JP2012160596A - Flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce crosstalk between wirings occurring at an overlapped portion of flexible printed circuit boards when they are arranged in an overlapped state inside an electronic device or a module in which multiple closely-spaced flexible printed circuit boards are wired.SOLUTION: A conductor layer 11 having a wiring pattern formed thereon is stacked on a base film 10, and a coverlay film 12 is stacked on the conductor layer. A shape of a flexible printed circuit board is characterized by a wave shape in a wiring direction. By configuring the flexible printed circuit board in the wave shape in the wiring direction, a section in which wirings are close to each other is shortened, even when another flexible printed circuit board or wiring board is arranged close to the flexible printed circuit board of the present invention so that the two flexible printed circuit boards or the flexible printed circuit board and the wiring board overlap each other. As a result, the effect of crosstalk between the wirings can be reduced.

Description

  The present invention relates to a flexible printed circuit board used for internal wiring of an optical pickup, a digital camera, a mobile phone, and the like.

  In recent years, flexible printed boards (also referred to as “flexible wiring boards”) that can be bent and have excellent flexibility in routing have been used in optical pickups for optical disk drives, and internal wiring of digital cameras and mobile phones.

  In the electronic device described above, a plurality of flexible printed boards are densely wired together with the miniaturization and integration of the elements and electronic boards connected by the flexible printed boards. For this reason, the flexible printed boards are arranged in an overlapping state, and there is a problem that crosstalk occurs between signals at the overlapping portion.

  As a means for solving this problem, for example, a technique has been used in which a double-sided flexible printed circuit board is employed, and a surface where signals overlap is used as a ground surface (shield surface) to avoid crosstalk. However, the double-sided flexible printed circuit board has a problem that the cost is higher than that of the single-sided flexible printed circuit board. Furthermore, since the double-sided flexible printed circuit board has a larger thickness than the single-sided flexible printed circuit board, there is a problem that the flexibility is deteriorated.

  In order to avoid crosstalk between signals, for example, a cover portion covering the front and back surfaces of the main body portion of the flexible wiring board is formed integrally with the main body portion so that it can be bent, and a pattern is formed on each cover portion. There has been proposed a flexible wiring board that is connected to a ground wire pattern formed on a main body portion, and that the cover portion is bent to cover both the front and back surfaces of the main body portion and bonded to the main body portion (see, for example, Patent Document 1). . This wiring board reliably shields the wiring portion, increases the strength, and does not require an extra process for production.

  Also, among adjacent wiring patterns in the same flexible printed circuit board, the shape of one wiring pattern is changed periodically to shorten the section where the wirings are close to each other, thereby reducing crosstalk between the wiring patterns. Has been proposed (see, for example, Patent Document 2). FIG. 9 is a top view showing the configuration of the flexible printed board described in Patent Document 2, and shows two wirings 90 and 91 having portions adjacent to each other. As shown in FIG. 9, with respect to the wiring 90, the wiring 91 adjacent to the wiring 90 is arranged so that the shape thereof periodically changes and the section in which the wirings are close to each other is shortened.

JP-A-4-263495 JP 2003-258394 A

  However, like the double-sided flexible printed board, the flexible wiring board having the configuration of Patent Document 1 has a problem that the flexibility is deteriorated because the thickness of the board after the cover portion is bent is increased. Further, in the wiring board of Patent Document 2, it is necessary to secure an area of a predetermined dimension in which the wiring 91 is arranged in order to periodically change the shape of the one wiring 91. Therefore, the width of the entire flexible printed circuit board is widened and the wiring property is deteriorated (that is, the number of wirings that can be arranged is reduced when the wiring width of the entire flexible printed circuit board is determined). have. Furthermore, since it is necessary to increase the width of the connector connected to the flexible printed circuit board according to the width of the flexible printed circuit board, there is a problem that the component placement area becomes large when the connector is mounted on the printed circuit board. ing.

  The present invention solves the above-mentioned conventional problems, and uses an inexpensive single-sided flexible printed circuit board to alleviate the influence of crosstalk due to the overlap between the substrates without deteriorating the flexibility and wiring performance, and is stable. An object of the present invention is to provide a flexible printed circuit board that enables signal transmission.

  In order to solve the above-described conventional problems, the present invention provides a flexible printed circuit board in which a conductor layer in which a wiring pattern is formed is laminated on a base film, and a coverlay film is laminated on the conductor layer. A flexible printed board having a wave shape in the wiring direction of the flexible printed board is provided. Here, the “wiring direction” refers to a direction in which the wiring extends from one end of the flexible printed board to the other end in the flexible printed board. According to this configuration, the flexible printed board of the present invention is another flexible printed board or a wiring board (here, the wiring board is not a flexible printed board (for example, a rigid wiring board and a rigid-flex wiring board). ), The section (distance) where the wiring of the flexible printed circuit board of the present invention and the wiring of the other board are close to each other is shortened. The influence can be reduced.

  The flexible printed circuit board of the present invention can be used in an electronic device or module in which a plurality of flexible printed circuit boards are densely wired, even when the flexible printed circuit board is arranged in a state of overlapping with another flexible printed circuit board or a printed circuit board. By having the shape, the interval in which the wires are close to each other is shortened. Therefore, when the flexible printed circuit board of the present invention is used, it is possible to reduce the influence of inter-wiring crosstalk in an overlapping portion with another flexible printed circuit board or a wiring substrate.

The perspective view which shows an example of a structure of the flexible printed circuit board of Embodiment 1 of this invention. Sectional drawing of the wiring direction of a flexible printed circuit board which shows the relationship between the flexible printed circuit board of Embodiment 1 of this invention, and another wiring board The side view of the wiring direction which shows an example of a structure of the flexible printed circuit board of Embodiment 1 of this invention The side view of the wiring direction which shows another example of a structure of the flexible printed circuit board of Embodiment 1 of this invention The side view of the wiring direction which shows another example of a structure of the flexible printed circuit board of Embodiment 1 of this invention The side view of the wiring direction which shows an example of the manufacturing method of the flexible printed circuit board of Embodiment 1 of this invention The side view of the wiring direction which shows the structure of the flexible printed circuit board of Embodiment 2 of this invention The top view which shows an example of the manufacturing method of the flexible printed circuit board of Embodiment 2 of this invention Sectional view in width direction cut along line A-A 'in FIG. 7a Sectional view in wiring direction cut along lines B-B 'and C-C' in FIG. 7a The top view which shows the structure of the flexible printed circuit board of Embodiment 3 of this invention. Top view showing the configuration of two adjacent wirings in a conventional flexible printed circuit board

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1a is a perspective view showing a configuration of a flexible printed board according to Embodiment 1 of the present invention. The illustrated flexible printed circuit board 100 has a configuration in which a conductor layer 11 on which a wiring pattern is formed is laminated on a base film 10, and a coverlay film 12 is laminated on the conductor layer 11. The flexible printed circuit board has a wave shape in the wiring direction. In the case of a narrow tape-like flexible printed circuit board, the wiring direction is a direction perpendicular to the width and parallel to the main surface (that is, the length direction). When the flexible printed circuit board has a wave shape in the wiring direction, when another flexible printed circuit board or the wiring board is close to each other, and the wirings of the two boards are close to each other, the section where the wirings are close to each other is shortened. Therefore, the influence of crosstalk between wirings can be reduced.

  Further, when the flexible printed circuit board is arranged in a complicated manner and / or connected to a movable part, only a part of the flexible printed circuit board is shielded from other flexible printed circuit boards or metal of the housing. It can happen that it contacts or is close to the part. In this case, since the impedance of only a part that is in contact with or close to the impedance is reduced, impedance mismatch with the other part occurs, and the transmission characteristics of the signal deteriorate due to reflection on the transmission line. Since the flexible printed circuit board according to the present invention has a wave shape, the portion of the flexible printed circuit board is in contact with or close to the shield part of the other flexible printed circuit board or the metal part of the housing, so that the impedance in the part is shortened. Can be suppressed.

  The relationship between the flexible printed board of the present invention and other flexible printed boards or wiring boards will be further described with reference to the drawings. FIG. 1 b shows a cross section in the wiring direction of the flexible printed circuit board 100 shown in FIG. 1 a and a cross section of another flexible printed circuit board or wiring substrate 101 (hereinafter referred to as “other substrate 101”). In FIG. 1b, the detailed layer structure of the substrate is omitted for easy understanding. In the figure, the alternate long and short dash line corresponds to the average of the distance between the flexible printed circuit board 100 of the present embodiment and another substrate 101. Compared with the case where the flexible printed circuit board having no wave shape is located on the one-dot chain line, the flexible printed circuit board 100 of the present embodiment is farther from the other substrate 101 in the portion located above the one-dot chain line. . Therefore, crosstalk is less likely to occur between the wiring of the flexible printed circuit board 100 of the present embodiment and the wiring of another substrate 101. Further, also in the portion below the alternate long and short dash line, the place where the distance between the flexible printed circuit board 100 of the present embodiment and the other substrate 101 is the shortest is the wave valley. Therefore, when the flexible printed circuit board 100 has a wave shape, as described above, the influence of contact or proximity between the substrates is effectively suppressed.

  When the wave shape of the flexible printed circuit board 100 is a regular sine wave as shown in the figure, the amplitude s and wavelength w are the width d of the wiring provided on the flexible printed circuit board 100 (the width when viewed from above). , And the pulse width λ of the signal transmitted via the wiring, and the average distance k between the flexible printed circuit board 100 and the other circuit board 101 are determined. If the distance between the wirings increases, the influence of crosstalk is reduced. Specifically, the amplitude s is preferably set so that k is 3d to 5d. Further, if the section in which the wirings are close to each other is shortened, the influence of crosstalk is reduced. Specifically, the distance between the sections where the wirings are close to each other is preferably ¼ or less of λ. When the amplitude s is set so that k is 3d, the distance of the section where the wirings are close to each other in the sine wave of one cycle (distance where the portion located below the one-dot chain line in the figure) is at most It becomes 1/2 of w. Therefore, it is preferable to set the wavelength w so as to be 1/2 or less of λ.

  When the flexible printed circuit board according to the present embodiment is arranged close to another board as shown in FIG. 1b, the signal transmitted by the wiring of the flexible printed board and the wiring of the other board are transmitted. This effectively reduces the crosstalk that occurs with the transmitted signal. Therefore, the present invention includes the flexible printed circuit board of the present invention (including the embodiment described below) and another flexible printed circuit disposed so as to face the flexible printed circuit board of the present invention in the thickness direction. Provided is a wiring board structure including a substrate or a wiring board. In the wiring board structure of the present invention, crosstalk between signals generated between flexible printed boards or between the flexible printed board and the wiring board is less likely to occur.

  FIG. 2 is a side view in the wiring direction showing another example of the configuration of the flexible printed board according to the first embodiment of the present invention. As shown in FIG. 2, in the flexible printed circuit board of the present invention, the wave frequency may not be constant but random. When a certain frequency continues in the wave, the frequency may be the resonance frequency of the signal to be transmitted. In that case, transmission characteristics at that frequency deteriorate. By making the wave frequency random, it is possible to avoid deterioration of transmission characteristics due to resonance, and thus stable signal transmission is possible.

  FIG. 3 is a side view in the length direction showing still another example of the configuration of the flexible printed circuit board according to Embodiment 1 of the present invention. As shown in FIG. 3, in the flexible printed circuit board of the present invention, the wave amplitude may not be constant but random. By making the amplitude of the wave random, when the flexible printed circuit board of the present invention is disposed close to another substrate, the section in which the wiring patterns are close to each other is further shortened. That is, in FIG. 3, the deepest valley portion (the portion indicated by Sm in the drawing) is closest to the other wiring substrate, and the other valley portion is located farther from the other wiring substrate than Sm. . Therefore, the influence of crosstalk between signals can be further reduced. Similarly, even if only a part of the flexible printed circuit board is in contact with or close to the shield part of another flexible printed circuit board or the metal part of the housing, the part that is in contact with or close to the shield metal part or the metal part of the housing is further increased. Can be reduced. Therefore, it is possible to further suppress a decrease in impedance in the part.

  FIG. 4 is a side view in the length direction showing still another example of the configuration of the flexible printed circuit board according to Embodiment 1 of the present invention. As shown in FIG. 4, in the flexible printed circuit board of the present invention, a portion f having a surface perpendicular to the thickness direction of the flexible printed circuit board between the portions Wa having a wave shape (this portion is used for convenience). (Also referred to as a “flat portion”). Dividing into a wave-shaped part and a flat part and reducing the frequency of occurrence of waves in the flexible printed circuit board (ie, the number of peaks and valleys) further shortens the section adjacent to the wiring of other boards. Therefore, the influence of crosstalk between signals can be further reduced. Similarly, when only a part of the flexible printed circuit board is in contact with or close to the shield part of another flexible printed circuit board or the metal part of the housing, the part that is in contact with or close to the shield part or the metal part is further increased. Can be reduced. Therefore, it is possible to further suppress a decrease in impedance in the part.

  Further, by forming the flat portion, it is possible to reduce the total line length of the wiring pattern in the flexible printed board, and it is possible to improve the signal transmission quality. The length of the flat portion should be as long as possible as long as reduction of the expected influence of crosstalk between signals can be ensured.

  As described above, the flexible printed circuit board according to the first embodiment is provided as a single-layer flexible printed circuit board, and the thickness of the entire board does not have a conventional wave shape. It is possible to maintain the same flexibility as a printed circuit board.

  Next, an example of the manufacturing method of the flexible printed circuit board of Embodiment 1 of this invention is demonstrated. FIG. 5 is a side view in the wiring direction showing an example of the method for manufacturing the flexible printed board according to the first embodiment of the present invention. First, the conductor layer 11 on which the wiring pattern is formed is formed on one surface of the base film 10. The base film is a flexible resin such as polyimide or polyester, and is generally made of a resin having heat resistance. The thickness of the base film is usually 10 to 30 μm. The conductor layer 11 is formed by adhering a foil made of a metal such as copper to the base film 10 and patterning the metal foil by etching or the like. The width d of the wiring constituting the wiring pattern is usually 50 to 200 μm although it depends on the use of the flexible printed circuit board. A method of adhering the metal foil to the base film and a method of patterning may be a conventionally used method.

  Next, the cover film 12 is laminated on the surface of the conductor layer 11 of the laminate composed of the film 10 and the conductor layer 11. The cover film 12 is usually a film made of the same material as the base film 10 and an adhesive, or a thermosetting liquid resist, and generally has a thickness of 10 to 30 μm. The cover film 12 is usually adhered to the conductor layer 11 by disposing the cover film 12 on the surface of the conductor layer 11 and applying heat and pressure. At this time, as shown in FIG. 5, in order to give the flexible printed circuit board a wave shape, a hot pressing process is performed using a mold 50 having an uneven shape. By appropriately selecting the shape of the mold 50, flexible printed circuit boards having various shapes shown in FIGS. 2 to 4 can be obtained. The laminated body including the base film 10, the conductor layer 11, and the cover film 12 after forming the wave shape is subjected to machining such as punching so as to have an appropriate dimension according to the use of the flexible printed wiring board. . In addition to the processes described above, other processes that are performed according to the manufacture of the flexible printed wiring board may be performed as necessary.

  The method of imparting the wave shape is not limited to the heating press using a mold, and other methods can be used as long as the desired wave shape is obtained and the shape is maintained even during use of the flexible printed circuit board. May be used. For example, the wave shape may be given by mechanical folding.

  The wave shape of the flexible printed circuit board according to the first embodiment of the present invention is not limited to a sine wave, and may be a square wave, a trapezoidal wave, a triangular wave, or a combination thereof, and is not particularly limited. In addition, when there are two or more wiring directions in one flexible printed circuit board (for example, when there are three or more ends, or when the wiring direction is bent according to the shape of the flexible printed circuit board), The effect of the present invention can be obtained by having a wave shape in at least one wiring direction.

(Embodiment 2)
FIG. 6 is a side view in the length direction showing the configuration of the flexible printed circuit board according to the second embodiment of the present invention. A flexible printed board 600 shown in FIG. 6 includes a base film 60a, a wiring layer 60 including a conductor layer 60b on which a wiring pattern is formed, and a coverlay film 60c, a base film 61a, a conductor layer 61b on which the wiring pattern is formed, and a cover. It has the wiring part 61 which consists of a ray film 61c. The wiring part 60 and the wiring part 61 are wiring parts adjacent to each other in the same flexible printed circuit board, and both of the wiring parts adjacent to each other have a wave shape (sine wave in the drawing) in the wiring direction. The flexible printed circuit board 600 has a configuration in which the phase of the wave shape of the wiring unit 61 is reversed with respect to the phase of the wave shape of the wiring unit 60. More specifically, when the shape of the wiring portion 60 is regarded as a sine wave having the wiring direction as the x axis and the thickness direction as the y axis, the shape of the wiring portion 61 is wired with the y axis as the symmetry axis. This is a reflection of the part 60. The fact that the phases of adjacent wiring portions are inverted means that the phases of adjacent wiring portions are inverted. Therefore, according to the configuration of the second embodiment, compared to a case where adjacent wirings are in the same phase, a section where the wirings are close to each other is shortened, and crosstalk between adjacent wirings in one substrate is reduced. It becomes possible.

  Further, in the wiring pattern of a pair that performs differential transmission, the phase of the wiring is inverted, so that the wiring of the pair forms a twisted pair structure. The formation of the twisted pair structure makes it possible to cancel the electromagnetic noise from the outside and the inside, and therefore, it is possible to improve the characteristics of the flexible printed circuit board from the viewpoint of resistance to electromagnetic noise. Similarly to the flexible printed circuit board of the second embodiment, each of the wirings has a wave shape, so that the other flexible printed circuit board or the printed circuit board is close to the flexible printed circuit board. When the wirings on the substrate are close to each other, the section in which the wirings are close to each other is shortened, so that the influence of crosstalk between the wirings can be reduced.

  As a technique for reducing crosstalk between adjacent wirings in the same flexible printed board, there is a method of widening the wiring interval in the width direction of the flexible printed board. However, when this method is employed, the entire width of the flexible printed circuit board becomes wide. Since the method for reducing crosstalk between adjacent wirings according to the second embodiment of the present invention uses phase inversion of wiring in the wiring direction of the flexible printed circuit board, the overall width of the flexible printed circuit board does not change.

  Next, an example of the manufacturing method of the flexible printed circuit board of Embodiment 2 of this invention is demonstrated with reference to FIG. FIG. 7 a is a top view showing an example of a method for manufacturing a flexible printed circuit board according to Embodiment 2 of the present invention. A laminated body 73 including a conductor layer 71 having a laminated wiring pattern is shown. FIG. 7B is a cross-sectional view in the width direction taken along line A-A ′ of FIG. 7A in a state in which the molds 76 are arranged above and below the laminate shown in FIG. 7A. 7c is a cross-sectional view in the wiring direction cut along lines B-B 'and C-C' of FIG. 7a in a state where the molds 76 are arranged above and below the laminate shown in FIG. 7a.

  As shown in FIGS. 7 a and 7 b, the laminate 73 is formed by laminating a conductor layer 71 having a wiring pattern formed on a base film 70. Before the cover lay film 72 is laminated on the laminated body 73, a certain length of cut is provided between the wiring portions 74 including the wiring pattern (in FIG. 7a, simplified and shown as a rectangle). 75 are provided at equal intervals in a direction parallel to the wiring direction. As in the manufacturing method of the first embodiment, the wave shape is imparted to the wiring portion 74 by performing a hot press process using a mold 76 when the coverlay film 72 is bonded. At this time, as shown in FIGS. 7b and 7c, in order to invert the phases of the adjacent wiring portions 74 in the wiring direction, and in turn invert the phases of the adjacent wiring patterns in the wiring direction, The phase of the shape of the portion that gives the wave shape to one wiring portion 74 of the two adjacent wiring portions 74 is reversed with the phase of the shape that gives the wave shape to the other wiring portion 74. It is formed.

  If necessary, the coverlay film 72 may also be cut.

  The width of one wiring part 74 is appropriately selected according to the use of the flexible printed circuit board and is not particularly limited, and may be, for example, 0.1 mm to 1.0 mm. Since the materials of the base film 70, the conductor layer 71, and the coverlay film 72 are as described in connection with the first embodiment, their description is omitted here. Further, the wave shape of the flexible printed board of the second embodiment is not limited to a sine wave, and may be a square wave, a trapezoidal wave, a triangular wave, or a combination thereof, and is not particularly limited. In addition, when there are two or more wiring directions in one flexible printed circuit board (for example, when there are three or more ends, or when the wiring direction is bent according to the shape of the flexible printed circuit board), The effect of the present invention can be obtained by having a wave shape in at least one wiring direction.

(Embodiment 3)
FIG. 8 is a top view showing the configuration of the flexible printed board according to Embodiment 3 of the present invention. The flexible printed circuit board 80 of FIG. 8 has a part or all of a portion having a wave shape of the flexible printed circuit board having the configuration described in the first embodiment (particularly, the configuration shown in FIGS. 1 to 3) on one side. It is configured so that the unfixed part can be deployed. In the flexible printed circuit board 80 having this configuration, by expanding the deployable portion, the portion having the wave shape is fixed from one side portion to the other side portion in a certain section or all sections. The structure is such that the wave period interval gradually changes from dense to coarse as it goes to. The components connected to the flexible printed circuit board can be moved in the developing direction by appropriately developing the deployable portion.

  In addition, after the components connected to the flexible printed circuit board are once arranged at a predetermined position in the apparatus, a deployable portion is expanded or closed in the apparatus (for example, with movement of other parts). By being configured in this way, it can be moved within the apparatus. Therefore, in the flexible printed circuit board according to the third embodiment, the moving direction of the components connected to the conventional flat flexible printed circuit board is limited to the direction in which the flexible printed circuit board can be bent. Allows movement of parts in the direction, i.e. increases the direction of movement of the parts. Furthermore, the flexible printed wiring board of this form has the advantage that the freedom degree of wiring in three-dimensional wiring increases. Also, the flexible printed wiring board of the third embodiment is similar to that of the first embodiment, because the wiring has a wave shape, so that the other flexible printed circuit boards or wiring boards are close to each other, and therefore the two boards. Even when these wires are close to each other, the section in which the wires are close to each other is shortened, so that the influence of crosstalk between wires can be reduced.

  The flexible printed circuit board of the present invention is excellent in reducing crosstalk between wirings due to overlapping with other flexible printed circuit boards or wiring boards, and for wiring inside electronic devices and modules in which a plurality of flexible printed circuit boards are densely wired. Is available.

DESCRIPTION OF SYMBOLS 10 Base film 11 Conductor layer 12 Coverlay film 50 Mold 60a, 61a Base film 60b, 61b Conductor layer 60c, 61c Coverlay film 60, 61 Wiring part 70 Base film 71 Conductive layer 72 Coverlay film 73 Laminate 74 Wiring part 75 Notch 76 Mold 80 Flexible printed circuit board 90, 91 Wiring

Claims (7)

  A flexible printed circuit board in which a conductor layer having a wiring pattern formed thereon is laminated on a base film, and a coverlay film is laminated on the conductor layer, wherein a wave shape is formed in a wiring direction of the flexible printed board. A flexible printed circuit board characterized by having   The flexible printed circuit board according to claim 1, wherein the wave shape has a random frequency.   The flexible printed circuit board according to claim 1, wherein the wave shape has a random amplitude.   The said flexible printed circuit board has a part which has a wave shape, and a part which has a surface perpendicular | vertical with respect to the thickness direction of the said flexible printed circuit board, The Claim 1 characterized by the above-mentioned. Flexible printed circuit board.   5. The flexible printed circuit board according to claim 1, wherein the wiring pattern has two mutually adjacent phases having phases reversed from each other.   5. A part or all of the part having the wave shape is fixed on one side of the flexible printed circuit board, and an unfixed part can be developed. A flexible printed circuit board according to 1.   The flexible printed circuit board according to any one of claims 1 to 6, and another flexible printed circuit board or a wiring board arranged to face the flexible printed circuit board in a thickness direction of the flexible printed circuit board. Including a wiring board structure.

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