Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
2001-07-03
2002-12-17
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
Reexamination Certificate
active
06495764
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a shielded flat cable in which effective countermeasure is taken to reduce noise levels of high frequency signals.
BACKGROUND ART
High frequency oscillators, for instance, require miniaturization with an increase of miniaturization of electronic apparatuses or the like. To such requirements, a shielded flat cable in which signal wirings (strip lines) are disposed and insulated from each other between insulating layers has been developed. When the signal wirings are formed between the insulating layers (internally formed), there is a likelihood that generated signal radiation adversely affects other signal wirings. In addition, an influence of an external electromagnetic noise may cause a malfunction in a wiring circuit including the signal wiring.
To deal with such problems, a configuration of a shielded flat cable is proposed. In the configuration, insulating and shield layers are concentrically stacked with each signal wiring to form a shield wire. Thereafter, the shield wires are disposed in parallel and covered by an insulator to integrate, thereby forming a shielded flat cable. The signal wiring (center conductor) is made of tin plated annealed copper wire or silver plated copper alloy wire, and the shield layer is made of a mesh of tin plated annealed copper wires. Furthermore, the aforementioned shield wires are arranged in parallel with a pitch of approximately 1.27 mm, followed by covering with an insulating layer of such as polyvinyl chloride resin to integrate with a thickness of approximately 2 mm.
Though the shielded flat cable mentioned above has an ability of reducing an adverse influence due to the signal wirings, there are still the following problems. That is, even in this kind of shielded flat cable, higher densification or finer patterning of signal wirings is required to provide greater compactness or higher functionality of the circuit.
However, in making the circuit more compact or denser, more complicated machine operations, and finer and more precise machining or the like are necessitated, thereby tending to result in a remarkable increase of the manufacturing costs or decrease of reliability. In other words, in the manufacture and formation of the aforementioned shield wirings, there is a limit in dimensional accuracy in the parallel arrangement of the shield wirings and in the covering and integration with the insulating layer. As a result, the densification is largely restricted.
As a means for stabilizing the signal wirings disposed inside the insulating layer, there is proposed the following configuration. That is, in the configuration the signal wirings are arranged sandwiched in plane between ground wirings, and are sandwiched from above and below between a pair of shield layers. In addition, the ground wiring and shield layer are electrically connected by means of a vertical shield conductor (via interconnection).
One shield layer is a grounding layer made of copper foil disposed integrally on the other main surface of the insulating layer on which the signal and ground wirings are disposed. The other shield layer is a conductive paste layer or the like disposed integrally on the other main surface of the insulating layer covering the signal wirings. However, in the configuration where the signal and ground wirings are sandwiched from right to left in plane and from above and below, the following operations are prerequisite. That is, when vertically connecting the ground wiring with the shield layer by means of a wiring conductor, it is suggested to bore in advance, at a corresponding position, a necessary hole by drilling, followed by the formation of a conductor layer or the like inside the hole.
In boring by means of a drill, a small diameter of approximately several hundreds &mgr;m is a lower limit to bore. This small diameter not only becomes an obstacle in higher densification and miniaturization of the signal wirings or the like, but also exerts a large adverse influence on yield or the like, resulting in an increase of manufacturing cost. A small hole of approximate 300 &mgr;m can be bored by means of laser machining in place of the boring due to the drilling. However, it is difficult to form a connection of high reliability through the hole.
The present invention is carried out in view of the aforementioned situations. The object of the present invention is to provide a shielded flat cable that has a simplified structure and high shielding reliability, and a manufacturing method thereof.
DISCLOSURE OF THE INVENTION
A first aspect of the present invention is a shielded flat cable, comprising an insulating layer that comprises liquid crystal polymer and is folded and stacked integrally, signal wirings disposed on a folded surface of the insulating layer and ground wirings disposed thereon, the signal wirings and the ground wirings being insulated from each other, a shield layer integrally disposed on an external surface of the insulating layer to cover a disposition area of the signal wirings and ground wirings, and a conducting portion piercing through the insulating layer to connect electrically the ground wiring with the shield layer.
In the shielded flat cable of the present invention, the shield layer may be excised at a plurality of positions corresponding to a fold area of the insulating layer.
A second aspect of the present invention is a manufacturing method of a shielded flat cable, comprising the steps of forming a wiring base substrate in which signal wirings and ground wirings are disposed and insulated from each other on one side area or a center area of one main surface of an insulating layer comprising liquid crystal polymer, and a conductive foil layer connected with the ground wiring which is disposed on the other main surface of the insulating layer, folding the wiring base substrate along the outside of a disposition area of the respective wirings so that a non-disposition area of the respective wirings faces the disposition area thereof, and bonding integrally opposing surfaces of the folded wiring base substrate to make the conductive foil layer a shield layer.
A third aspect of the present invention is a manufacturing method of a shielded flat cable, comprising the steps of, forming signal wirings and ground wirings insulated from each other on one side area or a center area of one main surface of an insulating layer comprising liquid crystal polymer, aligning a conductive foil layer having a conductive protrusion capable of connecting with the ground wiring on the other main surface of the insulating layer, and stacking to form a stacked body, compressing the stacked body integrally to bring the conductive protrusion into piercing through the insulating layer and electrical contact with the ground wiring, and forming a wiring base substrate, folding the wiring base substrate along the outside of a disposition area of the wirings of the insulating layer so that a non-disposition area of the wirings faces the disposition area thereof, and bonding integrally opposing surfaces of the folded wiring base substrate to make the conductive foil layer a shield layer.
In the manufacturing method of the shielded flat cable of the present invention, an insulating adhesive layer may be interposed between the opposing surfaces in the step of bonding integrally.
A part of the conductive foil layer corresponding to a fold area of the insulating layer may be excised in the step of bonding integrally.
In the present invention, the signal wiring, ground wiring and shield layer are composed of conductive metal such as copper, aluminum or the like and is generally formed in foil or thin film of a thickness of approximately from 12 to 35 &mgr;m. The signal wiring, ground wiring and shield layer are formed by patterning a copper foil of a copper clad liquid crystal polymer film for instance.
In general, widths of the signal and ground wirings are in the range of approximately 110 to 120 &mgr;m and a distance (pitch) between the signal wiring and the ground wiring is also in the range of a
Nguyen Chau N.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Yamaichi Electronics Co. Ltd.
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