Thin flat cable and method for manufacturing the same

Abstract

The present invention provides a flexible, thin, flat cable and a method for manufacturing the same, which can ensure shielding of the conductive parts inside the thin, flat cable against externally radiated millimeter waves while suppressing adverse effects on the surroundings due to the reflection of millimeter waves. [Solution] The device comprises a first insulating layer 219 and a second insulating layer 106 that sandwich a conductor 204 made of a conductive material, and a conductive electrode 105 that conducts electricity via a via structure 208. The horizontal surfaces of the insulating layers other than those around the conductive electrode are covered with a metal film 202, and furthermore, a millimeter-wave absorbing layer 211 made of a resin containing a millimeter-wave absorbing material is provided on at least one of the metal film surfaces, as well as on the longitudinal and transverse sides. This shields externally radiated millimeter waves and absorbs reflected waves, reducing the impact on the surroundings.

Description

Technical Field

[0001] The present disclosure relates to a flexible flat cable that improves shielding against millimeter-wave radiation noise radiated through an external space and suppresses reflection of the millimeter wave, and a method for manufacturing the same.

Background Art

[0002] In recent years, in a flat cable that transmits high-frequency signals in the millimeter-wave band, reduction of transmission loss, improvement of shielding against external electromagnetic waves, and suppression of crosstalk are required. On the other hand, in a configuration in which the outer surface of the flat cable is covered with a metal film, shielding can be easily obtained, but millimeter waves reflected from the outer surface of the flat cable may have an adverse effect on peripheral members. For this reason, a configuration that suppresses the influence of reflected millimeter waves while maintaining shielding is required.

[0003] For a flat cable used for transmission in the millimeter-wave band, reduction of transmission loss, impedance matching, and crosstalk suppression are required.

[0004] Due to its structure, a flat cable is easily affected by millimeter waves incident from the outside, and high shielding is required over the entire cable. In order to impart shielding, a metal foil, a conductive mesh, or a conductive layer is provided on the outer surface of the flat cable.

[0005] Patent Document 4 proposes a configuration in which the surface of a flat cable other than the periphery of the electrode is covered with a metal film. While the metal film can improve shielding against internal signal lines, since it reflects millimeter waves, the reflected waves may have an adverse effect on surrounding wirings and electronic components.

[0006] Patent Document 4 proposes a configuration in which the entire surface of a flat cable, excluding the area around the electrodes, is covered with a metal film to prevent the intrusion of external radiated noise. While the metal film provides high shielding of the internal signal lines against externally radiated millimeter waves, the metal layer reflects millimeter waves, leaving the problem that reflected millimeter waves may have a secondary effect on surrounding wiring and electronic components. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2009-177010 [Patent Document 2] Japanese Patent Publication No. 2013-193253 [Patent Document 3] Japanese Patent Publication No. 2016-171138 [Patent Document 4] International Publication No. 2020 / 195784 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As proposed in Patent Document 4, it is possible to shield the conductive parts that transmit signals inside a flat cable from externally radiated millimeter waves by covering everything except the conductor electrodes that serve as terminals and their surroundings with a metal film. However, the externally radiated millimeter waves reflected by the metal film may adversely affect surrounding wiring and components.

[0009] The present disclosure aims to provide a flexible, thin, flat cable and a method for manufacturing the same that can suppress the influence of reflected waves on the surrounding area while ensuring shielding of the conductive part inside the thin, flat cable from incident millimeter waves from the outside, i.e., externally radiated millimeter waves. Furthermore, the aim is to provide thin, flat cables that can achieve both shielding and reflection suppression in a wider range of applications by supporting multi-layering, single-insulation layer structures, and various via structures and manufacturing processes. [Means for solving the problem]

[0010] The thin flat cable according to this disclosure has a conductor made of a conductive material, a first insulator layer on which the conductor is formed, a second insulator layer in contact with the first insulator layer and sandwiching the conductor, a conductor electrode provided on the opposite surface of at least one of the first insulator layer and the second insulator layer from the surface in contact with the conductor, a via structure that electrically connects the conductor and the conductor electrode, a metal film covering the surface forming the horizontal plane of the insulator layer on which the conductor electrode is provided, other than the periphery of the conductor electrode, a metal film covering the surface forming the horizontal plane of the insulator layer on the side on which the conductor electrode is not provided, at least one of the metal film surfaces formed on the surfaces of the first insulator layer and the second insulator layer excluding the surface of the conductor electrode and the surface around the conductor electrode, and a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on the longitudinal and transverse sides of the first insulator layer and the second insulator layer.

[0011] Furthermore, in the thin flat cable according to the present disclosure, it is preferable that an insulating laminate is provided having one or more insulating layers between the first insulating layer and the second insulating layer, and / or on the outside of the first insulating layer or the second insulating layer, and that the millimeter-wave absorbing layer is provided on all the sides of the insulating layers that are exposed on the longitudinal and transverse sides.

[0012] Furthermore, in the thin flat cable according to this disclosure, it is preferable that the via structure is a through-hole that penetrates the first insulator layer and the second insulator layer in the thickness direction, and the inner wall surface of the through-hole is covered with a conductive material, or that the inside of the hole is filled with a conductive paste or plating to form a filled via.

[0013] Furthermore, in the thin flat cable according to this disclosure, the longitudinal and transverse sides include outer peripheral sides consisting of a surface perpendicular to the thickness direction of the thin flat cable, a tapered inclined surface, a stepped surface, and a curved surface, or a combination thereof, and the outer surface of the millimeter-wave absorbing layer preferably has a reflection suppression layer that suppresses the reflection of externally radiated millimeter waves.

[0014] Furthermore, in the thin flat cable according to this disclosure, the resin of the millimeter-wave absorbing layer is preferably an ultraviolet-curable resin.

[0015] Furthermore, in the thin flat cable according to this disclosure, the ultraviolet-curable resin is preferably a photosensitive resin composition containing an alkali-soluble main resin, a reactive diluent containing an acrylate compound, a photopolymerization initiator, an epoxy resin containing a bisphenol A type epoxy resin or a novolac type epoxy resin, and a thermosetting agent containing an imidazole compound or an amine compound.

[0016] Furthermore, in the thin flat cable according to this disclosure, it is preferable that the alkali-soluble main resin is a carboxyl group-containing photosensitive resin comprising at least one of a carboxyl group-containing urethane acrylate resin and a carboxyl group-containing novolac-type epoxy acrylate resin.

[0017] Furthermore, in the thin flat cable according to this disclosure, the millimeter-wave absorbing layer preferably contains 0.3% by mass or more and 60% by mass or less of the millimeter-wave absorbing material.

[0018] Furthermore, in the thin flat cable according to this disclosure, the millimeter-wave absorbing material is preferably one or more of the following: Mn ferrite, NiZn ferrite, CoFe2O4 ferrite, hexagonal ferrite, carbon black, graphite, carbon nanotubes, graphene, carbon microcoils, graphene oxide, carbon fibers, conductive polymers and their composites, BaTiO3, transition metal carbides, transition metal nitrides, transition metal carbonitrides, Fe-based soft magnetic metal powder, ε-Fe2O3, γ-Fe2O3, Ni, Fe, Co, Cr, Cu, Al, Ag, Ti, Zn, oxides of these metals, metal microcoils made of the said metals, metal nanowires and magnetic metal nanowires, and CoNi.

[0019] Furthermore, in the thin flat cable according to this disclosure, the resin constituting the millimeter-wave absorbing layer is preferably at least one selected from the group consisting of bismaleimide resin, liquid crystal polymer, and fluororesin, and the millimeter-wave absorbing material is preferably at least one selected from the group consisting of epsilon iron oxide and hexagonal ferrite.

[0020] Furthermore, in the thin flat cable according to this disclosure, the resin constituting the millimeter-wave absorbing layer is preferably at least one selected from the group consisting of polyvinylidene fluoride, aqueous polyurethane, and polyimide, and the millimeter-wave absorbing material is preferably at least one selected from the group consisting of transition metal carbides, transition metal nitrides, transition metal carbonitrides, graphene, graphene oxide, carbon nanotubes, metal nanowires, and magnetic metal nanowires.

[0021] Furthermore, in the thin flat cable according to this disclosure, the resin constituting the millimeter-wave absorbing layer is preferably at least one selected from the group consisting of silicone rubber, polyurethane elastomer, and low-viscosity epoxy resin, and the millimeter-wave absorbing material is preferably at least one selected from the group consisting of carbon microcoils and metal microcoils.

[0022] Also, in the thin flat cable according to the present disclosure, it is preferable that the first insulator layer contains 30% by mass or more of any one or more of polyimide resin, polytetrafluoroethylene, copolymer of ethylene tetrafluoride and perfluoroalkoxyethylene, polyphenylene ether resin, polyether ether ketone resin, liquid crystal polymer, alkene polymer, syndiotactic polystyrene, benzoxazine, bismaleimide resin, polyamideimide resin, and polyetherimide resin.

[0023] Also, in the thin flat cable according to the present disclosure, it is preferable that the second insulator layer contains 30% by mass or more of an alkene polymer and the millimeter-wave absorption layer has solder heat resistance.

[0024] Also, in the thin flat cable according to the present disclosure, it is preferable that the thin flat cable is formed by integrating a plurality of them in the horizontal direction of the flat surface of the thin flat cable.

[0025] Also, in the thin flat cable according to the present disclosure, it is preferable that the thin flat cable is formed by integrating a plurality of them in the direction perpendicular to the flat surface of the thin flat cable.

[0026] A method for manufacturing a thin flat cable according to this disclosure involves laminating metal films on both sides of a first insulator layer, forming a conductor made of a conductive material on one side of the first insulator layer by etching, printing, plating, vapor deposition, or sputtering, laminating a metal film on one side of a second insulator layer, bonding the side of the second insulator layer not laminating the metal film to the side of the first insulator layer on which the conductor is formed to form a laminate, and etching the metal film on at least one outer surface of the laminate to form an opening, by laser irradiation, mechanical drilling, or photolithography etching. The process involves forming holes for blind vias or through-holes, forming via structures in the formed holes by plating or filling with conductive paste, removing the metal film around the conductor electrodes by etching, forming the conductor electrodes, forming grooves in the areas that will form the outer surface of the thin flat cable by laser irradiation or by laser irradiation, forming grooves and cutting, forming the sides that will become the outer surface of the thin flat cable, and forming a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on the metal film surface formed on the surface of the laminate excluding the surface of the conductor electrodes, and on the sides in the longitudinal and transverse directions of the laminate.

[0027] Furthermore, in the method for manufacturing a thin flat cable according to the present disclosure, when forming the laminate, it is preferable to form an insulating laminate by laminating one or more insulating layers in addition to the first insulating layer and the second insulating layer, and to form holes for buried vias that are formed only between the inner layers of the insulating laminate, in addition to or instead of the holes for blind vias or through holes.

[0028] Furthermore, in the method for manufacturing a thin flat cable according to the present disclosure, it is preferable to form a metal film on the longitudinal and transverse sides of the laminate or the insulating laminate by sputtering, electroless plating, electrolytic plating, or conductive paste coating, and to form a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on the formed metal film surface.

[0029] Furthermore, in the method for manufacturing a thin flat cable according to this disclosure, it is preferable to form a reflection suppression layer on the outer surface of the millimeter-wave absorbing layer to suppress the reflection of externally radiated millimeter waves.

[0030] Furthermore, in the method for manufacturing a thin flat cable according to the present disclosure, it is preferable to form a sheet comprising the two layers, the millimeter-wave absorbing layer and the reflection suppression layer, and then to bring the millimeter-wave absorbing layer into contact with the outer surface of the thin flat cable on which the side surface is formed, and to heat-press it in a vacuum, thereby sequentially forming the millimeter-wave absorbing layer and the reflection suppression layer on the outer surface of the thin flat cable. Alternatively, it is preferable that the formation of the millimeter-wave absorbing layer be carried out by at least one method selected from the group consisting of coating, printing, inkjet, spray coating, dipping, lamination, and vacuum heat-pressing. [Effects of the Invention]

[0031] This disclosure provides a flexible, thin, flat cable and a method for manufacturing the same that can improve the shielding of the internal conductive part against millimeter waves incident from the outside and suppress the influence of reflected waves on the surrounding area. Furthermore, in an embodiment in which a reflection suppression layer is provided on the outer surface of the millimeter wave absorption layer, absorption can be enhanced while suppressing the reflection of incident millimeter waves. Furthermore, by employing a multilayer structure using insulating laminates and various via structures, excellent millimeter-wave shielding and reflection suppression effects can be achieved even in equipment requiring more complex and high-density wiring. [Brief explanation of the drawing]

[0032] [Figure 1] The following diagrams illustrate a thin flat cable according to an embodiment of the present disclosure. (A) shows a perspective view of the thin flat cable. (B) shows the terminal portion of the thin flat cable. (C) and (D) show other terminal portions of the thin flat cable. [Figure 2]The following diagrams illustrate a thin flat cable according to an embodiment of the present disclosure. (A) shows a cross-section perpendicular to the longitudinal direction including the conductor of the thin flat cable. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of the thin flat cable. (C) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to another embodiment. (D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable according to another embodiment. (E) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to another embodiment, which has a reflection-suppressing layer on its outer surface and no metal film on its side surface. (F) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable according to another embodiment, which has a reflection-suppressing layer on its outer surface and no metal film on its side surface. (G) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to another embodiment, which has a reflection-suppressing layer on its outer surface and a metal film on its side surface. (H) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable according to another embodiment, which has a reflection-suppressing layer on its outer surface and a metal film on its side surface. (I) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable having a reflection-suppressing layer on its outer surface and one side in contact with the base material, according to another embodiment. (J) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable having a reflection-suppressing layer on its outer surface and one side in contact with the base material, according to another embodiment. [Figure 3] The manufacturing process for a thin flat cable according to an embodiment of this disclosure is shown. [Figure 4] The manufacturing process for a thin flat cable according to another embodiment of this disclosure is shown. [Figure 5] The images show a conventional thin flat cable. (A) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of a conventional thin flat cable. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor of a conventional thin flat cable. [Figure 6] This invention relates to a manufacturing process for a thin flat cable, comprising the step of forming a groove or forming a groove and cutting to form a portion that will form the outer surface of the thin flat cable, thereby forming the side surface that will become the outer surface of the thin flat cable. [Figure 7] A thin flat cable according to an embodiment of the present disclosure, the thin flat cable having a multi-row structure in the horizontal direction. (A) shows a cross-section perpendicular to the longitudinal direction including the conductor of the thin flat cable having a multi-row structure in the horizontal direction. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of the thin flat cable having a multi-row structure in the horizontal direction. (C) shows a cross-section perpendicular to the longitudinal direction including the conductor of the thin flat cable having a multi-row structure in the horizontal direction according to another embodiment. (D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of the thin flat cable having a multi-row structure in the horizontal direction according to another embodiment. [Figure 8] A thin flat cable according to an embodiment of the present disclosure, the thin flat cable having a multi-row structure in the horizontal and vertical directions. (A) shows a cross-section perpendicular to the longitudinal direction including the conductors of the thin flat cable having a multi-row structure in the horizontal and vertical directions. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of the thin flat cable having a multi-row structure in the horizontal and vertical directions. (C) shows a cross-section perpendicular to the longitudinal direction including the conductors of the thin flat cable having a multi-row structure in the horizontal and vertical directions according to another embodiment. (D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of the thin flat cable having a multi-row structure in the horizontal and vertical directions according to another embodiment. [Modes for carrying out the invention]

[0033] The general configuration of the thin flat cable 101 according to this disclosure will be described. Figure 1 shows a perspective view of the thin flat cable 101 according to this disclosure. In this specification, "conductor" refers to a conductive member constituting a signal transmission path, and is used as a concept that includes conductor wiring and inner layer electrodes formed continuously with said conductor wiring.

[0034] Thin flat cables require low transmission loss, shielding, heat resistance, processability, and flexibility. Furthermore, it is desirable to suppress the transmission and reflection of millimeter waves incident from the outside. In this specification, "externally radiated millimeter waves" refers to millimeter waves incident from the outside of the thin flat cable, and "reflected radiated millimeter waves" refers to millimeter waves reflected by the thin flat cable.

[0035] The binder resin constituting the millimeter-wave absorbing layer is not particularly limited, but from the viewpoint of shortening the curing time in the manufacturing process and improving patterning accuracy, it is preferably an ultraviolet-curable resin. By irradiating it with ultraviolet light, curing can be performed in a short time, which can improve the continuous productivity of thin flat cables configured as flexible printed circuit boards, and their applicability to methods such as roll-to-roll systems. Furthermore, it can be adapted to various forming methods such as coating, printing, inkjet, spray coating, and dipping.

[0036] Furthermore, from the viewpoint of improving the resolution of the millimeter-wave absorption layer formation, i.e., patterning accuracy, in fine regions such as around the conductor electrodes, it is more preferable that the resin is a photosensitive resin composition containing an alkali-soluble main resin, a reactive diluent including an acrylate compound, a photopolymerization initiator, an epoxy resin such as a bisphenol A type epoxy resin or a novolac type epoxy resin which is a thermosetting component, and a thermosetting agent such as an imidazole compound. After forming a high-definition pattern by curing with ultraviolet light and developing with an alkaline aqueous solution, thermosetting is performed by crosslinking the epoxy resin by heating, thereby achieving both developability and the flexibility, bending resistance, and final toughness, heat resistance, and insulation reliability of the coating film, which are essential for thin flat cables.

[0037] In this case, as the alkali-soluble main resin, a carboxyl group-containing urethane acrylate resin having excellent flexibility derived from urethane bonding can be suitably used, from the viewpoint of ensuring good solubility in the developing solution while imparting the high flexibility characteristic of thin flat cables to the coating film after curing by ultraviolet irradiation. Furthermore, if excellent heat resistance due to a high crosslinking density is required to prevent deterioration or deformation of the millimeter-wave absorbing layer during soldering processes such as component mounting, the carboxyl group-containing urethane acrylate resin may be used as the main component, blended with an acid-modified epoxy acrylate such as a carboxyl group-containing novolac-type epoxy acrylate resin with excellent rigidity.

[0038] Furthermore, in one embodiment of the present disclosure, a photosensitive solder resist composition for flexible printed circuit boards may be used as the photosensitive resin composition for the millimeter-wave absorbing layer, with the millimeter-wave absorbing material added and dispersed therein. Furthermore, the millimeter-wave absorbing layer may be in a form that covers the side surface of the insulating layer, or in a form in which the millimeter-wave absorbing material is impregnated or dispersed in at least a portion of the surface layer of the insulating layer.

[0039] By utilizing commercially available photosensitive solder resist compositions that are pre-optimized for flexible printed circuit boards, including the main resin, reactive diluent, epoxy resin, thermosetting agent, and photopolymerization initiator, existing FPC manufacturing lines and photolithography processes such as exposure and development equipment can be leveraged. This allows existing exposure and development processes to be used for patterning the millimeter-wave absorption layer around the conductor electrodes.

[0040] (Thin flat cable) As shown in Figure 1, the thin flat cable 101 consists of a terminal portion 103 having a conductor electrode 105 that is in contact with an inner layer electrode 214 formed continuously from the conductor 204, and a conductor portion 102 in which the conductor 204 is located. Furthermore, the conductor is not limited to a structure sandwiched between the first and second insulating layers, but may also be embedded within a single insulating layer.

[0041] Figures 1(B), (C), and (D) show plan views of the terminal portion 103. Figure 1(B) shows the case where the conductor electrode 105 in Figure 1(A) is circular. Figure 1(C) shows the case where the conductor electrode 105 is rectangular and there are multiple electrodes. Figure 1(D) shows the case where the conductor electrode 105 is rectangular and is provided at the longitudinal end of the thin flat cable 101. The millimeter-wave absorbing layer 211 is not provided on the outer surface of the conductor electrode 105. The shape of the conductor electrode 105 can be anything. Also, multiple conductor electrodes 105 may be provided on a single conductor 204.

[0042] Figure 2 shows a thin flat cable 101 according to an embodiment of the present disclosure. Figure 2(A) shows a cross-section perpendicular to the longitudinal direction including the conductor 204 of the thin flat cable 101 according to the embodiment, and Figure 2(B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode 105 of the thin flat cable 101 according to the embodiment. Furthermore, Figure 2(C) shows a cross-section perpendicular to the longitudinal direction including the conductor 204 of the thin flat cable 101 according to another embodiment, and Figure 2(D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode 105 of the thin flat cable 101 according to another embodiment.

[0043] In this disclosure, the metal film 202 is a general term for the metal films provided on the thin flat cable 101. The metal film 202 includes a metal film 202A covering the surface of the first insulator layer 219 opposite to the surface in contact with the conductor 204, a metal film 202B forming the conductor 204 and the inner layer electrode 214, a metal film 202C covering the surface of the second insulator layer 106 opposite to the surface in contact with the conductor 204, a metal film 202D covering the longitudinal and transverse sides, and a metal film 202E separating the multiple conductors 204. In this specification, when the term metal film 202 is used simply, it is used as a concept that includes at least one or all of these. Furthermore, the conductor 204 is not limited to a structure sandwiched between the first and second insulating layers, but may also be embedded within a single insulating layer. Alternatively, it may be a multilayer structure of three or more layers comprising an insulating laminate having one or more additional insulating layers between the first and second insulating layers or outside of them, in which case a millimeter-wave absorbing layer 211 is provided on the sides of all insulating layers that are exposed on the sides.

[0044] As shown in Figures 2(A) and 2(C), the metal conductor 204 of the conductor portion 102 of the thin flat cable 101 is in contact with the first insulator layer 219 on which the conductor 204 is formed, and includes a second insulator layer 106 that sandwiches the conductor 204. The outer surfaces of the first insulator layer 219 and the second insulator layer 106 that form the plane of the thin flat cable 101 are covered with a metal film 202A on the first insulator layer 219 side and with a metal film 202C on the second insulator layer 106 side. A millimeter-wave absorbing layer 211 made of a resin containing a millimeter-wave absorbing material is provided on at least one surface of the metal film 202A and the metal film 202C covering the outer surface of the plane, as well as on the longitudinal and transverse sides of the first insulator layer 219 and the second insulator layer 106.

[0045] In Figure 2(A), the metal film 202D is not present on the longitudinal and transverse sides, but in Figure 2(C), the metal film 202D is present on the longitudinal and transverse sides, and a millimeter-wave absorbing layer 211 is present on the outer surface of the metal film 202D. Providing the metal film 202D on the longitudinal and transverse sides improves the shielding performance against externally radiated millimeter waves, but the process is complicated. By not providing the metal film 202D and instead providing the millimeter-wave absorbing layer 211, it is possible to reduce and absorb the effects of externally radiated millimeter waves irradiated on the sides. Since the aperture width is narrow on the sides, by ensuring a sufficient distance from the side to the conductor 204 and appropriately setting the position and number of through-holes 108, it is possible to make it difficult for externally radiated millimeter waves incident from the sides to reach the conductor 204.

[0046] As shown in Figures 2(B) and 2(D), the terminal portion 103 of the thin flat cable 101 has an inner layer electrode 214 formed continuously from the conductor 204, and a conductor electrode 105 for connecting to another device on the opposite side of at least one of the surfaces of the first insulator layer 219 or the second insulator layer 106 that is in contact with the conductor 204. It has a via structure 208 provided in the cross-sectional direction of the first insulator layer 219 or the second insulator layer 106, and the via structure 208 conducts electricity between the inner layer electrode 214 and the conductor electrode 105. The surfaces of the first insulator layer 219 and the second insulator layer 106 that form the horizontal plane of the thin flat cable 101, other than around the conductor electrode 105, are covered with a metal film 202A on the first insulator layer 219 side and with a metal film 202C on the second insulator layer 106 side. A millimeter-wave absorbing layer 211 containing a millimeter-wave absorbing material is provided on at least one surface of the metal film 202A and metal film 202C covering the first insulating layer 219 and the second insulating layer 106, excluding the area around the conductor electrode 105, and on the longitudinal and transverse sides of the first insulating layer 219 and the second insulating layer 106. Around the conductor electrode 105, the millimeter-wave absorbing layer 211 may extend beyond the metal film 202A or leave the metal film 202A uncovered.

[0047] In Figures 2(A) and 2(B), the metal film 202D is not present on the longitudinal and transverse sides, but in Figures 2(C) and 2(D), the metal film 202D is present on the longitudinal and transverse sides, and a millimeter-wave absorbing layer 211 is present on the outer surface of the metal film 202D. Providing the metal film 202D on the longitudinal and transverse sides improves the shielding performance against externally radiated millimeter waves, but the metal film 202D is unnecessary if there is sufficient distance from the side to the conductor 204. It is also possible to shield and absorb millimeter waves incident on the side by not providing the metal film 202D and instead providing the millimeter-wave absorbing layer 211. However, in the case of high-density mounting, it is necessary to more reliably block the intrusion of externally radiated millimeter waves from the side, so it is preferable to have the metal film 202D on the longitudinal and transverse sides. Here, the longitudinal and transverse sides are not limited to surfaces perpendicular to the thickness direction, but may also include outer peripheral sides consisting of tapered surfaces, stepped surfaces, and curved surfaces, or a combination thereof, and these include cut surfaces and end faces formed by laser processing, dicing, punching, or cutting.

[0048] Figure 2(E) shows a cross-section of the conductor portion 102 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211 shown in Figure 2(A), and Figure 2(F) shows a cross-section of the terminal portion 103 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211 shown in Figure 2(B). The reflection suppression layer 216 is a layer containing a reflection suppression material and can reduce reflection on the surface of the millimeter-wave absorption layer 211. In particular, when the millimeter-wave absorption layer 211 is a thin film, the effect of suppressing surface reflection becomes relatively important, so the formation of the reflection suppression layer 216 is preferable.

[0049] Figure 2(G) shows a cross-section of the conductor portion 102 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211 shown in Figure 2(C), and Figure 2(H) shows a cross-section of the terminal portion 103 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211 shown in Figure 2(D).

[0050] Figures 2(I) and 2(J) show cross-sectional views of the conductor portion 102 and terminal portion 103, where the base material is in contact with the side opposite to the side having the conductor electrode 105, and the side without the conductor electrode 105 does not have the millimeter-wave absorption layer 211 and the reflection suppression layer 216. When used in contact with the base material, the millimeter-wave absorption layer 211 and the reflection suppression layer 216 are unnecessary because externally radiated millimeter waves do not enter from the base material side. The surface of the metal film 202C on the side of the second insulator layer 106 that is in contact with the base material may be provided with solder resist, or surface treatment such as gold plating may be applied. Thus, the millimeter-wave absorbing layer 211 only needs to be provided on at least one side of the metal film surface, such as the side where the conductive electrodes are not provided.

[0051] On the surface in contact with the base material, the millimeter-wave absorbing layer 211 and the reflection suppression layer 216 can be omitted depending on the usage, but from the viewpoint of shielding performance, it is preferable to have the metal film 202C on the second insulating layer 106 side.

[0052] Base materials include enclosures, heat spreaders, radar radomes, and printed circuit boards surrounding devices and components that handle millimeter waves, such as antennas, radars, and wireless power transfer devices.

[0053] As shown in Figures 2(B) and 2(D), in the terminal portion 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and the via structure 208. The conductor electrode 105 is a terminal for connection to an external element and can be used as a connector terminal, soldering terminal, ACF connection terminal, etc. The surface of the conductor electrode 105 may be treated with solder, Ni / Au plating, tin plating, silver plating, or OSP as needed.

[0054] The area around the conductor electrode 105 is not covered by the metal film 202A that covers the first insulator layer 219. The insulating millimeter-wave absorbing layer 211 or the first insulator layer 219 not covered by the millimeter-wave absorbing layer 211 is exposed, isolating the metal film 202A from the conductor electrode 105 and creating a structure that prevents electrical conductivity between the metal film 202A and the conductor electrode 105.

[0055] As shown in Figure 2(B), if the thin flat cable 101 does not have a metal film 202D on its side surface, it is preferable that the thin flat cable 101 has a through-hole 108 with a metal film on the inner surface of the through-hole 220. The through-hole 108 conducts the metal films 202 on both sides and maintains the same potential on both sides. Multiple through-holes 108 may be provided, and their position and number are set appropriately according to the transmission characteristics of the conductor 204. In contrast, if the metal film 202D is provided on the side surface as shown in Figures 2(C) and 2(D), the through-hole 108 is not essential. Furthermore, the via structure 208 and through-hole 108 may be blind vias formed from one side, through-holes whose inner walls are covered with a conductive material, or filled vias whose interiors are filled with conductive paste or plating. In addition, multilayer structures may include buried vias formed only between the inner layers of an insulating laminate, or stacked via structures in which multiple vias are arranged in the stacking direction and electrically connected in series.

[0056] As shown in Figures 2(A), 2(B), 2(C), and 2(D), both surfaces forming the plane of the thin flat cable 101 have a metal film 202 except around the conductor electrode 105. As shown in Figures 2(B) and 2(D), a millimeter-wave absorbing layer 211 is provided on at least one surface of the metal film other than around the conductor electrode 105. As shown in Figure 2(D), the millimeter-wave absorbing layer 211 may also be provided on a portion of the surface of the first insulator layer 219 that does not have a metal film 202 around the conductor electrode 105.

[0057] As shown in Figures 2(A) and 2(B), even if the thin flat cable 101 does not have a metal film 202D on its longitudinal and transverse sides, the thin flat cable 101 must have a millimeter-wave absorbing layer 211 on its sides.

[0058] In the thin flat cable 101 according to this disclosure, the first insulating layer 219 and the second insulating layer 106 protect the conductor 204, and the metal film 202 and / or millimeter-wave absorbing layer 211 protect the first insulating layer 219 and the second insulating layer 106. The metal film 202 shields the conductor 204. In areas where the metal film 202 is not present, the millimeter-wave absorbing layer 211 reduces the influence of externally radiated millimeter waves by absorbing incident millimeter waves from the outside, and in areas where the metal film 202 is present, it reduces the influence of reflection on the outside by absorbing reflected waves on the surface of the metal film 202. Furthermore, the millimeter-wave absorbing layer has the function of at least partially absorbing millimeter waves radiated to the outside from the side surface.

[0059] The conductor 204 should be made of a material with good electrical conductivity, and gold, silver, copper, or aluminum are particularly preferred. Considering flexibility and conductivity, copper is the most preferred. If the conductor 204 is not gold or silver, it may be gold-plated or silver-plated.

[0060] The width of the conductor 204 is preferably 0.01 mm or more and 10 mm or less, and more preferably 0.02 mm or more and 5 mm or less. If it is less than 0.01 mm, it is difficult to control the dimensional accuracy and conductor loss tends to increase. If it exceeds 10 mm, the first insulator layer 219 and the second insulator layer 106 become thicker in order to obtain the desired characteristic impedance, which is disadvantageous for thinning.

[0061] Since the width of the conductor 204 affects the transmission characteristics, it is preferable to control it precisely. To improve line width accuracy, the MSAP method (Modified Semi Additive Process) may be used. Since the thin flat cable 101 according to this disclosure has a strip line structure, the characteristic impedance of the conductor 204 is determined by the width and thickness of the conductor 204, the thickness of the first insulator layer 219 and the second insulator layer 106, and the dielectric constant, etc. To obtain the desired impedance, the width of the conductor 204 is usually adjusted.

[0062] The thickness of the conductor 204 is preferably 1 μm or more and 75 μm or less, and more preferably 10 μm or more and 35 μm or less. If it is less than 1 μm, conductivity and bending resistance tend to be insufficient, and it becomes difficult to set the processing conditions when forming the via structure. If it exceeds 75 μm, it becomes difficult to ensure line width accuracy, and the first insulator layer 219 and the second insulator layer 106 become thicker, which is disadvantageous for thinning.

[0063] The adhesive strength between the first insulator layer 219 and the second insulator layer 106 at locations not in contact with the conductor 204 is preferably 3N / 15mm or more, and more preferably 6N / 15mm or more. The adhesive strength is a 15mm width equivalent value measured parallel to the longitudinal direction of the thin flat cable 101. If it is less than 3N / 15mm, delamination may occur due to tension or twisting during the manufacturing process or use, which may result in wire breakage. Furthermore, if the insulating laminate is formed with a multilayer structure of three or more layers, the same resin material can be used for the additional insulating layers.

[0064] The first insulating layer 219 and the second insulating layer 106 adhere to each other and to the conductor 204 and the inner layer electrode 214, providing insulation. The first insulating layer 219 and the second insulating layer 106 contain a thermosetting resin, a thermoplastic resin, or an ionizing radiation-curable resin. They may also contain two or more types of resin. Examples of ionizing radiation include active energy rays such as ultraviolet rays, electron beams, visible light, X-rays, and gamma rays.

[0065] The first insulating layer 219 and the second insulating layer 106 may have the same composition or different compositions. Furthermore, each layer may be composed of multiple layers of different compositions.

[0066] The thermosetting resin is not particularly limited, but epoxy resins, silicone resins, urethane resins, aromatic or aliphatic hydrocarbon resins, rubber resins, fluororesins, polyimide resins, benzoxazine, bismaleimide resins, and polyphenylene ether resins to which epoxy or allyl groups have been added are preferred. Furthermore, the thermosetting resin may be modified by acrylic modification or the addition of acid anhydrides. The thermosetting resin may be used alone or in combination of two or more types.

[0067] Thermosetting resins may contain a curing agent as needed, and may also contain additives such as inorganic fillers, thermoplastic resins, curing accelerators, flame retardants, and organic fillers.

[0068] The curing agent is not particularly limited as long as it has the function of curing the thermosetting resin, and may be used alone or in combination of two or more types.

[0069] When the first insulating layer 219 and / or the second insulating layer 106 are made of a thermosetting resin, the thermosetting resin and curing agent are combined and coated onto a peelable sheet surface, then thermoset and peeled off the peelable sheet to form a film, which can then be used in the manufacture of thin flat cables. Alternatively, the resin may be applied to one side of the metal constituting the metal film 202 and then thermoset.

[0070] Suitable thermoplastic resins include polyimide resins, polytetrafluoroethylene, copolymers of tetrafluoroethylene and perfluoroalkoxyethylene, polyphenylene ether resins, polyetheretherketone resins, liquid crystal polymers, alkene polymers, syndiotactic polystyrene, polyethylene terephthalate, polyamideimide, and polyetherimide. The thermoplastic resin may be used individually or in combination of two or more types.

[0071] Thermoplastic resins have a low dielectric constant and are suitable as materials for constructing thin flat cables 101. Furthermore, the first insulating layer 219 has a step in which a conductor 204 is provided, requiring heat resistance and chemical resistance. By selecting a thermoplastic resin that satisfies these requirements, the manufacturing of thin flat cables 101 can be easily carried out.

[0072] Alkene polymers have a low dielectric constant and are suitable as materials for constructing the thin flat cable 101. Furthermore, the second insulator layer 106 is bonded to the first insulator layer 219 on which the conductor 204 is provided. If the second insulator layer 106 and the first insulator layer 219 are made of different resins, good adhesion can be achieved through surface treatment, selection of appropriate resins, etc.

[0073] The thermoplastic resin is preferably formed into a film before the manufacture of the thin flat cable 101. Alternatively, it may be coated onto the metal constituting the metal film 202.

[0074] Examples of ionizing radiation-curable resins include monomers, oligomers, and prepolymers that have polymerizable functional groups in their molecules. Examples of polymerizable functional groups include ethylenically unsaturated bonds such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups.

[0075] Ionizing radiation-curable resins may contain additives such as inorganic fillers, flame retardants, and organic fillers, as needed. The inorganic fillers are the same as those used in thermosetting resins. UV-curable resins may contain photoinitiators as needed.

[0076] The thickness of the first insulating layer 219, the second insulating layer 106, and the other insulating layers in the multilayer structure is preferably 10 μm or more and 1000 μm or less, and more preferably 20 μm or more and 500 μm or less. If the thickness is less than 10 μm, interlayer insulation defects are likely to occur, and if it exceeds 1000 μm, it is disadvantageous for processability and thinning when forming via structures.

[0077] As shown in Figures 2(A) and 2(C), the first insulating layer 219 is in contact with the conductor 204 in the conductor portion 102, and in the portion not in contact with the conductor 204, it is in contact with the second insulating layer 106, and the other side is in contact with the metal film 202A. The longitudinal and transverse sides of the thin flat cable 101 are in contact with the millimeter-wave absorbing layer 211 in Figure 2(A) and with the metal film 202D in Figure 2(C), with the millimeter-wave absorbing layer 211 on the outer surface of the metal film 202D.

[0078] As shown in Figures 2(A) and 2(C), the second insulating layer 106 is in contact with the conductor 204 in the conductor portion 102, in the portion not in contact with the conductor 204 it is in contact with the first insulating layer 219, and the other side is in contact with the metal film 202C. In addition, the longitudinal and transverse sides of the thin flat cable 101 are in contact with the millimeter-wave absorbing layer 211 in Figure 2(A) and with the metal film 202D in Figure 2(C), with the millimeter-wave absorbing layer 211 on the outer surface of the metal film 202D. Furthermore, if the insulator laminate has three or more layers, the inner insulator layer is in contact with the conductor or other insulator layers, and at least a portion of its side surface is in contact with the millimeter-wave absorbing layer 211 or the metal film 202D.

[0079] In the terminal portion 103, the first insulating layer 219 is in contact with the metal formed through the hole wall of the via hole 208, and constitutes the peripheral edge of the conductor electrode 105 which is formed continuously above the via hole 208.

[0080] As shown in Figures 2(B) and 2(D), in the terminal portion 103, the first insulating layer 219 (or second insulating layer 106) is exposed in areas where the metal film 202A (or metal film 202C) and / or millimeter-wave absorbing layer 211 around the conductor electrode 105 are not provided, while the areas not exposed are covered by the metal film 202A (or metal film 202C) or the millimeter-wave absorbing layer 211.

[0081] As shown in Figure 2(D), the millimeter-wave absorbing layer 211 may also cover the first insulating layer 219 or the second insulating layer 106 around the conductor electrode 105.

[0082] Figure 5(A) shows a cross-section of the terminal portion 103 of a conventional thin flat cable 101. Figure 5(B) shows a cross-section of the conductor portion 102 of a conventional thin flat cable 101. The conductor electrode 105 is not surrounded by a metal film 202. The sides are not covered by a metal film 202 or a millimeter-wave absorbing layer 211. Externally radiated millimeter waves can penetrate even through small gaps, so they enter from the sides and adversely affect the signals passing through the conductor 204 and internal electrode 214. In addition, radiated millimeter waves emitted from the conductor 204 and internal electrode 214 pass through the sides and are radiated to the outside, adversely affecting the outside.

[0083] As shown in Figures 2(A), 2(B), 2(C), and 2(D), the metal film 202 is continuously provided on the outer surface forming the plane of the thin flat cable 101, except around the conductor electrode 105 of the terminal portion 103. Here, the metal film on the side of the first insulator layer 219 that forms the plane is metal film 202A, and the metal film on the side of the second insulator layer 106 is metal film 202C. The continuous metal film 202 suppresses thermal deformation of the first insulator layer 219 and the second insulator layer 106, defects due to peeling, and the influence of water vapor intrusion from the outside air on the electrical characteristics of the conductor 204. It is acceptable for the metal film 202 not to be provided on a portion of the surface of the first insulator layer 219 or the second insulator layer 106 to the extent that it does not cause damage to the shielding properties of the conductor 204, damage to its electrical properties, deformation of the first insulator layer 219 and the second insulator layer 106, or delamination of the metal film 202 from the first insulator layer 219 or the second insulator layer 106.

[0084] As shown in Figures 2(C) and 2(D), the metal film 202 may be continuously provided on the longitudinal and transverse sides of the thin flat cable 101. The metal film formed on these sides is the metal film 202D.

[0085] To improve the shielding of the conductor 204 of the thin flat cable 101, it is preferable that the metal film 202 be provided on the entire surface of the first insulator layer 219 and the second insulator layer 106, except around the conductor electrode 105. The metal film 202 is not provided around the conductor electrode 105. The periphery is defined as a distance such that there is no electrical conductivity between the end of the conductor electrode 105 and the end of the metal film 202 on the surface on which the conductor electrode is provided. It is preferable that the area on the surface of the insulator layer where the metal film 202 is not provided is small.

[0086] It is desirable that the longitudinal and transverse sides of the thin flat cable 101 are covered with a metal film 202D without exposing the first insulating layer 219 and the second insulating layer 106. To enhance shielding, it is preferable that the longitudinal and transverse sides are covered with a metal film 202D, and that the metal film 202 covers 80% or more of the area of ​​both sides and sides forming the plane of the thin flat cable 101. Alternatively, the metal film 202D may be omitted, and 80% or more of the surface area of ​​the side may be covered by the millimeter-wave absorbing layer 211.

[0087] As shown in Figure 2(B) or Figure 2(D), in areas where the metal film 202A or metal film 202C is not provided around the conductor electrode 105, the first insulator layer 219, the metal film 202A, or the millimeter-wave absorbing layer 211 is exposed to the outside air. It is important to minimize the area of ​​areas where the metal film 202A is not provided around the conductor electrode 105. If the area of ​​areas where the metal film 202A is not provided is large, water vapor from the outside air may reach the second insulator layer 106 through the insulator layer and / or the millimeter-wave absorbing layer 211, causing each insulator layer to absorb moisture and be affected by moisture absorption, which may degrade the transmission characteristics of the thin flat cable 101.

[0088] The conductor 204 is surrounded by the first insulator layer 219 and the second insulator layer 106, and a metal film 202A is continuously present on the surface of the first insulator layer 219, except around the conductor electrode 105. That is, by having the metal film 202 on the plane forming the thin flat cable 101, the protective function of the metal film 202 suppresses the influence of the outside air on the thin flat cable 101, allowing the transmission characteristics to be maintained for a long period of time. The protective function can be further improved by providing metal films 202D on the longitudinal and transverse sides of the thin flat cable 101. This also shields the conductor 204 from externally radiated millimeter waves.

[0089] The distance between the end of the conductor electrode 105 and the end of the metal film 202A or metal film 202C is 10 μm or more and 3000 μm or less. The insulating layer or millimeter-wave absorbing layer 211 is exposed to the outside air between the end of the conductor electrode 105 and the end of the metal film 202. If the distance is less than 10 μm, there is a risk of electrical conductivity between the end of the conductor electrode 105 and the end of the metal film 202. If the distance exceeds 3000 μm, water vapor from the outside air may penetrate into the interior through the insulating layer and / or the millimeter-wave absorbing layer 211, increasing the amount of moisture absorbed by the insulating layer and potentially degrading the transmission characteristics and heat resistance. The distance between the end of the conductor electrode 105 and the end of the metal film 202 may be equally spaced around the conductor electrode 105 or may be different.

[0090] In a thin flat cable 101 in which multiple rows of conductors 204 are formed, the distance between one end of a conductor electrode 105 and the end of an adjacent conductor electrode 105 is 10 μm or more and 3000 μm or less, for the same reasons as in the case between the end of a conductor electrode 105 and the end of a metal film 202A.

[0091] The conductor electrode 105 is usually circular, but it may also be rectangular. There may be multiple electrodes on the same terminal portion 103. The conductor electrode 105 may be provided on the longitudinal or transverse side of the thin flat cable 101, but this is undesirable because it is complicated to process and makes soldering work difficult. Also, multiple conductor electrodes 105 may be provided on a single conductor 204.

[0092] The metal film 202, which is provided continuously on the surface of the first insulator layer 219 and the second insulator layer 106 or the insulator laminate, except around the conductor electrode 105, prevents water vapor and chemicals from penetrating into the insulator layer from the outside. Furthermore, the metal film 202 prevents flames directed at the thin flat cable 101 from directly touching the insulator layer, thereby improving the flame retardancy of the thin flat cable 101. The metal film 202 is used as a ground. Here, the metal film 202 is a general term that includes the metal film 202A on the first insulator layer 219 side, the metal film 202C on the second insulator layer 106 side, and the metal film 202D formed on the side surface as needed.

[0093] The metal film 202 of the thin flat cable 101 uses a metal with good electrical conductivity, preferably gold, silver, copper, or aluminum, with copper being the most suitable. Considering flexibility and conductivity, copper is the most suitable. The metal films 202A and 202C on both sides forming the horizontal surface of the thin flat cable 101 can be copper foil, but the sides in the longitudinal and transverse directions of the thin flat cable 101 are preferably made of a metal film 202D made of copper formed by plating. The electrical resistivity of the metal film 202 is preferably 10 μΩ·cm or less. To add functions such as oxidation prevention and improved adhesion, the metal film 202 may be made of a combination of different metals. For example, nickel, zinc, chromium, tin, silver, gold, iron-based alloys, water-soluble preflux, etc., can be formed on the outside of the copper film.

[0094] The horizontal distance between the conductor 204 and the metal film 202D provided on the side surface of the thin flat cable 101 is 20 μm or more. If it is less than 20 μm, there is a possibility of a short circuit between the conductor 204 and the metal film 202D. The vertical distance between the conductor 204 and the metal film 202A or metal film 202C provided on the surface forming the plane of the thin flat cable 101 is 10 μm or more and 1000 μm or less. 50 μm or more is preferable. If it is less than 10 μm, there is a possibility of a short circuit, and if it exceeds 1000 μm, it takes a long time to form the linear grooves 206 in the first insulator layer 219 and the second insulator layer 106 using laser light. If it is less than 50 μm, the transmission loss will be large in high-speed and high-frequency transmission, so it is not preferable when used for high-speed and high-frequency transmission.

[0095] As shown in Figures 2(B) and 2(D), in the terminal section 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and the via structure 208. An electrical signal enters from one conductor electrode 105, exits through the via structure 208, the inner layer electrode 214, the conductor 204, the other inner layer electrode 214, the other via hole 208, and the other conductor electrode 105, transmitting the electrical signal from one to the other.

[0096] As shown in Figure 2, the inner layer electrode 214 is formed continuously from the conductor 204. Therefore, its thickness and material are the same as those of the conductor 204. To connect with the conductor electrode 105 via the via structure 208, the inner layer electrode 214 is made to have a diameter equal to or larger than that of the cylindrical via structure 208, as shown in Figure 2(B). The shape of the inner layer electrode 214 is preferably circular, but any shape is acceptable as long as it is equal to or larger than the cross-section of the via structure 208. Auxiliary shapes such as teardrops may also be added. In the case of a circular shape, the diameter is usually between 50 μm and 2 mm. A diameter of 100 μm or more and 800 μm or less is even more preferable. If the diameter is less than 50 μm, it is difficult to align the inner layer electrode 214 with the via structure 208, and if it exceeds 2 mm, it becomes difficult to match the characteristic impedance. The characteristic impedance matching of the signal line is required, and matching the characteristic impedance of the inner layer electrode 214 and the conductor 204 is difficult. Therefore, it is necessary to achieve characteristic impedance matching by making the diameter of the inner layer electrode 214 as small as possible.

[0097] The via structure 208 is formed by removing the insulating layer from the location where the conductive electrode 105 is formed to the inner layer electrode 214 by laser light, mechanical drilling, photolithography, or etching, and then plating or filling the holes 207 for the via structure formed by the removal of the insulating layer with conductive paste. Therefore, the cross-section is approximately circular. Plating is preferably done with copper. At the location where the conductive electrode 105 is formed, the metal film 202 is removed by etching to form a via structure opening 209, and a metal film is formed in the holes 207 for the via structure, which are formed by laser processing, etc., by plating, etc., and connected to the unetched metal film 202, integrating them to form the conductive electrode 105.

[0098] As shown in Figure 2(B), the thin flat cable 101 includes a first insulating layer 219 and a second insulating layer 106 or insulating laminate exposed on at least one surface of the metal films 202A and 202C that form the outer surface of the thin flat cable 101, on the longitudinal and transverse sides, and a millimeter-wave absorbing layer 211 on the surface of the insulating layer exposed around the conductor electrode 105 that is not covered by the metal film 202A (or metal film 202C). The millimeter-wave absorbing layer 211 does not need to be provided on the insulating layer exposed around the conductor electrode 105 that is not covered by the metal film 202 and / or on some surfaces of the metal film 202, but the millimeter-wave absorbing layer 211 is essential on the surface of the insulating layer exposed on the longitudinal and transverse sides that are not covered by the metal film 202D.

[0099] As shown in Figure 2(D), the millimeter-wave absorbing layer 211 may be provided on the surface of the first insulating layer 219 that is exposed around the conductor electrode 105 which is not covered by the metal film 202A that forms the outer surface of the thin flat cable 101. As shown in Figures 2(C) and 2(D), the longitudinal and transverse sides of the thin flat cable 101 are covered with the metal film 202D. Even in this case, the millimeter-wave absorbing layer 211 is provided on the longitudinal and transverse sides. The millimeter-wave absorbing layer 211 does not have to be provided on a part of the insulating layer and / or metal film 202 that is exposed around the conductor electrode 105 which is not covered by the metal film 202A or metal film 202C.

[0100] The millimeter-wave absorbing layer 211 is formed from a thermosetting resin, thermoplastic resin, or ionizing radiation-curable resin similar to that used for the first insulating layer 219 and the second insulating layer 106. The millimeter-wave absorbing layer 211 has the function of adhering to the first insulating layer 219, the second insulating layer 106, or the metal film 202. Preferably, the millimeter-wave absorbing layer 211 has heat resistance to soldering. This heat resistance is the same as that of the first insulating layer 219 and the second insulating layer 106. The millimeter-wave absorbing layer 211 also contains a millimeter-wave absorbing material. The millimeter-wave absorbing layer 211 contains the same filler as the first insulating layer 219 and the second insulating layer 106, and may contain the same amount of filler.

[0101] Millimeter-wave absorbing materials include one or more of the following: Mn ferrite, NiZn ferrite, CoFe2O4 ferrite, hexagonal ferrite, carbon black, graphite, carbon nanotubes, graphene, carbon microcoils, graphene oxide, carbon fibers, conductive polymers and composites thereof including poly(3,4-ethylenedioxythiophene), polyaniline, and polypyrrole; BaTiO3; transition metal carbides; transition metal nitrides; transition metal carbonitrides; Fe-based soft magnetic metal powders (FeSiAl, FeCo, FeB, FeSiB, etc.); ε-Fe2O3; γ-Fe2O3; Ni; Fe; Co; Cr; Cu; Al; Ag; Ti; Zn; oxides of these metals; metal microcoils, metal nanowires, and magnetic metal nanowires made from the aforementioned metals; and CoNi.

[0102] Suitable combinations of carbon black and FeSiAl powder, graphene and ferrite, carbon-based materials and conductive polymers, and carbon nanotubes and FeCo nanoparticles are suitable as millimeter-wave absorbers.

[0103] The binder resin constituting the millimeter-wave absorbing layer is not particularly limited as long as it has the desired binding properties and moldability, and a wide range of known resins can be used. Examples include thermosetting resins such as epoxy resins, phenolic resins, polyurethane resins, silicone resins, bismaleimide resins, cyanate ester resins, and benzoxazine resins; ionizing radiation curable resins such as ultraviolet curable resins or electron beam curable resins; thermoplastic resins such as polyethylene, polypropylene, polyester, polycarbonate, polyimide, polyamideimide, polyetherimide, liquid crystal polymers, fluororesins, polyvinylidene fluoride, polyvinyl alcohol, natural rubber, synthetic rubber, and various elastomers. These may be used individually or blended in groups of two or more.

[0104] Among the various binder resins exemplified above, the following (1) to (3) can be cited as preferred combinations of millimeter-wave absorbing material and binder resin, from the viewpoint of eliciting the characteristics of the target high-frequency band and the millimeter-wave absorbing mechanism of the millimeter-wave absorbing material. However, this disclosure is not limited to these specific combinations.

[0105] (1) When using high-frequency magnetic resonance type millimeter wave absorbers When using high-frequency magnetic resonance materials such as ε-Fe2O3 or hexagonal ferrite as millimeter-wave absorbing materials, bismaleimide resin, liquid crystal polymer, or fluororesin is preferred as the binder resin. Because these binder resins have low relative permittivity and dielectric loss tangent, they suppress the reflection of high frequencies such as millimeter waves from the resin surface, allowing electromagnetic waves to efficiently penetrate into the millimeter-wave absorbing layer 211 and increasing the magnetic loss by the millimeter-wave absorbing material. In particular, a combination with bismaleimide resin is preferred for automotive millimeter-wave radar peripheral components or semiconductor package applications where high heat resistance and high filling capacity of the millimeter-wave absorbing material are required.

[0106] (2) When using conductive nanomaterial millimeter-wave absorbing material When using highly conductive nanomaterials such as transition metal carbides, transition metal nitrides, transition metal carbonitrides, graphene, graphene oxide, carbon nanotubes, or metal nanowires as millimeter-wave absorbers, it is preferable to use polyvinylidene fluoride, aqueous polyurethane, or polyimide as the binder resin. In particular, when combined with resins having a strong dipole moment, such as polyvinylidene fluoride, the interfacial polarization at the interface between the conductive network formed by the nanomaterial and the resin increases, making it easy to exhibit large dielectric losses even in thin films. Furthermore, in applications where flexibility is required, a combination of transition metal carbides or graphene oxide having polar functional groups on the surface and aqueous polyurethane capable of forming hydrogen bonds is also preferable.

[0107] (3) When using a coiled millimeter-wave absorber When using a material having a three-dimensional helical structure, such as a carbon microcoil or a metal microcoil, as a millimeter-wave absorber, it is preferable to use a fluid or elastic resin such as silicone rubber, polyurethane elastomer, or low-viscosity epoxy resin as the binder resin. By using these binder resins, excessive shear stress during mixing with the resin can be avoided, and the unique helical structure of the microcoil can be prevented from breaking. Furthermore, when an elastomer material such as silicone rubber is used as the matrix, the internal coil pitch changes in response to elastic deformation due to external stress, making it possible to create a configuration in which the absorption frequency band can be adjusted according to the stress.

[0108] In this way, by selecting a binder resin suitable for the type of millimeter-wave absorbing material used in the millimeter-wave absorbing layer 211, it is possible to achieve a balance of film-forming properties, adhesion, heat resistance, flexibility, and millimeter-wave absorption performance for the millimeter-wave absorbing layer 211.

[0109] In particular, in the thin flat cable according to this disclosure, from the viewpoint of thinning the millimeter-wave absorbing layer 211 while ensuring excellent noise absorption performance against externally radiated millimeter waves, it is extremely preferable to use epsilon iron oxide, hexagonal ferrite, carbon microcoil, metal microcoil, transition metal carbide, transition metal nitride, or transition metal carbonitride as the millimeter-wave absorbing material.

[0110] In detail, high-frequency magnetic materials such as epsilon iron oxide (ε-Fe2O3) possess large crystalline magnetic anisotropy. Unlike conventional spinel-type ferrites, where magnetic loss decreases in the high-frequency band due to Snook's limit, these materials exhibit extremely high millimeter-wave absorption performance in the millimeter-wave band due to spontaneous resonance phenomena. Furthermore, transition metal carbides such as MXene, or its precursor MAX phase, possess both extremely high conductivity comparable to metals and large dielectric loss originating from surface functional groups. Therefore, even small amounts of these materials can efficiently convert electromagnetic wave energy in the millimeter-wave band into Joule heat.

[0111] Furthermore, when fillers with fine three-dimensional or network shapes, such as carbon microcoils (CMCs), metal microcoils, or metal nanowires, are used, when millimeter waves are irradiated from the outside, minute induced currents are generated along their helical or network structures, and these are efficiently converted and consumed as thermal energy due to electrical resistance.

[0112] Unlike interference-type absorption, which depends on the thickness of the material itself, these materials have a particularly high radio wave absorption capacity in the millimeter-wave band. Therefore, even when the content of the millimeter-wave absorbing material in the millimeter-wave absorbing layer 211 is in the range of 0.3% by mass or more and 60% by mass or less, it is possible to achieve the ability to absorb up to 50% or more of millimeter waves with frequencies from 23 GHz to 80 GHz when converted to a thickness of 1000 μm, without impairing the flexibility or insulation of the binder resin. As a result, it exhibits a sufficient noise suppression effect even when the thickness of the coating or lamination applied to the side surface of a thin flat cable 101, where flexibility is required, is reduced, making it extremely suitable.

[0113] The millimeter-wave absorbing layer 211 preferably contains 0.3% by mass or more and 60% by mass or less of millimeter-wave absorbing material. If the amount is less than 0.3% by mass, sufficient absorption performance may not be obtained. If it exceeds 60% by mass, the flexibility of the thin flat cable 101 may be impaired.

[0114] As shown in Figures 2(A) and 2(B), if the metal film 202D is not provided on the side surface, there is only one opportunity for absorption by the millimeter-wave absorbing layer 211. However, the externally radiated millimeter waves absorbed by the millimeter-wave absorbing layer 211 are attenuated from the end to the conductor 204 and do not affect the conductor 204. Because the metal film 202D is not provided, there is less reflection of externally radiated millimeter waves, and the impact on the surroundings from the reflected externally radiated millimeter waves is minimal. The distance from the end of the thin flat cable 101 to the conductor 204 must be such that externally radiated millimeter waves do not reach it.

[0115] Figures 2(E) and 2(G) show cross-sections of the conductor portion 102 of a thin flat cable 101 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211, and Figures 2(F) and 2(H) show cross-sections of the terminal portion 103 of a thin flat cable 101 in which a reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorption layer 211.

[0116] The film thickness of the reflection suppression layer 216 is preferably 1 μm or more and 20 μm or less. If the film thickness of the reflection suppression layer 216 is less than 1 μm, it is difficult to form a uniform coating and it is difficult to obtain a stable suppression effect. If it exceeds 20 μm, the combined film thickness of the reflection suppression layer 216 and the millimeter-wave absorption layer 211 becomes thick, making it difficult to thin the film. As a result, there is an unnecessary increase in weight and a loss of flexibility.

[0117] The reflection suppression layer 216 can use the millimeter-wave absorbing material of the millimeter-wave absorbing layer 211 as its reflection suppression material. Furthermore, in order to suppress the reflection of externally radiated millimeter waves and increase absorption, the reflection suppression layer 216 preferably contains one or more of the following as reflection suppression materials: conductive polymers and composites thereof including carbon nanotubes, graphene, graphene oxide, graphite, carbon black, poly(3,4-ethylenedioxythiophene), polyaniline, and polypyrrole; conductive metal oxides such as indium tin oxide (ITO), antimony-doped tin oxide (ATO), and aluminum-doped zinc oxide (AZO); transition metal carbides, transition metal nitrides, transition metal carbonitrides; Ni, Fe, Co, Cr, Cu, Al, Ag, Ti, Zn, oxides of these metals; metal nanowires and metal microcoils made of the aforementioned metals; and CoNi.

[0118] The reflection suppression layer 216 may contain the same filler as the first insulator layer 219 and the second insulator layer 106, and may contain the same amount of filler.

[0119] If the addition of the millimeter-wave absorbing material results in insufficient insulation, a solder resist layer or coverlay may be further formed on the outer surface of the millimeter-wave absorbing layer 211 or the reflection suppression layer 216 as an insulating resin layer that does not contain the millimeter-wave absorbing material or the reflection suppression material.

[0120] Solder resist or a coverlay may be formed on the outer surface of the millimeter-wave absorption layer 211. If the millimeter-wave absorption layer 211 has a reflection suppression layer 216 on its outer surface, solder resist or a coverlay may be formed on the outer surface of the reflection suppression layer 216. Commercially available solder resist for flexible printed circuit boards can be used as the solder resist formed on the outer surface of the millimeter-wave absorption layer 211 or the reflection suppression layer 216.

[0121] The millimeter-wave absorbing layer 211 and the reflection suppression layer 216 may be formed by silkscreen printing, spray coating, inkjet printing, slot die printing, bar coating, dipping, or dispensing. Alternatively, an uncured resin of a thermosetting resin or an ionizing radiation curable resin may be formed on the film beforehand and then bonded together by lamination or vacuum heat bonding.

[0122] The millimeter-wave absorbing layer 211 may have a non-conductive resin layer on one or both sides of the conductive millimeter-wave absorbing layer 211. By providing a conductive metal film 202 on the back surface of the millimeter-wave absorbing layer 211, the millimeter-wave absorption effect of the thin flat cable 101 is enhanced. This is because the externally radiated millimeter waves are absorbed twice: once by passing through the millimeter-wave absorbing layer 211 and once by being reflected by the metal film 202.

[0123] The thickness of the millimeter-wave absorbing layer 211 is preferably 10 μm or more and 2000 μm or less. 20 μm or more and 1000 μm or less is preferable. If the thickness is less than 10 μm, the millimeter-wave absorption rate may be insufficient, and the strength of the layer may be low. If the thickness exceeds 2000 μm, the thin flat cable will become thicker, which may impair flexibility. Regarding the manufacturing method

[0124] ~

[0125] The following modifications have been made to conform to the new claims (especially "manufacturing method using a two-layer base," "multilayering to form an insulating laminate by further laminating one or more insulating layers and forming holes such as hidden vias," "forming a millimeter-wave absorbing layer on at least one side of the metal film surface," "forming a side metal film by sputtering, etc."), and the modified parts are shown in bold.

[0126] (Manufacturing method for thin flat cables) An example of a manufacturing method for the thin flat cable 101 according to this disclosure is shown in Figure 3. Figures 3(A) to 3(L) show a cross-section of the terminal portion 103. The manufacturing method for the thin flat cable 101 involves laminating metal films 202 on both sides of a first insulator layer 219, forming a conductor 204 by etching the metal film 202 on one side of the first insulator layer 219, laminating a metal film 202 on one side of a second insulator layer 106, bonding the other side of the second insulator layer 106 that does not have a metal film 202 laminated on it to the side of the first insulator layer 219 where the conductor 204 is formed to form a laminate, etching the metal film 202 laminated on at least one outer surface of the laminate to form an opening 209 for forming a via structure, and removing the second insulator layer 106 using a laser beam, drill, etc., until the conductor 204 is exposed, forming a blind via Alternatively, holes 207 for through-holes are formed, via structures 208 are formed in the formed holes 207 by plating or conductive paste filling, the metal film 202 around the conductor electrode 105 is removed by etching to form the conductor electrode 105, the area that will form the outer surface of the thin flat cable 101 is formed by laser irradiation to form grooves or by laser irradiation to form grooves and cutting to form the outer surface of the thin flat cable 101, and a millimeter-wave absorbing layer 211 made of a resin containing a millimeter-wave absorbing material is formed on the surface of the metal film 202 formed on the surface of the laminate excluding the surface of the conductor electrode 105, and on the longitudinal and transverse sides of the laminate. Here, in the embodiment shown in Figure 3, the metal film on the first insulator layer 219 side is metal film 202A, and the metal film on the second insulator layer 106 side is metal film 202C. Furthermore, when forming a multilayer structure, when forming the laminate, in addition to the first and second insulating layers, one or more additional insulating layers are laminated to form an insulating laminate, and holes for buried vias are formed only between the inner layers of the insulating laminate, in addition to or instead of the holes for blind vias or through holes.

[0127] Figure 3 shows the manufacturing process of the thin flat cable 101 according to the embodiments of the present disclosure shown in Figures 2(A), 2(B), 2(E), and 2(F).

[0128] Figure 3(A) shows the process of laminating a metal film 202A onto one side of a film-like first insulating layer 219, and laminating a metal film 202B that forms a conductor onto the other side of the first insulating layer 219.

[0129] Lamination is performed by pressure bonding or heat bonding, but pretreatment may be performed before lamination to improve adhesion strength. For example, the first insulator layer 219 may be subjected to plasma treatment, corona treatment or UV treatment, and / or primer treatment or plasma treatment on the bonding side of the metal film 202A and the conductor-forming metal film 202B. Adhesives may also be used for lamination. Lamination can also be performed by inserting a bonding sheet between the film-like first insulator layer 219 and the metal film 202 and pressing them together. Furthermore, lamination can also be performed by extruding and pressing the molten first insulator layer 219 onto the metal film 202.

[0130] When the first insulating layer 219 is made of a thermosetting resin, the metal films 202A and 202B may be bonded to both sides of the first insulating layer 219 while it is uncured or semi-cured, and then the first insulating layer 219 may be heat-cured to bond them together.

[0131] The lamination of the first insulating layer 219 and the metal film 202 may be performed using the material constituting the first insulating layer 219 as an adhesive. An uncured thermosetting resin is coated onto the surface of the film constituting the first insulating layer 219, the metal film 202 is laminated, and then the uncured thermosetting resin is cured to bond the initial film-like first insulating layer 219 and the metal film 202. The first insulating layer 219 will consist of the initial film and the thermosetting resin used as an adhesive. In this case, the metal film 202 is either metal film 202A or metal film 202B.

[0132] The method for applying the thermosetting resin is not limited, and known coating methods can be used.

[0133] One method for producing the film-like first insulating layer 219 is to coat a separator with a composition containing an uncured thermosetting resin or an ionizing radiation-curable resin, cure it, and then peel it off the separator. When a thermoplastic resin is used as the first insulating layer 219, a conventional method can be used in which the thermoplastic resin is heated and melted in an extruder, extruded from a die, and formed into a film. When a film of thermoplastic resin is used as the first insulating layer 219, an unstretched film is preferred over a stretched film. Stretching can cause crystallization, which may prevent sufficient adhesion to the second insulating layer 106.

[0134] The conditions for curing the thermosetting resin are appropriately selected depending on the type of thermosetting resin. For example, the laminate is heated and pressed at a temperature of 80°C to 250°C. When curing an ionizing radiation-curable resin, the first insulating layer 219 is cured or partially cured by irradiating it with ionizing radiation before laminating the metal films 202A and 202B. When curing, heating and irradiation with ionizing radiation may be combined.

[0135] The lamination of the first insulating layer 219, the metal film 202A, and the metal film 202B forming the conductor may be carried out by heating, pressing, or adhesive under reduced pressure or vacuum. If air enters between the layers, blistering may occur due to heating during soldering, so it is preferable to laminate under reduced pressure or vacuum. For lamination in a vacuum atmosphere, a vacuum pressure molding machine, a vacuum laminator, a roll laminator, etc., can be used.

[0136] Metal foil is used for the metal film 202A and the metal film 202B that forms the conductor. Metal foil is a foil containing gold, silver, copper, aluminum, etc., and copper foil is particularly preferred.

[0137] Figure 3(B) shows a laminate in which a metal film 202B forming a conductor is laminated on one side of the first insulating layer 219, and a metal film 202A is laminated on the other side.

[0138] Figure 3(C) shows the process of forming a conductor 204 on the conductor portion 102 and an inner layer electrode 214 on the terminal portion 103, which will be the end of the conductor 204 and will be in electrical contact with the conductor electrode 105, by a circuit formation process that involves etching the conductor-forming metal film 202B.

[0139] The circuit formation process can utilize methods commonly used in the manufacture of printed circuit boards. For example, the conductor 204 and inner layer electrodes 214 are formed by steps such as etching mask formation, exposure, development, etching, and etching mask removal, while leaving a metal film 202B that forms the necessary conductor.

[0140] Figure 3(D) shows the process of sequentially laminating a film-like second insulating layer 106 and a metal film 202C onto the conductor 204 and inner layer electrode 214 formed on the surface of the first insulating layer 219. The lamination of the first insulating layer 219 and the film-like second insulating layer 106 is performed by thermocompression bonding. The conductor 204 and the inner layer electrode 214 are sandwiched and wrapped between the first insulating layer 219 and the second insulating layer 106. Since the conductor 204 becomes convex on the second insulating layer 106, it is preferable to perform the thermocompression bonding under vacuum conditions to ensure complete adhesion between the first insulating layer 219 and the film-like second insulating layer 106.

[0141] The second insulating layer 106, which is in the form of a film, is created in the same manner as the first insulating layer 219.

[0142] The step of sequentially laminating a film-like second insulating layer 106 and a metal film 202C on the first insulating layer 219, the formed conductor 204, and the inner layer electrode 214 may be carried out by a vacuum lamination method. In the vacuum lamination method, the heat-pressure temperature is preferably in the range of 60°C to 200°C, more preferably in the range of 80°C to 180°C, the heat-pressure pressure is preferably in the range of 0.05 MPa to 2.00 MPa, more preferably in the range of 0.1 MPa to 1.5 MPa, and the heat-pressure time is preferably in the range of 1 second to 500 seconds, more preferably in the range of 3 seconds to 300 seconds. Lamination is preferably carried out under reduced pressure conditions of 20 hPa or less.

[0143] The adhesive strength between the first insulating layer 219 and the second insulating layer 106 in areas not in contact with the conductor 204 is preferably 3N / 15mm or more.

[0144] When the second insulating layer 106 contains an alkene polymer and the first insulating layer 219 is made of a thermoplastic resin, sufficient adhesive strength can be obtained by heat bonding.

[0145] When laminating the conductor 204 and inner electrode 214 formed on the surface of the first insulator layer 219 with the film-like second insulator layer 106 by thermocompression bonding, it is preferable to provide a copolymer of a monomer having a carboxyl group and an alkene as a layer on both sides of the film-like second insulator layer 106 in order to increase the adhesive strength. The adhesive strength between the copolymer of a monomer having a carboxyl group and an alkene and the metal increases with thermocompression bonding. In particular, when polyethylene using ethylene as the alkene or polypropylene using propylene as the alkene is used as the polymer, it is preferable to use a polymer obtained by graft polymerization of polyethylene or polypropylene with maleic anhydride. Alternatively, an adhesive film may be used between the first insulator layer 219 and the second insulator layer 106. The metal film 202C is a metal film that covers the surface of the second insulator layer 106 opposite to the surface in contact with the conductor 204.

[0146] It is preferable that the metal film 202C be made of the same metal as the metal film 202A. The method for forming the metal film 202C may be to laminate the first insulating layer 219 onto the second insulating layer 106 and then sequentially laminate the metal film 202C, or to laminate the film-like second insulating layer 106 and the metal film 202C onto the first insulating layer 219 at the same time. Alternatively, the film-like second insulating layer 106 and the metal film 202C may be laminated together and then the first insulating layer 219 may be laminated onto the second insulating layer 106.

[0147] Figure 3(E) shows a laminate in which a metal film 202A is laminated on one side of a first insulating layer 219, and a conductor 204 and an inner layer electrode 214 are formed on the other side, and a laminate formed by sequentially laminating a second insulating layer 106 and a metal film 202C.

[0148] Figure 3(F) shows the process of forming a through-hole 220 for creating the through-hole 108 at the location where the through-hole 108 is to be formed, using a CNC drill or laser processing machine.

[0149] Furthermore, Figure 3(F) shows the process of removing the metal film 202C on the second insulator layer 106 side in the area where the conductor electrode 105 is formed by etching, forming an opening 209 for via structure formation, and forming a hole 207 for via structure to form a via structure 208 for electrical connection between the inner layer electrode 214 and the conductor electrode 105.

[0150] The step of removing the metal film 202A by etching to form the via structure opening 209 is the same as the circuit formation step described above. The area from which the metal film 202A is removed is the area where the conductor electrode 105 is formed and its surroundings. The via structure opening 209 may also be formed using a direct laser method, which involves laser irradiation at the same time as the hole 207. The area from which the metal film 202A has been removed is designated as the via hole opening 209.

[0151] To form the via structure 208, the holes 207 for the via structure are removed up to the inner layer electrode 214 from the second insulating layer 106 exposed to the via structure forming opening 209.

[0152] The holes 207 can be formed by laser processing, plasma processing, mechanical drilling, or photolithography etching, with laser processing or mechanical drilling being preferred from the viewpoint of processing speed. Laser processing can remove the second insulating layer 106 down to the inner electrode 214. If the metal film 202C is thin, the metal film 202C and the second insulating layer 106 may be removed simultaneously.

[0153] Examples of laser light used in laser processing machines include UV-visible lasers such as excimer lasers, UV lasers, and green lasers, as well as near-infrared or far-infrared lasers such as YAG lasers, fiber lasers, and carbon dioxide lasers.

[0154] Processing with UV and visible light lasers, by using both long and short pulses, results in a smooth surface and a clean shape, thus producing a high-quality finish.

[0155] Near-infrared and far-infrared lasers offer fast processing speeds even for thick first insulating layer 219 and second insulating layer 106.

[0156] Figure 3(G) shows the process of forming a through-hole 108 by plating or filling the inner surface of the through-hole 220 with conductive paste. The inner surface of the through-hole 220 is cleaned, the surfaces of the first insulating layer 219 and the second insulating layer 106 on the inner surface of the through-hole 220 are made conductive, and then metal plating or filling with conductive paste is performed. With the formation of the through-hole 108, the metal films 202A and 202C, which are the metal films 202 on both sides that form the plane of the thin flat cable 101, become conductive and their potentials become the same.

[0157] Figure 3(G) also shows the process of forming a conductor electrode 105, which will serve as a terminal, by plating or filling the inner surface of the hole 207 with conductive paste, and connecting the plated metal film or conductive paste with the metal film 202C, thereby establishing electrical conductivity between the conductor 204 and the conductor electrode 105. The exposed portions of the metal film 202C and the inner layer electrode 214 at the bottom of the hole 207 are cleaned, the surface of the second insulator layer 106 is made conductive, and then metal plating or filling with conductive paste is performed.

[0158] Metal plating can be formed by sequentially performing desmearing, catalyst formation, electroless plating, and electrolytic plating, as needed. Desmearing can be performed by a dry method using plasma or a wet method using an oxidizing agent, but the dry method is preferred from the viewpoint of suppressing moisture absorption. Conductivity may be achieved by catalyst formation and electroless plating, or by a dry method such as sputtering.

[0159] Figure 3(H) shows the process of removing a portion of the metal film 202A shown in Figure 3(G). This process involves removing a portion of the metal film 202A to form a gap 218 between the conductor electrode 105 and the metal film 202A. The metal film 202A is removed around the area that will become the conductor electrode 105 to form the gap 218. The area to be removed is such that there is no electrical conductivity between the end of the conductor electrode 105 formed by the removal and the end of the remaining metal film 202A.

[0160] The metal film 202A can be removed by the circuit formation process.

[0161] Figure 3(I) shows the process of forming the outer surface of the thin flat cable 101. At the point where the outer surface is formed, the metal film 202A, the first insulating layer 219, and the second insulating layer 106 are broken, and the metal film 202C may also be broken if necessary. Figure 3(N) shows a plan view of Figure 3(I). Figure 3(I) is a cross-sectional view along the dashed line a in Figure 3(N). Multiple through holes 220 for forming the through-holes 108 may be provided. In Figure 3(N), the shaded area shown in the plan view represents the metal film 202C.

[0162] Figure 6(A) is a plan view showing the formation locations of the linear grooves 206. The linear grooves 206 are an important component that determines the outer shape of the thin flat cable 101 and forms the longitudinal and transverse sides. In Figure 6(A), the shaded area shows the metal film 202C that covers the surface of the second insulator layer 106 opposite to the surface in contact with the conductor. The linear grooves 206 are formed along the outer circumference of the thin flat cable 101 by laser processing or cutting, and are processed to a depth that reaches at least the metal film 202C or metal film 202A.

[0163] Figure 6(B) is a plan view showing linear grooves 206 formed by laser processing, as well as through-holes 213 formed by cutting. The through-holes 213 are elongated holes formed by cutting and extend along the outer circumference of the thin flat cable 101. In Figure 6(B), the shaded area shows the linear grooves 206 formed by laser processing, and the metal film 202C that covers the surface opposite to the surface of the second insulator layer 106 that contacts the conductor remains. The linear grooves 206 can be formed by laser processing or by laser processing and cutting, but if the linear grooves 206 are formed by cutting alone, the groove processing extends to the metal film 202C provided on the outer surface on the second insulator layer 106 side, making the metal film 202C prone to breakage and making it difficult to carry out subsequent processes while maintaining the assembled state. Therefore, from the viewpoint of continuing manufacturing as an assembled unit while partially leaving the metal film 202C, it is preferable to use laser processing in combination.

[0164] When forming linear grooves 206 by laser processing, groove-forming openings 212 are provided as needed. The laser processing conditions can be set in the same way as for forming holes 207 for via structures. For deep drilling, near-infrared lasers or far-infrared lasers are preferred from the viewpoint of processing speed.

[0165] Figure 3(J) shows the process of forming a millimeter-wave absorbing layer 211 on the laminate with its outer shape and on its side surface. The millimeter-wave absorbing layer 211 is formed on at least one surface of the metal film 202A and metal film 202C on the upper and lower surfaces of the thin flat cable 101, and on the longitudinal and transverse side surfaces of the thin flat cable 101. As shown in Figures 3(J) and 3(K), the millimeter-wave absorbing layer 211 may be formed only on one side of the metal film, such as the side on which the conductor electrode 105 is not provided, or it may be formed on both sides of the metal film, as shown in Figure 3(L). In Figure 3(J), the millimeter-wave absorbing layer 211 is not formed on the surface of the first insulator layer 219 that is in contact with the conductor electrode 105. However, the millimeter-wave absorbing layer 211 may cover the first insulator layer 219 without covering the surface of the conductor electrode 105.

[0166] The millimeter-wave absorbing layer 211 is formed by applying a thermosetting resin, thermoplastic resin, or ionizing radiation-curable resin containing a millimeter-wave absorbing material to the area where it is to be formed using a coating method, printing method, inkjet method, spray coating method, dipping method, etc., or by laminating a film-like resin containing a millimeter-wave absorbing material using a lamination method or vacuum heating and pressure method, and curing it as necessary. The coating and curing can be performed in the same manner as the formation of the first insulating layer 219. In addition, although not shown in the figure, a solder resist or coverlay may be formed on the outer surface of the millimeter-wave absorbing layer 211 to prevent solder adhesion, to the extent that it does not affect the millimeter-wave absorption performance.

[0167] It is preferable to form the millimeter-wave absorbing layer 211 using an ultraviolet-curable resin. Alternatively, the millimeter-wave absorbing layer 211 may be formed by applying an ultraviolet-curable resin containing a millimeter-wave absorbing material to the surface of the conductor electrode 105, the surface of the metal film 202 formed on the surface of the first insulator layer 219 and the second insulator layer 106, and the longitudinal and transverse side surfaces of the first insulator layer 219 and the second insulator layer 106, curing all surfaces except the surface of the conductor electrode 105 and the surface of the conductor electrode 105, and then removing the ultraviolet-curable resin containing the millimeter-wave absorbing material from the uncured surface of the conductor electrode 105 and the surface of the conductor electrode 105. Here, the surface of the metal film 202 includes the surface of metal film 202A and the surface of metal film 202C, and further includes the surface of metal film 202D in the embodiment in which a metal film is formed on the side surface.

[0168] By separating the thin flat cable 101 shown in Figure 3(J) into individual segments, the thin flat cable 101 shown in Figures 2(A) and 2(B) can be obtained.

[0169] Figure 3(K) shows the process of forming a reflection suppression layer 216 on the outer surface of the millimeter-wave absorbing layer 211. The reflection suppression layer 216 can be formed in the same way as the millimeter-wave absorbing layer 211. The reflection suppression layer 216 is formed on the outer surface of the millimeter-wave absorbing layer 211 on the upper and lower surfaces of the thin flat cable 101, and on the outer surface of the millimeter-wave absorbing layer 211 on the longitudinal and transverse sides of the thin flat cable 101. In Figure 3(K), neither the millimeter-wave absorbing layer 211 nor the reflection suppression layer 216 is formed on the surface of the first insulator layer 219 that is in contact with the conductor electrode 105. However, the reflection suppression layer 216 may cover the first insulator layer 219 without covering the surface of the conductor electrode 105.

[0170] The reflection suppression layer 216 is formed by applying a thermosetting resin, thermoplastic resin, or ionizing radiation-curable resin containing a reflection suppression material to the area where it should be formed, or by laminating a resin containing a film-like reflection suppression material and curing it as necessary. The application and curing can be carried out in the same manner as the formation of the first insulating layer 219. Although not shown in the figure, a solder resist or coverlay may also be formed on the outer surface of the reflection suppression layer 216 to prevent solder adhesion, to the extent that it does not affect the millimeter-wave absorption performance.

[0171] It is preferable to form the reflection suppression layer 216 using an ultraviolet-curable resin. Alternatively, the reflection suppression layer 216 may be formed by applying an ultraviolet-curable resin containing a reflection suppression material to the surface of the millimeter-wave absorbing layer 211 formed on the surface of the conductor electrode 105, the surface surrounding the conductor electrode 105, the first insulating layer 219, and the second insulating layer 106, curing all surfaces except the surface of the conductor electrode 105 and the surface surrounding the conductor electrode 105, and then removing the ultraviolet-curable resin containing the reflection suppression material from the uncured surface of the conductor electrode 105 and the surface surrounding the conductor electrode 105. Here, the surface of the millimeter-wave absorbing layer 211 includes the surface of the millimeter-wave absorbing layer 211 formed on the outer surface of the metal film 202A or the metal film 202C, and further including the surface of the millimeter-wave absorbing layer 211 formed on the outer surface of the metal film 202D in an embodiment in which a metal film is formed on the side surface.

[0172] The formation of the millimeter-wave absorbing layer 211 and the reflection suppression layer 216 can be achieved by laminating a film-like resin containing a millimeter-wave absorbing material and / or a resin containing a reflection suppression material, respectively, using methods such as lamination or vacuum heating and pressing. Furthermore, a sheet consisting of two layers, a resin layer containing a millimeter-wave absorbing material and a resin layer containing a reflection suppression material on its outer surface, can be created. The millimeter-wave absorbing layer 211 can then be brought into contact with the surface of the metal film 202 of the thin flat cable 101, which has an outer surface formed thereon, and heated and pressed in a vacuum to sequentially form the millimeter-wave absorbing layer 211 and the reflection suppression layer 216 on at least one of the outer surfaces of the metal film 202. If the metal film 202D is not formed on the side surface, the millimeter-wave absorbing layer 211 and the reflection suppression layer 216 can be sequentially formed on the surfaces of the first insulator layer 219 and the second insulator layer 106.

[0173] The sheet, consisting of two layers—a resin layer containing a millimeter-wave absorbing material and a resin layer containing a reflection-suppressing material—is formed by creating a sheet by forming a resin layer that will become a reflection-suppressing layer 216 containing a reflection-suppressing material on one side of a film, and then forming a resin layer containing a millimeter-wave absorbing material that will become a millimeter-wave absorbing layer 211 on the surface of the reflection-suppressing layer 216. The millimeter-wave absorbing layer 211 of the sheet is then heat-pressed onto both sides of the plane of the thin flat cable 101 with its sides formed, with the thin flat cable 101 side facing the sheet. Alternatively, the millimeter-wave absorbing layer 211 and the reflection-suppressing layer 216 may be formed sequentially by bonding the sheet to the outer surface of the thin flat cable 101 with its sides formed after the sheet has been formed as a multilayer. Here, both sides of the plane are the surface of the metal film 202A on the first insulator layer 219 side and the surface of the metal film 202C on the second insulator layer 106 side.

[0174] Before performing heat-pressing, peel off the film that forms the base of the sheet. Alternatively, a protective film may be applied to the outer surface of the millimeter-wave absorbing layer 211 after the sheet has been formed. Peel off the protective film before performing heat-pressing.

[0175] Figures 3(L) and 3(M) show the process of separating the thin flat cable 101 into individual pieces. Figure 3(L) shows the terminal portion 103, and Figure 3(M) shows the conductor portion 102. This is the thin flat cable 101 shown in Figures 2(E) and 2(F). By separating Figure 3(J), which does not have the reflection suppression layer 216 formed, the thin flat cable 101 shown in Figures 2(A) and 2(B) can be obtained. Separation is performed by cutting the metal film 202C along the linear groove 206. For cutting to separate the pieces, the cutting method for flexible wiring boards can be used, and cutting with a die, cutting with a router, and cutting with a laser processing machine are common. This disclosure allows the thin flat cable 101 to be manufactured as an assembly and then separated into individual pieces at the end, resulting in good work efficiency.

[0176] Manufacturing a thin flat cable 101 as an assembly means that, as shown in Figure 3, a large number of thin flat cables 101 are formed in parallel in the longitudinal direction, and then separated into individual pieces, thereby obtaining a large number of thin flat cables 101 simultaneously. Alternatively, the thin flat cables 101 may be formed in series in multiple rows in the longitudinal direction.

[0177] Figure 4 shows the manufacturing process of a thin flat cable according to another embodiment of the present disclosure shown in Figures 2(C), 2(D), 2(G), and 2(H).

[0178] Figure 4(A) shows the process of laminating a metal film 202A onto one side of a film-like first insulating layer 219 and laminating a metal film 202B that forms a conductor onto the other side of the first insulating layer 219. This is the same as in Figure 3(A). Figure 4(B) shows a laminate in which the metal film 202A, the first insulating layer 219, and the metal film 202B that forms the conductor are sequentially laminated, similar to Figure 3(B).

[0179] Figure 4(C) shows the process of forming a conductor 204 on the conductor portion 102 and an inner layer electrode 214 on the terminal portion 103 by etching the metal film 202B that forms the conductor. Furthermore, it shows the process of forming via structure openings 209 and groove formation openings 212 by etching the metal film 202A. In the embodiment shown in Figure 3, the process of forming via structure openings 209 and groove formation openings 212 was not performed simultaneously with the formation of the conductor 204, but sequentially after laminating the second insulating layer 106 onto the conductor 204. However, even in the manufacturing process of the thin flat cable 101 according to the present disclosure shown in Figure 3, the conductor 204, inner layer electrode 214, via structure openings 209 and groove formation openings 212 may be formed simultaneously by etching the metal film 202B that forms the conductor, as shown in Figure 4(C).

[0180] When the process of forming the via structure openings 209 and groove formation openings 212 is performed simultaneously with the formation of the conductor 204, the alignment accuracy of the via structure 208 and the inner layer electrode 214 is better than that of the method in Figure 3, and the number of steps is also reduced, making it preferable. The same method as in Figure 4(C) is possible even with the method in Figure 3. In other words, performing the circuit formation process simultaneously on both the front and back of a single laminate and accurately aligning the inner layer electrode 214 and the via structure formation openings 209 is useful for obtaining a thin flat cable 101 of superior quality.

[0181] Etching can be performed by the circuit formation process described above.

[0182] Figure 4(D) shows the process of sequentially laminating a film-like second insulating layer 106 and a metal film 202C onto the side of a first insulating layer 219 that has a metal film 202A on one side with via structure formation openings 209 and groove formation openings 212 formed thereon, and a conductor 204 and an inner layer electrode 214 formed on the other side. The lamination process is the same as in Figure 3(D).

[0183] Figure 4(E) shows a laminate in which a film-like second insulating layer 106 and a metal film 202C having via structure formation openings 209 and groove formation openings 212 formed on one side are sequentially laminated on the side of a first insulating layer 219 on which a conductor 204 and an inner layer electrode 214 are formed.

[0184] Figure 4(F) shows the process of removing the second insulating layer 106 of the via structure formation opening 209, which was formed in the process shown in Figure 4(C), and forming a hole 207 for the via structure 208. It also shows the process of removing the first insulating layer 219 and the second insulating layer 106 at the location of the groove formation opening 212 of the second insulating layer 106 and forming a linear groove 206.

[0185] The formation of the hole 207 involves removing the second insulating layer 106 exposed to the via structure formation opening 209 down to the inner layer electrode 214. The removal of the second insulating layer 106 can be carried out in the same manner as shown in Figure 3(F).

[0186] The formation of the linear grooves 206 is a process for forming the outer surface of the thin flat cable 101. The first insulating layer 219 and the second insulating layer 106 in the area where the outer surface of the thin flat cable 101 is to be formed are broken, leaving at least a portion of the metal film 202C intact. The formation of the linear grooves 206 can be carried out by laser processing and / or cutting using a combination of cutting tools and router bits, similar to the process shown in Figure 3(I).

[0187] Figure 4(G) shows the process of plating or filling the inner surface of the hole 207 and the surface of the linear groove 206 formed in the process shown in Figure 4(F). Plating or filling the inner surface of the hole 207 with conductive paste is performed, and the plated metal film or conductive paste is connected to the metal film 202C to form a conductor electrode 105 that will serve as a terminal, thereby making the inner layer electrode 214 and the conductor electrode 105 electrically connected. The exposed parts of the metal film 202C and the inner layer electrode 214 that forms the bottom of the hole 207 are cleaned, the surface of the second insulating layer 106 that forms the inner surface of the hole 207 for the via structure is made conductive, and then metal plating or filling with conductive paste is performed. Metal plating can be performed in the same manner as shown in Figure 3(G). The plated metal film formed on the wall surface 205 of the linear groove 206 is the metal film 202D.

[0188] The step of forming a metal film 202D on the wall surface 205 of the linear groove 206 (i.e., the longitudinal and transverse sides) can be carried out by known film formation methods such as metal plating, application or filling of conductive paste, or dry film formation methods such as sputtering or vapor deposition. By providing the metal film 202D on the longitudinal and transverse sides of the thin flat cable 101, a metal film 202 is formed that continuously covers the entire outer surface of the thin flat cable 101. In other words, the metal films 202A, 202C, and 202D are continuously connected.

[0189] The thin flat cable 101 obtained in the manufacturing process shown in Figure 3 does not have a metal film 202D formed on its longitudinal and transverse sides. The thin flat cable 101 obtained in the manufacturing process shown in Figure 4 has a metal film 202D formed on its longitudinal and transverse sides, resulting in a high shielding effect.

[0190] Figure 4(H) shows the process of removing a portion of the metal film 202A shown in Figure 4(G). This process involves removing a portion of the metal film 202A, connecting the plated metal in the hole 207 with the metal film 202A surrounding the hole 207, and forming a gap 218 between the conductor electrode 105 formed by the connected metal film 202A and the metal film 202A. The metal film 202A around the area that will become the conductor electrode 105 is removed to form the gap 218. The area to be removed is such that the end of the conductor electrode 105 formed by the removal and the end of the metal film 202A do not conduct electricity. This is the same as the process in Figure 3(H).

[0191] While it is conceivable to simultaneously form the gap 218 around the conductor electrode during the process shown in Figure 4(D), the plating process that forms a metal film in the hole 207 shown in Figure 4(G) and the plating process that forms a metal film 202D on the wall surface 205 of the linear groove 206 may result in the gap 218 also being metal-plated. Therefore, forming the gap 218 as shown in Figure 4(H) during the circuit formation process shown in Figure 4(D) may be undesirable.

[0192] Figure 4(I) shows the process of forming a millimeter-wave absorbing layer 211 on both sides and sides that form the plane of the thin flat cable 101 in which the gap 218 is formed. The millimeter-wave absorbing layer 211 is formed on at least one side of the metal films 202A and 202C on both sides that form the plane of the thin flat cable 101, and on the outer surface of the metal film 202D on the longitudinal and transverse sides of the thin flat cable 101. In Figure 4(I), at least one of the millimeter-wave absorbing layers 211 is not formed on the surface of the first insulator layer 219 that is in contact with the conductor electrode 105. However, as shown in Figure 2(D), the millimeter-wave absorbing layer 211 may cover the first insulator layer 219 without covering the surface of the conductor electrode 105.

[0193] As shown in Figure 4(H), if a metal film 202 is formed on both sides and longitudinal and transverse sides that form the plane of the thin flat cable 101, a millimeter-wave absorbing layer 211 may optionally be provided on the surface of the metal film 202. Here, the surface of the metal film 202 includes the outer surfaces of metal film 202A, metal film 202C, and metal film 202D.

[0194] The millimeter-wave absorbing layer 211 is formed in the same manner as shown in Figure 3(J).

[0195] By separating the thin flat cable 101 shown in Figure 4(I) into individual segments, the thin flat cable 101 shown in Figures 2(C) and 2(D) can be obtained.

[0196] Figure 4(J) shows the process of forming reflection suppression layers 216 on both sides and sides that form the plane of a thin flat cable 101 on which a millimeter-wave absorbing layer 211 is formed. Reflection suppression layers 216 are formed on the outer surfaces of the millimeter-wave absorbing layers 211 on both sides that form the plane of the thin flat cable 101 and on the sides of the millimeter-wave absorbing layers 211 in the longitudinal and transverse directions of the thin flat cable 101. In Figure 4(J), the reflection suppression layer 216 is not formed on the surface of the first insulator layer 219 that is in contact with the conductor electrode 105. However, as shown in Figure 2(H), the reflection suppression layer 216 may cover the millimeter-wave absorbing layer 211 that covers the first insulator layer 219 without covering the surface of the conductor electrode 105.

[0197] The reflection suppression layer 216 is formed in the same manner as shown in Figure 3(K). Alternatively, after forming the millimeter-wave absorption layer 211 and the reflection suppression layer 216 into a sheet as described above, the millimeter-wave absorption layer 211 and the reflection suppression layer 216 may be sequentially formed on the outer surface of the metal film 202.

[0198] Figures 4(K) and 4(L) show the process of separating the thin flat cable 101 into individual pieces. Figure 4(K) shows the terminal portion 103, and Figure 4(L) shows the conductor portion 102. This is the thin flat cable 101 shown in Figures 2(G) and 2(H). By separating Figure 4(I), which does not have the reflection suppression layer 216 formed, the thin flat cable 101 shown in Figures 2(C) and 2(D) can be obtained. Separation is performed by cutting the metal film 202C and the millimeter-wave absorption layer 211 along the linear groove 206. Separation can be performed in the same manner as in Figures 3(L) and (M). The manufacturing of a large number of thin flat cables 101 is also done in the same manner. At this time, the metal film 202D has already been formed on the side surface.

[0199] (Multi-row thin flat cable) Figure 7 shows a thin flat cable 101 according to the present disclosure, which has a multi-row structure in the horizontal direction of the flat surface of the thin flat cable 101. Figure 7(A) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable with a multi-row structure in the horizontal direction according to an embodiment. Figure 7(B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable with a multi-row structure in the horizontal direction according to an embodiment. Figure 7(C) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable with a multi-row structure in the horizontal direction according to another embodiment. Figure 7(D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable with a multi-row structure in the horizontal direction according to another embodiment.

[0200] Figure 8 also shows a thin flat cable according to the present disclosure, in which the flat surface of the thin flat cable 101 has a multi-row structure in the horizontal and vertical directions. Figure 8(A) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to an embodiment. Figure 8(B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to an embodiment. Figure 8(C) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to another embodiment. Figure 8(D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to another embodiment.

[0201] In the embodiments described above, one conductor 204 was formed on one shielded thin flat cable 101. However, as shown in Figures 8(A), 8(B), 8(C), and 8(D), multiple conductors 204 can be provided on one shielded thin flat cable 101. This is the same as the embodiments described above, except that multiple shielded thin flat cables are integrated in the horizontal and / or vertical directions of the flat surface of the thin flat cable 101.

[0202] As shown in Figures 7 and 8, the thin flat cable may also include a conductor parallel metal film 215. The thin flat cable 101 having the parallel metal film 215 has the conductor parallel metal film 215 in parallel with the conductor 204 and the inner layer electrode 214. The conductor parallel metal film 215 is formed from the same conductor-forming metal film 202B as the conductor 204 and the inner layer electrode 214. Therefore, the material and thickness are the same as those of the conductor 204 and the inner layer electrode 214. The conductor parallel metal film 215 is electrically connected to the metal film 202 that continuously covers the outer surface of the thin flat cable 101 via a through-hole 108, and serves as the ground.

[0203] The distance between the end of the horizontal parallel conductor metal film 215 and the ends of the conductor 204 and inner layer electrode 214 is preferably 10 μm or more. This is because if the distance is less than 10 μm, there is a concern that a short circuit may occur between the parallel conductor metal film 215 and the conductor 204 and inner layer electrode 214. Within this range, the distance between the conductor 204 and inner layer electrode 214 may vary from place to place. It is preferable that the distance between the conductor 204 and inner layer electrode 214 be the same at all locations. The ends of the parallel conductor metal film 215 are provided along the shape of the conductor 204 and inner layer electrode 214.

[0204] As described above, the ends of the parallel conductor metal film 215 do not need to be provided along the conductor 204 and the inner layer electrode 214. The potential of the parallel conductor metal film 215 needs to be the same as that of the metal film 202. Therefore, the parallel conductor metal film 215 is made electrically connected to the metal film 202 by a through-hole 108. A through-hole 220 for forming the through-hole 108 is formed including a part or more of the parallel conductor metal film 215, and the inner surface of the through-hole 220 is plated to form the through-hole 108.

[0205] If the thin flat cable 101 does not have a metal film 202D on its side, it is necessary to form a through-hole 108. However, if the thin flat cable 101 does have a metal film 202D on its side, by providing the metal film 202D on the side in contact with the conductor parallel metal film 215, the conductor parallel metal film 215 and the metal film 202 become conductive and are at the same potential.

[0206] The parallel metal film 215 of the conductors stabilizes the signal transmission of the conductor 204 and can improve the transmission characteristics of the thin flat cable 101.

[0207] The conductor parallel metal film 215 shown in Figures 7 and 8 may be provided on one side of the conductor 204 and inner layer electrode 214, but it may also be provided on both sides. Furthermore, it may be provided partially along the conductor 204 and inner layer electrode 214. It is more preferable to provide it around the entire circumference to improve the transmission characteristics of the thin flat cable 101.

[0208] As shown in Figures 7(A) and 7(B), the thin flat cable may also have a parallel metal film 215 for the conductors in the horizontal direction. The parallel metal film 215 is not required. Since the thin flat cable 101 does not have a metal film 202D on its side, a through-hole 108 is necessary. If the parallel metal film 215 is present, the through-hole 108 is electrically connected to the parallel metal film 215. If the parallel metal film 215 is not present, a normal through-hole 108 is provided.

[0209] Figures 7(C) and 7(D) show that a metal film 202D is provided on the side of the thin flat cable 101, so a through-hole 108 is not required. However, if a conductor parallel metal film 215 is provided, the side metal film 202D and the conductor parallel metal film 215 must be connected, and the side metal film 202D and the conductor parallel metal film 215 must be electrically connected. Furthermore, if a conductor parallel metal film 215 that cannot be electrically connected to the side metal film 202D is provided, as shown in Figures 7(C) and 7(D), a metal film 202E that isolates multiple conductors 204 must be provided so that the metal films 202 on both sides forming a plane and the conductor parallel metal film 215 can be electrically connected. This can be replaced with a through-hole 108.

[0210] Figures 8(A) and 8(B) show a cable with multiple conductors 204 in the horizontal and vertical directions, and may also have a conductor parallel metal film 215. When multiple conductors 204 are provided in the vertical direction, a metal film 202E is required to separate the upper and lower conductors 204 in the vertical direction. The conductor parallel metal film 215 is not required. Since the thin flat cable 101 does not have a metal film 202D on its side, a through-hole 108 is required. When the conductor parallel metal film 215 is provided, the through-hole 108 is electrically connected to the upper and lower metal films 202, the conductor parallel metal film 215, and the metal film 202E that separates the upper and lower conductors 204. Alternatively, multiple conductors 204 may be provided only in the vertical direction, without multiple conductors 204 in the horizontal direction.

[0211] Figures 8(C) and 8(D) show a cable with multiple conductors 204 in the horizontal and vertical directions, and may also have a conductor parallel metal film 215. A metal film 202E is required to isolate the multiple conductors 204. The conductor parallel metal film 215 is not required. Since a metal film 202D is provided on the side of the thin flat cable 101, a through-hole 108 is not required. However, if the conductor parallel metal film 215 is provided, the side metal film 202D and the conductor parallel metal film 215 must be connected, and the side metal film 202D and the conductor parallel metal film 215 must be electrically connected. Also, if the conductor parallel metal film 215 cannot be electrically connected to the side metal film 202D, as shown in Figures 8(C) and 8(D), the metal film 202E that isolates the multiple conductors 204 must be provided as needed so that the upper and lower metal films 202, the conductor parallel metal film 215, and the metal film 202E that isolates the multiple conductors 204 can be electrically connected. This can be replaced with a through-hole 108. Alternatively, multiple conductors 204 may be provided only in the vertical direction, without multiple conductors 204 in the horizontal direction.

[0212] Although the thin flat cable 101 shown in Figures 7 and 8 does not show the reflection suppression layer 216, it is preferable to provide the reflection suppression layer 216 on the outer surface of the millimeter-wave absorption layer 211 when the thin flat cable 101 is made up of multiple rows and / or multiple layers.

[0213] The thin flat cable described herein can be used in communication equipment requiring high-density mounting, equipment using high-frequency and high-speed signals, equipment requiring EMI countermeasures, equipment requiring chemical resistance, etc. Specifically, it can be used in millimeter-wave radar, smartphones, camera modules, IoT devices, communication base station peripherals, automotive-related equipment such as ADAS, lithium-ion battery peripherals, etc.

[0214] The thin, flat cable disclosed herein is suitable for internal wiring of autonomous driving system units such as in-vehicle radars. In enclosed spaces such as housings, the millimeter-wave absorbing layers on the surface and sides suppress the multiple reflections of millimeter waves that occur with conventional metal-coated cables, preventing false detections by radar and contributing to high-precision sensing.

[0215] Furthermore, the thin cable disclosed herein is suitable for wiring around antennas of millimeter-wave and terahertz band communication equipment in fifth-generation and sixth-generation mobile communications. Because it prevents reflected waves from disrupting the antenna's radiation pattern due to the metal coating and absorbs incident externally radiated millimeter waves, it can minimize adverse effects on performance even when wiring at high density in close proximity to the antenna. [Explanation of Symbols]

[0216] 101 ··Thin flat cable 102. Conductor section 103...Terminal section 105 Conductor electrodes 106 ··Second insulating layer 108 ··Through-hole 202. Metal film 202A · A metal film covering the surface of the first insulator layer opposite to the surface in contact with the conductor. 202B · Metal film forming a conductor 202C - Metal film covering the surface of the second insulating layer opposite to the surface in contact with the conductor. 202D - Metal film covering the sides 202E · Metal film that isolates multiple conductors 204 ··Conductor 205 ··Wall surface 206. Linear grooves 207... Holes for via structures 208 Via Structure 209 ··Opening for forming via structure 211 mm-wave absorption layer 212...Groove formation opening 213. Through-hole 214 ··Inner layer electrode 215 ··Conductor parallel metal film 216·Reflection suppression layer 218...gap 219 ··First insulating layer 220 through hole

Claims

1. Conductors made of conductive materials, The first insulating layer on which the conductor is formed, A second insulating layer that is in contact with the first insulating layer and sandwiches the conductor, A conductor electrode provided on the surface opposite to the surface in contact with the conductor of at least one of the first insulator layer and the second insulator layer, A via structure that electrically connects the conductor and the conductor electrode, A metal film covering the surface forming the horizontal plane of the insulating layer on which the conductive electrode is provided, other than the area around the conductive electrode. A metal film covering the surface that forms the horizontal plane of the insulating layer on the side where the conductive electrode is not provided, A thin, flat cable having a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on at least one of the metal film surfaces formed on the surfaces of the first and second insulating layers, excluding the surface of the conductor electrode and the surface surrounding the conductor electrode, and on the longitudinal and transverse sides of the first and second insulating layers.

2. In the thin flat cable described in claim 1, The insulating laminate comprises one or more additional insulating layers between the first insulating layer and the second insulating layer, and / or outside the first insulating layer or the second insulating layer. A thin, flat cable having the millimeter-wave absorbing layer provided on all sides of the insulating layer that are exposed on the longitudinal and transverse sides.

3. In the thin flat cable according to claim 1 or 2, A thin flat cable in which the via structure is a through-hole penetrating the first insulator layer and the second insulator layer in the thickness direction, and the inner wall surface of the through-hole is covered with a conductive material.

4. In the thin flat cable according to any one of claims 1 to 3, A thin, flat cable in which the via structure is a filled via whose pores are filled with conductive paste or plating.

5. In the thin flat cable described in claim 2, A thin, flat cable including a bound via structure formed only between the inner layers of the insulating laminate.

6. In the thin flat cable described in claim 5, The via structure includes a stacked via structure in which multiple vias are arranged in a stacking direction and electrically connected in series, resulting in a thin, flat cable.

7. In the thin flat cable according to claim 1 or 2, A thin flat cable in which the via structure is formed by filling holes formed in the insulating layer with conductive paste.

8. In the thin flat cable according to any one of claims 1 to 7, The thin flat cable includes outer peripheral surfaces in the longitudinal and transverse directions that consist of any or a combination thereof: a surface perpendicular to the thickness direction of the thin flat cable, a tapered inclined surface, a stepped surface, and a curved surface.

9. In the thin flat cable according to any one of claims 1 to 8, The aforementioned longitudinal and transverse sides include cut surfaces and end faces formed by laser processing, dicing, punching, or cutting.

10. A thin, flat cable in which a conductor made of a conductive material is embedded in a single insulating layer, Conductor electrodes on the surface of the insulating layer where the conductor is not exposed, A via structure that electrically connects the conductor and the conductor electrode, the via structure comprising at least one selected from the group consisting of blind vias, through-holes, and filled vias. A metal film covering the surface forming the horizontal plane of the insulating layer other than the periphery of the conductive electrode, A thin, flat cable having millimeter-wave absorbing layers made of a resin containing a millimeter-wave absorbing material on the longitudinal and transverse sides of the insulating layer.

11. In the thin flat cable according to claim 1 or claim 10, The millimeter-wave absorbing layer includes either a form that covers the side surface of the insulator layer, or a form in which a millimeter-wave absorbing material is impregnated or dispersed in at least a portion of the surface layer of the insulator layer, and the thin flat cable has the function of absorbing at least partially millimeter waves radiated to the outside from the side surface.

12. In the thin flat cable according to claim 1 or claim 10, The millimeter-wave absorbing layer is formed by at least one method selected from the group consisting of coating, printing, inkjet, spray coating, dipping, lamination, and vacuum heat bonding.

13. In the thin flat cable according to claim 1 or claim 10, The resin in the millimeter-wave absorbing layer is an ultraviolet-curable resin in this thin, flat cable.

14. In the thin flat cable described in claim 13, The UV-curable resin is a photosensitive resin composition comprising an alkali-soluble main resin, a reactive diluent containing an acrylate compound, a photopolymerization initiator, an epoxy resin containing a bisphenol A type epoxy resin or a novolac type epoxy resin, and a thermosetting agent containing an imidazole compound or an amine compound, in a thin flat cable.

15. In the thin flat cable described in claim 14, A thin, flat cable in which the alkali-soluble main resin is a carboxyl group-containing photosensitive resin comprising at least one of a carboxyl group-containing urethane acrylate resin and a carboxyl group-containing novolac-type epoxy acrylate resin.

16. In the thin flat cable according to claim 1 or claim 10, The millimeter-wave absorbing layer is a thin, flat cable containing 0.3% by mass or more and 60% by mass or less of the millimeter-wave absorbing material.

17. In the thin flat cable according to claim 1 or claim 10, The resin constituting the millimeter-wave absorbing layer is at least one selected from the group consisting of bismaleimide resin, liquid crystal polymer, and fluororesin. The millimeter-wave absorbing material is a thin, flat cable comprising at least one selected from the group consisting of epsilon iron oxide and hexagonal ferrite.

18. In the thin flat cable according to claim 1 or claim 10, The resin constituting the millimeter-wave absorbing layer is at least one selected from the group consisting of polyvinylidene fluoride, aqueous polyurethane, and polyimide. The millimeter-wave absorbing material is a thin, flat cable comprising at least one selected from the group consisting of transition metal carbides, transition metal nitrides, transition metal carbonitrides, graphene, graphene oxide, carbon nanotubes, metal nanowires, and magnetic metal nanowires.

19. In the thin flat cable according to claim 1 or claim 10, The resin constituting the millimeter-wave absorbing layer is at least one selected from the group consisting of silicone rubber, polyurethane elastomer, and low-viscosity epoxy resin. The millimeter-wave absorbing material is a thin, flat cable containing at least one selected from the group consisting of carbon microcoils and metal microcoils.

20. In the thin flat cable described in claim 1, A thin flat cable wherein the first insulating layer contains 30% by mass or more of one or more of the following: polyimide resin, polytetrafluoroethylene, copolymer of tetrafluoroethylene and perfluoroalkoxyethylene, polyphenylene ether resin, polyetheretherketone resin, liquid crystal polymer, alkene polymer, syndiotactic polystyrene, benzoxazine, bismaleimide resin, polyamideimide resin, and polyetherimide resin.

21. In the thin flat cable described in claim 1, A thin, flat cable wherein the second insulating layer contains 30% by mass or more of an alkene polymer, and the millimeter-wave absorbing layer has soldering heat resistance.

22. In the thin flat cable described in claim 1, A thin flat cable formed by integrating multiple thin flat cables in the horizontal direction of the flat surface of the thin flat cable.

23. In the thin flat cable described in claim 1, A thin flat cable formed by integrating multiple thin flat cables in a direction perpendicular to the flat surface of the thin flat cable.

24. In the thin flat cable described in claim 20, A thin, flat cable in which the alkene is a monomer obtained from biomass.

25. Metal films are laminated on both sides of the first insulating layer. A conductor made of a conductive material is formed on one surface of the first insulating layer by etching, printing, plating, vapor deposition, or sputtering. A metal film is laminated on one side of the second insulating layer. The side of the second insulator layer that does not have the metal film laminated on it is bonded to the side of the first insulator layer on which the conductor is formed to form a laminate. A hole for a blind via or a hole for a through-hole is formed in an opening created by etching the metal film on at least one outer surface of the laminate by laser irradiation, mechanical drilling, or photolithography etching. The formed holes are subjected to a via structure by at least one of plating or conductive paste filling, the metal film around the conductive electrode is removed by etching, and the conductive electrode is formed. The portion forming the outer surface of the thin flat cable is formed by laser irradiation to create grooves or by laser irradiation to create grooves and cutting, thereby forming the side surface that will become the outer surface of the thin flat cable. A method for manufacturing a thin flat cable, comprising forming a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on the metal film surface formed on the surface of the laminate excluding the surface of the conductor electrode, and on the side surfaces in the longitudinal and transverse directions of the laminate.

26. In the method for manufacturing a thin flat cable according to claim 25, When forming the laminate, in addition to the first insulating layer and the second insulating layer, one or more insulating layers are further laminated to form an insulating laminate. A method for manufacturing a thin flat cable, comprising forming holes for bounded vias that are formed only between the inner layers of the insulating laminate, in addition to, or instead of, the holes for bounded vias or through-holes.

27. In the method for manufacturing a thin flat cable according to claim 25 or 26, A metal film is formed on the longitudinal and transverse sides of the laminate or the insulating laminate by sputtering, electroless plating, electrolytic plating, or conductive paste coating. A method for manufacturing a thin flat cable, comprising forming a millimeter-wave absorbing layer made of a resin containing a millimeter-wave absorbing material on the metal film surface.

28. In the method for manufacturing a thin flat cable according to any one of claims 25 to 27, A method for manufacturing a thin flat cable, comprising forming a reflection suppression layer on the outer surface of the millimeter-wave absorbing layer to suppress the reflection of externally radiated millimeter waves.

29. In the method for manufacturing a thin flat cable according to claim 28, A method for manufacturing a thin flat cable, comprising forming a sheet having two layers, a millimeter-wave absorbing layer and a reflection suppression layer, and then bringing the millimeter-wave absorbing layer into contact with the outer surface of the thin flat cable on which the side surface is formed, and heating and pressing it in a vacuum to sequentially form the millimeter-wave absorbing layer and the reflection suppression layer on the outer surface of the thin flat cable.

30. In the method for manufacturing a thin flat cable according to any one of claims 25 to 27, A method for manufacturing a thin flat cable, wherein the millimeter-wave absorbing layer is formed by at least one method selected from the group consisting of coating, printing, inkjet, spray coating, dipping, lamination, and vacuum heating and pressure bonding.

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