Thin flat cable and method for manufacturing the same

Abstract

The present invention provides a thin, flat cable in which an insulator containing polyolefin, which has excellent dielectric properties and is inexpensive, sandwiches and encloses a conductor, and also provides excellent shielding properties in which the insulator does not soften, expand and / or melt and flow out during soldering, as well as a method for manufacturing the same. [Solution] A thin flat cable characterized by having a conductor made of metal, an insulator containing 30% by weight or more of a polymer containing 80 mol% or more of alkenes, which sandwiches the conductor and encloses the conductor except for the conductor electrodes that are electrically conductive from the conductor and exposed on the surface, a first heat-resistant insulating layer having a heat resistance of 260°C or higher that covers the insulator in contact with the surface of the conductor electrodes on the insulator side and the periphery of the via holes in contact with the conductor electrodes, and a metal film that covers the surface of the first heat-resistant insulating layer except for the periphery of the conductor electrodes.

Description

Technical Field

[0001] The present disclosure relates to a thin flat cable used for communication and wiring of devices that require high-density mounting and weight reduction, and a method for manufacturing the same.

Background Art

[0002] In recent years, due to the high speed and high-frequency compatibility of electronic devices, in mobile devices and the like, a triple plate line is sometimes provided as a signal transmission line for transmitting high-frequency signals, such as a flexible wiring board for mounting components of electronic devices and the like at high density, or a flat cable for wiring through narrow gaps inside the device (see Patent Document 1 and Patent Document 2).

[0003] Even when a triple plate line is provided, it has been proposed to provide a wiring board that is easy to bend and whose transmission characteristics are unlikely to deteriorate even when bent (see Patent Document 3).

[0004] Due to the high frequency of communication represented by recent 5G communication and the high speed of the transmission speed of semiconductors, a low loss of the transmission line is required. For the insulator used for wiring, a small transmission loss is required.

[0005] A thin wiring board having a triple plate line or a microstrip line using a resin with low transmission loss represented by liquid crystal polymer has been proposed (see Patent Document 3). Since this wiring board can form the same circuit as a flexible wiring board, a plurality of signal lines can be formed on one wiring board, and thus it is expected to contribute to future mobile devices.

[0006] In a flat cable for high-speed transmission and high-frequency transmission, in addition to the original characteristics of the flat cable such as thinness and flexibility, it is required to be a transmission line that is not affected by moisture absorption from the outside air and has stable transmission characteristics, has a high electromagnetic shielding effect, has heat resistance to withstand soldering, etc., has flame retardancy, and has high productivity and can use inexpensive materials.

[0007] In response to the above requirements, a shielded, thin, flat cable has been proposed that has stable transmission characteristics unaffected by moisture absorption from the outside air, a high electromagnetic shielding effect, and is solderable even when using a general-purpose resin with low heat resistance as an insulator, and can accommodate complex shapes, as well as a method for manufacturing the same (see Patent Document 4).

[0008] The conductive electrodes for electrical connection with other devices in the shielded thin flat cable described in Patent Document 4 are for connecting to external elements, etc., and are used as connector terminals, soldering electrodes, terminals for ACF (Anisotropic Conducting Film) connections, etc. In all cases, the conductive electrodes are on the outermost surface of the flat cable.

[0009] The invention described in Patent Document 4 has a general-purpose resin insulator with low heat resistance exposed around the conductive electrode. When soldering to make electrical contact with the conductive electrode, the heat from the soldering, which is heated to about 250°C, can cause the exposed insulator to melt and flow out.

[0010] To avoid this problem, it has been suggested to cover the exposed insulating surface with a solder mask. However, it is difficult to cover only the exposed insulating surface with a solder mask, and the solder mask ends up covering a portion of the conductive electrode surface.

[0011] Because the conductor electrodes of flat cables are minute, soldering involves coating the surface and sides of the conductor electrodes with solder to increase the joint strength. Covering the surface and sides of the conductor electrodes with a solder mask can hinder soldering between the conductor electrodes and terminals of other devices, resulting in insufficient connection strength and potentially causing connection failures. Furthermore, in connector terminal connections and ACF connections, the connection principle necessitates that the sides of the conductor electrodes not be covered with insulating material.

[0012] In other words, if a part or side of the conductor electrode surface is covered with a solder mask, the conductor electrode cannot be used as a connection terminal in conventional connection methods such as connector terminal connection, electrode soldering connection, or ACF connection.

[0013] Patent Document 4 proposes a shielded, thin, flat cable in which the area other than the periphery of the conductor electrode is covered with a metal film, thereby having stable transmission characteristics unaffected by moisture absorption from the outside air, a high electromagnetic shielding effect, solderability even when using a general-purpose resin with low heat resistance as an insulator, and the ability to accommodate complex shapes. However, as mentioned above, there is a risk of problems such as the insulator melting and flowing out from around the conductor electrode, and connection failures. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2011-71403 [Patent Document 2] Japanese Patent Publication No. 2017-188307 [Patent Document 3] International Publication No. WO2014 / 156422 [Patent Document 4] International Publication No. WO2020 / 195784 [Overview of the project] [Problems that the invention aims to solve]

[0015] Currently, flexible circuit boards are widely used for wiring between components such as cameras and displays and the main circuit board inside mobile devices, including smartphones. On the other hand, coaxial cables are generally used for the RF (radio frequency) portion. In devices equipped with displays, such as smartphones, displays tend to be larger, so reducing the thickness is important in order to make smartphones smaller and lighter. However, it is difficult to make coaxial cables thin, and recently, the thickness of coaxial cables has become an obstacle to the design of device implementations. In other words, thinning the cables is necessary for implementation in devices with thickness limitations.

[0016] In mobile devices such as smartphones, the increasing sophistication of cameras and displays, the growing circuit size of application processors due to the evolution of applications, and the larger batteries required due to faster transmission speeds are making it difficult to fit these functions and components into a limited casing. On the other hand, the types of wireless signals used in smartphones are also increasing, leading to an increase in the number of wires connecting antennas to devices and wires connecting components to the main board.

[0017] To solve the above-mentioned problems, Patent Document 4 proposes a shielded thin flat cable and a method for manufacturing the same, which has stable transmission characteristics unaffected by moisture absorption from the outside air by covering the insulator surrounding the conductor with a metal film, has a high electromagnetic shielding effect, can be soldered even when a general-purpose thermoplastic resin with low heat resistance is used as the insulator, and can accommodate complex shapes.

[0018] However, as mentioned above, Patent Document 4 has the potential to cause problems such as the insulator melting and flowing out from around the conductor electrodes, and connection failures. Currently, flat cables using polyimide as an insulator, which are widely used, do not have the problem of insulator melting due to their high heat resistance, but their alkali resistance is poor, so their use is limited, for example, around lithium-ion batteries. Liquid crystal polymers have better alkali resistance than polyimide, but it is not sufficient. Also, PTFE, a representative fluororesin, is difficult to process such as lamination and plating, making it difficult to create a multilayer structure. There is a need for a thin flat cable that uses polyolefin, a general-purpose thermoplastic resin with excellent alkali resistance and high moisture resistance, as an insulator, and that does not cause the insulator to flow out during soldering.

[0019] This disclosure provides a thin, flat cable in which an insulator containing a polyolefin, which has excellent dielectric properties and is inexpensive, surrounds a conductor, and the insulator does not melt and flow out due to the heat during soldering, as well as a method for manufacturing the same. [Means for solving the problem]

[0020] The thin flat cable according to this disclosure comprises a conductor made of metal, an insulator containing 30% by weight of a polymer containing 80 mol% or more of alkenes, which sandwiches the conductor and encloses the conductor except for the conductor electrodes that are electrically conductive from the conductor and exposed on the surface, a first heat-resistant insulating layer having a heat resistance of 260°C or higher that covers the insulator in contact with the surface of the conductor electrodes on the insulator side and the periphery of the via holes in contact with the conductor electrodes, and a metal film that covers the surface of the first heat-resistant insulating layer except for the periphery of the conductor electrodes.

[0021] Furthermore, in the thin flat cable according to this disclosure, it is preferable that a metal film is provided on the outer surface of the insulator that is not in contact with the first heat-resistant insulating layer.

[0022] Further, in the thin flat cable according to the present disclosure, it is preferable to include a second heat-resistant insulator layer having a heat resistance of 260° C. or higher that covers the surface of the metal film, the surface of the first heat-resistant insulator layer, or the surface of the insulator.

[0023] Further, in the thin flat cable according to the present disclosure, it is preferable that the second heat-resistant insulator layer covers the surface of the insulator that is not covered by either the first heat-resistant insulator layer or the metal film.

[0024] Further, in the thin flat cable according to the present disclosure, it is preferable that the alkene is one or more of ethylene, propylene, butene, pentene, hexene, heptene, octene, 4-methylpentene-1, cyclopropene, cyclobutene, cyclopentene, cyclohexene, and cycloheptene.

[0025] Further, in the thin flat cable according to the present disclosure, it is preferable that the insulator contains any one or more of metal powder, carbon black, graphite, carbon fiber, crystalline silica, amorphous silica, hollow silica, black silica, silicic acid and its metal salts, glass, glass balloon, aluminum oxide, titanium oxide, iron oxide, zinc oxide, magnesium oxide, tin oxide, antimony oxide, nickel oxide, cobalt oxide, molybdenum oxide, copper oxide, manganese dioxide, calcium oxide, barium ferrite, strontium ferrite, aluminum hydroxide, magnesium hydroxide, calcium sulfate, magnesium sulfate, barium sulfate, aluminum sulfate, talc, clay, mica, calcium carbonate, magnesium carbonate, sodium phosphate, potassium dihydrogen phosphate, glass fiber, calcium titanate, lead zirconate titanate, aluminum nitride, boron nitride, silicon carbide, wood fiber, fullerene, carbon nanotube, titanium black, and melamine cyanurate.

[0026] Further, in the thin flat cable according to the present disclosure, it is preferable to have a metal film that covers the side surface.

[0027] A method for manufacturing a thin flat cable according to this disclosure involves laminating a metal film on one side of a first insulating film via a first heat-resistant insulating layer having a heat resistance of 260°C or higher, laminating a conductor-forming metal film on the other side of the first insulating film, forming a conductor by etching the conductor-forming metal film, laminating one side of a second insulating film containing 30% by weight or more of a polymer containing 80 mol% or more of alkene with the metal film, heat-pressing the surface of the first insulating film on which the conductor is formed with the non-metallic film surface of the second insulating film, and sandwiching the conductor between the first insulating film and the second insulating film. The portions of the metal film on the first insulating film side where the conductor electrodes are formed, the area around the portions where the conductor electrodes are formed, and the portions that form the outer surface of the thin flat cable are removed by etching, the exposed first heat-resistant insulating layer surface is irradiated with a laser to remove the first heat-resistant insulating layer and the first insulating film until the conductor is exposed, holes for forming via holes are formed, the conductor electrodes are formed by plating the formed holes, the conductor and the conductor electrodes are connected, the portions that form the outer surface of the thin flat cable are cut, and the sides that will become the outer surface of the thin flat cable are formed. [Effects of the Invention]

[0028] This disclosure provides a thin, flat cable in which an insulator containing polyolefin, which has excellent dielectric properties and is inexpensive, surrounds a conductor, and which also has excellent shielding properties, such as the insulator not melting and flowing out during soldering, and a method for manufacturing the same. [Brief explanation of the drawing]

[0029] [Figure 1] A perspective view of a thin flat cable according to an embodiment of the present disclosure is shown. [Figure 2]The thin flat cable according to this disclosure is shown. (A) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to an embodiment. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable according to an embodiment. (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 having a parallel metal film according to an embodiment. (F) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable having a parallel metal film according to an embodiment. (G) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable having a parallel metal film according to another embodiment. (D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable having a parallel metal film 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] A manufacturing process for a thin flat cable according to an embodiment of the present disclosure, which involves cutting a portion that will form the outer surface of the thin flat cable and forming a side surface that will become the outer surface of the thin flat cable. [Figure 7] This invention relates to a manufacturing process for a thin flat cable, comprising a step of laminating an insulating film and a metal film via a first heat-resistant insulating layer. [Figure 8]The present disclosure shows a 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 a thin flat cable having a multi-row structure in the horizontal direction according to an embodiment. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable having a multi-row structure in the horizontal direction according to an embodiment. (C) shows a cross-section perpendicular to the longitudinal direction including the conductor of a 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 a thin flat cable having a multi-row structure in the horizontal direction according to another embodiment. [Figure 9] The present disclosure shows a 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 a thin flat cable having a multi-row structure in the horizontal and vertical directions according to an embodiment. (B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of a thin flat cable having a multi-row structure in the horizontal and vertical directions according to an embodiment. (C) shows a cross-section perpendicular to the longitudinal direction including the conductors of a 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 a thin flat cable having a multi-row structure in the horizontal and vertical directions according to another embodiment. [Figure 10] This shows the thermal expansion of the insulator when soldering conventional thin flat cables. [Modes for carrying out the invention]

[0030] 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.

[0031] In addition to its inherent characteristics of being thin and flexible, and having low transmission loss, flat cables are required to meet the following requirements: they must be transmission lines with stable physical and electrical properties, free from the influence of external elements such as moisture absorption; they must have high electromagnetic shielding properties; they must have heat resistance to withstand soldering; they must be flame-retardant; they must have excellent chemical resistance; and they must be easy to process, highly productive, and allow the use of inexpensive materials. Transmission characteristics are particularly important for flat cables used for high-frequency and high-speed transmission.

[0032] (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.

[0033] Figure 2 shows a thin flat cable 101 according to an embodiment of the present disclosure, where Figure 2(A) shows a cross-section perpendicular to the longitudinal direction including the conductor of the thin flat cable according to the embodiment, and Figure 2(B) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of the thin flat cable according to the embodiment. Furthermore, Figure 2(C) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to another embodiment, and Figure 2(D) shows a cross-section perpendicular to the longitudinal direction including the conductor electrode of a thin flat cable according to another embodiment.

[0034] As shown in Figures 2(A) and 2(C), the conductor 204 of the conductor portion 102 of the thin flat cable 101 is sandwiched and wrapped by the insulator 106. The thin flat cable 101 has a first heat-resistant insulating layer 219, a metal film 202, and a second heat-resistant insulating layer 211 sequentially on one side of the insulator 106. The other side of the insulator 106 has a metal film 202 and a second heat-resistant insulating layer sequentially. The sides of the insulator 106 in the longitudinal and transverse directions have a second heat-resistant insulating layer.

[0035] 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 other devices, and has via holes 208 through which these are connected. The insulator 106 surrounding the conductor 204 sandwiches and surrounds the inner layer electrode 214 and is in contact with the side surface of the via hole 208. Furthermore, the thin flat cable 101 has a first heat-resistant insulating layer 219 having a heat resistance of 260°C or higher that covers the insulator 106, in contact with the surface of the conductor electrode 105 on the insulator 106 side and around the via holes 208 that are in contact with the conductor electrode 105. On the opposite side of the first heat-resistant insulating layer 219 from the insulator 106, there is a metal film 202 that covers the surface of the first heat-resistant insulating layer 219 other than around the conductor electrode 105. The metal film 202 has a second heat-resistant insulating layer that has heat resistance of 260°C or higher, except around the conductor electrode 105. The other surface of the insulator 106 has the metal film 202 and the second heat-resistant insulating layer in sequence. The sides of the insulator 106 in the longitudinal and transverse directions have the second heat-resistant insulating layer.

[0036] 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 via hole 208, and the inner layer electrode 214 and the conductor electrode 105 are electrically connected. The conductor electrode 105 is for connecting to external elements, etc., and is used as a connector connection terminal, SMT soldering electrode, soldering terminal for fixing connectors, terminal for ACF (Anisotropic Conducting Film) connection, soldering terminal to board terminals, etc. To achieve the above objectives, the surface of the conductor electrode 105 may be subjected to surface treatments such as solder coating, electrolytic nickel-gold plating, electroless nickel-gold plating, electroless nickel-palladium-gold plating, tin plating, silver plating, OSP (Organic Solderability Preservatives), etc., as necessary. A first heat-resistant insulating layer 219, which has insulating properties, is provided around the conductive electrode 105, and does not have a metal film 202 covering the insulator 106 formed thereon. This isolates the metal film 202 from the conductive electrode 105, creating a structure that prevents electrical conductivity between the metal film 202 and the conductive electrode 105.

[0037] As shown in Figures 2(A) and 2(B), when the thin flat cable 101 does not have a metal film 202 on its end face, the thin flat cable 101 has upper and lower through holes 220, and through holes 108 with a metal film on the inner surface of the through holes 220. The through holes 108 have a metal film on their inner surface, conduct electricity to the metal films 202 on the upper and lower surfaces of the thin flat cable 101, and maintain the same potential between them. If the potentials of the upper and lower metal films 202 are uneven, the potential of the conductor 204 may fluctuate. In Figures 2(A) and 2(B), the through holes 108 have a metal film on their inner surface, but the entire through hole 108 may be filled with metal. Also, multiple through holes 108 may be provided. When the end face has a metal film 202 as shown in Figures 2(C) and 2(D), it is not necessary to provide through holes 108. However, they may be provided.

[0038] As shown in Figures 2(A), 2(B), 2(C), and 2(D), the upper and lower horizontal surfaces of the thin flat cable 101 have a metal film 202 except around the conductor electrode 105. On the opposite side of the metal film 202 to the insulator 106, there is a second heat-resistant insulating layer 211 except around the conductor electrode 105. This second heat-resistant insulating layer 211 is optional. As shown in Figures 2(A) and 2(B), if the metal film 202 is not provided on the side surface of the thin flat cable 101, the second heat-resistant insulating layer 211 must be provided on the longitudinal and transverse sides. In this case, the second heat-resistant insulating layer 211 does not need to be provided on the outer surfaces of the upper and lower metal films 202.

[0039] In the thin flat cable 101 according to this disclosure, an insulator 106 protects the conductor 204, and a first heat-resistant insulating layer 219, a metal film 202, and a second heat-resistant insulating layer 211 protect the insulator 106. The metal film 202 shields the conductor 204.

[0040] 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.

[0041] 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 the width of the conductor 204 is less than 0.01 mm, it is difficult to control the dimensional accuracy of the finished width of the conductor 204. Therefore, impedance matching is difficult, and it is undesirable as a conductor. Also, if the width of the conductor 204 is less than 0.01 mm, the conductor loss becomes large, making it undesirable as a transmission line. Conversely, if the width of the conductor 204 exceeds 10 mm, the thickness of the insulator 106 required to obtain the desired characteristic impedance becomes thicker, making it unsuitable for thin flat cables 101 where thinness is a priority.

[0042] The width of the conductor 204 significantly affects the transmission characteristics, therefore, precise control of its width is necessary. Furthermore, to improve the line width accuracy of the conductor 204, the MSAP (Modified Semi Additive Process) method can be used. To further improve transmission characteristics, if the conductor 204 is not made of gold or silver, it may be gold-plated or silver-plated. 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 of the conductor 204, the thickness of the conductor 204, the thickness of the insulator 106, the dielectric constant of the insulator 106, etc. To obtain the desired impedance, the width of the conductor 204 is usually adjusted.

[0043] 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. Due to conductor loss and the skin effect, the electrical signal efficiency is low if the thickness is less than 1 μm. Also, if the thickness is less than 1 μm, there is a high possibility that the conductor 204 will break when bent. If the thickness of the conductor 204 is less than 10 μm, the laser light from the laser drilling machine used to form the via holes 208 may penetrate the inner layer electrode 214, making it difficult to set the conditions. If the thickness exceeds 75 μm, it is difficult to achieve width accuracy when forming the conductor 204, and the insulator 106 that surrounds the conductor 204 becomes thicker, making it unsuitable for thin flat cables 101 where thinness is the goal.

[0044] The insulator 106 contains 30% by weight or more of a polymer containing 80 mol% or more of an alkene. The alkene is preferably one or more of ethylene, propylene, butene, pentene, hexene, heptene, octene, 4-methylpentene-1, cyclopropene, cyclobutene, cyclopentene, cyclohexene, or cycloheptene.

[0045] Polymers containing 80 mol% or more of alkenes include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, cycloolefin polymer (COP), cycloolefin copolymer (COC), methylpentene polymer, and the like.

[0046] The alkenes used, such as ethylene and propylene, may be monomers obtained from biomass or through recycling. Using monomers obtained from biomass or recycling can contribute to reducing carbon dioxide emissions.

[0047] The polymer preferably contains less than 20 mol% of one or more of the following monomers other than alkenes: vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, and maleic anhydride.

[0048] The insulator 106 may contain resins such as polybutadiene, polyphenylene ether, fluororesin, liquid crystal polymer, polystyrene, and SBS.

[0049] The insulator 106 preferably contains a filler. The filler includes metal powder, carbon black, graphite, carbon fiber, crystalline silica, amorphous silica, hollow silica, black silica, silicic acid and its metal salts, glass, glass balloons, aluminum oxide, titanium oxide, iron oxide, zinc oxide, magnesium oxide, tin oxide, antimony oxide, nickel oxide, cobalt oxide, molybdenum oxide, copper oxide, manganese dioxide, calcium oxide, barium ferrite, strontium ferrite, aluminum hydroxide, magnesium hydroxide, calcium sulfate, magnesium sulfate, barium sulfate, aluminum sulfate, talc, clay, mica, calcium carbonate, magnesium carbonate, sodium phosphate, potassium dihydrogen phosphate, glass fiber, calcium titanate, lead zirconate titanate, aluminum nitride, boron nitride, silicon carbide, wood fiber, fullerene, carbon nanotubes, titanium black, melamine cyanurate, etc. The filler preferably contains 5% by mass or more and 80% by mass or less in the insulator 106, and preferably 15% by mass or more and 60% by mass or less.

[0050] The insulator 106 containing a filler increases the melt viscosity of the resin contained in the insulator 106 when heated, making it less likely to flow out when melted. This has the effect of preventing flow due to heating during soldering. This effect is achieved when the filler is present at 5% by mass or more, but when it exceeds 80% by mass, the processability and flexibility of the thin flat cable 101 decrease. Furthermore, the insulator 106 containing a filler can suppress the thermal expansion of the resin contained in the insulator 106 when heated, which has the effect of preventing flow due to heating during soldering. This effect is achieved when the filler is present at 15% by mass or more, and the flexibility of the thin flat cable 101 is sufficient when it is present at 60% by mass or less.

[0051] The insulator 106 may contain a laser light absorber that absorbs laser light. The laser light absorber is preferably one or more of the following: crystalline silica, amorphous silica, hollow silica, black silica, silicic acid and its metal salts, glass, glass balloons, magnesium oxide, nickel oxide, cobalt oxide, molybdenum oxide, copper oxide, iron oxide, tin oxide, manganese dioxide, aluminum oxide, titanium oxide, calcium oxide, aluminum nitride, sodium phosphate, potassium dihydrogen phosphate, barium sulfate, aluminum sulfate, aluminum hydroxide, carbon black, graphite, carbon nanotubes, titanium black, boron nitride, or mica.

[0052] Furthermore, crystalline silica, amorphous silica, hollow silica, black silica, silicic acid and its metal salts, glass, glass balloons, magnesium oxide, aluminum oxide, titanium oxide, aluminum nitride, carbon black, graphite, carbon nanotubes, titanium black, boron nitride, and mica are even more preferred as laser light absorbers that do not degrade the dielectric properties of the insulator 106. In addition to polymers containing 80 mol% or more of alkenes, fillers, laser light absorbers, and resins, additives such as viscosity modifiers, lubricants, and flame retardants can be appropriately blended into the insulator 106 within a range that does not degrade its dielectric properties.

[0053] The thickness of the insulator 106 is preferably 10 μm or more and 1000 μm or less. Furthermore, 30 μm or more and 500 μm or less is preferable. If it is less than 10 μm, interlayer insulation failure occurs between the conductor 204 and the metal film 202, and it becomes difficult to control the line width for impedance matching. If it exceeds 1000 μm, as will be described later, the speed of laser processing to form holes 207 or linear grooves 206 in the insulator 106 by laser becomes extremely slow. Also, the thickness of the thin flat cable 101 becomes excessive.

[0054] By including 30% by weight or more of a polymer containing 80 mol% or more of alkenes in the insulator 106, a thin flat cable 101 can be manufactured inexpensively. However, polymers containing 80 mol% or more of alkenes do not readily absorb laser light with wavelengths of 0.8 μm or more and 11.0 μm or less, making it difficult to form holes 207 or linear grooves 206 on the surface of the insulator 106 by irradiating it with laser light. However, by including a laser light absorber in the insulator 106, holes 207 or linear grooves 206 can be formed in a short time by laser light irradiation. When the insulator 106 has a thickness of 50 μm, the laser light absorber is included in the insulator 106 such that the minimum transmittance of light with wavelengths of 0.8 μm or more and 11.0 μm or less is 60% or less. If the transmittance exceeds 60%, it becomes difficult or time-consuming to form holes 207 or linear grooves 206 by laser light irradiation.

[0055] The first heat-resistant insulating layer 219, provided between the insulator 106 and the metal film 202, may have the function of bonding the insulator 106 and the metal film 202. The first heat-resistant insulating layer 219 has a heat resistance of 260°C or higher. A heat resistance of 260°C or higher means that the softening temperature determined by thermomechanical analysis as specified in JIS K7196-2012 is 260°C or higher.

[0056] The following describes the method for measuring the softening temperature by thermomechanical analysis as specified in JIS K7196-2012. The test specimen is made of the same resin as the first heat-resistant insulating layer 219, and is preferably in the form of a film. The thickness of the test specimen is specified in the standard as 0.01 to 1 mm, but a thinner thickness of 0.01 to 0.2 mm is preferable. The shape of the test specimen is square or circular as specified in the standard, and it is desirable that the length of one side or the diameter be approximately 5 mm. The surface of the test specimen is smooth enough to be in close contact with the sample stage. The standard specifies that the test specimen should be conditioned for 24 hours or more at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5%. However, it is preferable to perform the conditioning in accordance with JIS C60068-2-20:2010. This is called Aging 2, which involves conditioning for 10 days at a temperature of 40 ± 2 °C and a relative humidity of 93 ± 3%. This is to evaluate in advance the effect of moisture absorption on the heat resistance of the first heat-resistant insulating layer 219 during soldering. Even if the softening temperature is 260°C or higher in a dry state, it is necessary to eliminate the possibility that it may fall below 260°C in a humid state.

[0057] The heat resistance of the insulator 106, measured by a similar test method, is preferably 230°C or lower. Above 230°C, the manufacturing efficiency of the thin flat cable 101 decreases, the material becomes more expensive, and costs increase. Furthermore, 180°C or lower is preferable.

[0058] The first heat-resistant insulating layer 219 adheres to the insulator 106 and the metal film 202 and has heat resistance and insulating properties. The first heat-resistant insulating layer 219 includes, for example, a thermosetting resin, a thermoplastic resin, or an ionizing radiation curable resin.

[0059] The thermosetting resin is not particularly limited and includes, for example, epoxy resins, silicone resins, unsaturated polyester resins, saturated polyester resins, melamine resins, phenolic resins, polyamides, ketone resins, urethane resins, urea resins, acrylic resins, vinyl resins, alkyd resins, aminoalkyd resins, hydrocarbon resins (aromatic and aliphatic), rubber resins, fluororesins, polyimide resins, etc. 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.

[0060] Thermosetting resins contain a curing agent and may optionally contain additives such as inorganic fillers, thermoplastic resins, curing accelerators, flame retardants, and organic fillers.

[0061] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AF type epoxy resin, dicyclopentadiene type epoxy resin, trisphenol type epoxy resin, naphthol novolac type epoxy resin, phenol novolac type epoxy resin, tert-butyl-catechol type epoxy resin, naphthalene type epoxy resin, naphthol type epoxy resin, anthracene type epoxy resin, glycidylamine type epoxy resin, glycidyl ester type epoxy resin, cresol novolac type epoxy resin, biphenyl type epoxy resin, linear aliphatic epoxy resin, epoxy resin having a butadiene structure, alicyclic epoxy resin, heterocyclic epoxy resin, spiroring-containing epoxy resin, cyclohexanedimethanol type epoxy resin, naphthylene ether type epoxy resin, trimethylol type epoxy resin, tetraphenylethane type epoxy resin, polyester polyol resin, acrylic polyol resin, and the like. Epoxy resins may be used individually or in combination of two or more types.

[0062] The epoxy resin has epoxy groups in its molecule, and preferably has two or more epoxy groups per molecule.

[0063] The curing agent is not particularly limited as long as it has the function of curing epoxy resin, and examples include phenolic curing agents, naphthol curing agents, active ester curing agents, benzoxazine curing agents, cyanate ester curing agents, polyamine curing agents, imidazole curing agents, diaminodiphenylmethane and carbodiimide curing agents, and blocked isocyanates. The curing agent may be used alone or in combination of two or more types.

[0064] In the case of a thermosetting resin composition, combining the thermosetting resin and curing agent and curing it at 150°C or below is preferable because it allows the formation of the first heat-resistant insulating layer 219 without deforming the insulator 106.

[0065] Examples of inorganic fillers include crystalline silica, amorphous silica, aluminum oxide, glass, cordierite, silicon oxide, barium sulfate, barium carbonate, talc, clay, mica, zinc oxide, hydrotalcite, boehmite, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, magnesium oxide, boron nitride, aluminum nitride, manganese nitride, aluminum borate, strontium carbonate, strontium titanate, calcium titanate, magnesium titanate, bismuth titanate, titanium oxide, zirconium oxide, barium titanate, barium zirconate titanate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. Inorganic fillers may be used individually or in combination of two or more types.

[0066] The inorganic filler is preferably crystalline silica, amorphous silica, aluminum oxide, glass, barium sulfate, barium carbonate, talc, clay, mica, zinc oxide, aluminum hydroxide, magnesium hydroxide, boron nitride, aluminum nitride, manganese nitride, titanium oxide, zirconium oxide, barium titanate, or barium zirconate titanate.

[0067] Thermoplastic resins include phenoxy resins, polyvinyl acetal resins, polyimide resins, polyamide-imide resins, polyetherimide resins, polysulfone resins, polyethersulfone resins, polyphenylene ether resins, polycarbonate resins, polyetheretherketone resins, polyester resins, liquid crystal polymers, cycloolefin polymers, cyclic olefin copolymers, polytetrafluoroethylenes, copolymers of tetrafluoroethylene and perfluoroalkoxyethylenes, etc. Thermoplastic resins may be used individually or in combination of two or more types.

[0068] The thermoplastic resin may contain additives such as the inorganic fillers, thermosetting resins, flame retardants, and organic fillers mentioned above, as needed. It may also be laminated with a thermosetting resin. The inorganic fillers are the same as those used for thermosetting resins.

[0069] 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.

[0070] Examples of the monomers, oligomers, and prepolymers mentioned above include (meth)acrylates having polymerizable functional groups in their molecules, specifically monofunctional (meth)acrylates and polyfunctional (meth)acrylates. Among these, polyfunctional (meth)acrylates are preferred. A polyfunctional (meth)acrylate is a (meth)acrylate having two or more polymerizable functional groups in its molecule. The number of functional groups in a polyfunctional (meth)acrylate is not particularly limited, for example, 2 or more and 50 or less, preferably 2 or more and 8 or less, and more preferably 2 or more and 6 or less.

[0071] Examples of polyfunctional (meth)acrylates include urethane (meth)acrylate, caprolactone-modified urethane (meth)acrylate, alicyclic or aliphatic heterocyclic (meth)acrylate, polycarbonate (meth)acrylate, pentaerythritol-based (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, polybutadiene (meth)acrylate, silicone (meth)acrylate, and aminoplast resin (meth)acrylate. Ionizing radiation-curable resins may be used alone or in combination of two or more types.

[0072] Ionizing radiation-curable resins may contain additives such as the inorganic fillers, flame retardants, and organic fillers mentioned above, as needed. The inorganic fillers are the same as those used in thermosetting resins. UV-curable resins may contain photoinitiators as needed.

[0073] As shown in Figures 2(A) and 2(C), the first heat-resistant insulating layer 219 is provided between the insulator 106 and the metal film 202 in the conductor portion 102. The thickness of the first heat-resistant insulating layer 219 is preferably 0.1 μm or more and 100 μm or less. 1 μm or more and 30 μm or less is preferable. If it is less than 0.1 μm, the strength of the layer is low and it is not possible to prevent the insulator 106 from softening, expanding, and / or melting and flowing out during soldering. If it exceeds 100 μm, the thin flat cable 101 will become thicker, hindering its flexibility. Also, if it is less than 1 μm, there is a risk of cracking in the layer with repeated bending, and film formation is also difficult. If it exceeds 30 μm, due to the constraints of the thin flat cable, the insulator 106 must be thin, which raises concerns about a decrease in transmission characteristics.

[0074] As shown in Figures 2(B) and 2(D), at the terminal portion 103, the surface of the first heat-resistant insulating layer 219 opposite to the insulator 106 is in contact with the inner surface of the conductor electrode 105 extending from the via hole 208, and the cross-section of the first heat-resistant insulating layer 219 is in contact with the metal surrounding the via hole 208.

[0075] As shown in Figures 2(B) and 2(D), in the terminal portion 103, the first heat-resistant insulating layer 219 covers the insulator 106 in areas where the metal film 202 around the conductor electrode 105 is not provided. When soldering to the conductor electrode 105, even if the insulator 106 softens, expands, and / or melts, the heat-resistant first heat-resistant insulating layer 219 acts as a barrier, preventing the resin of the insulator 106 from flowing out.

[0076] Figure 10 shows a cross-section of the terminal portion 103 of a conventional thin flat cable 101. The conductor electrode 105 is not surrounded by a metal film 202. In the areas where the conductor electrode 105 is not surrounded by a metal film 202, the first heat-resistant insulating layer 219 is not present, and the insulator 106 is exposed. When soldering to the conductor electrode 105, the insulator 106 softens, expands and / or melts, causing the insulator to blow out 300, and the resin of the insulator 106 flows out from the exposed areas. As shown in Figure 2(B) or Figure 2(D), by covering the areas where the insulator 106 is exposed with the first heat-resistant insulating layer 219, the resin of the insulator 106 does not flow out when soldering to the conductor electrode 105.

[0077] As shown in Figures 2(A), 2(B), 2(C), and 2(D), the metal film 202 is continuously provided on the upper and lower surfaces of the thin flat cable 101, except around the conductor electrode 105 of the terminal portion 103. The continuous provision of the metal film 202 helps to suppress thermal deformation of the insulator 106, defects due to peeling, and the influence of water vapor from the outside air on the electrical properties of the conductor 204. It is acceptable for the metal film 202 not to be provided on a portion of the surface of the insulator 106 to the extent that it does not cause damage to the shielding properties of the conductor 204, damage to the electrical properties, deformation of the insulator 106, or peeling of the insulator 106 and the metal film 202.

[0078] As shown in Figures 2(C) and 2(D), the metal film 202 may be continuously provided on the longitudinal and transverse end faces of the thin flat cable 101.

[0079] 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 heat-resistant insulating layer 219 or insulator 106, except around the conductor electrode 105. The metal film 202 is not provided around the conductor electrode 105. "Around" means that the distance between the end of the conductor electrode 105 and the end of the metal film 202 is such that there is no electrical conductivity between the conductor electrode 105 and the metal film 202. It is preferable that the area on the surface of the first heat-resistant insulating layer 219 that is not provided with the metal film 202 is small.

[0080] Since the adhesion strength between the metal film 202 and the first heat-resistant insulating layer 219 or insulator 106 decreases with heat and they are prone to peeling, it is desirable that the lower surface and the longitudinal and transverse end faces of the thin flat cable 101 be covered with the metal film 202 without exposing the insulator 106. To improve shielding performance, it is preferable that the longitudinal and transverse end faces are covered with the metal film 202, and that the metal film 202 covers more than 80% of the surface of the insulator 106.

[0081] The portion of the first heat-resistant insulating layer 219 that is not provided with a metal film 202 around the conductor electrode 105 is exposed to the outside air. It is important to minimize the area of ​​the exposed portion of the first heat-resistant insulating layer 219 around the conductor electrode 105. If the exposed area is large, the insulator 106 may absorb moisture through the first heat-resistant insulating layer 219 due to water vapor in the outside air, and the transmission characteristics may deteriorate due to the effects of moisture absorption.

[0082] The conductor 204 is surrounded by the insulator 106, and the first heat-resistant insulating layer 219 has a metal film 202 continuously on its surface, except around the conductor electrode 105. That is, by having the metal film 202 on the upper and lower surfaces of the thin flat cable 101, the protective function of the metal film 202 suppresses the influence of the outside air, allowing the thin flat cable 101 to maintain its transmission characteristics for a long period of time. The protective function can be further improved by also providing the metal film 202 on the longitudinal and transverse end faces of the thin flat cable 101.

[0083] The distance between the end of the conductor electrode 105 and the end of the metal film 202 is 10 μm or more and 1000 μm or less. The first heat-resistant insulating layer 219 is exposed 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 1000 μm, water vapor from the outside air will penetrate more into the insulator 106 through the first heat-resistant insulating layer 219, which may degrade the transmission characteristics and heat resistance. In addition, the shielding performance of the conductor 204 may be impaired. 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.

[0084] 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 adjacent end of a conductor electrode 105 is 10 μm or more and 1000 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 202.

[0085] 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 end face in the longitudinal or transverse direction of a thin flat cable 101, but this is undesirable because it is complicated to process and makes soldering work difficult. In addition, multiple conductor electrodes 105 may be provided on a single conductor 204.

[0086] The metal film 202, which is continuously provided on the surface of the first heat-resistant insulating layer 219 and the surface of the insulator 106, except around the conductor electrode 105, prevents water vapor and chemicals from penetrating into the first heat-resistant insulating layer 219 and the insulator 106 from the outside. Furthermore, in the event of a flame directed at the thin flat cable 101 from the outside, the metal film 202 prevents the flame from directly touching the insulator 106, thereby improving the flame retardancy of the insulator 106. The metal film 202 is used as a ground.

[0087] The metal film 202 of the thin flat cable 101 is made of 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 film 202 on the upper and lower surfaces, which are the horizontally flat surfaces of the thin flat cable 101, can be made of copper foil, but the longitudinal and transverse end faces of the thin flat cable 101 are preferably made of copper formed by plating. The electrical resistivity of the metal film 202 is preferably 1 μΩ·m or less. To add functions such as oxidation prevention and noise reduction, 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.

[0088] The thickness of the metal film 202 is preferably 3 μm or more and 100 μm or less. 10 μm or more and 50 μm or less is preferable. If the thickness is less than 3 μm, pinholes and scratches will occur, the internal barrier properties cannot be maintained, and the metal film 202 will not melt during laser processing to form linear grooves 206. Also, cracks will form in the metal film 202 due to the expansion of the insulator 106 during heating. Furthermore, if the thickness exceeds 100 μm, the etching process for the groove-forming openings 212 for forming the linear grooves 206 and the via-hole-making openings 209 for forming via-holes 207 becomes complicated and time-consuming. Also, if the thickness exceeds 100 μm, when the metal film 202 is formed by plating, the plating time becomes longer, causing problems in the manufacturing process such as warping of the workpiece. For thicknesses less than 10 μm, slow UV laser processing is possible, but when using a high-speed carbon dioxide laser, the metal film 202 melts and penetrates the metal film 202, making it impossible to form linear grooves 206. For thicknesses exceeding 50 μm, etching the groove-forming openings 212 for forming linear grooves 206 and the via-hole openings 209 for forming via-holes 207 becomes complicated and time-consuming.

[0089] The planar distance between the conductor 204 and the metal film 202 provided on the end face or cross-sectional direction 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 202. The vertical distance between the conductor 204 and the metal film 202 is 10 μm or more and 700 μm or less. A distance of 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 700 μm, it takes a long time to form the linear groove 206 in the insulator 106 with a laser. 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.

[0090] As shown in Figures 2(B) and 2(D), at terminal 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and via hole 208. An electrical signal enters from one conductor electrode 105, exits through the via hole 208, inner layer electrode 214, 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.

[0091] 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. In order to connect the conductor electrode 105 via the via hole 208, the inner layer electrode 214 is made to be equal to or larger than the diameter of the cylindrical via hole 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 hole 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 hole 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.

[0092] The via hole 208 is formed by removing the first heat-resistant insulating layer 219 and insulator 106 from the location where the conductive electrode 105 is formed to the inner layer electrode 214 by laser irradiation, and then plating the hole 207, which is a via hole formed by the removal of the first heat-resistant insulating layer 219 and insulator 106. Therefore, the cross-section is approximately circular in shape. Plating is preferably done with copper. A metal film is formed by plating at the location corresponding to the hole 207 of the metal film 202 that was removed by etching as a via hole opening 209 at the location where the conductive electrode 105 is formed, and connects and integrates it with the metal film 202 that was not etched.

[0093] As shown in Figures 2(A) and (B), the thin flat cable 101 is provided with a second heat-resistant resin layer 211 on the surface of the metal film 202 which forms the outer surface of the thin flat cable 101, the insulator 106 exposed on the longitudinal and transverse end faces, or the first heat-resistant insulating layer 219 exposed around the conductor electrodes 105 that are not covered by the metal film 202. The second heat-resistant insulating layer 211 does not need to be provided on the surface of the metal film 202, but the second heat-resistant insulating layer 211 is essential on the outer surface of the insulator 106 exposed on the longitudinal and transverse end faces that are not covered by the metal film 202.

[0094] As shown in Figures 2(C) and (D), the thin flat cable 101 is provided with a second heat-resistant resin layer 211 on the surface of the first heat-resistant insulating layer 219 that is exposed around the conductor electrode 105 which is not covered by the metal layer 202 or metal film 202 that forms the outer surface of the thin flat cable 101. In Figures 2(C) and (D), the longitudinal and transverse end faces of the thin flat cable 101 are covered with the metal film 202. When the insulator 106 is covered with the metal film 202 and / or the first heat-resistant insulating layer 219, it is not necessary to provide the second heat-resistant insulating layer 211 on the surface of the outer metal film 202 or the first heat-resistant insulating layer 219.

[0095] The second heat-resistant insulating layer 211 is formed from a thermosetting resin, thermoplastic resin, or ionizing radiation-curable resin similar to that of the first heat-resistant insulating layer 219. The second heat-resistant insulating layer 211 has the function of adhering to the first heat-resistant insulating layer 219, the insulator 106, or the metal film 202. The second heat-resistant insulating layer 211 has heat resistance of 260°C or higher. Heat resistance of 260°C or higher means that the softening temperature determined by thermomechanical analysis as specified in JIS K7196-2012 is 260°C or higher. The method for measuring heat resistance is the same as that for the first heat-resistant insulating layer 219.

[0096] The second heat-resistant insulating layer 211 is preferably formed of an ionizing radiation-curable resin that hardens upon irradiation with ionizing radiation. Ionizing radiation-curable resins include ultraviolet-curable resins, electron beam-curable resins, etc. The second heat-resistant insulating layer 211 may contain multiple types of resins. For example, a combination of a thermosetting resin and an ionizing radiation-curable resin, or a combination of a thermoplastic resin and an ionizing radiation-curable resin. It may also contain all three types simultaneously. Furthermore, multiple resins may be laminated.

[0097] As shown in Figures 2(A) and 2(C), the second heat-resistant insulating layer 211 is provided on the surface of the insulator 106 or the metal film 202 in the conductor portion 102. The second heat-resistant insulating layer 211 does not need to be provided where the metal film 202 is provided on the upper or lower surface of the thin flat cable 101. However, as shown in Figure 2(C), if the metal film 202 is not provided on the longitudinal and transverse end faces of the thin flat cable 101, the second heat-resistant insulating layer 211 must be provided on the surface of the insulator 106. This is because if the insulator 106 is exposed, the heat from soldering may cause the insulator 106 to soften, expand, and / or melt and flow out. By providing the second heat-resistant insulating layer 211, it is possible to prevent the insulator 106 from flowing out.

[0098] Figure 10 shows the case where the insulator 106 is exposed at the end face of the thin flat cable 101. However, due to the heat of soldering, the insulator 106 may soften, expand, and / or melt, potentially flowing out as shown by the insulator blowout 301 on the side. Furthermore, the softening, expansion, and / or melting of the insulator 106 can cause the position of the conductor 204 to shift, resulting in poor alignment between the conductor 204 and the via hole 208. This can be prevented by covering the insulator 106 with a second heat-resistant insulating layer 211.

[0099] As shown in Figures 2(B) and 2(D), in the terminal portion 103, the second heat-resistant insulating layer 211 is provided on a portion of the first heat-resistant insulating layer 219 other than the surface of the conductor electrode 105, where the metal film 202 around the conductor electrode 105 is not provided. If the second heat-resistant insulating layer 211 is provided on the surface of the conductor electrode 105, connection failure may occur during soldering, as described above. The second heat-resistant insulating layer 211 does not need to be provided all the way to the edge of the metal film 202.

[0100] In the terminal section 103, similar to the conductor section 102, the second heat-resistant insulating layer 211 does not need to be provided in locations where a metal film 202 is provided on the upper or lower surface of the thin flat cable 101. However, as shown in Figures 2(A) and 2(C), if a metal film 202 is not provided on the longitudinal and transverse end faces of the thin flat cable 101, the second heat-resistant insulating layer 211 must be provided on the surface of the insulator 106. This is because, if the insulator 106 is exposed, the heat from soldering may cause the insulator 106 to soften, expand, and / or melt and flow out. By providing the second heat-resistant insulating layer 211, the second heat-resistant insulating layer 211 acts as a barrier, preventing the resin from flowing out of the insulator 106.

[0101] Even without the second heat-resistant insulating layer 211, the presence of the metal film 202 can prevent the insulator 106 from flowing out. By providing the second heat-resistant insulating layer 211 on the surface of the metal film 202, the barrier preventing the insulator 106 from flowing out becomes even stronger.

[0102] The thickness of the second heat-resistant insulating layer 211 is preferably 1 μm or more and 100 μm or less. 10 μm or more and 60 μm or less is preferable. If it is less than 1 μm, the strength of the layer is low and it cannot prevent the insulator from softening, expanding, and / or melting and flowing out during soldering. If it exceeds 100 μm, it makes the thin flat cable thicker and hinders its flexibility.

[0103] (Manufacturing method for thin flat cables) Figure 3 shows a method for manufacturing the thin flat cable 101 according to this disclosure. The method for manufacturing the thin flat cable 101 involves laminating a metal film 202A to one side of a first insulating film 106A containing 30% by weight or more of a polymer containing 80 mol% or more of alkenes and a laser light absorber, via a first heat-resistant insulating layer 219 having heat resistance of 260°C or higher; laminating a conductor-forming metal film 202B to the other side of the first insulating film 106A; forming a conductor 214 by etching the conductor-forming metal film 202B; laminating a metal film 202C to one side of a second insulating film 106B containing 30% by weight or more of a polymer containing 80 mol% or more of alkenes; and thermocompressing the side of the first insulating film 106A on which the conductor 214 is formed with the non-metallic film side of the second insulating film 106B. The conductor 214 is sandwiched and wrapped between the first insulating film 106A and the second insulating film 106B. The portion of the metal film 202A on the first insulating film 106A side that will form the conductor electrode 105 is removed by etching. A laser is irradiated onto the exposed surface of the first heat-resistant insulating layer 219 to remove the first heat-resistant insulating layer 219 and the first insulating film 106A until the conductor 214 is exposed. Holes 207 for forming via holes 208 are formed. Conductor electrodes 105 are formed by plating the formed holes 207. The conductor 214 and conductor electrodes 105 are made electrically connected. The portion that will form the outer surface of the thin flat cable 101 is cut to form the side surface 205 that will become the outer surface of the thin flat cable 101.

[0104] Figure 3 shows the manufacturing process of the thin flat cable 101 according to the embodiment of the present disclosure shown in Figures 2(A) and 2(B).

[0105] Figure 3(A) shows a process of laminating a metal film 202A onto one side of a film-like first insulating film 106A via a first heat-resistant insulating layer 219 having a heat resistance of 260°C or higher, and laminating a conductor-forming metal film 202B onto the other side of the first insulating film 106A. The first heat-resistant insulating layer 219 is applied to one side of the first insulating film 106A, the metal film 202A is laminated, and the conductor-forming metal film 202B is laminated onto the other side of the first insulating film 106A. Lamination may be performed under reduced pressure or vacuum. If air enters between 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, vacuum laminator, roll laminator, etc., can be used.

[0106] Lamination is performed by pressure bonding or heat bonding, but pretreatment may be performed before lamination to improve adhesion strength. For example, the first insulating film 106A 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. Lamination of the first insulating film 106A and the metal film 202A is preferably performed using the first heat-resistant insulating layer 219 as an adhesive. Other adhesives may be used for lamination. Lamination can also be performed by inserting a bonding sheet between the film-like insulator 106A and the conductor-forming metal film 202B and pressing them together. Furthermore, lamination can also be performed by extruding and pressing the molten first insulating film 106A onto the conductor-forming metal film 202B.

[0107] When laminating a first insulating film 106A and a metal film 202A using a first heat-resistant insulating layer 219 as an adhesive, one method is to coat one side of the metal film 202A with the first heat-resistant insulating layer 219 containing an uncured thermosetting resin, and then cure or partially cure the uncured thermosetting resin. Another method is to prepare a thermosetting resin film that will become the first heat-resistant insulating layer 219 containing an uncured thermosetting resin, place the first insulating film 106A on the metal film 202A, and then cure or partially cure the uncured thermosetting resin.

[0108] The method for coating the metal film 202A surface with the thermosetting resin composition is not limited, and known coating methods can be employed.

[0109] Another method for producing a thermosetting resin film involves coating a separator with a composition containing an uncured thermosetting resin. The separator can be prepared by placing the thermosetting resin film on the surface of the metal film 202A and then peeling it off.

[0110] 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 heat-resistant insulating layer 219 is cured or partially cured by irradiating it with ionizing radiation before laminating the conductive metal film 202B. When curing, heating and irradiation with ionizing radiation may be combined.

[0111] Metal foil is used for the metal film 202A and the conductor-forming metal film 202B. Metal foil is a foil containing gold, silver, copper, aluminum, etc. Copper foil is particularly preferred. The thickness of the metal foil is preferably 3 μm or more and 100 μm or less. Furthermore, 10 μm or more and 50 μm or less is preferred.

[0112] When laminating the first heat-resistant insulating layer 219 and the conductor-forming metal film 202B onto the surface of the first insulating film 106A by heat-pressure bonding, it is preferable to provide a layer of copolymer of a monomer having a carboxyl group and an alkene on the side of the first insulating film 106A that is in contact with the first heat-resistant insulating layer 219 and / or the metal film 202B 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 first heat-resistant insulating layer 219 and the metal film 202B increases with heat-pressure 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 resin obtained by graft polymerization of maleic anhydride onto polyethylene or polypropylene. The polymer preferably contains less than 20 mol% of the monomer having a carboxyl group, and more preferably less than 10 mol%. If it is less than 10 mol%, the effect on the transmission characteristics can be kept to a minimum.

[0113] The lamination of the metal film 202A, the first insulating film 106A, the first heat-resistant insulating layer 219, and the conductor-forming metal film 202B shown in Figure 3(A) may be carried out sequentially as shown in Figure 7.

[0114] In Figure 7(A), a conductor-forming metal film 202B is laminated onto a film-like first insulating film 106A, and then the first heat-resistant insulating layer 219 and the metal film 202A are laminated. The first insulating film 106 having carboxyl groups and the conductor-forming metal film 202B are laminated by thermocompression bonding.

[0115] In Figure 7(B), the first heat-resistant insulating layer 219 is provided on the first insulating film 106A, and then the metal film 202A and the conductor-forming metal film 202B are laminated on top of it.

[0116] In Figure 7(C), a first heat-resistant insulating layer 219 is provided on the metal film 202A, and then the first insulating film 106A and the conductor-forming metal film 202B are laminated.

[0117] In procedures other than those shown in Figure 7(C), it may be necessary to perform the thermal curing of the first heat-resistant insulating layer 219 including the first insulating film 106A. Since the thermal curing must be performed at a temperature below the heat resistance temperature of the first insulating film 106A, the procedure shown in Figure 7(C), in which the metal film 202A is the substrate and high-temperature heating is possible, is preferred.

[0118] Figure 3(B) shows a laminate in which a metal film 202A, a first heat-resistant insulating layer 219, a first insulating film 106A, and a conductor-forming metal film 202B are sequentially laminated.

[0119] 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.

[0120] 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 the necessary conductor-forming metal film 202B.

[0121] Figure 3(D) shows the process of sequentially laminating a second insulating film 106B and a metal film 202C onto a first insulating film 106A and a conductor 204 and inner layer electrode 214 formed on the surface of the first insulating film 106A. The material of the second insulating film 106B may be the same as that of the first insulating film 106A. Alternatively, insulating materials of different types may be used. The first insulating film 106A and the second insulating film 106B are bonded together by thermocompression. The conductor 204 and inner layer electrode 214 are sandwiched and wrapped between the first insulating film 106A and the second insulating film 106B. Since the conductor 214 is convex on the first insulating film 106A, it is preferable to perform the thermocompression under vacuum conditions to ensure complete adhesion between the first insulating film 106A and the second insulating film 106B.

[0122] The step of sequentially laminating the second insulating film 106B and the metal film 202C onto the first insulating film 106A, 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.

[0123] When laminating the conductor 204 and inner layer electrode 214 formed on the surface of the first insulating film 106A with the film-like insulator 106B, and laminating the second insulating film 106B with the metal film 202C, 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 second insulating film 106B 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 heat 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.

[0124] 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 is to laminate the second insulating film 106B onto the first insulating film 106A and then sequentially laminate the metal film 202C, or to laminate the second insulating film 106B and the metal film 202C onto the first insulating film 106A simultaneously. Alternatively, the second insulating film 106B may be laminated onto the first insulating film 106A after the second insulating film 106B and the metal film 202C have been laminated together.

[0125] Figure 3(E) shows a laminate in which a metal film 202A is laminated on one side of a first insulating film 106A via a first heat-resistant 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 the conductor 204 and inner layer electrode 214 with the second insulating film 106B and the metal film 202C.

[0126] Figure 3(F) shows the process of forming a through-hole 220 for creating the through-hole 108 using a CNC drilling machine at the location where the through-hole 108 will be formed.

[0127] Figure 3(F) also shows the process of removing the metal film 202A in the area where the conductive electrode 105 is formed by etching, forming an opening 209 for drilling via holes, and forming a hole 207 for forming a via hole 208 for electrical connection between the inner layer electrode 214 and the conductive electrode 105.

[0128] The process of removing the metal film 202A by etching to form the via hole opening 209 is the same as the circuit formation process described above. The area from which the metal film 202A is removed is the area where the conductor electrode 105 is formed. The area from which the metal film 202A has been removed is designated as the via hole opening 209.

[0129] The formation of the hole 207 for forming the via hole 208 involves removing the first heat-resistant insulating layer 219 and the first insulating film 106A exposed at the via hole opening 209, down to the inner layer electrode 214, without penetrating the metal film 202A.

[0130] The holes 207 are formed using, for example, a device equipped with a laser processing machine, a plasma processing machine, a sandblaster, etc. A laser processing machine is preferred due to its high processing speed. The first heat-resistant insulating layer 219 and the first insulating film 106A are removed down to the inner layer electrode 214 by irradiation with a laser from the laser processing machine. If the metal film 202A is thin, the metal film 202A, the first heat-resistant insulating layer 219, and the insulator 106 that are not removed by etching can also be removed simultaneously by the laser processing machine.

[0131] The wavelengths of laser light used in laser processing machines are as follows: excimer lasers have a wavelength of 0.248 μm, UV lasers have a wavelength of 0.355 μm, green lasers have a wavelength of 0.532 μm, near-infrared lasers around 1 μm, such as YAG lasers and fiber lasers, have a wavelength of 1.064 μm, and far-infrared lasers around 10 μm, such as carbon dioxide lasers, have wavelengths of 9.4 μm and 10.6 μm. Excimer lasers, UV lasers, and green lasers with wavelengths from 0.25 μm to 0.60 μm are collectively referred to as UV-visible lasers.

[0132] The selection of a laser processing machine requires consideration of matching the absorption wavelength of the insulator 106. In particular, YAG lasers, fiber lasers, and carbon dioxide laser processing machines are widely used because they offer high resin processing speeds, and are therefore preferred laser processing machines in this disclosure. The laser processing machine according to this disclosure preferably uses a UV / visible light laser with a wavelength of 0.25 μm to 0.6 μm, a near-infrared laser with a wavelength of around 1 μm, or a far-infrared laser with a wavelength of around 10 μm.

[0133] Many resins absorb UV and visible light lasers, eliminating the need for laser light absorbers. However, if the absorbance is low, adding a small amount of coloring pigment can increase the absorbance and speed up processing. A suitable amount is 10 mass percent or less, as this does not affect the electrical properties.

[0134] When the first insulating film 106A is 50 μm or thicker, the processing speed slows down rapidly due to the principle of UV-visible lasers, resulting in decreased productivity. While UV-visible laser processing is superior when the thickness of the first insulating film 106A to be removed is less than 50 μm, it is unsuitable for thicknesses exceeding this. UV-visible lasers can be used when the first insulating film 106A is less than 50 μm thick. By adding a coloring pigment, it can be used even when the first insulating film 106A is 50 μm or thicker. The amount of coloring pigment added can be increased to speed up the processing.

[0135] The insulator 106 contains 30% by weight or more of a polymer containing 80 mol% or more of alkenes, and a laser light absorber. When the insulator 106 has a thickness of 50 μm, it is preferable that the minimum transmittance of light with wavelengths of 0.2 μm or more and less than 0.8 μm is 85% or less. A colored pigment can be used as the laser light absorber for wavelengths of 0.2 μm or more and less than 0.8 μm. A colored pigment may also be added to the first heat-resistant insulator layer 219.

[0136] Coloring pigments include cyanine blue, cyanine green, ochre, red iron oxide, permanent red, carbon black, titanium dioxide, and zinc oxide. Organic compounds such as benzotriazole, benzophenone, and cyanoacrylate are also suitable as laser light absorbers with wavelengths between 0.2 μm and 0.8 μm.

[0137] 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.

[0138] Near-infrared lasers, such as YAG lasers or fiber lasers, and far-infrared lasers, such as carbon dioxide lasers, offer fast processing speeds and excellent productivity, even when the first insulating film 106A is thick. However, polymers containing 80 mol% or more of alkenes hardly absorb light with wavelengths from 0.8 μm to around 11 μm, making it impossible to form pores 207. Therefore, it is necessary to incorporate a laser light absorber into the first insulating film 106A. Even if the first insulating film 106A contains 30% by weight or more of a polymer containing 80 mol% or more of alkenes, the inclusion of a laser light absorber allows for efficient formation of pores 207 using near-infrared and far-infrared laser light.

[0139] The first insulating film 106A contains 30% by weight or more of a polymer containing 80 mol% or more of alkenes, thereby reducing the cost of the insulator 106. By including a laser light absorber, the rate at which holes 207 are formed by near-infrared and far-infrared laser light is increased, improving the smoothness and dimensional accuracy of the processed surface. When the insulator 106 containing the laser light absorber has a thickness of 50 μm, the minimum transmittance of light with wavelengths of 0.8 μm or more and 11.0 μm or less must be 85% or less.

[0140] Figure 3(G) shows the process of forming a through-hole 108 by plating the inner surface of the through-hole 220. The inner surface of the through-hole 220 is cleaned, the surface of the first heat-resistant insulating layer 219 and the insulating films 106A and 106B are made conductive, and then metal plating is performed. With the formation of the through-hole 108, the upper and lower metal films 202A and 202C of the thin flat cable 101 become conductive and their potentials become the same.

[0141] Figure 3(G) also shows the process of forming a conductor electrode 105, which will serve as a terminal, by plating the inner surface of the hole 207 and connecting the plated metal film with the metal film 202A, thereby creating electrical conductivity between the conductor 204 and the conductor electrode 105. The exposed portions of the metal film 202A and the inner layer electrode 214 at the bottom of the hole 207 are cleaned, the surfaces of the first heat-resistant insulating layer 219 and the first insulating film 106A are made conductive, and then metal plating is performed.

[0142] Typically, metal plating involves desmearing, catalyst formation, electroless plating, and electrolytic plating in that order. Desmearing is necessary if smear and other foreign matter remain on the metal film surface, but is unnecessary if the metal film surface is clean. Desmearing can be performed using a dry method with plasma or a wet method with an oxidizing agent such as permanganate, but in this disclosure, the dry method is superior from the viewpoint of preventing water absorption. Catalyst formation, electroless plating, and electrolytic plating can be performed using chemical systems from companies such as ATOTECH, JCU Corporation, DOW CHEMICAL, Uemura Kogyo Co., Ltd., Okuno Pharmaceutical Co., Ltd., and MacDermid Enson. Furthermore, to minimize moisture absorption during processing, instead of wet catalyst formation, a metal film may be continuously formed on the surface of the first heat-resistant insulating layer 219 on the inner surface of the pore 207 and the first insulating film 106A using a dry method such as sputtering. Additionally, as a method of conductivity, the Black Hole System from MacDermid Japan can be used instead of catalyst formation and electroless plating.

[0143] Fine metal powder or carbon that imparts conductivity may be added to the first heat-resistant insulating layer 219 and the insulator 106. When plating the through holes 220 and 207 by adding fine metal powder or carbon, it is not necessary to make the surfaces of the first heat-resistant insulating layer 219 and the insulator 106, which are the first insulating film 106A and the second insulating film 106B that form the through holes 220 and 207, conductive.

[0144] 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 metal film 202A that will become the metal film 202.

[0145] The metal film 202A can be removed using a circuit formation process similar to that used for forming the conductor 204 in Figure 3(C). Specifically, unwanted portions of the metal film 202A can be removed through a procedure involving etching mask formation, resist layer formation, exposure, development, etching, and etching mask removal, thereby forming the desired shape. As mentioned above, the distance between the end of the conductor electrode 105 and the end of the metal film 202A, i.e., the gap 218, is between 10 μm and 1000 μm.

[0146] Figure 3(I) shows the process of forming the outer surface of the thin flat cable 101. The metal film 202A, the first heat-resistant insulating layer 219, and the insulator 206 are ruptured at the locations where the outer surface of the thin flat cable 101 is to be formed. The metal film 202C may also be ruptured at the same time. Figure 3(I) is a cross-sectional view along the dashed line a in Figure 3(M). As shown in Figure 3(M), there may be more than one through-hole 220 for forming the through-hole 108. That is, there may be more than one through-hole 108 in the thin flat cable 101.

[0147] Figure 6(A) is a plan view of Figure 3(I), showing the approximate positional relationship when forming the linear groove 206 as a process for forming the outer surface of the thin flat cable 101. The formation of the linear groove 206 is an important process in this disclosure because it determines the outer circumferential shape of the thin flat cable 101 and forms all end faces, including the longitudinal and transverse sides. The width of the linear groove 206 is preferably 0.1 m or more and 10 mm or less. Forming a linear groove 206 less than 0.1 mm is technically difficult, and a width exceeding 10 mm results in wasted material. Figure 6 does not show the through-hole 220 for forming the through-hole 108.

[0148] Figure 6(B) shows the state after the linear grooves 206 have been formed by laser processing and cutting using a combination of cutting tools and router bits. The white areas in the linear grooves 206 indicate the areas where cutting was performed. Figure 6(A) shows all the linear grooves 206 formed by laser processing. Figure 6(Aa) is a cross-sectional view of Figure 6(A) in direction a. The metal film 202C is not penetrated. This is the same as in Figure 3(I). Figures 6(Bb) and (Bc) are cross-sectional views of Figure 6(B) in directions b and c, respectively. If the linear grooves 206 are cut with a cutting tool, the metal film 202C will also break. If the individual pieces are separated at this stage, the subsequent metal plating process will become complicated. Furthermore, it will become impossible to manufacture the thin flat cable 101 as an assembly, hindering productivity. Therefore, the metal film 202C needs to be left at least partially intact in order to fix the individual pieces, and laser processing is suitable for leaving the metal film 202C intact.

[0149] To perform laser processing, the metal film 202A in the area where the linear groove 206 will be formed must be removed to form the groove-forming opening 212. The removal of the metal film 202A can be performed by the circuit formation process described above. That is, unnecessary parts of the metal film 202A can be removed by the following steps: etching mask formation, resist layer formation, exposure, development, etching, and etching mask peeling, thereby forming the desired shape. Laser processing can be performed in the same manner as the hole formation process for forming the via hole 207 described above. In this disclosure, deep cutting of the insulator 106 is necessary to form the linear groove 206 in the insulator 106. With UV / visible light lasers, the speed of deep cutting is extremely slow. Near-infrared and far-infrared lasers have a faster processing speed and their use is preferred.

[0150] Figure 3(J) shows the process of forming a second heat-resistant insulating layer 211 on the upper, lower, and end faces of the thin flat cable 101 after its outer shape has been formed. The second heat-resistant insulating layer 211 is formed on the metal film 202 on the upper and lower faces of the thin flat cable 101 and on the end faces in the longitudinal and transverse directions of the thin flat cable 101. In Figure 3(J), the second heat-resistant insulating layer 211 is not formed on the surface of the conductor electrode 105 that faces the insulator 106, and on the surface of the first heat-resistant insulating layer 219 that covers the insulator 106 in contact with the periphery of the via hole 208 that contacts the conductor electrode 105. However, as shown in Figure 2(B), the second heat-resistant insulating layer may cover the first heat-resistant insulating layer 219 without covering the surface of the conductor electrode 105.

[0151] The second heat-resistant insulating layer 211 is formed by applying a thermosetting resin, thermoplastic resin, or ionizing radiation-curable resin that provides the required heat resistance to the area where it is to be formed, and curing it as necessary. The application and curing can be carried out in the same manner as the formation of the first heat-resistant insulating layer 219.

[0152] Figures 3(K) and 3(L) show the process of separating the thin flat cable 101 into individual pieces. Figure 3(K) shows the terminal portion 103, and Figure 3(L) shows the conductor portion 102. Separation is performed by cutting the metal film 202C along the linear groove 206. The cutting for separating the pieces can be done using the cutting methods for flexible wiring boards, and cutting with a die, cutting with a router, and cutting with a laser processing machine are common. This disclosure allows for the manufacture of the thin flat cable 101 as an assembly and then separating it into individual pieces at the end, thus improving work efficiency.

[0153] 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.

[0154] Figure 4 shows the manufacturing process for a thin flat cable according to another embodiment of the present disclosure shown in Figures 2(C) and 2(D).

[0155] Figure 4(A) shows the process of laminating a metal film 202A to one side of the first insulating film 106A via a first heat-resistant insulating layer 219 having a heat resistance of 260°C or higher, and laminating a conductor-forming metal film 202B to the other side of the first insulating film 106A. This is the same as in Figure 3(A). Figure 4(B) shows a laminate in which the metal film 202A, the first heat-resistant insulating layer 219, the first insulating film 106A, and the conductor-forming metal film 202B are sequentially laminated, similar to Figure 3(B).

[0156] 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 conductor-forming metal film 202B, and forming via hole openings 209 and groove-forming openings 212 by etching the metal film 202A. In the embodiment shown in Figure 3, the process of forming the via hole openings 209 and groove-forming openings 212 was not performed simultaneously with the formation of the conductor 204, but sequentially after the conductor 204 was sandwiched between the second insulating film 106B. 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 hole openings 209 and groove-forming openings 212 may be formed simultaneously by etching the conductor-forming metal film 202B, as shown in Figure 4(C).

[0157] As shown in Figure 4(C), performing the circuit formation process simultaneously on both the front and back surfaces of a single laminate and accurately aligning the inner layer electrodes 214 with the via hole openings 209 is useful for obtaining a high-quality thin flat cable 101.

[0158] Etching can be performed by the circuit formation process described above.

[0159] Figure 4(D) shows the process of sequentially laminating a second insulating film 106B and a metal film 202C onto the side of a first insulating film 106A that has a metal film 202A on one side with via hole openings 209 and groove-forming openings 212, and a conductor 204 and an inner layer electrode 214 on the other side. The lamination process is the same as in Figure 3(D).

[0160] Figure 4(E) shows a laminate in which a second insulating film 106B and a metal film 202C are sequentially laminated on the side of a first insulating film 106A that has a metal film 202A on one side with via hole openings 209 and groove-forming openings 212 formed thereon, and a conductor 204 and an inner layer electrode 214 formed thereon.

[0161] Figure 4(F) shows the process of removing the first heat-resistant insulating layer 219 and the insulator 106 at the locations of the via hole opening 209 and groove formation opening 212 formed in the process shown in Figure 4(C), and forming holes 207 and linear grooves 206 for forming via holes 208.

[0162] The formation of the hole 207 involves removing the first heat-resistant insulating layer 219 and the first insulating film 106A on its underside, which are exposed to the via hole opening 209, down to the inner layer electrode 214. The removal of the first heat-resistant insulating layer 219 and the first insulating film 106A can be carried out in the same manner as shown in Figure 3(F).

[0163] The formation of the linear grooves 206 is a process for forming the outer surface of the thin flat cable 101. The first heat-resistant insulating layer 219 and the insulating layer 106 are cut in the area where the outer surface of the thin flat cable 101 is to be formed, leaving 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).

[0164] Figure 4(G) shows plating being performed on 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 is performed on the inner surface of the hole 207, and the plated metal film is connected to the metal film 202A to form a conductive electrode 105 that will serve as a terminal, thereby making the inner layer electrode 214 and the conductive electrode 105 electrically connected. The exposed parts of the metal film 202A and the inner layer electrode 214 that forms the bottom of the hole 207 are cleaned, the surface of the first heat-resistant insulating layer 219 and the first insulating film 106A that form the inner surface of the hole 207 is made conductive, and then metal plating is performed. The metal plating can be performed in the same manner as the process shown in Figure 3(G).

[0165] The process of forming a metal film 202D on the wall surface 205 of the linear groove 206 is carried out by metal plating. The metal film 202D is provided on the longitudinal and transverse end faces of the thin flat cable 101, forming a metal film 202 that continuously covers the entire outer surface of the thin flat cable 101.

[0166] The thin flat cable 101 obtained in the manufacturing process shown in Figure 3 does not have a metal film formed on its longitudinal and transverse end faces. The thin flat cable 101 obtained in the manufacturing process shown in Figure 4 has a metal film 202D on its longitudinal and transverse end faces, resulting in a high shielding effect.

[0167] 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).

[0168] While it is conceivable to form the gap 218 simultaneously during the process shown in Figure 4(D), the plating process that forms a metal film in the hole 207 in Figure 4(G) and the plating process that forms a metal film 202D on the wall surface 205 of the linear groove 206 would also result in the gap 218 being metal-plated. Therefore, forming the gap 218 as shown in Figure 4(H) during the circuit formation process shown in Figure 4(D) is inconvenient.

[0169] Figure 4(I) shows the process of forming a second heat-resistant insulating layer 211 on the upper, lower, and end faces of the thin flat cable 101 in which the gap 218 is formed. The second heat-resistant insulating layer 211 is formed on the metal film 202 on the upper and lower faces of the thin flat cable 101 and on the metal film 202 on the end faces in the longitudinal and transverse directions of the thin flat cable 101. In Figure 4(I), the second heat-resistant insulating layer 211 is not formed on the surface of the conductor electrode 105 on the insulator 106 side, and on the surface of the first heat-resistant insulating layer 219 that covers the insulator 106 in contact with the periphery of the via hole 208 that contacts the conductor electrode 105. However, as shown in Figure 2(D), the second heat-resistant insulating layer 211 may cover the first heat-resistant insulating layer 219 without covering the surface of the conductor electrode 105.

[0170] As shown in Figure 4(H), if a metal film 202 is formed on the top surface, bottom surface, and longitudinal and transverse end faces of the thin flat cable 101, the second heat-resistant insulating layer 211 does not need to be provided on the surface of the metal film 202. The second heat-resistant insulating layer 211 may optionally be provided on the surface of the metal film 202.

[0171] The second heat-resistant insulating layer 211 is formed in the same manner as shown in Figure 3(J).

[0172] Figures 4(J) and 4(K) show the process of separating the thin flat cable 101 into individual pieces. Figure 4(J) shows the terminal portion 103, and Figure 4(K) shows the conductor portion 102. Separation is performed by cutting the metal film 202C and the second heat-resistant insulating layer 211 along the linear groove 206. Separation can be performed in the same manner as in Figures 3(K) and (L). The manufacturing of a large number of thin flat cables 101 is also carried out in the same manner.

[0173] (Thin, flat cable with parallel metal film) Figure 2(E) shows a cross-section perpendicular to the longitudinal direction including the conductor of a thin flat cable having parallel metal films according to the embodiment. Figure 2(F) shows a cross-section perpendicular to the longitudinal direction including the conductor electrodes of a thin flat cable having parallel metal films according to the embodiment.

[0174] The thin flat cable 101, which has a parallel metal film, has a conductor parallel metal film 215 in parallel with the conductor 204 and inner layer electrode 214. The conductor parallel metal film 215 is formed from the same metal film 202B as the conductor 204 and inner layer electrode 214. Therefore, the material and thickness are the same as those of the conductor 204 and 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.

[0175] The distance between the ends of the horizontal parallel conductor metal film 215 and the ends of the conductor 204 and inner layer electrode 214 is 10 μm or more. If it is less than 10 μm, there is a concern that a short circuit will 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 depending on the location. It is preferable that the distance between the conductor 204 and inner layer electrode 214 be the same at all locations. In this case, as shown in Figures 2(E) and 2(F), the ends of the parallel conductor metal film 215 are provided along the shape of the conductor 204 and inner layer electrode 214.

[0176] 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.

[0177] As shown in Figures 2(E) and 2(F), if the thin flat cable 101 does not have a metal film 202 on its end face, it is necessary to form a through-hole 108. However, as shown in Figures 2(G) and 2(H), if the thin flat cable 101 does have a metal film 202 on its end face, by providing the metal film 202 on the end face in contact with the conductor parallel metal film 215, the conductor parallel metal film 215 and the metal film 202 become conductive and reach the same potential.

[0178] The parallel metal film 215 of the conductor can stabilize the signal transmission of the conductor 204 and improve the transmission characteristics of the shielded thin flat cable 101.

[0179] The conductor parallel metal layer 215 shown in Figures 2(E), 2(F), 2(G), and 2(H) is provided on one side of the conductor 204 and the inner layer electrode 214, but it may also be provided on both sides. Furthermore, it may be provided partially along the conductor 204 and the inner layer electrode 214. It is more preferable to provide it around the entire circumference in order to improve the transmission characteristics of the shielded thin flat cable 101.

[0180] (Multi-row thin flat cable) Figure 8 shows a thin flat cable 101 according to the present disclosure, which has a multi-row structure in the horizontal direction. (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. (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. (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. (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.

[0181] Figure 9 also shows a thin flat cable according to the present disclosure, which has a multi-row structure in the horizontal and vertical directions. Figure 9(A) shows a cross-section perpendicular to the longitudinal direction including the conductors of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to an embodiment. Figure 9(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 9(C) shows a cross-section perpendicular to the longitudinal direction including the conductors of a thin flat cable with a multi-row structure in the horizontal and vertical directions according to another embodiment. Figure 9(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.

[0182] In the embodiments described so far, one conductor 204 was formed on one shielded thin flat cable 101. As shown in Figures 8(A), 8(B), 9(A), and 9(B), 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 planar direction.

[0183] Figures 8(A) and 8(B) show a configuration with multiple conductors 204 in the horizontal direction, and may also include a conductor parallel metal film 215. The conductor parallel metal film 215 is optional. Since the thin flat cable 101 does not have a metal film 202 on its end face, a through-hole 108 is required. If the conductor parallel metal film 215 is included, the through-hole 108 is electrically connected to the conductor parallel metal film 215. If the conductor parallel metal film 215 is not included, a normal through-hole 108 is provided.

[0184] Figures 8(C) and 8(D) show a configuration with multiple conductors 204 arranged horizontally, and may also include a conductor parallel metal film 215. The conductor parallel metal film 215 is not required. Since a metal film 202 is provided on the end face of the thin flat cable 101, a through-hole 108 is not required. However, if a conductor parallel metal film 215 is provided, the end face metal film 202 and the conductor parallel metal film 215 must be connected, and the end face metal film 202 and the conductor parallel metal film 215 must be electrically connected. Furthermore, if a conductor parallel metal film 215 is provided that cannot be electrically connected to the end face metal film 202, a metal film 202D must be provided to isolate the multiple conductors 204 so that the upper and lower metal films 202 and the conductor parallel metal film 215 can be electrically connected, as shown in Figures 8(C) and 8(D). This may be replaced by a through-hole 108.

[0185] Figures 9(A) and 9(B) 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 separate the upper and lower conductors 204 in the vertical direction. The conductor parallel metal film 215 is not required. Since the end face of the thin flat cable 101 does not have a metal film 202, a through-hole 108 is required. If 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 separating the upper and lower conductors 204. If the conductor parallel metal film 215 is not provided, a through-hole 108 is provided. In this case, the through-hole 108 is electrically connected to the upper and lower metal films 202 and the metal film 202E separating the upper and lower conductors 204. Multiple conductors 204 may be provided only in the vertical direction, without multiple conductors 204 in the horizontal direction.

[0186] Figures 9(C) and 9(D) show a cable with multiple conductors 204 in the horizontal and vertical directions, and may also include a conductor parallel metal film 215. 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 end face of the thin flat cable 101 is provided with a metal film 202, a through-hole 108 is not required. However, if the conductor parallel metal film 215 is provided, the end face metal film 202 and the conductor parallel metal film 215 must be connected, and the end face metal film 202 and the conductor parallel metal film 215 must be electrically connected. Furthermore, if the conductor parallel metal film 215 cannot be electrically connected to the end face metal film 202, as shown in Figures 9(C) and 9(D), a metal film 202D separating 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 separating the upper and lower conductors 204 in the vertical direction 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.

[0187] 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 smartphones, IoT devices, communication base station peripherals, automotive-related equipment such as ADAS, lithium-ion battery peripherals, etc. [Explanation of Symbols]

[0188] 101 ··Thin flat cable 102. Conductor section 103...Terminal section 105 Conductor electrodes 106. Insulator 108 ··Through-hole 202. Metal film 204 ··Conductor 205 ··Wall surface 206. Linear grooves 207...hole 208 Beer Hall 209 ··Opening for drilling beer holes 211. Second heat-resistant insulating layer 212...Groove formation opening 214 ··Inner layer electrode 215 ··Conductor parallel metal film 218... Gap 219 ··First heat-resistant insulating layer 220 through hole 300 · Insulator blowout 301...Side insulator outlet

Claims

1. A conductor made of metal, An insulator comprising 30% by weight or more of a polymer containing 80 mol% or more of alkene, which sandwiches the conductor and encloses the conductor other than the conductive electrode that is electrically conductive from the conductor and exposed on the surface, A via hole that connects the conductor and the conductor electrode, A first heat-resistant insulating layer having a heat resistance of 260°C or higher covers the insulating material in contact with the insulating material on the insulating material side of the conductive electrode and around the via hole in contact with the conductive electrode, and A thin, flat cable having a metal film covering the surface of the first heat-resistant insulating layer, excluding the area around the conductor electrode.

2. In the thin flat cable described in claim 1, A thin, flat cable having a metal film on the outer surface of the insulator that is not in contact with the first heat-resistant insulating layer.

3. In the thin flat cable described in claim 1, A thin, flat cable having a second heat-resistant insulating layer having heat resistance of 260°C or higher that covers the surface of the metal film, the first heat-resistant insulating layer, or the surface of the insulator.

4. In the thin flat cable described in claim 3, A thin, flat cable in which the second heat-resistant insulating layer covers the surface of the insulator that is not covered by either the first heat-resistant insulating layer or the metal film.

5. In the thin flat cable according to any one of claims 1 to 4, A thin, flat cable in which the alkene is one or more of ethylene, propylene, butene, pentene, hexene, heptene, octene, cyclopropene, cyclobutene, cyclopentene, cyclohexene, and cycloheptene.

6. In the thin flat cable according to any one of claims 1 to 4, A thin, flat cable in which the insulator contains one or more of the following: metal powder, carbon black, graphite, carbon fiber, crystalline silica, amorphous silica, hollow silica, black silica, silicic acid and its metal salts, glass, glass balloons, aluminum oxide, titanium oxide, iron oxide, zinc oxide, magnesium oxide, tin oxide, antimony oxide, nickel oxide, cobalt oxide, molybdenum oxide, copper oxide, manganese dioxide, calcium oxide, barium ferrite, strontium ferrite, aluminum hydroxide, magnesium hydroxide, calcium sulfate, magnesium sulfate, barium sulfate, aluminum sulfate, talc, clay, mica, calcium carbonate, magnesium carbonate, sodium phosphate, potassium dihydrogen phosphate, glass fiber, calcium titanate, lead zirconate titanate, aluminum nitride, boron nitride, silicon carbide, wood fiber, fullerene, carbon nanotube, titanium black, and melamine cyanurate.

7. In the thin flat cable according to any one of claims 1 to 4, A thin, flat cable with a metal film covering its sides.

8. A first insulating film containing 30% by weight or more of a polymer containing 80 mol% or more of alkenes, and a laser light absorber, is laminated with a metal film on one side of the first insulating film via a first heat-resistant insulating layer having a heat resistance of 260°C or higher. A conductor-forming metal film is laminated on the other side of the first insulating film. A conductor is formed by etching the aforementioned conductor-forming metal film. A second insulating film containing 30% by weight or more of a polymer containing 80 mol% or more of alkenes is laminated to one side of a metal film. The surface of the first insulating film on which the conductor is formed and the non-metallic film surface of the second insulating film are heat-pressed together, and the conductor is sandwiched between the first insulating film and the second insulating film. The areas on the first insulating film side where the conductive electrodes of the metal film are formed, the area around where the conductive electrodes are formed, and the area forming the outer surface of the thin flat cable are removed by etching. The exposed surface of the first heat-resistant insulating layer is irradiated with a laser to remove the first heat-resistant insulating layer and the first insulating film until the conductor is exposed, thereby forming holes for via holes. The conductor electrode is formed by plating the formed hole, and the conductor and the conductor electrode are connected electrically. A method for manufacturing a thin flat cable, comprising cutting a portion that forms the outer surface of the thin flat cable to form a side surface that becomes the outer surface of the thin flat cable.

Images