JP5174793B2 - Flexible printed circuit board - Google Patents

Description

  The present invention relates to a flexible printed circuit board.

  Conventionally, flexible printed circuits (FPC) have been used as wiring members between a plurality of boards built in high-density mounting products such as mobile phone terminals and car navigation systems.

  A flexible printed circuit board has a structure in which a wiring pattern formed of a conductive foil is sandwiched between thin insulating films such as polyimide, and it can be used by bending it softly like paper. It is used for wiring while greatly deforming small gaps. Further, it may be used while being bent in accordance with the movement of the parts passing between the moving mechanical parts such as the hinge part of the folding mobile phone terminal.

  In recent years, with the miniaturization of the product, the wiring space inside the product has been reduced. However, if the curvature of the bent part increases, the distortion generated in the flexible printed circuit board increases, and the conductor is caused by repeated stretching and bending. There is a high possibility that the foil will fatigue and break. In order to increase the curvature while preventing disconnection even after repeated bending and stretching a certain number of times, it is necessary to accurately grasp the strain that actually occurs in the flexible printed circuit board, and to determine the appropriate amount from the correlation between strain and repeated bending and stretching durability. It is necessary to set the bending shape.

  By the way, when measuring distortion of an object, a strain gauge is generally used. The strain gauge is a structure in which a very narrow line formed from a metal resistor (metal foil) is arranged in a zigzag pattern on a thin insulator film, and is used by being attached to an object to be measured. When the object to be measured is deformed, the strain gauge is deformed in the same manner, so that the length and width of the metal resistor change, and the electrical resistance changes. It is possible to measure the amount of distortion of the object to be measured by measuring the change in electric resistance.

  When using the strain gauge, it is premised that the object to be measured has the rigidity of the strain gauge itself or the rigidity that can ignore the influence of the adhesive used in the pasting. For this reason, when measuring the strain of an object with very low rigidity, such as paper, the strain changes due to the strain gauge or adhesive when the strain gauge is attached. It is difficult to measure.

  Patent Document 1 discloses a rigid substrate capable of measuring strain with a built-in strain gauge.

  In Patent Document 2, an object to be measured (soil) is obtained by arranging a plurality of strain gauges made of an insulating film and a metal foil on a flexible laminated substrate made of a metal plate, an insulating layer, and a conductive wiring, and arranging a plurality of strain gauges. A flexible wiring board with a strain gauge is disclosed which is embedded in and measures the internal displacement of an object to be measured.

JP 2001-15882 A JP 2008-157830 A

  The technique of the above-mentioned patent document 1 is for measuring the amount of distortion of a semiconductor package mounting portion of a rigid substrate. That is, the invention described in Patent Document 1 measures a strain that can occur in an arbitrary direction within a substrate surface at a specific position on a rigid substrate, and is flexible and can be greatly deformed. It is not intended to measure the distortion of the measurement object.

  Moreover, although the technique of patent document 2 is a structure which arrange | positions a strain gauge in a pair on the front and back of a flexible wiring board, it installs a strain gauge on a conductive wiring in each surface of front and back, and also the surface and back surface The strain gauges are stacked in the thickness direction of the flexible printed circuit board. Therefore, the conductive substrate and the strain gauge are arranged so as to overlap each other on the entire substrate, which affects the rigidity of the flexible printed circuit board. That is, the invention disclosed in Patent Document 2 has a problem that the rigidity of a flexible printed board having flexibility and low rigidity is affected by the lamination of strain gauges, and the distortion cannot be measured accurately.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the flexible printed circuit board which can measure the distortion of the curved part correctly.

  In order to solve the above-described problems and achieve the object, the present invention provides a wiring layer formed by arranging a base material layer made of a strip-shaped base film and a conductive foil provided with a wiring pattern on the base film. The wiring pattern includes a strain gauge portion formed as a line shape in which a part of the conductor foil is arranged in a zigzag manner.

  According to the present invention, it is possible to bend a flexible printed circuit board with a curvature as large as possible while ensuring that no disconnection occurs, and it is possible to achieve a reduction in the size and life of a device to which the flexible printed circuit board is applied. .

FIG. 1 is a diagram showing a cross-sectional configuration of a first embodiment of a flexible printed circuit board according to the present invention. FIG. 2 is a perspective view of the flexible printed circuit board according to the first embodiment. FIG. 3 is a plan view of the flexible printed circuit board. FIG. 4 is a diagram showing a configuration of a general strain gauge. FIG. 5 is a plan view of a dummy flexible printed circuit board for strain measurement. FIG. 6 is a diagram showing a cross-sectional configuration of the second embodiment of the flexible printed circuit board according to the present invention.

  Embodiments of a flexible printed board according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a cross-sectional configuration of a first embodiment of a flexible printed board according to the present invention. The flexible printed circuit board (FPC) 20 includes a base film 21 as a base material layer, a conductor foil 22 as a wiring layer, and a coverlay film 23 as a protective layer. The base film 21 is a film-like insulator having a thickness of about 12 to 50 μm. The conductor foil 22 is made of copper having a thickness of about 12 to 50 μm. The cover lay film 23 is a film-like insulator for protecting the conductor foil 22 and has a thickness similar to that of the base film 21.

  FIG. 2 is a perspective view of the FPC 20. The conductor foil 22 is formed with a wiring pattern including a strain gauge function part 26 and a wiring 25. The cross section shown in FIG. 1 is a cross section at a portion where the conductor foil 22 is present as a wiring pattern, and thus has a three-layer structure. It becomes a layer structure. The FPC 20 includes terminals 24a and 24b at end portions in the longitudinal direction, and is used as a wiring material between substrates.

  FIG. 3 shows a plan view of the FPC 20. As shown in FIG. 3, a plurality of strain gauge function units 26 are aligned along the longitudinal direction of the FPC 20 and are arranged side by side with the wiring 25. Since the strain gauge function portion 26 and the wiring 25 are formed of the same conductor foil 22 and do not overlap in the thickness direction, the rigidity of the FPC 20 is not partially increased. By forming the strain gauge function part 26 on the FPC 20 using the same conductor foil 22 as that of the wiring 25, it becomes possible to observe the strain state of the FPC 20 in real time during use of the product.

  FIG. 4 shows a configuration of a general strain gauge. A thin film-like insulator 11 and a metal resistor (line) 12 arranged in a zigzag thereon are provided, and a lead wire 13 taken out from an end of the metal resistor 12 is connected to an electric circuit in which a bridge circuit is configured. Is done. When this is affixed to the object to be measured, the resistance of the metal resistor 12 changes when the object to be measured is deformed. Therefore, the strain is measured by reading the change in resistance.

  Similar to the general strain gauge shown in FIG. 4, the strain gauge function unit 26 has a structure in which a very narrow line (a part of the conductor foil 22) is laid out in a zigzag manner. From, a signal line (corresponding to the conducting wire 13 in FIG. 4) is drawn out and reaches the terminals 24a and 24b. The change in resistance of the conductor foil 22 caused by the deformation of the FPC 20 is transferred from the terminals 24a and 24b at the end of the FPC 20 to another board having a bridge circuit via a connector or the like and read. At this time, if the terminal numbers of the terminals 24a and 24b are compared with the position of the strain gauge function section 26, which position of the FPC 20 is deformed to what extent (in other words, which position in the longitudinal direction of the FPC 20). The strain distribution such as how much strain is generated in the strain gauge function unit 26 in FIG. Further, in the case of being housed in a movable part such as a hinge part of a foldable portable terminal, the opening angle of the terminal can be detected based on the output value of the strain gauge function part 26.

  Since the conductor foil 22 is covered with the cover lay film 23, it is possible to prevent the fine-width conducting wire forming the strain gauge function portion 26 from being disconnected due to friction or the like. Here, a configuration including the coverlay film 23 is shown as an example, but a configuration without the coverlay film 23 may be used.

  If the FPC 20 is intended only for the strain test and the electrical wiring function of the product is not required, the wiring 25 may be omitted. The dummy FPC 20 'for strain measurement shown in FIG. 5 is obtained by omitting the wiring 25, and the strain gauge function unit 26 can be used after cutting out at an appropriate position and adjusting the length.

  The bent portion of the FPC 20 has an upper limit in curvature from the viewpoint of preventing disconnection, and therefore has a certain length in the longitudinal direction (in other words, the FPC 20 is curved rather than bent). For this reason, by arranging the strain gauge function portions 26 in the longitudinal direction of the FPC 20, it is possible to measure the strain of the bent portion in the flexible FPC 20 that can be deformed greatly.

  As described above, the flexible printed circuit board according to the present embodiment can measure distortion generated over a certain length in the longitudinal direction. Therefore, it is possible to bend with a curvature close to the limit while preventing disconnection, and it is possible to reduce the size of the high-density mounting product. Further, by bending the flexible printed circuit board with a curvature that does not cause disconnection, it is possible to extend the useful life of a product using the flexible printed circuit board and to extend the service life.

Embodiment 2. FIG.
FIG. 6 is a view showing a cross-sectional configuration of a second embodiment of the flexible printed board according to the present invention. The FPC 30 according to the present embodiment is configured to include two wiring layers, and includes a base film 31a, a conductor foil 32a, a base film 31b, a conductor foil 32b, and a coverlay film 33. Here, the base films 31a and 31b are the same as the base film 21 of the first embodiment. The conductor foils 32a and 32b are the same as the conductor foil 22 of the first embodiment. The coverlay film 33 is the same as the coverlay film 23 of the first embodiment. Note that the cross section shown in FIG. 6 has a five-layer structure because the cross section of the conductor foils 32a and 32b exists as a wiring pattern, but the wiring pattern of the conductor foil 32a or the wiring pattern of the conductor foil 32b The non-existing portion has a four-layer configuration, and the cross section in the portion where the wiring patterns of both conductor foils 32a and 32b do not exist has a three-layer configuration.

  In the present embodiment, the strain gauge function section is provided on each of the conductor foils 32a and 32b. Even when the strain gauge function portions are provided in the two wiring layers, the strain gauge function portions are accommodated within the thickness of the conductor foils 32a and 32b, so that the rigidity of the FPC 30 is not partially increased. Therefore, the strain of the FPC 30 can be accurately measured using the built-in strain gauge function unit.

  Since other aspects are the same as those in the first embodiment, a duplicate description is omitted.

  As described above, the flexible printed board according to the present invention is useful for accurately measuring the distortion of a curved portion.

20, 30 Flexible printed circuit board (FPC)
20 'dummy FPC
21, 31a, 31b Base film 22, 32a, 32b Conductive foil 23, 33 Coverlay film 24a, 24b Terminal 25 Wiring 26 Strain gauge function section

Claims (4)

It possesses a belt-like base film, a wiring pattern formed on the base film based on a sheet of conductive foil, and a terminal portion provided on both ends in the longitudinal direction of the base film, the terminal portion by being connected to the two substrates via, a flexible printed circuit board that is used as a wiring material between the two substrates,
The wiring pattern includes a connection line connecting the terminal portions, and the strain gage portion formed in a zigzag line shape on the side of the connecting line, the distortion circuit for measuring a change in electrical resistance in the strain gauge section look including a strain gauge signal line for connecting the gauge portion, and wherein said connecting wires, said strain gauge section and the strain gauge signal lines are formed in the same layer by said one conductive foil Flexible printed circuit board.   The flexible printed circuit board according to claim 1, wherein the wiring pattern includes a plurality of strain gauge portions, and the plurality of strain gauge portions are arranged in alignment with a longitudinal direction of the base film. The base film and said wiring pattern are stacked by two or more alternately, a flexible printed circuit board according to claim 1 or 2 each of two or more of the wiring pattern, characterized in including that the strain gauge unit. The flexible printed circuit board according to any one of claims 1 to 3 , wherein a protective layer is formed on the surface.

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