Cables for differential signal transmission

Abstract

A differential signal transmission cable comprises an insulating layer extending along the length of the cable; a pair of signal lines extending along the length and embedded within the insulating layer; an intermediate layer covering the outer periphery of the insulating layer; a shield; and catalyst particles. The shield comprises an electroless plating layer covering the outer periphery of the intermediate layer. The catalyst particles are dispersed between the intermediate layer and the electroless plating layer.

Description

Technical Field

[0001] The present invention relates to a cable for transmitting differential signals. Background Art

[0002] Patent Document 1 (Japanese Patent Application Publication No. 2019-16451) describes a differential signal transmission cable. The differential signal transmission cable described in Patent Document 1 includes an insulating layer, a pair of signal wires, and an electroless plating layer. The pair of signal wires are embedded within the insulating layer. The electroless plating layer is formed on the outer circumference of the insulating layer.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2019-16451 Summary of the Invention

[0004] The differential signal transmission cable according to the present invention comprises: an insulation layer extending along the length of the differential signal transmission cable; a pair of signal lines extending along the length and embedded within the insulation layer; an intermediate layer covering the outer periphery of the insulation layer; a shield; and catalyst particles. The shield comprises an electroless plating layer covering the outer periphery of the intermediate layer. The catalyst particles are dispersed between the intermediate layer and the electroless plating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 It is a perspective view of the differential signal transmission cable 10 .

[0006] Figure 2A It is a cross-sectional view of the differential signal transmission cable 10 .

[0007] Figure 2B The area near the interface between the intermediate layer 40 and the electroless plating layer 51 Figure 2A Magnified image of .

[0008] Figure 3 1 and 2 are process diagrams showing a method for manufacturing the differential signal transmission cable 10 .

[0009] Figure 4 It is a cross-sectional view of the process target member 10A prepared in the preparation step S1.

[0010] Figure 5 It is a cross-sectional view of the process target member 10A after the intermediate layer forming step S2 is performed.

[0011] Figure 6 10A is a cross-sectional view of the treatment target member 10A after the catalyst particle arrangement step S3 has been performed.

[0012] Figure 7 It is a cross-sectional view of the treatment target member 10A after the electroless plating step S4 is performed.

[0013] Figure 8It is an enlarged cross-sectional view of the vicinity of the interface between the intermediate layer 40 and the electroless plating layer 51 of the differential signal transmission cable 70 .

[0014] Figure 9A It is a graph showing the attenuation characteristics of the differential signal transmission cable 70 .

[0015] Figure 9B It is a graph showing the attenuation characteristics of the differential signal transmission cable 10 .

[0016] Figure 10 It is a cross-sectional view of the differential signal transmission cable 80 . DETAILED DESCRIPTION

[0017] [Problems to be Solved by the Invention]

[0018] In the differential signal transmission cable described in Patent Document 1, the outer peripheral surface of the insulating layer is roughened by etching, thereby obtaining an anchor effect between the insulating layer and the electroless plating layer, thereby ensuring adhesion between the insulating layer and the electroless plating layer.

[0019] However, since the outer peripheral surface of the insulating layer is uniformly roughened by etching, minute irregularities are periodically present on the outer peripheral surface of the insulating layer after etching. These periodically present minute irregularities deteriorate the attenuation characteristics in the high frequency range of 30 GHz or higher.

[0020] The present invention has been made in view of the above-mentioned problems of the prior art. More specifically, the present invention provides a differential signal transmission cable that can ensure the adhesion of the electroless plating layer without deteriorating the attenuation characteristics in the high-frequency region.

[0021] [Effects of the Invention]

[0022] According to the differential signal transmission cable according to the present invention, it is possible to suppress deterioration of attenuation characteristics in a high-frequency region and ensure adhesion of the electroless plating layer.

[0023] [Description of Embodiments of the Invention]

[0024] First, embodiments of the present invention will be described by way of examples.

[0025] (1) A differential signal transmission cable according to one embodiment includes: an insulating layer extending along the longitudinal direction of the differential signal transmission cable; a pair of signal lines extending along the longitudinal direction and embedded within the insulating layer; an intermediate layer covering the outer periphery of the insulating layer; a shield; and catalyst particles. The shield includes an electroless plating layer covering the outer periphery of the intermediate layer. The catalyst particles are dispersed between the intermediate layer and the electroless plating layer.

[0026] According to the differential signal transmission cable of (1) above, it is possible to suppress deterioration of attenuation characteristics in a high-frequency region and ensure adhesion of the electroless plating layer.

[0027] (2) In the differential signal transmission cable of (1) above, the content of the catalyst particles contained in the differential signal transmission cable may be 0.1 μg or more and 10 μg or less per cm in the longitudinal direction.

[0028] According to the differential signal transmission cable of (2) above, it is possible to suppress deterioration of attenuation characteristics in a high-frequency region and ensure adhesion of the electroless plating layer.

[0029] (3) In the differential signal transmission cable described in (1) or (2) above, the arithmetic mean roughness of the outer peripheral surface of the insulating layer may be 2.0 μm or less.

[0030] According to the differential signal transmission cable of (3) above, it is possible to further suppress the deterioration of the attenuation characteristics in the high frequency region.

[0031] (4) In the differential signal transmission cable described in (1) to (3) above, the arithmetic mean roughness of the outer peripheral surface of the insulating layer may be less than 0.6 μm.

[0032] According to the differential signal transmission cable of (4) above, it is possible to further suppress the deterioration of the attenuation characteristics in the high frequency region.

[0033] (5) In the differential signal transmission cable described in (1) to (4) above, the bonding strength between the intermediate layer and the electroless plating layer may be 0.1 N / cm or more and 6 N / cm or less.

[0034] According to the differential signal transmission cable of (5) above, it is possible to suppress peeling of the electroless plating when twisting a plurality of differential signal transmission cables, and to suppress peeling of the insulation layer together with the intermediate layer when performing terminal processing on the differential signal transmission cables.

[0035] (6) In the differential signal transmission cable described in (1) to (5) above, the thickness of the intermediate layer may be 1 μm or less.

[0036] According to the differential signal transmission cable of (6) above, it is possible to suppress deterioration of attenuation characteristics in the high frequency region due to the difference in impedance between the insulating layer, the electroless plating layer, and the intermediate layer.

[0037] (7) In the differential signal transmission cables described in (1) to (6) above, the thickness of the electroless plating layer may be not less than 0.05 μm and not more than 0.5 μm.

[0038] According to the differential signal transmission cable described in (7), the generation of holes at the interface between the electroless plating and the intermediate layer due to gas generated during the formation of the electroless plating can be suppressed, and the generation of areas on the outer peripheral surface of the intermediate layer where the electroless plating is not attached can be suppressed.

[0039] (8) In the differential signal transmission cables described in (1) to (7) above, the shield portion may further include an electrolytic plating layer covering the outer periphery of the electroless plating layer.

[0040] According to the differential signal transmission cable of (8) above, the resistance value of the shield portion can be reduced.

[0041] (9) In the differential signal transmission cable of (8) above, the electrolytic plating layer may be an electrolytic copper plating layer, and the average particle size of the copper crystal grains in the electrolytic plating layer may be 0.5 μm or more.

[0042] According to the differential signal transmission cable of (9) above, it is possible to suppress the occurrence of cracks in the electrolytic plating layer when the differential signal transmission cable is bent.

[0043] (10) In the differential signal transmission cable of (8) or (9) above, the total thickness of the electroless plating layer and the electrolytic plating layer may be 6 μm or less.

[0044] According to the differential signal transmission cable of (10) above, the manufacturing cost associated with forming the shield portion can be reduced.

[0045] (11) In the differential signal transmission cable described in (1) to (10) above, the catalyst particles may contain palladium.

[0046] (12) In the differential signal transmission cable described in (1) to (11) above, the insulating layer may include polyolefin having a melting point of 140° C. or higher.

[0047] (13) In the differential signal transmission cable described in (1) to (11) above, the insulating layer may include at least one of polypropylene, cyclic olefin polymer, and polymethylpentene.

[0048] (14) In the differential signal transmission cable described in (1) to (11), the insulating layer may include polypropylene crystal grains. The polypropylene crystal grains may have a crystallinity X calculated by the following formula (1): c is greater than 0.3. In formula (1), I c is the X-ray diffraction intensity of the crystalline component, I a is the X-ray diffraction intensity of the amorphous component.

[0049] [Formula 1]

[0050] Formula (1)

[0051] According to the differential signal transmission cable of (14) above, the adhesion of the electroless plating layer is improved, thereby making it possible to suppress the transmission loss of the differential signal transmission cable.

[0052] (15) The differential signal transmission cable according to other embodiments comprises: an insulating layer extending in the longitudinal direction of the differential signal transmission cable; a pair of signal lines extending in the longitudinal direction and buried in the interior of the insulating layer; an intermediate layer covering the outer periphery of the insulating layer; and a shielding portion covering the outer periphery of the intermediate layer. The shielding portion has a non-electrolytic plating layer covering the outer periphery of the intermediate layer. The insulating layer contains polypropylene grains. The polypropylene grains have a monoclinic crystal structure, a hexagonal crystal structure, or a state in which at least one of them coexists, and are oriented along no more than two specific crystal axes. In the insulating layer, the degree of crystal orientation O calculated by the following formula (2) is 110 is less than 0.65. In formula (2), I 110 is the integrated intensity of X-ray diffraction with index 110, I 040 is the integrated intensity of X-ray diffraction with index 0.40.

[0053] [Formula 2]

[0054] Formula (2)

[0055] According to the differential signal transmission cable of (15) above, the adhesion of the electroless plating layer is improved, thereby making it possible to suppress the transmission loss of the differential signal transmission cable.

[0056] (16) A differential signal transmission cable according to another embodiment includes: an insulating layer extending in the longitudinal direction of the differential signal transmission cable; a pair of signal lines extending in the longitudinal direction and embedded in the insulating layer; an intermediate layer covering the outer periphery of the insulating layer; and a shield covering the outer periphery of the intermediate layer. The shield includes an electroless plating layer covering the outer periphery of the intermediate layer. The insulating layer includes polypropylene grains. The crystallinity X of the polypropylene grains is calculated by the above-mentioned formula (1): c It is above 0.3.

[0057] According to the differential signal transmission cable of (16) above, the adhesion of the electroless plating layer is improved, thereby making it possible to suppress the transmission loss of the differential signal transmission cable.

[0058] [Details of the embodiments of the present invention]

[0059] Next, the details of the embodiment will be described with reference to the accompanying drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0060] (First embodiment)

[0061] Next, a differential signal transmission cable according to the first embodiment (hereinafter referred to as “differential signal transmission cable 10 ”) will be described.

[0062] <Structure of Differential Signal Transmission Cable 10>

[0063] Figure 1 It is a perspective view of the differential signal transmission cable 10 . Figure 2A It is a cross-sectional view of the differential signal transmission cable 10 . Figure 2B The area near the interface between the intermediate layer 40 and the electroless plating layer 51 Figure 2A Magnified image of . Figure 1 、 Figure 2A and Figure 2B As shown, the differential signal transmission cable 10 includes an insulating layer 20 , a signal line 30 , an intermediate layer 40 , a shield 50 , and catalyst particles 60 .

[0064] The insulating layer 20 extends along the length of the differential signal transmission cable 10. The insulating layer 20 is formed of an insulating material. For example, the insulating layer 20 is formed of polyethylene. However, the insulating layer 20 may also be formed of materials other than polyethylene. For example, the insulating layer 20 may be formed of polyolefin. From the perspective of heat resistance, the melting point of the polyolefin is preferably 140°C or higher, and more preferably 150°C or higher.

[0065] The insulating layer 20 has an outer peripheral surface 20a. The arithmetic mean roughness of the outer peripheral surface 20a is preferably 2 μm or less. More preferably, the arithmetic mean roughness of the outer peripheral surface 20a is less than 0.6 μm. The arithmetic mean roughness of the outer peripheral surface 20a is measured using a VM-X150 laser microscope (manufactured by KEYENCE CORPORATION). More specifically, the outer peripheral surface 20a is observed using a 50x objective lens. The analysis software VK-H1XM is used to calculate the arithmetic mean roughness of the differential signal transmission cable in the longitudinal direction based on the observation results.

[0066] The signal lines 30 form a pair (hereinafter referred to as "signal line 30a" and "signal line 30b"). A signal with an opposite phase to that of the signal applied to the signal line 30a is applied to the signal line 30b. In this way, a differential signal is transmitted through the differential signal transmission cable 10.

[0067] The signal lines 30a and 30b are embedded within the insulating layer 20. The signal lines 30a and 30b extend along the length of the differential signal transmission cable 10. The signal lines 30a and 30b are formed from a conductive material. For example, the signal lines 30a and 30b are formed from copper (Cu). However, the signal lines 30a and 30b may also be formed from materials other than copper.

[0068] The intermediate layer 40 is formed so as to cover the outer peripheral surface 20a. The intermediate layer 40 has a thickness T1. Thickness T1 is, for example, 1.5 μm or less. Thickness T1 is preferably 1 μm or less. The intermediate layer 40 has an outer peripheral surface 40a. The intermediate layer 40 is formed of an insulating material. For example, the intermediate layer 40 is formed of polyolefin. However, the intermediate layer 40 may also be formed of materials other than polyolefin.

[0069] The shield portion 50 is formed so as to cover the outer peripheral surface 40a. The shield portion 50 has conductivity. The shield portion 50 has an electroless plating layer 51. The electroless plating layer 51 is a plating layer formed by an electroless plating method.

[0070] The electroless plating layer 51 is formed to cover the outer peripheral surface 40a. The electroless plating layer 51 has a thickness T2. Thickness T2 is, for example, 0.05 μm or greater. Thickness T2 is, for example, 0.5 μm or less. Thickness T2 is preferably 0.05 μm or greater and 0.5 μm or less. The electroless plating layer 51 is, for example, electroless copper plating. The electroless plating layer 51 has an outer peripheral surface 51a.

[0071] The resistance value of the electroless plating layer 51 is preferably less than 50 mΩ / cm. The defect rate of the electroless plating layer 51 is preferably less than 1.5. The defect rate of the electroless plating layer 51 is the value obtained by dividing the measured resistance value of the electroless plating layer 51 by the theoretical resistance value of the electroless plating layer 51.

[0072] The bonding strength between the intermediate layer 40 and the electroless plating layer 51 is, for example, 0.1 N / cm or greater. The bonding strength between the intermediate layer 40 and the electroless plating layer 51 is, for example, 6 N / cm or less. The bonding strength between the intermediate layer 40 and the electroless plating layer 51 is preferably 0.3 N / cm or greater and 6 N / cm or less. The bonding strength between the intermediate layer 40 and the electroless plating layer 51 is measured by a tensile test.

[0073] The shield portion 50 may further include an electrolytic plating layer 52. The electrolytic plating layer 52 is formed by electrolytic plating. The electrolytic plating layer 52 is formed so as to cover the outer peripheral surface 51a. The electrolytic plating layer 52 has a thickness T3. The total thickness T2 and T3 is preferably 6 μm or less. The electrolytic plating layer 52 is, for example, electrolytic copper plating.

[0074] When the electrolytic plating layer 52 is an electrolytic copper plating layer, the electrolytic plating layer 52 contains a plurality of copper crystal grains. The average particle size of the copper crystal grains in the electrolytic plating layer 52 is, for example, 0.5 μm or greater. The average particle size of the copper crystal grains in the electrolytic plating layer 52 is the average value obtained by observing a cross section of the electrolytic plating layer 52 using a scanning electron microscope (SEM) and measuring the thickness of the electrolytic plating layer 52 at five locations within a predetermined measurement field (e.g., 30 μm × 20 μm).

[0075] The catalytic particles 60 are dispersed between the electroless plating layer 51 and the intermediate layer 40 (at the interface between the electroless plating layer 51 and the intermediate layer 40). That is, the catalytic particles 60 do not form a layer between the electroless plating layer 51 and the intermediate layer 40. When the area of ​​the region on the outer peripheral surface 40a where the catalytic particles 60 are not disposed is 90 percent or more of the overall area of ​​the outer peripheral surface 40a, "the catalytic particles 60 are dispersed between the electroless plating layer 51 and the intermediate layer 40." The average distance between the catalytic particles 60 is preferably 50 nm or greater.

[0076] The average particle size of the catalyst particles 60 is, for example, 300 nm or less. The average particle size of the catalyst particles 60 is measured using a TEM (Transmission Electron Microscope). The catalyst particles 60 contain, for example, palladium (Pd). However, the catalyst particles 60 may also contain materials other than palladium. For example, the catalyst particles 60 may contain copper, silver (Ag), gold (Au), or the like.

[0077] The content of the catalyst particles 60 contained in the differential signal transmission cable 10 is, for example, 0.1 μg or more per 1 cm along the length of the differential signal transmission cable 10. The content of the catalyst particles 60 contained in the differential signal transmission cable 10 is, for example, 10 μg or less per 1 cm along the length of the differential signal transmission cable 10. The content of the catalyst particles 60 contained in the differential signal transmission cable 10 is preferably 0.1 μg or more and 10 μg or less per 1 cm along the length of the differential signal transmission cable 10.

[0078] The content of the catalytic particles 60 per 1 cm along the length of the differential signal transmission cable 10 was measured using an inductively coupled plasma mass spectrometer. According to the findings of the present inventors, when the content of the catalytic particles 60 per 1 cm along the length of the differential signal transmission cable 10 is between 0.1 μg and 10 μg, the catalytic particles 60 do not form a layer between the electroless plating layer 51 and the intermediate layer 40, but are dispersed between the electroless plating layer 51 and the intermediate layer 40.

[0079] <Method of Manufacturing Differential Signal Transmission Cable 10>

[0080] Figure 3 1 is a process diagram showing a method for manufacturing the differential signal transmission cable 10. Figure 3 As shown, the method for manufacturing the differential signal transmission cable 10 includes a preparation step S1 , an intermediate layer forming step S2 , a catalyst particle disposing step S3 , an electroless plating step S4 , and an electrolytic plating step S5 .

[0081] The intermediate layer forming step S2 is performed after the preparation step S1. The catalyst particle placement step S3 is performed after the intermediate layer forming step S2. The electroless plating step S4 is performed after the catalyst particle placement step S3. The electrolytic plating step S5 is performed after the electroless plating step S4.

[0082] In the preparation step S1 , the process target component 10A is prepared. Figure 4 1 is a cross-sectional view of the processing target component 10A prepared in the preparation step S1. Figure 4 As shown, the processing target component 10A includes an insulating layer 20 and a signal line 30. The intermediate layer 40, the shield portion 50, and the catalyst particles 60 are not formed on the processing target component 10A.

[0083] Figure 5 10A is a cross-sectional view of the object component 10A after the intermediate layer forming step S2 is performed. Figure 5 As shown, in the intermediate layer forming step S2, the intermediate layer 40 is formed so as to cover the outer peripheral surface 20a. In the intermediate layer forming step S2, a material constituting the intermediate layer 40 is applied to the outer peripheral surface 20a and the applied material is cured, thereby forming the intermediate layer 40 so as to cover the outer peripheral surface 20a.

[0084] Figure 6 1 is a cross-sectional view of the treatment target component 10A after the catalyst particle arrangement step S3 is performed. Figure 6 As shown, in the catalyst particle disposing step S3, the catalyst particles 60 are dispersed on the outer peripheral surface 40a. In the catalyst particle disposing step S3, a solution containing the catalyst particles 60 is applied to the outer peripheral surface 40a and the solution is volatilized, thereby dispersing the catalyst particles 60 on the outer peripheral surface 40a.

[0085] Figure 7 10A is a cross-sectional view of the treatment target component 10A after the electroless plating step S4 is performed. Figure 7 As shown, in the electroless plating step S4, the electroless plating layer 51 is formed so as to cover the outer peripheral surface 40a. In the electroless plating step S4, the treatment target member 10A is immersed in a plating solution in which the material contained in the electroless plating layer 51 is dissolved. As a result, the material constituting the electroless plating layer 51 is precipitated so as to cover the outer peripheral surface 40a using the catalyst particles 60 dispersed on the outer peripheral surface 40a as a catalyst, thereby forming the electroless plating layer 51.

[0086] In the electrolytic plating step S5, the electrolytic plating layer 52 is formed so as to cover the outer peripheral surface 51a. In the electrolytic plating step S5, the treatment target member 10A is immersed in the plating solution in which the material contained in the electrolytic plating layer 52 is dissolved, and the electroless plating layer 51 is energized. As a result, the material constituting the electrolytic plating layer 52 is deposited on the outer peripheral surface 51a, and the outer peripheral surface 51a is produced. Figure 2A and Figure 2B A differential signal transmission cable 10 having the structure shown.

[0087] <Effects of the Differential Signal Transmission Cable 10>

[0088] In the differential signal transmission cable 10, catalytic particles 60 are dispersed between the intermediate layer 40 and the electroless plating layer 51. Therefore, the outer peripheral surface 40a has fine irregularities caused by the catalytic particles 60. These fine irregularities produce an anchoring effect when the electroless plating layer 51, which is formed so as to cover the outer peripheral surface 40a, and the intermediate layer 40 are bonded together, thereby ensuring the adhesion of the electroless plating layer 51.

[0089] As described above, by dispersing the catalyst particles 60 between the intermediate layer 40 and the electroless plating layer 51, the adhesion of the electroless plating layer 51 is ensured, eliminating the need to roughen the outer peripheral surface 20a. Consequently, the differential signal transmission cable 10 is less likely to experience the degradation of attenuation characteristics in the high-frequency region that would otherwise occur if the outer peripheral surface 20a were roughened. As described above, the differential signal transmission cable 10 can suppress degradation of attenuation characteristics in the high-frequency region while ensuring the adhesion of the electroless plating layer 51.

[0090] In the differential signal transmission cable 10 , when the content of the catalytic particles 60 per 1 cm in the longitudinal direction of the differential signal transmission cable 10 is less than 0.1 μg, a portion not bonded to the electroless plating layer 51 may be formed on the outer peripheral surface 40 a .

[0091] On the other hand, in the differential signal transmission cable 10, if the content of the catalyst particles 60 exceeds 10 μg per 1 cm along the length of the differential signal transmission cable 10, the unevenness caused by the catalyst particles 60 on the outer peripheral surface 20a becomes excessively large, potentially deteriorating the attenuation characteristics in the high-frequency region. Therefore, by setting the content of the catalyst particles 60 per 1 cm along the length of the differential signal transmission cable 10 to between 0.1 μg and 10 μg, it is possible to suppress the deterioration of the attenuation characteristics in the high-frequency region while ensuring the adhesion of the electroless plating layer 51.

[0092] When the arithmetic mean roughness of the outer peripheral surface 20 a is 2.0 μm or less (particularly, less than 0.6 μm), deterioration of the attenuation characteristics in the high-frequency region can be further suppressed.

[0093] The differential signal transmission cable 10 is sometimes formed by twisting multiple strands. If the bonding strength between the intermediate layer 40 and the electroless plating layer 51 is less than 0.1 N / cm, the electroless plating layer 51 may peel off when the differential signal transmission cable 10 is twisted.

[0094] When the differential signal transmission cable 10 is connected to a connector or the like, a termination process is performed to peel off the shield 50. If the bond strength between the intermediate layer 40 and the electroless plating 51 exceeds 6 N / cm, the shield 50 will not be peeled off at the interface between the electroless plating 51 and the intermediate layer 40 during this termination process. When the shield 50 is peeled off, there is a possibility that a portion of the insulating layer 20 may be peeled off along with the intermediate layer 40.

[0095] Therefore, by setting the bonding strength between the intermediate layer 40 and the insulating layer 20 to be greater than 0.1 N / cm and less than 6 N / cm, it is possible to prevent the electroless plating 51 from being peeled off when a plurality of differential signal transmission cables 10 are twisted together, and to prevent the insulating layer 20 from being peeled off together with the intermediate layer 40 when the differential signal transmission cables 10 are terminated.

[0096] When thickness T1 is 1 μm or less, degradation of attenuation characteristics in the high-frequency region caused by impedance disparity between insulating layer 20, electroless plating layer 51, and intermediate layer 40 can be suppressed. When the total of thickness T2 and thickness T3 is 6 μm or less, the manufacturing cost associated with forming shield portion 50 can be reduced.

[0097] When the shield 50 further includes the electrolytic plating 52, the resistance of the shield can be reduced. When the average particle size of the copper crystal grains in the electrolytic plating 52 is 1 μm or greater, the electrolytic plating 52 is made of a relatively soft material, thereby suppressing cracks from forming in the electrolytic plating 52 when the differential signal transmission cable is bent (for example, when subjected to bending deformation with a radius of approximately 300 mm).

[0098] <Experimental Example>

[0099] The following describes the results of comparative tests of a differential signal transmission cable (hereinafter referred to as "differential signal transmission cable 70") according to a comparative example and differential signal transmission cable 10. Differential signal transmission cable 70 includes an insulating layer 20, a signal line 30, an intermediate layer 40, a shield 50 including an electroless plating layer 51 and an electrolytic plating layer 52, and catalyst particles 60. In this respect, the structure of differential signal transmission cable 70 is similar to that of differential signal transmission cable 10.

[0100] Figure 8FIG. 1 is an enlarged cross-sectional view of the interface between the intermediate layer 40 and the electroless plating layer 51 of the differential signal transmission cable 70. Figure 8 As shown, in the differential signal transmission cable 70, the catalyst particles 60 are arranged in layers between the intermediate layer 40 and the electroless plating layer 51. In the differential signal transmission cable 70, the layers of catalyst particles 60 have a porous structure containing voids. In these respects, the structure of the differential signal transmission cable 70 differs from that of the differential signal transmission cable 10.

[0101] Figure 9A It is a graph showing the attenuation characteristics of the differential signal transmission cable 70 . Figure 9B is a graph showing the attenuation characteristics of the differential signal transmission cable 10. Figure 9A and Figure 9B In the figure, the horizontal axis is the frequency of the signal applied to the signal line 30 (unit: GHz), and the vertical axis is the transmission loss (unit: dB) evaluated by Sdd21 (differential mode insertion loss). Figure 9A and Figure 9B In the graph shown, the thickness T2 and the defect rate of the electroless plating layer 51 are 5 μm and 1.1, respectively.

[0102] like Figure 9A As shown, in the differential signal transmission cable 70, there is a frequency band where the transmission loss locally increases significantly around 50 GHz due to the gaps existing inside the catalyst particles 60. Figure 9B As shown, in the frequency range up to at least 60 GHz, there is no frequency band where the transmission loss locally increases significantly (no suck-out occurs) in the differential signal transmission cable 10. As described above, experiments have also shown that dispersing the catalyst particles 60 between the intermediate layer 40 and the electroless plating layer 51 can suppress the deterioration of the attenuation characteristics in the high-frequency range.

[0103] In addition, in the differential signal transmission cable 70 in which the catalyst particles 60 are arranged in layers between the intermediate layer 40 and the electroless plating layer 51, the bonding strength between the electroless plating layer 51 and the intermediate layer 40 becomes too high, and when the shielding part 50 (electroless plating layer 51) is peeled off during terminal processing, a portion of the insulating layer 20 may be peeled off together with the intermediate layer 40.

[0104] (Second embodiment)

[0105] Next, a differential signal transmission cable according to a second embodiment (hereinafter referred to as a "differential signal transmission cable 80") will be described. Here, differences from the differential signal transmission cable 10 will be mainly described, and redundant description will not be repeated.

[0106] <Structure of Differential Signal Transmission Cable 80>

[0107] Figure 10 : is a cross-sectional view of the differential signal transmission cable 80. Figure 10 As shown, the differential signal transmission cable 80 includes an insulating layer 20, a signal line 30, an intermediate layer 40, a shield 50, and catalyst particles 60 (in Figure 10 (not shown in the figure). In addition, the differential signal transmission cable 80 may not include the catalyst particles 60.

[0108] In the differential signal transmission cable 80, the shield portion 50 includes an electroless plating layer 51 and an electrolytic plating layer 52. In the differential signal transmission cable 80, catalyst particles 60 are dispersed between the intermediate layer 40 and the electroless plating layer 51. In these respects, the structure of the differential signal transmission cable 80 is similar to that of the differential signal transmission cable 10. However, the structure of the differential signal transmission cable 80 differs from that of the differential signal transmission cable 10 in that the insulating layer 20 is formed of polypropylene.

[0109] The insulating layer 20 includes crystal particles of polypropylene (hereinafter referred to as "polypropylene crystal particles"). The insulating layer 20 may include an amorphous phase of polypropylene. The crystallinity X of the polypropylene constituting the insulating layer 20 is c In addition, the crystallinity X c The calculation is performed using the above-mentioned formula (1).

[0110] The polypropylene crystal grains in the insulating layer 20 have a monoclinic crystal structure, a hexagonal crystal structure, or a state where at least one of them coexists. The polypropylene crystal grains in the insulating layer 20 are oriented along two or less specific crystal axes. The crystal orientation degree of the polypropylene crystal grains in the insulating layer 20 is 0. 110 The crystal orientation degree of the polypropylene crystal grains in the insulating layer 20 is calculated by the above-mentioned formula (2).

[0111] Modifications

[0112] In the above description, the insulating layer 20 is formed of polypropylene, but the insulating layer 20 may be formed of a material other than polypropylene. More specifically, the insulating layer 20 may be formed of a cyclic olefin polymer or polymethylpentene.

[0113] <Effects of the Differential Signal Transmission Cable 80>

[0114] According to the differential signal transmission cable 80, the adhesion between the insulating layer 20 and the intermediate layer 40 and the adhesion between the intermediate layer 40 and the catalyst particles 60 are improved, and the adhesion of the electroless plating layer 51 is improved, so that the transmission loss of the differential signal transmission cable can be suppressed. cWhen the ratio is 0.3 or more, the adhesion between the insulating layer 20 and the intermediate layer 40 and the adhesion between the intermediate layer 40 and the catalyst particles 60 are further improved, and the adhesion of the electroless plating layer 51 is further improved, thereby further suppressing the transmission loss of the differential signal transmission cable.

[0115] The embodiments disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is defined not by the embodiments described above but by the claims, and is intended to encompass all modifications within the scope and equivalents of the claims.

[0116] Description of the label

[0117] 10, 70, 80 Cables for differential signal transmission, 10A processing target component, 20 insulating layer, 20a outer peripheral surface, 30, 30a, 30b signal line, 40 intermediate layer, 40a outer peripheral surface, 50 shielding portion, 51 electroless plating layer, 51a outer peripheral surface, 52 electrolytic plating layer, 60 catalyst particles, S1 preparation step, S2 intermediate layer forming step, S3 catalyst particle configuration step, S4 electroless plating step, S5 electrolytic plating step, T1, T2, T3 thickness.

Claims

1. A cable for differential signal transmission, comprising: an insulating layer extending along the length direction of the differential signal transmission cable; a pair of signal lines extending along the length direction and buried inside the insulating layer; an intermediate layer covering the outer periphery of the insulating layer; a shielding portion covering an outer periphery of the intermediate layer; as well as Catalyst particles, The shield portion includes an electroless plating layer covering the outer periphery of the intermediate layer. The catalytic particles are dispersed between the intermediate layer and the electroless plating layer so that the catalytic particles do not form a layer, and the area of ​​the outer peripheral surface of the intermediate layer where no catalytic particles are arranged is more than 90 percent of the entire area of ​​the outer peripheral surface of the intermediate layer.

2. The differential signal transmission cable according to claim 1, wherein: The content of the catalyst particles contained in the differential signal transmission cable is 0.1 μg or more and 10 μg or less per 1 cm along the longitudinal direction.

3. The differential signal transmission cable according to claim 1 or 2, wherein: The arithmetic mean roughness of the outer peripheral surface of the insulating layer is 2.0 μm or less.

4. The differential signal transmission cable according to claim 1 or 2, wherein: The arithmetic mean roughness of the outer peripheral surface of the insulating layer is less than 0.6 μm.

5. The differential signal transmission cable according to claim 1 or 2, wherein: The bonding strength between the intermediate layer and the electroless plating layer is not less than 0.1 N / cm and not more than 6 N / cm.

6. The differential signal transmission cable according to claim 1 or 2, wherein: The thickness of the intermediate layer is 1 μm or less.

7. The differential signal transmission cable according to claim 1 or 2, wherein: The thickness of the electroless plating layer is not less than 0.05 μm and not more than 0.5 μm.

8. The differential signal transmission cable according to claim 1 or 2, wherein: The shield portion further includes an electrolytic plating layer that covers an outer peripheral surface of the electroless plating layer.

9. The differential signal transmission cable according to claim 8, wherein: The electrolytic plating layer is an electrolytic copper plating layer, The average particle size of copper crystal grains in the electrolytic plating layer is 0.5 μm or more.

10. The differential signal transmission cable according to claim 8, wherein: The total thickness of the electroless plating layer and the electrolytic plating layer is 6 μm or less.

11. The differential signal transmission cable according to claim 1 or 2, wherein: The catalyst particles contain palladium.

12. The differential signal transmission cable according to claim 1 or 2, wherein: The insulating layer includes polyolefin having a melting point of 140° C. or higher.

13. The differential signal transmission cable according to claim 1 or 2, wherein: The insulating layer includes at least any one of polypropylene, cyclic olefin polymer, and polymethylpentene.

14. The differential signal transmission cable according to claim 1 or 2, wherein: The insulating layer comprises polypropylene grains, The crystallinity X of the polypropylene crystals is calculated by the following formula (1): c is 0.3 or more, [Formula 1] In the formula (1), I c is the X-ray diffraction intensity of the crystalline component, I a is the X-ray diffraction intensity of the amorphous component.

15. The differential signal transmission cable according to claim 1, wherein: The insulating layer comprises polypropylene grains, The polypropylene crystal grains have a monoclinic crystal structure, a hexagonal crystal structure, or a state where at least one of them coexists, and are oriented along two or less specific crystal axes. In the insulating layer, the crystal orientation degree O is calculated by the following formula (2): 110 is below 0.65, [Formula 2] In the formula (2), I 110 is the integrated intensity of X-ray diffraction with index 110, I 040 is the integrated intensity of X-ray diffraction with index 0.40.

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