Flexible multilayer circuit board

Abstract

To provide a flexible multilayer circuit board equipped with conductive portions that have high adhesion to the holes for conductive portions. [Solution] A flexible multilayer circuit board comprising an insulating layer having a porous insulating layer and a non-porous insulating layer, a conductor layer disposed on one side of the insulating layer, and a conductive portion electrically connected to the conductor layer, wherein the outermost position P of the conductive portion hole formed in the porous insulating layer and the non-porous insulating layer, as specified below, is on the non-porous insulating layer side of the center of the porous insulating layer in the thickness direction. Outermost position P: In a cross-sectional view in the thickness direction, the outermost position P is defined as the position on the side of the conductive portion hole that is furthest from the line segment S, with respect to a line segment S connecting a first connection point C1 where one side of the insulating layer and the side surface of the conductive portion hole are in contact, and a second connection point C2 where the side of the conductive portion hole opposite to the conductor layer side and the side surface of the conductive portion hole are in contact.

Description

Technical Field

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

Background Art

[0002] A wiring circuit board including a first conductor layer, an insulating layer, and a second conductor layer in this order in the thickness direction is known (see, for example, Patent Document 1). In the wiring circuit board described in Patent Document 1, the insulating layer has blind vias. The wiring circuit board further includes a conduction part. The conduction part is arranged on the inner surface facing the blind via in the insulating layer. In the wiring circuit board, the first conductor layer and the second conductor layer are electrically connected by the conduction part.

[0003] In addition, a wiring circuit board has been proposed that includes an insulating layer having vias penetrating in the thickness direction, a first conductor layer arranged on one surface of the insulating layer in the thickness direction, a second conductor layer arranged on the other surface of the insulating layer in the thickness direction, and a conduction part arranged on the inner surface of the via and electrically connecting the first conductor layer and the second conductor layer, and has a specific length L (see Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a wiring circuit board, if the adhesion of the conduction part to the side surface of the hole for the conduction part is low, the conduction part is likely to peel off from the side surface of the hole for the conduction part during bending or reliability tests such as a high-temperature and high-humidity test or a temperature cycle test. Therefore, in the wiring circuit board, high adhesion of the conduction part to the side surface of the hole for the conduction part is required.

[0006] Therefore, the present invention aims to provide a flexible multilayer circuit board equipped with conductive portions that have high adhesion to the holes for conductive portions. [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] An insulating layer having holes for conductive parts, A conductive layer disposed on one side of the insulating layer in the thickness direction, It comprises a conductive portion disposed in the conductive portion hole and electrically connected to the conductor layer, The insulating layer comprises a porous insulating layer and a non-porous insulating layer in contact with the porous insulating layer and the conductor layer. The conductive holes are formed in the porous insulating layer and the non-porous insulating layer. A flexible multilayer circuit board in which the outermost position P, as specified below, is located on the non-porous insulating layer side of the center of the porous insulating layer in the thickness direction. Outermost position P: In the cross-sectional view in the thickness direction, draw a line segment S connecting a first connection point C1 where one surface of the insulating layer and the side surface of the conductive hole are in contact, and a second connection point C2 where the surface of the conductive hole opposite to the conductor layer side and the side surface of the conductive hole are in contact. In the cross-sectional view, identify the outermost position P on the side surface of the conductive hole that is furthest from the line segment S. [2] The flexible multilayer circuit board described in [1], wherein the length L measured below is 5 μm or more and 20 μm or less. Length L: The length L is measured as the shortest distance from the line segment S to the outermost position P. [3] An insulating layer having a first hole for conductive parts and a second hole for conductive parts, A first conductor layer is disposed on one side of the insulating layer in the thickness direction, A second conductor layer is disposed on the other side of the insulating layer in the thickness direction, A first conductive portion is disposed within the first hole for the conductive portion and electrically connected to the first conductor layer, A second conductive portion is disposed within the second hole for the conductive portion and electrically connected to the second conductor layer, The insulating layer includes an interlayer connection portion embedded in the insulating layer that electrically connects the first conductive portion and the second conductive portion, A flexible multilayer circuit board in which lengths L1 and L2, as measured below, are 5 μm or more and 20 μm or less, respectively. Length L1: In the cross-sectional view in the thickness direction, draw a line segment S1 connecting a first connection point C11 where one surface of the insulating layer and the side surface of the first conductive hole are in contact, and a second connection point C12 where the side surface of the first conductive hole in the insulating layer and the surface of the interlayer connection on the first conductor layer side are in contact. In the cross-sectional view, identify the outermost position P1 on the side surface of the first conductive hole that is furthest from the line segment S1. Measure the length L1 as the shortest distance from the line segment S1 to the outermost position P1. Length L2: In the cross-sectional view in the thickness direction, draw a line segment S2 connecting a first connection point C21 where the other surface of the insulating layer and the side surface of the second hole for the conductive portion are in contact, and a second connection point C22 where the side surface of the second hole for the conductive portion of the insulating layer and the surface of the interlayer connection on the second conductor layer side are in contact. In the cross-sectional view, identify the outermost position P2 on the side surface of the second hole for the conductive portion that is furthest from the line segment S2. Measure the length L2 as the shortest distance from the line segment S2 to the outermost position P2. [4] The outermost position P1 is located in the thickness direction, closer to the first conductor layer than the interlayer connection portion, The outermost position P2 is located in the thickness direction, closer to the second conductor layer than the interlayer connection portion. [3] The flexible multilayer circuit board described above. [5] The insulating layer comprises an adhesive insulating layer, a first porous insulating layer disposed between the adhesive insulating layer and the first conductor layer, and a second porous insulating layer disposed between the adhesive insulating layer and the second conductor layer. The interlayer connection portion is embedded in the adhesive insulating layer. The flexible multilayer circuit board according to [3] or [4].

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a flexible multilayer circuit board including a conductive portion having high adhesion to a hole for a conductive portion.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of an embodiment of a flexible multilayer circuit board. [Figure 2] FIG. 2 is a schematic cross-sectional view of another embodiment of a flexible multilayer circuit board. [Figure 3A] FIG. 3A is a diagram (part 1) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3B] FIG. 3B is a diagram (part 2) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3C] FIG. 3C is a diagram (part 3) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3D] FIG. 3D is a diagram (part 4) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3E] FIG. 3E is a diagram (part 5) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3F] FIG. 3F is a diagram (part 6) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2. [Figure 3G] FIG. 3G is a diagram (part 7) for explaining an embodiment of a method for manufacturing the flexible multilayer circuit board of FIG. 2.

Modes for Carrying Out the Invention

[0011] (Flexible Multilayer Circuit Board) A first embodiment of the flexible multilayer circuit board of the present invention comprises an insulating layer, a conductive layer, and a conductive portion. The insulating layer has holes for conductivity. The conductive layer is positioned on one side of the insulating layer in the thickness direction. The conductive portion is positioned within a hole for the conductive portion. The conductive portion is electrically connected to the conductor layer. The insulating layer comprises a porous insulating layer and a non-porous insulating layer. The non-porous insulating layer is in contact with the porous insulating layer and the conductive layer. The holes for conductivity are formed in the porous insulating layer and the non-porous insulating layer. In the first embodiment, the outermost position P, as defined below, is located on the non-porous insulating layer side of the center of the porous insulating layer in the thickness direction. Outermost position P: In a cross-sectional view in the thickness direction, draw a line segment S connecting a first connection point C1 where one side of the insulating layer and the side of the conductive hole are in contact, and a second connection point C2 where the side of the conductive hole opposite to the conductor layer side and the side of the conductive hole are in contact. In a cross-sectional view, identify the outermost position P on the side of the conductive hole that is furthest from line segment S.

[0012] Identifying the outermost position P means that the length of the side surface of the conductive hole is longer than the line segment S. Because the length of the side surface of the conductive hole is longer than the line segment S, the contact area between the side surface of the conductive hole and the conductive part increases, resulting in better adhesion of the conductive part to the conductive hole. Furthermore, because the outermost position P is located on the non-porous insulating layer side of the center of the porous insulating layer in the thickness direction, the non-porous insulating layer protrudes significantly toward the center of the conductive hole in the insulating layer, and the non-porous insulating layer closes the periphery of the conductive hole. As a result, it is expected that the adhesion of the conductive portion filled in the conductive hole will be improved. These factors combined result in a flexible multilayer circuit board with conductive sections that exhibit high adhesion. Furthermore, if the side of the insulating layer towards the center of the conductive hole is considered the inside of the conductive hole, and the side of the insulating layer opposite to the center of the conductive hole is considered the outside of the conductive hole, then the outermost position P is located outside the conductive hole.

[0013] In the first embodiment, the longer the length L measured below, the better the adhesion of the conductive portion. On the other hand, if the length L is too long, defects in the formation of the conductive portion are more likely to occur, which may reduce connection reliability. In this regard, the length L is preferably 1 μm or more and 20 μm or less, and more preferably 5 μm or more and 20 μm or less. Length L: The length L is measured as the shortest distance from line segment S to the outermost point P.

[0014] Figure 1 shows an example of a first embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 1 comprises an insulating layer 1, a conductive layer 2, a conductive portion 3, and a second conductive layer 4. The insulating layer 1 has holes for conductive parts. The conductive layer 2 is arranged on one side of the insulating layer 1 in the thickness direction. The conductive portion 3 is positioned within the hole for the conductive portion. The conductive portion 3 is electrically connected to the conductor layer 2. The conductive portion 3 is further electrically connected to the second conductor layer 4. That is, the conductor layer 2 is electrically connected to the second conductor layer 4 via the conductive portion 3. The insulating layer 1 comprises a porous insulating layer 1b and a non-porous insulating layer 1a. The insulating layer 1 further comprises a non-porous insulating layer 1c and an adhesive insulating layer 1d. The non-porous insulating layer 1a is in contact with the porous insulating layer 1b and the conductive layer 2. The non-porous insulating layer 1c is in contact with the porous insulating layer 1b and the adhesive insulating layer 1d. The adhesive insulating layer 1d is in contact with the non-porous insulating layer 1c and the second conductor layer 4. The holes for conductivity are formed in the porous insulating layer 1b, the non-porous insulating layer 1a, the non-porous insulating layer 1c, and the adhesive insulating layer 1d. The second conductor layer 4 is positioned on the other side of the insulating layer 1. The outermost position P, as defined below, is located on the non-porous insulating layer 1a side of the center of the porous insulating layer 1b in the thickness direction. Outermost position P: In a cross-sectional view in the thickness direction, draw a line segment S connecting a first connection point C1 where one surface of the insulating layer 1 and the side surface 1x of the conductive hole are in contact, and a second connection point C2 where the surface s1 of the conductive hole opposite to the conductor layer 2 side and the side surface 1x of the conductive hole are in contact. In a cross-sectional view, identify the outermost position P on the side surface 1x of the conductive hole that is furthest from the line segment S.

[0015] The flexible multilayer circuit board shown in Figure 1 can be manufactured by referring to the manufacturing method for the flexible multilayer circuit board shown in Figure 2.

[0016] A second embodiment of the flexible multilayer circuit board of the present invention comprises an insulating layer, a first conductor layer, a second conductor layer, a first conductive portion, a second conductive portion, and an interlayer connection portion. The insulating layer has a first hole for conductive parts and a second hole for conductive parts. The first conductor layer is positioned on one side of the insulating layer in the thickness direction. The second conductor layer is positioned on the other side of the insulating layer in the thickness direction. The first conductive portion is positioned within the first hole for the conductive portion. The first conductive portion is electrically connected to the first conductor layer. The second conductive portion is positioned within the second conductive hole. The second conductive portion is electrically connected to the second conductor layer. The interlayer connection is embedded in the insulating layer. The interlayer connection electrically connects the first conductive section and the second conductive section. In the second embodiment, the lengths L1 and L2 measured below are 5 μm or more and 20 μm or less, respectively. Length L1: In a cross-sectional view in the thickness direction, draw a line segment S1 connecting the first connection point C11, where one side of the insulating layer and the side surface of the first hole for the conductive portion are in contact, and the second connection point C12, where the side surface of the first hole for the conductive portion of the insulating layer and the surface of the interlayer connection on the first conductor layer side are in contact. In a cross-sectional view, identify the outermost position P1 on the side surface of the first hole for the conductive portion that is furthest from line segment S1. Measure length L1 as the shortest distance from line segment S1 to the outermost position P1. Length L2: In a cross-sectional view in the thickness direction, draw a line segment S2 connecting the first connection point C21, where the other surface of the insulating layer and the side surface of the second hole for the conductive portion are in contact, and the second connection point C22, where the side surface of the second hole for the conductive portion of the insulating layer and the surface of the interlayer connection on the second conductor layer side are in contact. In a cross-sectional view, identify the outermost position P2 on the side surface of the second hole for the conductive portion, which is furthest from line segment S2. Measure length L2 as the shortest distance from line segment S2 to the outermost position P2.

[0017] Because the side surface of the first hole for the conductive portion is longer than the line segment S1, the contact area between the insulating layer and the first conductive portion increases, and the adhesion of the first conductive portion improves. Furthermore, because L1 is 5 μm or more, the contact area between the insulating layer and the first conductive portion increases even further, and the adhesion of the first conductive portion improves even more. Having L1 at 20 μm or less reduces the likelihood of formation defects in the first conductive section, thereby improving connection reliability. Because the side surface of the second hole for the conductive portion is longer than the line segment S2, the contact area between the insulating layer and the second conductive portion increases, and the adhesion of the second conductive portion improves. Furthermore, because L2 is 5 μm or more, the contact area between the insulating layer and the second conductive portion increases even further, and the adhesion of the second conductive portion improves even more. Having L2 at 20 μm or less reduces the likelihood of formation defects in the first conductive section, thereby improving connection reliability.

[0018] When the flexible multilayer circuit board of the second embodiment, which has conductive layers on both sides, is bent, tensile stress is generated in one conductive layer (e.g., the first conductive layer) and compressive stress is generated in the other conductive layer (e.g., the second conductive layer). In the flexible multilayer circuit board of the second embodiment of the present invention, which has excellent adhesion of the conductive parts, interfacial delamination between the conductive parts and the conductive layers can be suppressed even in such cases.

[0019] In the second embodiment, it is preferable that the outermost position P1 is located closer to the first conductor layer than the interlayer connection portion in the thickness direction. By doing so, the surface of the insulating layer in contact with the first conductor layer protrudes significantly toward the center of the first hole for the conductive portion, and the surface of the insulating layer in contact with the first conductor layer closes the periphery of the first hole for the conductive portion. As a result, it is expected that the adhesion of the first conductive portion filled in the first hole for the conductive portion will be further improved. In the second embodiment, it is preferable that the outermost position P2 is located closer to the second conductor layer than the interlayer connection portion in the thickness direction. By doing so, the surface of the insulating layer in contact with the second conductor layer protrudes significantly towards the center of the second hole for the conductive portion, and the surface of the insulating layer in contact with the second conductor layer closes the periphery of the second hole for the conductive portion. As a result, it is expected that the adhesion of the second conductive portion filled in the second hole for the conductive portion will be improved. Furthermore, when the side of the first conductive hole in the insulating layer that is closer to the center of line segment S1 is considered the inside of the first conductive hole, and the side of the insulating layer that is opposite to the center of line segment S1 is considered the outside of the first conductive hole, the outermost position P1 is located outside the first conductive hole. When the side of the second conductive hole in the insulating layer that is closer to the center of line segment S2 is considered the inside of the second conductive hole, and the side of the insulating layer that is opposite to the center of line segment S2 that is considered the outside of the second conductive hole, the outermost position P2 is located outside the second conductive hole.

[0020] In the second embodiment, for example, the insulating layer includes an adhesive insulating layer, a first porous insulating layer disposed between the adhesive insulating layer and the first conductor layer, and a second porous insulating layer disposed between the adhesive insulating layer and the second conductor layer. The interlayer connection portion is embedded in the adhesive insulating layer.

[0021] The following describes each component.

[0022] <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.

[0023] The insulating layer may be a single-layer structure or a multi-layer structure.

[0024] The insulating layer includes, for example, a porous insulating layer (a porous insulating layer, a first porous insulating layer, and a second porous insulating layer). The insulating layer includes, for example, a porous insulating layer and a non-porous insulating layer (non-porous insulating layer, first non-porous insulating layer, second non-porous insulating layer, third non-porous insulating layer, fourth non-porous insulating layer). The insulating layer may, for example, have an adhesive insulating layer.

[0025] Examples of materials for the porous insulating layer and the non-porous insulating layer include the resins exemplified as materials for the insulating layer.

[0026] The porous insulating layer is porous. The porous insulating layer has closed cells and / or open cells. The porosity of the porous insulating layer 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 of the porous insulating layer is, for example, less than 100%, and even more preferably 99% or less. When the material of the porous insulating layer is polyimide resin, the porosity of the porous insulating layer can be determined by calculation based on the following formula.

[0027] Relative permittivity of a porous insulating layer = Relative permittivity of air × porosity + Relative permittivity of polyimide × (1 - porosity) Here, the relative permittivity of air is 1, and the relative permittivity of polyimide resin is 3.5, Relative permittivity of a porous insulating layer = porosity + 3.5(1 - porosity) Porosity (%) = [(3.5 - relative permittivity of porous insulating layer) / 2.5] × 100

[0028] The relative permittivity of the porous insulating layer at a frequency of 60 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 of the porous insulating layer is measured by a resonator method using a frequency of 60 GHz.

[0029] The dielectric loss tangent of a porous insulating layer at a frequency of 60 GHz is, for example, 0.006 or less, and also, for example, greater than 0. The dielectric loss tangent of a porous insulating layer is measured using a resonator method at a frequency of 60 GHz.

[0030] 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.

[0031] 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, 100 μm or less, preferably 80 μm or less.

[0032] <Conductor layer> The material of the conductive layers (conducting layer, 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 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.

[0033] <Conductive section> The material of the conductive parts (conductive part, first conductive part, second 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.

[0034] <Interlayer connection section> The material of the interlayer connection is not particularly limited and can be, for example, copper, iron, silver, gold, aluminum, nickel, or their alloys (e.g., stainless steel, bronze). Copper is preferred. The thickness of the interlayer connection 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.

[0035] Figure 2 shows an example of a second embodiment of a flexible multilayer circuit board. The flexible multilayer circuit board shown in Figure 2 comprises an insulating layer 11, a first conductor layer 12, a second conductor layer 13, a first conductive portion 14, a second conductive portion 15, and an interlayer connection portion 16. The insulating layer 11 has a first hole for conductive parts and a second hole for conductive parts. The first conductor layer 12 is arranged on one side of the insulating layer 11 in the thickness direction. The second conductor layer 13 is positioned on the other side of the insulating layer 11 in the thickness direction. The first conductive portion 14 is positioned in the first hole for conductive portions and is electrically connected to the first conductor layer 12. The second conductive portion 15 is positioned within the second hole for conductive portions and is electrically connected to the second conductor layer 13. The interlayer connection portion 16 is embedded in the insulating layer 11 and electrically connects the first conductive portion 14 and the second conductive portion 15. The insulating layer 11 comprises, in this order, a first non-porous insulating layer 11a, a first porous insulating layer 11b, a second non-porous insulating layer 11c, an adhesive insulating layer 11g, a fourth non-porous insulating layer 11f, a second porous insulating layer 11e, and a third non-porous insulating layer 11d. The interlayer connection portion 16 is embedded in the adhesive insulating layer 11g. In Figure 2, the end of the interlayer connection portion 16 penetrates the adhesive insulating layer 11g. This improves the reliability of the interlayer connection. The lengths L1 and L2 measured below are 5 μm or more and 20 μm or less, respectively. Length L1: In a cross-sectional view in the thickness direction, draw a line segment S1 connecting a first connection point C11 where one surface of the insulating layer 11 and the side surface 11x of the first conductive hole in the insulating layer 11 are in contact, and a second connection point C12 where the side surface 11x of the first conductive hole in the insulating layer 11 and the surface of the interlayer connection 16 on the first conductor layer 12 side are in contact. In a cross-sectional view, identify the outermost position P1 on the side surface 11x of the first conductive hole in the insulating layer that is furthest from line segment S1. Measure length L1 as the shortest distance from line segment S1 to the outermost position P1. Length L2: In a cross-sectional view in the thickness direction, draw a line segment S2 connecting the first connection point C21 where the other surface of the insulating layer 11 and the side surface 21x of the second conductive hole in the insulating layer 11 are in contact, and the second connection point C22 where the side surface 21x of the second conductive hole in the insulating layer 11 and the surface of the interlayer connection 16 on the second conductor layer 13 side are in contact. In a cross-sectional view, identify the outermost position P2 on the side surface 21x of the second conductive hole in the insulating layer that is furthest from line segment S2. Measure length L2 as the shortest distance from line segment S2 to the outermost position P2.

[0036] The following describes a manufacturing example of a second embodiment of a flexible multilayer circuit board using diagrams. Figures 3A to 3G are schematic diagrams illustrating manufacturing examples of the flexible multilayer circuit board shown in Figure 2. First, a laminate is prepared in which a first conductor film 12A, a first non-porous insulating layer 11a, a first porous insulating layer 11b, a second non-porous insulating layer 11c, an adhesive insulating layer 11g-1, and a third conductor layer 16A are laminated in this order (Figure 3A). As for the material of the first conductor film 12A, for example, the same material as the conductor used to form the first conductive portion 14 can be used. Copper is preferred as such a material. Next, the third conductive layer 16A is patterned using photolithography with a photoresist (for example, subtractive method) to form an interlayer connection portion 16 (Figure 3B). The interlayer connection portion 16 is formed in a rectangular shape, for example, when viewed from a direction perpendicular to the thickness direction. Next, a laminate is prepared in which the second conductor film 13A, the third non-porous insulating layer 11d, the second porous insulating layer 11e, the fourth non-porous insulating layer 11f, and the adhesive insulating layer 11g-2 are laminated in this order (Figure 3C). As for the material of the second conductor film 13A, for example, the same material as the conductor used to form the second conductive portion 15 can be used. Copper is preferred as such a material. Next, the laminate shown in Figure 3B and the laminate prepared in Figure 3C are placed so that adhesive insulating layer 11g-1 and adhesive insulating layer 11g-2 face each other, and the two adhesive resin layers are bonded together (Figure 3D). By doing so, the two adhesive insulating layers are integrated to form an adhesive insulating layer 11g, and a laminate is obtained having the first conductor film 12A, the insulating layer 11, and the second conductor film 13A in that order from one side in the thickness direction to the other (Figure 3E). The insulating layer 11 has the first nonporous insulating layer 11a, the first porous insulating layer 11b, the second nonporous insulating layer 11c, the adhesive insulating layer 11g, the fourth nonporous insulating layer 11f, the second porous insulating layer 11e, and the third nonporous insulating layer 11d in that order from one side in the thickness direction to the other. At this time, the interlayer connection portion 16 is embedded in the adhesive insulating layer 11g.

[0037] Next, from one side in the thickness direction, first via holes 14A for conductive parts that reach the interlayer connection portion 16 are made in the first conductor film 12A, the first nonporous insulating layer 11a, the first porous insulating layer 11b, the second nonporous insulating layer 11c, and the adhesive insulating layer 11g. From the other side in the thickness direction, second via holes 15A for conductive parts that reach the interlayer connection portion 16 are made in the second conductor film 13A, the third nonporous insulating layer 11d, the second porous insulating layer 11e, the fourth nonporous insulating layer 11f, and the adhesive insulating layer 11g (Figure 3F). The first conductive hole 14A and the second conductive hole 15A are formed by irradiating with a laser. An example of a laser irradiation method is the method described in Japanese Patent Application Publication No. 2023-77787. If there are multiple holes for electrical connections, the process of forming each hole may be divided and the holes may be formed alternately. For example, the first electrical connection hole 14A may be partially drilled, then the second electrical connection hole 15A may be partially drilled. After that, the first electrical connection hole 14A may be completely drilled, and then the second electrical connection hole 15A may be completely drilled. By doing so, thermal damage during the drilling process can be reduced compared to forming a single hole continuously. Examples of lasers include YAG lasers and carbon dioxide lasers. The laser irradiation process may be one or more, preferably two, from the viewpoint of high manufacturing efficiency and good via hole shape. That is, the process of forming the first conductive hole 14A and the second conductive hole 15A respectively includes a first irradiation process and a second irradiation process in order. Here, the energy density in the second irradiation step is lower than the energy density in the first irradiation step. In the first irradiation step, it is necessary to create holes in the conductive films (first conductive film 12A and second conductive film 13A), so the laser irradiation is performed at a relatively high energy density. On the other hand, the energy density required to create holes in the insulating layer can be lower than the energy density required to create holes in the conductive films, so the energy density is lowered in the second irradiation step. In the first irradiation step, when holes are created in the conductive films, the insulating layer near the conductive films is also irradiated with a laser at a relatively high energy density, so the holes in the insulating layer near the conductive films become relatively large. On the other hand, if the insulating layers are stacked in the order of a non-porous insulating layer and a porous insulating layer from the side in contact with the conductive films, the non-porous insulating layer is less ablated by the laser than the porous insulating layer, so the holes in the non-porous insulating layer near the conductive films become smaller than the holes in the porous insulating layer. As a result, the first conductive hole 14A and the second conductive hole 15A shown in Figure 3F are formed. In other words, in Figure 2, the outermost position P1 is located closer to the first conductor layer 12 than to the interlayer connection portion 16 in the thickness direction, and the outermost position P2 is located closer to the second conductor layer 13 than to the interlayer connection portion 16 in the thickness direction. The energy density in the first irradiation step is, for example, 1 J / cm². 2 Preferably, 10 J / cm 2 That's all, and also, for example, 20 J / cm 2 Preferably, 18 J / cm 2 The following applies: If the energy density in the first irradiation process is above the lower limit mentioned above, manufacturing efficiency can be improved. If the energy density in the first irradiation process is below the upper limit mentioned above, lengths L1 and L2 can be controlled to be below the upper limit mentioned above, and furthermore, the first conductive hole 14A and the second conductive hole 15A can be made tapered. The energy density in the second irradiation step is, for example, lower than the energy density in the first irradiation step. By making the energy density in the second irradiation step lower than that in the first irradiation step, each layer up to the adhesive insulating layer 11g can be removed while leaving the interlayer connection portion 16 intact. Specifically, the ratio of the energy density in the second irradiation step to the energy density in the first irradiation step is, for example, 0.01 or more, preferably 0.02 or more, and also, for example, 0.4 or less, preferably 0.1 or less. Specifically, the energy density in the second irradiation step is, for example, 0.01 J / cm³. 2 That's all, and also, for example, 0.1 J / cm² 2 The following applies: In the process of forming the first conductive hole 14A and the second conductive hole 15A, when viewed in the thickness direction, the irradiation method used involves rotating the laser from the inside outward within the region where the hole is formed, and rotating it from the outside inward. The number of rotations is multiple. Preferably, when viewed in the thickness direction, the laser is rotated from the inside outward within the region where the hole is formed. With this irradiation method, the spot with the highest energy in the laser irradiation remains on the wall surface of the hole for a long time in the first half of the irradiation time, so the side surface of the insulating layer can be made tapered when viewed macroscopically in cross-section.

[0038] Next, the first conductor film 12A, the first non-porous insulating layer 11a, the first porous insulating layer 11b, the second non-porous insulating layer 11c, and the first holes 14A for conductive parts of the adhesive insulating layer 11g, as well as the surface of the first conductor film 12A, are plated. As a result, the first holes 14A for conductive parts are filled with conductor, and the first conductive part 14 is formed. Furthermore, the first conductor film 12A and the plating 12B on the first conductor film 12A become one, forming the first conductor layer 12. Furthermore, plating is applied to the second conductor film 13A, the third non-porous insulating layer 11d, the second porous insulating layer 11e, the fourth non-porous insulating layer 11f, and the second conductive hole 15A of the adhesive insulating layer 11g, as well as to the surface of the second conductor film 13A. As a result, the second conductive hole 15A is filled with conductor, and the second conductive part 15 is formed. Also, the second conductor film 13A and the plating 13B on the second conductor film 13A become one, forming the second conductor layer 13 (Figure 3G). As a result, the flexible multilayer circuit board shown in Figure 2 is obtained. [Explanation of symbols]

[0039] 1. Insulating layer 1a Non-porous insulating layer 1b Porous insulating layer 1c Non-porous insulating layer 1d Adhesive insulating layer 1x side 2 Conductor layers 3. Conductive section 4. Second Conductor Layer 11 Insulating layer 11a First non-porous insulating layer 11b First porous insulating layer 11c Second non-porous insulating layer 11d Third non-porous insulating layer 11e Second porous insulating layer 11f Fourth non-porous insulating layer 11g Adhesive insulating layer 11g-1 Adhesive insulating layer 11g-2 Adhesive insulating layer 11x sides 12. First Conductor Layer 12A First Conductor Film 12B Plating 13. Second Conductor Layer 13A Second Conductor Film 13B Plated 14. First conductive section 14A First hole for conductive part 15. Second conductive section 15A 2nd hole for conduction part 16 Interlayer connection section 16A Third Conductor Layer 21x sides C1 First connection point C2 Second connection point C11 First connection point C12 Second connection point C21 First Connection Point C22 Second Connection Point P outermost position P1 outermost position P2 outermost position S line segment S1 line segment S2 line segment S1 side

Claims

1. An insulating layer having holes for conductive parts, A conductive layer disposed on one side of the insulating layer in the thickness direction, It comprises a conductive portion disposed in the conductive portion hole and electrically connected to the conductor layer, The insulating layer comprises a porous insulating layer and a non-porous insulating layer in contact with the porous insulating layer and the conductor layer. The conductive holes are formed in the porous insulating layer and the non-porous insulating layer. A flexible multilayer circuit board in which the outermost position P, as specified below, is located on the non-porous insulating layer side of the center of the porous insulating layer in the thickness direction. Outermost position P: In the cross-sectional view in the thickness direction, draw a line segment S connecting a first connection point C1 where one surface of the insulating layer and the side surface of the conductive hole are in contact, and a second connection point C2 where the surface of the conductive hole opposite to the conductor layer side and the side surface of the conductive hole are in contact. In the aforementioned cross-sectional view, the outermost position P, which is furthest from the line segment S on the side surface of the conductive hole, is identified.

2. The flexible multilayer circuit board according to claim 1, wherein the length L measured below is 5 μm or more and 20 μm or less. Length L: The length L is measured as the shortest distance from the line segment S to the outermost position P.

3. An insulating layer having a first hole for conductive parts and a second hole for conductive parts, A first conductor layer is disposed on one side of the insulating layer in the thickness direction, A second conductor layer is disposed on the other side of the insulating layer in the thickness direction, A first conductive portion is disposed within the first hole for the conductive portion and electrically connected to the first conductor layer, A second conductive portion is disposed within the second hole for the conductive portion and electrically connected to the second conductor layer, The insulating layer includes an interlayer connection portion embedded in the insulating layer that electrically connects the first conductive portion and the second conductive portion, A flexible multilayer circuit board in which lengths L1 and L2, as measured below, are 5 μm or more and 20 μm or less, respectively. Length L1: In a cross-sectional view in the thickness direction, draw a line segment S1 connecting a first connection point C11 where one surface of the insulating layer and the side surface of the first hole for the conductive portion are in contact, and a second connection point C12 where the side surface of the first hole for the conductive portion of the insulating layer and the surface of the interlayer connection portion on the first conductor layer side are in contact. In the cross-sectional view, the outermost position P1, which is furthest from the line segment S1 on the side surface of the first hole for the conductive portion, is identified. The length L1 is measured as the shortest distance from the line segment S1 to the outermost position P1. Length L2: In a cross-sectional view in the thickness direction, draw a line segment S2 connecting a first connection point C21 where the other surface of the insulating layer and the side surface of the second hole for the conductive portion are in contact, and a second connection point C22 where the side surface of the second hole for the conductive portion of the insulating layer and the surface of the interlayer connection portion on the second conductor layer side are in contact. In the cross-sectional view, the outermost position P2, which is furthest from the line segment S2 on the side surface of the second hole for the conductive portion, is identified. The length L2 is measured as the shortest distance from the line segment S2 to the outermost position P2.

4. The outermost position P1 is located in the thickness direction, closer to the first conductor layer than the interlayer connection portion. The outermost position P2 is located in the thickness direction, closer to the second conductor layer than the interlayer connection portion. The flexible multilayer circuit board according to claim 3.

5. The insulating layer comprises an adhesive insulating layer, a first porous insulating layer disposed between the adhesive insulating layer and the first conductor layer, and a second porous insulating layer disposed between the adhesive insulating layer and the second conductor layer. The interlayer connection portion is embedded in the adhesive insulating layer. The flexible multilayer circuit board according to claim 3.

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