JP3690445B2 - Semi-rigid coaxial cable - Google Patents

Description

【００１３】
この関係式において、Ｚｏとｄを一定に規定した場合、ＰＴＦＥ絶縁体層を半焼成とすることにより、炉内を通過したとき、その表面から熱を伝達するので焼成の度合いによってＰＴＦＥ絶縁体層の内周部は連続気泡の多孔質となり、結果として比誘電率Ｅｒを小さくすることができるので、ＰＴＦＥ絶縁体層の直径を小さくすることができる。そのため、同軸ケーブルの直径が同じであれば、ＰＴＦＥ絶縁体層の直径を小さくした分だけ外部導体層を厚肉とすることができることになり、セミリジッド同軸ケーブルとしての半田耐熱性が向上する。
【００１４】
このＰＴＦＥ絶縁体層には、半田耐熱性を向上させると共に曲げ加工により高周波特性が低下するのを防止するため、無機フィラーを好ましくは５％以上配合することができ、また、半田耐熱性を更に向上させるため、有機フィラーを好ましくは１０％以上配合することができる。無機フィラーとしては、アルミナ、シリカ等のセラミックなどを挙げることができる。有機フィラーとしては、ＰＥＥＫ等の高機能性樹脂などを挙げることができる。
【００１５】
本発明における外部導体は、銅、アルミニウム、ステンレス、ベリリウム銅、銀、ニオブ、リン青銅等の通常シールド層として使用される金属あるいはその合金、ポリマーアロイなどの導電性の被覆である。
【００１６】
【実施例】
以下、本発明を実施例により更に詳しく説明する。
【００１７】
実施例１
直径０．２０３ｍｍの銀メッキ銅覆鋼線上に、ＰＴＦＥファインパウダーと押し出し助剤としてホワイトオイルとの混合物を押出成形し、電気炉中をキャプスタン速度１５．５ｍ／分で通し乾燥及び半焼成して、外径０．６８ｍｍの半焼成ＰＴＦＥ絶縁体層を被覆した。これを内径０．８ｍｍ、外径１．０３ｍｍの銅管に挿入した後、半焼成ＰＴＦＥ絶縁体と銅管とが隙間なく密着するように銅管をダイス引きで絞りこみ、外径０．８６ｍｍ（銅管の厚さ０．１１５ｍｍ）で特性インピーダンスＺｏ＝５０．５Ωのセミリジッド同軸ケーブルを製造した。
この製造したセミリジッド同軸ケーブルの乾燥及び半焼成の電気炉の温度条件と物性と性能をまとめて表１に示す。また、この半焼成のＰＴＦＥ絶縁体層のＤＳＣのチャートを図１に示す。
【００１８】
比較例１
ＰＴＦＥ絶縁体層の被覆の形成において半焼成しないこと（すなわち未焼成であること）と内径０．８ｍｍ、外径１．０５ｍｍの銅管を用いたことを除いて実施例１と同様にして、外径０．８６ｍｍ（銅管の厚さ０．１２５ｍｍ）で特性インピーダンスＺｏ＝５０．４Ωのセミリジッド同軸ケーブルを製造した。
このセミリジッド同軸ケーブルの乾燥の電気炉の温度条件と物性と性能をまとめて表１に示す。また、この（未焼成の）ＰＴＦＥ絶縁体層のＤＳＣのチャートを図２に示す。
【００１９】
比較例２
ＰＴＦＥ絶縁体層の被覆の形成において半焼成のかわりに焼成したことと内径０．８ｍｍ、外径１．０ｍｍの銅管を用いたことを除いて実施例１と同様にして、外径０．８６ｍｍ（銅管の厚さ０．１ｍｍ）で特性インピーダンスＺｏ＝５０．９Ωのセミリジッド同軸ケーブルを製造した。
このセミリジッド同軸ケーブルの乾燥及び焼成の電気炉の温度条件と物性と性能をまとめて表１に示す。また、この焼成ＰＴＦＥ絶縁体層のＤＳＣのチャートを図３に示す。
【００２０】
【表１】

【００２１】
［物性及び性能試験］
（１）比重
ＰＴＦＥ絶縁体層の比重は、水中置換法で測定した。但し、ＰＴＦＥ絶縁体層の水中における重量が変動するため、測定値は概算値である。
【００２２】
（２）ＤＳＣ分析
ＪＩＳ Ｋ７１２２プラスチックの転移熱測定方法によりＰＴＦＥ絶縁体層のＤＳＣを行った。
【００２３】
（３）比誘電率
ベクトルネットワークアナライザーを用いて該ケーブルの電気長を測定し、次に該ケーブルの物理長を直尺等で測り、計算にて比誘電率を求めた。
【００２４】
（４）ＰＴＦＥ絶縁体層の寸法安定性
１００ｍｍのセミリジッド同軸ケーブルを２３０℃の電気炉中に３分間入れた後、室温で１５分間放置した。このときのＰＴＦＥ絶縁体層の長さ方向への膨張収縮量を測定した。
表１において、＋は膨張を意味し、＋０．１ｍｍ以下とは、膨張した寸法が０．１ｍｍを越えず、０．０１ｍｍの単位では測定できないことを意味する。
【００２５】
（５）ＰＴＦＥ絶縁体層の端末加工性
セミリジッド同軸ケーブルの外部導体（銅管）を安全剃刀でカットし除去した後、ＰＴＦＥ絶縁体層を安全剃刀でカットし除去して、中心導体（銀メッキ銅覆鋼線）を剥き出しにするまでの作業性を次の基準により評価した。
評価基準：
優；ＰＴＦＥ絶縁体層の除去作業が容易。
良；ＰＴＦＥ絶縁体層の除去作業が比較的容易。
不良；ＰＴＦＥ絶縁体層の除去作業が非常に困難。
【００２６】
（６）セミリジッド同軸ケーブルの高周波特性
セミリジッド同軸ケーブルを使用して周波数１ＧＨｚ、３ＧＨｚ、５ＧＨｚ、１０ＧＨｚ、１８ＧＨｚの高周波をそれぞれ伝送した場合の減衰量を測定した。
【００２７】
（７）セミリジッド同軸ケーブルの半田耐熱性
各温度にコントロールされたコテ先（半田コテ：コテ先の直径２ｍｍ、２４Ｖ、５０Ｗ）に半田（直径１．０ｍｍ、錫６０％と鉛４０％の合金）を乗せて溶融した。セミリジッド同軸ケーブルにコテ先を３０ｍｍ間隔で５箇所（３秒間／箇所）接触させて、ケーブルの外部導体（銅管）に亀裂が発生しない最も高い温度を測定した。
【００２８】
【発明の効果】
以上説明した通り、本発明のセミリジッド同軸ケーブルは半焼成のＰＴＦＥ絶縁体層であるためＰＴＦＥ絶縁体層の一部（この場合内周部）が連続気泡の多孔質体となり、結果として比誘電率を小さくすることができ、絶縁体層の厚みを小さくすることができる。そのため、その分だけ外部導体の厚みを増やすことができるので、半田耐熱性を向上させることができる。あるいは、同じ半田耐熱温度では、セミリジッド同軸ケーブルの外径を小さくすることができるので、ケーブルの細線化、軽量化を図ることができ、例えば携帯電話といった移動通信装置用などに特に有利である。
【００２９】
また、本発明のセミリジッド同軸ケーブルは加熱時のＰＴＦＥ絶縁体層の寸法変化が小さく、しかも、半焼成のＰＴＦＥ絶縁体層は延伸してもＰＴＦＥが繊維化することなく、円滑に切断、除去することができるので、中心導体の剥き出しも容易である。
【００３０】
更に、本発明のセミリジッド同軸ケーブルは、ＰＴＦＥ絶縁体の比誘電率が小さいため、各種周波数における高周波の減衰量が少なく、高周波特性も優れている。
【図面の簡単な説明】
【図１】 実施例１で得られた半焼成のＰＴＦＥ絶縁体層のＤＳＣのチャートを示す図面である。
【図２】 比較例１で得られた（未焼成の）ＰＴＦＥ絶縁体層のＤＳＣのチャートを示す図面である。
【図３】 比較例２で得られた焼成ＰＴＦＥ絶縁体層のＤＳＣのチャートを示す図面である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-quality, high-performance semi-rigid coaxial cable used for high-frequency signal transmission in mobile communication devices and the like.
[0002]
[Prior art]
As a coaxial cable used for signal transmission in a high frequency band exceeding several hundred megahertz, conventionally, an insulated electric wire uniformly coated with a fluororesin having excellent electrical characteristics at high frequencies on a central conductor is made of copper or aluminum. A semi-rigid coaxial cable having a structure in which a metal tube is uniformly processed so that there is no gap between the metal tube and the insulated wire after being inserted into the metal tube is widely known.
[0003]
Since the semi-rigid coaxial cable uses a metal tube as an outer conductor, it has excellent transmission characteristics at high frequencies. However, for example, it is technically difficult to make a dedicated connector with a thin cable having an outer diameter of 2 mm or less. The connection to the device must be a connection method of soldering a metal tube as an external conductor on a circuit board or a metal plate for shielding. However, the semi-rigid coaxial cable with a small diameter has a thin outer conductor, and the external expansion due to heat transfer from the soldering iron tip during soldering under various conditions (temperature, time, etc.) Since the conductor could not resist, the trouble that the external conductor cracked often occurred, and the workability and yield of connection with the equipment were poor.
[0004]
In order to improve this point, high-frequency transmission characteristics can be achieved by using an insulator layer structure combining a solid insulating layer and a porous layer having non-independent pores between the central conductor and the (external) metal layer. A semi-rigid coaxial cable that is good and does not cause cracks in the outer conductor due to heat during soldering has been proposed (see JP-A-8-31242).
[0005]
[Problems to be solved by the invention]
However, the semi-rigid coaxial cable employing polytetrafluoroethylene (hereinafter referred to as PTFE) as a material for the porous layer having non-independent pores disclosed in the above publication still has insufficient transmission characteristics and solder heat resistance at high frequencies. In addition, the semi-rigid coaxial cable has a problem of expanding in the length direction when passed through a solder reflow furnace.
[0006]
On the other hand, a semi-rigid coaxial cable using (unfired) PTFE among the fluororesins as an insulator is completely separated from each other even if the (unfired) PTFE insulator is cut with a cutter and pulled. If not cut, the unsintered PTFE would be drawn into fibers and could not be cut smoothly, so that there was a problem in its end workability.
[0007]
An object of this invention is to provide the semi-rigid coaxial cable for high frequency signal transmission excellent in solder heat resistance, dimensional stability, terminal workability, etc.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a semi-rigid coaxial cable in which one or more insulator layers and an outer conductor layer are sequentially provided on the outer periphery of a central conductor, and at least one of the insulator layers is semi-fired. The semi-rigid coaxial cable is made of PTFE.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The semi-rigid coaxial cable of the present invention has a structure in which an insulator layer and an outer conductor layer are sequentially provided on the outer periphery of the center conductor, and one or more insulator layers may be provided. The body layer is one layer.
[0010]
The central conductor in the semi-rigid coaxial cable of the present invention is a metal or alloy wire used as a normal conductor such as copper, gold, silver, niobium, beryllium, tungsten, palladium, and aluminum. Those whose surface is plated with the above metal or alloy are also preferred, and examples thereof include a silver-plated copper wire and a silver-plated copper-clad steel wire.
[0011]
The semi-fired PTFE insulator layer in the present invention has a peak around 340 ° C. (peak of unfired PTFE insulator) and a peak around 323 ° C. (peak of fired PTFE insulator) by differential scanning calorimetry (DSC). The ratio of the two DSC peak sizes differs depending on the method and degree of semi-firing. The semi-fired PTFE insulator layer in the present invention preferably has a high degree of firing on the outer surface of the layer and a low degree of firing on the inside of the layer.
In general, the following relationship is established in a coaxial cable.
[Expression 1]

[0013]
In this relational expression, when Zo and d are defined to be constant, the PTFE insulator layer is semi-fired, so that when passing through the furnace, heat is transferred from the surface, so the PTFE insulator layer depends on the degree of firing. Since the inner peripheral portion is porous with open cells and as a result, the dielectric constant Er can be reduced, the diameter of the PTFE insulator layer can be reduced. Therefore, if the diameters of the coaxial cables are the same, the outer conductor layer can be made thicker by reducing the diameter of the PTFE insulator layer, and the solder heat resistance as a semi-rigid coaxial cable is improved.
[0014]
In order to improve the solder heat resistance and prevent the high frequency characteristics from being lowered by bending, the PTFE insulator layer can contain an inorganic filler, preferably 5% or more, and further improve the solder heat resistance. In order to improve, an organic filler can be preferably blended by 10% or more. Examples of the inorganic filler include ceramics such as alumina and silica. Examples of the organic filler include a highly functional resin such as PEEK.
[0015]
The outer conductor in the present invention is a conductive coating such as a metal usually used as a shield layer such as copper, aluminum, stainless steel, beryllium copper, silver, niobium, phosphor bronze, an alloy thereof, or a polymer alloy.
[0016]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0017]
Example 1
A mixture of PTFE fine powder and white oil as an extrusion aid is extruded on a silver-plated copper-clad steel wire with a diameter of 0.203 mm, and then dried and semi-fired through an electric furnace at a capstan speed of 15.5 m / min. Then, a semi-fired PTFE insulator layer having an outer diameter of 0.68 mm was coated. After inserting this into a copper tube having an inner diameter of 0.8 mm and an outer diameter of 1.03 mm, the copper tube is squeezed with a die so that the semi-fired PTFE insulator and the copper tube are in close contact with each other, and the outer diameter is 0.86 mm. A semi-rigid coaxial cable having a characteristic impedance Zo = 50.5Ω with a copper tube thickness of 0.115 mm was manufactured.
Table 1 summarizes the temperature conditions, physical properties and performance of the dried and semi-fired electric furnace of the manufactured semi-rigid coaxial cable. A DSC chart of the semi-fired PTFE insulator layer is shown in FIG.
[0018]
Comparative Example 1
In the same manner as in Example 1 except that the PTFE insulator layer coating was not semi-fired (that is, not fired), and a copper tube having an inner diameter of 0.8 mm and an outer diameter of 1.05 mm was used. A semi-rigid coaxial cable having an outer diameter of 0.86 mm (copper tube thickness of 0.125 mm) and a characteristic impedance Zo = 50.4Ω was manufactured.
Table 1 summarizes the temperature conditions, physical properties, and performance of the electric furnace for drying the semi-rigid coaxial cable. A DSC chart of this (unfired) PTFE insulator layer is shown in FIG.
[0019]
Comparative Example 2
In the same manner as in Example 1, except that the PTFE insulator layer was baked instead of semi-fired and a copper tube having an inner diameter of 0.8 mm and an outer diameter of 1.0 mm was used. A semi-rigid coaxial cable with a characteristic impedance Zo = 50.9Ω at 86 mm (copper tube thickness 0.1 mm) was manufactured.
Table 1 summarizes the temperature conditions, physical properties and performance of the electric furnace for drying and firing the semi-rigid coaxial cable. Further, FIG. 3 shows a DSC chart of the sintered PTFE insulator layer.
[0020]
[Table 1]

[0021]
[Physical properties and performance tests]
(1) Specific gravity The specific gravity of the PTFE insulator layer was measured by an underwater substitution method. However, since the weight of the PTFE insulator layer in water varies, the measured value is an approximate value.
[0022]
(2) DSC analysis The PTFE insulator layer was subjected to DSC by the method for measuring the transition heat of JIS K7122 plastic.
[0023]
(3) The relative dielectric constant vector network analyzer was used to measure the electrical length of the cable, then the physical length of the cable was measured with a straight scale or the like, and the relative dielectric constant was determined by calculation.
[0024]
(4) Dimensional stability of PTFE insulator layer A 100 mm semi-rigid coaxial cable was placed in an electric furnace at 230 ° C. for 3 minutes and then allowed to stand at room temperature for 15 minutes. The amount of expansion and contraction in the length direction of the PTFE insulator layer at this time was measured.
In Table 1, + means expansion, and +0.1 mm or less means that the expanded dimension does not exceed 0.1 mm and cannot be measured in units of 0.01 mm.
[0025]
(5) End processability of PTFE insulator layer After the outer conductor (copper tube) of the semi-rigid coaxial cable is cut and removed with a safety razor, the PTFE insulator layer is cut and removed with a safety razor, and the center conductor (silver plated) The workability until stripping the copper-clad steel wire was evaluated according to the following criteria.
Evaluation criteria:
Excellent: Easy removal of PTFE insulator layer.
Good: The removal work of the PTFE insulator layer is relatively easy.
Defect: It is very difficult to remove the PTFE insulator layer.
[0026]
(6) High-frequency characteristics of semi-rigid coaxial cable Attenuation amount was measured when high-frequency characteristics of 1 GHz, 3 GHz, 5 GHz, 10 GHz, and 18 GHz were transmitted using a semi-rigid coaxial cable.
[0027]
(7) Solder heat resistance of semi-rigid coaxial cable Solder (soldering iron: iron tip diameter 2 mm, 24 V, 50 W) solder (alloy 1.0 mm diameter, 60% tin and 40% lead alloy) And melted. The tip of the semi-rigid coaxial cable was brought into contact with 5 points (3 seconds / location) at intervals of 30 mm, and the highest temperature at which no crack was generated in the outer conductor (copper tube) of the cable was measured.
[0028]
【The invention's effect】
As described above, since the semi-rigid coaxial cable of the present invention is a semi-fired PTFE insulator layer, a part of the PTFE insulator layer (in this case, the inner peripheral portion) becomes a porous body of open cells, resulting in a relative dielectric constant. The thickness of the insulator layer can be reduced. Therefore, since the thickness of the outer conductor can be increased by that amount, the solder heat resistance can be improved. Alternatively, since the outer diameter of the semi-rigid coaxial cable can be reduced at the same solder heat resistance temperature, the cable can be made thinner and lighter, which is particularly advantageous for mobile communication devices such as mobile phones.
[0029]
Moreover, the semi-rigid coaxial cable of the present invention has a small dimensional change of the PTFE insulator layer when heated, and the semi-fired PTFE insulator layer can be cut and removed smoothly without PTFE becoming fiber even when stretched. Therefore, it is easy to expose the central conductor.
[0030]
Furthermore, since the semi-rigid coaxial cable of the present invention has a small relative permittivity of the PTFE insulator, the attenuation amount of high frequency at various frequencies is small, and the high frequency characteristics are excellent.
[Brief description of the drawings]
1 is a drawing showing a DSC chart of a semi-fired PTFE insulator layer obtained in Example 1. FIG.
2 is a drawing showing a DSC chart of (unfired) PTFE insulator layer obtained in Comparative Example 1. FIG.
3 is a drawing showing a DSC chart of a fired PTFE insulator layer obtained in Comparative Example 2. FIG.

Claims (1)

In a semi-rigid coaxial cable in which one or more insulator layers and an outer conductor layer are sequentially provided on the outer periphery of the central conductor,
The semi-rigid coaxial cable, wherein at least one of the insulator layers is made of semi-baked polytetrafluoroethylene.

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