Thin flat cable and its manufacturing method

Abstract

To provide a thin flat cable in which an insulator having excellent dielectric properties and containing inexpensive polyolefin sandwiches and wraps a conductor, and which has excellent shielding properties and does not soften, expand and / or melt and flow out during soldering, and 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% by mole or more of an alkene, which sandwiches the conductor and wraps the conductor except for the conductor electrodes that are conductive to the conductor and exposed on the surface, a via hole that connects the conductor to the conductor electrode, a first heat-resistant insulator layer with a heat resistance of 260°C or more that covers the insulator and comes into contact with the surface of the conductor electrode facing the insulator and the periphery of the via hole that comes into contact with the conductor electrode, and a metal film that covers the surface of the first heat-resistant insulator layer except for the periphery of the conductor electrode.

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 lightweight construction, and a method for manufacturing the same. [Background technology]

[0002] In recent years, as electronic devices have become faster and more capable of handling high frequencies, triplate lines are sometimes used in mobile devices and the like as signal transmission lines for transmitting high-frequency signals, such as in flexible wiring boards that densely mount electronic device components, and in flat cables that route wiring through narrow gaps inside devices (see Patent Documents 1 and 2).

[0003] It has been proposed to provide a wiring board that is easy to bend even when a triplate line is provided, and that is less likely to cause deterioration in transmission characteristics even when bent (see Patent Document 3).

[0004] The recent trend toward higher frequencies in communications, such as 5G communications, and faster transmission speeds in semiconductors has created a demand for low loss in transmission lines, and the insulators used in wiring are required to have low transmission loss.

[0005] Thin wiring boards with triplate lines and microstrip lines that use low-transmission-loss resins, such as liquid crystal polymers, have been proposed (see Patent Document 3). These wiring boards allow for the formation of circuits similar to flexible wiring boards, making it possible to form multiple signal lines on a single wiring board, and are therefore expected to contribute to future mobile devices.

[0006] In addition to the inherent flat cable characteristics of thin and flexible flat cables, flat cables for high-speed and high-frequency transmission are required to be transmission lines with stable transmission characteristics that are not affected by moisture absorption from the outside air, to have high electromagnetic wave shielding effects, to have heat resistance to withstand soldering and other processes, to be flame retardant, and to be highly manufacturable and use inexpensive materials.

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

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

[0009] In the invention described in Patent Document 4, a general-purpose resin insulator with low heat resistance is exposed around the conductor electrode. When soldering to establish electrical continuity with the conductor electrode, the exposed insulator can melt and flow out due to the heat of soldering, which is heated to about 250°C.

[0010] To avoid this, it has been proposed to cover the exposed surface of the insulator with a solder mask, but it is difficult to cover only the exposed insulator with the solder mask, and the solder mask ends up covering part of the conductor electrode surface.

[0011] Because the conductor electrodes of flat cables are tiny, soldering increases the joint strength by covering the conductor electrode surface and side surfaces with solder. Covering the conductor electrode surface and side surfaces with solder mask hinders soldering between the conductor electrode and the terminal of another device, preventing sufficient connection strength and potentially resulting in connection failure. Furthermore, in connector terminal connections and ACF connections, the connection principles dictate that the side surfaces of the conductor electrodes must not be covered with an insulator.

[0012] That is, if a part of the surface or side of a conductor electrode is covered with a solder mask, the conductor electrode cannot be used as a connection terminal for ordinary connection methods such as connector terminal connection, electrode soldering connection, ACF connection, and the like.

[0013] Patent Document 4 proposes a shielded thin flat cable that has stable transmission characteristics that are not affected by moisture absorption from the outside air by covering everything except the periphery of the conductor electrodes with a metal film, has a high electromagnetic wave shielding effect, can be soldered even when using a general-purpose resin with low heat resistance as an insulator, and can be used to accommodate complex shapes. However, as mentioned above, there is a risk that the insulator will melt and flow out from around the conductor electrodes, or that poor connections will occur. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-71403 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-188307 [Patent Document 3] International Publication No. WO2014 / 156422 [Patent Document 4] International Publication No. WO2020 / 195784 Summary of the Invention [Problem to be solved by the invention]

[0015] Currently, flexible wiring boards are widely used to connect components such as cameras and displays inside mobile devices, including smartphones, to the main board. On the other hand, coaxial cables are generally used for RF components. In devices equipped with displays, such as smartphones, the trend is toward larger displays, so reducing the thickness of the cable is important in order to make the smartphone smaller and lighter. However, it is difficult to make coaxial cables thinner, and recently, the thickness of coaxial cables has become an obstacle in the packaging design of devices. In other words, thinner cables are necessary to be installed in devices with thickness restrictions.

[0016] In mobile devices such as smartphones, the functionality of cameras and displays is becoming more sophisticated, the circuit scale of application processors is increasing as applications evolve, and batteries are becoming larger as transmission speeds become faster, making it difficult to fit all of these functions and components into the limited space inside the housing.On the other hand, the number of wireless types used by smartphones is also increasing, and the number of wires connecting antennas to devices and wires connecting components to main boards is also increasing.

[0017] In order to solve the above-mentioned problems, Patent Document 4 proposes a shielded thin flat cable and a manufacturing method thereof, which has stable transmission characteristics that are not affected by moisture absorption from the outside air, has a high electromagnetic wave shielding effect, is solderable even when a general-purpose thermoplastic resin with low heat resistance is used for the insulator, and can be used in complex shapes, by covering the insulator surrounding the conductor with a metal film.

[0018] However, as mentioned above, Patent Document 4 has the risk of problems such as the insulation melting and flowing out from around the conductor electrodes and poor connection. Currently, flat cables using widely used polyimide as an insulator have no problem of insulator melting due to their high heat resistance, but their poor alkali resistance limits their use, for example, around lithium-ion batteries. Liquid crystal polymers have better alkali resistance than polyimides, but their resistance is still insufficient. Furthermore, PTFE, a representative fluororesin, is difficult to process, such as laminating and plating, making it difficult to create a multilayer structure. There is a demand for thin flat cables that use polyolefin, an inexpensive, general-purpose thermoplastic resin with excellent alkali resistance and moisture resistance, as an insulator and that do not allow the insulation to flow out during soldering.

[0019] The present disclosure provides a thin flat cable in which an insulator containing an inexpensive polyolefin having excellent dielectric properties wraps around a conductor, and in which the insulator does not melt and flow due to heat during soldering, and a method for manufacturing the thin flat cable. [Means for solving the problem]

[0020] The thin flat cable according to the present disclosure comprises a conductor made of metal, an insulator sandwiching the conductor and encasing the conductor except for conductor electrodes that are conductive to the conductor and exposed on the surface, the insulator containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene, via holes that connect the conductor and the conductor electrodes, a first heat-resistant insulator layer having a heat resistance of 260°C or more that covers the insulator and contacts the surface of the conductor electrode facing the insulator and the periphery of the via hole that contacts the conductor electrode, and a metal film that covers the surface of the first heat-resistant insulator layer except for the periphery of the conductor electrode. and a second heat-resistant insulator layer having a heat resistance of 260° C. or higher that covers the surface of the metal film, the first heat-resistant insulator layer, or the surface of the insulator. With The second heat-resistant insulator layer covers a surface of the insulator that is not covered by either the first heat-resistant insulator layer or the metal film. do.

[0021] In the thin flat cable according to the present 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 insulator layer.

[0024] 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] In the thin flat cable according to the present disclosure, it is preferable that the insulator contains 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 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, and melamine cyanurate.

[0026] In addition, the thin flat cable according to the present disclosure preferably has a metal film covering the side surface.

[0027] A method for manufacturing a thin flat cable according to the present disclosure includes 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 more, laminating a conductor-forming metal film on the other side of the first insulating film, etching the conductor-forming metal film to form a conductor, laminating the metal film on one side of a second insulating film containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene, thermocompression bonding the surface of the first insulating film on which the conductor is formed and the non-metallic film surface of the second insulating film, and bonding the conductor to the first insulating film and the non-metallic film surface of the second insulating film. The metal film is sandwiched between second insulating films, and the portions of the metal film on the first insulating film side where the conductor electrodes are to be formed, the periphery of the portions where the conductor electrodes are to be formed, and the portions where the outer surface of the thin flat cable is to be formed are removed by etching. A laser is irradiated onto the exposed surface of the first heat-resistant insulating layer, and the first heat-resistant insulating layer and the first insulating film are removed until the conductor is exposed. Holes for forming via holes are formed, and the formed holes are plated to form the conductor electrodes, thereby conducting the conductor and the conductor electrodes. , the first insulating film or the second insulating film a second heat-resistant insulator layer having a heat resistance of 260°C or more covering the surface of the first heat-resistant insulator layer and the second heat-resistant insulator layer not covering the first heat-resistant insulator layer or the metal film; The first insulating film and the second insulating film The surface of the thin flat cable is covered with the thin flat cable, and the thin flat cable is cut at a location that will form the outer surface of the thin flat cable. [Effects of the Invention]

[0028] The present disclosure makes it possible to provide a thin flat cable in which an insulator containing an inexpensive polyolefin having excellent dielectric properties wraps around a conductor, and which also has excellent shielding properties in which the insulator does not melt and flow out during soldering, and a method for manufacturing the thin flat cable. [Brief explanation of the drawings]

[0029] [Figure 1] 1 shows a perspective view of a thin flat cable according to an embodiment of the present disclosure; [Figure 2] 1 shows a thin flat cable according to the present disclosure. (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 parallel metal films according to an embodiment. (F) shows a cross section perpendicular to the longitudinal direction, including the conductor electrode, of a thin flat cable having parallel metal films according to an embodiment. (G) shows a cross section perpendicular to the longitudinal direction, including the conductor, of a thin flat cable having parallel metal films according to another embodiment. (D) shows a cross section perpendicular to the longitudinal direction, including the conductor electrode, of a thin flat cable having parallel metal films according to another embodiment. [Figure 3] 3 illustrates a manufacturing process for a thin flat cable according to an embodiment of the present disclosure. [Figure 4] 6 illustrates a manufacturing process for a thin flat cable according to another embodiment of the present disclosure. [Figure 5] 1 shows a conventional thin flat cable. (A) shows a cross section perpendicular to the longitudinal direction of the conventional thin flat cable, including the conductor electrodes. (B) shows a cross section perpendicular to the longitudinal direction of the conventional thin flat cable, including the conductors. [Figure 6] 10A and 10B show a manufacturing process for a thin flat cable according to an embodiment of the present disclosure, in which a portion that will form the outer surface of the thin flat cable is cut to form a side surface that will become the outer surface of the thin flat cable. [Figure 7] 1 shows a manufacturing process for a thin flat cable according to an embodiment of the present disclosure, illustrating a step of laminating an insulating film and a metal film with a first heat-resistant insulating layer interposed therebetween. [Figure 8]1 shows a thin flat cable according to the present disclosure, the thin flat cable having a horizontally multi-row structure. (A) shows a cross section perpendicular to the longitudinal direction, including the conductor of the thin flat cable having a horizontally multi-row structure according to an embodiment. (B) shows a cross section perpendicular to the longitudinal direction, including the conductor electrode of the thin flat cable having a horizontally multi-row structure according to an embodiment. (C) shows a cross section perpendicular to the longitudinal direction, including the conductor of the thin flat cable having a horizontally multi-row structure according to another embodiment. (D) shows a cross section perpendicular to the longitudinal direction, including the conductor electrode of the thin flat cable having a horizontally multi-row structure according to another embodiment. [Figure 9] 1 shows a thin flat cable according to the present disclosure, which has a multi-row structure in the horizontal and vertical directions. (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 and vertical directions 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 and vertical directions 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 and vertical directions 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 and vertical directions according to another embodiment. [Figure 10] 1 shows the thermal expansion of the insulation when soldering a conventional thin flat cable. DETAILED DESCRIPTION OF THE INVENTION

[0030] The following describes the general configuration of a thin flat cable 101 according to the present disclosure. Fig. 1 shows a perspective view of a thin flat cable 101 according to the present disclosure.

[0031] In addition to the inherent characteristics of flat cables, such as thinness and flexibility, and low transmission loss, flat cables are required to have the following characteristics: a transmission line that is resistant to the effects of external factors such as moisture absorption and has stable physical and electrical properties, a high electromagnetic wave shielding effect, heat resistance that can withstand soldering and other processes, flame retardancy, excellent chemical resistance, good processability, high productivity, and the ability to use 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 FIG. 1, a thin flat cable 101 is composed of a terminal portion 103 having a conductor electrode 105 that is electrically connected to an inner layer electrode 214 formed continuously from a conductor 204, and a conductor portion 102 in which the conductor 204 exists.

[0033] Fig. 2 shows a thin flat cable 101 according to an embodiment of the present disclosure, where Fig. 2(A) shows a cross section perpendicular to the longitudinal direction including the conductor of the thin flat cable according to the embodiment, Fig. 2(B) shows a cross section perpendicular to the longitudinal direction including the conductor electrode of the thin flat cable according to the embodiment, Fig. 2(C) shows a cross section perpendicular to the longitudinal direction including the conductor of a thin flat cable according to another embodiment, and Fig. 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 in the insulator 106. The thin flat cable 101 has a first heat-resistant insulator layer 219, a metal film 202, and a second heat-resistant insulator layer 211, which are formed in this order on one surface of the insulator 106. The other surface of the insulator 106 has a metal film 202 and a second heat-resistant insulator layer, which are formed in this order. The insulator 106 has a second heat-resistant insulator layer on the longitudinal and lateral sides thereof.

[0035] 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, a conductor electrode 105 for connection to another device, and a via hole 208 for electrically connecting them. The insulator 106 surrounding the conductor 204 sandwiches and surrounds the inner-layer electrode 214, and is in contact with the side of the via hole 208. The thin flat cable 101 also has a first heat-resistant insulator layer 219, which has a heat resistance of 260°C or higher and covers the insulator 106, on the surface of the conductor electrode 105 facing the insulator 106 and in contact with the periphery of the via hole 208 that is in contact with the conductor electrode 105. The first heat-resistant insulator layer 219 has a metal film 202 on the surface opposite the insulator 106, covering the surface of the first heat-resistant insulator layer 219 except for the periphery of the conductor electrode 105. A second heat-resistant insulator layer having a heat resistance of 260°C or higher is provided on the surface of the metal film 202 except for the area around the conductor electrode 105. The other surface of the insulator 106 has the metal film 202 and the second heat-resistant insulator layer in that order. The surface of the insulator 106 on the side surfaces in the longitudinal and lateral directions has the second heat-resistant insulator layer.

[0036] 2(B) and 2(D), in the terminal portion 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and the via hole 208, and the inner layer electrode 214 and the conductor electrode 105 are electrically connected. The conductor electrode 105 is for connection to an external element, etc., and is used as a connector connection terminal, an SMT soldering electrode, a soldering terminal for fixing a connector, a terminal for connecting an anisotropic conducting film (ACF), a soldering terminal for connecting to a substrate, etc. To achieve the above purposes, the surface of the conductor electrode 105 may be subjected to surface treatment such as solder coating, electrolytic nickel gold plating, electroless nickel gold plating, electroless nickel palladium gold plating, tin plating, silver plating, or OSP (Organic Solderability Preservatives), as needed. A first heat-resistant insulator layer 219 having insulating properties where the metal film 202 covering the insulator 106 is not formed is provided around the conductor electrode 105, isolating the metal film 202 from the conductor electrode 105 and preventing electrical conduction between the metal film 202 and the conductor electrode 105.

[0037] As shown in FIGS. 2A and 2B, when the end surface of the thin flat cable 101 does not include a metal film 202, 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 the inner surface, which conducts electricity between the metal films 202 on the upper and lower surfaces of the thin flat cable 101 and maintains the same potential on both surfaces. If the potentials of the upper and lower metal films 202 are uneven, the potential of the conductor 204 may fluctuate. In FIGS. 2A and 2B, the through-holes 108 have a metal film on the inner surface, but the entire through-hole 108 may be filled with metal. Multiple through-holes 108 may also be provided. When the end surface includes a metal film 202 as shown in FIGS. 2C and 2D, the through-holes 108 are not required. 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 metal films 202 except around the conductor electrodes 105. The surface of the metal film 202 opposite the insulator 106 has a second heat-resistant insulator layer 211 except around the conductor electrodes 105. This second heat-resistant insulator layer 211 is optional. As shown in Figures 2(A) and 2(B), if the thin flat cable 101 does not have a metal film 202 on its side, it must have a second heat-resistant insulator layer 211 on its longitudinal and lateral side. In this case, the second heat-resistant insulator layer 211 may not be provided on the outer surfaces of the upper and lower metal films 202.

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

[0040] Conductor 204 should be made of a material with good electrical conductivity, and is preferably made of gold, silver, copper, or aluminum. Considering flexibility and conductivity, copper is most suitable. If conductor 204 is not made of gold or silver, conductor 204 may be plated with gold or silver.

[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 precision of the finished width of the conductor 204. As a result, impedance matching is difficult, making it undesirable as a conductor. Furthermore, if the width of the conductor 204 is less than 0.01 mm, conductor loss increases, 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 too thick, making it unsuitable for a thin flat cable 101 that pursues thinness.

[0042] The width of the conductor 204 has a significant effect on transmission characteristics, so the width must be precisely controlled. Furthermore, to improve the line width precision 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- or silver-plated. Since the thin flat cable 101 according to the present disclosure has a stripline 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, and the like. 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, electrical signal efficiency is low at thicknesses less than 1 μm. Furthermore, at thicknesses 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 will be difficult to achieve precision in the width when forming the conductor 204, and the insulator 106 used to encase the conductor 204 will become thick, making it unsuitable for the thin flat cable 101, which requires a thin design.

[0044] The insulator 106 contains 30% by weight or more of a polymer containing 80% by mole 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, and 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 alkene, such as ethylene or propylene, may be a monomer obtained from biomass or a monomer obtained by recycling. The use of a monomer obtained from biomass or a monomer obtained by recycling can contribute to the reduction of carbon dioxide emissions.

[0047] The polymer preferably contains, as a monomer other than an alkene, less than 20 mol % of one or more of vinyl acetate, acrylic acid, methyl acrylate, ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, and maleic anhydride.

[0048] The insulator 106 may include a resin such as polybutadiene, polyphenylene ether, fluororesin, liquid crystal polymer, polystyrene, or SBS.

[0049] The insulator 106 preferably contains a filler, such as 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 content in the insulator 106 is preferably 5% by mass or more and 80% by mass or less, and more preferably 15% by mass or more and 60% by mass or less.

[0050] When the insulator 106 contains a filler, the melt viscosity of the resin contained in the insulator 106 increases when heated, making it less likely to flow out when melted. This is effective in preventing flow out when heated during soldering. A content of 5% by mass or more is effective, but a content of more than 80% by mass reduces processability and the flexibility of the thin flat cable 101. Furthermore, when the insulator 106 contains a filler, thermal expansion of the resin contained in the insulator 106 when heated can be suppressed, which is effective in preventing flow out when heated during soldering. A content of 15% by mass or more is effective, but a content of 60% by mass or less ensures sufficient flexibility of the thin flat cable 101.

[0051] The insulator 106 may contain a laser light absorber that absorbs laser light. The laser light absorber is preferably one or more of 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, and 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 more suitable as laser light absorbers that do not deteriorate the dielectric properties of insulator 106. In addition to the polymer containing 80 mol % or more of alkene, filler, laser light absorber, and resin, insulator 106 can also contain additives such as viscosity modifiers, lubricants, and flame retardants as appropriate, within the range that does not deteriorate the dielectric properties.

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

[0054] By including 30% by weight or more of a polymer containing 80% by mole or more of an alkene in the insulator 106, a thin flat cable 101 can be manufactured inexpensively. However, polymers containing 80% by mole or more of an alkene have poor absorption properties for 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 by irradiating the surface of the insulator 106 with laser light. However, by including a laser light absorber in the insulator 106, the holes 207 or linear grooves 206 can be formed in a short time by irradiating the surface with laser light. The laser light absorber is included in the insulator 106 so that, when the insulator 106 is 50 μm thick, 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 takes a long time to form holes 207 or linear grooves 206 by irradiating the surface with laser light.

[0055] The first heat-resistant insulator layer 219 provided between the insulator 106 and the metal film 202 may have a function of bonding the insulator 106 and the metal film 202. The first heat-resistant insulator layer 219 has a heat resistance of 260°C or higher. The heat resistance of 260°C or higher means that the softening temperature measured by thermomechanical analysis according to 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 preferably made of the same resin as the first heat-resistant insulator layer 219 and is preferably in the form of a film. The standard specifies a thickness of 0.01 to 1 mm, but a thinner thickness of 0.01 to 0.2 mm is preferred. The test specimen should be square or circular, as specified, with a side length or diameter of approximately 5 mm. The surface of the test specimen should be smooth enough to fit tightly against the sample stage. The standard specifies that the test specimen should be conditioned for at least 24 hours at a temperature of 23±2°C and a relative humidity of 50±5%. However, conditioning is preferably performed in accordance with JIS C60068-2-20:2010. Aging 2 involves conditioning the specimen 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 on the heat resistance of the first heat-resistant insulator layer 219 of moisture absorption 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 will fall below 260°C in a moisture-absorbed state.

[0057] The heat resistance of the insulator 106 measured by the same test method is preferably 230°C or less. If the temperature exceeds 230°C, the efficiency of manufacturing the thin flat cable 101 will be low, and the materials will be expensive, resulting in increased costs. Furthermore, a temperature of 180°C or less is preferable.

[0058] The first heat-resistant insulator layer 219 has heat resistance and insulating properties and is bonded to the insulator 106 and the metal film 202. The first heat-resistant insulator 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 examples thereof include 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-based resins, fluororesins, and polyimide-based resins. The thermosetting resin may be modified by acrylic modification or addition of an acid anhydride. One type of thermosetting resin may be used alone, or two or more types may be used in combination.

[0060] The thermosetting resin contains a curing agent, and may contain additives such as an inorganic filler, a thermoplastic resin, a curing accelerator, a flame retardant, and an organic filler, as needed.

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

[0062] The epoxy resin has an epoxy group in the molecule, and preferably has two or more epoxy groups in one molecule.

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

[0064] In the case of a thermosetting resin composition, it is preferable to combine a thermosetting resin with a curing agent and cure it at 150° C. or less, since this allows the first heat-resistant insulator layer 219 to be formed 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 titanate zirconate, barium zirconate, calcium zirconate, zirconium phosphate, and zirconium tungstate phosphate. One type of inorganic filler may be used alone, or two or more types may be used in combination.

[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 titanate zirconate.

[0067] Thermoplastic resins include phenoxy resin, polyvinyl acetal resin, polyimide resin, polyamideimide resin, polyetherimide resin, polysulfone resin, polyethersulfone resin, polyphenylene ether resin, polycarbonate resin, polyetheretherketone resin, polyester resin, liquid crystal polymer, cycloolefin polymer, cyclic olefin copolymer, polytetrafluoroethylene, copolymer of tetrafluoroethylene and perfluoroalkoxyethylene, etc. Thermoplastic resins may be used alone or in combination of two or more types.

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

[0069] Examples of the ionizing radiation curable resin include monomers, oligomers, prepolymers, etc., each having a polymerizable functional group in the molecule. Examples of the polymerizable functional group include an ethylenically unsaturated bond such as a (meth)acryloyl group, a vinyl group, or an allyl group, and an epoxy group.

[0070] The above-mentioned monomers, oligomers, and prepolymers include (meth)acrylates having a polymerizable functional group in the molecule, specifically, monofunctional (meth)acrylates and polyfunctional (meth)acrylates. Among these, polyfunctional (meth)acrylates are preferred. Polyfunctional (meth)acrylates are (meth)acrylates having two or more polymerizable functional groups in the molecule. The number of functional groups in the polyfunctional (meth)acrylate is not particularly limited, and is, 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, (meth)acrylate having an alicyclic or aliphatic heterocyclic ring, polycarbonate (meth)acrylate, pentaerythritol-based (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, polybutadiene (meth)acrylate, silicone (meth)acrylate, aminoplast resin (meth)acrylate, etc. The ionizing radiation curable resins may be used alone or in combination of two or more.

[0072] The ionizing radiation curable resin may contain additives such as the aforementioned inorganic filler, flame retardant, and organic filler, as needed. The inorganic filler is the same as that of the thermosetting resin. The ultraviolet curable resin may contain a photoinitiator as needed.

[0073] As shown in FIGS. 2A and 2C, the first heat-resistant insulator 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 insulator layer 219 is preferably 0.1 μm or more and 100 μm or less. A thickness of 1 μm or more and 30 μm or less is preferable. A thickness of less than 0.1 μm results in a low layer strength, making it impossible to prevent the insulator 106 from softening, expanding, and / or melting and flowing out during soldering. A thickness of more than 100 μm increases the thickness of the thin flat cable 101, reducing its flexibility. Furthermore, a thickness of less than 1 μm may cause cracks in the layer due to repeated bending, and film formation may be difficult. A thickness of more than 30 μm may require the insulator 106 to be thin due to limitations on the thin flat cable, which may result in a decrease in transmission characteristics.

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

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

[0076] FIG. 10 shows a cross section of the terminal portion 103 of a conventional thin flat cable 101. The metal film 202 is not provided around the conductor electrode 105. The first heat-resistant insulator layer 219 is not provided in the area where the metal film 202 is not provided around the conductor electrode 105, so the insulator 106 is exposed. When soldering to the conductor electrode 105, the insulator 106 softens, expands, and / or melts, causing an insulator blowout 300, and the resin of the insulator 106 flows out from the exposed area. As shown in FIG. 2(B) or 2(D), the first heat-resistant insulator layer 219 covers the exposed area of the insulator 106, so the resin of the insulator 106 does not flow out when soldering to the conductor electrode 105.

[0077] 2(A), 2(B), 2(C), and 2(D), the metal film 202 is provided continuously on the upper and lower surfaces of the thin flat cable 101, except around the conductor electrodes 105 of the terminal portion 103. The continuous metal film 202 can suppress the effects of thermal deformation of the insulator 106, defects due to peeling, and the intrusion of water vapor from the outside air on the electrical properties of the conductor 204. The metal film 202 may be absent from part of the surface of the insulator 106, as long as 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 between the insulator 106 and the metal film 202.

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

[0079] In order to improve the shielding properties of the conductor 204 of the thin flat cable 101, it is preferable that the metal film 202 is provided on the entire surface of the first heat-resistant insulator layer 219 or the insulator 106 except for the periphery of the conductor electrode 105. The metal film 202 is not provided on the periphery of the conductor electrode 105. By "on the periphery," we mean that the distance between the end of the conductor electrode 105 and the end of the metal film 202 is set to a distance that does not allow electrical conduction between the conductor electrode 105 and the metal film 202. It is preferable that the area on the surface of the first heat-resistant insulator layer 219 where the metal film 202 is not provided is small.

[0080] Because heat reduces the adhesive strength between the metal film 202 and the first heat-resistant insulator layer 219 or the insulator 106 and they are prone to peeling, it is desirable that the bottom surface and the longitudinal and lateral end surfaces of the thin flat cable 101 are covered with the metal film 202 without exposing the insulator 106. To improve shielding properties, the longitudinal and lateral end surfaces are covered with the metal film 202, and it is preferable that the metal film 202 be provided on 80% or more of the surface of the insulator 106.

[0081] The exposed portion of the first heat-resistant insulator layer 219 around the conductor electrode 105, where the metal film 202 is not provided, is exposed to the outside air. It is important to minimize the area of the exposed portion of the first heat-resistant insulator layer 219 around the conductor electrode 105. If the exposed area is large, the insulator 106 may absorb moisture through the first heat-resistant insulator layer 219 due to water vapor from the outside air, and the transmission characteristics may be affected by the moisture absorption.

[0082] The conductor 204 is wrapped in an insulator 106, and a metal film 202 is provided continuously on the surface of the first heat-resistant insulator layer 219 except for the area surrounding the conductor electrode 105. That is, by providing the metal film 202 on the upper and lower surfaces of the thin flat cable 101, the thin flat cable 101 is prevented from being affected by the outside air due to the protective function of the metal film 202, and the transmission characteristics can be maintained for a long period of time. By providing the metal film 202 on the longitudinal end faces and lateral end faces of the thin flat cable 101, the protective function can be further improved.

[0083] The distance between the edge of the conductor electrode 105 and the edge of the metal film 202 is 10 μm or more and 1000 μm or less. The first heat-resistant insulator layer 219 is exposed between the edge of the conductor electrode 105 and the edge of the metal film 202. If the distance is less than 10 μm, there is a risk of electrical continuity between the edge of the conductor electrode 105 and the edge of the metal film 202. If the distance is more than 1000 μm, there is a risk of water vapor from the outside air penetrating into the interior of the insulator 106 through the first heat-resistant insulator layer 219, which may deteriorate the transmission characteristics and heat resistance. There is also a risk of the shielding properties of the conductor 204 being impaired. The distance between the edge of the conductor electrode 105 and the edge of the metal film 202 may be equal or variable around the periphery of the conductor electrode 105.

[0084] In the thin flat cable 101 in which multiple rows of conductors 204 are formed, the distance between the end of a conductor electrode 105 and the end of an adjacent conductor electrode 105 is 10 μm or more and 1000 μm or less for the same reasons as in the case of the end of the conductor electrode 105 and the end of the metal film 202.

[0085] The conductor electrode 105 is usually circular, but may be rectangular. Multiple conductor electrodes 105 may be provided on the same terminal portion 103. The conductor electrode 105 may be provided on the end surface of the thin flat cable 101 in the longitudinal or lateral direction, but this is not preferred as it requires complicated processing and reduces workability during soldering. Furthermore, multiple conductor electrodes 105 may be provided on one conductor 204.

[0086] The metal film 202, which is provided continuously on the surface of the first heat-resistant insulator layer 219 and on the surface of the insulator 106 except for the area around the conductor electrode 105, prevents water vapor and chemicals from penetrating into the first heat-resistant insulator layer 219 and the insulator 106. Furthermore, when a flame is 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 preferred. Considering flexibility and electrical conductivity, copper is most preferred. The metal film 202 on the upper and lower horizontal flat surfaces of the thin flat cable 101 can be copper foil, but the longitudinal and lateral end faces of the thin flat cable 101 are preferably copper plated. The electrical resistivity of the metal film 202 is preferably 1 μΩ·m or less. To add functionality such as oxidation prevention and noise reduction, the metal film 202 may be 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, and more preferably 10 μm or more and 50 μm or less. If the thickness is less than 3 μm, pinholes and scratches may occur, resulting in an inability to maintain the internal barrier properties, and the metal film 202 may melt during laser processing, making it impossible to form the linear grooves 206. Furthermore, the expansion of the insulator 106 during heating may cause cracks in the metal film 202. Furthermore, if the thickness exceeds 100 μm, etching to form the groove formation openings 212 for forming the linear grooves 206 and the via hole drilling openings 209 for forming the via holes 207 is complicated and takes a long time. Furthermore, if the thickness exceeds 100 μm, when the metal film 202 is formed by plating, the plating time may be long, causing problems in the manufacturing process, such as warping of the work plate. If the thickness is less than 10 μm, slow UV laser processing is possible, but if a carbon dioxide laser is used for laser processing, which has a fast processing speed, the metal film 202 melts and penetrates the metal film 202, making it impossible to form the linear groove 206. If the thickness exceeds 50 μm, the etching process for the groove formation opening 212 for forming the linear groove 206 and the via hole drilling opening 209 for forming the hole 207 as the via hole becomes complicated and takes a long time.

[0089] The distance in the planar direction between the conductor 204 and the metal film 202 provided on the end face or cross section of the thin flat cable 101 is 20 μm or more. If it is less than 20 μm, there is a possibility that the conductor 204 and the metal film 202 may short-circuit. Furthermore, 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 that a short-circuit may occur, 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, transmission loss increases during high-speed, high-frequency transmission, making it undesirable for use in high-speed, high-frequency transmission.

[0090] 2(B) and 2(D), in the terminal portion 103, the conductor 204 is connected to the conductor electrode 105 via an inner layer electrode 214 and a via hole 208. An electrical signal enters from one conductor electrode 105, passes through the via hole 208, the inner layer electrode 214, the conductor 204, the other inner layer electrode 214, the other via hole 208, and the other conductor electrode 105, and is transmitted from one to the other.

[0091] As shown in FIG. 2, the inner layer electrode 214 is formed continuously from the conductor 204. Therefore, its thickness and material are the same as those of the conductor 204. To connect the conductor electrode 105 to the via hole 208, the inner layer electrode 214 is made equal to or larger than the diameter of the cylindrical via hole 208, as shown in FIG. 2(B). The shape of the inner layer electrode 214 is preferably circular, but any shape may be used as long as it is equal to or larger than the cross section of the via hole 208. A supplementary shape such as a teardrop shape may also be added. When the inner layer electrode 214 is circular, its diameter is typically 50 μm or more and 2 mm or less. 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. If the diameter exceeds 2 mm, it is difficult to match the characteristic impedance. The characteristic impedance of the signal line must be matched, but it is difficult to match the characteristic impedance of the inner layer electrode 214 and the conductor 204, so the diameter of the inner layer electrode 214 must be made as small as possible to achieve characteristic impedance matching.

[0092] The via hole 208 is formed by removing the first heat-resistant insulator layer 219 and the insulator 106 from the location where the conductor electrode 105 is to be formed to the inner-layer electrode 214 by irradiating them with laser light, and plating the hole 207 as a via hole formed by removing the first heat-resistant insulator layer 219 and the insulator 106. Therefore, the cross section has a shape that is approximately circular. The plating is preferably performed with copper. A metal film is formed by plating at the location where the conductor electrode 105 is to be formed, at the location corresponding to the hole 207 in the metal film 202 that was removed by etching to form the via hole opening 209, and the metal film 202 that was not etched is connected and integrated with it.

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

[0094] 2(C) and 2(D), a second heat-resistant resin layer 211 is provided on the surface of the first heat-resistant insulator layer 219 that is exposed around the conductor electrodes 105 that are not covered by the metal layer 202 or the metal film 202, which forms the outer surface of the thin flat cable 101. In FIGS. 2(C) and 2(D), the longitudinal and lateral end faces of the thin flat cable 101 are covered with the metal film 202. When the insulator 106 is covered by the metal film 202 and / or the first heat-resistant insulator layer 219, the second heat-resistant insulator layer 211 does not have to be provided on the surface of the metal film 202 or the first heat-resistant insulator layer 219 that forms the outer surface.

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

[0096] The second heat-resistant insulator layer 211 is preferably formed from an ionizing radiation curable resin that is cured by irradiation with ionizing radiation. Examples of ionizing radiation curable resins include ultraviolet curable resins and electron beam curable resins. The second heat-resistant insulator layer 211 may contain multiple types of resins. For example, it may be 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 three types simultaneously. Furthermore, multiple resins may be laminated.

[0097] As shown in FIGS. 2A and 2C, the second heat-resistant insulator 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 insulator layer 211 does not necessarily have 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 FIG. 2C, if the metal film 202 is not provided on the longitudinal and lateral end surfaces of the thin flat cable 101, the second heat-resistant insulator layer 211 must be provided on the surface of the insulator 106. This is because, if the insulator 106 is exposed, it may soften, expand, and / or melt and flow out due to the heat of soldering. By providing the second heat-resistant insulator layer 211, it is possible to prevent the insulator 106 from flowing out.

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

[0099] As shown in FIGS. 2(B) and 2(D), in the terminal portion 103, in the area where the metal film 202 around the conductor electrode 105 is not provided, the second heat-resistant insulator layer 211 is provided on a part of the surface of the first heat-resistant insulator layer 219 other than the surface of the conductor electrode 105. If the second heat-resistant insulator layer 211 is provided on the surface of the conductor electrode 105, there is a risk of poor connection occurring during soldering, as described above. The second heat-resistant insulator layer 211 does not have to be provided up to the end of the metal film 202.

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

[0101] Even if the second heat-resistant insulator layer 211 is not provided, the provision of the metal film 202 can prevent the insulator 106 from flowing out. By providing the second heat-resistant insulator layer 211 on the surface of the metal film 202, the barrier that prevents the insulator 106 from flowing out becomes stronger.

[0102] The thickness of the second heat-resistant insulator layer 211 is preferably 1 μm or more and 100 μm or less, and more preferably 10 μm or more and 60 μm or less. If the thickness is less than 1 μm, the strength of the layer is low and it is not possible to prevent the insulator from softening, expanding, and / or melting and flowing out during soldering. If the thickness exceeds 100 μm, the thin flat cable becomes too thick, which reduces its flexibility.

[0103] (Manufacturing method of thin flat cables) 3 shows a manufacturing method of thin flat cable 101 according to the present disclosure. In the manufacturing method of thin flat cable 101, metal film 202A is laminated on one side of first insulator film 106A containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene and a laser light absorber, via first heat-resistant insulator layer 219 having a heat resistance of 260°C or more, conductor-formed metal film 202B is laminated on the other side of first insulator film 106A, conductor 214 is formed by etching conductor-formed metal film 202B, metal film 202C is laminated on one side of second insulator film 106B containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene, and the surface of first insulator film 106A on which conductor 214 is formed and the non-metallic film surface of second insulator film 106B are thermocompression-bonded. The conductor 214 is sandwiched and wrapped between the first insulator film 106A and the second insulator film 106B, the portion of the metal film 202A on the first insulator film 106A side where the conductor electrode 105 will be formed is removed by etching, the exposed surface of the first heat-resistant insulator layer 219 is irradiated with a laser, the first heat-resistant insulator layer 219 and the first insulator film 106A are removed until the conductor 214 is exposed, holes 207 that will form the via holes 208 are formed, the formed holes 207 are plated to form the conductor electrodes 105, the conductor 214 and the conductor electrode 105 are made conductive, the portion that will form the outer surface of the thin flat cable 101 is cut, and the side surface 205 that will become the outer surface of the thin flat cable 101 is formed.

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

[0105] FIG. 3A shows a process for laminating a metal film 202A on one side of a film-like first insulator film 106A via a first heat-resistant insulator layer 219 having a heat resistance of 260°C or higher, and then laminating a conductor-formed metal film 202B on the other side of the first insulator film 106A. The first heat-resistant insulator layer 219 is applied to one side of the first insulator film 106A, the metal film 202A is laminated thereon, and the conductor-formed metal film 202B is laminated on the other side of the first insulator film 106A. Lamination may be performed under reduced pressure or in a vacuum. Air infiltration between the layers can cause swelling due to heating during soldering, so lamination under reduced pressure or in a vacuum is preferred. Lamination in a vacuum atmosphere can be performed using a vacuum pressure molding machine, vacuum laminator, roll laminator, or the like.

[0106] The lamination is performed by pressure bonding or thermocompression bonding, but pretreatment may be performed before lamination to improve adhesion strength. For example, plasma treatment, corona treatment, or UV treatment may be performed on the first insulator film 106A, and / or primer treatment or plasma treatment may be performed on the bonding side of the metal film 202A and the conductor-formed metal film 202B. The lamination of the first insulator film 106A and the metal film 202A is preferably performed using the first heat-resistant insulator layer 219 as an adhesive. Other adhesives may also be used for lamination. Lamination can also be performed by inserting a bonding sheet between the film-like insulator 106A and the conductor-formed metal film 202B and pressure bonding them. Furthermore, lamination can also be performed by extruding a molten first insulator film 106A onto the conductor-formed metal film 202B and pressure bonding it.

[0107] When laminating the first insulator film 106A and the metal film 202A using the first heat-resistant insulator layer 219 as an adhesive, methods include applying the first heat-resistant insulator layer 219 containing an uncured thermosetting resin to one side of the metal film 202A and then curing or semi-curing the uncured thermosetting resin, or preparing a thermosetting resin film that will become the first heat-resistant insulator layer 219 containing the uncured thermosetting resin, placing the first insulator film 106A on the metal film 202A, and then curing or semi-curing the uncured thermosetting resin.

[0108] The method for applying the thermosetting resin composition to the surface of the metal film 202A is not limited, and any known application method can be used.

[0109] The thermosetting resin film can be produced by coating a composition containing an uncured thermosetting resin on a separator, which can then be peeled off after the thermosetting resin film is placed on the surface of metal film 202A.

[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 insulator layer 219 is cured or semi-cured by irradiating it with ionizing radiation before laminating the conductor-forming 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 suitable. The thickness of the metal foil is preferably 3 μm or more and 100 μm or less. More preferably, it is 10 μm or more and 50 μm or less.

[0112] When laminating the first heat-resistant insulator layer 219 and the conductor-forming metal film 202B onto the surface of the first insulator film 106A by thermocompression bonding, a layer of a copolymer of a carboxyl group-containing monomer and an alkene is preferably provided on the side of the first insulator film 106A that contacts the first heat-resistant insulator layer 219 and / or the metal film 202B to enhance adhesive strength. The adhesive strength between the copolymer of a carboxyl group-containing monomer and an alkene and the first heat-resistant insulator layer 219 and the metal film 202B is enhanced by thermocompression bonding. In particular, when using polyethylene, which uses ethylene as the alkene, or polypropylene, which uses propylene as the alkene, as the polymer, it is preferable to use a resin obtained by graft-polymerizing polyethylene or polypropylene with maleic anhydride. The polymer preferably contains less than 20 mol %, and more preferably less than 10 mol %, of a carboxyl group-containing monomer. Less than 10 mol % minimizes the impact on transmission characteristics.

[0113] The metal film 202A, the first insulating film 106A, the first heat-resistant insulator layer 219, and the conductor-forming metal film 202B shown in FIG. 3(A) may be laminated in this order as shown in FIG.

[0114] 7(A), a conductor-forming metal film 202B is laminated on a film-like first insulator film 106A, and then a first heat-resistant insulator layer 219 and a metal film 202A are laminated on the first insulator film 106 having a carboxyl group and the conductor-forming metal film 202B by thermocompression bonding.

[0115] In FIG. 7B, after the first heat-resistant insulator layer 219 is provided on the first insulator film 106A, the metal film 202A and the conductor-forming metal film 202B are laminated thereon.

[0116] In FIG. 7C, after the first heat-resistant insulator layer 219 is provided on the metal film 202A, the first insulator film 106A and the conductor-forming metal film 202B are laminated thereon.

[0117] In procedures other than that of Figure 7(C), there may be cases where the first heat-resistant insulator layer 219 needs to be thermally cured including the first insulating film 106A, and the thermal curing needs to be performed at a temperature lower than the heat resistance temperature of the first insulating film 106A. Therefore, the procedure of Figure 7(C) is preferable, in which the metal film 202A is the base material and high-temperature heating is possible.

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

[0119] Figure 3(C) shows a process of forming a conductor 204 in the conductor portion 102 and an inner layer electrode 214 that serves as the end of the conductor 204 and is electrically connected to the conductor electrode 105 in the terminal portion 103 by a circuit formation process of etching the conductor-forming metal film 202B.

[0120] The circuit formation process can be performed using a method commonly used in the manufacture of printed wiring boards. For example, the conductor 204 and inner layer electrode 214 are formed by leaving the necessary conductor-forming metal film 202B through the steps of forming an etching mask, exposing, developing, etching, and peeling off the etching mask.

[0121] FIG. 3(D) shows the process of sequentially laminating a second insulator film 106B and a metal film 202C on the first insulator film 106A and the conductor 204 and inner-layer electrode 214 formed on the first insulator film 106A. The material of the second insulator film 106B may be the same as that of the first insulator film 106A. Alternatively, a different insulator material may be used. The first insulator film 106A and the second insulator film 106B are bonded together by thermocompression bonding. The conductor 204 and inner-layer electrode 214 are sandwiched and wrapped between the first insulator film 106A and the second insulator film 106B. Because the conductor 214 is convex on the first insulator film 106A, thermocompression bonding is preferably performed in a vacuum to ensure complete adhesion between the first insulator film 106A and the second insulator film 106B.

[0122] The step of sequentially laminating the second insulator film 106B and the metal film 202C onto the first insulator film 106A and the formed conductor 204 and inner-layer electrode 214 may be performed by vacuum lamination. In vacuum lamination, the thermocompression temperature is preferably in the range of 60°C to 200°C, more preferably 80°C to 180°C, the thermocompression pressure is preferably in the range of 0.05 MPa to 2.00 MPa, more preferably 0.1 MPa to 1.5 MPa, and the thermocompression time is preferably in the range of 1 second to 500 seconds, more preferably 3 seconds to 300 seconds. The lamination is preferably performed 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 insulator film 106A with the film-like insulator 106B, and laminating the second insulator film 106B with the metal film 202C by thermocompression bonding, it is preferable to provide a layer of a copolymer of a monomer having a carboxyl group and an alkene on both sides of the second insulator film 106B to enhance adhesive strength. The adhesive strength between the copolymer of a monomer having a carboxyl group and an alkene and the metal is increased by thermocompression bonding. In particular, when using polyethylene using ethylene as the alkene or polypropylene using propylene as the alkene as the polymer, it is preferable to use a polymer obtained by graft-polymerizing maleic anhydride onto polyethylene or polypropylene.

[0124] It is preferable that the metal film 202C is made of the same metal as the metal film 202A. The metal film 202C may be formed by laminating the second insulator film 106B on the first insulator film 106A and then laminating the metal film 202C thereon, or by simultaneously laminating the second insulator film 106B and the metal film 202C on the first insulator film 106A. It is also possible to laminate the second insulator film 106B and the metal film 202C on the first insulator film 106A after laminating them together.

[0125] Figure 3(E) shows a laminate in which a metal film 202A is laminated on one side of a first insulator film 106A via a first heat-resistant insulator layer 219, and a conductor 204 and an inner layer electrode 214 are formed on the other side, and a second insulator film 106B and a metal film 202C are sequentially laminated on the surface on which the conductor 204 and inner layer electrode 214 are formed.

[0126] FIG. 3(F) shows a process of forming a penetrating hole 220 for forming the through hole 108 by a CNC drilling machine at the location where the through hole 108 is to be formed.

[0127] FIG. 3(F) shows a process of etching away the metal film 202A at the location where the conductor electrode 105 of the metal film 202A is to be formed, forming an opening 209 for drilling a via hole, and forming a hole 207 for forming a via hole 208 for electrically connecting the inner layer electrode 214 and the conductor electrode 105.

[0128] The process of removing the metal film 202A by etching and forming the opening 209 for drilling a via hole 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 to be formed. The area from which the metal film 202A has been removed is defined as the opening 209 for drilling a via hole.

[0129] The formation of the hole 207 for forming the via hole 208 removes the first heat-resistant insulator layer 219 and the first insulator film 106A exposed in the via hole drilling 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, or the like. A laser processing machine is preferred due to its fast processing speed. The first heat-resistant insulator layer 219 and the first insulator film 106A are removed down to the inner layer electrode 214 by irradiating a laser from the laser processing machine. If the metal film 202A is thin, the metal film 202A, the first heat-resistant insulator layer 219, and the insulator 106 that are not removed by etching can also be simultaneously removed by the laser processing machine.

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

[0132] When selecting a laser processing machine, consideration must be given to matching it with the absorption wavelength of the insulator 106. In particular, YAG lasers, fiber lasers, and carbon dioxide laser processing machines are widely used due to their fast resin processing speed, and are preferred laser processing machines in this disclosure. The laser processing machine according to this disclosure preferably uses a UV / visible 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 laser light, so there is no need to use a laser light absorber. However, if the absorbance is low, it is possible to add a small amount of coloring pigment to increase the absorbance and speed up the processing speed. The amount added is preferably 10 mass percent or less, as it does not affect the electrical properties.

[0134] When the first insulator film 106A is 50 μm or thicker, the processing speed rapidly slows down due to the principles of UV / visible lasers, resulting in reduced productivity. When the thickness of the first insulator film 106A to be removed is less than 50 μm, processing with a UV / visible laser is effective, but it is not suitable for thicknesses greater than that. If the first insulator film 106A is less than 50 μm, a UV / visible laser can be used. By adding a coloring pigment, the first insulator film 106A can be used even when it is 50 μm or thicker. The amount of coloring added can be increased to speed up the processing speed.

[0135] The insulator 106 preferably contains 30% by weight or more of a polymer containing 80% by mole or more of an alkene and a laser light absorber, and when the insulator 106 is 50 μm thick, the minimum transmittance of light with a wavelength of 0.2 μm or more and less than 0.8 μm is 85% or less. A color pigment can be used as the laser light absorber for wavelengths of 0.2 μm or more and less than 0.8 μm. A color pigment may be added to the first heat-resistant insulator layer 219.

[0136] Color pigments include cyanine blue, cyanine green, yellow ochre, red iron oxide, permanent red, carbon black, titanium oxide, and zinc oxide. In addition, organic compounds such as benzotriazoles, benzophenones, and cyanoacrylates are also suitable as laser light absorbers for wavelengths of 0.2 μm or more and less than 0.8 μm.

[0137] Processing with UV and visible light lasers uses long and short pulses to produce smooth processed surfaces with clean shapes, resulting in a good finish.

[0138] Near-infrared lasers, such as YAG lasers or fiber lasers, and far-infrared lasers, such as carbon dioxide lasers, have high processing speeds and excellent productivity, even when the first insulator film 106A is thick. However, polymers containing 80 mol % or more of alkenes hardly absorb light with wavelengths around 0.8 μm to 11 μm, and therefore cannot form holes 207. To achieve this, it is necessary to incorporate a laser light absorber into the first insulator film 106A. Even if the first insulator film 106A contains 30 wt % or more of a polymer containing 80 mol % or more of alkenes, the inclusion of a laser light absorber allows for efficient formation of holes 207 using near-infrared laser light and far-infrared laser light.

[0139] When first insulator film 106A contains 30% by weight or more of a polymer containing 80% by mole or more of an alkene, insulator 106 can be made inexpensive, and when it contains a laser light absorber, it can increase the speed at which holes 207 are formed with near-infrared laser light and far-infrared laser light, and improve the smoothness and dimensional accuracy of the machined surface. When insulator 106 contains a laser light absorber and has a thickness of 50 μm, it is necessary for the minimum transmittance of light with a wavelength of 0.8 μm or more and 11.0 μm or less to be 85% or less.

[0140] 3(G) shows a process of forming through-hole 108 by plating the inner surface of through-hole 220. The inner surface of through-hole 220 is cleaned, and the surfaces of insulator 106, which are first heat-resistant insulator layer 219 and first and second insulator films 106A and 106B, are made conductive, and then metal plating is performed. By forming through-hole 108, metal film 202A and metal film 202C, which are the upper and lower metal films 202 of thin flat cable 101, become conductive and have the same potential.

[0141] 3(G) shows a process of plating the inner surface of the hole 207 and connecting the plated metal film to the metal film 202A to form the conductor electrode 105 that serves as a terminal, thereby establishing electrical continuity between the conductor 204 and the conductor electrode 105. The metal film 202A and the exposed portion of the inner-layer electrode 214 that forms the bottom of the hole 207 are cleaned, and the surfaces of the first heat-resistant insulator layer 219 and the first insulator film 106A are made conductive, after which metal plating is performed.

[0142] Typically, metal plating involves the sequential steps of desmearing, catalyst formation, electroless plating, and electrolytic plating. Desmearing is necessary when smears or other foreign matter remain on the metal film surface; it is unnecessary if the metal film surface is clean. Desmearing can be performed using dry methods using plasma or wet methods using oxidizing agents such as permanganate. In this disclosure, however, dry methods are preferred in terms of preventing water absorption. Catalyst formation, electroless plating, and electrolytic plating can be performed using chemical systems from, for example, ATOTECH, JCU Corporation, DOW CHEMICAL, Uemura Industries, Ltd., Okuno Pharmaceutical Industries, Ltd., and MacDermid Enthon. To minimize moisture absorption during processing, a continuous metal film may be formed on the first heat-resistant insulator layer 219 on the inner surface of the hole 207 and the surface of the first insulator film 106A by a dry method such as sputtering, instead of wet catalyst formation. Furthermore, as a conductive method, a Black Hole system from Japan MacDermid can also be used instead of catalyst formation and electroless plating.

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

[0144] 3(G) shows a process of removing a portion of the metal film 202A shown in FIG. 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 from around the portion that will become the conductor electrode 105, thereby forming the gap 218. The area to be removed is such that the edge of the conductor electrode 105 formed by the removal and the edge of the metal film 202A that will become the metal film 202 are not electrically connected.

[0145] The metal film 202A can be removed in the same circuit formation process as the formation of the conductor 204 in Fig. 3(C). That is, the desired shape can be formed by removing unnecessary portions of the metal film 202A through the steps of forming an etching mask, forming a resist layer, exposing, developing, etching, and peeling off the etching mask. As described above, the distance between the edge of the conductor electrode 105 and the edge of the metal film 202A, i.e., the distance of the gap 218, is 10 µm or more and 1000 µm or less.

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

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

[0148] FIG. 6(B) shows the linear grooves 206 formed by laser cutting using a combination of laser processing and a blade or router bit. The white portions of the linear grooves 206 indicate the cut portions. FIG. 6(A) shows the entire linear groove 206 formed by laser processing. FIG. 6(Aa) is a cross-sectional view taken along the a-axis in FIG. 6(A). The metal film 202C does not penetrate the entire groove. This is the same as FIG. 3(I). FIGS. 6(Bb) and 6(Bc) are cross-sectional views taken along the b-axis and c-axis in FIG. 6(B). Cutting the linear grooves 206 with a blade also fractures the metal film 202C. Slicing at this stage complicates the subsequent metal plating process. Furthermore, it becomes impossible to manufacture the thin flat cable 101 as an assembly, impairing productivity. Therefore, at least a portion of the metal film 202C must be left intact to secure the individual pieces. Laser processing is suitable for preserving the metal film 202C.

[0149] To perform laser processing, the metal film 202A must be removed from the area where the linear groove 206 is to be formed, thereby forming the groove formation opening 212. The removal of the metal film 202A can be performed using the circuit formation process described above. That is, the desired shape can be formed by removing unnecessary portions of the metal film 202A through procedures such as etching mask formation, resist layer formation, exposure, development, etching, and etching mask removal. The laser processing can be performed in the same manner as the process for forming the hole 207 that forms the via hole 208 described above. In the present disclosure, deep engraving of the insulator 106 is required to form the linear groove 206 in the insulator 106. The deep engraving speed is significantly slow with UV / visible light lasers. Near-infrared and far-infrared lasers are preferred because of their fast processing speed.

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

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

[0152] 3(K) and 3(L) show the process of dividing the thin flat cable 101 into individual pieces. FIG. 3(K) shows the terminal portion 103, and FIG. 3(L) shows the conductor portion 102. Dividing into individual pieces is performed by cutting the metal film 202C along the linear grooves 206. The cutting to divide into individual pieces can be performed using any cutting method for flexible wiring boards, and cutting with a mold, cutting with a router, or cutting with a laser processing machine are common methods. In the present disclosure, the thin flat cable 101 is manufactured as an assembly and then divided into individual pieces, resulting in good work efficiency.

[0153] Manufacturing the thin flat cable 101 as an assembly means forming the thin flat cables 101 in multiple rows in parallel in the longitudinal direction as shown in Figure 3 and finally dividing them into individual pieces to simultaneously obtain multiple thin flat cables 101. Alternatively, the thin flat cables 101 in the longitudinal direction may be formed in multiple rows in series.

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

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

[0156] 4(C) shows a process of etching the conductor-forming metal film 202B to form the conductor 204 in the conductor portion 102 and the inner-layer electrode 214 in the terminal portion 103, and then etching the metal film 202A to form the via-hole opening 209 and the groove-forming opening 212. In the embodiment shown in FIG. 3, the processes of forming the via-hole opening 209 and the groove-forming opening 212 are not performed simultaneously with the formation of the conductor 204, but are performed sequentially after the conductor 204 is sandwiched between the second insulating films 106B. However, in the manufacturing process of the thin flat cable 101 according to the present disclosure shown in FIG. 3, the conductor 204, the inner-layer electrode 214, the via-hole opening 209, and the groove-forming opening 212 may also be simultaneously formed by etching the conductor-forming metal film 202B, as shown in FIG. 4(C).

[0157] As shown in Figure 4(C), it is useful to perform the circuit formation process simultaneously on the front and back of one laminate and accurately align the inner layer electrodes 214 with the openings 209 for drilling via holes in order to obtain a thin flat cable 101 of excellent quality.

[0158] The etching can be carried out by the above-mentioned circuit formation step.

[0159] 4(D) shows a process of laminating a second insulator film 106B and a metal film 202C in this order on the surface of a first insulator film 106A having a metal film 202A with via hole openings 209 and groove openings 212 formed on one surface and a conductor 204 and an inner-layer electrode 214 formed on the other surface. The lamination process is the same as that shown in FIG. 3(D).

[0160] Figure 4(E) shows a laminate in which a first insulator film 106A has a metal film 202A on one side of which an opening 209 for drilling a via hole and an opening 212 for forming a groove are formed, and a conductor 204 and an inner layer electrode 214 on the other side, and a second insulator film 106B and a metal film 202C are laminated in order on the side on which the conductor 204 and the inner layer electrode 214 are formed.

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

[0162] The hole 207 is formed by removing the first heat-resistant insulator layer 219 exposed in the opening 209 for drilling a via hole and the first insulator film 106A on its underside down to the inner-layer electrode 214. The removal of the first heat-resistant insulator layer 219 and the first insulator film 106A can be performed in the same manner as in the process shown in FIG. 3(F).

[0163] The linear groove 206 is formed in a process for forming the outer surface of the thin flat cable 101. The first heat-resistant insulator layer 219 and the insulator 106 are broken at the location where the outer surface of the thin flat cable 101 will be formed, leaving the metal film 202C. The linear groove 206 can be formed by laser processing and / or cutting processing using a combination of a blade and a router bit, similar to the process shown in FIG. 3(I).

[0164] 4(G) shows plating of the inner surface of the hole 207 and the surface of the linear groove 206 formed in the process shown in FIG. 4(F). The inner surface of the hole 207 is plated, and the plated metal film is connected to the metal film 202A to form the conductor electrode 105 serving as a terminal, thereby establishing electrical continuity between the inner layer electrode 214 and the conductor electrode 105. The metal film 202A and the exposed portions of the inner layer electrode 214 that form the bottom of the hole 207 are cleaned, and the surfaces of the first heat-resistant insulator layer 219 and first insulator film 106A that form the inner surface of the hole 207 are made conductive, after which metal plating is performed. The metal plating can be performed in the same manner as in the process shown in FIG. 3(G).

[0165] The metal film 202D is formed on the wall surfaces 205 of the linear grooves 206 by metal plating. The metal film 202D is provided on the longitudinal and lateral end surfaces of the thin flat cable 101, thereby 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 by the manufacturing process of Fig. 3 does not have a metal film formed on the longitudinal and lateral end faces. The thin flat cable 101 obtained by the manufacturing process of Fig. 4 has a metal film 202D formed on the longitudinal and lateral end faces, thereby achieving a high shielding effect.

[0167] Fig. 4(H) shows the process of removing a portion of the metal film 202A shown in Fig. 4(G). This is the process of removing a portion of the metal film 202A, connecting the metal plated into the hole 207 with the metal film 202A around the hole 207, and forming a gap 218 between the metal film 202A and the conductor electrode 105 formed by the connected metal film 202A. The metal film 202A around the portion that will become the conductor electrode 105 is removed to form the gap 218. The area to be removed is such that the edge of the conductor electrode 105 formed by the removal and the edge of the metal film 202A are not electrically connected. This is the same as the process of Fig. 3(H).

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

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

[0170] 4(H), when the metal film 202 is formed on the top surface, bottom surface, and longitudinal and lateral end surfaces of the thin flat cable 101, the second heat-resistant insulator layer 211 does not have to be provided on the surface of the metal film 202. The second heat-resistant insulator layer 211 may be provided on the surface of the metal film 202 as desired.

[0171] The second heat-resistant insulator layer 211 is formed in the same manner as in FIG.

[0172] 4(J) and 4(K) show the process of dividing the thin flat cable 101 into individual pieces. FIG. 4(J) shows the terminal portion 103, and FIG. 4(K) shows the conductor portion 102. The division is performed by cutting the metal film 202C and the second heat-resistant insulator layer 211 along the linear grooves 206. The division can be performed in the same manner as in FIGS. 3(K) and (L). A large number of thin flat cables 101 can be manufactured in the same manner.

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

[0174] The thin flat cable 101 having parallel metal films 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 the through-hole 108, and serves as ground.

[0175] The horizontal distance between the end of the conductor-parallel metal film 215 and the ends of the conductor 204 and the inner-layer electrode 214 is 10 μm or more. If the distance is less than 10 μm, there is a risk of short-circuiting between the conductor-parallel metal film 215 and the conductor 204 and the inner-layer electrode 214. Within this range, the distance between the conductor 204 and the inner-layer electrode 214 may vary depending on the location. It is preferable that the distance between the conductor 204 and the inner-layer electrode 214 is the same everywhere. In this case, as shown in FIGS. 2(E) and 2(F), the ends of the conductor-parallel metal film 215 are provided along the shapes of the conductor 204 and the inner-layer electrode 214.

[0176] By providing the spacing as described above, the ends of the conductor parallel metal film 215 do not have to be provided along the conductor 204 and the inner layer electrode 214. The potential of the conductor parallel metal film 215 needs to be the same as that of the metal film 202. Therefore, the conductor parallel metal film 215 is electrically connected to the metal film 202 by the through hole 108. A through hole 220 for forming the through hole 108 is formed including at least a part of the conductor parallel metal film 215, and the inner surface of the through hole 220 is plated to form the through hole 108.

[0177] 2(E) and 2(F), if the end face of the thin flat cable 101 does not have a metal film 202, it is necessary to form a through hole 108. However, if the end face of the thin flat cable 101 has a metal film 202, as shown in FIGS. 2(G) and 2(H), 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 have the same potential.

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

[0179] 2(E), 2(F), 2(G), and 2(H) are provided on one side of the conductor 204 and the inner-layer electrode 214, but they may be provided on both sides. They may also be provided partially along the conductor 204 and the inner-layer electrode 214. Providing them around the entire circumference improves the transmission characteristics of the shielded thin flat cable 101, so it is more preferable to provide them around the entire circumference.

[0180] (Thin, multi-row flat cable) 8 shows a thin flat cable 101 according to the present disclosure, which is a thin flat cable with a horizontally multi-row structure. (A) shows a cross section perpendicular to the longitudinal direction and including the conductor of a thin flat cable with a horizontally multi-row structure according to an embodiment. (B) shows a cross section perpendicular to the longitudinal direction and including the conductor electrode of a thin flat cable with a horizontally multi-row structure according to an embodiment. (C) shows a cross section perpendicular to the longitudinal direction and including the conductor of a thin flat cable with a horizontally multi-row structure according to another embodiment. (D) shows a cross section perpendicular to the longitudinal direction and including the conductor electrode of a thin flat cable with a horizontally multi-row structure according to another embodiment.

[0181] FIG. 9 also shows a thin flat cable according to the present disclosure, which has a horizontally and vertically multi-row structure. FIG. 9(A) shows a cross section perpendicular to the longitudinal direction, including the conductors, of a thin flat cable having a horizontally and vertically multi-row structure according to an embodiment. FIG. 9(B) shows a cross section perpendicular to the longitudinal direction, including the conductor electrodes, of a thin flat cable having a horizontally and vertically multi-row structure according to an embodiment. FIG. 9(C) shows a cross section perpendicular to the longitudinal direction, including the conductors, of a thin flat cable having a horizontally and vertically multi-row structure according to another embodiment. FIG. 9(D) shows a cross section perpendicular to the longitudinal direction, including the conductor electrodes, of a thin flat cable having a horizontally and vertically multi-row structure according to another embodiment.

[0182] In the embodiments shown so far, one conductor 204 is 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 above-described embodiments except that multiple shielded thin flat cables are integrated in the planar direction.

[0183] 8(A) and 8(B) have multiple conductors 204 in the horizontal direction, and may also have a conductor-parallel metal film 215. The conductor-parallel metal film 215 does not have to be provided. Since no metal film 202 is provided on the end face of the thin flat cable 101, through holes 108 are required. When the conductor-parallel metal film 215 is provided, the through holes 108 are electrically connected to the conductor-parallel metal film 215. When the conductor-parallel metal film 215 is not provided, normal through holes 108 are provided.

[0184] 8(C) and 8(D) show 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 the thin flat cable 101 has a metal film 202 on its end face, the through-hole 108 is not required. However, if the conductor-parallel metal film 215 is provided, the metal film 202 on the end face and the conductor-parallel metal film 215 must be connected to establish electrical continuity between them. Furthermore, if the conductor-parallel metal film 215 cannot be electrically connected to the end face metal film 202, a metal film 202D must be provided to isolate the multiple conductors 204, as shown in FIGS. 8(C) and 8(D), so that the upper and lower metal films 202 and the conductor-parallel metal film 215 can be electrically connected. This may be replaced with a through-hole 108.

[0185] 9(A) and 9(B) show 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 no metal film 202 is provided on the end face of the thin flat cable 101, a through hole 108 is required. When the conductor-parallel metal film 215 is provided, the through hole 108 is electrically connected to the upper and lower metal films 202, the conductor-parallel metal film 215, and the metal film 202E separating the upper and lower conductors 204. When 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. It is also possible to provide multiple conductors 204 only in the vertical direction, without providing multiple conductors 204 in the horizontal direction.

[0186] 9(C) and 9(D) include 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. Because the metal film 202 is provided on the end face of the thin flat cable 101, the through-hole 108 is not required. However, if the conductor-parallel metal film 215 is provided, the metal film 202 on the end face and the conductor-parallel metal film 215 must be connected to establish electrical continuity between the end face metal film 202 and the conductor-parallel metal film 215. Furthermore, if the conductor-parallel metal film 215 cannot be electrically connected to the end face metal film 202, a metal film 202D is required to separate the multiple conductors 204 as needed, as shown in FIGS. 9(C) and 9(D), 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 may be replaced by a through hole 108. It is also possible to provide a plurality of conductors 204 only in the vertical direction, without providing a plurality of conductors 204 in the horizontal direction.

[0187] The thin flat cable according to the present disclosure can be used in communication devices that require high-density mounting, devices that use high-frequency and high-speed signals, devices that require EMI countermeasures, devices that require chemical resistance, and more specifically, smartphones, IoT devices, communication base station peripheral devices, automotive-related devices such as ADAS, and lithium-ion battery peripheral devices. [Explanation of symbols]

[0188] 101··Thin Flat Cable 102 Conductor section 103...Terminal section 105 Conductor electrode 106··Insulator 108 through-hole 202 Metal Film 204 Conductor 205··Wall 206··Linear groove 207...hole 208··Beer Hall 209··Opening for via hole drilling 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 insulation blowout

Claims

1. a conductor made of a metal; an insulator that sandwiches the conductor and wraps the conductor except for the conductor electrodes that are conductive from the conductor and exposed on the surface, the insulator containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene; a via hole that electrically connects the conductor and the conductor electrode; a first heat-resistant insulator layer having a heat resistance of 260° C. or higher, the first heat-resistant insulator layer being in contact with the insulator-side surface of the conductor electrode and the periphery of the via hole in contact with the conductor electrode, and covering the insulator; a metal film covering the surface of the first heat-resistant insulator layer except for the periphery of the conductor electrode; and a second heat-resistant insulator layer having a heat resistance of 260°C or higher and covering the surface of the metal film, the first heat-resistant insulator layer, or the surface of the insulator; A thin flat cable in which the second heat-resistant insulator layer covers a surface of the insulator that is not covered by either the first heat-resistant insulator layer or the metal film.

2. 2. The thin flat cable according to 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 insulator layer.

3. The thin flat cable according to claim 1 or 2, The alkene is one or more of ethylene, propylene, butene, pentene, hexene, heptene, octene, cyclopropene, cyclobutene, cyclopentene, cyclohexene, and cycloheptene.

4. The thin flat cable according to claim 1 or 2, a thin flat cable, wherein the insulator contains 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 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.

5. The thin flat cable according to claim 1 or 2, A thin flat cable having the metal film covering the side surface.

6. a metal film is laminated on one side of a first insulator film containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene and a laser light absorber, with a first heat-resistant insulator layer having a heat resistance of 260°C or more interposed therebetween; a conductor-forming metal film is laminated on the other surface of the first insulating film; forming a conductor by etching the conductor-forming metal film; a metal film is laminated on one side of a second insulating film containing 30% by weight or more of a polymer containing 80% by mole or more of an alkene; a surface of the first insulating film on which the conductor is formed and a non-metallic film surface of the second insulating film are thermocompression-bonded to each other, and the conductor is sandwiched between the first insulating film and the second insulating film; removing by etching a portion of the metal film on the first insulating film side where a conductor electrode is to be formed, a periphery of the portion where the conductor electrode is to be formed, and a portion where an outer surface of the thin flat cable is to be formed; irradiating a laser onto the exposed surface of the first heat-resistant insulator layer to remove the first heat-resistant insulator layer and the first insulator film until the conductor is exposed, thereby forming a hole to form a via hole; The formed hole is plated to form the conductor electrode, and the conductor and the conductor electrode are electrically connected to each other; providing a second heat-resistant insulator layer having a heat resistance of 260°C or higher, which covers a surface of the metal film, the first heat-resistant insulator layer, the first insulator film, or the second insulator film; the second heat-resistant insulator layer covers the surfaces of the first insulator film and the second insulator film that are not covered by either the first heat-resistant insulator layer or the metal film; A method for manufacturing a thin flat cable includes cutting the thin flat cable at a location that will form the outer surface thereof, and forming a side surface that will become the outer surface of the thin flat cable.

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