JP2015146298A - Cable for differential signal transmission and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve uniformity of an insulator formed around signal line conductors.SOLUTION: A cable 1A for differential signal transmission includes a pair of signal line conductors 2a and 2b and an insulator 3 formed of a foamed insulating material and collectively covering the pair of signal line conductors 2a and 2b. When the foaming degree of the insulator 3 around one signal line conductor 2a is a first foaming degree and the foaming degree of the insulator 3 around the other signal line conductor 2b is a second foaming degree, the difference between the first foaming degree and the second foaming degree is kept within 5.0% in two or more different regions (a first region 11 and a second region 21) in the longitudinal direction.

Description

  The present invention relates to a differential signal transmission cable for transmitting two or more signals having different phases, and a method of manufacturing the same.

  In devices such as servers, routers, and storages that handle high-speed digital signals of several Gbit / s or more, a differential interface standard (for example, LVDS (Low Voltage Differential Signal)) is adopted, and each circuit between devices or in each device. Differential signals are transmitted between the substrates using a differential signal transmission cable. The differential signal has an advantage that it is highly resistant to external noise while realizing a low system power supply voltage.

  A general differential signal transmission cable includes a pair of signal line conductors arranged in parallel, an insulator provided around these signal line conductors, a shield tape wound around the insulator, and a shield. And a pressing tape wound around the tape. That is, the two signal line conductors are collectively covered with the insulator. A positive side signal (positive) and a negative side (negative) signal with the phase inverted by 180 degrees are transmitted to the respective signal line conductors. The potential difference between these two signals (plus signal and minus signal) becomes a signal level. For example, if the potential difference is plus, it is “High”, and if it is minus, it is “Low”. It can be recognized.

  Here, the insulator that collectively covers the pair of signal line conductors is formed by extruding and covering the foamed insulating material around the pair of signal line conductors (Patent Document 1). Specifically, two preheated signal line conductors are introduced into the extrusion head of the coating apparatus. The extrusion head has a double structure composed of a base and a mandrel disposed inside the base. A through hole is provided at the center of the mandrel, and a gap is provided between the mandrel and the base over the entire circumference of the mandrel. That is, an annular supply path is provided around the through hole.

  In the manufacturing process of the differential signal transmission cable, the two preheated signal line conductors are sent out of the mandrel through the through hole of the mandrel, and the foam insulating material is passed through the supply path around the signal line conductor to be sent out. By discharging, an insulator (insulating layer) covering the two signal line conductors at once is formed.

JP 2000-48653 A

  As described above, the method for manufacturing a differential signal transmission cable includes a step of forming an insulator by extruding a foam insulating material around a signal line conductor (hereinafter referred to as a “coating step”). However, if the uniformity of the insulator formed in such a coating process is low, the transmission characteristics of the differential signal transmission cable will deteriorate. In particular, when the bubble diameter around one signal line conductor is different from the bubble diameter around the other signal line conductor, the skew increases significantly.

  An object of the present invention is to improve the uniformity of an insulator formed around a signal line conductor.

  The manufacturing method according to the present invention is a method for manufacturing a differential signal transmission cable comprising a pair of signal line conductors and an insulator that is formed of a foamed insulating material and collectively covers the pair of signal line conductors. In one aspect of the present invention, the temperature difference between the pair of signal line conductors is maintained within 10 ° C. in the covering step of extruding the foamed insulating material around the pair of signal line conductors.

  In another aspect of the present invention, a preheating step of heating the pair of signal line conductors prior to the covering step so that a temperature difference between the pair of signal line conductors in the covering step is maintained within 10 ° C. Done.

  In another aspect of the present invention, in the preheating step, at least one of a heating temperature for one signal line conductor and a heating temperature for the other signal line conductor is adjusted based on a temperature difference between the pair of signal line conductors. Is done.

  A differential signal transmission cable according to the present invention includes a pair of signal line conductors and an insulator formed of a foamed insulating material and covering the pair of signal line conductors at once. Further, when the foaming degree of the insulator around one signal line conductor is the first foaming degree and the foaming degree of the insulator around the other signal line conductor is the second foaming degree, the longitudinal direction is different. In two or more regions, the difference between the first foaming degree and the second foaming degree is within 5.0%.

  In another aspect of the present invention, in the first region including one end surface and the second region including the other end surface of the differential signal transmission cable cut to an arbitrary length, the first foaming degree and the The difference from the second degree of foaming is within 5.0%.

  In another aspect of the invention, the difference between the capacitance of the one signal line conductor and the capacitance of the other signal line conductor is within 1.0%.

  According to the present invention, a differential signal transmission cable in which a signal line conductor is covered with a highly uniform insulator is realized.

It is a perspective view which shows the structure of the cable for differential signal transmission to which this invention was applied. It is sectional drawing which shows the cross section of the cable for differential signal transmission shown by FIG. It is a perspective view which shows the horizontal cross section of the cable for differential signal transmission shown by FIG. It is a perspective view which shows the vertical cross section of the cable for differential signal transmission shown by FIG. (A) is a top view of the cable for differential signal transmission shown in FIG. 1, (b) is an enlarged view which shows the horizontal cross section of a sample. (A) is a block diagram of the coating | coated apparatus used for manufacture of the cable for differential signal transmission shown by FIG. 1, (b) is an expanded sectional view of the extrusion head shown by (a).

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. A differential signal transmission cable 1A shown in FIG. 1 includes a pair of signal line conductors 2a and 2b, an insulator 3 that collectively covers these signal line conductors 2a and 2b, and a skin layer 4 that covers the insulator 3. The shield layer 5 that covers the skin layer 4 and the pressing tape 6 that covers the shield layer 5 are provided.

  Each of the pair of signal line conductors 2a and 2b is an annealed copper wire (Silver Plated Copper Wire) having a circular cross section whose surface is subjected to silver plating. A plus side (positive) signal is transmitted to one of the pair of signal line conductors 2a and 2b, and a minus side (negative) signal is transmitted to the other of the pair of signal line conductors 2a and 2b.

  The insulator 3 is made of a foam insulating material, and the insulator 3 contains a large number of bubbles. The insulator 3 holds the signal line conductors 2a and 2b so that the two signal line conductors 2a and 2b are arranged in parallel at a predetermined interval. Further, the thickness of the insulator 3 around each signal line conductor 2a, 2b is substantially the same.

  The skin layer 4 provided around the insulator 3 is a thin film that is not foamed or a thin film having a lower foaming degree than the insulator 3. Examples of the material for the skin layer 4 include tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and ethylene / tetrafluoroethylene copolymer (ETFE). Etc. can be used. However, the material of the skin layer 4 is not limited to a specific material.

  The shield layer 5 provided around the skin layer 4 is formed of a shield tape wound around the skin layer 4. Although illustration is omitted, the shield tape has a double structure composed of a sheet-like base material and a metal conductor layer formed on one surface of the base material. Or aluminum foil.

  The shield tape forming the shield layer 5 is wound side by side around the skin layer 4 with the metal conductor layer inside. Therefore, both ends of the shield tape overlap each other. However, there is also an embodiment in which the shield layer 5 is formed by a spirally wound (laterally wound) shield tape. In some embodiments, the shield tape is vertically wound around the skin layer 4 with the metal conductor layer on the outside, or spirally wound (laterally wound).

  A pressing tape 6 for holding the shielding tape is spirally wound around the shielding layer 5. Further, a jacket (sometimes referred to as “sheath”) is provided around the pressing tape 6. As the jacket material, polyethylene, polypropylene, polyvinyl chloride, ethylene-vinyl acetate copolymer, fluororesin, halogen-free flame-retardant polyolefin, soft vinyl chloride resin, or the like can be used.

  The differential signal transmission cable 1A shown in FIG. 1 is manufactured by a manufacturing method to be described later, and the insulator 3 has high uniformity. Specifically, the variation in the foaming degree of the insulator 3 is small in the longitudinal direction (Z direction) of the differential signal transmission cable 1A. In other words, in the differential signal transmission cable 1A according to the present embodiment, the difference between the foaming degree of the insulator 3 around the signal line conductor 2a and the foaming degree of the insulator 3 around the signal line conductor 2b is predetermined. It is kept within range. “Foaming degree” is the ratio between the area of an arbitrary cross section of the insulator 3 and the area of bubbles in the cross section.

  Here, as shown in FIG. 2, a straight line connecting the center of the signal line conductor 2a and the center of the signal line conductor 2b is defined as "straight line S1". A straight line orthogonal to the straight line S1 at the midpoint of the straight line S1 is defined as a “straight line S2”. In the following description, a cross section of the differential signal transmission cable 1A including the straight lines S1 and S2 is referred to as a “cross section”. The cross section of the differential signal transmission cable 1A including the straight line S1 is referred to as a “horizontal cross section”. Further, the cross section of the differential signal transmission cable 1A including the straight line S2 is referred to as a “vertical cross section”.

  That is, the cross section shown in FIG. 2 is one of the cross sections of the differential signal transmission cable 1A. The cross section shown in FIG. 3 is one of the horizontal cross sections of the differential signal transmission cable 1A. Further, the cross section shown in FIG. 4 is one of the vertical cross sections of the differential signal transmission cable 1A. In other words, the cross section of the differential signal transmission cable 1A is a cross section perpendicular to the longitudinal direction (Z direction) of the differential signal transmission cable 1A. On the other hand, the horizontal cross section and the vertical cross section of the differential signal transmission cable 1A are parallel to the longitudinal direction (Z direction) of the differential signal transmission cable 1A. Furthermore, the horizontal cross section and the vertical cross section of the differential signal transmission cable 1A are cross sections orthogonal to each other.

  In addition, there are many cross sections of the differential signal transmission cable 1A along the longitudinal direction (Z direction) of the differential signal transmission cable 1A. On the other hand, the horizontal cross section of the differential signal transmission cable 1A has two cross sections, the cross section shown in FIG. The vertical cross section of the differential signal transmission cable 1A has two cross sections, the cross section shown in FIG. 4 and the cross section facing the cross section.

  As described above, in the differential signal transmission cable 1A according to the present embodiment, there is a difference between the foaming degree of the insulator 3 around the signal line conductor 2a and the foaming degree of the insulator 3 around the signal line conductor 2b. It is kept within a predetermined range. Here, the insulator 3 around the signal line conductor 2a is divided into two when the insulator 3 is bisected by a plane including the straight line S2 shown in FIG. 2, that is, as shown in FIG. Means a part of the insulator 3 (half of the insulator 3) remaining around the signal line conductor 2a. On the other hand, the insulator 3 around the signal line conductor 2b is divided into two when the insulator 3 is bisected by a plane including the straight line S2 shown in FIG. 2, that is, as shown in FIG. Sometimes, it means the other part of the insulator 3 (the other half of the insulator 3) remaining around the signal line conductor 2b. That is, in FIG. 2, a part of the insulator 3 located on the left side of the straight line S2 is the insulator 3 around the signal line conductor 2a, and the other part of the insulator 3 located on the right side of the straight line S2. Is the insulator 3 around the signal line conductor 2b. Therefore, in the following description, the insulator 3 around the signal line conductor 2a is referred to as “left insulator 3a”, and the insulator 3 around the signal line conductor 2b is referred to as “right insulator 3b”. Further, the foaming degree of the left insulator 3a is referred to as “first foaming degree”, and the foaming degree of the right insulator 3b is referred to as “second foaming degree”. That is, in the differential signal transmission cable 1A according to the present embodiment, the difference between the first foaming degree and the second foaming degree is kept within a predetermined range. Specifically, the difference between the first foaming degree and the second foaming degree is kept within 5.0% in two or more regions having different longitudinal directions (Z direction) of the differential signal transmission cable 1A. . 2 to 4, the illustration of the pressing tape 6 shown in FIG. 1 is omitted.

  Therefore, when the differential signal transmission cable 1A according to the present embodiment is cut to an arbitrary length, the first foaming degree and the second foaming degree at one end of a part of the cutout differential signal transmission cable 1A. The difference between the first foaming degree and the second foaming degree at the other end of a part of the cutout differential signal transmission cable 1A is also within 5.0%. It is. Hereinafter, a specific description will be given with reference to FIGS.

  As shown in FIG. 5A, the differential signal transmission cable 1A is cut to an arbitrary length. In FIG. 5A, the cutting position of the differential signal transmission cable 1A is indicated by two broken lines. In the following description, a part of the differential signal transmission cable 1A cut out to an arbitrary length is referred to as “sample 1a”. That is, the difference between the first foaming degree and the second foaming degree is kept within 5.0% at both ends of the sample 1a shown in FIG.

  More specific description will be given with reference to FIG. FIG.5 (b) is an enlarged view which shows the horizontal cross section of the sample 1a. The length (L) of the sample 1a shown in FIG. 5 (b) is 10 cm. In addition, one end portion (first region 11) of the sample 1a is a portion within a range of 0.5 cm from the end surface 12 including the one end surface 12 of the sample 1a. The other end portion (second region 21) of the sample 1a is a portion within the range of 0.5 cm from the end surface 22 including the other end surface 22 of the sample 1a. That is, the length (L1) of the first region 11 and the length (L2) of the second region 21 are 0.5 cm (L1 = L2).

  As shown in FIG. 5B, in the first region 11 of the sample 1a, the left insulator 3a and the right insulator 3b contain a large number of bubbles 30 having substantially the same diameter. Similarly, in the second region 21 of the sample 1a, the left insulator 3a and the right insulator 3b contain a large number of bubbles 30 having substantially the same diameter. Specifically, the difference in the degree of foaming between the left insulator 3a and the right insulator 3b in the first region 11 shown in FIG. 5B is within 5.0%. Further, the difference in the degree of foaming between the left insulator 3a and the right insulator 3b in the second region 21 shown in FIG. 5B is also within 5.0%.

Here, the degree of foaming in each region was determined as follows. First, a horizontal section of the sample 1a shown in FIG. Next, the foaming degree of the insulator 3 included in the sample 1a is obtained by measuring the specific gravity of the insulator 3. The measuring method follows JIS Z 8807: 2012 “Method for measuring density and specific gravity of solid”. Next, the captured image is binarized into black and white, and the horizontal cross section of the sample 1a is divided into a bubble 30 portion and a bubble wall portion (a portion other than the bubble 30). The ratio of black and white is adjusted to the measured degree of foaming. Thereafter, the area (number of pixels) of the white portion and the black portion in the image is obtained, and the foaming degree in the horizontal section is calculated by the following equation.
Foaming degree = B / (A + B) × 100 (%)
A: Bubble wall pixel count (black)
B: Bubble pixel count (white)
As described above, the foaming degree of the left insulator 3a and the right insulator 3b in the first region 11 is calculated and compared. Similarly, the foaming degree of the left insulator 3a and the right insulator 3b in the second region 21 is calculated and compared.

  As described above, in the differential signal transmission cable 1A according to the present embodiment, the variation in the foaming degree of the insulator 3 in the longitudinal direction (Z direction) is kept within a predetermined range. Therefore, the difference between the capacitance of one signal line conductor 2a and the capacitance of the other signal line conductor 2b is kept within 1.0%. As a result, the differential signal transmission cable 1A according to the present embodiment has good transmission characteristics, and an increase in skew is suppressed in the differential transmission using the differential signal transmission cable 1A. .

  Next, a method for manufacturing the differential signal transmission cable 1A according to the present embodiment will be described. The manufacturing method of the differential signal transmission cable 1A includes a preheating step of heating the pair of signal line conductors 2a and 2b and a covering step of forming the insulator 3 around the preheated signal line conductors 2a and 2b. Including at least.

  The coating process is performed using, for example, a coating apparatus 40 shown in FIG. The illustrated coating apparatus 40 includes an extrusion head 50 and a supply mechanism 60 that supplies foamed insulating material to the extrusion head 50.

  As shown in FIG. 6A, the supply mechanism 60 includes a hopper 61 into which the foamed insulating material 31 is charged, a cylinder 62 that communicates with the hopper 61 and the extrusion head 50, and a screw 63 that rotates within the cylinder 62. And. On the other hand, as shown in FIG. 6B, the extrusion head 50 has a double structure including a base 51 and a core 52 disposed inside the base 51. The mandrel 52 has a substantially conical shape, and a through hole (not shown) is provided at the center thereof. A gap 53 is provided between the base 51 and the core 52 over the entire circumference of the core 52. That is, an annular supply path 53 is provided around the mandrel 52.

  As shown in FIG. 6A, the foamed insulating material 31 formed into a pellet is put into a hopper 61 of the supply mechanism 60. Here, the foam insulating material 31 includes a resin material and a chemical foaming agent. As the resin material, for example, polyolefin can be used. Specifically, low density polyethylene, high density polyethylene, linear low density polyethylene, ultra low density polyethylene, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-vinyl acetate copolymer, ethylene-ethyl Examples include acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer, polypropylene, ethylene copolymer polypropylene, reactor blend type polypropylene, cycloolefin polymer, and poly-4-methyl-1-pentene. . These resin materials may be used alone or in combination of two or more.

  On the other hand, as the chemical foaming agent, azodicarbonamide, azobisisobutyronitrile, barium azodicarboxylate, dinitrosopentamethylenetetramine, 4,4′-oxybis (benzenesulfonylhydrazide), N, N′-di Examples thereof include organic chemical blowing agents such as nitrosopentamethylenetetramine, benzenesulfonylhydrazide, bistetrazole / diammonium, bistetrazole / piperazine, and 5-phenyltetrazole. Examples of the chemical foaming agent include inorganic chemical foaming agents such as carbonates, bicarbonates, nitrites, and hydrides. Furthermore, examples of the chemical foaming agent include foaming aids such as metal oxides such as zinc oxide and magnesium oxide, fatty acid salts, inorganic zinc compounds, organic zinc compounds, urea compounds, organic acids, and amine compounds. These chemical foaming agents may be used alone or in combination of two or more.

  As shown in FIG. 6 (a), the pellet-shaped foamed insulating material 31 put into the hopper 61 is supplied to the cylinder 62, and is kneaded by the screw 63 that rotates in the cylinder 62 to form a paste. . Further, the foamed insulating material 31 kneaded into a paste is fed into the extrusion head 50 as the screw 63 rotates. At the same time, heated (preheated) signal line conductors 2 a and 2 b are introduced into the extrusion head 50. Specifically, as shown in FIG. 6B, the preheated signal line conductors 2 a and 2 b are sent out from the mandrel 52 through the through holes of the mandrel 52. On the other hand, the pasty foam insulating material 31 fed to the extrusion head 50 is discharged around the signal line conductors 2 a and 2 b delivered from the mandrel 52 through the supply path 53 of the extrusion head 50. As a result, an insulator 3 is formed around the pair of signal line conductors 2a and 2b to collectively cover the signal line conductors 2a and 2b. That is, the insulator 3 is formed through a covering process for extruding the foam insulating material 31 around the pair of signal line conductors 2a and 2b and a preheating process for heating the pair of signal line conductors 2a and 2b prior to the covering process. The

  Here, in the covering step, the temperature difference between the two signal line conductors 2a and 2b is maintained within 10 ° C. Specifically, the temperature difference between the signal line conductors 2a and 2b when the insulator 3 is formed is maintained within 10 ° C. More specifically, the signal line conductors 2a and 2b in the preheating step are set so that the temperature difference between the signal line conductors 2a and 2b when being sent out from the mandrel 52 shown in FIG. The heating temperature is adjusted. For example, the temperature of the signal line conductors 2a and 2b is measured before being introduced into the extrusion head 50, and the heating temperature for one signal line conductor 2a and 2b and the other signal line conductor 2b and 2a are measured based on the measurement result. At least one of the heating temperatures is adjusted.

  Here, in the preheating step, the signal line conductors 2a and 2b are heated (preheated) by direct heating or induction heating. When the signal line conductors 2a and 2b are preheated by direct heating, a heat source such as a heating wire heater or a gas burner is provided for each of the signal line conductors 2a and 2b. In this case, the temperature difference between the signal line conductors 2a and 2b is measured between the heat source and the extrusion head 50, and based on the measurement result, the heat source for one signal line conductor and the heat source for the other signal line conductor At least one of them is adjusted manually or automatically.

  When the signal line conductors 2a and 2b are preheated by induction heating, a coil connected to an AC power source is provided for each of the signal line conductors 2a and 2b. Each signal line conductor 2a, 2b is heated (preheated) by Joule heat when passing inside the corresponding coil. In this case, the temperature difference between the signal line conductors 2a and 2b is measured between the coil and the extrusion head 50, and based on the measurement result, the coil for one signal line conductor and the coil for the other signal line conductor are The applied voltage to at least one of them is adjusted manually or automatically.

  In any case, it is desirable to measure the temperature difference between the signal line conductors 2a and 2b immediately before the signal line conductors 2a and 2b are introduced into the extrusion head 50. Therefore, it is desirable that measurement means such as a sensor for measuring the temperature of the signal line conductors 2 a and 2 b is disposed immediately before the extrusion head 50.

  As described above, the foaming degree of the insulator 3 can be kept uniform by maintaining the temperature difference between the signal line conductors 2a and 2b in the covering step within 10 ° C. That is, the differential signal transmission cable 1A (FIG. 1) in which the difference between the first foaming degree and the second foaming degree is maintained within 5.0% in two or more regions having different longitudinal directions is manufactured. In other words, the differential signal transmission cable 1A (FIG. 1) in which the difference between the capacitance of one signal line conductor 2a and the capacitance of the other signal line conductor 2b is kept within 1.0% is manufactured. .

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, various alloy wires can be used for the signal line conductors 2a and 2b instead of copper wires. The signal line conductors 2a and 2b may be single wires or stranded wires. Further, the surface of the signal line conductors 2a and 2b can be subjected to various types of plating such as tin plating, nickel plating and gold plating instead of silver plating.

  The method of foaming the resin that forms the insulator 3 is not limited to the chemical foaming method described above, and may be a physical foaming method. For example, a gas may be dissolved in the resin material in the supply mechanism 60 shown in FIG. Examples of the gas dissolved in the resin material include nitrogen gas, carbon dioxide gas, air, pentane, butane, and chlorofluorocarbon compounds.

1A Cable for differential signal transmission 1a Sample 2a, 2b Signal line conductor 3 Insulator 3a Left insulator 3b Right insulator 4 Skin layer 5 Shield layer 6 Holding tape 11 First region 12, 22 End face 21 Second region 30 Bubble 31 Foam insulation material 40 Coating device 50 Extrusion head 51 Base 52 Core metal 53 Supply path (gap)
60 Supply mechanism 61 Hopper 62 Cylinder 63 Screw

Claims (6)

A differential signal transmission cable manufacturing method comprising: a pair of signal line conductors; and an insulator that is formed of a foam insulating material and collectively covers the pair of signal line conductors,
In the covering step of extruding the foamed insulating material around the pair of signal line conductors, the temperature difference between the pair of signal line conductors is maintained within 10 ° C.
A method for manufacturing a cable for differential signal transmission. It is a manufacturing method of the cable for differential signal transmission according to claim 1,
A preheating step of heating the pair of signal line conductors prior to the covering step so that a temperature difference between the pair of signal line conductors in the covering step is maintained within 10 ° C.
A method for manufacturing a cable for differential signal transmission. It is a manufacturing method of the cable for differential signal transmission according to claim 2,
In the preheating step, based on the temperature difference between the pair of signal line conductors, the heating temperature for one signal line conductor and the heating temperature for the other signal line conductor are adjusted.
A method for manufacturing a cable for differential signal transmission. A differential signal transmission cable comprising: a pair of signal line conductors; and an insulator that is formed of a foam insulating material and collectively covers the pair of signal line conductors,
When the foaming degree of the insulator around one signal line conductor is a first foaming degree, and the foaming degree of the insulator around the other signal line conductor is a second foaming degree,
In two or more regions having different longitudinal directions, the difference between the first foaming degree and the second foaming degree is within 5.0%.
Cable for differential signal transmission. The differential signal transmission cable according to claim 4,
In the first region including one end face of the differential signal transmission cable cut to an arbitrary length and the second region including the other end face, a difference between the first foaming degree and the second foaming degree is Within 5.0%,
Cable for differential signal transmission. The differential signal transmission cable according to claim 4 or 5,
The difference between the capacitance of the one signal line conductor and the capacitance of the other signal line conductor is within 1.0%.
Cable for differential signal transmission.

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