Cable for high-frequency signal transmission and method for manufacturing the same

Abstract

The present invention provides a cable for high-frequency signal transmission and a manufacturing method thereof. When transmitting high-frequency signals, it is difficult for the cable to attenuate, and even when bending and wiring high-frequency signals in a narrow space, the transmission characteristics are hardly reduced. The cable (1) for high-frequency signal transmission at least includes a conductor (2), an insulator (3) covering the periphery of the conductor (2), a coating layer (4) covering the periphery of the insulator (3), and a sheath (6) covering the periphery of the coating layer (4). Among them, an anti-cracking layer (7) is provided between the insulator (3) and the coating layer (4). The anti-cracking layer (7) is arranged in contact with the insulator (3) and has a coating layer (4) on its outer surface. The anti-cracking layer (7) is composed of a resin film (71). In response to the bending of the insulator (3), it bends while relatively moving in the cable length direction, thereby suppressing cracking of the coating layer (4).

Description

Technical Field

[0001] The present invention relates to a cable for high-frequency signal transmission and a method for manufacturing the same. Background Art

[0002] As a coaxial cable for high-frequency signal transmission used for internal wiring of a camera device used in, for example, autonomous driving or electronic devices such as smartphones and tablet terminals, a coaxial cable having a small diameter with an outer diameter of 2 mm or less is used.

[0003] As such a coaxial cable, among conventionally known cables, a tape member such as a copper tape having a copper foil provided on a resin layer is used for an outer conductor. It is known that when a tape member such as a copper tape is wound in a spiral shape, a phenomenon called suck-out occurs in which a sharp attenuation occurs in a specified frequency region (for example, a region of several GHz such as 1.25 GHz to 6 GHz). In order to suppress this suck-out, it is possible to consider forming an outer conductor by longitudinally winding and winding a tape member in a state of being in close contact with the entire outer periphery of an insulator.

[0004] It should be noted that as prior art document information related to the invention of this application, there is Patent Document 1.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 3671729 Gazette Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, in many cases, coaxial cables for internal wiring of camera devices and electronic devices are routed in a bent shape such as an L shape or an S shape according to substrate circuit design. In a coaxial cable formed by longitudinally winding and winding a tape member in a state of being in close contact with the entire outer periphery of an insulator, when the coaxial cable is bent, the tape member is bent to generate wrinkles and breaks, and the transmission characteristics of high-frequency signals may be reduced.

[0010] In addition, the tape member wound in a state of being in close contact with the entire outer periphery of the insulator is hard and difficult to bend, so it is difficult to route the cable in a narrow space of a small electronic device. In such a case where the coaxial cable cannot be bent and routed, there is a possibility that the transmission characteristics of high-frequency signals are reduced due to the hard tape member pressing on the insulator in close contact with the tape member. Therefore, there is a need for a coaxial cable for high-frequency signal transmission that has both good high-frequency signal transmission characteristics (attenuation characteristics) and flexibility (flexibility).

[0011] Therefore, an object of the present invention is to provide a high-frequency signal transmission cable and a manufacturing method thereof, which are difficult to attenuate when transmitting high-frequency signals and whose transmission characteristics of high-frequency signals are difficult to degrade even when the wiring is bent in a narrow space.

[0012] Method for solving the problem

[0013] For the purpose of solving the above problems, the present invention provides a high-frequency signal transmission cable, which at least includes a conductor, an insulator covering the periphery of the conductor, a coating covering the periphery of the insulator, and a sheath covering the periphery of the coating. Among them, an anti-cracking layer is provided between the insulator and the coating, which is arranged in contact with the insulator and has the coating on its outer surface. The anti-cracking layer is composed of a resin film, and bends while relatively moving in the cable length direction in response to the bending of the insulator, thereby suppressing cracking of the coating.

[0014] In addition, for the purpose of solving the above problems, the present invention provides a manufacturing method of a high-frequency signal transmission cable, which at least includes a conductor, an insulator covering the periphery of the conductor, a coating covering the periphery of the insulator, and a sheath covering the periphery of the coating. After winding a resin film around the outer periphery of the insulator, the resin film is heated to form a fusion part formed by fusing the wrapped part of the resin film and a non-fusion part where the resin film is not fused, thereby forming an anti-cracking layer between the insulator and the coating, which is arranged in contact with the insulator and has the coating on its outer surface. The anti-cracking layer bends while relatively moving in the cable length direction in response to the bending of the insulator, thereby suppressing cracking of the coating.

[0015] Advantages of the invention

[0016] According to the present invention, it is possible to provide a high-frequency signal transmission cable and a manufacturing method thereof, which are difficult to attenuate when transmitting high-frequency signals and whose transmission characteristics of high-frequency signals are difficult to degrade even when the wiring is bent in a narrow space. Description of the drawings

[0017] Figure 1 A cross-sectional view showing a cross-section perpendicular to the cable length direction of the high-frequency signal transmission cable according to an embodiment of the present invention.

[0018] Figure 2 (a) to (d) are diagrams for explaining the manufacturing method of the high-frequency signal transmission cable according to an embodiment of the present invention.

[0019] Figure 3 A diagram for explaining the effect brought by the relative movement of the anti-cracking layer with respect to the insulator.

[0020] [[ID=3 (b)]]Symbol description

[0021] 1: Cable for high-frequency signal transmission; 2: Inner conductor (conductor); 3: Insulator; 4: Plating; 7: Anti-cracking layer; 71: Resin film; 71a: Fusion portion; 71b: Non-fusion portion; 71c: Wrapping portion; 71d: Non-wrapping portion; 5: Metal shielding layer; 6: Sheath. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0023] Figure 1 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of the high-frequency signal transmission cable according to this embodiment. Figure 1 As shown, the high-frequency signal transmission cable 1 includes an inner conductor 2 as a conductor arranged in the center of the cable, an insulator 3 covering the inner conductor 2, a plating 4 covering the insulator 3, a metal shield 5 covering the plating 4, and a sheath 6 covering the metal shield 5. That is, the high-frequency signal transmission cable 1 involved in this embodiment is a coaxial cable comprising an inner conductor 2, an insulator 3, an outer conductor 8 (plating 4 and metal shield 5) and a sheath 6. It should be noted that a structure in which the metal shield 5 is not arranged between the plating 4 and the sheath 6 is also possible. However, in order to improve the transmission characteristics, it is more preferable to arrange the metal shield 5 between the plating 4 and the sheath 6. The high-frequency signal transmission cable 1 is used for internal wiring of electronic devices such as camera devices used in autonomous driving, or smart phones and tablet terminals, and its outer diameter (outer diameter of the sheath 6) is as thin as 2 mm or less, and more preferably 1.5 mm or less. It should be noted that "covering" also includes the case where it is arranged through other layers. For example, other layers may be disposed between the inner conductor 2 and the insulator 3 , between the insulator 3 and the outer conductor 8 , or between the outer conductor 8 and the sheath 6 .

[0024] (Inner conductor 2)

[0025] The inner conductor 2 can be a single-wire conductor or a stranded conductor formed by twisting together multiple bare wires. Furthermore, the inner conductor 2 can also be formed by twisting together multiple bare wires, or it can be composed of a compressed stranded conductor that has been compressed so that the cross-section perpendicular to the length of the cable is a predetermined shape, such as a circle. By using a compressed stranded conductor as the inner conductor 2, the bare wires are tightly fitted together, leaving no gaps between them. This improves conductivity, achieves good attenuation characteristics, and maintains flexibility. Furthermore, compared to single-wire conductors, compressed stranded conductors and stranded conductors are less likely to break when bent.

[0026] In order to obtain good attenuation characteristics, it is preferable that the conductivity of the inner conductor 2 be set to 99% IACS or more. For example, in the case where the inner conductor 2 is a compressed stranded conductor, in order to achieve high conductivity, as the bare wire of the inner conductor 2, soft copper wire made of pure copper without plating can be used. In addition, plating with a conductivity of 99% IACS or more can also be carried out. For example, soft copper wire plated with silver can also be used as the bare wire. In addition, although the conductivity will decrease when strain is imparted to the bare wire during the compression process, the conductivity of 99% IACS or more can be achieved by removing the strain through heat treatment (annealing treatment) thereafter.

[0027] (Insulator 3)

[0028] As the insulator 3, in order to improve the transmission characteristics of high-frequency signals (more specifically, for example, it is difficult to attenuate when transmitting high-frequency signals in the 10 MHz to 6 GHz region), it is preferable to use an insulator with as low a dielectric constant as possible. In the present embodiment, as the insulator 3, an insulator made of a fluororesin is used. Examples of the fluororesin used in the insulator 3 include PFA (perfluoroalkoxy alkane), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene), and the like. The insulator 3 can be provided in contact with the entire outer periphery of the inner conductor 2.

[0029] It should be noted that it is also possible to consider using a foamed resin as the insulator 3. However, since the outer diameter of the high-frequency signal transmission cable 1 is as thin as 2 mm or less, the thickness of the insulator 3 will also be very thin. Since it is difficult to stably manufacture a thin foamed resin, a fluororesin with a relatively low dielectric constant is used as the insulator 3 in the present embodiment.

[0030] (Metal shielding layer 5)

[0031] An anti-cracking layer 7 and a plating layer 4 are sequentially provided around the insulator 3, and a metal shielding layer 5 is provided in contact with the outer surface of the plating layer 4 around the plating layer 4. The anti-cracking layer 7 and the plating layer 4 will be described below. In the high-frequency signal transmission cable 1, the plating layer 4 and the metal shielding layer 5 function as an outer conductor 8.

[0032] The metal shielding layer 5 and the plating layer 4 (described later) together constitute an outer conductor, which is formed by braiding or horizontally winding (horizontally winding) metal bare wires. As will be described in detail later, the metal shielding layer 5 also functions to press the plating layer 4 and the anti-cracking layer 7 described later inward, and to maintain the distance between the inner conductor 2 and the plating layer 4 substantially constant in the longitudinal direction of the cable. Examples of the metal bare wire used in the metal shielding layer 5 include soft copper wire and hard copper wire made of copper or a copper alloy. In addition, metal bare wire made of aluminum or an aluminum alloy can also be used. Plating can also be carried out on the outer surface of the metal bare wire.

[0033] (Sheath 6)

[0034] The sheath 6 is made of an insulating resin composition such as PVC (polyvinyl chloride), urethane, or polyolefin. The sheath 6 is formed by extrusion molding. However, if solid forming (filling forming) is performed, there is a possibility that the resin constituting the sheath 6 will enter between the bare wires of the metal shielding layer 5, and the high-frequency signal transmission cable 1 will become hard and difficult to bend. Therefore, in the present embodiment, the sheath 6 is formed by tube extrusion. Thereby, the resin constituting the sheath 6 entering between the bare wires of the metal shielding layer 5 is suppressed, and the sheath 6 is separated from the metal shielding layer 5. That is, in the present embodiment, the sheath 6 and the metal shielding layer 5 are not adhered, and the metal shielding layer 5 can move relatively freely within the sheath 6. Thereby, the high-frequency signal transmission cable 1 becomes easier to bend.

[0035] (Plating layer 4 and anti-cracking layer 7)

[0036] An anti-cracking layer 7 is provided around the insulator 3, which is set to be in contact with the outer surface of the insulator 3 without generating a gap, and at the same time, when the high-frequency signal transmission cable 1 is bent, it can bend while relatively moving in the cable length direction in a state of being in contact with the outer surface of the insulator 3 without a gap (in a state of being in contact with the insulator), and a plating layer 4 is provided on the outer surface of the anti-cracking layer 7. It should be noted that the anti-cracking layer 7 being in contact with the outer surface of the insulator 3 without a gap can be observed, for example, using an optical microscope or an electron microscope.

[0037] The anti-cracking layer 7 is a layer that serves as the basis for the plating layer 4 and is a layer that suppresses the insulator 3 from bending as the high-frequency signal transmission cable 1 bends, thereby causing cracking in the plating layer 4. That is, the anti-cracking layer 7 is a layer that bends while relatively moving in the cable length direction with respect to the bending of the insulator 3, thereby suppressing cracking of the plating layer 4. Here, the "cracking" referred to herein is the cracking of the plating layer 4 occurring within the range from the outer surface of the plating layer 4 to the inner surface of the plating layer 4 (the surface in contact with the anti-cracking layer 7). In addition, the "suppressing cracking of the plating layer 4" referred to herein means that it is more difficult for the plating layer 4 to crack compared to the case where the anti-cracking layer 7 of the present embodiment is not provided.

[0038] The anti-cracking layer 7 is provided between the insulator 3 and the plating layer 4 and is provided in such a manner that even when in contact with the outer surface of the insulator 3 without a gap, it can relatively move in the cable length direction while maintaining a state of being in contact with the insulator 3 without a gap (able to slide in the cable length direction with respect to the insulator 3). The anti-cracking layer 7 is not joined to the insulator 3 and is provided in a state where it can be peeled off from the insulator 3. In addition, the anti-cracking layer 7 covers the insulator 3 in a tubular state.

[0039] When the outer diameter of the cable 1 for high-frequency signal transmission is as thin as 2 mm or less, it is not easy to form the anti-cracking layer 7 by extrusion molding. Therefore, in the present embodiment, the anti-cracking layer 7 is formed by winding the resin film 71 around the outer periphery of the insulator 3 (see Figure 2 (a)), and the resin film 71 is heated to self-fuse to form a tubular anti-cracking layer 7 (see Figure 2 (b)). By heating the resin film 71 to self-fuse, a fused portion 71a formed by the self-fusion of the wrapped portion of the resin film 71 and a non-fused portion 71b that does not wrap the resin film 71 and does not self-fuse are formed in the anti-cracking layer 7. The "self-fusion" mentioned here means that the resin films 71 fuse with each other at the overlapping interfaces.

[0040] In order not to bond to the insulator 3 when the resin film 71 self-fuses, as the resin film 71, a film made of a resin having a melting point (softening temperature) lower than that of the resin used in the insulator 3 can be used, and more preferably a film made of a resin having a melting point (softening temperature) 20 °C or more lower than that of the resin used in the insulator 3 and capable of self-fusing due to heat can be used. Specifically, as the resin film 71, for example, a film made of polyethylene or PET (polyethylene terephthalate) can be used.

[0041] After self-fusion, the thickness of the anti-cracking layer 7 (the size of the straight-line distance from the inner surface in contact with the insulating layer 3 to the outer surface in contact with the plating layer 4) is thinner than the thickness of the insulator 3 and thicker than the thickness of the plating layer 4. More specifically, the thickness of the anti-cracking layer 7 can be 6 μm or more and 20 μm or less. If the thickness of the anti-cracking layer 7 is 6 μm or more, the mechanical strength is improved and it is difficult to break. If the thickness of the anti-cracking layer 7 is 20 μm or less, compared with the case where the thickness exceeds 20 μm, the outer diameter of the cable 1 for high-frequency signal transmission becomes smaller. Therefore, even when the cable 1 for high-frequency signal transmission is bent with a small bending radius, etc., the stress applied to the plating layer 4 (the stress applied to the plating layer 4 due to the deformation of the plating layer 4 as the cable 1 for high-frequency signal transmission bends) can be reduced, it is difficult for cracks to occur in the plating layer 4, and in addition, the diameter of the cable 1 for high-frequency signal transmission can be made small. In order to achieve the anti-cracking layer 7 with such a thickness, the thickness of the resin film 71 used in the anti-cracking layer 7 can be, for example, 3 μm or more and 10 μm or less.

[0042] The plating layer 4 and the metal shielding layer 5 together constitute the outer conductor. As described above, in the metal shielding layer 5, it is formed by braiding or horizontally winding metal bare wires. With only the metal shielding layer 5, there is a possibility that internal signals will radiate to the outside from the gaps between the metal bare wires and the attenuation amount will increase. By providing the plating layer 4, the gaps between the metal bare wires of the metal shielding layer 5 are filled, and the attenuation amount is further reduced. It should be noted that the plating layer 4 and the metal shielding layer 5 are in contact and electrically connected.

[0043] As the coating layer 4, a coating layer made of a metal with a conductivity of 99% or more (99% IACS or more) can be used. For example, a coating layer made of copper or silver can be used.

[0044] The thickness of the coating layer 4 can be 2 μm or more and 5 μm or less. If the thickness of the coating layer 4 is 2 μm or more, even when bending is applied or the like and the metal shielding layer 5 comes into contact with the coating layer 4, cracking is less likely to occur in the coating layer 4. In addition, if the thickness of the coating layer 4 is 5 μm or less, it is possible to prevent the high-frequency signal transmission cable 1 from being difficult to bend due to the hardening of the coating layer 4.

[0045] (Manufacturing method of the high-frequency signal transmission cable 1)

[0046] When manufacturing the high-frequency signal transmission cable 1, first, an insulator 3 made of fluororesin is coated around the inner conductor 2 by extrusion molding. Thereafter, as Figure 2 (a) shows, the resin film 71 is wound around the outer periphery of the insulator 3 in a spiral shape. At this time, the resin film 71 is wound in such a manner that a part in its width direction overlaps. Hereinafter, the overlapping part of the resin film 71 will be referred to as the wrapped part 71c, and the non-overlapping part of the resin film 71 will be referred to as the non-wrapped part 71d. In addition, when winding the resin film 71, it is wound while applying a predetermined tension to the resin film 71. Thereby, the resin film 71 is wound in a state of being in contact with the entire outer periphery of the outer surface of the insulator 3.

[0047] Thereafter, as Figure 2As shown in Fig. (b), the resin film 71 is heated to soften it and cause the resin film 71 to self-fuse. At this time, with respect to the temperature of the resin film 71, it is heated in such a way that the temperature is above the softening temperature of the resin film 71 and below the melting point of the insulator 3. As a result, the resin films 71 in the overlapping portion of the wrapping portion 71c are melted and integrated with each other to form a fused portion 71a. It should be noted that the fusion of the resin films 71 with each other can also be carried out by methods other than heating. In addition, the non-wrapping portion 71d becomes a non-fused portion 71b where the resin films 71 do not fuse with each other. As a result, even when it comes into contact with the outer surface of the insulator 3, it will not adhere to the insulator 3, and a tubular anti-cracking layer 7 that can move relative to the insulator 3 is formed. It should be noted that in the present embodiment, the resin film 71 is wound in a spiral shape, so that the fused portion 71a and the non-fused portion 71b are alternately formed in the cable length direction. That is, the anti-cracking layer 7 is alternately formed with a wrapping portion 71c where the resin films 71 overlap each other and a non-wrapping portion 71d where the resin films 71 do not overlap each other in the cable length direction. In the wrapping portion 71c, the resin films 71 are fused with each other. By forming such a structure, when the high-frequency signal transmission cable 1 is bent, the anti-cracking layer 71 can prevent the resin film 71 forming the wrapping portion 71c from peeling off radially outward, and ensure the flexibility that enables the anti-cracking layer 7 to be bent. Therefore, when the high-frequency signal transmission cable 1 is bent, it is assumed that the plating layer in close contact with the outer surface of the anti-cracking layer 7 is integrated with the anti-cracking layer 7, making it easier to bend. In addition, with respect to the bending of the insulating layer 3, when the anti-cracking layer 7 and the plating layer 4 are integrated and bend while moving relative to each other, the generation of cracks in the plating layer 4 due to the bending of the anti-cracking layer 7 can be suppressed.

[0048] By heating the resin film 71, the resin film 71 shrinks, so that a part of the wall of the wrapping portion 71c moves toward the non-wrapping portion 71d. As a result, compared with the thickness of the wrapping portion 71c before self-fusion, the thickness of the fused portion 71a after self-fusion becomes thinner. In addition, compared with the thickness of the non-wrapping portion 71d before self-fusion, the thickness of the non-fused portion 71b after self-fusion becomes thicker. As a result, the change in thickness in the anti-cracking layer 7 becomes smaller, and a smooth curved surface without steps is formed on the surface of the anti-cracking layer 7. It should be noted that in this state, the thickness of the fused portion 71a is slightly larger than the thickness of the non-fused portion 71b, and the surface of the anti-cracking layer 7 becomes a somewhat wavy state.

[0049] After that, as Figure 2As shown in (c), a plating layer 4 is formed on the anti-cracking layer 7. Before forming the plating layer 4, a prescribed treatment may be performed on the outer surface of the anti-cracking layer 7. Specifically, the outer surface of the anti-cracking layer 7 is subjected to sandblasting treatment by spraying a powder composed of dry ice, metal particles, carbon particles, oxide particles, carbide particles, nitride particles, etc., to roughen the outer surface of the anti-cracking layer 7 and form a prescribed roughness, and further modified by corona discharge exposure treatment, etc. Thereafter, the plating layer 4 is formed by electroless plating so as to cover the periphery of the anti-cracking layer 7. Thus, when the plating layer 4 is formed on the outer surface of the anti-cracking layer 7, the plating layer 4 extends over the entire outer periphery of the outer surface of the anti-cracking layer 7 and firmly adheres. When the high-frequency signal transmission cable 1 is bent, etc., for the bending of the insulating layer 3, the anti-cracking layer 7 and the plating layer 4 are integrated and bend while relatively moving. Thereby, the effect of suppressing cracking of the plating layer 4 can be improved. It should be noted that electroplating may be further performed after electroless plating to form the plating layer 4. Since the plating layer 4 is formed along the outer surface of the anti-cracking layer 7, the surface of the plating layer 4 in contact with the anti-cracking layer 7 becomes somewhat wavy, similar to the anti-cracking layer 7.

[0050] Thereafter, as Figure 2 As shown in (d), a metal shielding layer 5 is formed around the plating layer 4. Since the metal shielding layer 5 is formed while applying a prescribed tension to the bare metal wire 5a, by forming the metal shielding layer 5, a squeezing force is applied to the plating layer 4 and the anti-cracking layer 7 in the radially inward direction. Using this force, the anti-cracking layer 7, which is more flexible than the plating layer 4, deforms, and the thicker fusion part 71a is squeezed in the radially inward direction, and a part of the wall of the fusion part 71a moves to the non-fusion part 71b, and the anti-cracking layer 7a forms a substantially uniform thickness. That is, by forming the metal shielding layer 5, the plating layer 4 and the anti-cracking layer 7 are pressed in the radially inward direction, and the surface corrugations of the anti-cracking layer 7 and the plating layer 4 become very small. As a result, the plating layer 4 and the anti-cracking layer 7 are substantially flat in the cable length direction, and the distance between the inner conductor 2 and the plating layer 4 is kept substantially constant in the direction of the cable length, and a uniform characteristic impedance is achieved in the direction of the cable length.

[0051] Thereafter, if a sheath 6 is formed by tube extrusion around the metal shielding layer 5, the high-frequency signal transmission cable 1 according to the present embodiment is obtained.

[0052] In the high-frequency signal transmission cable 1 according to this embodiment, when the metal shield layer 5 is provided, the anti-crack layer 7 is generally flat, making it difficult to confirm that the anti-crack layer 7 has the fusion portion 71a and the non-fusion portion 71b. However, by disassembling the high-frequency signal transmission cable 1 and removing the anti-crack layer 7, the presence of the fusion portion 71a and the non-fusion portion 71b can be confirmed. For example, the fusion portion 71a is slightly thicker than the non-fusion portion 71b, so by observing this thickness difference using a microscope or the like, the presence of the fusion portion 71a and the non-fusion portion 71b can be confirmed. Furthermore, since the anti-crack layer 7 is difficult to cleave at the fusion portion 71a but easy to cleave at the non-fusion portion 71b, the presence of the fusion portion 71a and the non-fusion portion 71b can be inferred by determining whether the easily cleavable portions are periodically distributed along the length of the cable.

[0053] Here, the effect of providing the anti-crack layer 7 so as to be movable relative to the insulator 3 will be described. Figure 3 As shown, the anti-crack layer 7 can bend while moving relative to the insulator 3. Therefore, when the high-frequency signal transmission cable 1 is bent, the anti-crack layer 7 can bend without following the insulator 3's elongation in the cable's longitudinal direction, while the insulator 3 bends while elongating in the cable's longitudinal direction. Consequently, the elongation of the plating 4 in the cable's longitudinal direction is suppressed. In contrast, if the anti-crack layer 7 cannot bend while moving relative to the insulator 3, when the high-frequency signal transmission cable 1 is bent, the plating 4 is stretched along the outer surface of the insulator 3 to follow the elongation of the insulator 3 in the cable's longitudinal direction. This results in a large load being applied to the plating 4, making cracks 9 more likely to occur.

[0054] If cracks 9 occur in the plating 4, cracks 9 may also occur simultaneously in the base of the plating 4 (the anti-crack layer 7, the insulator 3). This phenomenon is called co-crack (co-cut). Therefore, when the plating 4 is directly formed on the outer surface of the insulator 3, if cracks 9 occur in the plating 4 due to bending, etc., there is a risk that the plating 4 and the insulator 3 will co-crack, resulting in poor insulation and other undesirable conditions. In this embodiment, the plating 4 is formed via the anti-crack layer 7, which is a component separate from the insulator 3, and the anti-crack layer 7 can bend while moving relative to the bending of the insulator 3, so cracks 9 are less likely to occur in the plating 4. In addition, even if cracks 9 occur in the plating 4, co-cracks are unlikely to occur in the insulator 3, and undesirable conditions such as poor insulation can be suppressed.

[0055] Furthermore, since the plating layer 4 is formed on the crack-resistant layer 7 made of a resin film, even when the high-frequency signal transmission cable 1 with an outer diameter of 2 mm or less is appropriately bent corresponding to the narrow layout inside the small electronic device, it can slide relative to the insulator 3 while maintaining the state of contact between the crack-resistant layer 7 and the outer surface of the insulator 3 without gaps. Therefore, the distance between the inner conductor 2 and the plating layer 4 can be kept substantially constant. For example, in the case of replacing the plating layer 4 and the crack-resistant layer 7 with a longitudinally wound metal strip (which has a metal layer formed on one surface of the resin layer), the metal strip will form wrinkles and fractures due to bending, and gaps will be generated between the insulator and the metal strip, resulting in local changes in the characteristic impedance and an increase in the return loss due to the inconsistency of the characteristic impedance. In the high-frequency signal transmission cable 1 according to the present embodiment, the crack-resistant layer 7 deforms softly corresponding to the bending, so the distance between the inner conductor 2 and the plating layer 4 can be kept substantially constant, and the characteristic impedance of the high-frequency signal transmission cable 1 can be kept substantially constant in the cable length direction, suppressing the return loss and obtaining good attenuation characteristics.

[0056] A connector is installed at the end of the high-frequency signal transmission cable 1, for example. At this time, terminal treatment is performed on the end of the high-frequency signal transmission cable 1 to expose the plating layer 4, the insulator 3, and the inner conductor 2 in a stepped manner. In the present embodiment, the crack-resistant layer 7 and the insulator 3 are not bonded or joined, so it is easy to peel off the plating layer 4 and the crack-resistant layer 7 from the outer surface of the insulator 3, and terminal treatment can be easily performed.

[0057] In addition, the exposed plating layer 4 and the inner conductor 2 through terminal treatment are connected to the substrate inside the connector using solder or the like. When connecting the plating layer 4 using solder or the like, the plating layer 4 is heated. At this time, for example, when the plating layer 4 is directly formed on the outer surface of the insulator 3, the insulator 3 expands due to heat, and the plating layer 4 will be stretched as the insulator 3 expands, so there may be a situation where cracks are generated in the plating layer 4. In the present embodiment, even when the insulator 3 expands when the plating layer 4 is heated, the crack-resistant layer 7 does not follow this expansion but functions in a way that slides relative to the insulator 3. Therefore, it also has the advantage that it is difficult for the plating layer 4 to crack due to the thermal expansion of the insulator 3.

[0058] (Functions and effects of the embodiment)

[0059] As described above, in the high-frequency signal transmission cable 1 according to the present embodiment, there is a crack-resistant layer 7 provided in a state of contacting the insulator 3 between the insulator 3 and the plating layer 4, and the outer surface of the crack-resistant layer 7 is provided with the plating layer 4. The crack-resistant layer 7 is composed of a resin film 71, and bends while relatively moving in the cable length direction in response to the bending of the insulator 3, thereby suppressing cracking of the plating layer 4.

[0060] By winding the resin film 71 and causing it to self-fuse, an anti-cracking layer 7 that is very thin and can move relative to the insulator 3 in the cable length direction can be formed. As a result, even when the outer diameter is as small as less than 2 mm, a high-frequency signal transmission cable 1 having an anti-cracking layer 7 can be realized. As a result, even when the high-frequency signal transmission cable 1 is bent and routed in a narrow space inside an electronic device or the like, when the insulator 3 is stretched in the cable length direction due to the bending, the plating layer 4 does not elongate along with the elongation of the insulator 3, but deforms (bends) in a manner that slides relative to the insulator 3. Therefore, wrinkles and cracks will not occur in the plating layer 4, and the distance between the inner conductor 2 and the plating layer 4 can be kept constant. As a result, even when high-frequency (for example, in the region of 10 MHz to 6 GHz) signals are transmitted over a long distance in the high-frequency signal transmission cable 1, good transmission characteristics (attenuation characteristics) that are difficult to attenuate can be achieved.

[0061] Among them, in the high-frequency signal transmission cable 1 according to the present embodiment described above, the anti-cracking layer 7 has been described in a form in which the wrapped portions of the resin films 71 are self-fused with each other. However, as long as it is within the range where the above-mentioned functions and effects can be obtained, methods other than fusion can also be used to join the resin films 71 of the wrapped portions to each other. In addition, in the anti-cracking layer 7, it is more preferable that the interface where the resin films 71 in the wrapped portion contact each other is fused throughout the entire surface. However, as long as it is within the range where the above-mentioned functions and effects can be obtained, it may also be that a part of the interface where the resin films 71 of the wrapped portion contact each other is fused. In this case, at least the boundary portion between the wrapped portion and the non-wrapped portion is fused.

[0062] In addition, by providing a metal shielding layer 5 around the plating layer 4, the metal shielding layer 5 presses the plating layer 4 and the anti-cracking layer 7 inward in the radial direction, the plating layer 4 and the anti-cracking layer 7 become substantially flat, the distance between the inner conductor 2 and the plating layer 4 can be kept substantially constant, and a uniform characteristic impedance can be formed throughout the cable length direction, achieving better attenuation characteristics.

[0063] In addition, since the anti-cracking layer 7 can move relative to the insulator 3 in the cable length direction, it is easy to bend the high-frequency signal transmission cable 1, and a high-frequency signal transmission cable 1 can be realized in which the transmission characteristics of high-frequency signals are hardly reduced even when routed in a narrow space such as inside an electronic device.

[0064] (Summary of Embodiments)

[0065] Next, the technical idea understood from the embodiments described above will be described by citing the symbols and the like in the embodiments. Among them, the symbols and the like in the following description do not limit the components in the claims to the specific components given in the embodiments.

[0066] [1]A cable (1) for high-frequency signal transmission includes at least a conductor (2), an insulator (3) covering the periphery of the conductor (2), a coating (4) covering the periphery of the insulator (3), and a sheath (6) covering the periphery of the coating (4). Among them, an anti-cracking layer (7) is provided between the insulator (3) and the coating (4). The anti-cracking layer (7) is in contact with the insulator (3) and has the coating (4) on its outer surface. The anti-cracking layer (7) is composed of a resin film (71). When the insulator (3) is bent, the anti-cracking layer (7) bends while relatively moving in the cable length direction, thereby suppressing cracking of the coating (4).

[0067] [2]For the cable (1) for high-frequency signal transmission according to [1], the anti-cracking layer (7) alternately forms a wrapped portion where the resin films (71) overlap each other and a non-wrapped portion where the resin films (71) do not overlap in the cable length direction. In the wrapped portion, the resin films (71) are fused together.

[0068] [3]For the cable (1) for high-frequency signal transmission according to [1] or [2], the thickness of the anti-cracking layer (7) is thinner than the thickness of the insulator (3) and thicker than the thickness of the coating (4).

[0069] [4]For the cable (1) for high-frequency signal transmission according to any one of [1] to [3], the thickness of the anti-cracking layer (7) is 6 μm or more and 20 μm or less.

[0070] [5]For the cable (1) for high-frequency signal transmission according to any one of [1] to [4], the thickness of the coating (4) is 2 μm or more and 5 μm or less.

[0071] [6]For the cable (1) for high-frequency signal transmission according to any one of [1] to [5], the melting point of the resin film (71) is lower than the melting point of the resin used in the insulator (3).

[0072] [7]For the cable (1) for high-frequency signal transmission according to any one of [1] to [6], the insulator (3) is made of fluororesin.

[0073] [8]A manufacturing method of a cable for high-frequency signal transmission. The cable for high-frequency signal transmission includes at least a conductor (2), an insulator (3) covering the periphery of the conductor (2), a coating (4) covering the periphery of the insulator (3), and a sheath (6) covering the periphery of the coating (4). The outer diameter of the sheath (6) is 2 mm or less.

[0074] After winding the resin film (71) around the outer periphery of the aforementioned insulator (3), the aforementioned resin film (71) is heated to cause the wrapped portion of the aforementioned resin film (71) to fuse by itself, forming a fused portion (71a) and a non-fused portion (71b), thereby forming an anti-cracking layer (7) that can bend while relatively moving in the cable length direction with respect to the bending of the aforementioned insulator (3) in a state of being in contact with the aforementioned insulator (3) between the aforementioned insulator (3) and the aforementioned plating (4).

[0075] The embodiments of the present invention have been described above, but the embodiments described above do not limit the invention related to the claims. In addition, it should be noted that not all combinations of features described in the embodiments are necessary for the method of solving the invention problem.

[0076] Within the scope not departing from its gist, the present invention can be implemented with appropriate modifications. For example, in the above embodiment, the resin film 71 is spirally wound around the insulator 3 and then self-fused to form the anti-cracking layer 7, but it is not limited thereto. It may also be that the resin film 71 is longitudinally wound around the insulator 3 and then self-fused to form the anti-cracking layer 7. In this case, for example, the resin film 71 may be longitudinally wound, and a tape or a wire may be spirally wound in a manner to maintain the winding state of the resin film 71. After heating the resin film 71 to cause it to self-fuse, the tape or the wire is removed.

Claims

1. A cable for high-frequency signal transmission, comprising at least a conductor, an insulator covering the periphery of the conductor, a coating covering the periphery of the insulator, and a sheath covering the periphery of the coating, wherein, an anti-cracking layer is provided between the insulator and the coating, which is arranged in contact with the insulator and has the coating on its outer surface, the anti-cracking layer is composed of a resin film, and bends while relatively moving in the cable length direction in response to the bending of the insulator, thereby suppressing cracking of the coating, in the anti-cracking layer, a wrapped portion where the resin films overlap each other and a non-wrapped portion where the resin films do not overlap each other are alternately formed in the cable length direction, and in the wrapped portion, the resin films are fused together.

2. The cable for high-frequency signal transmission according to claim 1, wherein, The thickness of the anti-cracking layer is thinner than the thickness of the insulator and thicker than the thickness of the coating.

3. The high-frequency signal transmission cable according to claim 1 or 2, wherein The thickness of the anti-cracking layer is 6 μm or more and 20 μm or less.

4. The high-frequency signal transmission cable according to claim 1 or 2, wherein The thickness of the coating is 2 μm or more and 5 μm or less.

5. The cable for high-frequency signal transmission according to claim 1 or 2, wherein, The melting point of the resin film is lower than the melting point of the resin used in the insulator.

6. The high-frequency signal transmission cable according to claim 1 or 2, wherein, The insulator is made of a fluororesin.

7. A manufacturing method of a cable for high-frequency signal transmission, the cable for high-frequency signal transmission comprises at least a conductor, an insulator covering the periphery of the conductor, a coating covering the periphery of the insulator, and a sheath covering the periphery of the coating, after winding a resin film around the outer periphery of the insulator, the resin film is heated to alternately form a wrapped portion where the resin films overlap each other and a non-wrapped portion where the resin films do not overlap each other in the cable length direction. In the wrapped portion, the resin films are fused together, and the non-wrapped portion becomes a non-fused portion where the resin films are not fused together, thereby forming an anti-cracking layer between the insulator and the coating, which is arranged in contact with the insulator and has the coating on its outer surface. The anti-cracking layer bends while relatively moving in the cable length direction in response to the bending of the insulator, thereby suppressing cracking of the coating.

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