Signal line

Abstract: Shielding portions (6 and 7) are superposed on opposite sides of an elongate flexible circuit board (4) on which signal wires are formed by folding about fold lines ( a and b ) to provide a flexible shielded signal wire. The flexible shielded signal wire is especially suitable for transmission of signals to and from a rotary head drum of a digital audio tape recorder.

Description: The invention relates to a shielded signal wire. Such a shielded signal wire may be used to transmit a head output signal reproduced from a recording medium by a rotary head of a rotary head type digital audio tape recorder (DAT) or to transmit a recording signal to the rotary head. In a conventional rotary head type tape recorder (see for example document DE-A-3 318 987), head output signals obtained from the rotary head are of very low amplitude, and hence the wire by means of which they are conducted to a circuit board having the necessary signal processing unit arranged on it must be shielded. The shielding prevents noise from the surroundings from infiltrating the signals and degrading them. However, such a shielded wire, which includes a mesh wire for shielding arranged around the signal wire, is quite thick. Hence there is a significant spatial problem particularly when the tape recorder is to be of only small size. Moreover, soldering is required to order to connect the shielded wire to the rotary head and the circuit board, and this increases the number of production steps. In addition, reliability deteriorates because in a percentage of cases the soldering may be imperfect. The rotary heads normally have two channels, channel A and channel B, and when multicore shielded wire is used for conducting the signals of the two channels, the shield wire becomes stiff. Thus, in a tape recorder in which the drum on which the rotary head is mounted is movable in accordance with its mode of operation, there is the problem that the load on the actuator for controlling movement of the drum increases. An actuator of substantial size and power is required, which further militates against miniaturisation. According to one aspect of the invention there is provided a one piece shielded signal wire in the form of flexible printed board means comprising: first and second shielding portions in the shape of a strip and having a pre-determined shield pattern; first and second spaced-apart connection portions; and a signal line pattern portion in the shape of a strip and having a conductive pattern that forms a pre-determined signal line connecting the first and second connection portions; the first and second shielding portions being folded in a predetermined manner, thereby to superpose the signal line between the first and second shielding portions. According to another aspect of the invention there is provided a method of manufacturing a one piece shielded signal wire comprising the steps of: forming a substantially flat flexible circuit board having a substantially flat signal wire portion on which signal wire are provided and first and second substantially flat shielding portions; folding the first shielding portion over one side of the signal wire portion; and folding the second shielding portion over an opposite side of the signal wire portion; thereby substantially to enclose the signal wire portion within the first and second shielding portions. The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view showing a preferred embodiment of a tape recorder using a shielded signal wire according to the invention; Figure 2 is a diagrammatic plan view illustrating the shielded signal wire of Figure 1 prior to folding about fold lines a and b ; Figure 3 is a diagrammatic sectional view taken on line III-III of Figure 1 and showing the shielded signal wire in cross section; and Figure 4 is a diagrammatic view illustrating deformation of the shielded signal wire in response to movement of a head drum of the apparatus of Figure 1. Referring to Figure 1, a drum 1 on which a rotary head of a rotary head type tape recorded is mounted supplies channel A and channel B signals to a separate circuit board (not shown) together with an earth signal through a shielded signal wire 2. In practice, the shielded signal wire 2 as a whole is formed by punching out a single flexible circuit board and has a shape before folding as shown in Figure 2. The shielded signal wire 2 is provided with a drum mounting portion 3, a signal wire pattern portion 4, a connector portion 5, and first and second shielding portions 6 and 7. The drum mounting portion 3 is semi-circular and provided at its central portion with signal wire terminals 3 a , 3 b , and 3 c which are connectable to channel A and B signal terminals and an earth signal terminal on an upper end surface 1A of the drum 1. The drum mounting portion 3 further has a shielding pattern 3 d formed around it, and the shielding pattern 3 d is provided at pre-determined positions with fastening holes 3 e and 3 f . The signal wire pattern portion 4 which is connected to the drum mounting portion 3 is in the shape of a strip and is provided with signal patterns 4 a and 4 b for channel A and B signals, respectively. The signal patterns 4 a and 4 b are respectively connected to the signal wire terminals 3 a and 3 b of the drum mounting portion 3. Between the signal patterns 4 a and 4 b there is formed a signal pattern 4 c for earth signals. The signal pattern 4 c is connected to the terminal 3 c . Along the signal patterns 4 a , 4 b and 4 c there is provided a shielding pattern 4 d . Opposite the drum mounting portion 3 of the signal wire pattern portion 4 and on opposite sides of an intermediate portion of the signal wire pattern portion 4 there are respectively formed first, second and third fastening hole pattern portions 8A, 9A and 10A. The portions 8A, 9A and 10A are semi-circular shielding patterns, and each has a through-hole at a central portion thereof. The first shielding portion 6 is formed near one end of the signal wire pattern portion 4 (Figure 2) and is in the shape of a strip substantially symmetrical to the signal wire pattern portion 4 about a first fold line a . Also, the first shielding portion 6 has first, second and third fastening hole pattern portions 8B, 9B and 10B respectively corresponding to the fastening hole pattern portions 8A, 9A and 10A in the signal wire pattern portion 4. The second shielding portion 7 extends from a pre-determined position of the first shielding portion 6 on the side of the fold line a (Figure 2) opposite the signal wire pattern portion 4. The second shielding portion 7 has a shielding pattern in the shape of a strip substantially symmetrical to the first shielding portion 6 about a second fold line b . An elongate connection portion 11 is perpendicular to the shielding portions 6 and 7 and is bisected by the fold line b , which extends parallel to the shielding portions 6 and 7 and perpendicular to the fold line a . Alternatively, the shielding portions 6 and 7 may extend from opposite edges of the wire pattern portion 4 and the fold lines a and b may be parallel to each other. Other relative arrangements of the fold lines a and b will readily occur to those skilled in the art. The second shielding portion 7 is provided with first, second and third fastening hole pattern portions 8C, 9C and 10C corresponding respectively to the fastening hole pattern portions 8A, 9A, and 10A in the signal wire pattern portion 4. In practice, the signal wire pattern portion 4 and the first shielding portion 6 are folded relative to each other along the first fold line a so that pattern surfaces over which an insulation resist or a like material is applied are brought into contact to each other. Then, the signal wire pattern portion 4 and the folded shielding portion 6 on the one hand and the second shielding portion 7 on the other hand are folded relative to each other along the second fold line b so that the back of the signal wire pattern portion 4 and a pattern surface of the second shielding portion 7 over which an insulation resist or a like material is applied make contact with each other. In this manner, the shielded signal wire 2 is formed. In the shielded signal wire 2, the three single flexible circuit boards, the first shielding portion 6, the signal wire pattern portion 4 and the second shielding portion 7 are superposed. As the section of Figure 3 shows, a shielding pattern 12 is arranged so as to surround the signal pattern 4 a for the channel A signals, the signal pattern 4 b for the channel B signals, and the signal pattern 4 c for the earth signals of the signal wire pattern portion 4. The shielded signal wire 2 thus provides a sufficient shield for the signal patterns 4 a , 4 b and 4 c . A high shield effect against magnetic noise leaking from the rotary head of the drum 1 is obtained by the arrangement of the signal pattern 4 c for each signals between the signal pattern 4 a for the channel A signals and the signal pattern 4 b for the channel B signals. As Figure 1 shows, the drum mounting position 3 of the shielded signal wire 2, which has been formed by superposing the three single flexible circuit boards, is fastened to the drum upper end surface 1A of the drum 1 by screws 14A and 14B through a shaped shielding plate 13 and is further secured to the circumferential surface 1B of the drum 1 by a screw 14C through the shielding plate 13 and the fastening pattern portion 8. The shielded signal wire 2 is fastened to a supporting member 16 within the tape recorder by screws 14D and 14E through the second and third fastening hold pattern portions 9 and 10. The three superposed single flexible circuit boards adhere to one another and form a predetermined bend 15 (Figures 1 and 4). The shielded signal wire 2, which has the three single flexible circuit boards superposed and is secured in position as described above, is significantly reduced in vertical projected area as compared to a conventional shielding wire. As shown by the solid and the dot-and-dash lines in Figure 4, the shielded signal wire 2 deforms in accordance with the displacement of the drum 1 (indicated by the arrow d ). Since the three single circuit boards are individually flexible and are not bonded to one another, the shielded signal wire 2 as a whole is not stiff and in particular is highly flexible at the bent portion 15. Since the three single flexible circuit boards are superposed and adhere to one another in a bend condition to form a pre-determined bent portion 15, the shielding effect can be effectively maintained even during displacement of the drum 1. In the structure described above, the three single flexible circuit boards respectively provide the first shielding portion 6, the signal wire pattern portion 4 and the second shielding portion 7 and include the bent portion 15. There is thus provided a shielded signal wire 2 that has a thin and flexible structure and provides superior electrical and magnetic shielding. Moreover, in the construction described above, the connector portion 5 is formed at the distal end of the signal wire pattern portion 4 and thereby the parts to be soldered are minimised. The shielded signal wire 2 thus simplifies the production process and remarkably enhances reliability. The single flexible circuit boards can be punched out in a predetermined shape and then superposed, but the manufacture of the shielded signal wire 2 does not have to be performed in this way. It is essential only that three elongate flexible circuit boards be superposed to achieve the same effect as in the embodiment described above. In the embodiment of the invention described above, the signal patterns 4 a and 4 b for two channels are arranged on the flexible circuit board of the signal wire pattern portion 4. However, the number of the signal patterns may be selected according to the number of the channels to be provided. In the embodiment of the invention described above, the signal pattern 4 c for earth signals is disposed between the signal patterns 4 a and 4 b for two channels of the signal wire pattern portion 4. Alternatively, when magnetic shielding is not necessary, the signal pattern 4 c for earth signals may itself be used to form part of the shielding pattern. In the embodiment of the invention described above, the shielding pattern 4 d is arranged on both sides of the signal patterns 4 a and 4 b of the signal wire pattern portion 4. However, the same or practically equivalent effect can be achieved without the shielding pattern 4 d if shielding needs to be effected only in some directions or only to some degree. The present invention as described above is applied to a case where head output signals are obtained from the rotary head of the tape recorder. The present invention is not limited to this case; on the contrary, the invention may be suitably applied to various shielded signal wire for drawing out output signals from optical pick-ups of an optical disc drive, various sensors or the like.

Claims: A one piece shielded signal wire (2) in the form of flexible printed board means comprising: first (6) and second (7) shielding portions in the shape of a strip and having a pre-determined shield pattern; first (3) and second (5) spaced-apart connection portions; and a signal line pattern portion (4) in the shape of a strip and having a conductive pattern that forms a pre-determined signal line connecting the first and second connection portions; the first (6) and second (7) shielding portions being folded in a pre-determined manner, thereby to superpose the signal line (4) between the first (6) and second (7) shielding portions. A shielded signal wire according to claim 1, in which the conductive pattern of the signal line pattern portion (4) is formed at a first location on a surface of the flexible printed board means and the shield patterns of the first (6) and second (7) shielding portions are respectively formed at second and third locations on the surface, the first, second and third locations being spaces apart from one another before folding of the first (6) and second (7) shielding portions. A shielded signal wire according to claim 1, in which the signal line pattern portion (4) has shielding patterns at least at one end of the conductive pattern on the same surface as the surface on which the conductive pattern is formed. A shielded signal wire according to claim 1, in which the conductive pattern of the signal wire pattern portion has first (4 a ), second (4 c ) and third (4 b ) conductive patterns formed in parallel with one another, the second conductive pattern (4 c ) being between the first (4 a ) and third (4 b ) conductive patterns and used as an earth line. A shielded signal wire according to claim 1, further comprising a movable rotary head drum (1), an electronic circuit and a printed board mounting the electronic circuit, the first connection portion (3), being connected to the rotary head drum (1) and the second connection portion (5) being connected to the printed board, and the electronic circuit providing a recording signal to or receiving a reproduced signal from the rotary head drum (1). A shielded signal wire according to claim 1, in which the first (6) and second (7) shielding portions are in parallel with each other and are folded about a pair of fold lines ( a , b ) that respectively extend in different directions so that the first shielding portion (6) when folded about one ( a ) of the fold lines overlies the signal line pattern portion (4) on one side thereof and the second shielding portion (7) when folded about the other ( b ) of the fold lines overlies the signal line pattern portion (4) on another side thereof. A method of manufacturing a one piece shielded signal wire (2) comprising the steps of: forming a substantially flat flexible circuit board having a substantially flat signal wire portion (4) on which signal wires (4 a , 4 b , 4 c ) are provided and first (6) and second (7) substantially flat shielding portions; folding the first shielding portion (6) over one side of the signal wire portion (4); and folding the second shielding portion (7) over an opposite side of the signal wire portion (4); thereby substantially to enclose the signal wire portion (4) within the first (6) and second (7) shielding portions. A method according to claim 7, wherein the first shielding portion (6) is folded about a first fold line ( a ) and the second shielding portion (7) is folded about a second fold line ( b ), the first ( a ) and second ( b ) fold lines being perpendicular to each other.

Inventors: HIMENO TAKUJI C O PATENTS DIVI, HIMENO, TAKUJI, C/O PATENTS DIVISION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H01R9
IPC codes: H05K1, H05K9, G11B20, A47G33