulating layer is bent and arranged at a hinge portion or the like, the flexibility may become insufficient.

[0006] Therefore, the present invention aims to provide a laminate for circuit boards that can be used in flexible multilayer circuit boards that have excellent flexibility when bent and arranged, and a flexible multilayer circuit board using the same. [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] comprising a metal layer and an insulating layer disposed on one side of the metal layer in the thickness direction, The insulating layer has a porous insulating region and a non-porous insulating region. The insulating layer, in a cross-section of the insulating layer perpendicular to the thickness direction, has a portion in which the porous insulating region, the non-porous insulating region, and the porous insulating region are arranged in this order in the longitudinal direction. Laminate for circuit boards. [2] comprising a metal layer and an insulating layer disposed on one side of the metal layer in the thickness direction, The insulating layer has a first porous insulating region and a second porous insulating region. The insulating layer has a cross-section of the insulating layer perpendicular to the thickness direction in which the first porous insulating region, the second porous insulating region, and the first porous insulating region are arranged in this order in the longitudinal direction. The average pore diameter of the second porous insulator region is smaller than the average pore diameter of the first porous insulator region. Laminate for circuit boards. [3] The laminate for circuit board according to [1], wherein the porous insulating region contains hollow particles. [4] The first porous insulator region contains hollow particles, The second porous insulating region contains hollow particles. [2] The laminate for circuit boards described above. [5] A flexible multilayer circuit board having a laminate for circuit boards as described in any of [1] to [4]. [6] The flexible multilayer circuit board according to [5], wherein the metal layer in the laminate for the circuit board has a wiring pattern. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a laminate for circuit boards that can be used in flexible multilayer circuit boards that have excellent flexibility when bent and arranged, and a flexible multilayer circuit board using the same. [Brief explanation of the drawing]

[0010] [Figure 1A] Figure 1A is a schematic cross-sectional view of an example of a first embodiment of a laminate for a circuit board. [Figure 1B] Figure 1B is a cross-sectional view taken along line A-A' in Figure 1A. [Figure 1C] Figure 1C is a top view of an example of a first embodiment of a laminate for a circuit board. [Figure 2A] Figure 2A is a schematic cross-sectional view illustrating an example of the manufacturing of the laminate for circuit boards shown in Figures 1A to 1C (Part 1). [Figure 2B] Figure 2B is a schematic cross-sectional view illustrating an example of the manufacturing of the laminate for circuit boards shown in Figures 1A to 1C (part 2). [Figure 2C] Figure 2C is a schematic cross-sectional view illustrating an example of the manufacturing of the laminate for circuit boards shown in Figures 1A to 1C (Part 3). [Figure 2D] Figure 2D is a schematic cross-sectional view illustrating an example of the manufacturing of the laminate for circuit boards shown in Figures 1A to 1C (Part 4). [Figure 3A] Figure 3A is a schematic cross-sectional view of an example of a second embodiment of a laminate for a circuit board. [Figure 3B] Figure 3B is a cross-sectional view taken along line A-A' in Figure 3A. [Figure 3C] Figure 3C is a top view of an example of a second embodiment of a laminate for circuit boards. [Figure 4A]FIG. 4A is a schematic cross-sectional view (part 1) for explaining a manufacturing example of the laminate for a circuit board of FIGS. 3A to 3C. [Figure 4B] FIG. 4B is a schematic cross-sectional view (part 2) for explaining a manufacturing example of the laminate for a circuit board of FIGS. 3A to 3C. [Figure 4C] FIG. 4C is a schematic cross-sectional view (part 3) for explaining a manufacturing example of the laminate for a circuit board of FIGS. 3A to 3C. [Figure 4D] FIG. 4D is a schematic cross-sectional view (part 4) for explaining a manufacturing example of the laminate for a circuit board of FIGS. 3A to 3C. [Figure 5A] FIG. 5A is a perspective view of an example of a flexible multilayer circuit board. [Figure 5B] FIG. 5B is a cross-sectional view taken along line A-A' of FIG. 5A. [Figure 5C] FIG. 5C is a cross-sectional view taken along line B-B' of FIG. 5A. F [Figure 5D] FIG. 5D is a cross-sectional view taken along line C-C' of FIG. 5A. [Figure 6A] FIG. 6A is a schematic cross-sectional view (part 1) of another example of a flexible multilayer circuit board. [Figure 6B] FIG. 6B is a schematic cross-sectional view (part 2) of another example of a flexible multilayer circuit board. [Figure 7A] FIG. 7A is a perspective view of another example of a flexible multilayer circuit board. [Figure 7B] FIG. 7B is a cross-sectional view taken along line A-A' of FIG. 7A. <E [Figure 7C] FIG. 7C is a cross-sectional view taken along line B-B' of FIG. 7A. [Figure 7D] FIG. 7D is a cross-sectional view taken along line C-C' of FIG. 7A. [Figure 8A] FIG. 8A is a schematic cross-sectional view (part 1) of another example of a flexible multilayer circuit board. [Figure 8B] FIG. 8B is a schematic cross-sectional view (part 2) of another example of a flexible multilayer circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] (Laminate for circuit boards) A first embodiment of the laminate for circuit boards of the present invention comprises a metal layer and an insulating layer. In the first embodiment, the insulating layer is arranged on one side of the metal layer in the thickness direction. In the first embodiment, the insulating layer has a porous insulating region and a non-porous insulating region. In the first embodiment, the insulating layer has a cross-section of the insulating layer perpendicular to the thickness direction in which a porous insulating region, a non-porous insulating region, and a porous insulating region are arranged in that order in the longitudinal direction. Porous insulator regions tend to have low flexibility because they are porous, while non-porous insulator regions have better flexibility than porous insulator regions because they are not porous. When the bending point (folded section) is a porous insulator, cracks may occur in the porous insulator starting from the pores during bending. Also, when the bending point (folded section) is a porous insulator containing hollow particles, delamination may occur at the interface between the shell of the hollow particles and the resin (the resin that makes up the insulator) during bending, resulting in cracks in the porous insulator. On the other hand, when the bending point (folded section) is a non-porous insulator, cracks caused by pores do not occur because non-porous insulators do not have pores. Therefore, in the first embodiment, the insulating layer of the circuit board laminate has a non-porous insulating region, making it possible to use it in a flexible multilayer circuit board that has excellent flexibility when bent and positioned. For example, when a flexible multilayer circuit board made using the circuit board laminate is bent and positioned, by positioning a non-porous insulating region at the bending point, it is possible to prevent the insulating layer of the flexible multilayer circuit board from cracking at that bending point.

[0012] In the first embodiment, in a region where a porous insulator region, a non-porous insulator region, and a porous insulator region are arranged in this order along the longitudinal direction, the longitudinal length of the non-porous insulator region is not particularly limited, but from the viewpoint of flexibility, 10 mm or more is preferred. Furthermore, from the viewpoint of electrical properties, 8.0 mm or less is preferred, and more preferably 3.0 mm to 7.0 mm.

[0013] A second embodiment of the circuit board laminate of the present invention comprises a metal layer and an insulating layer. In the second embodiment, the insulating layer is located on one side of the metal layer in the thickness direction. In the second embodiment, the insulating layer has a first porous insulating region and a second porous insulating region. In the second embodiment, the insulating layer has a cross-section of the insulating layer perpendicular to the thickness direction in which a first porous insulating region, a second porous insulating region, and a first porous insulating region are arranged in this order in the longitudinal direction. In the second embodiment, the average pore diameter of the second porous insulator region is smaller than the average pore diameter of the first porous insulator region. If the bending point (folded section) is made of a porous insulator, cracks may occur in the porous insulator starting from the pores during bending. Also, if the bending point (folded section) is made of a porous insulator containing hollow particles, delamination may occur at the interface between the shell of the hollow particles and the resin (the resin that makes up the insulator) during bending, resulting in cracks in the porous insulator. These problems are less likely to occur as the size of the pores decreases. In other words, the more the size of the pores constituting the porous material is, the better the flexibility tends to be. Therefore, in the second embodiment, the insulating layer has a second porous insulating region having an average pore diameter smaller than the average pore diameter of the first porous insulating region. Since the second porous insulating region has better flexibility than the first porous insulating region, the circuit board laminate of the second embodiment can be used in a flexible multilayer circuit board that has excellent flexibility when bent and positioned. For example, when a flexible multilayer circuit board made using the circuit board laminate is bent and positioned, the insulating layer of the flexible multilayer circuit board can be prevented from cracking at the bending point by positioning the second porous insulating region at the bending point.

[0014] In the second embodiment, the longitudinal length of the second porous insulator region in a location where the first porous insulator region and the second porous insulator region are arranged in that order in the longitudinal direction is not particularly limited, but from the viewpoint of flexibility, 10 mm or more is preferred. Furthermore, from the viewpoint of electrical properties, 8.0 mm or less is preferred, and more preferably 3.0 mm to 7.0 mm.

[0015] Furthermore, the longitudinal length of the circuit board laminate is longer than the width of the circuit board laminate (the width of the circuit board laminate). The width of the circuit board laminate is longer than the thickness of the circuit board laminate (the thickness of the circuit board laminate).

[0016] <Metal layer> The material of the metal 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 metal layer may be in a patterned form. The metal layer may have a wiring pattern. The thickness of the metal 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.

[0017] <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.

[0018] In the first embodiment, the insulating layer has a porous insulating region and a non-porous insulating region. The first porous insulator region is porous. Non-porous insulators are non-porous. The first porous insulating region may have hollow particles. Non-porous insulators typically do not contain hollow particles.

[0019] The average pore diameter (median diameter) of the first porous insulator region in the first embodiment is not particularly limited, but is, for example, 1.0 μm to 15 μm, and preferably 2.0 μm to 10 μm.

[0020] In the second embodiment, the insulating layer has a first porous insulating region and a second porous insulating region. The first porous insulator region is porous. The second porous insulator region is porous. The first porous insulating region may have hollow particles. The second porous insulating region may have hollow particles. When the first porous insulator region and the second porous insulator region each have hollow particles, the average pore size of the hollow particles in the second porous insulator region is smaller than the average pore size of the hollow particles in the first porous insulator region.

[0021] In the second embodiment, the average pore diameter (median diameter) of the first porous insulator region is not particularly limited, but for example, it is 2.0 μm to 15 μm, and preferably 3.0 μm to 10 μm. In the second embodiment, the average pore diameter (median diameter) of the second porous insulator region is not particularly limited, but is, for example, 0.1 μm to 0.9 μm, and preferably 0.2 μm to 0.8 μm. The difference (S1-S2) between the average pore diameter (median diameter) (S1) of the first porous insulator region and the average pore diameter (median diameter) (S2) of the second porous insulator region is not particularly limited, but is, for example, 1.0 μm to 10 μm, and preferably 2.0 μm to 8.0 μm.

[0022] The average pore size (median diameter) of the porous insulator region (first porous insulator region, second porous insulator region) and the average pore size (median diameter) of the hollow particles can be determined, for example, by cross-sectional observation using a scanning electron microscope. The hollow particles may be organic hollow particles or inorganic hollow particles.

[0023] Furthermore, if the porous insulator region (first porous insulator region, second porous insulator region) does not contain hollow particles, the porous insulator region may be formed using, for example, a porosizing agent. In that case, a method for forming the porous insulator region may be, for example, a method of applying a resin solution containing a resin and a porosizing agent, drying it, and then extracting the porosizing agent. An example of an extraction method may be extraction using supercritical carbon dioxide.

[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] A specific example of the first embodiment of the laminate for circuit boards will be described with reference to the figures. Figures 1A to 1C are schematic diagrams of an example of a first embodiment of a laminate for a circuit board. Figure 1A is a cross-sectional view. Figure 1B is a cross-sectional view taken along line A-A' in Figure 1A. Figure 1C is a top view. The laminate for circuit boards shown in Figures 1A to 1C has a metal layer 2 and an insulating layer 1. The insulating layer 1 is located on one side of the metal layer 2 in the thickness direction. The insulating layer 1 has a porous insulating region 11 and a non-porous insulating region 12. In the cross-section of the insulating layer 1, in a cross-section perpendicular to the thickness direction (A-A' section), there are locations in the longitudinal direction where a porous insulating region 11, a non-porous insulating region 12, and a porous insulating region 11 are arranged in this order. The porous insulating region 11 is layered. The non-porous insulating region 12 is layered. The porous insulator region 11 is divided into two regions. The non-porous insulating region 12 is sandwiched between two separate porous insulating regions 11. The width of the non-porous insulating region 12 extends across the entire width of the insulating layer 1.

[0026] The manufacturing example of the laminate for circuit boards shown in Figures 1A to 1C will be explained using Figures 2A to 2D. Figures 2A to 2D are schematic cross-sectional views illustrating examples of the manufacturing process for laminates used in circuit boards. First, a laminate is prepared in which a metal layer 2 and a photosensitive porous insulating layer 11A are laminated together (Figure 2A). As a method for forming the photosensitive porous insulating layer 11A, for example, a resin solution having hollow particles and a photosensitive resin is applied to the metal layer 2 and then dried. Next, light is selectively irradiated onto the areas of the photosensitive porous insulating layer 11A that will become porous insulating regions 11, and these areas are photocured. Light is not irradiated onto the areas of the photosensitive porous insulating layer 11A that will become non-porous insulating regions 12. This process forms the porous insulating regions 11 (Figure 2B). Next, the remaining photosensitive porous insulating layer 11A is removed (Figure 2C). The removal method is not particularly limited and can be, for example, dissolution and removal using an organic solvent or an alkaline solution. Next, a non-porous insulating region 12 is formed in the area where the photosensitive porous insulating layer 11A has been removed (Figure 2D). One method for forming the non-porous insulating region 12 is to apply a resin solution containing resin but not hollow particles to the area that will become the non-porous insulating region 12, and then dry it. As a result, the laminate for circuit boards shown in Figures 1A to 1C is obtained.

[0027] In the embodiments shown in Figures 1A to 1C, the thickness of the non-porous insulator region was 100% of the thickness of the insulating layer, but the thickness of the non-porous insulator region does not have to be 100% of the thickness of the insulating layer. For example, the thickness of the non-porous insulator region may be 50% to 100% of the thickness of the insulating layer. For example, if the thickness of the non-porous insulator region is 50% of the thickness of the insulating layer, the insulating layer has a non-porous insulator region having a thickness of 50% of the thickness of the insulating layer and a porous insulator region having a thickness of 50% of the thickness of the insulating layer in the thickness direction. A flexible multilayer circuit board using a laminate for a wiring board having such an embodiment is shown in Figures 6A and 6B. Figures 6A and 6B will be described later.

[0028] A specific example of a second embodiment of the laminate for circuit boards will be explained with reference to the figures. Figures 3A to 3C are schematic diagrams of an example of a second embodiment of a laminate for circuit boards. Figure 3A is a cross-sectional view. Figure 2B is a cross-sectional view taken along line A-A' in Figure 2A. Figure 2C is a top view. The laminate for circuit boards shown in Figures 3A to 3C has a metal layer 2 and an insulating layer 1. The insulating layer 1 is located on one side of the metal layer 2 in the thickness direction. The insulating layer 1 has a first porous insulating region 21 and a second porous insulating region 22. The insulating layer 1 has a cross-section (A-A' section) perpendicular to the thickness direction in which the first porous insulating region 21, the second porous insulating region 22, and the first porous insulating region 21 are arranged in this order along the longitudinal direction. The first porous insulating region 21 is layered. The second porous insulating region 22 is layered. The first porous insulator region 21 is divided into two regions. The second porous insulator region 22 is sandwiched between the two divided first porous insulator regions 21. The width of the second porous insulating region 22 extends across the entire width of the insulating layer 1.

[0029] The manufacturing example of the laminate for circuit boards shown in Figures 3A to 3C will be explained using Figures 4A to 4D. Figures 4A to 4D are schematic cross-sectional views illustrating examples of the manufacturing process for laminates used in circuit boards. First, a laminate is prepared in which a metal layer 2 and a photosensitive porous insulating layer 21A are laminated together (Figure 4A). As a method for forming the photosensitive porous insulating layer 21A, for example, a resin solution having hollow particles and a photosensitive resin is applied to the metal layer 2 and then dried. Next, light is selectively irradiated onto the areas of the photosensitive porous insulating layer 21A that will become the first porous insulating region 21, and these areas are photocured. Note that light is not irradiated onto the areas of the photosensitive porous insulating layer 21A that will become the second porous insulating region 22. This process forms the first porous insulating region 21 (Figure 4B). Next, the remaining photosensitive porous insulating layer 21A is removed (Figure 4C). The removal method is not particularly limited and can be, for example, dissolution and removal using an organic solvent or an alkaline solution. Next, a second porous insulating region 22 is formed in the area where the photosensitive porous insulating layer 21A has been removed (Figure 4D). One method for forming the second porous insulating region 22 is to apply a resin solution containing hollow particles and resin to the area that will become the second porous insulating region 22 and then dry it. The average pore size of the hollow particles in the resin solution here is smaller than the average pore size of the hollow particles in the resin solution used to form the photosensitive porous insulating layer 21A. As a result, the laminate for circuit boards shown in Figures 3A to 3C is obtained.

[0030] In the embodiments shown in Figures 3A to 3C, the thickness of the second porous insulator region was 100% of the thickness of the insulating layer, but the thickness of the second porous insulator region does not have to be 100% of the thickness of the insulating layer. For example, the thickness of the second porous insulator region may be 50% to 100% of the thickness of the insulating layer. For example, if the thickness of the second porous insulator region is 50% of the thickness of the insulating layer, the insulating layer has a second porous insulator region having a thickness of 50% of the thickness of the insulating layer in the thickness direction, and a first porous insulator region having a thickness of 50% of the thickness of the insulating layer. A flexible multilayer circuit board using a laminate for a wiring board having such an embodiment is shown in Figures 8A and 8B. Figures 8A and 8B will be described later.

[0031] (Flexible multilayer circuit board) The flexible multilayer circuit board of the present invention has a laminate for circuit boards of the present invention. In a flexible multilayer circuit board, the metal layer of the circuit board laminate may be in the shape of a pattern. In a flexible multilayer circuit board, the metal layer of the circuit board laminate may have a wiring pattern.

[0032] An example of a flexible multilayer circuit board has a first embodiment of the circuit board laminate of the present invention. In this embodiment, a non-porous insulating region is provided in the area that is bent during use. Another example of a flexible multilayer circuit board has a second embodiment of the circuit board laminate of the present invention, wherein a second porous insulating region is provided in the area that is bent during use.

[0033] A flexible multilayer circuit board may be formed using one circuit board laminate, or it may be formed using two circuit board laminates.

[0034] Flexible multilayer circuit boards may have other components such as adhesive insulating layers and conductive parts.

[0035] A flexible multilayer circuit board is, for example, a stripline.

[0036] <Adhesive insulating layer> 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. There are no particular restrictions on the thickness of the adhesive insulating layer.

[0037] <Conductive section> The conductive portion, for example, penetrates the insulating layer in the thickness direction. A conductive part, for example, electrically connects two conductors. 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 conductive part is, for example, columnar. 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.

[0038] In the longitudinal direction of a flexible multilayer circuit board, if a non-porous insulating region is sandwiched between two conductive portions aligned in the longitudinal direction, the longitudinal length of the non-porous insulating region is preferably 50% to 100% of the distance between the two conductive portions, from the viewpoint of ensuring sufficient flexibility. In the longitudinal direction of a flexible multilayer circuit board, if the second porous insulator region is sandwiched between two conductive portions aligned in the longitudinal direction, the longitudinal length of the second porous insulator region is preferably 50% to 100% of the distance between the two conductive portions, from the viewpoint of ensuring sufficient flexibility. Here, the distance between the two conductive parts refers to the shortest distance between the ends of each conductive part on the non-porous insulator side or the second porous insulator side.

[0039] An embodiment of a flexible multilayer circuit board will be explained with reference to the figures. Figures 5A to 5D are schematic diagrams of an example of a flexible multilayer circuit board. This example uses a first embodiment of the laminate for circuit boards. The flexible multilayer circuit boards shown in Figures 5A to 5D are striplines. Figure 5A is a perspective view. Figure 5B is a cross-sectional view taken along line A-A' in Figure 5A. Figure 5C is a cross-sectional view taken along line B-B' in Figure 5A. Figure 5D is a cross-sectional view taken along line C-C' in Figure 5A. The section shown in Figure 5C (B-B' section) is the area where the flexible multilayer circuit board is bent when it is used. Figures 5A to 5D are schematic diagrams. Therefore, for example, in Figure 5B, the ratio of the length in the longitudinal direction to the length in the thickness direction is not accurate. The flexible multilayer circuit board has a metal layer 102, an insulating layer 101, an adhesive insulating layer 171, an insulating layer 151, and a metal layer 152 in this order. The flexible multilayer circuit board further includes a wiring section 173 which is a signal line and a conductive section 172. The wiring section 173 is embedded in the adhesive insulating layer 171 (Figures 5C and 5D). The conductive portion 172 electrically connects the metal layer 102 and the metal layer 152. The metal layer 102, the metal layer 152, and the conductive portion 172 constitute a ground. The metal layer 102 and the insulating layer 101 are formed using a first embodiment of the circuit board laminate of the present invention. The metal layer 152 and the insulating layer 151 are formed using a first embodiment of the circuit board laminate of the present invention. As shown in Figure 5B, the insulating layer 101 has a porous insulating region 111 and a non-porous insulating region 112. In a cross-section of the insulating layer 101 perpendicular to the thickness direction, there is a region in the longitudinal direction in which the porous insulating region 111, the non-porous insulating region 112, and the porous insulating region 111 are arranged in this order. Furthermore, as shown in Figure 5B, the insulating layer 151 has a porous insulating region 161 and a non-porous insulating region 162. In a cross-section of the insulating layer 151 perpendicular to the thickness direction, there are locations in the longitudinal direction where the porous insulating region 161, the non-porous insulating region 162, and the porous insulating region 161 are arranged in this order. In the flexible multilayer circuit board, the insulating layer 101 and the insulating layer 151 are arranged such that the non-porous insulating region 112 and the non-porous insulating region 162 face each other. The non-porous insulating region 112 and the non-porous insulating region 162 are located in the area including the cross-section (B-B' cross-section) shown in Figure 5C (the area where the flexible multilayer circuit board is bent for use). Furthermore, as shown in Figures 5A and 5D, the two conductive portions 172 are positioned on either side of the longitudinally extending wiring portion 173. The conductive portions 172 are also spaced apart along the wiring portion 173. Because a non-porous insulating region exists in the area where a flexible multilayer circuit board is bent, it is possible to prevent the insulating layer of the flexible multilayer circuit board from cracking at that bending point.

[0040] A flexible multilayer circuit board using the first embodiment of the laminate for circuit boards may be, for example, the embodiment shown in Figures 6A and 6B. Figure 6A is a cross-sectional view corresponding to the A-A' section in Figure 5A. Figure 6B is a cross-sectional view corresponding to the B-B' section in Figure 5A. The differences between the embodiments shown in Figures 5A to 5D and the embodiments shown in Figures 6A and 6B will be explained. In the embodiments shown in Figures 5A to 5D, in the thickness direction, the non-porous insulating region 112 extends over the entire thickness direction of the insulating layer 101, and the non-porous insulating region 162 extends over the entire thickness direction of the insulating layer 151 (Figures 5B and 5C). On the other hand, in the embodiments shown in Figures 6A and 6B, in the thickness direction, the non-porous insulator region 112 does not extend over the entire thickness of the insulating layer 101, and a portion of the porous insulator region 111 is located on the side of the non-porous insulator region 112 opposite to the metal layer 102. Also, in the thickness direction, the non-porous insulator region 162 does not extend over the entire thickness of the insulating layer 151, and a portion of the porous insulator region 161 is located on the side of the non-porous insulator region 162 opposite to the metal layer 152. In the D-D' section of Figure 6A, similar to Figure 1B, the porous insulator region 111, the non-porous insulator region 112, and the porous insulator region 111 are arranged in this order along the longitudinal direction. Furthermore, in the E-E' section of Figure 6A, similar to Figure 1B, the porous insulator region 161, the non-porous insulator region 162, and the porous insulator region 161 are arranged in this order along the longitudinal direction. In the embodiments shown in Figures 6A and 6B, a non-porous insulating region exists at the point where the flexible multilayer circuit board is bent during use, thus preventing the insulating layer of the flexible multilayer circuit board from cracking at that point.

[0041] Other embodiments of the flexible multilayer circuit board will be described with reference to the figures. Figures 7A to 7D are schematic diagrams of an example of a flexible multilayer circuit board. This example uses a second embodiment of the laminate for circuit boards. The flexible multilayer circuit boards shown in Figures 7A to 7D are striplines. Figure 7A is a perspective view. Figure 7B is a cross-sectional view taken along line A-A' in Figure 7A. Figure 7C is a cross-sectional view taken along line B-B' in Figure 7A. Figure 7D is a cross-sectional view taken along line C-C' in Figure 7A. The section shown in Figure 7C (B-B' section) is the area where the flexible multilayer circuit board is bent when it is used. Note that Figures 7A to 7D are schematic diagrams. Therefore, for example, in Figure 7B, the ratio of the length in the longitudinal direction to the length in the thickness direction is not accurate. The flexible multilayer circuit board has a metal layer 202, an insulating layer 201, an adhesive insulating layer 271, an insulating layer 251, and a metal layer 252 in this order. The flexible multilayer circuit board further includes a wiring section 273 which is a signal line and a conductive section 272. The wiring section 273 is embedded in the adhesive insulating layer 271 (Figures 7C and 7D). The conductive portion 272 electrically connects the metal layer 202 and the metal layer 252. The metal layer 202, the metal layer 252, and the conductive portion 272 constitute a ground. The metal layer 202 and the insulating layer 201 are formed using a second embodiment of the circuit board laminate of the present invention. The metal layer 252 and the insulating layer 251 are formed using a second embodiment of the circuit board laminate of the present invention. As shown in Figure 7B, the insulating layer 201 has a first porous insulating region 211 and a second porous insulating region 212. In a cross-section of the insulating layer 201 perpendicular to the thickness direction, there is a region in the longitudinal direction in which the first porous insulating region 211, the second porous insulating region 212, and the first porous insulating region 211 are arranged in this order. Furthermore, as shown in Figure 7B, the insulating layer 251 has a first porous insulating region 261 and a second porous insulating region 262. In a cross-section of the insulating layer 251 perpendicular to the thickness direction, there is a region in the longitudinal direction in which the first porous insulating region 261, the second porous insulating region 262, and the first porous insulating region 261 are arranged in this order. In the flexible multilayer circuit board, the insulating layer 201 and the insulating layer 251 are arranged such that the second porous insulating region 212 and the second porous insulating region 262 face each other. The second porous insulator region 212 and the second porous insulator region 262 are located in the area including the cross-section (B-B' cross-section) shown in Figure 7C (the area where the flexible multilayer circuit board is bent for use). Furthermore, as shown in Figures 7A and 7D, the two conductive portions 272 are positioned on either side of the longitudinally extending wiring portion 273. The conductive portions 272 are also spaced apart along the wiring portion 273. Because a second porous insulating region exists at the point where the flexible multilayer circuit board is bent during use, it is possible to prevent the insulating layer of the flexible multilayer circuit board from cracking at that point.

[0042] A flexible multilayer circuit board using the second embodiment of the laminate for circuit boards may be, for example, the embodiment shown in Figures 8A and 8B. Figure 8A is a cross-sectional view corresponding to the A-A' section in Figure 7A. Figure 8B is a cross-sectional view corresponding to the B-B' section in Figure 7A. The differences between the embodiments shown in Figures 7A to 7D and the embodiments shown in Figures 8A and 8B will be explained. In the embodiments shown in Figures 7A to 7D, the second porous insulator region 212 extends over the entire thickness of the insulating layer 201, and the second porous insulator region 262 extends over the entire thickness of the insulating layer 251 (Figures 7B and 7C). On the other hand, in the embodiments shown in Figures 8A and 8B, in the thickness direction, the second porous insulator region 212 does not extend over the entire thickness of the insulating layer 201, and a portion of the first porous insulator region 211 is located on the side of the second porous insulator region 212 opposite to the metal layer 202. Also, in the thickness direction, the second porous insulator region 262 does not extend over the entire thickness of the insulating layer 251, and a portion of the first porous insulator region 261 is located on the side of the second porous insulator region 262 opposite to the metal layer 252. In the D-D' section of Figure 8A, similar to Figure 3B, the first porous insulator region 211, the second porous insulator region 212, and the first porous insulator region 211 are arranged in this order along the longitudinal direction. Furthermore, in the E-E' section of Figure 8A, similar to Figure 3B, the first porous insulator region 261, the second porous insulator region 262, and the first porous insulator region 261 are arranged in this order along the longitudinal direction. In the embodiments shown in Figures 8A and 8B, a second porous insulating region exists at the point where the flexible multilayer circuit board is bent during use, thus preventing the insulating layer of the flexible multilayer circuit board from cracking at that point. [Explanation of Symbols]

[0043] 1. Insulating layer 2 metal layers 11 Porous insulator region 11A Photosensitive porous insulating layer 12 Non-porous insulating region 21 First porous insulator region 21A Photosensitive porous insulating layer 22 Second porous insulating region 101 Insulating layer 102 Metal layer 111 Porous insulator region 112 Non-porous insulating region 151 Insulating layer 152 Metal layer 161 Porous insulator region 162 Non-porous insulating region 171 Adhesive insulating layer 172 Conductive section 173 Wiring section 201 Insulating layer 202 Metal layer 211 First porous insulator region 212 Second porous insulator region 251 Insulating layer 252 Metal layer 261 First porous insulator region 262 Second porous insulator region 271 Adhesive insulating layer 272 Conductive section 273 Wiring section

Claims

1. The system comprises a metal layer and an insulating layer disposed on one side of the metal layer in the thickness direction, The insulating layer has a porous insulating region and a non-porous insulating region. The insulating layer, in a cross-section of the insulating layer perpendicular to the thickness direction, has a portion in which the porous insulating region, the non-porous insulating region, and the porous insulating region are arranged in this order in the longitudinal direction. Laminate for circuit boards.

2. The system comprises a metal layer and an insulating layer disposed on one side of the metal layer in the thickness direction, The insulating layer has a first porous insulating region and a second porous insulating region. The insulating layer has a cross-section of the insulating layer perpendicular to the thickness direction in which the first porous insulating region, the second porous insulating region, and the first porous insulating region are arranged in this order in the longitudinal direction. The average pore diameter of the second porous insulator region is smaller than the average pore diameter of the first porous insulator region. Laminate for circuit boards.

3. The laminate for a circuit board according to claim 1, wherein the porous insulating region contains hollow particles.

4. The first porous insulating region contains hollow particles, The second porous insulating region contains hollow particles, The laminate for circuit boards according to claim 2.

5. A flexible multilayer circuit board having a laminate for circuit boards according to any one of claims 1 to 4.

6. The flexible multilayer circuit board according to claim 5, wherein the metal layer in the laminate for the circuit board has a wiring pattern.

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