Shielded thin flat cable and method for manufacturing the same

Abstract

The present invention provides a shielded, thin, flat cable that has sufficient adhesion between the film-like insulator, the conductor, the inner layer electrode, and the other insulator, without melting the other insulator by heating the film-like insulator above its melting point and below its melting point. [Solution] A shielded thin flat cable having a metal conductor 204, an insulator 106 that sandwiches the conductor and surrounds the conductor other than the conductor electrode that is electrically conductive from the conductor and exposed on the surface, and a metal film 202 continuous on the surface of the insulator other than around the conductor electrode, wherein the melting point of the conductor, the inner electrode and the second film-like insulator 106B which is bonded to the first film-like insulator 106A surface containing a syndiotactic polystyrene homopolymer and the conductor and inner layer electrode 214 which is electrically conductive to the conductor and conductor electrode is made 10°C or more lower than the melting point of the first film-like insulator.

Description

Technical Field

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

Background Art

[0002] For wiring of high-speed transmission line portions, also referred to as high-frequency portions such as RF circuits inside electronic devices and their peripheries, power supply lines mainly connecting televisions, radios, and antennas to antennas, connection for measurement devices, transmission of audio and video signals, coaxial cables with a core material covered by a shield layer are widely used.

[0003] Generally, the structure of a coaxial cable often involves wrapping a core wire made of copper or the like with an insulator such as polyethylene, further wrapping it with a shield layer called a braided wire formed by braiding thin wires, and finally covering the outside with a protective coating such as vinyl chloride. Since the braided wire blocks electromagnetic waves from the outside, noise and attenuation can be suppressed, and leakage of electromagnetic waves from the inside is also reduced. The transmission frequency range is wide, and transmission from direct current to millimeter waves is possible (see Non-Patent Document 1).

[0004] On the other hand, in mobile devices and the like, in resin multilayer substrates made of thermoplastic resins such as flexible wiring boards for high-density mounting of components in electronic devices and flat cables for wiring through narrow gaps inside the device, a triple plate line may be provided as a signal transmission line for transmitting high-frequency signals. The triple plate line is a signal transmission line in which a line conductor and a ground conductor are provided on a wiring board, and a ground conductor wider than the line conductor is opposed to both sides of the line conductor (see Patent Document 1 and Patent Document 2). The triple plate line has features such as suppressing noise from the outside and being less likely to cause a phenomenon called unnecessary radiation or unwanted radiation because ground conductors are provided on both sides.

[0005] It has been proposed to provide a wiring board that is easy to bend even when a triplate line is provided, and in which bending does not easily cause deterioration of transmission characteristics (see Patent Document 3).

[0006] To improve the shielding effect, a method has been employed in which metal foil tape is attached to the flat cable and wrapped around it (see Patent Document 4). However, in the short direction of such a flat cable, the insulator is exposed to the outside air, and this exposed insulator is exposed to water vapor, which penetrates into the interior of the insulator and causes it to absorb moisture. The absorbed moisture affects the transmission characteristics. Insulators with a high moisture absorption rate are susceptible to the effects of water vapor, and this effect is particularly pronounced in the high-frequency range, causing changes in the transmission characteristics.

[0007] One method for strengthening the longitudinal shielding is to wrap it with shielding tape (see Patent Documents 5 and 6), but this involves wrapping a shielding film as the shielding layer, and gaps or contact resistance occur at the overlapping or contact points of the shielding film, so it does not provide complete shielding. Also, the overlapping of the shielding film makes the flat cable thicker. Furthermore, organic materials such as adhesive or bonding layers are exposed to the outside air at the contact points, causing the insulator to absorb moisture.

[0008] As described above, moisture absorption alters the electrical properties of the insulator, which in turn changes the transmission characteristics of the cable. The impact of moisture absorption on transmission characteristics is particularly pronounced when dealing with high-frequency or high-speed signals.

[0009] Flat cables have also been proposed in which a seamless shielding film in the longitudinal direction is formed by copper plating (see Patent Document 7). However, in the short direction, the cable is cut into individual pieces, and the cross-section is not plated, exposing the conductor and insulator. In other words, the end faces in the short direction are affected by humidity, and water vapor penetrates them. Therefore, in this case, for flat cables where stable transmission characteristics are required, there are limitations on using highly hygroscopic resins as insulators. Furthermore, terminals need to be formed separately in order to connect to other components.

[0010] The increasing frequency of communications, exemplified by recent 5G communications, and the resulting increase in semiconductor transmission speeds have created a demand for low-loss transmission lines. This necessitates insulators with low transmission loss. For example, general-purpose hydrocarbon resins such as polyethylene, polystyrene, and polypropylene have low transmission loss, are easy to process, and are inexpensive, making them suitable materials for high-frequency and high-speed transmission. However, these materials lack heat resistance and flame retardancy, making them unsuitable for use in portable and automotive equipment where heat resistance and flame retardancy are required.

[0011] In flat cables with an exposed resin insulator, the temperature reaches approximately 250°C during the reflow soldering process. Using a general-purpose hydrocarbon resin for the insulator can lead to defects such as delamination of the shielding metal film from the insulator and resin leakage from the flat cable end face during heating. For this reason, currently, highly heat-resistant resins such as fluororesins and liquid crystal polymers are used as insulators in applications involving high-speed transmission of high frequencies.

[0012] Furthermore, in flat cables using copper wire as the conductor, only the same shape can be formed in the longitudinal direction, and in the case of flat cables with multiple conductors, it is difficult to form a bent shape while maintaining flatness. In addition, at the ends of the copper wire, the conductor wire is exposed from the resin insulator.

[0013] To address this phenomenon, thin wiring boards with triplate lines or microstrip lines using low-transmission-loss resins such as liquid crystal polymers have been proposed (see Patent Document 3). Because these wiring boards can form circuits similar to flexible wiring boards, multiple signal lines can be formed on a single wiring board, and are therefore expected to contribute to future mobile devices.

[0014] Thin wiring boards with triplate or microstrip lines using low-transmission-loss resins such as liquid crystal polymers have less complete shielding compared to coaxial cables, and ground stability is limited because the upper and lower grounds are connected by vias. Therefore, there are concerns regarding low transmission loss and EMI shielding for further increases in frequency and speed.

[0015] Even low-transmission-loss resins, such as liquid crystal polymers, are affected by ambient air. For example, polyimide, a low-dielectric resin, has excellent transmission characteristics, but its high moisture absorption rate means its transmission characteristics are affected by humidity, making it unsuitable for current RF circuit applications. In other words, thin printed circuit boards with triplate or microstrip lines require the selection of resins that are less affected by humidity, severely limiting the types of resins that can be used. As high-frequency applications advance, further stabilization of transmission characteristics will be required, necessitating the minimization of the effects of water vapor from the ambient air.

[0016] Polyimide and air-containing resins absorb moisture through the penetration of water vapor in the air, causing significant changes in their electrical properties. Therefore, they are difficult to use in current FFCs (Flat Flexible Cables), and fluoropolymers such as PTFE or liquid crystal polymers are primarily used. However, these resins are expensive, require high-temperature processing, and have poor adhesive properties, resulting in low productivity and limited application.

[0017] Flat cables for high-speed and high-frequency transmission require not only the inherent characteristics of flat cables, such as thinness and flexibility, but also to be transmission lines that are unaffected by moisture absorption from the outside air and have stable transmission characteristics, have a high electromagnetic shielding effect, have heat resistance to withstand soldering, are flame retardant, and can be manufactured using inexpensive materials with good productivity.

[0018] In response to the above requirements, a shielded, thin, flat cable has been proposed that has stable transmission characteristics unaffected by moisture absorption from the outside air, high electromagnetic shielding effect, can be soldered even when using a general-purpose resin with low heat resistance as an insulator, and can accommodate complex shapes, as well as a method for manufacturing the same (see Patent Document 8). Figure 1 is a diagram illustrating Patent Document 8, showing the structure of a shielded, thin, flat cable that is unaffected by the outside air due to moisture absorption, etc., and has stable electrical characteristics, and in which a thermoplastic resin with a low melting point can be used as an insulator for the transmission line.

[0019] Patent Document 8 proposes a shielded, thin, flat cable in which the conductor and insulator are covered with a metal film, thereby providing stable transmission characteristics unaffected by moisture absorption from the outside air, offering high electromagnetic shielding effects, allowing soldering even when using a general-purpose resin with low heat resistance as the insulator, and enabling the creation of complex shapes.

[0020] Flat cables using polyimide as an insulator, which are currently widely used, have poor alkali resistance, limiting their use, for example, around lithium-ion batteries. Liquid crystal polymers have better alkali resistance than polyimide, but it is not sufficient. Furthermore, PTFE, a representative fluororesin, is difficult to laminate, making it difficult to create a multilayer structure like the one shown in Figure 1. Flat cables using insulators with excellent alkali resistance are desired. [Prior art documents] [Patent Documents]

[0021] [Patent Document 1] Japanese Patent Publication No. 2011-71403 [Patent Document 2] Japanese Patent Publication No. 2017-188307 [Patent Document 3] International Publication No. WO2014 / 156422 [Patent Document 4] Japanese Patent Publication No. 2010-182576 [Patent Document 5] Japanese Patent Application Publication No. 5-242736 [Patent Document 6] International Publication WO2016 / 104066 [Patent Document 7] Japanese Unexamined Patent Application Publication No. 61-131306 [Patent Document 8] International Publication WO2020 / 195784 [Non-Patent Document]

[0022] [Non-Patent Document 1] Diatrend Co., Ltd., Glossary, Coaxial Cable [Summary of the Invention] [Problems to be Solved by the Invention]

[0023] Currently, flexible printed boards are frequently used for the wiring between components such as cameras and displays inside mobile devices including smartphones and the main board. On the other hand, coaxial cables are generally used for the RF part. In devices equipped with displays typified by smartphones, the displays tend to be larger, so in order to miniaturize and lighten smartphones, thinning in the thickness direction becomes important. However, it is difficult to thin coaxial cables, and recently, the thickness of coaxial cables has become an obstacle to the mounting design of devices. That is, in order to mount in a device with a limited thickness, it is necessary to thin the cable.

[0024] In mobile devices typified by smartphones, with the advancement of high functionality such as cameras and displays, the increase in the circuit scale of application processors accompanying the evolution of applications, and the increase in battery size accompanying the increase in transmission speed, it has become difficult to accommodate these functions and components inside a limited housing. On the other hand, the types of wireless handled by smartphones are also increasing, and the number of wirings connecting antennas to devices and the wirings connecting components to the main board is increasing.

[0025] To solve the above-mentioned problems, Patent Document 8 proposes a shielded thin flat cable and a method for manufacturing the same, which has stable transmission characteristics unaffected by moisture absorption from the outside air by covering the insulator surrounding the conductor with a metal film, has a high electromagnetic shielding effect, can be soldered even when a general-purpose thermoplastic resin with low heat resistance is used as the insulator, and can accommodate complex shapes.

[0026] When using a general-purpose thermoplastic resin with low heat resistance as an insulator, in the manufacturing of shielded thin flat cables, the resin flows out from the edges during the heat-sealing lamination process, resulting in large variations in the thickness of the flat cable. Furthermore, setting processing conditions is difficult, leading to low productivity.

[0027] To fabricate signal lines with low transmission loss, matching characteristic impedance is crucial. Therefore, the characteristic impedance of the signal line, via land, and conductor electrodes must be matched to the characteristic impedance of the conductor. In other words, the diameter of the signal line and via land must be as small as possible. However, general-purpose thermoplastic resins with low heat resistance are easily susceptible to dimensional changes and deformation due to thermal and mechanical stress. As a result, compared to thermosetting resins with high heat resistance such as polyimide and epoxy resins, the accuracy of layer alignment during processing is inferior, leading to larger diameters for the signal line and via land.

[0028] As described in Reference 8, when forming grooves in an insulator, if the laser absorption of the laser processing machine used to form the grooves is extremely low, the laser penetrates the general-purpose thermoplastic resin, which has low heat resistance, and is absorbed by the metal body, generating heat which causes the insulator to melt, resulting in the disadvantage that the desired shape cannot be obtained.

[0029] Laser processing is suitable for creating grooves, and infrared lasers are particularly suitable. When using ultraviolet or visible light lasers, the processing speed is slow and the laser beam life is short.

[0030] Carbon dioxide laser processing equipment allows for high-speed processing and is widely used in industrial production. For efficient carbon dioxide laser processing, the processing wavelength is mainly around 10 μm, so the insulator needs to absorb this wavelength. If the absorption efficiency is poor, processing may be possible by changing the processing conditions, but the processing time will be longer.

[0031] In the manufacturing of shielded, thin, flat cables in which an insulator surrounding a conductor is covered with a metal film, there is a need for a simple, highly productive method for manufacturing shielded, thin, flat cables that does not undergo shape changes due to lamination processes or laser processing.

[0032] Furthermore, there is a need for a manufacturing method for flat cables in which the characteristic impedance of the signal lines, via lands, conductor electrodes, and conductors are matched.

[0033] This disclosure provides a shielded thin flat cable and a method for manufacturing the same, which solve the above-mentioned problems, by providing a continuous metal film on the surface of an insulator surrounding a conductor. [Means for solving the problem]

[0034] The shielded thin flat cable according to this disclosure comprises a conductor made of metal, an insulator that sandwiches the conductor and surrounds the conductor except for conductor electrodes that are conductive from the conductor and exposed on the surface, and a metal film continuous with the surface of the insulator except around the conductor electrodes, wherein the melting point of the conductor, the inner electrode and a second film-like insulator bonded to the first film-like insulator surface on which the conductor and inner electrode conductive to the conductor electrodes are formed is 10°C or more lower than the melting point of the first film-like insulator, and the shielded thin flat cable comprises a third film-like insulator having a melting point equal to or higher than the melting point of the second film-like insulator on the opposite side of the surface of the second film-like insulator that sandwiches the conductor, wherein the first film-like insulator contains a syndiotactic polystyrene homopolymer and the second film-like insulator contains a syndiotactic polystyrene copolymer.

[0035] Furthermore, in the shielded thin flat cable according to the present disclosure, it is preferable that the first film-like insulator contains 20 parts by mass or more but less than 450 parts by mass of filler per 100 parts by mass of the syndiotactic polystyrene homopolymer, and the second film-like insulator contains 20 parts by mass or more but less than 450 parts by mass of filler per 100 parts by mass of the syndiotactic polystyrene copolymer, and the filler is one or more of amorphous silica, crystalline silica, hollow silica, black silica, silicic acid and its metal salts, glass, titanium oxide, aluminum nitride, carbon black, graphite, carbon nanotubes, titanium black, boron nitride, and mica.

[0036] Furthermore, in the shielded thin flat cable according to this disclosure, it is preferable that a plurality of shielded thin flat cables, each having the metal film continuously on the outer surface of the insulator surrounding the conductor, are integrally formed.

[0037] A method for manufacturing a shielded thin flat cable according to this disclosure involves laminating metal films to both sides of a first film-like insulator containing a syndiotactic polystyrene homopolymer, forming an inner layer electrode that conducts to a conductor and a conductor electrode that becomes an external terminal continuous with the conductor by performing a circuit formation step on the metal film on one side of the first film-like insulator, forming an opening for via hole drilling by performing a circuit formation step on the metal film on the other side, and then placing a syndiotactic polystyrene having a melting point 10°C or more lower than the melting point of the first film-like insulator on the conductor and the inner layer electrode formed on one side of the first film-like insulator. The method is characterized by laminating a second film-like insulator containing a lencopolymer, laminating a metal film to the other surface of the second film-like insulator, removing the metal film, the first film-like insulator, and the second film-like insulator from the other surface of the first film-like insulator, or rupturing the metal film on the other surface of the first film-like insulator, the first film-like insulator, the second film-like insulator, and the metal film on the other surface of the second film-like insulator, thereby forming the end face of the shielded thin flat cable to have the outer circumference shape of the shielded thin flat cable, and forming a metal film on the end face.

[0038] Furthermore, in the method for manufacturing a shielded thin flat cable according to the present disclosure, it is preferable to provide a third film-like insulator containing a syndiotactic polystyrene homopolymer having a melting point equal to or higher than that of the first film-like insulator on the opposite side of the conductor-side surface of the second film-like insulator.

[0039] Furthermore, in the method for manufacturing a shielded thin flat cable according to the present disclosure, a circuit formation step is performed on the metal film on one side of the first film-like insulator to form the conductor and the inner layer electrode that is conductive to the conductor electrode continuous with the conductor, and a circuit formation step is performed on the metal film on the other side to form the via hole opening of the intermediate product of the shielded thin flat cable, the second film-like insulator, the metal film, another second film-like insulator and the shielded thin flat cable on the conductor side of the first film-like insulator. Preferably, the conductors of other intermediate products of the cable are laminated simultaneously or sequentially with the other second film-like insulator on the side thereof, and a plurality of intermediate products of the shielded thin flat cable are integrated vertically, and a laser beam is shone on the upper and lower first film-like insulators of the shielded thin flat cable, removing the first film-like insulator and the second film-like insulator down to the metal film of the other shielded thin flat cable, and a metal film is formed on the wall surface of the groove formed by removing the first film-like insulator and the second film-like insulator.

[0040] Furthermore, in the method for manufacturing a shielded thin flat cable according to the present disclosure, a circuit formation step is performed on the metal film on one side of the first film-like insulator to form the conductor and the inner layer electrode that is electrically connected to the conductor electrode continuous with the conductor, and a circuit formation step is performed on the metal film on the other side to form the via hole opening, and the second film-like insulator, the metal film, another second film-like insulator, and the conductor of another intermediate product of the shielded thin flat cable are laminated on the conductor side of the first film-like insulator of the intermediate product of the shielded thin flat cable with the other second film-like insulator on the conductor side, and the upper and lower metal films, the first film-like insulator and the second film-like insulator are cut along the outer shape of the shielded thin flat cable in which a plurality of the shielded thin flat cable intermediate products are integrated vertically, and a metal film is formed on the end face of the formed shielded thin flat cable. [Effects of the Invention]

[0041] This disclosure provides a shielded, thin, flat cable with excellent shielding properties, high precision, high energy efficiency, and superior transmission characteristics, as well as a method for manufacturing the same. [Brief explanation of the drawing]

[0042] [Figure 1] The first embodiment of the present disclosure shows a shielded, thin, flat cable, where (A) is a perspective view. (B) is an enlarged perspective view of the terminal portion of the shielded, thin, flat cable. (C) is a perspective cross-sectional view of the conductor portion of the shielded, thin, flat cable. (B-1), (B-2), and (B-3) are plan views of the exposed terminal portion of the shielded, thin, flat cable, where (B-1) is a plan view of B, and (B-2) and (B-3) show other terminal portions. [Figure 2] This document shows the manufacturing process for a shielded, thin, flat cable according to Embodiment 1 of the present disclosure. [Figure 3] This shows the manufacturing process for conventional shielded, thin, flat cables. [Figure 4] This document shows the manufacturing process for a shielded, thin, flat cable according to Embodiment 2 of the present disclosure. [Figure 5] This shows the inner layer electrodes of a shielded, thin, flat cable according to an embodiment of the present disclosure. [Figure 6] This shows a manufacturing process for a conventional shielded, thin, flat cable, specifically the step of cutting the insulation. [Figure 7] This shows the structure of a conventional shielded, thin, flat cable. [Figure 8] This shows part of the manufacturing process for a shielded, thin, flat cable according to Embodiment 3 of the present disclosure. [Figure 9] This shows the structure of a shielded, thin flat cable in which multiple thin flat cables are integrated horizontally according to Embodiment 4 of the present disclosure. [Figure 10] This shows the structure of a shielded, thin, flat cable in which multiple shielded, thin, flat cables are integrated in the horizontal and vertical directions according to Embodiment 5 of the present disclosure. [Figure 11] This invention illustrates a manufacturing process for a shielded, thin, flat cable in which multiple shielded, thin, flat cables are integrated horizontally according to Embodiment 4 of this disclosure. [Figure 12] This invention illustrates a manufacturing process for a shielded, thin, flat cable in which multiple shielded, thin, flat cables are integrated horizontally and vertically according to Embodiment 5 of this disclosure. [Figure 13] This invention shows a shielded, thin, flat cable having conductive electrodes provided on the end faces of a shielded, thin, flat cable according to Embodiment 6 of this disclosure. [Figure 14] This invention illustrates the manufacturing process of a shielded thin flat cable in which the conductor electrodes of the shielded thin flat cable according to Embodiment 6 of this disclosure are provided on the end faces. [Figure 15]This shows a shielded, thin, flat cable according to Embodiment 6 of the present disclosure, in which the shielded, thin, flat cable has two conductors and the conductor electrodes are provided on the end faces. [Figure 16] This shows part of the manufacturing process for a shielded, thin, flat cable according to Embodiment 4 of the present disclosure. [Figure 17] This shows part of the manufacturing process for a shielded, thin, flat cable according to Embodiment 5 of the present disclosure. [Modes for carrying out the invention]

[0043] (Embodiment 1) Figure 1 shows a shielded thin flat cable 101 according to Embodiment 1 of the present disclosure, where (A) is a perspective view. (B) is an enlarged perspective view of the terminal portion 103 of the shielded thin flat cable 101. (C) is a perspective cross-sectional view of the conductor portion 102 of the shielded thin flat cable 101 where the conductor 204 is located. (B-1), (B-2), and (B-3) are plan views of the terminal portion 103 of the shielded thin flat cable, where (B-1) is a plan view of B, and (B-2) and (B-3) show other terminal portions 103.

[0044] In addition to its inherent characteristics of being thin and flexible, and having low transmission loss, flat cables are required to meet the following requirements: They must be transmission lines with stable physical and electrical properties, free from the influence of external elements such as moisture absorption; they must have high electromagnetic shielding properties; they must have heat resistance to withstand soldering; they must be flame-retardant; they must have excellent chemical resistance; and they must be easy to process, highly productive, and allow the use of inexpensive materials. Transmission characteristics are particularly important for flat cables used for high-frequency and high-speed transmission.

[0045] The shielded thin flat cable 101 according to this disclosure has a conductor 204 made of metal, an insulator 106 that sandwiches the conductor 204 and surrounds the conductor 204 except for the conductor electrode 105 that is electrically conductive from the conductor 204 and exposed on the surface, and a metal film 202 that is continuous with the surface of the insulator 106 except around the conductor electrode 105.

[0046] As shown in Figure 1(A), the shielded thin flat cable 101 consists of a terminal section 103 equipped with a conductor electrode 105 through which the conductor 204 conducts, and a conductor section 102 in which the conductor 204 resides. The terminal section 103 consists of a conductor electrode 105 that conducts to the conductor 204, an exposed insulator 106 that does not have a metal film 202 around the conductor electrode 105, and a metal film 202 that is continuously provided on the surface of the insulator 106 other than the exposed insulator 106 that does not have a metal film 202. The conductor section 102 consists of a conductor 204, an insulator 106 that surrounds the conductor 204, and a metal film 202 that is continuously provided on the surface of the insulator 106.

[0047] As shown in Figure 1(B), the short-side end face of the shielded thin flat cable 101 also has a metal film 202. As shown in Figure 1(C), the shielded thin flat cable 101 has a conductor 204 that conducts electricity, and the insulator 106 surrounds the conductor 204 except for the conductor electrode 105 that is exposed on the surface of the shielded thin flat cable 101, and the metal film 202 is continuous on the surface of the insulator 106 except around the conductor electrode 105.

[0048] The metal film 202 is provided continuously in the short and long directions of the shielded thin flat cable 101. It is also provided continuously on the end face in the long direction. The continuous provision of the metal film 202 helps to suppress thermal deformation of the insulator 106, defects due to peeling, and the influence of water vapor from the outside air on the electrical properties of the conductor 204. It is acceptable for the metal film 202 not to be provided on a portion of the surface of the insulator 106 to the extent that there is no impairment of the shielding properties of the conductor 204, no impairment of electrical properties, no deformation of the insulator 106, and no peeling of the insulator 106 and the metal film 202.

[0049] To enhance the shielding of the conductor 204 of the shielded thin flat cable 101, it is preferable that the metal film 202 be provided on the entire surface of the insulator 106 except around the conductor electrode 105. The metal film 202 is not provided around the conductor electrode 105. The periphery must have a gap sufficient to prevent electrical conductivity between the end of the conductor electrode 105 and the end of the metal film 202. It is preferable that the area of ​​the surface of the insulator 106 that is not covered by the metal film 202 is small. Furthermore, since the adhesion strength between the metal film 202 and the insulator 106 decreases with heat and they are prone to peeling, it is desirable that the longitudinal and transverse end faces of the shielded thin flat cable 101 be covered by the metal film 202 without exposing the insulator 106. The longitudinal and transverse end faces are covered with the metal film 202, and it is preferable that the metal film 202 covers 95% or more of the surface of the insulator 106.

[0050] The portion of the insulator 106 that is not provided with a metal film 202 around the conductor electrode 105 is exposed to the outside air. It is important to minimize the area of ​​the exposed portion of the insulator 106 around the conductor electrode 105. If the exposed area is large, the insulator 106 may absorb moisture from water vapor in the outside air, and the transmission characteristics may deteriorate due to the effects of moisture absorption.

[0051] The insulator 106 encloses the conductors 204 other than the conductor electrodes 105, and the surface of the insulator 106, excluding the area around the conductor electrodes 105, has a continuous metal film 202. In other words, by having the metal film 202 not only on the upper and lower flat surfaces of the shielded thin flat cable 101, but also on the longitudinal and transverse end faces, the protective function of the metal film 202 suppresses the influence of the outside air on the shielded thin flat cable 101, allowing it to maintain its transmission characteristics for a long period of time.

[0052] A conventional flat cable is shown in Figure 7. The flat cable does not have a metal film 202 on its longitudinal and transverse end faces. In such a flat cable, the insulator 106 may absorb moisture from the ambient air, and the transmission characteristics may deteriorate due to the effects of moisture absorption. In addition, due to moisture absorption, the adhesion strength between the metal film 202 and the insulator 106 may decrease due to heat such as that generated during soldering reflow, which may cause delamination or melting deformation of the insulator 106.

[0053] The distance between the end of the conductor electrode 105 and the end of the metal film 202 is 10 μm or more and 1000 μm or less. The insulator 106 is exposed in this space. If the distance is less than 10 μm, there is a risk of electrical conductivity between the end of the conductor electrode 105 and the end of the metal film 202. If the distance exceeds 1000 μm, there is a risk that water vapor from the outside air will penetrate more into the insulator 106, potentially degrading the transmission characteristics and heat resistance. In addition, the shielding properties of the conductor 204 may be impaired. Furthermore, there is a risk that the insulator 106 may melt and change shape during thermal processes such as reflow. The distance between the end of the conductor electrode 105 and the end of the metal film 202 may be equally spaced around the conductor electrode 105 or may be different.

[0054] Figures 1(B-1), (B-2), and (B-3) show plan views of the terminal section 103. (B-1) shows the case where the conductor electrode 105 in Figure 1(B) is circular. (B-2) shows the case where the conductor electrode 105 is rectangular and there are multiple electrodes. (B-3) shows the case where the conductor electrode 105 is rectangular and is provided at the ends of the longitudinal plane of the shielded thin flat cable 101. The metal film 202 is provided along the shape of the conductor electrode 105 and not around the conductor electrode 105. The shape of the conductor electrode 105 can be anything. Also, multiple conductor electrodes 105 may be provided on a single conductor 204. The metal film 202 is used as ground.

[0055] As shown in Figure 2(G), in the terminal section 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and via hole 208. The conductor electrode 105 is for connecting to external elements, etc., and is used as a connector connection terminal, SMT soldering electrode, soldering terminal for fixing connectors, terminal for ACF (Anisotropic Conducting Film) connection, etc. To achieve the above purpose, the surface of the conductor electrode 105 may be subjected to surface treatment such as solder coating, gold plating, tin plating, silver plating, OSP (Organic Solderability Preservatives), etc., as needed. The area around the conductor electrode 105 is constructed such that there is no electrical conductivity between the metal film 202 and the conductor electrode 105, by an insulator 106 on which the metal film 202 is not formed.

[0056] The shielded, thin, flat cable 101 according to this disclosure has an insulator 106 that protects the conductor 204, and a metal film 202 that protects the insulator 106. The metal film 202 shields the conductor 204.

[0057] The metal film 202, which is continuously provided on the surface of the insulator 106 except around the conductor electrode 105, prevents water vapor and chemicals from penetrating into the insulator 106 from the outside. Furthermore, in the event of a flame directed at the shielded 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.

[0058] The insulator 106 comprises syndiotactic polystyrene and / or a laser light absorber, and when the insulator 106 has a thickness of 50 μm, the minimum transmittance of light with wavelengths of 0.8 μm or more and 11.0 μm or less is 85% or less. Laser processing is possible even if it exceeds 85%, but for efficient processing, it is preferably 60% or less, and more preferably 30% or less.

[0059] The insulator 106 includes a resin containing syndiotactic polystyrene, a laser light absorber, a filler, additives, etc. Preferably, 70% or more by mass of the resin is syndiotactic polystyrene. Syndiotactic polystyrene is a polymer composed of styrene monomers, and may contain monomers other than styrene monomers. The styrene in the polymer has a syndiotactic structure.

[0060] As shown in Figure 2(C), the insulator 106 may consist of a first film-like insulator 106A on which the conductor 204 is formed and a second film-like insulator 106B laminated on the conductor 204 side.

[0061] The first film-like insulator 106A shown in Figure 2(C) contains 70% by mass or more of syndiotactic polystyrene homopolymer, which is a polymer of styrene, as the resin component. The second film-like insulator 106B contains 70% by mass or more of syndiotactic polystyrene copolymer as the resin component.

[0062] Syndiotactic polystyrene copolymer is a copolymer of styrene and other monomers. Preferably, the copolymer contains at least one of the following monomers in an amount of 1% by mass or more and less than 40% by mass: olefin monomers such as ethylene, α-olefins other than ethylene, and cyclic olefins; diene monomers such as 1,3-butadiene, chloroprene, isoprene, and 1,3-hexadiene; vinylstyrene such as divinylbenzene and divinyltoluene; and styrene monomers such as o-methylstyrene, m-methylstyrene, and p-methylstyrene. If the amount is less than 1% by mass, the melting point will not decrease, and if it is 40% by mass or more, the adhesive strength with syndiotactic polystyrene homopolymer will decrease, making it difficult to process.

[0063] The first film-like insulator 106A and the second film-like insulator 106B preferably contain less than 30% by mass of a resin component, such as polybutadiene, polyphenylene ether, fluororesin, or liquid crystal polymer, in order to improve adhesion, flexibility, and processability. If the resin content is 30% by mass or more, it becomes difficult to form the film, and the strength of the film decreases, making it more prone to breakage.

[0064] Since the first film-like insulator 106A and the second film-like insulator 106B are laminated by thermocompression bonding, unstretched films are preferable. Stretched films have poor adhesion when heat-compressed.

[0065] The melting point of the second film-like insulator 106B is at least 10°C lower than the melting point of the first film-like insulator 106A. The first film-like insulator 106A contains at least 70% by mass of syndiotactic polystyrene homopolymer as its resin component, while the second film-like insulator 106B contains at least 70% by mass of syndiotactic polystyrene copolymer. Due to the difference in melting points between syndiotactic polystyrene homopolymer and syndiotactic polystyrene copolymer, the melting point of the second film-like insulator 106B can be made at least 10°C lower than that of the first film-like insulator 106A.

[0066] Since syndiotictactic polystyrene homopolymer and syndiotictactic polystyrene copolymer have low absorbance depending on the wavelength of the laser light, it is preferable to include a laser light absorber as a filler in the insulator 106.

[0067] The laser light absorber contained in the insulator 106 is preferably amorphous silica, crystalline 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, carbon nanotubes, titanium black, boron nitride, or mica.

[0068] Furthermore, it is even more preferable that the laser light absorber used in the insulator 106 is one or more of amorphous silica, crystalline silica, hollow silica, black silica, silicic acid and its metal salts, glass, titanium oxide, aluminum nitride, carbon black, graphite, carbon nanotubes, titanium black, boron nitride, or mica, as long as the dielectric properties do not deteriorate. In addition, the insulator 106 can be appropriately blended with additives such as viscosity modifiers, lubricants, and flame retardants, in addition to the resin and fillers, as long as the dielectric properties do not deteriorate.

[0069] As shown in Figure 8(A), a third film-like insulator 106C may be provided on the side of the second film-like insulator 106B opposite to the first film-like insulator 106A. The third film-like insulator 106C is not particularly limited as long as it has a melting point equivalent to or higher than that of the second film-like insulator 106B, but considering electrical properties and adhesion, it is preferable that it be one or more of syndiotictac polystyrene homopolymer, syndiotictac polystyrene copolymer, polyphenylene ether, liquid crystal polymer, and polyimide. Furthermore, considering the warping of the shielded thin flat cable 101, it is even more preferable that it be one or more of syndiotictac polystyrene homopolymer and syndiotictac polystyrene copolymer.

[0070] The thickness of the insulator 106 is preferably between 10 μm and 1000 μm. More preferably between 30 μm and 500 μm. If it is thinner than 10 μm, interlayer insulation failure occurs between the conductor 204 and the metal film 202, and it becomes difficult to control the line width for impedance matching. If it is thicker than 1000 μm, the laser processing speed for forming grooves in the insulator 106, as described later, becomes extremely slow.

[0071] By including syndiotactic polystyrene in the insulator 106, a shielded, thin, flat cable 101 can be manufactured inexpensively. However, because syndiotactic polystyrene does not readily absorb laser light with wavelengths between 0.8 μm and 11.0 μm, it is difficult to remove the insulator 106 and form grooves by irradiating the surface of the insulator 106 with laser light. However, by including a laser light absorber in the insulator 106, grooves can be formed by laser light irradiation. When the insulator 106 has a thickness of 50 μm, the laser light absorber is included in the insulator 106 such that the minimum transmittance of light with wavelengths between 0.8 μm and 11.0 μm is 85% or less. If the transmittance is 85% or higher, groove formation by laser light irradiation becomes difficult or takes a long time.

[0072] The conductor 204 should be made of a material with good electrical conductivity, and gold, silver, copper, or aluminum are particularly preferred. Considering flexibility and conductivity, copper is the most preferred. If the conductor 204 is not gold or silver, it may be gold-plated or silver-plated.

[0073] The width of the conductor 204 is preferably 0.01 mm to 10 mm, and more preferably 0.02 mm to 5 mm. If the conductor width is less than 0.01 mm, it is difficult to control the dimensional accuracy of the finished width of the conductor 204. Therefore, impedance matching is difficult and it is not suitable as a conductor. Also, if the width of the conductor 204 is less than 0.01 mm, the conductor loss becomes large and it is not suitable as a transmission line. Conversely, if the width of the conductor 204 exceeds 10 mm, the thickness of the insulator 106 required to obtain the desired characteristic impedance becomes thicker, making it unsuitable for shielded thin flat cables 101 where thinness is a priority.

[0074] The width of the conductor 204 significantly affects the transmission characteristics, therefore, precise control of its width is necessary. Furthermore, to improve the line width accuracy of the conductor 204, the Modified Semi Additive Process (MSAP) can be used. To further improve transmission characteristics, if the conductor 204 is not made of gold or silver, it may be gold-plated or silver-plated. Since the shielded thin flat cable 101 according to this disclosure has a strip line structure, the characteristic impedance of the conductor 204 is determined by the conductor width, conductor thickness, insulator thickness, dielectric constant of the insulator, etc. To obtain the desired impedance, the width of the conductor 204 is usually adjusted.

[0075] The thickness of the conductor 204 is preferably between 1 μm and 75 μm. Due to conductor loss and the skin effect, electrical signals are not efficiently transmitted if the thickness is less than 1 μm. Also, if the thickness is less than 1 μm, there is a high possibility of the conductor 204 breaking when bent. If the thickness exceeds 75 μm, it becomes difficult to achieve width accuracy when manufacturing the conductor 204, and the insulator 106 that surrounds the conductor 204 becomes thicker, making it unsuitable for shielded thin flat cables 101 where thinness is a priority.

[0076] The metal film 202 of the shielded thin flat cable 101 is made of a metal with good electrical conductivity, preferably gold, silver, copper, or aluminum, with copper being the most suitable. Considering flexibility and conductivity, copper is the most suitable. The metal film 202 on the flat top and bottom surfaces of the shielded thin flat cable 101 can be made of copper foil, but the longitudinal and transverse end faces of the shielded thin flat cable 101 are preferably made of copper formed by plating. The electrical resistivity of the metal film 202 is preferably 1 μΩ·m or less. To add functions such as oxidation prevention and noise reduction, the metal film 202 may be made of a combination of dissimilar metals; for example, nickel, zinc, chromium, or an iron-based alloy can be formed on the outside of the copper film.

[0077] The thickness of the metal film 202 is preferably 3 μm to 100 μm. If it is less than 3 μm, pinholes and scratches will occur, and the internal barrier properties cannot be maintained, preventing the metal film 202 from melting during laser processing and forming linear grooves 206. Also, cracks will form in the metal film 202 due to the expansion of the insulator 106 during heating. Furthermore, if it exceeds 100 μm, the processing of forming linear grooves 206 and holes 207 as via holes becomes complicated and time-consuming. If the metal film 202 is formed by plating, the plating time will be long, causing problems in the manufacturing process such as warping of the work plate.

[0078] The planar distance between the conductor 204 and the metal film 202 is 20 μm or more. If it is less than 20 μm, there is a possibility of a short circuit between the conductor 204 and the metal film 202. The vertical distance between the conductor 204 and the metal film 202 is 10 μm or more and 700 μm or less. If it is less than 10 μm, there is a possibility of a short circuit, and if it exceeds 700 μm, it will take a long time to form the linear groove 206 in the insulator 106 using a laser.

[0079] As shown in Figure 2(G), at terminal 103, the conductor 204 is connected to the conductor electrode 105 via the inner layer electrode 214 and via hole 208. The electrical signal enters from one conductor electrode 105, passes through the via hole 208, the inner layer electrode 214, the conductor 204, the opposite inner layer electrode 214, the opposite via hole 208, and the opposite conductor electrode 105, transmitting the electrical signal to the other.

[0080] As shown in Figure 5(A), the inner layer electrode 214 is formed continuously from the conductor 204. Therefore, its thickness and material are the same as those of the conductor 204. In order to connect the conductor electrode 105 with the via hole 208, the inner layer electrode 214 is made to be equal to or larger than the diameter of the cylindrical via hole 208, as shown in Figure 5(B). The shape of the inner layer electrode 214 is preferably circular, but any shape is acceptable as long as it is equal to or larger than the cross-section of the via hole 208. Auxiliary shapes such as teardrops may also be added. In the case of a circular shape, the diameter is usually between 50 μm and 2 mm. A diameter of 100 μm or more and 800 μm or less is even more preferable. If the diameter is less than 50 μm, it is difficult to align the inner layer electrode 214 with the via hole 208, and if it exceeds 2 mm, it becomes difficult to match the characteristic impedance. The characteristic impedance matching of the signal line is required, and matching the characteristic impedance of the inner layer electrode 214 and the conductor 204 is difficult. Therefore, it is necessary to achieve characteristic impedance matching by making the diameter of the inner layer electrode 214 as small as possible.

[0081] The via hole 208 is formed by removing the insulator 106 from the location where the conductive electrode 105 is formed to the inner layer electrode 214 by laser irradiation, and then plating the hole 207 formed as a via hole after the insulator 106 has been removed. Therefore, the cross-section is approximately circular in shape. Plating is preferably done with copper.

[0082] Figure 2 shows the manufacturing method for the shielded thin flat cable 101 according to this disclosure. The shielded thin flat cable 101 sandwiches a conductor 204 made of metal, and is provided with an insulator 106 that surrounds the conductor 204 except for the conductor electrode 105 that is electrically conductive from the conductor 204 and exposed on the surface, and a metal film 202 is provided continuously on the surface of the insulator 106 except around the conductor electrode 105.

[0083] Figure 2 shows the manufacturing process for a shielded, thin, flat cable according to Embodiment 1 of the present disclosure.

[0084] Figure 2(A) shows a laminated sheet of metal film 202 and insulator 106, in which metal films 202A and 202B are bonded to both sides of an insulator 106A (hereinafter referred to as film-like insulator 106A) containing a film-like syndiotictac polystyrene homopolymer. The film-like insulator 106A and the metal films 202A and 202B are bonded by heat pressing, but pretreatment may be performed before bonding to improve adhesion strength. For example, the film-like insulator 106A may be subjected to plasma treatment, corona treatment or UV treatment, or the bonding side of the metal films 202A and 202B may be subjected to primer treatment or plasma treatment. Bonding is also possible by dry lamination using an adhesive. Furthermore, it is also possible to bond the two metal films 202 by extruding the molten film-like insulator 106A onto one of the metal films 202 while pressing the other metal film 202 onto it.

[0085] Metal foil is used for metal films 202A and 202B, and it is preferable that metal foil is used for metal film 202 used for lamination. Copper foil is particularly preferred.

[0086] Figure 2(B) shows a circuit formation process in which the metal film 202B is used as the conductor 204 and the inner layer electrode 214, and the metal film 202A is used as the metal film 202 formed on the outer surface of the conductor electrode 105 and the insulator 106. Here, by removing a portion of the metal film 202A, a via hole opening 209 and a groove formation opening 212 are formed.

[0087] The circuit formation process can utilize methods commonly used in the manufacture of printed circuit boards. For example, by following steps such as etching mask formation, exposure, development, etching, and etching mask removal, the conductor 204 and inner layer electrodes 214 are formed by leaving the necessary metal film 202B, and the metal film 202 is formed on the surface of the conductor electrode 105 and insulator 106 by leaving the metal film 202A. By removing a portion of the metal film 202A, via hole openings 209 and groove openings 212 are formed.

[0088] Figure 2(C) shows the process of laminating a film-like insulator 106B (hereinafter referred to as "film-like insulator 106B") containing a film-like syndiotictac polystyrene copolymer and a metal film 202C onto a film-like insulator 106A, a formed conductor 204, and an inner layer electrode 214. The lamination of the film-like insulator 106A, the film-like insulator 106B, and the metal film 202C is performed by thermocompression bonding. The conductor 204 and the inner layer electrode 214 are sandwiched between the film-like insulator 106A and the film-like insulator 106B. It is preferable to perform the thermocompression bonding under vacuum conditions.

[0089] It is preferable that the metal film 202C be made of the same metal as the metal film 202A. The laminate can be formed by laying up the film-like insulator 106A, the film-like insulator 106B, and the metal film 202C in that order, either simultaneously or sequentially. Figure 2(D) shows a laminate formed by laminating the film-like insulator 106A, the film-like insulator 106B, and the metal film 202C.

[0090] Figure 2(E) shows the process of forming linear grooves 206 and via holes 207 parallel to the conductor 204 along both sides of the conductor 204 and the inner layer electrode 214. To form the linear groove 206, the insulator 106 exposed to the groove-forming opening 212 is removed. The insulator 106 is removed linearly, leaving the metal film 202C on the other side without penetrating the metal film 202A on one side in contact with the insulator 106, thereby forming the linear groove 206.

[0091] The formation of the via hole 207 involves removing the insulator 106 exposed at the via hole opening 209 down to the inner layer electrode 214 without penetrating the metal film 202A.

[0092] The linear grooves 206 and the holes 207 as via holes are formed using, for example, a device equipped with a laser processing machine, a plasma processing machine, or a sandblaster. A laser processing machine is preferred due to its high processing speed. By forming the linear grooves 206, the insulator 106 is exposed on the wall surface 205.

[0093] The wavelengths of laser light used in laser processing machines are as follows: excimer lasers have a wavelength of 0.248 μm, UV lasers have a wavelength of 0.355 μm, green lasers have a wavelength of 0.532 μm, near-infrared lasers around 1 μm, such as YAG lasers and fiber lasers, have a wavelength of 1.064 μm, and far-infrared lasers around 10 μm, such as carbon dioxide lasers, have wavelengths of 9.4 μm and 10.6 μm. Excimer lasers, UV lasers, and green lasers with wavelengths from 0.25 μm to 0.60 μm are collectively referred to as UV-visible lasers. In this disclosure, deep cutting of the insulator 106 is necessary to form linear grooves 206 in the insulator 106. With UV-visible lasers, the speed of deep cutting is significantly slow. Near-infrared and far-infrared lasers have a faster processing speed and their use is preferred.

[0094] The selection of a laser processing machine requires consideration of matching the absorption wavelength of the insulator 106. In particular, YAG lasers, fiber lasers, and carbon dioxide laser processing machines are widely used because they offer high resin processing speeds, and are therefore preferred laser processing machines in this disclosure. The laser processing machine according to this disclosure preferably uses a UV / visible light laser with a wavelength of 0.25 μm to 0.6 μm, a near-infrared laser with a wavelength of around 1 μm, or a far-infrared laser with a wavelength of around 10 μm.

[0095] Many resins absorb UV and visible light lasers, eliminating the need for laser light absorbers. However, if the absorbance is low, adding a small amount of coloring pigment can increase the absorbance and speed up processing. A suitable amount is 10 mass percent or less, as this does not affect the electrical properties.

[0096] When the thickness of the insulator 106 exceeds 50 μm, the processing speed rapidly slows down due to the principle of UV-visible lasers, resulting in decreased productivity. While UV-visible laser processing is superior for insulator 106 thicknesses up to 50 μm, it is unsuitable for thicknesses greater than that. UV-visible lasers can be used if the insulator 106 thickness is less than 50 μm. By adding a coloring pigment, it can be used even when the thickness of the insulator 106 exceeds 50 μm. The amount of coloring pigment added can be increased to speed up the processing.

[0097] The insulator 106 contains a laser light absorber, and when the insulator 106 has a thickness of 50 μm, it is preferable that the minimum transmittance of light with wavelengths of 0.2 μm or more and less than 0.8 μm is 60% or less. A colored pigment can be used as the laser light absorber for wavelengths of 0.2 μm or more and less than 0.8 μm.

[0098] Coloring pigments include cyanine blue, cyanine green, ochre, red iron oxide, permanent red, carbon black, titanium dioxide, and zinc oxide. Organic compounds such as benzotriazole, benzophenone, and cyanoacrylate are also suitable as laser light absorbers with wavelengths between 0.2 μm and 0.8 μm.

[0099] Processing with UV and visible light lasers, by using both long and short pulses, results in a smooth surface and a clean shape, thus producing a high-quality finish.

[0100] Near-infrared lasers, such as YAG lasers or fiber lasers, and far-infrared lasers, such as carbon dioxide lasers, offer fast processing speeds and excellent productivity even with thick insulators 106. However, syndiotictac polystyrene homopolymer and syndiotictac polystyrene copolymer hardly absorb light with wavelengths from approximately 0.8 μm to 11 μm, making it impossible to form linear grooves 206 with far-infrared lasers. Therefore, it is necessary to incorporate a laser light absorber into the insulator 106. By including a laser light absorber in the insulator 106, linear grooves 206 can be formed using near-infrared and far-infrared laser light.

[0101] By including a laser light absorber in the insulator 106, the speed at which linear grooves 206 are formed by near-infrared and far-infrared laser light can be increased, thereby improving the smoothness and dimensional accuracy of the processed surface. When the insulator 106 containing the laser light absorber has a thickness of 50 μm, the minimum transmittance of light with wavelengths of 0.8 μm or more and 11.0 μm or less must be 60% or less.

[0102] Figure 2(E) is a cross-sectional view of the area where the conductor electrode 105 is formed. Figure 6(A) is a top view of Figure 2(E), showing the approximate positional relationship when forming the linear groove 206 and the holes 207 as via holes. The formation of the linear groove 206 is an important step in this disclosure because it determines the outer periphery of the shielded thin flat cable 101 and forms all end faces, including the longitudinal and transverse sides.

[0103] Figure 6(B) shows the state after the linear grooves 206 have been formed by laser processing and cutting using a combination of cutting tools and router bits. The white areas in the linear grooves 206 indicate the areas where cutting was performed. Figure 6(A) shows all the linear grooves 206 formed by laser processing. Figure 6(Aa) is a cross-sectional view of Figure 6(A) in direction a. The metal film 202C is not penetrated. This is the same as in Figure 2(E). Figures 6(Bb) and (Bc) are cross-sectional views of Figure 6(B) in directions b and c, respectively. If the linear grooves 206 are cut with a cutting tool, the metal film 202C will also break. If the individual pieces are separated at this stage, the subsequent metal plating process will become complicated. Furthermore, it will become impossible to manufacture the shielded thin flat cable 101 as an assembly, hindering productivity. Therefore, the metal film 202C needs to be left at least partially intact in order to fix the individual pieces, and laser processing is suitable for leaving the metal film 202C intact.

[0104] Figure 2(F) shows the steps of forming a metal film 202D in the linear groove 206 in the state shown in Figure 2(E), and forming a metal body in the holes 207 which serve as via holes, and providing via holes 208 for drawing conductivity from the conductor 204. In the step of forming the metal film 202D in the linear groove 206, the metal film 202D is formed on the wall surface 205 of the linear groove 206. In addition, the formation of the metal body in the via holes 208 involves covering the via holes 208 with metal. Metal plating is suitable for forming the metal film 202D and the metal body in the via holes 208. Typically, the exposed portion of the inner layer electrode 214 at the bottom of the metal film 202A and the holes 207 which serve as via holes is cleaned, the surface other than the insulator 106 is made conductive, and then metal plating is performed. The metal plating that forms the metal film 202D forms a metal film 202 that continuously covers the entire outer surface of the shielded thin flat cable 101 of this disclosure.

[0105] Typically, metal plating involves desmearing, catalyst formation, electroless plating, and electroplating in that order. Desmearing is necessary if smear and other foreign matter remain on the metal film surface, but is unnecessary if the metal film surface is clean. Desmearing can be performed using a dry method with plasma or a wet method with an oxidizing agent such as permanganate, but in this disclosure, the dry method is superior from the viewpoint of preventing water absorption. Catalyst formation, electroless plating, and electroplating can be performed using chemical systems from companies such as ATOTECH, JCU Corporation, DOW CHEMICAL, Uemura Industries Co., Ltd., Okuno Pharmaceutical Co., Ltd., and MacDermid Enson. Furthermore, to minimize moisture absorption, instead of wet catalyst formation, a metal film 202 may be continuously formed on the surface of the insulator 106 using a dry method such as sputtering. Additionally, as a method of conductivity, the Black Hole System from MacDermid Japan can be used instead of catalyst formation and electroless plating.

[0106] Figure 2(G) shows the process of removing a portion of the metal film 202A shown in Figure 2(F). This process involves removing a portion of the metal film 202A to form a gap 218 between the conductor electrode 105 and the metal film 202A. The metal film 202A is removed around the area that will become the conductor electrode 105 to form the gap 218. The area to be removed is such that the end of the conductor electrode 105 formed by the removal and the end of the metal film 202A that will become the metal film 202 do not conduct electricity.

[0107] The removal of the metal film 202A can be carried out using a circuit formation process similar to that used for forming the conductor 204 in Figure 2(B). Specifically, unwanted portions of the metal film 202A can be removed through steps such as etching mask formation, resist layer formation, exposure, development, etching, and etching mask removal, thereby forming the desired shape.

[0108] Figure 2(H) shows the process of forming a solder mask 211, which serves as an insulating layer, on the surface of the metal film 202 of the laminate shown in Figure 2(G), and then cutting the metal film 202C into individual pieces. The solder mask 211 can be provided with openings as needed to expose the conductive electrodes 105. The solder mask can be formed using methods commonly used in printed circuit board manufacturing. Specifically, methods such as forming solder mask ink by photographic or silkscreen printing, or forming a film-like solder mask by printing can be used. Examples of solder mask inks include the PSR series from Taiyo Ink Mfg. Co., Ltd., the PAF series and DSR series from Tamura Corporation, and the SPSR series from Sanwa Chemical Industries, Ltd. As for film-like solder masks, Raytec from Hitachi Chemical Co., Ltd. and the PSR series from Taiyo Ink Mfg. Co., Ltd. can be used. It is also possible to form the solder mask on the surface of the exposed insulator 106. Alternatively, the cutting process may be carried out without forming the solder mask 211.

[0109] The shielded thin flat cable 101 is separated into individual pieces by cutting the metal film 202C along the linear groove 206. The cutting for separating the pieces can be done using methods for cutting flexible printed circuit boards, and commonly, this includes cutting with a die, cutting with a router, and cutting with a laser cutter. This disclosure offers good work efficiency because it allows for the manufacture of a shielded thin flat cable 101 in a bundle and then separating it into individual pieces.

[0110] Manufacturing a bundle of shielded thin flat cables 101 means that, as shown in Figure 2, a large number of longitudinally shielded thin flat cables 101 are formed in parallel rows and then separated into individual cables, thereby obtaining a large number of shielded thin flat cables 101 simultaneously. Alternatively, the longitudinally shielded thin flat cables 101 may be formed in series rows.

[0111] While it is conceivable to form a gap 218 as shown in Figure 2(J) during the process shown in Figure 2(B), the gap 218 would also be metal-plated during the process of forming a metal film 202D on the wall surface 205 of the linear groove 206 shown in Figure 2(F), and the plating process of forming a metal body in the holes 207 that serve as via holes. Therefore, forming a gap 218 as shown in Figure 2(J) during the circuit formation process shown in Figure 2(B) is inconvenient.

[0112] Figure 3 shows a process different from that in Figure 2. In Figure 3(A), metal films 202A and 202B are bonded to both sides of a film-like insulator 106A, similar to Figure 2(A). In Figure 3(B), a conductor 204 and an inner layer electrode 214 are formed, and unlike Figure 2(B), groove-forming openings 212 and via-hole drilling openings 209 are not formed. In Figure 3(C), a film-like insulator 106B and a metal film 202C are bonded sequentially onto the film-like insulator 106A and the formed conductor 204 and inner layer electrode 214. Figure 3(D) shows the laminate obtained by the process in Figure 3(C). In Figure 3(E), groove-forming openings 212 and via-hole drilling openings 209 are provided in the metal film 202C by the circuit formation process. In Figure 3(F), linear grooves 206 and holes 207 as via holes are formed. Figure 3(G) shows the process of forming a metal film 202D on the wall surface 205 of the linear groove 206, and the process of forming a metal body in the hole 207 which serves as a via hole. Figure 3(H) shows the formation of a gap 218.

[0113] It appears that a shielded thin flat cable 101 can be obtained by the process in Figure 3, similar to that in Figure 2. As shown in Figure 2(B), by performing the circuit formation process simultaneously on both sides of a single laminate, the positions of the front and back can be precisely aligned. The inner layer electrodes 214 and the via hole openings 209 must be precisely aligned. If the positions of the inner layer electrodes 214 and the via hole openings 209 are not aligned, the inner layer electrodes 214 and the conductor electrodes 105 will not conduct electricity. In the method in Figure 3, the formation of the inner layer electrodes 214 and the formation of the via hole openings 209 are performed on laminates in separate states. When the bonding in Figure 3(C) is performed by thermocompression, heat is applied to the insulator 106. Due to this process, the insulator 106 may flow due to the heat, which may cause the position of the inner layer electrodes 214 to change. As a result, the positions of the inner layer electrode 214 and the via hole opening 209 may not align, potentially preventing current from flowing between the inner layer electrode 214 and the via hole 208.

[0114] Currently, polyimide, which is commonly used as an insulator, has high heat resistance and undergoes almost no deformation or shrinkage during thermocompression bonding, so the positions of the inner layer electrode 214 and the via hole opening 209 can be precisely aligned in the process shown in Figure 3.

[0115] When using a polymer with a relatively low melting point for the insulator 106 of the shielded thin flat cable 101 according to this disclosure, as shown in Figure 2(B), it is necessary to perform the circuit formation process simultaneously on both the front and back surfaces of a single laminate and to accurately align the inner layer electrodes 214 and the via hole openings 209 to obtain a shielded thin flat cable 101 of excellent quality.

[0116] (Embodiment 2) A shielded thin flat cable 101 according to Embodiment 2 is shown in Figures 4(H) and (I). Figure 4(H) shows a cross-section of the terminal portion 103. Figure 4(I) shows a cross-section of the conductor portion 102. Embodiment 2 has a conductor parallel metal film 215 in parallel with the conductor 204 and the inner layer electrode 214. The conductor parallel metal film 215 is formed from the same metal film 202B as the conductor 204 and the inner layer electrode 214. Therefore, the material and thickness are the same as the conductor 204 and the inner layer electrode 214. The conductor parallel metal film 215 is electrically connected to the metal film 202 that continuously covers the outer surface of the shielded thin flat cable 101, and serves as the ground.

[0117] The distance between the end of the conductor parallel metal film 215 and the ends of the conductor 204 and inner layer electrode 214 is 10 μm or more. If it is less than 10 μm, there is a concern that a short circuit will occur between the conductor parallel metal film 215 and the conductor 204 and inner layer electrode 214. Within this range, the distance between the conductor 204 and inner layer electrode 214 may vary depending on the location. It is preferable that the distance between the conductor 204 and inner layer electrode 214 be the same at all locations. In this case, as shown in Figure 4(J), the end of the conductor parallel metal film 215 is provided along the shape of the conductor 204 and inner layer electrode 214.

[0118] As described above, the ends of the conductor parallel metal film 215 do not need to be provided along the conductor 204 and the inner layer electrode 214. Since the conductor parallel metal film 215 is electrically connected to the metal film 202, the potential of the conductor parallel metal film 215 must be the same as that of the metal film 202. For this reason, it is preferable that the ends of the conductor parallel metal film 215 that are not on the conductor 204 and inner layer electrode 214 side are connected to the metal film 202 on the longitudinal and transverse end faces of the shielded thin flat cable 101. Alternatively, the ends of the conductor parallel metal film 215 that are not on the conductor 204 and inner layer electrode 214 side may be partially connected to the metal film 202 on the longitudinal and transverse end faces of the shielded thin flat cable 101.

[0119] The parallel metal film 215 of the conductor can stabilize the signal transmission of the conductor 204 and improve the transmission characteristics of the shielded thin flat cable 101.

[0120] In the conventional flat cable shown in Figure 7, the connection between the metal film 202A and the metal film 202C is made via a through-hole 108. In the shielded thin flat cable 101 of this disclosure, the metal film 202 is provided continuously on the surface of the insulator 106, and the metal films 202 on the upper and lower surfaces of the flat surface are electrically connected by the metal films 202 provided on the longitudinal and transverse end faces of the shielded thin flat cable 101, eliminating the need for a through-hole 108. Furthermore, by connecting the entire circumference or part of the end of the conductor parallel metal film 215 to the end face of the shielded thin flat cable 101, the potential is more stable than in conventional flat cables equipped with a through-hole 108, the ground is strengthened, and the transmission characteristics can be stabilized.

[0121] The conductor parallel metal layer 215 shown in Figures 4(H) and (I) is provided on both sides of the conductor 204 and the inner layer electrode 214, but it may be provided on only one side. Alternatively, it may be provided partially along the conductor 204 and the inner layer electrode 214. Providing it around the entire circumference is more preferable in order to improve the transmission characteristics of the shielded thin flat cable 101.

[0122] Figure 4 shows the manufacturing process for a shielded thin flat cable 101 equipped with a conductor parallel metal film 215. This manufacturing process is identical to that of the shielded thin flat cable 101 shown in Figure 2, except for the addition of the conductor parallel metal film 215.

[0123] In Figure 4(A), metal films 202A and 202B are bonded to both sides of a film-like insulator 106A. In Figure 4(B), a circuit formation process is performed on the metal film 202B to form a conductor 204, an inner layer electrode 214, and a conductor parallel metal film 215. A groove formation opening 212 and a via hole drilling opening 209 are formed on 202A by performing the circuit formation process. In Figure 4(C), a film-like insulator 106B and a metal film 202C are sequentially bonded onto the film-like insulator 106A and the formed conductor 204, inner layer electrode 214, and conductor parallel metal film 215. Figure 4(D) shows the resulting laminate.

[0124] In Figure 4(E), a linear groove 206 and a via hole 207 are formed by removing the insulator 106 using laser processing. At this time, the linear groove 206 is formed so that the ends of the conductive parallel metal film 215 that are not on the conductor 204 and inner layer electrode 214 side are exposed. Therefore, the ends of the conductive parallel metal film 215 that are not on the conductor 204 and inner layer electrode 214 side must be shaped to follow the linear groove 206. A straight line is preferable.

[0125] In Figure 4(F), a metal film 202D is formed on the wall surface 205 of the linear groove 206, and a metal body is formed in the hole 207 which serves as a via hole. The metal film 202D is in contact with the entire circumference or part of the end of the parallel conductor metal layer 215, enabling current to flow.

[0126] Figure 4(G) shows the process of removing a portion of the metal film 202A shown in Figure 4(F) to form a gap 218. The metal film 202A around the area that will become the conductor electrode 105 is removed to form a gap 218. Figure 4(H) shows the process of forming a solder mask 211, which will be an insulating layer, on the surface of the metal film 202 of the laminate shown in Figure 4(G), and cutting the metal film 202C into individual pieces. Similar to Embodiment 1, a thin flat cable 101 shielded by an assembly may be manufactured.

[0127] (Embodiment 3) As shown in Figure 2(C) of Embodiment 1 and Figure 4(C) of Embodiment 2, the film-like insulator 106B is bonded to the film-like insulator 106A and the conductor 204 in contact. Embodiment 3 is characterized in that the melting point of the film-like insulator 106B bonded to the film-like insulator 106A is 10°C lower than the melting point of the film-like insulator 106A. In other words, in the shielded thin flat cable 101, the melting points of the insulators 106 that sandwich the conductor 204 will differ by 10°C or more.

[0128] The difference between Embodiments 1 and 2 and Embodiment 3 is that the film-like insulator 106A and the film-like insulator 106B on the side that is bonded to the conductor 204, inner electrode 214, or parallel metal film 215 provided on the surface of the film-like insulator 106A have a melting point 10°C lower than that of the film-like insulator 106A. Other than this point, it is the same as Embodiments 1 and 2.

[0129] By lowering the melting point of the film-like insulator 106B by 10°C or more compared to the melting point of the film-like insulator 106A, it is possible to relax the heating conditions when bonding the film-like insulator 106A and the film-like insulator 106B by thermocompression. Since the insulator 106A does not melt, the positional relationship of the conductor 204, the inner electrode 214, or the parallel metal film 215 does not change, and damage to the conductor 204, the inner electrode 214, or the parallel metal film 215 can be prevented. Furthermore, the adhesive strength due to bonding can be increased. Below 10°C, it is difficult to control the heating conditions, and it is difficult to melt the film-like insulator 106B without melting the film-like insulator 106A, and to obtain sufficient adhesive strength by thermocompression bonding with the film-like insulator 106A.

[0130] The insulator 106 contains syndiotictactic polystyrene homopolymer or syndiotictactic polystyrene copolymer. When using resins with similar or identical melting points as the resins contained in the film-like insulator 106A and the film-like insulator 106B, it is necessary to strictly control the heating temperature, pressurization amount, and bonding timing. If the conditions are not appropriate, molten resin will flow out from the edges during bonding, resulting in uneven thickness of the insulator 106. In addition, since molten resin flows into the groove-forming opening 212 and the via-hole drilling opening 209, an inflow prevention film is required.

[0131] To prevent leakage, one method involves inserting a bonding sheet between the film-like insulator 106A and the film-like insulator 106B and bonding them at a low temperature. However, inserting a bonding sheet complicates the processing steps, and considering the increased cost due to the bonding sheet, it is preferable not to use it. According to the method of Embodiment 3, there is no need to use a bonding sheet.

[0132] By lowering the melting point of the film-like insulator 106B by 10°C compared to the melting point of the film-like insulator 106A, and heating it to a temperature above the melting point of the film-like insulator 106B and below the melting point of the insulator 106A, sufficient adhesion can be obtained between the film-like insulator 106A, conductor 204, inner layer electrode 214 or parallel metal film 215 and the insulator 106B required for the shielded thin flat cable 101 without melting the insulator 106A.

[0133] The film-like insulator 106B is melted and bonded with the film-like insulator 106A, the conductor 204, or the parallel metal film 215. To suppress flow from the edges due to melting and the inflow of molten resin into the groove-forming opening 212 and the via-hole drilling opening 209, the film-like insulator 106B is preferably thin. The thickness of the film-like insulator 106B is 20 μm or more and 700 μm or less. A thinner adhesive layer is better, but considering the transmission characteristics, a thickness of 20 μm or more and 700 μm or less is preferable.

[0134] As shown in Figure 8(B), the film-like insulator 106 to be bonded to the film-like insulator 106A can consist of two layers: film-like insulator 106B and film-like insulator 106C. The insulator 106 may have three or more layers. The film-like insulator 106B on the side that is in contact with and bonded to the film-like insulator 106A and the conductor 204 has a melting point at least 10°C lower than that of the film-like insulator 106A that sandwiches the conductor 204. The melting point of the film-like insulator 106C may be higher than that of the film-like insulator 106B. It may also be equal to or higher than the melting point of the film-like insulator 106A. The film-like insulator 106C and the metal film 202C may be bonded together in advance, and then the film-like insulator 106B and the film-like insulator 106A may be bonded together by heat compression.

[0135] A film-like insulator consisting of two layers, a film-like insulator 106B and a film-like insulator 106C, can be formed by co-extrusion to achieve sufficient adhesion between the film-like insulator 106B and the film-like insulator 106C. Alternatively, a film-like insulator consisting of at least a film-like insulator 106B and a film-like insulator 106C may be obtained by other processing methods such as extrusion lamination or dry lamination, instead of co-extrusion. Since the film-like insulator 106B is melted and bonded with the film-like insulator 106A, the conductor 204, or the parallel metal film 215, it is preferable that it be thin to suppress flow from the edges due to melting and to suppress the inflow of molten resin into the groove-forming opening 212 and the via-hole drilling opening 209. Here, when a film-like insulator consisting of two or more layers is provided, the film-like insulator 106BD is 10 μm or less, more preferably 5 μm or less. The resin layer with a low melting point is preferably thin to suppress flow.

[0136] By thinning the film-like insulator 106B and adjusting the film-like insulator 106C to a thickness that satisfies the electrical properties, a shielded, thin, flat cable 101 with stable dimensions and adhesion can be formed. The combined thickness of the film-like insulator 106B and the film-like insulator 106C is preferably 20 μm to 700 μm.

[0137] Furthermore, as shown in Figure 8(A), the film-like insulator 106B and the film-like insulator 106C may be separate films. The lamination method can be simultaneous, sequential, or a combination of simultaneous and sequential lamination, as long as the order is film-like insulator 106A, film-like insulator 106B, film-like insulator 106C, and metal film 202C. Similar to Figure 8(B), the melting point of the film-like insulator 106B is at least 10°C lower than that of the film-like insulator 106A that sandwiches the conductor 204. The melting point of the film-like insulator 106C may be higher than that of the film-like insulator 106B. It may also be equal to or higher than that of the film-like insulator 106A.

[0138] (Embodiment 4) The shielded thin flat cable 101 according to Embodiment 4 is a shielded thin flat cable 101 formed by integrating a plurality of shielded thin flat cables in the planar direction.

[0139] In Embodiments 1 and 2, one conductor 204 was formed on one shielded thin flat cable 101. As shown in Figure 9(A), multiple conductors 204 can be provided on one shielded thin flat cable 101. Furthermore, a shielded thin flat cable 101 can be formed by integrating multiple shielded thin flat cables, each encased in multiple insulators 106 separated by a metal film 202D, in the planar direction. Except for integrating multiple shielded thin flat cables in the planar direction, this is the same as Embodiments 1 and 2.

[0140] The right side of Figure 9(A) shows a shielded thin flat cable in which multiple conductors 204 are encased in an insulator 106 isolated by a metal film 202D, and the metal film 202 is continuous on the surface of the insulator 106 except around the conductor electrodes 105. The left side of Figure 9(A) shows a shielded thin flat cable in which the conductors 204 are encased in an insulator 106 isolated by a metal film 202D, and the metal film 202 is continuous on the surface of the insulator 106 except around the conductor electrodes 105. The two shielded thin flat cables on the right and left form an integrated shielded thin flat cable 101.

[0141] By integrating multiple shielded, thin, flat cables in a horizontal direction, it becomes possible to wire multiple shielded lines in a lightweight, thin, and high-density manner.

[0142] Figure 9(A) shows a cross-section of the conductor portion 102, and Figure 9(B) shows a cross-section of the terminal portion 103. This is the same as Embodiment 1 except that multiple conductors 204 are provided on the shielded thin flat cable 101, and multiple shielded thin flat cables are integrated in the planar direction.

[0143] The distance between multiple conductors 204 in the shielded thin flat cable shown on the right of Figure 9(A) is between 5 μm and 10,000 μm. Below 5 μm, there is a concern about crosstalk and the risk of short circuits. Above 10,000 μm, the product becomes large and the number of components per unit area decreases, making it impractical. The spacing between multiple internal electrodes 214 is determined by the mounting design and there are no particular constraints, but the spacing should be 10 μm or more. Below 10 μm, there is a risk of short circuits during processing or soldering. In Figure 9(A), the multiple internal electrodes 214 are provided at the same position along the longitudinal direction of the shielded thin flat cable 101, but the positions of the multiple internal electrodes 214 can be changed to change the length of the multiple conductors 204. The same applies to the shielded thin flat cable on the left of Figure 9(A), and the length of the conductors 204 can be changed from that of the shielded thin flat cable on the right.

[0144] Figure 11 shows the manufacturing process of a shielded thin flat cable 101, which is formed by integrating multiple shielded thin flat cables as shown in Figure 9.

[0145] Figure 11(A) shows a laminate in which metal films 202A and 202B are bonded to both sides of a film-like insulator 106A. It can be obtained by the same process as in Embodiment 1.

[0146] Figure 11(B) shows a circuit formation process in which the metal film 202B is formed as the required number of conductors 204 and inner layer electrodes 214, and the metal film 202A is formed as a metal film 202 continuously on the surface of the required number of conductor electrodes 105 and insulator 106. Here, by removing a portion of the metal film 202A, the required number of via hole openings 209 and groove openings 212 are formed.

[0147] Figure 11(C) shows the process of sequentially laminating a film-like insulator 106B and a metal film 202C onto a film-like insulator 106A, a plurality of formed conductors 204, and an inner layer electrode 214. The film-like insulators 106A and 106B are laminated by thermocompression bonding. The plurality of conductors 204 and the inner layer electrode 214 are sandwiched between the film-like insulators 106A and 106B.

[0148] Figure 16 shows a configuration in which a film-like insulator 106C is inserted between a film-like insulator 106B and a metal film 202C, compared to Figure 11(C), and Figure 11(D) is obtained by thermocompression bonding. The melting point of the film-like insulator 106B is at least 10°C lower than that of the film-like insulator 106A that sandwiches the conductor 204. The melting point of the film-like insulator 106C may be higher than that of the film-like insulator 106B. It may also be equal to or higher than the melting point of the film-like insulator 106A.

[0149] Figure 11(D) shows a laminate formed by bonding together a film-like insulator 106, a film-like insulator 106B, and a metal film 202C.

[0150] Figure 11(E) shows the process of forming a plurality of linear grooves 206 and via holes 207 parallel to the conductor 204 along both sides of the conductor 204 and the inner layer electrode 214. The linear grooves 206 are formed by a device that can remove the insulator 106 without penetrating the metal film 202A on one side of the insulator 106, leaving the metal film 202C on the other side, thereby forming the linear grooves 206 and via holes 207. The device is, for example, a device equipped with a laser processing machine, a plasma processing machine, a sandblaster, etc. A laser processing machine is preferred because of its high processing speed.

[0151] Figure 11(F) shows the process of forming a metal film 202D in multiple linear grooves 206 in the state shown in Figure 11(E), and the process of forming a metal body in multiple via holes 207 to provide via holes 208 for drawing conductivity from the conductor 204. Metal plating is suitable for forming the metal bodies of the metal film 202D and the via holes 208. By metal plating the linear grooves 206 formed between one conductor 204 and three conductors 204, the shielded thin flat cable on the left and the shielded thin flat cable on the right in Figure 9(A) are separated by the metal film 202D, and a configuration in which multiple shielded thin flat cables are integrated can be achieved.

[0152] Figure 11(G) shows the step of removing a portion of the metal film 202A. This step involves removing a portion of the metal film 202A to form the necessary gaps 218 between the conductor electrode 105 and the metal film 202. Although not shown in the figure, a solder mask 211, which serves as an insulating layer, is formed on the outer surface of the shielded thin flat cable 101 as needed.

[0153] Figure 11(H) shows the process of cutting the metal film 202C into individual pieces. The shielded thin flat cable 101 is divided into individual pieces by cutting the metal film 202C along the linear groove 206 so that it forms the outer shape of the integrated shielded thin flat cable 101.

[0154] As described in Embodiment 1, production efficiency can be increased by manufacturing a bundled, shielded thin flat cable 101 and then separating it into individual pieces. Alternatively, individual shielded thin flat cables 101 and integrated shielded thin flat cables 101 may be formed simultaneously and then separated into individual pieces.

[0155] (Embodiment 5) The shielded thin flat cable 101 according to Embodiment 5 is a shielded thin flat cable 101 formed by integrating a plurality of shielded thin flat cables in the planar and vertical directions. It may also be integrated only in the vertical direction and not in the horizontal direction.

[0156] In Embodiments 1 and 2, one conductor 204 was formed on one shielded thin flat cable 101. As shown in Figure 10(A), a shielded thin flat cable 101 can be formed by integrating multiple shielded thin flat cables in the horizontal and vertical directions. Except for the fact that a shielded thin flat cable 101 can be formed by integrating multiple shielded thin flat cables in the horizontal and vertical directions, it is the same as Embodiments 1, 2 and 4.

[0157] The upper left of Figure 10(A) shows a shielded thin flat cable with a conductor parallel metal layer 215 provided along the conductor 204 and inner layer electrode 214, similar to Embodiment 2. The upper right shows a shielded thin flat cable with one conductor 204. The lower left shows a shielded thin flat cable with one conductor 204. The lower right shows a shielded thin flat cable with multiple conductors 204. The shielded thin flat cable 101 in Figure 10(A) is a configuration in which four shielded thin flat cables are integrated. These four shielded thin flat cables are isolated by metal films 202D and 202E.

[0158] The vertically integrated shielded thin flat cable 101 can have any configuration. There can be one or more conductors 204. A conductor parallel metal film 215 may be provided in parallel with the conductors 204.

[0159] Embodiment 5 differs from Embodiment 4 in that multiple shielded thin flat cables are integrated in the vertical direction. While two or more shielded thin flat cables can be integrated in the horizontal direction, it is appropriate to integrate two shielded thin flat cables in the vertical direction. Integrating three or more shielded thin flat cables would complicate the configuration because the intermediate shielded thin flat cable would need to have conductor electrodes 105 on its end face. It is also acceptable to provide conductor electrodes 105 on the end face and integrate three or more shielded thin flat cables in the vertical direction.

[0160] By integrating multiple shielded, thin, flat cables in the vertical direction, it is possible to obtain a shielded, thin, flat cable 101 that is even smaller, lighter, and has higher density than integration in a planar direction.

[0161] Figure 10(A) shows a cross-section of the conductor portion 102, and Figure 10(B) shows a cross-section of the terminal portion 103.

[0162] Figure 12 shows the manufacturing process of a shielded thin flat cable 101 in which multiple shielded thin flat cables shown in Figure 10 are integrated in the horizontal and vertical directions.

[0163] Figure 12(A) shows two laminates in which metal films 202A and 202B are bonded to both sides of a film-like insulator 106A. The manufacturing process for the laminates is the same as in Embodiment 1. By using two laminates, two shielded thin flat cables can be integrated in the vertical direction.

[0164] Figure 12(B) shows the circuit formation process for forming the necessary via hole openings 209, groove formation openings 212, conductors 204, inner layer electrodes 214, and conductor parallel metal films 215.

[0165] When integrated, the upper metal film 202 of the laminate constituting multiple shielded thin flat cables has multiple via hole openings 209 and groove-forming openings 212, and the lower metal film 202 of the laminate has multiple conductors 204 and inner layer electrodes 214, as shown in Figure 10(A). The lower metal film 202 of the laminate constituting multiple shielded thin flat cables has multiple via hole openings 209 and groove-forming openings 212, and the upper metal film 202 of the laminate has multiple conductors 204, inner layer electrodes 214 and conductor parallel metal 215, as needed.

[0166] Figure 12(C) shows the process of laminating a laminate that constitutes the upper part of a shielded thin flat cable 101, with a metal film 202E sandwiched between two film-like insulators 106B, onto the upper film-like insulator 106B, and laminating a laminate that constitutes the lower part of a shielded thin flat cable 101, with the lower film-like insulator 106B being used. As shown in Figure 12(C), five constituent materials are laminated together. Thermocompression bonding is a suitable method for lamination.

[0167] Figure 17 shows a configuration in which an insulator 106C is inserted between the film-like insulator 106B and the metal film 202E, compared to Figure 12(C), and Figure 12(D) is obtained by thermocompression bonding. The melting point of the film-like insulator 106B is at least 10°C lower than that of the film-like insulator 106A that sandwiches the conductor 204. The melting point of the film-like insulator 106C may be higher than that of the film-like insulator 106B. It may also be equal to or higher than the melting point of the film-like insulator 106A.

[0168] Figure 12(D) shows a laminate formed by bonding together a metal film 202 having via hole openings 209 and groove formation openings 212, an insulator 106 enclosing a conductor 204, an inner electrode 214, and a conductor parallel metal film 215, a metal film 202E, an insulator 106 enclosing the conductor 204 and the inner electrode 214, and the metal film 202 having via hole openings 209 and groove formation openings 212.

[0169] Figure 12(E) shows the process of forming multiple linear grooves 206 and via holes 207 in the upper and lower insulators 106 of the metal film 202E, parallel to the conductor 204, along both sides of the conductor 204 and the inner layer electrode 214. The linear grooves 206 are formed by laser processing, which removes the upper and lower insulators 106 of the metal film 202E in a linear manner, leaving the metal film 202E intact, without penetrating the upper metal film 202 of the insulator 106 or the lower metal film 202 of the insulator 106, thereby forming the linear grooves 206 and via holes 207. The linear grooves 206 are formed not only in the longitudinal direction along the sides of the conductor 204 and the inner layer electrode 214, but also in the transverse direction.

[0170] Figure 12(F) shows the process of forming a metal film 202D in the multiple linear grooves 206 of Figure 12(E), and the process of forming a metal body in the multiple via holes 207 to provide via holes 208 for drawing conductivity from the conductor 204. Metal plating is suitable for forming the metal bodies of the metal film 202D and the via holes 208. By metal plating the wall surface 205 of the linear groove 206 formed between the conductor parallel metal film 215 provided along one conductor 204 and the one conductor 204, and forming the metal film 202D, the two shielded thin flat cables at the top of Figure 10(A), which are isolated by the metal film 202D and metal film 202E, are formed. Furthermore, by metal plating the wall surface 205 of the linear groove 206 formed between one conductor 204 and three conductors 204 to form a metal film 202D, two shielded thin flat cables at the bottom of Figure 10(A) are formed, which are separated by the metal films 202D and 202E. Multiple shielded thin flat cables can be integrated in both the horizontal and vertical directions.

[0171] Figure 12(G) shows the process of removing a portion of the metal film 202 to form multiple gaps 218 necessary between the conductive electrode 105 and the metal film 202.

[0172] Figure 12(H) shows the process of removing an unnecessary portion of the metal film 202E. Although not shown in the figure, a solder mask 211, which serves as an insulating layer, is formed on the outer surface of the shielded thin flat cable 101 as needed.

[0173] As described in Embodiment 1, production efficiency can be increased by manufacturing a bundled, shielded thin flat cable 101 and then separating it into individual pieces. Alternatively, individual shielded thin flat cables 101 and integrated shielded thin flat cables 101 may be formed simultaneously and then separated into individual pieces.

[0174] (Embodiment 6) As shown in Figures 1(B), (B-1), (B-2), and (B-3), the conductor electrode 105, which is a terminal for transmitting and receiving signals by drawing conductivity from the conductor 204, is usually provided on the flat surface of the shielded thin flat cable 101. The shielded thin flat cable 101 according to Embodiment 6 is a shielded thin flat cable 101 with the conductor electrode 105 provided on the end face, as shown in Figure 13.

[0175] Figure 13 shows a conductor electrode 105 provided on the end face of a shielded thin flat cable 101. Figure 13(A) is a left side view, (B) is a top view, (C) is a right side view, and (D) is a bottom view. The conductor electrode 105 is provided on the end face and a portion of the top and bottom of the flat surface of the shielded thin flat cable 101. The metal film 202 and the conductor electrode 105 are separated by a gap 218 and do not conduct electricity. The conductor electrode 105 is a metal film that is continuous with the conductor 204 provided inside the shielded thin flat cable 101. In Figure 13, the conductor electrode 105 is provided on the longitudinal end face of the shielded thin flat cable 101, but it may also be provided on the short end face.

[0176] The conductor 204, conductor parallel metal film 215, conductor electrode 105, gap 218, insulator 106, and metal film 202 of the shielded thin flat 101 with a conductor electrode 105 on its end face according to Embodiment 6 are made of the same materials and have the same shape as those of Embodiments 1 and 2.

[0177] Figure 14 shows the manufacturing process of a shielded thin flat cable 101 with a conductor electrode 105 on its end face. This manufacturing process is the same as that shown in Figure 2, which shows the manufacturing process of Embodiment 1, except that a conductor electrode 105 is provided on the end face of the shielded thin flat cable 101. However, since the conductor electrode 105 on the end face is continuous with the conductor 204, it is not necessary to provide a via hole 208.

[0178] In Figure 14(A), metal films 202A and 202B are bonded to both sides of a film-like insulator 106A. In Figure 14(B), a circuit formation process is performed on the metal film 202B to provide a conductor 204 and groove-forming openings 212. The conductor 204 is provided to continuously extend from the end face of the shielded thin flat cable 101.

[0179] Figure 14(B) shows a cross-section of the conductor portion 102. A plan view of Figure 14(B) is shown in Figure 14(B-1). As shown in Figure 14(B-1), the conductor 204 is bent and provided so as to be pulled out to the longitudinal end face of the shielded thin flat cable 101. Alternatively, the conductor 204 may be pulled out in a straight line to the short end face of the shielded thin flat cable 101. As shown in Figure 14(B-1), it is preferable to make the conductor 204 wider than the width of the conductor 204 along the end face. By making it wider, a secure connection can be made with the metal plating 202D provided on the wall surface 205 of the end face.

[0180] In Figure 14(C), a film-like insulator 106A and a metal film 202C are sequentially bonded onto the formed conductor 204. Figure 14(D) shows the resulting laminate.

[0181] In Figure 14(E), a linear groove 206 is formed by removing the insulator 106 from the groove-forming opening 212 using laser processing. The wall surface 205 of the linear groove 206 is provided in contact with the end of the conductor 204 at the end face of the shielded thin flat cable 101. This is to connect the metal film 202D provided on the wall surface 205 of the linear groove 206 to the end of the conductor 204. Laser processing and router processing may be combined to form the linear groove 206.

[0182] In Figure 14(F), a metal film 202D is formed on the wall surface 205 of the linear groove 206 by metal plating, and the end of the conductor 204 is connected to the metal film 202D provided on the wall surface 205 of the linear groove 206.

[0183] Figure 14(G) shows a cross-section of the terminal portion 103 of the shielded thin flat cable 101. Figure 14(G) shows the process of removing a portion of the metal films 202A, 202C, and 202D shown in Figure 14(F) to form a gap 218. In the circuit formation process, the metal film 202 around the portion that will become the conductor electrode 105 is removed, and a gap 218 is formed between the conductor electrode 105 and the metal film 202. The gap 218 is provided at two locations: on both sides of the flat surface of the shielded thin flat cable 101, and at the end face of the shielded thin flat cable 101 that extends continuously from the gap 218 provided on the flat surface.

[0184] Figure 14(H) shows the process of forming a solder mask 211, which serves as an insulating layer, on the surface of the metal film 202 of the laminate shown in Figure 14(G), and then cutting the metal film 202C into individual pieces. Similar to Embodiment 1, a thin flat cable 101 shielded by an assembly may be manufactured.

[0185] Figure 15 shows a shielded thin flat cable 101 with two conductors and conductor electrodes 105 provided on the end faces. Figure 15(A) is a plan view corresponding to the process in Figure 14(B-1). During the circuit formation process, two conductors 204 and a conductor parallel metal 215 are provided on the outside of the two conductors 204 from the metal film 202A. The two conductors 204 are bent and provided so as to be pulled out to locations that will be different end faces in the longitudinal direction of the shielded thin flat cable 101. As shown in Figure 15(A), it is preferable to make the conductors 204 wider than the width of the conductor 204 along the end face. By making the width wider, a secure connection can be made with the metal plating 202D provided on the wall surface 205 of the end face.

[0186] The thickness of the conductor 204 is preferably between 9 μm and 100 μm. If it is less than 9 μm, a secure connection with the metal plating on the end face wall 205 cannot be made, and it is prone to breakage. If it exceeds 100 μm, the processing accuracy of the width of the conductor 204 deteriorates significantly.

[0187] Figure 15(B) shows a shielded thin flat cable 101 with conductive electrodes 105 provided on both end faces. Figure 15(B) shows the case where a gap 218 is formed by a circuit formation process. The end of the gap 218 can be made straight. Removing the metal film 202D formed on the wall surface 205 of the linear groove 206 by the circuit formation process is complicated because it is not a flat surface, making the resist film curing process difficult. To form circuits on the end face, the etching resist is not a dry film, but a liquid etching resist is applied to the end face by electrostatic coating or roll coating. Also, since exposure is also performed on the end face, it is done by a method such as laser light. Circuit formation on the end face differs from the normal printed circuit board processing method, so it is necessary to control the conditions.

[0188] The process of removing a portion of the metal film 202D formed on the wall surface 205 of the linear groove 206 to form a gap 218 may be carried out by cutting. Specifically, cutting can be performed using a drill bit or a router bit. Figure 15(C) shows the metal film 202D formed on the wall surface 205 removed by cutting, and the removed end surface is curved.

[0189] By providing the conductor electrode 105 on the end face, the conductor 204 is drawn out to the conductor electrode 105 using the end face, thus eliminating the need to form a via hole opening 209. Furthermore, since the metal films 202 on the end face and the upper and lower surfaces can be used as part of the conductor electrode 105, a fillet can be formed during soldering, improving the soldering strength.

[0190] The shielded, thin, flat cable described herein can be used in communication equipment requiring high-density mounting, equipment using high-frequency and high-speed signals, equipment requiring EMI countermeasures, equipment requiring chemical resistance, etc. Specifically, it can be used in smartphones, IoT devices, communication base station peripherals, automotive-related equipment such as ADAS, lithium-ion battery peripherals, etc. [Explanation of symbols]

[0191] 101 · Shielded, slim, flat cable 102. Conductor section 103...Terminal section 105 Conductor electrodes 106. Insulator 108 through-hole 202. Metal film 204 ··Conductor 205 ··Wall surface 206. Linear grooves 207. Hole as a beer hall 208 Beer Hall 209 ··Opening for drilling beer holes 211 Solder Mask 212...Groove formation opening 214 ··Inner layer electrode 215 ··Conductor parallel metal film 218...gap

Claims

1. A conductor made of metal, An insulator that sandwiches the conductor and surrounds the conductor other than the conductor electrodes that are electrically conductive from the conductor and exposed on the surface, and A shielded thin flat cable having a metal film continuous with the surface of the insulator other than the periphery of the conductor electrode, A shielded thin flat cable having a first film-like insulator surface on which an inner layer electrode that conducts with the conductor and the conductor electrode is formed, the conductor, the inner layer electrode and the second film-like insulator bonded to the first film-like insulator having a melting point at least 10°C lower than the melting point of the first film-like insulator, and a third film-like insulator having a melting point equal to or higher than the melting point of the second film-like insulator on the opposite side of the surface of the second film-like insulator that sandwiches the conductor, A shielded, thin, flat cable characterized in that the first film-like insulator contains a syndiotactic polystyrene homopolymer, and the second film-like insulator contains a syndiotactic polystyrene copolymer.

2. In the shielded thin flat cable according to claim 1, A shielded thin flat cable characterized in that the first film-like insulator contains 20 parts by mass or more but less than 450 parts by mass of a filler per 100 parts by mass of the syndiotactic polystyrene homopolymer, and the second film-like insulator contains 20 parts by mass or more but less than 450 parts by mass of a filler per 100 parts by mass of the syndiotactic polystyrene copolymer, and the filler is one or more of amorphous silica, crystalline silica, hollow silica, black silica, silicic acid and its metal salts, glass, titanium oxide, aluminum nitride, carbon black, graphite, carbon nanotubes, titanium black, boron nitride, and mica.

3. In the shielded thin flat cable according to claim 1 or claim 2, A shielded thin flat cable characterized in that a plurality of shielded thin flat cables, each having the metal film continuously on the outer surface of the insulator surrounding the conductor, are integrally formed.

4. A metal film is bonded to both sides of a first film-like insulator containing syndiotactic polystyrene homopolymer. By performing a circuit formation process on the metal film on one side of the first film-like insulator, an inner layer electrode that conducts to a conductor and a conductive electrode that becomes an external terminal continuous with the conductor is formed. By performing a circuit formation process on the metal film on the other surface, an opening for drilling via holes is formed. A second film-like insulator containing a syndiotactic polystyrene copolymer having a melting point at least 10°C lower than the melting point of the first film-like insulator is bonded to the conductor and the inner layer electrode formed on one side of the first film-like insulator. A metal film is bonded to the other surface of the second film-like insulator. The end face of the shielded thin flat cable is formed such that it has the outer circumference shape of the shielded thin flat cable by removing the metal film on the other side of the first film-like insulator, the first film-like insulator, the second film-like insulator, and the metal film on the other side of the second film-like insulator, A method for manufacturing a shielded thin flat cable, characterized by forming a metal film on the end face.

5. In the method for manufacturing a shielded thin flat cable according to claim 4, A method for manufacturing a shielded thin flat cable, characterized by providing a third film-like insulator containing a syndiotactic polystyrene homopolymer having a melting point equal to or higher than that of the first film-like insulator on the opposite side of the conductor-side surface of the second film-like insulator.

6. In the method for manufacturing a shielded thin flat cable according to claim 4, By performing a circuit formation process on the metal film on one side of the first film-like insulator, the inner layer electrode that conducts to the conductor and the conductor electrode continuous with the conductor is formed. By performing a circuit formation process on the metal film on the other side, the second film-like insulator, the metal film, another second film-like insulator, and the conductor of another intermediate product of the shielded thin flat cable are simultaneously or sequentially laminated on the conductor side of the first film-like insulator of the intermediate product of the shielded thin flat cable, with the conductor on the other second film-like insulator side. A method for manufacturing a shielded thin flat cable, characterized by irradiating the upper and lower first film-like insulators of a shielded thin flat cable, in which a plurality of intermediate products of the shielded thin flat cable are integrated vertically, with laser light to remove the first film-like insulator and the second film-like insulator down to the metal film of the other shielded thin flat cable, and forming a metal film on the wall surface of the groove formed by removing the first film-like insulator and the second film-like insulator.

7. In the method for manufacturing a shielded thin flat cable according to claim 4, By performing a circuit formation process on the metal film on one side of the first film-like insulator, the inner layer electrode that conducts to the conductor and the conductor electrode continuous with the conductor is formed. By performing a circuit formation process on the metal film on the other side, the second film-like insulator, the metal film, another second film-like insulator, and the conductor of another intermediate product of the shielded thin flat cable are laminated on the conductor side of the first film-like insulator of the intermediate product of the shielded thin flat cable, with the conductor on the other second film-like insulator side. A method for manufacturing a shielded thin flat cable, characterized by cutting the upper and lower metal films and the first and second film-like insulators along the outer shape of a shielded thin flat cable in which a plurality of the shielded thin flat cable intermediate products are integrated vertically, and forming a metal film on the end face of the shielded thin flat cable formed thereon.

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