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

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] It may be necessary to manufacture a flexible multilayer circuit board by laminating two or more layer precursors. An example thereof will be described below. Figure 9 is a schematic diagram of an example of a conventional flexible multilayer circuit board. The flexible multilayer circuit board 60 shown in Figure 9 comprises an insulating layer 52, a first conductor layer 51 disposed on one side of the insulating layer 52 in the thickness direction, a second conductor layer 53 disposed on the other side of the insulating layer 52 in the thickness direction, wiring portions 54 embedded in the insulating layer 52, and connecting vias 56 that connect to the first conductor layer 51 and the second conductor layer 53, and the connecting vias 56 penetrate the insulating layer 52 in the thickness direction. The flexible multilayer circuit board 60 shown in Figure 9 is manufactured by the method shown in Figures 10A to 10G. The method is described below. First, a laminate of the wiring precursor 54A and the first insulating layer precursor 52A is prepared (Figure 10A). Next, a first connecting via precursor 56A is formed that penetrates the first insulating layer precursor 52A of the prepared laminate in the thickness direction (Figure 10B). Next, the wiring precursor 54A is selectively etched to form the wiring portion 54, thereby obtaining the first circuit board precursor 70A (Figure 10C). Next, a second circuit board precursor 70B is prepared, which includes a second conductor layer 53, a second insulating layer precursor 52B positioned on one side of the second conductor layer 53 in the thickness direction, and a second connecting via precursor 56B that penetrates the second insulating layer precursor 52B in the thickness direction (Figure 10D). Next, the first circuit board precursor 70A and the second circuit board precursor 70B are placed side by side so that the wiring section 54 and the second insulating layer precursor 52B face each other (Figure 10E). Then, the first circuit board precursor 70A and the second circuit board precursor 70B are bonded together so that the first connecting via precursor 56A and the second connecting via precursor 56B are in contact. In this way, the first insulating layer precursor 52A and the second insulating layer precursor 52B become one to form the insulating layer 52. Furthermore, the first connecting via precursor 56A and the second connecting via precursor 56B become one to form the connecting via 56 (Figure 10F). Next, the first conductor layer 51 is bonded to one side of the insulating layer 52 in the thickness direction (Figure 10G). This yields the flexible multilayer circuit board 60 shown in Figure 9. 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. This deformation of the insulating layer 52 changes its insulating properties (e.g., dielectric properties), and as a result, the electrical properties of the wiring section 54 may deviate from the desired electrical properties.

[0006] The present invention aims to provide a flexible multilayer circuit board that can suppress fluctuations in the electrical characteristics of the wiring section, and a flexible multilayer circuit board assembly that can suppress fluctuations in the electrical characteristics of the wiring section. [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. In other words, the present invention encompasses the following:

[0008] [1] Insulating layer and, A first conductor layer is arranged on one side in the thickness direction of the insulating layer, A second conductive layer is arranged on the other side in the thickness direction of the insulating layer, The wiring section embedded in the aforementioned insulating layer, A connecting via that connects the first conductor layer and the second conductor layer, wherein the connecting via penetrates the insulating layer in the thickness direction, A flexible multilayer circuit board comprising, Furthermore, a flexible multilayer circuit board is provided with non-connected vias embedded in the insulating layer that do not penetrate the insulating layer in the thickness direction. [2] The flexible multilayer circuit board according to [1], wherein the insulating layer comprises 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] Multiple 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 [1] to [3]. Flexible multilayer circuit board assembly.

Advantages of the Invention

[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.

Brief Description of the Drawings

[0010] [Figure 1A] FIG. 1A is a schematic diagram of an embodiment of a flexible multilayer circuit board. [Figure 1B] FIG. 1B is a cross-sectional view taken along line A-A of the flexible multilayer circuit board of FIG. 1A. [Figure 2A] FIG. 2A is a schematic diagram (part 1) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 2B] FIG. 2B is a schematic diagram (part 2) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 2C] FIG. 2C is a schematic diagram (part 3) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 2D] FIG. 2D is a schematic diagram (part 4) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [[ID=i34]] [Figure 2E] FIG. 2E is a schematic diagram (part 5) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 2F] FIG. 2F is a schematic diagram (part 6) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 2G] FIG. 2G is a schematic diagram (part 7) for explaining an embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 3] FIG. 3 is a schematic diagram of another embodiment of a flexible multilayer circuit board. [Figure 4] FIG. 4 is a schematic diagram for explaining another embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 5] FIG. 5 is a schematic diagram of another embodiment of a flexible multilayer circuit board. [Figure 6] FIG. 6 is a schematic diagram for explaining another embodiment of a method for manufacturing a flexible multilayer circuit board. [Figure 7] FIG. 7 is a schematic diagram of another embodiment of a flexible multilayer circuit board. [Figure 8A] FIG. 8A is a schematic diagram of an embodiment of a flexible multilayer circuit board assembly. [Figure 8B] FIG. 8B is a cross-sectional view taken along line A-A of the flexible multilayer circuit board assembly of FIG. 8A. [Figure 9] FIG. 9 is a schematic diagram of an example of a conventional flexible multilayer circuit board. [Figure 10A] FIG. 10A is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 1). [Figure 10B] FIG. 10B is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 2). [Figure 10C] FIG. 10C is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 3). [Figure 10D] FIG. 10D is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 4). [Figure 10E] FIG. 10E is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 5). [Figure 10F] FIG. 10F is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 6). [Figure 10G] FIG. 10G is a schematic diagram for explaining a manufacturing method of an example of a conventional flexible multilayer circuit board (Part 7).

Embodiments for Carrying Out the Invention

[0011] (Flexible multilayer circuit board) The flexible multilayer circuit board of the present invention comprises an insulating layer, a first conductor layer, a second conductor layer, a wiring section, and connecting vias. The first conductor layer is positioned on one side in the thickness direction of the insulating layer. The second conductor layer is positioned on the opposite side in the thickness direction of the insulating layer. The wiring is embedded in the insulating layer. The connecting vias connect to the first and second conductor layers. The connecting vias penetrate the insulating layer in the thickness direction. The flexible multilayer circuit board further includes unconnected vias. Non-connected vias are embedded in the insulating layer and do not penetrate the insulating layer in the thickness direction.

[0012] Non-connected vias are sufficiently harder than the insulating layer and are less susceptible to deformation under pressure. Because non-connected vias are embedded in the insulating layer, deformation of the insulating layer due to pressure during the manufacturing of the flexible multilayer circuit board of the present invention can be suppressed. As a result, fluctuations in the electrical characteristics of the wiring section of the flexible multilayer circuit board can be suppressed.

[0013] An example of the flexible multilayer circuit board of the present invention will be described below with reference to Figures 1A and 1B. Figure 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 length direction of the wiring section. Figure 1B is a cross-sectional view AA of the flexible multilayer circuit board shown in Figure 1A. The flexible multilayer circuit board 10 shown in Figure 1A comprises an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring section 4, and connection vias 6. The flexible multilayer circuit board 10 further comprises non-connection vias 5. The first conductor layer 1 is positioned on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 is in contact with the insulating layer 2 on one side in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction of the paper in Figure 1A. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 2. The second conductor layer 3 is in contact with the insulating layer 2 on the other side of the thickness direction of the insulating layer 2. The other side is the opposite side from the one side. The wiring section 4 is embedded in the insulating layer 2. The wiring section 4 transmits electrical signals, for example. The connecting via 6 is electrically connected to the first conductor layer 1 and the second conductor layer 3. The connecting via 6 penetrates the insulating layer 2 in the thickness direction. The non-connected via 5 is embedded in the insulating layer 2 and does not penetrate the insulating layer 2 in the thickness direction.

[0014] In the flexible multilayer circuit board 10 shown in Figures 1A and 1B, the first conductor layer 1 and the second conductor layer 3 extend in the longitudinal direction of the wiring section 4. In Figure 1A, the longitudinal direction of the wiring section 4 is the direction perpendicular to the vertical and horizontal directions of the paper, and in Figure 1B, it is the vertical direction of the paper. As shown in Figure 1B, the connection vias 6 are arranged in rows along the length of the wiring section 4. In Figures 1A and 1B, there are two rows of connection vias 6, and the wiring section 4 is sandwiched between these two rows. The connection vias 6 serve, for example, to ground weak currents that may affect the wiring section 4. The non-connected vias 5 are regularly spaced along the length of the wiring section 4. The arrangement of the non-connected vias 5 along the length of the wiring section 4 may be regularly spaced or irregularly spaced, but regularly spaced arrangement is preferable. Regular spacing allows the pressure applied to the insulating layer 2 during the manufacturing of the flexible multilayer circuit board to be evenly distributed, thereby further suppressing deformation of the insulating layer 2 due to pressure. In the flexible multilayer circuit board 10 shown in Figure 1A, each of the multiple non-connected vias 5 is electrically in contact with either the first conductor layer 1 or the second conductor layer 3. However, the non-connected vias 5 may or may not be electrically in contact with either the first conductor layer 1 or the second conductor layer 3. If the non-connected vias 5 are not electrically in contact with either the first conductor layer 1 or the second conductor layer 3, then the non-connected vias 5 can be said to be completely embedded in the insulating layer 2.

[0015] In the flexible multilayer circuit board 10 shown in Figures 1A and 1B, some of the multiple unconnected vias 5 are positioned between the wiring portion 4 and the connecting via 6 in a direction perpendicular to the thickness direction of the insulating layer 2 and the length direction of the wiring portion 4 (the width direction of the flexible multilayer circuit board 10). Some of the multiple unconnected vias 5 are positioned in locations other than between the wiring portion 4 and the connecting via 6 (outside of the connecting via 6) in the width direction of the flexible multilayer circuit board 10.

[0016] In Figure 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 are sandwiched between the insulating layer 2.

[0017] In Figure 1A, the wiring section 4 is not in contact with the first conductor layer 1, the second conductor layer 3, or the connecting via 6. Furthermore, the wiring section 4 is not in contact with the non-connecting via 5.

[0018] The materials of the first and second conductor layers are not particularly limited, and examples include metallic materials. Examples of metallic materials include copper, nickel, gold, solder, and alloys of two or more of these materials. 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 also, for example, 50 μm or less, preferably 30 μm or less. The thicknesses of the first conductor layer and the second conductor layer may be the same or different. In this invention, "thickness" refers to the length of the flexible multilayer circuit board in the thickness direction. The thickness direction of the flexible multilayer circuit board refers, for example, to the direction perpendicular to the plane direction of the first conductor layer and the second conductor layer.

[0019] The material of the wiring section is not particularly limited, and examples 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, but is, for example, 3 μm or more, preferably 5 μm or more, and also, for example, 50 μm or less, preferably 30 μm or less. 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 section (the length of the wiring section in a direction perpendicular to the thickness and length directions of the wiring section) is not particularly limited, but is usually shorter than the width of the first and second conductor layers (the length of the first and second conductor layers in a direction perpendicular to the thickness and length directions of the first and second conductor layers), for example, 1 / 5 to 1 / 2 of the width of the first and second conductor layers. Also, since the wiring section is embedded in the insulating layer, the width of the wiring section 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 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. From the viewpoint of high insulating 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, but is, for example, 5 μm or more, preferably 10 μm or more, and also, 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 becomes more susceptible to deformation under pressure. Therefore, when the insulating layer is porous, the effect of the present invention—suppressing fluctuations in the electrical characteristics of the wiring section by suppressing the deformation of the insulating layer—is significantly enhanced. In this respect, it is preferable that the insulating layer be porous. Furthermore, because the insulating layer is porous, the dielectric constant of the insulating layer can be reduced, making the flexible multilayer circuit board suitable for use as a flexible multilayer circuit board for high-speed transmission. In that respect, it is preferable that the insulating layer be porous. If the insulating layer is porous, it may have closed cells or open cells.

[0021] The material of the connecting vias is not particularly limited, and examples include metallic materials. Examples of metallic materials include copper, nickel, gold, solder, and alloys of two or more of these. The material of the connecting via may be the same as or different from the material of the first conductor layer and the second conductor layer. The shape of the connection via is not particularly limited; for example, in a cross-section perpendicular to the thickness direction of the flexible multilayer circuit board (e.g., cross-section AA in Figure 1A), it can be a square, rectangular, circular, or elliptical shape. The ratio (X1:Y1) of the length of the connection via in the longitudinal direction of the wiring section (X1) to the length of the connection via in the width direction of the wiring section (Y1) may be, for example, 3:1 to 1:3, 1:2 to 2:1, or 1:1. When the ratio (X1:Y1) 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 unconnected via is not particularly limited, and examples include metallic materials. Examples of metallic materials include copper, nickel, gold, solder, and alloys of two or more of these. The material of the unconnected via may be the same as or different from the material of the first conductor layer, the second conductor layer, and the connecting via. The shape of the unconnected via is not particularly limited, and examples include square, rectangular, circular, and elliptical shapes in a cross-section perpendicular to the thickness direction of the flexible multilayer circuit board (for example, cross-section AA in Figure 1A). The ratio (X2:Y2) of the length of unconnected vias in the longitudinal direction of the wiring section (X2) to the length of unconnected vias in the width direction of the wiring section (Y2) may be, for example, 3:1 to 1:3, 1:2 to 2:1, or 1:1. When the ratio (X2:Y2) is 1:1, the shape of the unconnected vias 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 the manufacturing method for the flexible multilayer circuit board shown in Figures 1A and 1B will be explained using Figures 2A to 2G. First, a laminate of the wiring precursor 4A and the first insulating layer precursor 2A is prepared (Figure 2A). Both the wiring precursor 4A and the first insulating layer precursor 2A are layered. Next, connecting vias (first precursor 6A) and non-connecting vias (5) are formed, penetrating the first insulating layer (first precursor 2A) of the prepared laminate in the thickness direction (Figure 2B). The method for forming the connecting vias (first precursor 6A) and non-connecting vias (5) is not particularly limited. For example, one method is to form through holes in the first insulating layer (first precursor 2A) using a laser, and then fill the formed through holes with connecting vias (first precursor 6A) and non-connecting vias (5), respectively, by plating. The non-connecting vias (5) may or may not penetrate the first insulating layer (first precursor 2A) in the thickness direction. Next, the wiring precursor 4A is selectively etched to form the wiring portion 4, thereby obtaining the first circuit board precursor 20A (Figure 2C). Next, a second circuit board precursor 20B is prepared, comprising a second conductor layer 3, a second insulating layer precursor 2B positioned on one side of the second conductor layer 3 in the thickness direction, and a second connecting via precursor 6B and a non-connecting via 5 penetrating the second insulating layer precursor 2B in the thickness direction (Figure 2D). The second insulating layer precursor 2B is layered. The method for forming the second connecting via precursor 6B and the non-connecting via 5 is not particularly limited. For example, a method can be used in which through holes are formed in the second insulating layer precursor 2B by a laser, and then the second connecting via precursor 6B and the non-connecting via 5 are filled into the formed through holes by plating. The non-connecting via 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 placed side by side so that the wiring section 4 and the second insulating layer precursor 2B face each other (Figure 2E). Then, the first circuit board precursor 20A and the second circuit board precursor 20B are bonded together such that the first connecting via precursor 6A and the second connecting via precursor 6B are in contact. There are no particular restrictions on the pressure and temperature during bonding. In this way, the first insulating layer precursor 2A and the second insulating layer precursor 2B become one, forming insulating layer 2. Furthermore, the first connecting via precursor 6A and the second connecting via precursor 6B become one, forming connecting via 6 (Figure 2F). Next, the first conductor layer 1 is bonded to one side of the insulating layer 2 in the thickness direction (Figure 2G). There are no particular restrictions on the pressure and temperature during bonding. Based on the above, the flexible multilayer circuit board 10 shown in Figure 1A is obtained.

[0024] Figure 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 length direction of the wiring section. The flexible multilayer circuit board 10 shown in Figure 3 comprises an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring section 4, and connection vias 6. The flexible multilayer circuit board 10 further comprises non-connection vias 5. The first conductor layer 1 is positioned on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 is in contact with the insulating layer 2 on one side in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction of the paper in Figure 3. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 2. The second conductor layer 3 is in contact with the insulating layer 2 on the other side of the thickness direction of the insulating layer 2. The other side is the opposite side from the one side. The wiring section 4 is embedded in the insulating layer 2. The connecting via 6 is electrically connected to the first conductor layer 1 and the second conductor layer 3. The connecting via 6 penetrates the insulating layer 2 in the thickness direction. The non-connected via 5 is embedded in the insulating layer 2 and does 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 electrically in contact with the first conductor layer 1 or the second conductor layer 3, while other non-connected vias 5 are not electrically in contact with both the first conductor layer 1 and the second conductor layer 3.

[0026] Figure 4 is a schematic diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 3. The flexible multilayer circuit board 10 shown in Figure 3 can be 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 Figure 4.

[0027] The first precursor circuit board 20C comprises an insulating layer first precursor 2C, a second conductor layer 3, a wiring section 4, a non-connected via 5, and a connecting via first precursor 6C. The second conductor layer 3 is positioned on one side in the thickness direction of the first insulating layer precursor 2C. The wiring section 4 is positioned on the other side in the thickness direction of the first insulating layer precursor 2C. The non-connected via 5 penetrates the first insulating layer precursor 2C in the thickness direction. The non-connected via 5 is in electrical contact with the second conductor layer 3. The non-connected via 5 may also be filled into a non-penetrating hole formed in the first insulating layer precursor 2C; in this case, the non-connected via 5 does not penetrate the first insulating layer precursor 2C in the thickness direction. Furthermore, the non-connected via 5 does not necessarily have to be in electrical contact with 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 in electrical contact with the second conductor layer 3.

[0028] The circuit board second precursor 20D comprises an insulating layer second precursor 2D, a non-connected via 5, and a connected via second precursor 6D. The unconnected via 5 penetrates the second insulating layer precursor 2D in the thickness direction. Alternatively, the unconnected via 5 may be filled into a non-penetrating hole formed in the second insulating layer precursor 2D; in this case, the unconnected via 5 does not penetrate the second insulating layer precursor 2D in the thickness direction. The second precursor connecting via 6D penetrates the second precursor insulating layer 2D in the thickness direction.

[0029] The circuit board third precursor 20E comprises an insulating layer third precursor 2E, a first conductor layer 1, a non-connected via 5, and a connecting via third precursor 6E. The first conductor layer 1 is positioned on one side in the thickness direction of the third insulating layer precursor 2E. The non-connected via 5 penetrates the third precursor insulating layer 2E in the thickness direction. The non-connected via 5 is in electrical contact with the first conductor layer 1. Alternatively, the non-connected via 5 may be filled into a non-penetrating hole formed in the third precursor insulating layer 2E; in this case, the non-connected via 5 does not penetrate the third precursor insulating layer 2E in the thickness direction. Furthermore, the non-connected via 5 does not necessarily have to be in electrical contact with the first conductor layer 1. The third precursor connecting via 6E penetrates the third precursor insulating layer 2E in the thickness direction. The third precursor connecting via 6E is electrically in 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 such that the first connecting via precursor 6C and the second connecting via precursor 6D are in contact, and the second connecting via precursor 6D and the third connecting via precursor 6E are in contact. In this way, the first insulating layer precursor 2C, the second insulating layer precursor 2D, and the third insulating layer precursor 2E are integrated to form insulating layer 2. Furthermore, the first connecting via precursor 6C, the second connecting via precursor 6D, and the third connecting via precursor 6E are integrated to form connecting via 6. As a result, the flexible multilayer circuit board 10 shown in Figure 3 is obtained.

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

[0032] Figure 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 section. The flexible multilayer circuit board 10 shown in Figure 5 comprises an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring section 4, and connection vias 6. The flexible multilayer circuit board 10 further comprises non-connection vias 5. The first conductor layer 1 is positioned on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 is in contact with the insulating layer 2 on one side in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction of the paper in Figure 5. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 2. The second conductor layer 3 is in contact with the insulating layer 2 on the other side of the thickness direction of the insulating layer 2. The other side is the opposite side from the one side. The wiring section 4 is embedded in the insulating layer 2. The connecting via 6 is electrically connected to the first conductor layer 1 and the second conductor layer 3. The connecting via 6 penetrates the insulating layer 2 in the thickness direction. The non-connected via 5 is embedded in the insulating layer 2 and does 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 in contact with the first conductor layer 1 or the second conductor layer 3, while other non-connected vias 5 are not electrically in contact with both the first conductor layer 1 and the second conductor layer 3.

[0034] Figure 6 is a schematic diagram illustrating one embodiment of the manufacturing method for the flexible multilayer circuit board shown in Figure 5. The flexible multilayer circuit board 10 shown in Figure 5 can be obtained, for example, by bonding together 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 Figure 6.

[0035] The first precursor circuit board 20F comprises an insulating layer first precursor 2F, a second conductor layer 3, a non-connected via 5, and a connecting via first precursor 6F. The second conductor layer 3 is positioned on one side in the thickness direction of the first insulating layer precursor 2F. The non-connected via 5 penetrates the first insulating layer precursor 2F in the thickness direction. The non-connected via 5 is in electrical contact with the second conductor layer 3. The non-connected via 5 may also be filled into a non-penetrating hole formed in the first insulating layer precursor 2F; in this case, the non-connected via 5 does not penetrate the first insulating layer precursor 2F in the thickness direction. Furthermore, the non-connected via 5 does not necessarily have to be in electrical contact with the second conductor layer 3. The first precursor connecting via 6F penetrates the first precursor insulating layer 2F in the thickness direction. The first precursor connecting via 6F is in electrical contact with the second conductor layer 3.

[0036] The circuit board second precursor 20G comprises an insulating layer second precursor 2G, a wiring section 4, a non-connected via 5, and a connected via second precursor 6G. The wiring section 4 is positioned on one side in the thickness direction of the second insulating layer precursor 2G. The unconnected via 5 is filled into a non-through hole formed in the second precursor insulating layer 2G. The connecting via second precursor 6G penetrates the insulating layer second precursor 2G in the thickness direction.

[0037] The circuit board third precursor 20H comprises an insulating layer third precursor 2H, a non-connected via 5, and a connected via third precursor 6H. The non-connected via 5 penetrates the third precursor insulating layer 2H in the thickness direction. Alternatively, the non-connected via 5 may be filled into a non-penetrating hole formed in the third precursor insulating layer 2H; in this case, the non-connected via 5 does not penetrate the third precursor insulating layer 2H in the thickness direction. The connecting via third precursor 6H penetrates the insulating layer third precursor 2H in the thickness direction.

[0038] The fourth precursor circuit board 20I comprises an insulating layer fourth precursor 2I, a first conductor layer 1, unconnected vias 5, and a connecting via fourth precursor 6I. The first conductor layer 1 is positioned on one side in the thickness direction of the fourth insulating layer precursor 2I. The non-connected via 5 penetrates the fourth precursor insulating layer 2I in the thickness direction. The non-connected via 5 is in electrical contact with the first conductor layer 1. The non-connected via 5 may also be filled into a non-penetrating hole formed in the fourth precursor insulating layer 2I; in this case, the non-connected via 5 does not penetrate the fourth precursor insulating layer 2I in the thickness direction. Furthermore, the non-connected via 5 does not necessarily have to be in electrical contact with the first conductor layer 1. The fourth precursor connecting via 6I penetrates the fourth precursor insulating layer 2I in the thickness direction. The fourth precursor connecting via 6I is in electrical contact with 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 such that the first connecting via precursor 6F and the second connecting via precursor 6G are in contact, the second connecting via precursor 6G and the third connecting via precursor 6H are in contact, and the third connecting via precursor 6H and the fourth connecting via precursor 6I are in contact. In this way, 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 insulating layer 2. Furthermore, the first connecting via precursor 6F, the second connecting via precursor 6G, the third connecting via precursor 6H, and the fourth connecting via precursor 6I are integrated to form connecting via 6. As a result, the flexible multilayer circuit board 10 shown in Figure 5 is obtained.

[0040] Figure 7 is a schematic diagram of another embodiment of the flexible multilayer circuit board. This schematic diagram is a cross-sectional view perpendicular to the length direction of the wiring section. The flexible multilayer circuit board shown in Figure 7 has the same structure as the flexible multilayer circuit board shown in Figure 1A, except that the wiring section 4 has two signal lines (first signal line 41, second signal line 42). The flexible multilayer circuit board 10 shown in Figure 7 comprises an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring section 4, and connection vias 6. The flexible multilayer circuit board 10 further comprises non-connection vias 5. The first conductor layer 1 is positioned on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 is in contact with the insulating layer 2 on one side in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction of the paper in Figure 7. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 2. The second conductor layer 3 is in contact with the insulating layer 2 on the other side of the thickness direction of the insulating layer 2. The other side is the opposite side from the one side. The wiring section 4 is embedded in the insulating layer 2. The connecting via 6 is electrically connected to the first conductor layer 1 and the second conductor layer 3. The connecting via 6 penetrates the insulating layer 2 in the thickness direction. The non-connected via 5 is embedded in the insulating layer 2 and does not penetrate the insulating layer 2 in the thickness direction. The wiring section 4 has two signal lines (first signal line 41 and second signal line 42). The first signal line 41 and the second signal line 42 constitute differential wiring for differential signal transmission.

[0041] Flexible multilayer circuit boards are used in electronic devices such as mobile phones, smartphones, tablet devices, and digital cameras, for example, as flexible multilayer circuit boards for high-speed transmission, in response to the need for miniaturization, weight reduction, and high functionality.

[0042] (Flexible multilayer circuit board assembly) The flexible multilayer circuit board assembly of the present invention comprises a plurality of flexible multilayer circuit boards and a frame portion. The frame is formed around the outer periphery of multiple flexible multilayer circuit boards.

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

[0044] There are no particular restrictions on the number of flexible multilayer circuit boards that a flexible multilayer circuit board assembly may contain, but it is usually two or more.

[0045] The frame portion includes, for example, a third conductor layer and a fourth conductor layer. The materials of the third and fourth conducting layers are not particularly limited, and examples include metallic materials. Examples of metallic materials include copper, nickel, gold, solder, and two or more alloys thereof. The thickness of the third and fourth conductor layers is not particularly limited, and is, for example, 3 μm or more, preferably 5 μm or more, and also, for example, 50 μm or less, preferably 30 μm or less. It is preferable that the third conductor layer be integrated with each first conductor layer of the multiple flexible multilayer circuit boards, as this facilitates the manufacturing of the flexible multilayer circuit board assembly. It is preferable that the fourth conductor layer be integrated with each second conductor layer of the multiple flexible multilayer circuit boards, as this facilitates the manufacturing of the flexible multilayer circuit board assembly. The statement that the third conductor layer is integrated with each of the first conductor layers of multiple flexible multilayer circuit boards means that the third conductor layer and the first conductor layer are formed from a single sheet of material. The statement that the fourth conductor layer is integrated with each second conductor layer of multiple flexible multilayer circuit boards means that the fourth conductor layer and the second conductor layer are formed from a single sheet of material.

[0046] The frame portion includes, for example, a second insulating layer. Examples of materials constituting the second insulating layer include resins. 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. Preferably, polyimide resin, cycloolefin polymer, and liquid crystal polymer are used. 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 also, 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 integrated with each insulating layer of the multiple flexible multilayer circuit boards, as this facilitates the manufacturing of the flexible multilayer circuit board assembly. The statement that the second insulating layer is integrated with each insulating layer of multiple flexible multilayer circuit boards means that the second insulating layer of the frame portion is formed simultaneously when each insulating layer of multiple flexible multilayer circuit boards is formed.

[0048] <First aspect> In a first embodiment, which is an 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-connected vias.

[0049] In the first embodiment, the frame portion may or may not have a second disconnected via. If the frame portion has a second disconnected via, for example, the frame portion comprises 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 disconnected via is embedded in the second insulating layer and does not penetrate the second insulating layer in the thickness direction.

[0050] <Second aspect> A second embodiment, which is an example of a flexible multilayer circuit board assembly, has a frame portion that includes disconnected vias. In this case, for example, the frame portion includes a second insulating layer, a third conductor layer arranged on one side of the second insulating layer in the thickness direction, and a fourth conductor layer arranged on the other side of the second insulating layer in the thickness direction. Furthermore, the second disconnected via is embedded in the second insulating layer and does not penetrate the second insulating layer in the thickness direction.

[0051] In the second embodiment, unlike the first embodiment, the flexible multilayer circuit board does not have non-connecting vias. Such a flexible multilayer circuit board includes, for example, an insulating layer, a first conductor layer disposed on one side in the thickness direction of the insulating layer, a second conductor layer disposed on the other side in the thickness direction of the insulating layer, wiring portions embedded in the insulating layer, and connecting vias that connect the first conductor layer and the second conductor layer and penetrate the edge layer in the thickness direction.

[0052] In a second embodiment of the flexible multilayer circuit board assembly of the present invention, by providing unconnected vias in the frame portion, deformation of the insulating layer of the flexible multilayer circuit board due to pressure during the manufacturing of the flexible multilayer circuit board assembly can be suppressed. As a result, fluctuations in the electrical characteristics of the wiring portion of the flexible multilayer circuit board can be suppressed.

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

[0054] An example of a flexible multilayer circuit board assembly will be explained using a diagram. Figure 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 section. Figure 8B is a cross-sectional view AA of the flexible multilayer circuit board assembly of Figure 8A. The flexible multilayer circuit board assembly 100 shown in Figure 8A comprises 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 a 2x7 grid, with a frame 11 surrounding their outer perimeter. Each flexible multilayer circuit board 10 is fixed to the frame 11 by tabs provided at four locations on the top, bottom, left, and right sides of each flexible multilayer circuit board 10.

[0055] Each flexible multilayer circuit board 10 in the flexible multilayer circuit board assembly 100 shown in Figure 8A has a structure similar to that shown in Figure 1A, as shown in Figure 8B.

[0056] Specifically, the flexible multilayer circuit board 10 comprises an insulating layer 2, a first conductor layer 1, a second conductor layer 3, a wiring section 4, and connecting vias 6. The flexible multilayer circuit board 10 further comprises non-connecting vias 5. The first conductor layer 1 is positioned on one side of the insulating layer 2 in the thickness direction. The first conductor layer 1 is in contact with the insulating layer 2 on one side in the thickness direction. The thickness direction of the insulating layer 2 is the vertical direction of the paper in Figure 8B. The second conductor layer 3 is positioned on the other side of the thickness direction of the insulating layer 2. The second conductor layer 3 is in contact with the insulating layer 2 on the other side of the thickness direction of the insulating layer 2. The other side is the opposite side from the one side. The wiring section 4 is embedded in the insulating layer 2. The wiring section 4 transmits electrical signals, for example. The connecting via 6 is electrically connected to the first conductor layer 1 and the second conductor layer 3. The connecting via 6 penetrates the insulating layer 2 in the thickness direction. The non-connected via 5 is embedded in the insulating layer 2 and does not penetrate the insulating layer 2 in the thickness direction.

[0057] The frame portion 11 in the flexible multilayer circuit board assembly 100 shown in Figure 8A comprises a second insulating layer 22, a third conductor layer 21 arranged on one side in the thickness direction of the second insulating layer 22, a fourth conductor layer 23 arranged on the other side in the thickness direction of the second insulating layer 22, and non-connected vias 5 embedded in the second insulating layer 22 that do not penetrate the second insulating layer 22 in the thickness direction. The arrangement of the unconnected vias 5 in the frame portion 11 is not particularly limited; they may be regularly spaced or irregularly spaced, but it is preferable that they be regularly spaced. [Explanation of symbols]

[0058] 1. First Conductor Layer 2. Insulating layer 2A Insulating layer first precursor 2B Insulating layer second precursor 2C insulating layer first precursor 2D insulating layer second precursor 2E Insulating layer third precursor 2F Insulating layer first precursor 2G insulating layer second precursor 2H insulating layer third precursor 2I Insulating layer fourth precursor 3. Second Conductor Layer 4 Wiring section 4A Wiring section precursor 5 unconnected vias 6 connection vias 6A Connection via First Precursor 6B Connecting via Second Precursor 6C Connection Via First Precursor 6D Connection via Second Precursor 6E Connection via Third Generator 6F Connection via First Series 6G Connection Via Second Precursor 6H Connection via Third Generator 6I Connecting via fourth precursor 10 Flexible multilayer circuit boards 11 Frame section 20A circuit board first precursor 20B Circuit board second precursor 20C circuit board first precursor 20D circuit board second precursor 20E circuit board third precursor 20F Circuit board first precursor 20G circuit board second precursor 20H circuit board third precursor 20I circuit board fourth 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 Insulating layer first precursor 52B Insulating layer second precursor 53 Second Conductor Layer 54 Wiring section 54A Wiring section precursor 56 Connection Vias 56A Connecting via, first precursor 56B Connecting via Second Precursor 60 Flexible Multilayer Circuit Boards 70A circuit board first precursor 70B Circuit board second precursor 100 Flexible Multilayer Circuit Board Assortment

Claims

1. Insulating layer and, A first conductor layer is arranged on one side in the thickness direction of the insulating layer, A second conductive layer is arranged on the other side in the thickness direction of the insulating layer, The wiring section embedded in the aforementioned insulating layer, A plurality of connecting vias connecting the first conductor layer and the second conductor layer, wherein the plurality of connecting vias penetrate the insulating layer in the thickness direction, A flexible multilayer circuit board comprising, Furthermore, the insulating layer is provided with a plurality of non-connected vias that are embedded in the insulating layer and do not penetrate the insulating layer in the thickness direction, The plurality of connection vias are arranged in two rows along the length of the wiring section, The aforementioned wiring section is sandwiched between the two rows, The plurality of disconnected vias include disconnected vias located between the wiring section and one of the two rows, and disconnected vias located between the wiring section and the other of the two rows. 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 according to claim 1, wherein the insulating layer is porous.

4. Multiple 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 described in any one of claims 1 to 3. Flexible multilayer circuit board assembly.

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