Flexible multilayer circuit board and flexible multilayer circuit board assembly

Abstract

The present invention provides a flexible multilayer circuit board comprising: an insulation layer; a first conductor layer disposed on one side of the insulation layer in a thickness direction; a second conductor layer disposed on the other side of the insulation layer in the thickness direction; a wiring part embedded in the insulation layer; and a connection via connected to the first conductor layer and the second conductor layer and penetrating the insulation layer in the thickness direction. The flexible multilayer circuit board further comprises a non-connection via embedded in the insulation layer and not penetrating the insulation layer in the thickness direction.

Description

Flexible multilayer circuit board and flexible multilayer circuit board assembly

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

[0002] In recent years, development of wireless communication standards for the so-called "fifth generation (5G)" has been progressing. Wireless communication standards for the "fifth generation (5G)" enable the transmission of large volumes of data at high speeds. Wireless communication standards for the "fifth generation (5G)" use high frequencies, including millimeter waves. Substrates for high-frequency antennas that emit such millimeter waves require substrates with low dielectric constants (low-dielectric substrates). Furthermore, flexible printed circuit boards (FPCs) are in demand for high-speed transmission FPCs that transmit data at high speeds, and low-dielectric substrates are also required for the substrates for these high-speed transmission FPCs.

[0003] As a flexible multilayer circuit board, for example, a wired circuit board has been proposed which includes a porous insulating layer and a conductor layer arranged in that order toward one side in the thickness direction, and the conductor layer has a first wiring portion and a second wiring portion that is thicker than the first wiring portion (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2022-182956

[0005] Flexible multilayer circuit boards are sometimes manufactured by bonding two or more layered precursors. An example of such a method is described below. FIG. 9 is a schematic diagram of an example of a conventional flexible multilayer circuit board. The flexible multilayer circuit board 60 shown in FIG. 9 includes an insulating layer 52, a first conductor layer 51 disposed on one thickness-wise side of the insulating layer 52, a second conductor layer 53 disposed on the other thickness-wise side of the insulating layer 52, a wiring portion 54 embedded in the insulating layer 52, and a connection via 56 connecting the first conductor layer 51 and the second conductor layer 53 and penetrating the insulating layer 52 in the thickness direction. The flexible multilayer circuit board 60 shown in FIG. 9 is manufactured by the method shown in FIGS. 10A to 10G. This method is described below. First, a laminate of a wiring portion precursor 54A and a first insulating layer precursor 52A is prepared ( FIG. 10A ). Next, a first connection via precursor 56A is formed to penetrate the first insulating layer precursor 52A of the prepared laminate in the thickness direction ( FIG. 10B ). Next, the wiring portion precursor 54A is selectively etched to form the wiring portion 54, thereby obtaining a first circuit board precursor 70A ( FIG. 10C ). Next, a second circuit board precursor 70B is prepared, which includes a second conductor layer 53, a second insulating layer precursor 52B disposed on one thickness-wise side of the second conductor layer 53, and a second connecting via precursor 56B penetrating the second insulating layer precursor 52B in the thickness direction ( FIG. 10D ). Next, the first circuit board precursor 70A and the second circuit board precursor 70B are aligned so that the wiring portion 54 faces the second insulating layer precursor 52B ( FIG. 10E ). The first circuit board precursor 70A and the second circuit board precursor 70B are then bonded together so that the first connecting via precursor 56A and the second connecting via precursor 56B are in contact with each other. This causes the first insulating layer precursor 52A and the second insulating layer precursor 52B to be integrated into the insulating layer 52. Furthermore, the first connection via precursor 56A and the second connection via precursor 56B are integrated to form the connection via 56 (FIG. 10F). Next, the first conductor layer 51 is bonded to one side of the insulating layer 52 in the thickness direction (FIG. 10G). By doing so, the flexible multilayer circuit board 60 shown in FIG. 9 is obtained. Here, when the first circuit board precursor 70A and the second circuit board precursor 70B are bonded together, the resulting insulating layer 52 is deformed by pressure.The deformation of the insulating layer 52 changes the insulating properties (for example, dielectric properties) of the insulating layer 52, which may result in the electrical properties of the wiring portion 54 deviating from the desired electrical properties.

[0006] An object of the present invention is to provide a flexible multilayer circuit board capable of suppressing fluctuations in the electrical characteristics of the wiring portion, and a flexible multilayer circuit board assembly capable of suppressing fluctuations in the electrical characteristics of the wiring portion.

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved, and have completed the present invention having the following gist.

[0008] [1] A flexible multilayer circuit board comprising: an insulating layer; a first conductor layer disposed on one side of the insulating layer in a thickness direction; a second conductor layer disposed on the other side of the insulating layer in the thickness direction; a wiring portion embedded in the insulating layer; and a connection via connecting the first conductor layer and the second conductor layer, the connection via penetrating the insulating layer in a thickness direction, the flexible multilayer circuit board further comprising a non-connection via embedded in the insulating layer and not penetrating the insulating layer in a thickness direction. [2] The flexible multilayer circuit board according to [1], wherein the insulating layer contains a liquid crystal polymer, a cycloolefin polymer, or a polyimide resin. [3] The flexible multilayer circuit board according to [1] or [2], wherein the insulating layer is porous. [4] A flexible wiring board assembly comprising: a plurality of flexible multilayer circuit boards; and a frame portion formed on the outer periphery of the plurality of flexible multilayer circuit boards, wherein the flexible multilayer circuit board is the flexible multilayer circuit board according to any one of [1] to [3].

[0009] According to the present invention, it is possible to provide a flexible multilayer circuit board capable of suppressing fluctuations in the electrical characteristics of the wiring portion, and a flexible multilayer circuit board assembly capable of suppressing fluctuations in the electrical characteristics of the wiring portion.

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

[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, a wiring portion, and a connection via. The first conductor layer is arranged on one side of the insulating layer in the thickness direction. The second conductor layer is arranged on the other side of the insulating layer in the thickness direction. The wiring portion is embedded in the insulating layer. The connection via connects the first conductor layer and the second conductor layer. The connection via penetrates the insulating layer in the thickness direction. The flexible multilayer circuit board further comprises a non-connection via. The non-connection via is embedded in the insulating layer and does not penetrate the insulating layer in the thickness direction.

[0012] The non-connection vias are sufficiently harder than the insulating layer and are less likely to deform due to pressure. By embedding the non-connection vias in the insulating layer, in the flexible multilayer circuit board of the present invention, deformation of the insulating layer due to pressure during manufacturing of the flexible multilayer circuit board can be suppressed. As a result, fluctuations in the electrical properties of the wiring portion of the flexible multilayer circuit board can be suppressed.

[0013] An example of a flexible multilayer circuit board of the present invention will be described below with reference to FIGS. 1A and 1B. FIG. 1A is a schematic diagram of one embodiment of a flexible multilayer circuit board. This schematic diagram is a cross-sectional view perpendicular to the longitudinal direction of the wiring portion. FIG. 1B is a cross-sectional view taken along the line A-A of the flexible multilayer circuit board of FIG. 1A. The flexible multilayer circuit board 10 shown in FIG. 1A includes an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring portion 4, and connection vias 6. The flexible multilayer circuit board 10 further includes non-connection vias 5. The first conductor layer 1 is disposed on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 contacts the insulating layer 2 on one side of the insulating layer 2 in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction on the paper surface in FIG. 1A. The second conductor layer 3 is disposed on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 3 contacts the insulating layer 2 on the other side of the insulating layer 2 in the thickness direction. The other side is opposite to the one side. The wiring portion 4 is embedded in the insulating layer 2. The wiring portion 4 transmits, for example, an electrical signal. The connection vias 6 electrically connect the first conductor layer 1 and the second conductor layer 3. The connection vias 6 penetrate the insulating layer 2 in the thickness direction. The non-connection vias 5 are embedded in the insulating layer 2 and do not penetrate the insulating layer 2 in the thickness direction.

[0014] In the flexible multilayer circuit board 10 shown in FIGS. 1A and 1B , the first conductor layer 1 and the second conductor layer 3 extend in the length direction of the wiring portion 4. The length direction of the wiring portion 4 is a direction perpendicular to the vertical and horizontal directions of the paper in FIG. 1A , and is the vertical direction of the paper in FIG. 1B . As shown in FIG. 1B , the connection vias 6 are arranged in rows in the length direction of the wiring portion 4. In FIGS. 1A and 1B , there are two rows of multiple connection vias 6, and the wiring portion 4 is sandwiched between these two rows. The connection vias 6 have the role of, for example, earthing weak currents that affect the wiring portion 4. The non-connection vias 5 are regularly scattered in the length direction of the wiring portion 4. The non-connection vias 5 may be regularly scattered or irregularly scattered in the length direction of the wiring portion 4, but are preferably regularly scattered. By being regularly scattered, the pressure applied to the insulating layer 2 during the manufacture of the flexible multilayer circuit board can be evenly distributed, thereby further suppressing deformation of the insulating layer 2 due to the pressure. In the flexible multilayer circuit board 10 shown in Figure 1A, the multiple non-connection vias 5 are each electrically connected to the first conductor layer 1 or the second conductor layer 3, but the non-connection vias 5 may or may not be electrically connected to the first conductor layer 1 or the second conductor layer 3. When the non-connection vias 5 are not electrically connected to the first conductor layer 1 or the second conductor layer 3, it can be said that the non-connection vias 5 are completely embedded in the insulating layer 2.

[0015] 1A and 1B , some of the non-connection vias 5 are arranged between the wiring portion 4 and the connection vias 6 in the direction (width direction of the flexible multilayer circuit board 10) perpendicular to the thickness direction of the insulating layer 2 and the length direction of the wiring portion 4. Some of the non-connection vias 5 are arranged in locations other than between the wiring portion 4 and the connection vias 6 (outside the connection vias 6) in the width direction of the flexible multilayer circuit board 10.

[0016] 1A, the first conductor layer 1 and the second conductor layer 3 are the outermost layers constituting the flexible multilayer circuit board 10. The first conductor layer 1 and the second conductor layer 3 sandwich the insulating layer 2 therebetween.

[0017] 1A, the wiring portion 4 is not in contact with the first conductor layer 1, the second conductor layer 3, and the connection vias 6. Furthermore, the wiring portion 4 is not in contact with the non-connection vias 5 either.

[0018] The material of the first conductor layer and the second conductor layer is not particularly limited, and examples thereof include metal materials. Examples of metal materials include copper, nickel, gold, solder, and alloys of two or more of these. The materials of the first conductor layer and the second conductor layer may be the same or different. The thickness of the first conductor layer and the second conductor layer is not particularly limited, and is, for example, 3 μm or more, preferably 5 μm or more, and, for example, 50 μm or less, preferably 30 μm or less. The thickness of the first conductor layer and the second conductor layer may be the same or different. In the present invention, "thickness" refers to the length in the thickness direction of the flexible multilayer circuit board. The thickness direction of the flexible multilayer circuit board refers, for example, to the direction perpendicular to the surface direction of the first conductor layer and the second conductor layer.

[0019] The material of the wiring portion is not particularly limited, and examples thereof include metal materials. Examples of metal materials include copper, nickel, gold, solder, and alloys of two or more of these. The thickness of the wiring portion is not particularly limited, and is, for example, 3 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 30 μm or less. Note that, since the wiring portion is embedded in the insulating layer, the thickness of the wiring portion is usually thinner than the thickness of the insulating layer. The width of the wiring portion (the length of the wiring portion in the thickness direction and the direction perpendicular to the length direction of the wiring portion) is not particularly limited, but is usually shorter than the width of the first conductor layer and the second conductor layer (the length of the first conductor layer and the second conductor layer in the thickness direction and the direction perpendicular to the length direction of the first conductor layer and the second conductor layer), for example, 1 / 5 to 1 / 2 of the width of the first conductor layer and the second conductor layer. Note that, since the wiring portion is embedded in the insulating layer, the width of the wiring portion is usually shorter than the width of the insulating layer.

[0020] Examples of materials constituting the insulating layer include resins. In other words, the insulating layer contains, for example, a resin. Examples of resins include polycarbonate resins, polyimide resins, fluorinated polyimide resins, epoxy resins, phenolic resins, urea resins, melamine resins, diallyl phthalate resins, silicone resins, thermosetting urethane resins, fluororesins, cycloolefin polymers, and liquid crystal polymers. From the viewpoints of high insulation properties, high heat resistance, and high mechanical strength, polyimide resins, cycloolefin polymers, and liquid crystal polymers are preferred. The thickness of the insulating layer is not particularly limited and is, for example, 5 μm or more, preferably 10 μm or more, and, for example, 1000 μm or less, preferably 600 μm or less. The insulating layer may be porous or non-porous. If the insulating layer is porous, it is more likely to deform under pressure. Therefore, if the insulating layer is porous, suppressing deformation of the insulating layer significantly enhances the effect of the present invention, which is to suppress fluctuations in the electrical properties of the wiring portion. In this respect, it is preferable that the insulating layer be porous. Furthermore, by making the insulating layer porous, the dielectric constant of the insulating layer can be reduced, and the flexible multilayer circuit board can be suitably used as a flexible multilayer circuit board for high-speed transmission. In this respect, it is preferable that the insulating layer is porous. When the insulating layer is porous, the insulating layer may have closed cells or open cells.

[0021] The material of the connection via is not particularly limited, and examples thereof include metal materials. Examples of metal materials include copper, nickel, gold, solder, and alloys of two or more of these. The material of the connection via may be the same as or different from the materials of the first conductor layer and the second conductor layer. The shape of the connection via is not particularly limited, and examples thereof include square, rectangular, circular, elliptical, etc. in a cross section perpendicular to the thickness direction of the flexible multilayer circuit board (for example, cross section A-A in FIG. 1A). The length (X １ ) and the length of the connection via in the width direction of the wiring part (Y １ ) and the ratio (X １ :Y １) may be, for example, 3:1 to 1:3, 1:2 to 2:1, or 1:1. １ :Y １ ) is 1:1, the shape of the connection via in a cross section perpendicular to the thickness direction of the flexible multilayer circuit board is, for example, square or circular.

[0022] The material of the non-connection via is not particularly limited, and examples thereof include metal materials. Examples of metal materials include copper, nickel, gold, solder, and alloys of two or more of these. The material of the non-connection via may be the same as or different from the materials of the first conductor layer, the second conductor layer, and the connection via. The shape of the non-connection via is not particularly limited, and examples thereof include a square, rectangle, circle, ellipse, etc. in a cross section (e.g., cross section A-A in FIG. 1A) perpendicular to the thickness direction of the flexible multilayer circuit board. The length (X ２ ) and the length of the unconnected via in the width direction of the wiring part (Y ２ ) and the ratio (X ２ :Y ２ ) may be, for example, 3:1 to 1:3, 1:2 to 2:1, or 1:1. ２ :Y ２ ) is 1:1, the shape of the non-connected via in a cross section perpendicular to the thickness direction of the flexible multilayer circuit board is, for example, square or circular.

[0023] One embodiment of a method for manufacturing the flexible multilayer circuit board shown in FIGS. 1A and 1B will be described with reference to FIGS. 2A to 2G. First, a laminate of a wiring portion precursor 4A and a first insulating layer precursor 2A is prepared ( FIG. 2A ). Both the wiring portion precursor 4A and the first insulating layer precursor 2A are layered. Next, a first connecting via precursor 6A and a non-connecting via 5 are formed to penetrate the first insulating layer precursor 2A in the thickness direction of the prepared laminate ( FIG. 2B ). The method for forming the first connecting via precursor 6A and the non-connecting via 5 is not particularly limited, and examples include a method in which through-holes are formed in the first insulating layer precursor 2A using a laser, and then the first connecting via precursor 6A and the non-connecting via 5 are filled into the formed through-holes by plating. Note that the non-connecting via 5 may or may not penetrate the first insulating layer precursor 2A in the thickness direction. Next, the wiring portion precursor 4A is selectively etched to form the wiring portion 4, thereby obtaining a first circuit board precursor 20A ( FIG. 2C ). Next, a second circuit board precursor 20B is prepared, including a second conductor layer 3, a second insulating layer precursor 2B disposed on one side of the second conductor layer 3 in the thickness direction, and second connection via precursors 6B and non-connection vias 5 penetrating the second insulating layer precursor 2B in the thickness direction (FIG. 2D). The second insulating layer precursor 2B is layered. The method for forming the second connection via precursor 6B and the non-connection vias 5 is not particularly limited, and examples include a method in which through holes are formed in the second insulating layer precursor 2B using a laser, and then the second connection via precursors 6B and non-connection vias 5 are filled into the formed through holes by plating. The non-connection vias 5 may or may not penetrate the second insulating layer precursor 2B in the thickness direction. Next, the first circuit board precursor 20A and the second circuit board precursor 20B are arranged so that the wiring portion 4 and the second insulating layer precursor 2B face each other (FIG. 2E). The first circuit board precursor 20A and the second circuit board precursor 20B are then bonded together so that the first connection via precursor 6A and the second connection via precursor 6B are in contact with each other. The pressure and temperature during lamination are not particularly limited. By doing so, the first insulating layer precursor 2A and the second insulating layer precursor 2B are integrated to form the insulating layer 2. Furthermore, the first connecting via precursor 6A and the second connecting via precursor 6B are integrated to form the connecting via 6 (FIG. 2F).Next, the first conductor layer 1 is bonded to one side of the insulating layer 2 in the thickness direction (FIG. 2G). The pressure and temperature during bonding are not particularly limited. In this manner, the flexible multilayer circuit board 10 shown in FIG. 1A is obtained.

[0024] FIG. 3 is a schematic diagram of another embodiment of a flexible multilayer circuit board. This schematic diagram is a cross-sectional view perpendicular to the longitudinal direction of the wiring portion. The flexible multilayer circuit board 10 shown in FIG. 3 includes an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring portion 4, and a connection via 6. The flexible multilayer circuit board 10 further includes a non-connection via 5. The first conductor layer 1 is disposed on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 contacts the insulating layer 2 on one side of the insulating layer 2 in the thickness direction. The thickness direction of the insulating layer 2 is the up-and-down direction on the paper surface in FIG. 3. The second conductor layer 3 is disposed on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 3 contacts the insulating layer 2 on the other side of the insulating layer 2 in the thickness direction. The other side is opposite to the one side. The wiring portion 4 is embedded in the insulating layer 2. The connection via 6 electrically connects the first conductor layer 1 and the second conductor layer 3. The connection via 6 penetrates the insulating layer 2 in the thickness direction. The non-connection vias 5 are embedded in the insulating layer 2 and do not penetrate the insulating layer 2 in the thickness direction.

[0025] In the flexible multilayer circuit board 10 shown in Figure 3, some non-connected vias 5 are in electrical contact with the first conductor layer 1 or the second conductor layer 3, while other non-connected vias 5 are not in electrical contact with the first conductor layer 1 or the second conductor layer 3.

[0026] Fig. 4 is a schematic diagram for explaining one embodiment of a method for manufacturing the flexible multilayer circuit board shown in Fig. 3. The flexible multilayer circuit board 10 shown in Fig. 3 is obtained, for example, by bonding together a first circuit board precursor 20C, a second circuit board precursor 20D, and a third circuit board precursor 20E, as shown in Fig. 4.

[0027] The first circuit board precursor 20C includes a first insulating layer precursor 2C, a second conductor layer 3, a wiring portion 4, a non-connection via 5, and a first connecting via precursor 6C. The second conductor layer 3 is disposed on one thickness-wise side of the first insulating layer precursor 2C. The wiring portion 4 is disposed on the other thickness-wise side of the first insulating layer precursor 2C. The non-connection via 5 penetrates the first insulating layer precursor 2C in the thickness direction. The non-connection via 5 is electrically connected to the second conductor layer 3. The non-connection via 5 may be filled in a non-through hole formed in the first insulating layer precursor 2C. In this case, the non-connection via 5 does not penetrate the first insulating layer precursor 2C in the thickness direction. The non-connection via 5 does not need to be electrically connected to the second conductor layer 3. The first connecting via precursor 6C penetrates the first insulating layer precursor 2C in the thickness direction. The first connecting via precursor 6C is electrically connected to the second conductor layer 3.

[0028] The second circuit board precursor 20D has a second insulating layer precursor 2D, a non-connection via 5, and a second connecting via precursor 6D. The non-connection via 5 penetrates the second insulating layer precursor 2D in the thickness direction. The non-connection via 5 may be filled in a non-through hole formed in the second insulating layer precursor 2D, in which case the non-connection via 5 does not penetrate the second insulating layer precursor 2D in the thickness direction. The second connecting via precursor 6D penetrates the second insulating layer precursor 2D in the thickness direction.

[0029] The third circuit board precursor 20E includes a third insulating layer precursor 2E, a first conductor layer 1, a non-connection via 5, and a third connecting via precursor 6E. The first conductor layer 1 is disposed on one side of the third insulating layer precursor 2E in the thickness direction. The non-connection via 5 penetrates the third insulating layer precursor 2E in the thickness direction. The non-connection via 5 is in electrical contact with the first conductor layer 1. The non-connection via 5 may be filled in a non-through hole formed in the third insulating layer precursor 2E. In this case, the non-connection via 5 does not penetrate the third insulating layer precursor 2E in the thickness direction. The non-connection via 5 does not need to be in electrical contact with the first conductor layer 1. The third connecting via precursor 6E penetrates the third insulating layer precursor 2E in the thickness direction. The third connecting via precursor 6E is in electrical contact with the first conductor layer 1.

[0030] The first circuit board precursor 20C, the second circuit board precursor 20D, and the third circuit board precursor 20E are bonded together so that the first connection via precursor 6C and the second connection via precursor 6D are in contact, and the second connection via precursor 6D and the third connection via precursor 6E are in contact. By doing so, the first insulating layer precursor 2C, the second insulating layer precursor 2D, and the third insulating layer precursor 2E are integrated to form the insulating layer 2. Furthermore, the first connection via precursor 6C, the second connection via precursor 6D, and the third connection via precursor 6E are integrated to form the connection via 6. As a result, the flexible multilayer circuit board 10 shown in FIG. 3 is obtained.

[0031] 4, three circuit board precursors (first circuit board precursor 20C, second circuit board precursor 20D, and third circuit board precursor 20E) are bonded together at one time. The number of circuit board precursors bonded together at one time may be two, three, or more.

[0032] FIG. 5 is a schematic diagram of another embodiment of a flexible multilayer circuit board. This schematic diagram is a cross-sectional view perpendicular to the longitudinal direction of the wiring portion. The flexible multilayer circuit board 10 shown in FIG. 5 includes an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring portion 4, and a connection via 6. The flexible multilayer circuit board 10 further includes a non-connection via 5. The first conductor layer 1 is disposed on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 contacts the insulating layer 2 on one side of the insulating layer 2 in the thickness direction. The thickness direction of the insulating layer 2 is the up-and-down direction on the paper surface in FIG. 5. The second conductor layer 3 is disposed on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 3 contacts the insulating layer 2 on the other side of the insulating layer 2 in the thickness direction. The other side is opposite to the one side. The wiring portion 4 is embedded in the insulating layer 2. The connection via 6 electrically connects the first conductor layer 1 and the second conductor layer 3. The connection via 6 penetrates the insulating layer 2 in the thickness direction. The non-connection vias 5 are embedded in the insulating layer 2 and do not penetrate the insulating layer 2 in the thickness direction.

[0033] In the flexible multilayer circuit board 10 shown in Figure 5, some non-connected vias 5 are electrically connected to the first conductor layer 1 or the second conductor layer 3, while other non-connected vias 5 are not electrically connected to the first conductor layer 1 or the second conductor layer 3.

[0034] Fig. 6 is a schematic diagram for explaining one embodiment of a method for manufacturing the flexible multilayer circuit board shown in Fig. 5. The flexible multilayer circuit board 10 shown in Fig. 5 is obtained by bonding together, for example, a first circuit board precursor 20F, a second circuit board precursor 20G, a third circuit board precursor 20H, and a fourth circuit board precursor 20I, as shown in Fig. 6.

[0035] The first circuit board precursor 20F includes a first insulating layer precursor 2F, a second conductor layer 3, a non-connection via 5, and a first connection via precursor 6F. The second conductor layer 3 is disposed on one side of the first insulating layer precursor 2F in the thickness direction. The non-connection via 5 penetrates the first insulating layer precursor 2F in the thickness direction. The non-connection via 5 is electrically connected to the second conductor layer 3. The non-connection via 5 may be filled in a non-through hole formed in the first insulating layer precursor 2F. In this case, the non-connection via 5 does not penetrate the first insulating layer precursor 2F in the thickness direction. The non-connection via 5 does not need to be electrically connected to the second conductor layer 3. The first connection via precursor 6F penetrates the first insulating layer precursor 2F in the thickness direction. The first connection via precursor 6F is electrically connected to the second conductor layer 3.

[0036] The second circuit board precursor 20G has a second insulating layer precursor 2G, a wiring portion 4, a non-connection via 5, and a second connecting via precursor 6G. The wiring portion 4 is arranged on one side of the second insulating layer precursor 2G in the thickness direction. The non-connection via 5 is filled in a non-through hole formed in the second insulating layer precursor 2G. The second connecting via precursor 6G penetrates the second insulating layer precursor 2G in the thickness direction.

[0037] The third circuit board precursor 20H has a third insulating layer precursor 2H, a non-connection via 5, and a third connecting via precursor 6H. The non-connection via 5 penetrates the third insulating layer precursor 2H in the thickness direction. The non-connection via 5 may be filled in a non-through hole formed in the third insulating layer precursor 2H, in which case the non-connection via 5 does not penetrate the third insulating layer precursor 2H in the thickness direction. The third connecting via precursor 6H penetrates the third insulating layer precursor 2H in the thickness direction.

[0038] The fourth circuit board precursor 20I includes a fourth insulating layer precursor 2I, a first conductor layer 1, a non-connection via 5, and a fourth connection via precursor 6I. The first conductor layer 1 is disposed on one side of the fourth insulating layer precursor 2I in the thickness direction. The non-connection via 5 penetrates the fourth insulating layer precursor 2I in the thickness direction. The non-connection via 5 is electrically connected to the first conductor layer 1. The non-connection via 5 may be filled in a non-through hole formed in the fourth insulating layer precursor 2I. In this case, the non-connection via 5 does not penetrate the fourth insulating layer precursor 2I in the thickness direction. The non-connection via 5 does not need to be electrically connected to the first conductor layer 1. The fourth connection via precursor 6I penetrates the fourth insulating layer precursor 2I in the thickness direction. The fourth connection via precursor 6I is electrically connected to the first conductor layer 1.

[0039] The first circuit board precursor 20F, the second circuit board precursor 20G, the third circuit board precursor 20H, and the fourth circuit board precursor 20I are bonded together so that the first connection via precursor 6F and the second connection via precursor 6G are in contact, the second connection via precursor 6G and the third connection via precursor 6H are in contact, and the third connection via precursor 6H and the fourth connection via precursor 6I are in contact. By doing so, the first insulating layer precursor 2F, the second insulating layer precursor 2G, the third insulating layer precursor 2H, and the fourth insulating layer precursor 2I are integrated to form the insulating layer 2. Furthermore, the first connection via precursor 6F, the second connection via precursor 6G, the third connection via precursor 6H, and the fourth connection via precursor 6I are integrated to form the connection via 6. As a result, the flexible multilayer circuit board 10 shown in FIG. 5 is obtained.

[0040] FIG. 7 is a schematic diagram of another embodiment of a flexible multilayer circuit board. This schematic diagram is a cross-sectional view perpendicular to the longitudinal direction of the wiring portion. The flexible multilayer circuit board shown in FIG. 7 has the same structure as the flexible multilayer circuit board shown in FIG. 1A , except that the wiring portion 4 has two signal lines (a first signal line 41 and a second signal line 42). The flexible multilayer circuit board 10 shown in FIG. 7 includes an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring portion 4, and a connection via 6. The flexible multilayer circuit board 10 further includes a non-connection via 5. The first conductor layer 1 is disposed on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 contacts the insulating layer 2 on one side of the insulating layer 2 in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction on the paper in FIG. 7. The second conductor layer 3 is disposed on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 3 contacts the insulating layer 2 on the other side of the insulating layer 2 in the thickness direction. The other side is opposite to the one side. The wiring portion 4 is embedded in the insulating layer 2. The connection vias 6 electrically connect the first conductor layer 1 and the second conductor layer 3. The connection vias 6 penetrate the insulating layer 2 in the thickness direction. The non-connection vias 5 are embedded in the insulating layer 2 and do not penetrate the insulating layer 2 in the thickness direction. The wiring portion 4 has two signal lines (a first signal line 41 and a second signal line 42). The first signal line 41 and the second signal line 42 constitute differential wiring for differential signal transmission.

[0041] BACKGROUND ART Flexible multilayer circuit boards are used as flexible multilayer circuit boards for high-speed transmission in electronic devices such as mobile phones, smartphones, tablet terminals, and digital cameras, as they become smaller, lighter, and more functional.

[0042] (Flexible Multilayer Circuit Board Assembly) The flexible multilayer circuit board assembly of the present invention includes a plurality of flexible multilayer circuit boards and a frame portion, which is formed around the periphery of the plurality of flexible multilayer circuit boards.

[0043] Each flexible multilayer circuit board is used after being separated from the flexible multilayer circuit board assembly. The timing of separating each flexible multilayer circuit board from the flexible multilayer circuit board assembly is not particularly limited, and may be, for example, after or before components are mounted.

[0044] The number of flexible multilayer circuit boards included in the flexible multilayer circuit board assembly is not particularly limited, but is usually two or more.

[0045] The frame portion includes, for example, a third conductor layer and a fourth conductor layer. The materials for the third conductor layer and the fourth conductor layer are not particularly limited and include, for example, metal materials. Examples of metal materials include copper, nickel, gold, solder, and alloys of two or more of these. The thicknesses of the third conductor layer and the fourth conductor layer are not particularly limited and are, for example, 3 μm or more, preferably 5 μm or more, and for example, 50 μm or less, preferably 30 μm or less. It is preferable that the third conductor layer be integral with each of the first conductor layers of the multiple flexible multilayer circuit boards, in terms of ease of manufacturing the flexible multilayer circuit board assembly. It is preferable that the fourth conductor layer be integral with each of the second conductor layers of the multiple flexible multilayer circuit boards, in terms of ease of manufacturing the flexible multilayer circuit board assembly. The phrase "the third conductor layer is integral with each of the first conductor layers of the multiple flexible multilayer circuit boards" means that the third conductor layer and the first conductor layer are formed from a single plate material. The fourth conductor layer being integral with each of the second conductor layers of the plurality of flexible multilayer circuit boards means that the fourth conductor layer and the second conductor layer are formed from a single plate material.

[0046] The frame portion includes, for example, a second insulating layer. Examples of materials constituting the second insulating layer include resin. In other words, the second insulating layer includes, for example, a resin. 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, cycloolefin polymer, and liquid crystal polymer. Preferred examples include polyimide resin, cycloolefin polymer, and liquid crystal polymer. The thickness of the second insulating layer is not particularly limited and is, for example, 5 μm or more, preferably 10 μm or more, and, for example, 1000 μm or less, preferably 600 μm or less. The second insulating layer may be porous or non-porous.

[0047] It is preferable that the second insulating layer be integral with each of the insulating layers of the plurality of flexible multilayer circuit boards, since this facilitates the production of the flexible multilayer circuit board assembly. The second insulating layer being integral with each of the insulating layers of the plurality of flexible multilayer circuit boards means that the second insulating layer of the frame portion is formed simultaneously when each of the insulating layers of the plurality of flexible multilayer circuit boards is formed.

[0048] <First Aspect> In a first aspect, which is one example of a flexible multilayer circuit board assembly, the flexible multilayer circuit board is the flexible multilayer circuit board of the present invention. That is, the flexible multilayer circuit board includes non-connecting vias.

[0049] In the first aspect, the frame portion may or may not include a second non-connected via. When the frame portion includes the second non-connected via, for example, the frame portion includes a second insulating layer, a third conductor layer disposed on one side of the second insulating layer in the thickness direction, and a fourth conductor layer disposed on the other side of the second insulating layer in the thickness direction. Furthermore, the second non-connected via is embedded in the second insulating layer and does not penetrate the second insulating layer in the thickness direction.

[0050] <Second Aspect> In a second aspect, which is an example of a flexible multilayer circuit board assembly, the frame portion includes a non-connected via. In this case, for example, the frame portion includes a second insulating layer, a third conductor layer disposed on one thickness-wise side of the second insulating layer, and a fourth conductor layer disposed on the other thickness-wise side of the second insulating layer. Furthermore, the second non-connected via is embedded in the second insulating layer and does not penetrate the second insulating layer in the thickness direction.

[0051] In the second aspect, unlike the first aspect, the flexible multilayer circuit board does not include a non-connection via, and such a flexible multilayer circuit board includes, for example, an insulating layer, a first conductor layer disposed on one side of the insulating layer in the thickness direction, a second conductor layer disposed on the other side of the insulating layer in the thickness direction, a wiring portion embedded in the insulating layer, and a connection via connecting the first conductor layer and the second conductor layer and penetrating the edge layer in the thickness direction.

[0052] In the second aspect of the flexible multilayer circuit board assembly of the present invention, by providing non-connecting vias in the frame portion, deformation of the insulating layer of the flexible multilayer circuit board due to pressure during production of the flexible multilayer circuit board assembly can be suppressed, thereby suppressing fluctuations in the electrical characteristics of the wiring portion of the flexible multilayer circuit board.

[0053] Examples and preferred examples of the material and shape of the non-connected via (second non-connected via) in the frame portion include the materials and shapes mentioned in the description of the non-connected via in the flexible multilayer circuit board.

[0054] An example of a flexible multilayer circuit board assembly will be described using the drawings. FIG. 8A is a schematic diagram of one embodiment of a flexible multilayer circuit board assembly. This schematic diagram is a cross-sectional view perpendicular to the longitudinal direction of the wiring portion. FIG. 8B is a cross-sectional view taken along the line A-A of the flexible multilayer circuit board assembly of FIG. 8A. The flexible multilayer circuit board assembly 100 shown in FIG. 8A has a flexible multilayer circuit board 10 and a frame portion 11. In the flexible multilayer circuit board assembly 100, 14 flexible multilayer circuit boards 10 are arranged in two rows and seven columns, with a frame portion 11 surrounding the flexible multilayer circuit boards 10. Each flexible multilayer circuit board 10 and the frame portion 11 are fixed to the frame portion 11 by lugs provided at four locations on the top, bottom, left, and right of each flexible multilayer circuit board 10.

[0055] As shown in FIG. 8B, each flexible multilayer circuit board 10 in the flexible multilayer circuit board assembly 100 shown in FIG. 8A has a structure roughly similar to that shown in FIG. 1A.

[0056] That is, the flexible multilayer circuit board 10 includes an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring portion 4, and a connection via 6. The flexible multilayer circuit board 10 further includes a non-connection via 5. The first conductor layer 1 is disposed on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 contacts the insulating layer 2 on one side in the thickness direction of the insulating layer 2. The thickness direction of the insulating layer 2 is the up-and-down direction on the paper in FIG. 8B. The second conductor layer 3 is disposed on the other side of the insulating layer 2 in the thickness direction. The second conductor layer 3 contacts the insulating layer 2 on the other side in the thickness direction of the insulating layer 2. The other side is opposite to the one side. The wiring portion 4 is embedded in the insulating layer 2. The wiring portion 4 transmits, for example, an electrical signal. The connection via 6 electrically connects the first conductor layer 1 and the second conductor layer 3. The connection via 6 penetrates the insulating layer 2 in the thickness direction. The non-connection vias 5 are embedded in the insulating layer 2 and do not penetrate the insulating layer 2 in the thickness direction.

[0057] 8A includes a second insulating layer 22, a third conductor layer 21 disposed on one thickness-wise side of the second insulating layer 22, a fourth conductor layer 23 disposed on the other thickness-wise side of the second insulating layer 22, and non-connected vias 5 embedded in the second insulating layer 22 and not penetrating the second insulating layer 22 in the thickness direction. The arrangement of the non-connected vias 5 in the frame 11 is not particularly limited, and they may be regularly scattered or irregularly scattered, although regularly scattered vias are preferred.

[0058] 1 First conductor layer 2 Insulating layer 2A First insulating layer precursor 2B Second insulating layer precursor 2C First insulating layer precursor 2D Second insulating layer precursor 2E Third insulating layer precursor 2F First insulating layer precursor 2G Second insulating layer precursor 2H Third insulating layer precursor 2I Fourth insulating layer precursor 3 Second conductor layer 4 Wiring portion 4A Wiring portion precursor 5 Non-connecting via 6 Connection via 6A First connecting via precursor 6B Second connecting via precursor 6C First connecting via precursor 6D Second connecting via precursor 6E Third connecting via precursor 6F First connecting via precursor 6G Second connecting via precursor 6H Third connecting via precursor 6I Fourth connecting via precursor 10 Flexible multilayer circuit board 11 Frame portion 20A First circuit board precursor 20B Second circuit board precursor 20C First circuit board precursor 20D Second circuit board precursor 20E Third circuit board precursor 20F First circuit board precursor 20G: Second circuit board precursor 20H: Third circuit board precursor 20I: Fourth circuit board precursor 21: Third conductor layer 22: Second insulating layer 23: Fourth conductor layer 41: First signal line 42: Second signal line 51: First conductor layer 52: Insulating layer 52A: First insulating layer precursor 52B: Second insulating layer precursor 53: Second conductor layer 54: Wiring portion 54A: Wiring portion precursor 56: Connection via 56A: First connection via precursor 56B: Second connection via precursor 60: Flexible multilayer circuit board 70A: First circuit board precursor 70B: Second circuit board precursor 100: Flexible multilayer circuit board assembly

Claims

1. an insulating layer; a first conductor layer disposed on one side of the insulating layer in a thickness direction; a second conductor layer disposed on the other side of the insulating layer in the thickness direction; a wiring portion embedded in the insulating layer; a connection via that connects the first conductor layer and the second conductor layer and penetrates the insulating layer in a thickness direction; A flexible multilayer circuit board comprising: Further, the insulating layer includes a plurality of non-connected vias that are embedded in the insulating layer and do not penetrate the insulating layer in a thickness direction, the plurality of non-connection vias include a non-connection via that is arranged between the wiring portion and the connection via in the width direction of the flexible multilayer circuit board, Flexible multilayer circuit board.

2. The flexible multilayer circuit board according to claim 1 , wherein the insulating layer comprises a liquid crystal polymer, a cycloolefin polymer, or a polyimide resin.

3. The flexible multilayer circuit board of claim 1 , wherein the insulating layer is porous.

4. a plurality of flexible multilayer circuit boards; a frame portion formed on the outer periphery of the plurality of flexible multilayer circuit boards; A flexible wiring board assembly having: The flexible multilayer circuit board is the flexible multilayer circuit board according to any one of claims 1 to 3. Flexible multilayer circuit board assembly.