JPS6338883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises disposing elongated electrically conductive conductors in the longitudinal direction on both sides of a strip-shaped dielectric material, each pair consisting of two or more electrically conductive materials facing each other and spaced parallel to each other. An object of the present invention is to provide a flexible stripline cable of this type which has particularly good electrical signal transmission characteristics, dimensional stability, and good properties for removing resin portions at the ends. It is.

Good electrical signal transmission characteristics can be achieved by using a material with low dielectric constant and dielectric loss and low frequency dependence as the dielectric for such flexible stripline cables. is generally known. That is, if the dielectric constant of the dielectric used is small, the structural dimensions of the flexible stripline cable can be reduced even if the characteristic impedance of the flexible stripline cable is the same, and the signal propagation speed becomes faster. The smaller the dielectric loss, the smaller the signal attenuation. Furthermore, if the frequency dependence of the dielectric constant and dielectric loss is small, the waveform rounding of the pulse signal can be kept small, for example, when a pulse signal is transmitted through the flexible stripline cable.

Thus, the dielectric material that can be used in flexible stripline cables as described above is
As mentioned above, it is required that the dielectric constant and dielectric loss be small, and their frequency dependence should be small. It is made of material and has many small nodules as its internal structure.
Materials are known that have a porous microstructure of open pores connected by fibers and with a large number of voids formed between these fibrils and nodules. Various types of such materials are known, including polyolefins (polyethylene, polypropylene, polystyrene), nylon, and polyester that have been processed into a porous state by a stretching method, an admixture extraction method, a papermaking method, etc. , fluororesin [polytetrafluoroethylene (FE), ethylene-tetrafluoroethylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFB) )] etc. A typical example thereof is expanded porous polytetrafluoroethylene (PTFE) produced by the method disclosed in Japanese Patent Publication No. 18991/1983. However, porous crystalline polymer materials, such as expanded porous PTFE, are too flexible and have poor shape stability. However, it is unsuitable for use as a dielectric for flexible stripline cables having the structure described above.

However, the present inventor has discovered that the porous crystalline polymer material as described above has a small dielectric constant and dielectric loss, and also has small frequency dependence. Using such a porous material as the dielectric material of a flexible stripline cable,
Various experimental considerations were made to find out how to take advantage of the inherent excellent characteristics of flexible stripline cables while still meeting the other requirements mentioned above, namely shape stability. As a result of repeated research, a new and improved flexible stripline cable structure according to the present invention was conceived.

Briefly stated, in the present invention, electrically good conductors are placed on both upper and lower surfaces of a flat band-shaped dielectric made of expanded porous PTFE, and if necessary, in the middle of the dielectric, pairs of electrically conductive materials are arranged facing each other with the dielectric interposed therebetween. A non-porous or solid plastic material such as PTFE, PFA, FEP, etc.
A tape layer made of ETFE or polyester is formed by any suitable method, such as integral molding, fusing or gluing. A portion of the band-shaped dielectric material on at least one side in the width direction of at least one set of electrically conductive materials is crushed in the thickness direction so that the dielectric constant of this portion is larger than that of the other portion.

The invention will now be explained in more detail with reference to the embodiments shown in the drawings.

Referring to the drawings, a flexible stripline cable according to one embodiment of the present invention is shown in fragmentary cross-sectional view. In this example,
An unburned PTFE tape formed from a mixture of fine PTFE powder and liquid lubricant by a known process of paste extrusion, rolling, and removal of lubricant is stretched three times in the longitudinal direction in an atmosphere at 300°C. Then, maintain the stretched state and heat it to 360℃ to obtain the thickness
A fired expanded porous PTFE tape 1 of 0.127 mm was prepared. In this case, the degree of firing of Tape 1 was close to complete firing, and its dielectric constant was 1.3. next,
2a, 2a'; 2b, 2b'; 2c, 2c', respectively;
2d, 2d'; 2e, 2e' as shown
Five sets of conductors, each consisting of two conductors, are arranged on both sides of the stretched porous tape 1, with each set of conductors facing each other in the thickness direction, and adjacent sets of conductors extending in a parallel and spaced relationship with each other in the longitudinal direction. Established. In this case, each conductor 2a, 2a'; 2e, 2e' was a silver-plated rectangular copper conductor with a width of 0.5 mm and a thickness of 0.1 mm. Although it has been stated that five sets of such conductors are provided, this is only for the convenience of illustration and explanation, and it is clear that the number of sets of conductors can be selected as necessary. . After each conductor is arranged on both sides of the stretched porous PTFE tape 1 in this way, an unstretched unfired PTFE tape with a thickness of 0.25 mm is attached to both sides of the tape 1. The resulting composite structure is passed between at least a pair of pressure rolls (not shown), and then placed in a molten salt bath (not shown) at 370°C.
I was able to get through it in 30 seconds. As a result, the unstretched PTFE tapes applied to both sides of the stretched porous tape 1 as described above are fired and fused to the stretched porous PTFE tape 1 as outer shape stable layers 3, 3'. and became one with it.

In this case, when applying the composite structure to a crimping roll, for example, use a crimping roll in which only the part that is crimped to the area between adjacent conductor pairs is convex, so that each outer shape is The corresponding parts of the stabilizing layers 3 and 3' are made concave as shown by 3a and 3a', respectively, and the internal dielectric 1 is also crushed in the thickness direction as shown by 1'. It is said to be in the form of Due to this shape, the degree of porosity of the crushed portion 1' formed on at least one side in the width direction of at least one set of conductors of the dielectric body 1 is lowered than that of other portions, and the dielectric The dielectric constant is increased, and therefore each of The conductor sets 2a, 2a'; . . .; 2e, 2e' are surrounded.

The thickness of the portion of the dielectric material formed as the porous PTFE tape 1 existing between the opposing conductors of the flexible stripline cable thus obtained is
0.11 mm, the spacing between adjacent conductors was 1.27 mm, and the characteristic impedance of the flexible stripline cable was 49 ohms. In addition, the propagation delay time of this flexible stripline cable was 3.9 nanoseconds/meter, and when unstretched PTFE was used as the dielectric, it was 4.7 nanoseconds/meter.
In comparison, it was faster, and the pulse transmission characteristics and crosstalk characteristics between layers and adjacent conductors were also better than when unexpanded PTFE was used as the dielectric.

As understood from the above explanation, according to the present invention, expanded porous PTFE has a small dielectric constant and a small dielectric loss, and also has a small frequency dependence.
By using PTFE as a dielectric material, it is possible to achieve excellent electrical signal transmission characteristics, and in addition, by integrally providing shape-stable layers on both sides of the dielectric material, it is better than expanded porous PTFE. By compensating for shape instability caused by the flexibility of the material of the dielectric itself, sufficient shape stability can be ensured as a whole.

In addition, the shape-stabilizing layer attached to both sides of the dielectric made of expanded porous PTFE has a larger dielectric constant than the dielectric, and therefore, by creating a structure with the shape-stabilizing layer attached, each Since the electric field between the conductors is less likely to be radiated to the outside, signal crosstalk between layers and crosstalk between adjacent strips, which are problems when using the flexible stripline cables according to the present invention in a stacked manner, are reduced. It is.

In particular, in the embodiment of the present invention, as is clear from the drawings, the portion 1' of the band-shaped dielectric 1 whose dielectric constant is increased by being crushed, and the portion 1' which has a dielectric constant originally higher than that of the band-shaped dielectric 1. Each conductor set 2a, 2a' by the outer shape stable layer 3, 3';
...; 2e and 2e' are surrounded, which can reduce the diffusion of electromagnetic waves, reduce line crosstalk,
This makes it possible to further reduce interlayer crosstalk. Furthermore, by crimp-bonding each conductor set so as to form a concave shape in this manner, there is an effect that deformation due to pressure applied in the thickness direction of the stripline cable can be prevented.

In addition, according to the structure of the present invention described above, when terminating a flexible stripline cable, it is possible to terminate the flexible stripline cable in a direction perpendicular to the longitudinal direction with respect to the outer insulating layer thereof, such as with a razor or knife. Another advantage is that the resin can be easily cut and separated by making a cut with a sharp knife and moving the knife in the longitudinal direction, making it very easy to process the ends. It goes without saying that, depending on the purpose, an electromagnetic wave shielding layer made of metal, conductive fluororesin, or the like may be provided on the outer surface of the outer insulating layer.

In addition, in the above-mentioned examples, stretched porous
A layer of non-porous plastic material may be provided on at least one side of the dielectric strip 1 made of PTFE, thereby improving the dielectric strength.

Furthermore, the good electrical conductors that can be used in the flexible stripline cable according to the present invention are not limited to those mentioned above, and in addition to rectangular conductors and wires with a circular cross section, twisted wires and grouped wires thereof can also be used. Any suitable material may be used, such as copper wire, silver-plated copper wire, copper-coated steel wire, gold-plated stainless steel wire, etc.

Furthermore, the shapes and combinations of conductors and the number of conductors in each set are not limited to those shown in the drawings. For example, when using rectangular conductors, the thickness of the conductor for the signal line is equal to the thickness of the conductor for the ground line. The interlayer crosstalk characteristics may be improved by making the layer thinner than the
Those skilled in the art will readily understand that various modifications and changes can be made within the scope of the present invention.

In addition, when forming a flat cable shape as a multi-pair flexible stripline cable, the terminals may be cut out into a sash shape, or the non-terminal portions may be formed into a sash shape to improve crosstalk and bending. Of course, it is possible to obtain ease of use.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view showing a flexible stripline cable according to an embodiment of the present invention, and in the drawing, 1 is a dielectric made of expanded porous PTFE, 2a, 2a';;2a″,…
..., 2e'' are good electrical conductors, and 3 and 3' are outer shape-stable layers, respectively.

Claims (1)

[Scope of Claims] 1. At least two wires on both sides of a strip-shaped dielectric made of a porous crystalline polymer material, facing each other with the strip-shaped dielectric sandwiched therebetween, and having a parallel and spaced relationship.
At least one pair of elongated electrically conductive material is provided in the longitudinal direction, and a shape-stable layer made of a non-porous plastic material is provided on each of the two surfaces of the strip-shaped dielectric material, covering and fixing the electrically conducting material. A portion of the band-shaped dielectric material on at least one side in the width direction of the at least one set of electrically conductive materials is crushed in the thickness direction so that the dielectric constant of this portion is lower than the dielectric constant of the other portion. A flexible stripline cable characterized by being made larger than the ratio. 2. The flexible stripline cable according to claim 1, wherein the strip dielectric made of porous crystalline polymer material is made of expanded porous polytetrafluoroethylene.