JP2012038851A - Flexible printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible printed wiring board with high bending characteristic.SOLUTION: A flexible printed wiring board 1 comprises: a plurality of metal film layers 5 and 6; and an insulating layer 4 arranged between the plurality of metal film layers 5 and 6. The flexible printed wiring board 1 includes: a bent portion 2 where bendability is required; and an unbent portion 3 where bendability is not required. The metal film layers 5 and 6 are not plated. The unbent portion 3 is provided with a through-hole 10 penetrating through the plurality of metal film layers 5 and 6, and the portion provided with the through-hole 10 is attached with conductive films 11 on both sides. By bringing the conductive films 11 into contact with each other in the through-hole 10, the plurality of metal film layers 5 and 6 are electrically connected to each other.

Description

  The present invention relates to a flexible printed wiring board having improved bending characteristics.

  A flexible printed wiring board is used for wiring of a movable part of an electronic device. Therefore, the flexible printed wiring board is required to have high bending characteristics. For example, a pan / tilt mechanism of a surveillance camera is required to have a bending characteristic that can withstand bending and stretching over 3.7 million round trips in a bending test.

  Incidentally, in recent years, various functions have been installed in electronic devices, and high-speed signal transmission may be required depending on the model of the electronic device. In response to such demands, a method of using LVDS (Low Voltage Differential Signaling) with a flexible printed wiring board has been proposed (for example, see Patent Document 1).

  In this conventional method, a flexible printed wiring board is multilayered, an insulating layer is provided between two metal line layers (signal line layer and ground line layer), and the ground line layer is meshed to adjust the characteristic impedance. This enables high-speed transmission by LVDS. In the conventional flexible printed wiring board, the two metal line layers (signal line layer and ground line layer) are plated, and the signal line layer and the ground line layer are electrically connected through the through hole. is doing.

JP 2007-227469 (page 5-7, FIG. 1)

  However, in the conventional method, since the flexible printed wiring board is multi-layered, the bending characteristics are reduced accordingly. In particular, when the metal line layer (signal line layer or ground line layer) is plated, there is a problem that the bending characteristics are remarkably deteriorated.

  For example, when a plating process is performed to electrically connect an LVDS signal line layer and a ground line layer, the thickness of the plating layer needs to be approximately the same as that of the metal line layer. The bending characteristics of the flexible printed wiring board greatly depend on the thickness of the metal wire layer and the plating layer. Therefore, when each of the two metal wire layers is plated, the metal wire layer is substantially 2 The same effect as the thickness of the layer is produced, and as a result, the bending characteristics are remarkably deteriorated.

  The present invention has been made to solve the above-described conventional problems, and an object thereof is to provide a flexible printed wiring board capable of improving the bending characteristics.

  The flexible printed wiring board of the present invention includes a plurality of metal film layers and an insulating layer provided between the plurality of metal film layers, and has a bent portion that requires flexibility and a non-flexible material. In the flexible printed wiring board configured with a bent portion, the metal film layer is not plated, and the non-bent portion is provided with a through-hole penetrating the plurality of metal film layers. A conductive film is affixed to both sides of the through hole, and the plurality of metal film layers are electrically connected by contacting the conductive film inside the through hole. It has a configuration.

    With this configuration, since the metal film layer is not plated, the bending characteristics of the flexible printed wiring board are improved. In this case, a conductive film is used for electrical connection between the metal film layers. Specifically, the metal film layer is electrically connected by attaching a conductive film to the through hole of the non-bent portion and bringing the conductive film into contact with the inside of the through hole. Since this conductive film is affixed to the non-bent part, the bending characteristic of the bent part (bending characteristic of the flexible printed wiring board) is not hindered.

  In the flexible printed wiring board of the present invention, the plurality of metal film layers include at least one signal line layer and at least one ground line layer, and the ground line layer is a mesh for adjusting characteristic impedance. It has the structure made into a structure.

  With this configuration, the ground line layer has a mesh structure, whereby the characteristic impedance can be adjusted, and high-speed signal transmission using LVDS becomes possible.

  In the flexible printed wiring board of the present invention, the mesh structure has a configuration in which at least the bent portion has a line-symmetric pattern about the center line of the bent portion.

  With this configuration, when the flexible printed circuit board is bent and stretched, the stress applied to the bent portion is equalized (symmetrized) and can be prevented from being disconnected due to the distortion of the stress. Will improve.

  Moreover, in the flexible printed wiring board of this invention, the said mesh structure has a structure which has the pattern by which the mesh center part which should be made into space was buried in the edge part of the said bending part.

  With this configuration, the strength of the end portion of the bent portion is increased, so that the load when the flexible printed wiring board is bent and stretched can be received at the end portion (high strength portion). The bending property of the is improved.

  In the flexible printed circuit board of the present invention, the non-bent portion is provided with a signal line for LVDS, and the conductive film is attached to a portion where the signal line for LVDS is provided. It has a configuration that is not.

  With this configuration, the influence on the characteristic impedance due to the conductive film can be prevented, and high-speed signal transmission using LVDS becomes possible.

  This invention can provide the flexible printed wiring board which has the effect that a bending characteristic improves since the metal film layer is not plated.

The top view of the flexible printed wiring board (state which stuck the conductive film) in embodiment of this invention The top view of the flexible printed wiring board (before sticking a conductive film) in embodiment of this invention Sectional drawing of the bending part of the flexible printed wiring board in embodiment of this invention Sectional drawing of the non-bending part (part of a through-hole) of the flexible printed wiring board in embodiment of this invention Explanatory drawing of the mesh structure of the flexible printed wiring board in embodiment of this invention The figure which shows the relation between the number of layers of the flexible printed circuit board and the bending characteristic Sectional view of the bent part of a conventional flexible printed circuit board (comparative example)

  Hereinafter, the flexible printed wiring board of embodiment of this invention is demonstrated using drawing. In this embodiment, the case of a flexible printed circuit board used for an electronic product or the like having a movable part such as a monitoring camera is illustrated.

  The structure of the flexible printed wiring board of embodiment of this invention is demonstrated with reference to drawings. 1 and 2 are plan views of the flexible printed wiring board of the present embodiment, and FIGS. 3 and 4 are cross-sectional views of the flexible printed wiring board of the present embodiment.

  As shown in FIGS. 1 and 2, the flexible printed wiring board 1 has a bent portion 2 and a non-bent portion 3 according to the design of the electronic device to be mounted. The bent part 2 is a part that is required to be flexible in design, for example, a part corresponding to a movable part of an electronic device. The non-bending portion 3 is a portion that is not required to be flexible in design, for example, a portion that is connected to a terminal (not shown) of a module of an electronic device. In addition, although the non-bending part 3 says the part by which a flexibility is not requested | required by design, it cannot be overemphasized that it may have a certain amount of flexibility.

  As shown in FIGS. 3 and 4, the flexible printed wiring board 1 includes a flexible insulating layer 4 and a signal line layer 5 provided on one surface (for example, the upper surface of FIG. 3) of the insulating layer 4. And a ground line layer 6 provided on the other surface of the insulating layer 4 (for example, the lower surface of FIG. 3). The signal line layer 5 and the ground line layer 6 are made of a metal film such as a copper foil, and can also be called a metal film layer. The signal line layer 5 is etched so as to form a predetermined circuit pattern. In this case, patterns of normal signal lines 7 and LVDS signal lines 8 are formed (see FIGS. 1 and 2), and the ground line layer 6 is etched to form a mesh structure 9 (see FIG. 1). (See FIG. 5). The mesh structure 9 will be described in detail later. The signal line layer 5 and the ground line layer 6 are not plated.

  As shown in FIG. 2, the non-bent portion 3 of the flexible printed circuit board 1 includes a portion where a signal line is provided and a portion where a signal line is not provided, and a portion where a signal line is not provided. A through hole 10 is provided. As shown in FIG. 1, the conductive film 11 is affixed to the part provided with the through-hole 10 from both sides (both sides) of the upper surface and the lower surface. As shown in FIG. 4, the conductive films 11 are in contact (adhesion) with each other inside the through hole 10, and the signal line layer 5 and the ground line layer 6 are electrically connected via the conductive film 11. ing. As shown in FIG. 1, the conductive film 11 is not attached to the portion where the signal line 8 for LVDS is provided. As the conductive film 11, an anisotropic conductive film 11 (ACF) or the like is used.

  As shown in FIG. 3, the bent portion 2 of the flexible printed wiring board 1 is preferably protected by a cover layer 12. In this case, the cover layer 12 is provided on the signal line layer 5 and the ground line layer 6 via the adhesive layer 13. The cover layer 12 and the adhesive layer 13 have sufficient flexibility and have little influence on the bending characteristics.

  Here, the mesh structure 9 of the ground line layer 6 will be described. The mesh structure 9 is for adjusting the characteristic impedance so that signals can be transmitted by LVDS. As shown in FIG. 5, the mesh structure 9 has a pattern in which meshes (diamond portions in FIG. 5) are arranged symmetrically about the center line of the bent portion 2 (dotted line in FIG. 5). Further, the mesh structure 9 has a pattern in which a mesh central portion (a triangular portion in FIG. 5) to be a space is buried at the end portion. The mesh structure 9 may be formed on the entire flexible printed wiring board 1 or may be formed only on the bent portion 2.

  According to such a flexible printed wiring board 1 of the present embodiment, since the metal film layer is not plated, the bending characteristics of the flexible printed wiring board 1 are improved.

  FIG. 6 is a diagram showing the relationship between the number of layers of the flexible printed wiring board 1 and the bending characteristics. As shown in FIG. 6, the flexible printed wiring board 1 has lower bending characteristics as the number of layers (the number of metal wire layers) increases. In particular, when plating is performed to electrically connect the LVDS signal line layer 5 and the ground line layer 6 as in the prior art, the thickness of the plating layer 20 is approximately the same as that of the metal line layers 5 and 6. It is necessary to make it thick (see FIG. 7). Therefore, when the number of layers (the number of metal wire layers) is increased, the thickness of the plating layer 20 is also increased correspondingly, and the bending characteristics are remarkably deteriorated.

  On the other hand, in the flexible printed wiring board 1 of the present embodiment, even if the number of layers is the same (the number of metal wire layers), since the plating layer does not exist, the bending characteristics are improved accordingly. To do. For example, when the number of layers is “2”, the conventional technique can provide only a low bending characteristic because the plating layer 20 exists, but in the present invention, since there is no plating layer, the high bending characteristic (substantially the metal wire layer is not present). A two-layer bending property). That is, in the present invention, even when the number of layers is “2”, it is possible to obtain bending characteristics (high bending characteristics) close to the conventional number of layers “1”.

  In the present embodiment, the conductive film 11 is used for electrical connection between the metal film layers. Specifically, the metal film layer is electrically connected by attaching the conductive film 11 to the through hole 10 of the non-bent portion 3 and bringing the conductive film 11 into contact with the inside of the through hole 10. Since this conductive film 11 is affixed to the non-bending part 3, the bending characteristic of the bending part 2 (the bending characteristic of the flexible printed wiring board 1) is not hindered.

  In the present embodiment, the ground line layer 6 has the mesh structure 9, whereby the characteristic impedance can be adjusted, and high-speed signal transmission using LVDS becomes possible.

  Further, in the present embodiment, since a line-symmetric mesh pattern is adopted in the bent portion 2, the stress applied to the bent portion 2 is equalized (symmetrized) when the flexible printed wiring board 1 is bent and stretched. Therefore, it is possible to prevent disconnection due to stress distortion, and the bending characteristics of the flexible printed wiring board 1 are improved.

  Moreover, in this Embodiment, since the mesh pattern by which the mesh center part was embedded in the edge part of the bending part 2 is employ | adopted, since the intensity | strength of the edge part of the bending part 2 becomes high, the flexible printed wiring board 1 is The load at the time of bending and stretching can be received at the end portion (high strength portion), and therefore the bending characteristics of the flexible printed wiring board 1 are improved.

  In this embodiment, since the conductive film 11 is not attached to the portion where the signal line 8 for LVDS is provided, the influence on the characteristic impedance by the conductive film 11 can be prevented, and the LVDS is reduced. Utilizing high-speed signal transmission becomes possible.

  The embodiments of the present invention have been described above by way of example, but the scope of the present invention is not limited to these embodiments, and can be changed or modified according to the purpose within the scope of the claims. is there.

  For example, in the above description, the case where each of the signal line layer and the ground line layer is one has been described. However, when the number of signals is larger, the number of signal line layers may be two or more.

  As described above, the flexible printed wiring board according to the present invention has an effect of high bending characteristics and is useful for being applied to an electronic product having a movable part such as a surveillance camera.

DESCRIPTION OF SYMBOLS 1 Flexible printed wiring board 2 Bending part 3 Non-bending part 4 Insulating layer 5 Signal line layer 6 Ground line layer 7 Normal signal line 8 Signal line for LVDS 9 Mesh structure 10 Through-hole 11 Conductive film 12 Cover layer 13 Adhesive layer 20 Plating layer

Claims (5)

A plurality of metal film layers, and an insulating layer provided between the plurality of metal film layers,
In a flexible printed circuit board composed of a bent part that requires flexibility and a non-bent part that does not require flexibility,
The metal film layer is not plated,
The non-bent portion is provided with a through-hole penetrating the plurality of metal film layers,
A conductive film is affixed from both sides to the portion provided with the through hole, and the plurality of metal film layers are electrically connected by contacting the conductive film inside the through hole. A flexible printed wiring board characterized by   The plurality of metal film layers include at least one signal line layer and at least one ground line layer, and the ground line layer has a mesh structure for adjusting characteristic impedance. Item 8. The flexible printed wiring board according to Item 1.   The flexible printed wiring board according to claim 2, wherein the mesh structure has a line-symmetric pattern about a center line of the bent portion at least in the bent portion.   The flexible printed wiring board according to claim 3, wherein the mesh structure has a pattern in which a mesh center portion to be a space is buried at an end portion of the bent portion. The non-bent part is provided with a signal line for LVDS,
5. The flexible printed wiring board according to claim 1, wherein the conductive film is not affixed to a portion where the signal line for LVDS is provided. 6.

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