JP6504828B2 - Flexible printed circuit board and method of manufacturing flexible printed circuit board - Google Patents

Description

  The present invention relates to a flexible printed circuit and a method of manufacturing the flexible printed circuit.

  In recent years, robots have been rapidly developed, for example, robots having various movements have appeared. In addition, wearable electronic devices that can be worn on the human body and clothes have also been developed and put into practical use in various devices. A large number of electric wires for power supply and electric signal transmission are used in these robots and wearable electronic devices, but in general, the electric wire has a core of copper wire and the outer periphery is covered with an insulator. Therefore, the wire itself has little elasticity. For this reason, for example, in a robot or the like, it is necessary to allow sufficient wire length so as not to prevent movement of the joint, etc., which is a practical obstacle in designing for downsizing and weight reduction, etc. Become.

  In particular, in applications such as state-of-the-art humanoid robots and power assist devices that are attached to the human body to assist muscle strength, they are placed at the end of the electric wire for moving the end motor via joints and at the end. A number of electric wires for transmitting electric signals from various sensors are wired. And, in order to increase the degree of freedom of these wires in the multi-degree-of-freedom joint, there is an increasing demand for telescopically configured electric wires.

  On the other hand, in recent years, arm robots are widely used as industrial robots. In this type of arm robot, depending on the driving method of the end effector (corresponding to the hand in human body) attached to the tip side of the robot arm or the joint of the robot arm, from the root side to the tip side of the robot arm In addition to the electrical cable, it may be necessary to wire an air hose or hydraulic hose for applying air pressure. When such a cable or hose is wired to a joint, the cable may be bent or broken. Therefore, the cables and hoses are temporarily moved outward at a position nearer to the proximal end than the joints of the robot arms, and the cables are arranged in the outer space of the joints, and again in the arms at a position closer to the tip than the joints. The wiring method to be introduced to However, the method of disposing the cable in the outer space of the robot arm requires a space for loosening the cable around the joint of the robot arm.

  Further, for example, in Patent Document 1, a support rod is provided at a joint rotation center position in a joint portion of a robot arm, a cable is wound around the support rod, and the cable is stored in advance inside the robot arm. By doing this, a structure is disclosed that prevents the cable from bending or breaking. However, there is a possibility that the functional deterioration (operating speed, accuracy, etc.) may occur due to the weight increase by separately providing the support rod. There are cases where a motor with high specs is used to compensate for the deterioration of the function or the number of necessary members is increased, but in such a case, the manufacturing cost is increased. Furthermore, since the structure of the storage portion of the cable becomes complicated, there is a problem that it becomes very complicated when disassembling by cable wiring at the time of assembling the robot arm, maintenance, etc. and taking out and replacing the cable. From this, also in the robot arm, there is an increasing demand for an expandable electric transmission member capable of avoiding such a problem.

  For example, Patent Document 2 discloses the technology disclosed in Japanese Patent Application Publication No. JP-A-2006-324118. In Patent Document 2, a plurality of pins formed of a desired R are arranged in a jig at intervals that the flexible printed board can pass, and heating is performed by passing the flexible printed board while applying a constant tension to the jig. A method of forming is described.

  In addition to the single-sided flexible printed substrate having a conductor layer only on one side, Patent Document 2 also discloses a three-layer flexible printed substrate having three conductive layers in relation to the structure of the flexible printed substrate. There is. As an application using a three-layer flexible printed circuit, there is generally a so-called stripline transmission path in which a signal line whose characteristic impedance is matched is disposed in the inner layer and the outer layer is GND (ground). For example, an image sensor is attached to the tip side of the above-mentioned movable part, and it is required when transmitting large-capacity data such as high-definition moving image data via an expandable flexible printed circuit, and external noise It is intended to cut off and achieve both high quality signal transmission and elasticity.

  Further, Patent Document 3 discloses a configuration in which shield layers using a conductive adhesive and a metal foil are disposed on outer layers on the front and back of a stripline transmission path using a three-layer flexible printed circuit.

JP-A-8-57792 JP, 2011-233822, A JP, 2010-177472, A

  By the way, in the stripline transmission line as disclosed in Patent Document 2, since the outer layer is solid GND, a plating film is also present on the outer layer. Therefore, it is solid as a flexible printed circuit board. Therefore, the followability to the jig is poor, and it is difficult to form a pleated shape in which a plurality of bent portions exist. In particular, the outer layer side has a large bending stress at the time of molding into a pleated shape, and the bent portion in the pleated shape has a high possibility of breaking due to expansion and contraction within 1000 times. Therefore, it is necessary to frequently replace the disconnected flexible printed circuit board, which results in high maintenance costs. Moreover, when using said flexible printed circuit board for production facilities, there also exists a problem that production will be interrupted by disconnection.

  Therefore, in the stripline transmission line as disclosed in Patent Document 2, as disclosed in Patent Document 3, a shield layer using a conductive adhesive or metal foil may be disposed on the outer layer side of the flexible printed circuit board. Conceivable. However, since the configuration disclosed in Patent Document 3 does not have high shieldability as compared with solid GND, it has been found that high frequency current does not easily flow and transmission loss increases as compared with solid GND. In particular, when the configuration of Patent Document 3 is applied to the configuration of Patent Document 2, the signal lines are close to each other at the pleated portion, so electrical interference is likely to occur, and the transmission loss increases. It will

  The present invention has been made based on the above-described circumstances, and the object of the present invention is a flexible printed circuit board capable of high-quality signal transmission with small transmission loss while having pleated portions having stretch resistance, and flexible print An object of the present invention is to provide a method of manufacturing a substrate.

In order to solve the above problems, according to a first aspect of the present invention, a signal line, an insulating layer made of thermoplastic resin and covering the signal line from both sides, and a signal line sandwiching the respective insulating layers And a pair of opposing ground layers to form a flexible printed circuit board having at least one set of strip line transmission paths, wherein curved portions curved at a plurality of locations are formed, and the curved portions are opened. Or, the ground layer is provided with a pleated portion that curves so as to be closed, and the ground layer is provided with a metal surface to provide electromagnetic wave shielding properties, and is more flexible than the hard ground layer and is electromagnetic wave more than the hard ground layer of the shielding inferior soft ground layer, have, on the ground layer, the one end and the soft ground layer of the hard ground layer other end side and is electrically conductive Optionally superposed overlapping portions in a state in which there is provided the soft ground layer is disposed on at least one side of the outer peripheral side and inner peripheral side of the bending portion, the flexible printed circuit board is provided, characterized in that Ru.

  Further, according to another aspect of the present invention, in the above-mentioned invention, the soft ground layer is a thin film conductive film comprising a conductive paste in which a conductive filler is mixed with a binder resin composition, and a metal thin film layer formed by vapor deposition. It is preferable to have at least one of

  Furthermore, according to another aspect of the present invention, in the above-mentioned invention, it is preferable that the soft ground layer is disposed on the outer peripheral side of the curved portion, and the hard ground layer is disposed on the inner peripheral side of the curved portion. .

  Further, according to another aspect of the present invention, in the above-mentioned invention, the pleat portion is provided in a bellows shape by alternately switching the direction of the curve of the curved portion, and the soft ground layer is provided on the surface side of the signal line. It is preferable to arrange | position on the outer peripheral side of a curved part in the state which exists in a back surface side alternately.

  In another aspect of the present invention, in the above-mentioned invention, the pleat portion is provided in a bellows shape by alternately switching the direction of the curve of the curved portion, and the soft ground layer is on the surface side of the signal line It is preferable to arrange | position on the outer peripheral side of a curved part in the state which exists in any one of the back surface side.

  Further, according to another aspect of the present invention, in the above-mentioned invention, the insulating layer is preferably formed of a material of LCP (Liquid Crystal Polymer) which is a thermoplastic resin.

  Further, according to another aspect of the present invention, in the above-described invention, it is preferable that a plating film for interlayer connection is not formed on the ground layer located in the curved portion.

Further, according to the second aspect of the present invention, a signal line, an insulating layer made of thermoplastic resin and covering the signal line from both sides, and a pair of grounds facing the signal line with the respective insulating layers interposed therebetween. And manufacturing a flexible printed circuit board having at least one set of strip line transmission paths, wherein at least one of the double-sided copper-clad laminates having a base copper foil layer on both sides of the insulating layer. The first step of forming a signal line on the base copper foil layer on one side, and the insulating layer of a single-sided copper-clad laminate having the base copper foil layer on one side of the insulating layer via double-sided adhesive A second step of laminating on one side of the double-sided copper-clad laminate on which the signal line is formed in a state covering the insulating layer constituting the laminate, and a predetermined portion of the intermediate product formed in the second step Through holes A third step of forming, by forming a conductive film on the through-hole and the opening periphery, and a fourth step of forming a conductive through hole,
In the intermediate product formed in the fourth step, the base copper foil layer facing the signal line is patterned to remove the base copper foil layer from a predetermined portion on one of the surfaces. And a fifth step of forming a hard ground layer in which the conductive portion is provided in a planar shape on the opposite surface side, and the removal portion is more flexible and hard than the hard ground layer. A sixth step of forming to cover a soft ground layer having a lower electromagnetic wave shielding property than the ground layer, and a seventh step of covering the soft ground layer and the hard ground layer with an insulating resin layer through an adhesive layer And heat-forming the flexible printed circuit board before the heat-forming formed in the seventh step in a state in which a plurality of portions are curved, and after the heat-forming, a plurality of curves in which the soft ground layer is positioned on the outer peripheral side Department Eighth step and, the production method of a flexible printed circuit board, characterized in that it comprises forming a pleat portion standing is provided.

  According to the present invention, the flexible printed circuit board enables high-quality signal transmission with small transmission loss while the pleated portion has expansion and contraction resistance.

It is a top view which concerns on one embodiment of this invention, and shows the structure of the flexible printed circuit board of the 1st structural example before shaping | molding. It is sectional drawing of the flexible printed circuit board before and behind shaping | molding, and is a figure which shows the state cut | disconnected along the AA of FIG. It is sectional drawing of the flexible printed circuit board before and behind shaping | molding, and is a figure which shows the state cut | disconnected along the BB line of FIG. It is sectional drawing of the flexible printed circuit board before and behind shaping | molding, and is a figure which shows the state cut | disconnected along the CC line of FIG. It is sectional drawing of the flexible printed circuit board before and behind shaping | molding, and is a figure which shows the state cut | disconnected along the DD line of FIG. It is sectional drawing of the flexible printed circuit board before and behind shaping | molding, and is a figure which shows the state cut | disconnected along the EE line of FIG. It is a side view which shows the shape of the flexible printed circuit board after shaping | molding. It is a top view which shows the 2nd structural example of the flexible printed circuit board before shaping | molding corresponding to the modification of FIG. It is a side view which shows the shape of the flexible printed circuit board after shaping | molding in a 2nd structural example. It is a figure which shows the image which applied the flexible printed circuit board which concerns on the 2nd structural example to the rotation site | part of external devices, such as joints of arms, such as a robot, and shows the state which two arms are maintaining horizontal state. FIG. It is a figure which shows the state which two arms in FIG. 10 rotated. FIG. 11 is a diagram showing a state in which signal lines and receiving lands are formed in the A-A cross section of FIG. 1 and FIG. 8 in the first step; It is a figure which shows the state in which the signal line was formed in the BB cross section of FIG.1 and FIG.8, CC cross section, and DD cross section which concern on a 1st process. It is a figure which shows a mode that it concerns on a 2nd process and the single-sided copper clad laminated board is laminated | stacked on a double-sided copper clad laminated board in the AA cross section of FIG. 1 and FIG. It is a figure which shows a mode that it concerns on a 2nd process and the single-sided copper clad laminated board is laminated | stacked on a double-sided copper clad laminated board in the BB cross section of FIG.1 and FIG.8, CC cross section, and DD cross section. FIG. 11 is a diagram showing a state in which a through hole is formed in the AA cross section of FIG. 1 and FIG. 8 in the third step; FIG. 10 is a side cross-sectional view showing a configuration in cross-sections BB, CC, and DD of FIGS. 1 and 8 according to a third process; It is a figure which shows the state which concerned on the 4th process and formed the conductive film layer for forming a conductive film in a through-hole in the AA cross section of FIG. 1 and FIG. FIG. 11 is a view related to a fifth step, showing a state in which patterning is performed in the A-A cross section of FIG. 1 and FIG. 8; FIG. 11 is a view related to a fifth step, showing a state in which patterning is performed in the B-B cross section of FIG. 1 and FIG. 8; It is a figure which concerns on a 5th process and shows the state in which patterning was made in the CC cross section of FIG. FIG. 11 is a view related to a fifth step, showing a state in which patterning is performed in the DD section of FIG. 1 and FIG. 8; It is a figure which concerns on a 5th process and shows the state by which patterning was made in the EE cross section of FIG. It is a figure which concerns on a 6th process and shows the structure in the CC cross section of FIG. 1 when a soft gland | gland layer is formed. FIG. 11 is a diagram showing a state in which the soft ground layer is formed in the D-D cross section in FIG. 1 and FIG. 8 in the sixth step. It is a figure which concerns on a 6th process and shows the state in which the soft gland | gland layer was formed in the EE cross section of FIG. It is a figure which concerns on a 7th process and shows the structure in the AA cross section of FIG. 1 and FIG. 8 when a cover layer is formed. FIG. 19 is a diagram related to the seventh step, showing a state in which the cover layer is formed in the B-B cross section of FIG. 1 and FIG. 8; It is a figure which concerns on a 7th process and shows the state in which the cover layer was formed in the CC cross section of FIG. FIG. 19 is a diagram related to the seventh step, showing a state in which the cover layer is formed in the DD cross section of FIGS. 1 and 8. It is a figure which concerns on the 8th process and shows the state which set the flexible printed circuit board before shaping | molding to a jig | tool. It is a top view which shows the structure of the flexible printed circuit board of conventional structure. It is sectional drawing of the flexible printed circuit board of conventional structure, and is a figure which shows the state cut | disconnected along the AA of FIG. It is sectional drawing of the flexible printed circuit board of conventional structure, and is a figure which shows the state cut | disconnected along the BB line of FIG.

  Hereinafter, a flexible printed circuit board 10 according to an embodiment of the present invention will be described below. The following description may be made using an XYZ orthogonal coordinate system. Among them, the X direction is the longitudinal direction of the flexible printed circuit 10, the X1 side is the right side of FIG. 1, and the X2 side is the left side. The Y direction is the width direction of the flexible printed circuit 10, the Y1 side is the front side in the drawing of FIG. 1, and the Y2 side is the rear in the drawing. Further, the Z direction is the thickness direction of the flexible printed circuit 10, Z1 is the back side in the drawing of FIG. 2, and Z2 is the front side in the drawing.

<About the 1st example of composition of a flexible printed circuit board>
FIG. 1 is a plan view showing the configuration of the flexible printed circuit board 10 before molding. FIG. 2 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, showing a state of being cut along the line A-A of FIG. FIG. 3 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, showing a state of being cut along the line B-B in FIG. FIG. 4 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and is a view taken along the line C-C in FIG. FIG. 5 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, showing a state of being cut along the line D-D of FIG. FIG. 6 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and is a view taken along the line E-E of FIG.

  As shown in FIGS. 1 to 6, the flexible printed circuit board 10 in the present embodiment is a three-layer flexible printed circuit board which is a kind of multilayer flexible printed circuit board, and has a configuration in which three conductor portions exist. Specifically, the flexible printed circuit 10 has the signal line 20 on the inner layer side. The signal line 20 is a portion formed by removing a copper foil portion transmitting a signal by etching or the like so that the characteristic impedance is matched for high-speed transmission by a manufacturing method which will be described later.

  As shown in FIG. 1, the flexible printed circuit board 10 is provided in an elongated shape. In the present embodiment, the flexible printed board 10 has, for example, a width (dimension in the Y direction) of 5 mm and a length before molding (dimension in the X direction) of 200 mm. However, as shown in FIG. 7 to be described later, the length is, for example, about 75 mm when it is formed in a pleated shape (bellows shape) such that the radius of the curved portion PL2 is 1 mm. However, the dimension example is not limited to this, and can be set to various dimensions (the same applies to dimension examples described later).

  Further, as shown in FIG. 1, the flexible printed circuit board 10 is provided with signal pads 11 exposed on the front and back. That is, the signal pad 11 is exposed to the outside on the front surface side and the rear surface side without being covered with the cover layers 80 and 90 described later. The signal pad 11 is a portion electrically connected to the signal line 20 between layers to input or output a signal to the signal line 20. Therefore, the conductive through holes 12 are electrically connected to the signal pads 11. The conductive through hole 12 has a through hole 12a penetrating the flexible printed circuit board 10 and a conductive film 12b such as plating formed on the inner wall side of the through hole 12a, and through the conductive film 12b The signal pad 11 is electrically connected to the signal line 20.

  Further, similarly to the signal pad 11 described above, the flexible printed board 10 is also provided with the GND pads 13 exposed on the front and back of the flexible printed board 10 without being covered with the cover layers 80 and 90 described later. . The GND pad 13 is also electrically connected to the two ground layers 60 and 70 on the front and back sides via the conductive through holes 14. Similar to the conductive through hole 12 described above, the conductive through hole 14 also includes a through hole 14 a penetrating the flexible printed circuit 10 and a conductive film 14 b such as plating formed on the inner wall side of the through hole 14 a. The GND pad 13 and the ground layers 60 and 70 are electrically connected through the conductive film 14b.

  The diameter of the conductive through holes 12 and 14 is, for example, 25 μm.

  As shown in FIG. 3, the signal line 20 is stacked on the insulating layer 30. Furthermore, the insulating layer 40 is laminated on the upper surface side of the signal line 20 and the insulating layer 30 with the adhesive layer 50 interposed therebetween. In the present embodiment, insulating layers 30 and 40 are made of, for example, a thermoplastic resin such as LCP (Liquid Crystal Polymer: LCP). Further, the adhesive layer 50 is a portion having adhesion and electrical insulation. The thickness of insulating layers 30 and 40 may be, for example, 25 μm. The thickness of the adhesive layer 50 may be, for example, 15 μm.

  Further, as shown in FIG. 3, on the upper surface side of the insulating layer 40, a solid ground layer 61 (corresponding to a hard ground layer) which constitutes a part of the ground layer 60 is provided. Furthermore, the solid ground layer 71 that constitutes a part of the ground layer 70 is also provided on the lower surface side of the insulating layer 30. The solid ground layers 61 and 71 are conductive portions made of, for example, copper foil, and are so-called solid GND (solid-like (solid-like; planar portion having a large area of copper foil) ground portion).

  The solid ground layers 61 and 71 are portions having a uniform thickness in the width direction (Y direction) as shown in FIG. The solid ground layers 61 and 71 are present on both upper and lower surfaces of the signal line 20, and the signal line 20 can be shielded from external electromagnetic waves by covering the signal line 20 with an insulator such as the insulating layers 30 and 40. . That is, the interference from the external electromagnetic wave is suppressed, and a strip transmission path for propagating the electromagnetic wave in a state of small transmission loss is configured.

  The thickness of the signal line 20 and the solid ground layers 61 and 71 may be, for example, 12 μm.

  Here, the ground layers 60 and 70 have soft ground layers 62 and 72 in addition to the solid ground layers 61 and 71. That is, in the configuration shown in FIG. 4, the soft ground layer 62 which constitutes a part of the ground layer 60 is provided on the upper surface side of the insulating layer 40. In the configuration shown in FIG. 4, the solid ground layer 71 is provided on the lower surface side of the insulating layer 30. Further, in the configuration shown in FIG. 5, on the lower surface side of the insulating layer 30, a soft ground layer 72 that constitutes a part of the ground layer 70 is provided. In the configuration shown in FIG. 5, the solid ground layer 61 is provided on the upper surface side of the insulating layer 40.

  The solid ground layers 61 and 71 (hard ground layers) are portions provided with a metal surface and provided with electromagnetic wave shielding properties, and the soft ground layers 62 and 72 are more acceptable than the solid ground layers 61 and 71. It is a portion which is excellent in flexibility and inferior in shielding property of electromagnetic waves to the solid ground layers 61, 71. The details of the soft ground layers 62, 72 will be described later.

  Also, cover layers 80 and 90 are arranged to cover ground layers 60 and 70 having solid ground layers 61 and 71 and soft ground layers 62 and 72, respectively (see FIGS. 3 to 5). . That is, the cover layer 80 is provided on the upper surface side of the ground layer 60, and the cover layer 80 covers the ground layer 60. In addition, a cover layer 90 is provided on the lower surface side of the ground layer 70, and the cover layer 90 covers the ground layer 70.

  The cover layers 80 and 90 have an insulating resin layer 81 and 91 made of a thermoplastic resin such as LCP (Liquid Crystal Polymer: LCP), for example, and an adhesive material layer 82 having adhesiveness and electrical insulation. It has 92. The insulating resin layers 81 and 91 have a thickness of, for example, 25 μm with respect to the ground layers 60 and 70 having a thickness of 12 μm. The thickness of the adhesive layers 82 and 92 is, for example, 15 μm. There is something. In this case, there is no problem such as delamination (delamination), and it is in a state where bonding can be performed.

<Details of Configuration of First Soft Ground Layers 62 and 72 (First Configuration Example)>
Next, details of the arrangement and configuration of the soft ground layers 62 and 72 described above will be described. FIG. 7 is a side view showing the shape of the flexible printed board 10 after molding. As shown in FIG. 7, the flexible printed circuit board 10 after molding has a pleated portion PL formed in a pleated shape (bellows shape). The pleated portion PL is provided with a linear portion PL1 and a curved portion PL2. Then, due to the deformation of the curved portion PL2, in the flexible printed circuit board 10 after molding, it is possible to fold short or expand long at the pleated portion PL. That is, in the flexible printed circuit board 10 after molding, the entire length is provided so as to be extensible and contractible due to the presence of the pleat portion PL. Moreover, the flexible printed circuit board 10 after shaping | molding can also perform the deformation | transformation which bends to each direction easily by presence of pleat part PL.

  The soft ground layers 62 and 72 described above are located on the outer peripheral side of the curve drawn by the curved portion PL2 in the curved portion PL2 of the pleated portion PL. In other words, the soft ground layers 62, 72 are provided on the outer peripheral side of the curve drawn by the curved portion PL2 as shown in FIG. 7, but are provided on the inner peripheral side of the curve drawn by the linear portion PL1 and the curved portion PL2. It is not done. In addition, when advancing along the molded flexible printed circuit board 10 shown in FIG. 7, the direction of the curve drawn by the curved portion PL2 is provided so as to be switched alternately. Therefore, as shown in FIG. 1, the soft ground layers 62 and 72 are provided alternately on the front surface side and the back surface side of the flexible printed circuit board 10.

  On the other hand, the solid ground layers 61 and 71 are present on both sides in the straight portion PL1, as shown in FIG. 3, but in the curved portion PL2 of the pleat portion PL, the curved portion drawn by the curved portion PL2 It is located on the circumferential side.

  7 corresponds to FIG. 3, the C-C line corresponds to FIG. 4, and the D-D line corresponds to FIG.

  The soft ground layers 62 and 72 are shield layers having a function of shielding the signal line 20 from external electromagnetic waves while having flexibility. A conductive paste and / or a thin film conductive film can be used as the flexible ground layers 62 and 72 having such flexibility.

  As a typical thing of an electroconductive paste, silver paste which contains silver as an electroconductive filler, such as SW1600C by Asahi Chemical Co., Ltd., etc. is mentioned, for example. However, the silver paste is not limited to such a product, and various materials can be used as long as they contain silver as the conductive filler. Further, the conductive filler of the conductive paste may be any conductive particle other than silver as long as it is a conductive particle, and examples of the conductive filler other than silver include copper, nickel, solder, aluminum and copper powder. The silver-coated copper filler which gave silver plating, the filler which metal-plated to the resin ball, the glass bead, etc. further, or the mixture of these fillers are mentioned. The diameter of the particles of the conductive filler is, for example, in the range of 10 nm to 5 μm, but any diameter may be used as long as the loss when transmitting the high frequency signal is lower than the specified value. .

  The thickness of the silver paste may be, for example, 10 μm to 15 μm, but the thickness of the conductive paste containing conductive particles other than silver can also be equal.

  Moreover, it is possible to use various resins for the binder resin composition of the conductive paste, and the material is not particularly limited. For example, acrylic resin, polystyrene resin, vinyl acetate resin, polyester resin, polyethylene resin, polypropylene resin can be used. And thermoplastic resins such as polyamides and rubbers can be used, and thermosetting resins such as epoxy resins, urethane resins, phenol resins, melamine resins and alkyd resins can also be used. Mixtures can be used. Among various resins, epoxy resins, urethane resins and acrylic resins are preferable in view of their small thermal expansion coefficient.

  In addition, as the thin film conductive film, for example, one surface side of a metal thin film layer such as SF-PC5500 manufactured by Tatsuta Electric Wire Co., Ltd. is covered with a protective layer etc., and the other surface side is a conductive adhesive layer. The thing covered is mentioned. The metal thin film layer is a portion in which a metal is formed in a thin film shape, and the thickness thereof is extremely thin, for example, 0.1 μm. The thickness of the metal thin film layer is not limited to 0.1 μm, and various thicknesses can be used without impairing the flexibility while maintaining the shielding property of the electromagnetic wave. Practically, for example, it can be appropriately selected in the range of 0.05 μm to 2 μm.

  Such thin metal thin film layers are generally formed by physical vapor deposition (PVD) such as vacuum evaporation, sputtering, ion plating, or chemical vapor deposition (CVD), for example. Etc.) is formed by vapor deposition. The overall thickness of the conductive film is, for example, 5 to 20 μm. As a metal material which comprises a metal thin film layer, various metal materials, such as silver, aluminum, copper, gold, nickel, chromium, zinc, can be used, for example. Among them, it is preferable to form the metal thin film layer using inexpensive aluminum or highly reliable silver.

  In addition, as the conductive adhesive layer of the thin film conductive film, the conductive filler having conductivity as described above is dispersed in the inside of the adhesive made of resin, and the conductive fillers are brought into contact with each other by applying pressure. The thing using an anisotropically conductive adhesive layer which expresses the electroconductivity to a pressurization direction by carrying out is mentioned. However, it may be configured to have anisotropic conductivity by self-condensing conductive fillers with each other without pressurization. Moreover, as an adhesive agent of an anisotropically conductive adhesive layer, the adhesive layer formed from the material similar to the above-mentioned conductive paste may be sufficient. Moreover, as a conductive adhesive layer, the thing which does not express the anisotropy (directionality) in conduction may be sufficient.

  The soft ground layers 62 and 72 may be formed using a method other than the above-described conductive paste and / or thin film conductive film. As such a method, for example, a metal thin film layer may be formed in a gap between the solid ground layers 61 and 71 by physical vapor deposition (PVD) such as vacuum evaporation, sputtering, ion plating, etc. ), Chemical vapor deposition (CVD) or the like.

  The arrangement of the flexible ground layers 62 and 72 in the flexible printed circuit 10 will be described later.

  Further, as shown in FIG. 6, the end portions of the solid ground layers 61 and 71 and the end portions of the soft ground layers 62 and 72 are provided so as to overlap with each other. Hereinafter, this portion will be referred to as overlapping portions 64 and 74 (only overlapping portion 64 is shown in FIG. 6; overlapping portion 74 is not shown but is present). The overlapping portions 64 and 74 have a length of, for example, about 0.5 mm to 1 mm, and the overlapping portions 64 and 74 ensure conduction between the solid ground layers 61 and 71 and the soft ground layers 62 and 72. There is. Thus, the solid ground layers 61, 71 and the soft ground layers 62, 72 constitute an integral ground layer.

  Further, by adopting a configuration in which conduction is secured between such solid ground layers 61, 71 and soft ground layers 62, 72, the distance between signal line 20 and soft ground layer 62 It does not change with respect to the distance of the layer 61. Therefore, the line widths of the signal lines 20 matched so that the characteristic impedance is 50 Ω can be made constant between the solid ground layers 61 and 71 and the soft ground layers 62 and 72 without change. Such a line width is, for example, 35 μm, but this line width can be set variously.

  Generally, when the soft ground layers 62 and 72 are provided, the transmission loss at the time of high frequency transmission tends to be large. However, the soft ground layers 62, 72 are provided on the curved portion PL2 of the pleated portion PL and provided on the minimum necessary portion, and the soft ground layers 62, 72 are provided on the outer peripheral side of the curve drawn by the curved portion PL2. positioned. Therefore, the influence on the characteristics such as transmission loss is small. The soft ground layers 62, 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, and the signal lines 20 are not directly opposed to each other, so that the electric lines between the signal lines 20 are electrically connected. Interference effects can be reduced.

  Further, since the soft ground layers 62, 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, bending stress at the time of molding can be reduced. Moreover, since the bending stress is reduced, it is possible to secure the durability in the case where the flexible printed board 10 is repeatedly expanded and contracted.

  On the other hand, in the case where the soft ground layers 62, 72 exist on the inner peripheral side of the curve drawn by the curved portion PL2, electrical interference is somewhat generated at the portion where the signal lines 20 face each other in the pleated portion PL. It may also happen. This is because the shielding function of the soft ground layers 62, 72 is generally inferior to that of the solid ground layers 61, 71. Therefore, when the high frequency current flows in a state in which the soft ground layers 62 and 72 whose shield function is inferior to the solid ground layers 61 and 71 face each other, electrical interference may occur.

  However, as in the present embodiment, when the soft ground layers 62, 72 exist on the outer peripheral side of the curved portion PL2 and the solid ground layers 61, 71 exist on the inner peripheral side of the curved portion PL2, There is no portion where the flexible ground layers 62, 72 face each other. Therefore, electrical interference between the signal lines 20 can be prevented, and fluctuations in the characteristic impedance of the flexible printed circuit 10 can also be prevented.

Regarding Configuration of Soft Ground Layers 62 and 72 (Second Configuration Example)
Next, a second configuration example in the arrangement of the flexible ground layer 62 (soft ground layer 72) in the flexible printed circuit 10 will be described. FIG. 8 is a plan view showing a second configuration example of the flexible printed circuit board 10 before molding, which corresponds to the modification of FIG. In the following description of the flexible printed circuit board 10 in the second configuration example, the description of the portions common to the flexible printed circuit board 10 in the first configuration example will be omitted.

  As shown in FIG. 8, the flexible printed circuit board 10 in the second configuration example has the same configuration in most parts as the flexible printed circuit board 10 in the first configuration example as shown in FIG. 1. However, in the flexible printed circuit board 10 of the second configuration example, the arrangement of the soft ground layer 62 (soft ground layer 72) is different from that of the flexible printed circuit board 10 of the first configuration example.

  FIG. 9 is a side view showing the shape of the flexible printed circuit board 10 after molding in the second configuration example. As shown in FIGS. 8 and 9, in the second configuration example, of the pleated portion PL of the flexible printed circuit board 10 after molding, the outer peripheral side of the curved portion PL2 of the right curve or the curved portion PL2 of the left curve Soft ground layers 62 and 72 are disposed on the outer peripheral side. Therefore, although the soft ground layer 62 (soft ground layer 72) is provided in a certain curved portion PL2, every other one (jumps) such as not provided in the adjacent curved portion PL2. It is provided in the outer peripheral side of curved part PL2 in the state which becomes.

  9 to 11 (described later), only the soft ground layer 72 is present, and the soft ground layer 62 is not present. However, only the soft ground layer 62 is present, and the soft ground layer 72 is present. Of course, a configuration that does not exist may be adopted.

  Therefore, the flexible printed circuit board 10 of the second configuration example is largely different from the first configuration example in the configuration in which the soft ground layers 62 and 72 alternately exist on the front surface side and the back surface side of the flexible printed substrate 10. It is different. That is, in the flexible printed circuit board 10 of the second configuration example, the soft ground layer 62 exists only on the front surface side (upper surface side) of the flexible printed circuit substrate 10 or soft only on the back surface side (lower surface side) of the flexible printed substrate 10 The ground layer 72 is either present.

  Also in the flexible printed circuit board 10 of the second configuration example, as is apparent from FIG. 9, the soft ground layer 72 (or the soft ground layer 62 in the configurations other than FIG. Exist on the outer side of Therefore, there is no portion where the openings 72b (openings 72b) of the soft ground layer 72 (soft ground layer 62) are in a positional relationship facing each other. Thus, electrical interference between the signal lines 20 can be prevented, and fluctuations in the characteristic impedance of the flexible printed circuit board 10 can also be prevented.

  In addition, the soft ground layer 72 (soft ground layer 62) is located on the outer peripheral side of the curve drawn by the curved portion PL2 as in the first configuration example, but the number of provided is smaller than that in the first configuration example. It is halved. Therefore, the influence on the characteristics such as transmission loss is further reduced. The soft ground layers 62, 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, and the signal lines 20 are not directly opposed to each other, so that the electric lines between the signal lines 20 are electrically connected. Interference effects can be reduced.

  Also in the second configuration example, since the soft ground layer 72 (soft ground layer 62) is positioned on the outer peripheral side of the curve drawn by the curved portion PL2, bending stress at the time of molding is reduced. be able to. Moreover, since the bending stress is reduced, it is possible to secure the durability in the case where the flexible printed board 10 is repeatedly expanded and contracted.

  FIG. 10 is a view showing an image in which the flexible printed circuit board 10 according to the second configuration example is applied to a rotating portion of an external device such as a joint of an arm of a robot or the like, and the two arms are kept horizontal. It is a figure which shows the state which is. FIG. 11 is a view showing a state in which two arms in FIG. 10 are rotated. In the application examples shown in FIGS. 10 and 11, the soft ground layer 72 is located at the bending portion PL2 on the inner diameter side of the rotation portion. That is, the soft ground layer 62 located in the curved portion PL2 on the outer diameter side of the rotation portion does not exist.

  As shown in FIG. 10, when the flexible printed circuit board 10 of the second configuration example is placed along the rotation portion, the curved portion PL2 positioned on the inner diameter side (inner side) is deformed so as to be largely opened. Therefore, by disposing the soft ground layer 72 on the outer peripheral side (that is, the side closest to the inner diameter) of the curved portion PL2 on the inner diameter side (inner side), the curved portion PL2 located on the inner diameter side (inner side) is It deforms so as to open easily.

  At this time, in the curved portion PL2 on the inner diameter side, the soft ground layer 72 on the outer peripheral side is largely deformed by the action of the compressive stress, but although a tensile stress acts on the solid ground layer 61 on the inner peripheral side, The solid ground layer 61 on the circumferential side is less likely to be deformed than the soft ground layer 72 on the outer circumferential side. Therefore, the neutral axis of stress moves to the outer peripheral side and separates from the inner peripheral side. Thereby, not the tensile stress but the compressive stress acts on the signal line 20.

  As shown in FIG. 11, the curved portion PL2 located on the outer diameter side (outer side) is deformed so as to be closed. However, in the curved portion PL2 located on the outer diameter side (outside), the solid ground layer 61 is provided on both the inner peripheral side and the outer peripheral side. Therefore, in the curved portion PL2 positioned on the outer diameter side (outside), the deformation in the closing direction is smaller than the deformation in the soft ground layer 72 which is open. That is, as shown in FIG. 11, the curved portion PL2 positioned on the inner diameter side (inner side) is deformed so as to selectively open largely depending on the presence or absence of the soft ground layer 72, but the outer diameter side The curved portion PL2 located at) deforms only to a small extent.

  With the above configuration, the stress applied to the signal line 20 at the time of operation is reduced by using the flexible printed circuit board 10 of the second configuration example for the rotation part of an external device such as a joint of an arm such as a robot. And can withstand repeated operation.

<About the manufacturing method of flexible printed circuit board 10>
Subsequently, a method of manufacturing the flexible printed circuit board 10 in the first configuration example and the second configuration example will be described below. In the following description, steps 1 to 8 will be sequentially described, but in the method of manufacturing flexible printed circuit board 10 in each embodiment, various other steps may be present. Of course.

(1) First Step: Formation of Signal Line 20 FIG. 12 is a diagram showing a state in which the signal line 20 and the receiving land 21 are formed in the A-A cross section of FIG. 1 and FIG. 8 in the first step. . FIG. 13 is a diagram showing a state in which the signal line 20 is formed in the BB cross section, the CC cross section (only in FIG. 1 is present), and the DD cross section in FIGS. . As shown in FIGS. 12 and 13, a double-sided copper-clad laminate 100 having base copper foil layers 101 and 102 on both sides of the insulating layer 30 is prepared. Then, the signal line 20 to be positioned on the inner layer side later and the receiving land 21 of the conductive through holes 12 and 14 are formed using a normal photofabrication method such as etching. Thereby, an intermediate product C1 as shown in FIGS. 12 and 13 is formed.

(2) Second step: Lamination of single-sided copper-clad laminate 200 FIG. 14 relates to the second step, and in the AA cross section of FIGS. 1 and 8, single-sided copper-clad laminate 200 on double-sided copper-clad laminate 100. Is a figure which shows a mode that is laminated. FIG. 15 relates to the second step, and in the double-sided copper-clad laminate 100 in the BB cross section, the CC cross section (only FIG. 1 is present), and the DD cross section of FIGS. It is a figure which shows a mode that 200 is laminated | stacked.

  As shown in FIGS. 14 and 15, a single-sided copper clad laminate 200 and a laminated adhesive 300 are prepared. Then, the laminated adhesive 300 is attached to cover the upper surface side of the insulating layer 30, and thereafter, the single-sided copper-clad laminate 200 is attached to the upper surface of the laminated adhesive 300. The single-sided copper-clad laminate 200 includes an insulating layer 40, and a base copper foil layer 201 is provided on the surface (upper surface) on one side thereof. In addition, let the product after sticking be the intermediate product C2.

  The laminated adhesive 300 is a portion to be the adhesive layer 50 after pasting. As such a laminate adhesive 300, one having a low elasticity is preferable so as not to hinder the later molding. Specifically, since the elastic modulus of the LCP film is about 3 to 4 GPa, by using the laminated adhesive 300 having an elastic modulus of 2 GPa or less equal to or less than half thereof, it is possible to bond without affecting the formability. It is possible. Moreover, at the time of shaping | molding, it heats at about 200 degreeC for about 30 minutes. Therefore, as the lamination adhesive material 300, it is preferable that the adhesive property and the electrical insulation property are not significantly deteriorated by the heat history.

(3) Third Step: Formation of Through Holes 12a and 14a FIG. 16 is a diagram showing a state in which through holes 12a and 14a are formed in the AA cross section of FIG. 1 and FIG. 8 in the third step. . FIG. 17 is a side cross sectional view showing a configuration in a B-B cross section, a C-C cross section (only in FIG. 1 is present), and a D-D cross section in FIGS. As shown in FIG. 16, through holes 12a and 14a for interlayer connection with the signal pad 11 and the GND pad 13 are formed in the intermediate product C2 later. Although this drilling processing may be performed by processing using an NC drill, it is also possible to use interlayer connection with a non-penetrating bottomed via hole by a laser or the like. In addition, let the product after this drilling process be the intermediate product C3.

(4) Fourth Step: Formation of Conductive Coatings 12b and 14b FIG. 18 relates to the fourth step, in which conductive coatings 12b and 14b are formed in the through holes 12a and 14a in the A-A cross section of FIGS. It is a figure which shows the state in which the conductive film layer 15 was formed. As shown in FIG. 18, in the intermediate product C3 after the hole drilling process, partial plating is applied to a portion corresponding to the cross section A-A to form the conductive film layer 15 which is the source of the conductive films 12b and 14b. . Thereby, interlayer conduction in which the three layers are electrically connected can be obtained. In addition, let the product by partial plating be the intermediate product C4.

(5) Fifth Process: Patterning of Base Copper Foil Layers 101 and 102 FIG. 19 is a diagram showing a state in which patterning is performed in the A-A cross section of FIGS. 1 and 8 according to the fifth process. FIG. 20 is a diagram showing a state in which patterning is performed in the B-B cross sections in FIG. 1 and FIG. 8 in the fifth step. Moreover, FIG. 21 is a figure which concerns on a 5th process and shows the state in which patterning was made in the CC cross section of FIG. FIG. 22 is a diagram related to the fifth step, showing a state in which patterning is performed in the DD section of FIGS. 1 and 8. FIG. 23 is a diagram showing a state in which patterning is performed in the EE cross section in FIG. 1, regarding the fifth step.

  As shown in FIGS. 19 to 23, the conductive film layer 15 and the base copper foil layers 101 and 102 are patterned using a normal photofabrication method such as etching to form necessary patterns. . As shown in FIGS. 19 to 23, the pattern formed by such patterning is a necessary pattern in the flexible printed circuit 10, such as the signal pad 11, the GND pad 13, the solid ground layers 61, 71, etc. .

  Note that, in FIG. 21, a removed portion 63 is formed by removing the solid ground layer 61 on the upper surface side of the insulating layer 40 by patterning, but the removed portion 63 is provided with a soft ground layer 62 later. Further, in FIG. 22, a removed portion 73 is formed by removing the solid ground layer 71 on the lower surface side of the insulating layer 30 by patterning, but the soft ground layer 72 is provided to the removed portion 73 later. Moreover, in FIG. 23, the boundary part of the solid ground layer 61 and the removal part 63 is shown in the upper surface side of the insulating layer 40 by patterning. In FIG. 23, the solid ground layer 61 remains on the X2 side, but the removed portion 63 from which the solid ground layer 61 is removed is on the X1 side, and the soft ground layer 62 Is provided. The product obtained by patterning is referred to as an intermediate product C5.

(6) Sixth Process: Formation of Soft Ground Layers 62 and 72 FIG. 24 is a view showing a configuration in a C-C cross section of FIG. 1 when the soft ground layer 62 is formed in the sixth process. FIG. 25 is a diagram related to the sixth step, showing a state in which the soft ground layer 72 is formed in the DD cross section of FIGS. 1 and 8. FIG. 26 is a diagram showing a state in which the soft ground layer 62 is formed in the EE cross section of FIG. 1 in the sixth step.

  As shown in FIGS. 24 to 26, the soft ground layers 62, 72 are formed on the intermediate product C5. When the soft ground layers 62 and 72 are formed of, for example, a conductive paste such as silver paste, the conductive paste is printed so as to cover the removed portions 63 and 73, and the printed portion is heated or irradiated with ultraviolet light. Harden by etc. At this time, as shown in FIG. 26, the conduction between the solid ground layer 61 and the conductive paste (soft ground layer 62) is performed in a state where the solid ground layer 61 and a part of the conductive paste (soft ground layer 62) overlap. Secure. Although not shown, a similar overlapping portion is provided between the solid ground layer 71 and the conductive paste (soft ground layer 72) to form the solid ground layer 71 and the conductive paste (soft ground layer 72). Ensure continuity between

  When the soft ground layers 62 and 72 are formed of a thin film conductive film, the thin film conductive film is formed into a strip by cutting or the like so as to have a length capable of covering the removed portions 63 and 73. Do. After that, a strip-like thin film conductive film is attached so as to cover the removing portions 63 and 73. Also in such affixing, as the solid ground layer 61 overlaps with the thin film conductive film (soft ground layer 62), the conduction between the solid ground layer 61 and the thin film conductive film (soft ground layer 62) is secured. Do. Similarly, although not shown, a similar overlapping portion is provided between the solid ground layer 71 and the thin film conductive film (soft ground layer 72) to form the solid ground layer 71 and the thin film conductive film (soft ground layer). Ensure continuity between 72).

  In the formation of the soft ground layers 62, 72 described above, plating such as electroless gold plating is partially applied to portions which become contact points of the solid ground layers 61, 71 and the soft ground layers 62, 72. The surface treatment may be performed in the treatment. In such a partial plating process, a portion not to be subjected to the plating process may be masked using a photosensitive dry film resist or the like having resistance to a plating solution to be used. The intermediate product in which the soft ground layers 62 and 72 are formed is referred to as an intermediate product C6.

(7) Seventh Step: Formation of Cover Layers 80 and 90 FIG. 27 is a view showing a configuration in an AA cross section of FIGS. 1 and 8 when the cover layers 80 and 90 are formed in the seventh step. It is. FIG. 28 relates to the seventh step and shows a state in which cover layers 80 and 90 are formed in the B-B cross section of FIGS. 1 and 8. FIG. 29 is a diagram showing a state in which the cover layers 80 and 90 are formed in the CC cross section of FIG. 18 in the seventh step. FIG. 30 relates to the seventh step and shows a state in which cover layers 80 and 90 are formed in the DD cross section of FIGS. 1 and 8.

  As shown in FIG. 27 to FIG. 30, the cover layers 80 and 90 including the insulating resin layers 81 and 91 and the adhesive layers 82 and 92 are formed on the intermediate product C6. The formation of the cover layers 80 and 90 is performed by sticking the adhesive layers 82 and 92 to the intermediate product C6. The signal pad 11 and the GND pad 13 need not be covered by the cover layers 80 and 90. Therefore, among the cover layers 80 and 90, portions corresponding to the signal pad 11 and the GND pad 13 can be provided with fine openings by a method such as a photo solder resist. However, the other solid ground layers 61 and 71 and the soft ground layers 62 and 72 are covered with the cover layers 80 and 90.

  As shown in FIGS. 29 and 30, conductive ground layers such as silver paste and soft ground layers 62 and 72 formed using a thin film conductive film are also covered with cover layers 80 and 90. It is protected. That is, the curved portion (curved portion PL2) of the flexible printed circuit 10 is also covered by the cover layers 80 and 90. For this reason, the top coat which protects a curved site and becomes a surface protection layer is unnecessary.

  In addition, it is also possible to surface-treat an electroless gold plating etc. to the location which is not coat | covered with the cover layers 80 and 90 as needed. Through the steps as described above, the flexible printed circuit board 10 before molding can be obtained.

(8) Eighth Process: Heat Forming of Flexible Printed Circuit Board 10 FIG. 31 shows a state in which the flexible printed circuit board 10 before forming is set in the jig 400 in the eighth process. As shown in FIG. 31, the flexible printed circuit board 10 before molding is set in the jig 400 in a state of being aligned. Here, the jig 400 is provided with a tip fixing member 410. The front end fixing member 410 is provided with a front end receiving portion 411 for mounting the front end side of the flexible printed circuit 10, and a hooking pin 412 inserted into a hole on the front end side of the flexible printed circuit 10 not shown. Is provided.

  The hole on the front end side of the flexible printed circuit 10 is inserted into the hooking pin 412, and in that state, the flexible printed circuit 10 is meandered along the jig pin 420 disposed at the predetermined position of the jig 400. , And complete the setting of the flexible printed circuit 10 on the jig 400. After the setting, a constant tension is applied to the rear end side of the flexible printed circuit 10. In this state, heating is performed in an oven or the like to form a flexible printed circuit board 10 of a three-layer configuration including a thermoplastic LCP material in a pleated shape (bellows shape), and the flexible printed circuit board 10 is shown in FIGS. It has a pleated portion PL as shown in FIG.

  Here, the thermoforming in an oven or the like is performed, for example, by heating at 200 ° C. for 30 minutes. When the heat molding is performed in this manner, the heat printing is performed in a state where the setting position of the flexible printed circuit 10 and the tension at the time of setting to the jig 400 are stable. Therefore, in flexible printed circuit board 10 after molding, the product shape is stable, and soft ground layers 62 and 72 are disposed on the outer peripheral side of the desired portion of curved portion PL2 as intended. .

  Further, after this molding, unnecessary portions of the flexible printed circuit board 10, such as the tip end positioned by the tip fixing member 410 and the like, are cut, if necessary, to complete the final product. As a method of cutting such an unnecessary portion, the hole portion of the flexible printed circuit board 10 into which the retaining pin 412 is inserted is diverted, the starting point side is positioned, and the opposite side is positioned by butting or the like. And it is possible to cut using a cutting jig such as a pinnacle or a mold. However, the unnecessary part may be cut using a method other than the method described above. As such a method, for example, laser cutting using a laser, router cutting using a router bit, and the like can be mentioned.

<About the test results>
Table 1 shows the results of the expansion and contraction test performed on the flexible printed circuit 10 having the pleat portion PL, which is formed as described above. In the expansion and contraction test, the flexible printed circuit board 10 is repeatedly expanded and contracted, and the presence or absence of disconnection of the signal line 20 during the test, the amount of expansion of the flexible printed circuit board 10 before and after the test, and the flexible printed circuit board 10 before and after the test Changes in DC resistance, transmission loss before the test, and transmission loss before and after the test were evaluated.

  The same test was also performed on a conventional configuration and a comparative example for evaluation. The conventional configuration corresponds to a flexible printed circuit 10F as shown in FIG. 32 to FIG. The flexible printed circuit 10F has a configuration in which solid ground layers 61 and 71 are provided over the entire length of both surfaces without the soft ground layers 62 and 72. FIG. 32 is a plan view showing the configuration of the flexible printed circuit board 10F of the conventional configuration. FIG. 33 is a cross-sectional view of a flexible printed circuit board 10F having a conventional configuration, showing a state of being cut along the line AA of FIG. FIG. 34 is a cross-sectional view of a flexible printed circuit board 10F having a conventional configuration, and is a view taken along the line B-B of FIG.

  The comparative example corresponds to a configuration in which all of the ground layers 60 and 70 are soft ground layers 62 and 72. That is, the configuration in which the soft ground layers 62 and 72 are provided over the entire length of both sides sandwiching the signal line 20 corresponds to the comparative example (not shown).

  In this expansion and contraction test, the total length of the flexible printed circuit boards 10 and 10F was extended by 50%, and was performed up to 5,000,000 times. Also, after the test, if the elongation rate is within 10%, the test on the elongation was regarded as passing. Moreover, the test was performed using ten pieces for each structure.

  As can be seen from the results in Table 1, the flexible printed circuit board 10 of the first configuration example and the flexible printed circuit board 10 of the second configuration example have high extension test resistance, and the elongation rate after 5 million extension tests is 5 % Or less, and no break was observed. In addition, it was confirmed that the rate of change of the direct current resistance and the transmission loss was 3% or less, and the change in the electrical characteristics was not observed so much. With regard to transmission loss, solid ground layers 61 and 71 are provided over the entire length of the flexible printed circuit board 10 of the first configuration example and the flexible printed circuit board 10 of the second configuration example, which is the lowest loss. As compared with the conventional configuration, it was confirmed that there is only a difference of 5% or less, and that there is only a loss in a range that does not have a problem in signal transmission.

  On the other hand, in the conventional configuration, the signal line 20 was disconnected for any of the ten tested within 1000 times. In the evaluation of such a conventional configuration, although it is in a disconnected state, the elongation rate is 5% or less, the resistance value is OPEN, and the transmission loss is 0.22 dB / 10 mm, which is the lowest. Was unmeasurable because a break occurred. In the configuration of the comparative example, the signal line 20 was not broken, the change rate of the DC resistance was 3% or less, and the change rate of the transmission loss was 3% or less. However, it has been confirmed that the transmission loss is large, particularly about twice as large as that of the flexible printed circuit board 10 of the first configuration example. From the above results, it was confirmed that the conventional configuration can not be used due to disconnection, and that the comparative example also has a large transmission loss, and the performance is inferior to the flexible printed circuit 10 of the first configuration example and the second configuration example. .

  From the above results, it is revealed that the flexible printed circuit board 10 of the first configuration example and the flexible printed circuit board 10 of the second configuration example in the present embodiment can achieve both high-quality signal transmission and stretchability. did.

<About the effect>
According to the flexible printed circuit board 10 and the method of manufacturing the flexible printed circuit board 10 having the above-described configuration, the following effects are produced.

  That is, the curved portions PL2 at a plurality of locations in the pleated portion PL of the flexible printed circuit 10 having the strip line transmission path deform so as to open or close. On the other hand, the ground layers 60 and 70 are provided with a metal surface to provide electromagnetic wave shielding properties, and the ground layers 60 and 70 (hard ground layers) are more flexible than the solid ground layers 61 and 71. And soft ground layers 62 and 72 which are inferior in shielding property to electromagnetic waves than the solid ground layers 61 and 71. The soft ground layers 62, 72 are disposed on the outer peripheral side of the curved portion PL2, and the solid ground layers 61, 71 are disposed on the inner peripheral side of the curved portion PL2.

  For this reason, in the curved portion PL2, since the soft ground layers 62, 72 exist on the outer peripheral side of the curved portion PL2, the bending stress at the time of forming the flexible printed circuit board 10 into a pleated shape (corrugated shape) is reduced. be able to. In addition, since the bending stress is reduced, the durability in the case where the flexible printed board 10 is repeatedly expanded and contracted is also secured. In particular, the flexible ground layers 62 and 72 are disposed on the outer peripheral side of the curved portion PL2, and the solid ground layers 61 and 71 are disposed on the inner peripheral side of the curved portion PL2. Later, the soft gland layers 62, 72 deform easily to be compressed. As a result, compressive stress can be generated in the signal line 20, and the signal line 20 is less likely to be broken.

  Furthermore, in the present embodiment, in the flexible printed circuit board 10, a strip transmission path for propagating an electromagnetic wave is configured, so the function of blocking external noise is not impaired. In particular, in the curved portion PL2, when the solid ground layers 61 and 71 exist on the inner peripheral side of the curved portion PL2, it is possible to prevent the soft ground layers 62 and 72 from becoming in a positional relationship facing each other. Therefore, even when the linear portions PL1 are close to each other in the pleat portion PL, electrical interference between the signal lines 20 can be prevented. In general, when the flexible ground layers 62 and 72 are provided over the entire length of the flexible printed board 10, the transmission loss at the time of high frequency transmission tends to be large. However, the soft ground layers 62, 72 are provided on the minimum necessary portion such as the curved portion PL2 of the pleated portion PL. Moreover, the soft ground layers 62, 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2. Therefore, the influence on characteristics such as transmission loss can be reduced. Further, since the soft ground layers 62, 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, the influence of electrical interference between the signal lines 20 can be reduced.

  Moreover, in the present embodiment, the soft ground layers 62, 72 are at least one of a conductive paste obtained by mixing a conductive filler with a binder resin composition, and a thin film conductive film provided with a metal thin film layer formed by vapor deposition. I have one. Here, in the conductive paste, since the conductive filler can move in the binder resin composition in a state separated from the other conductive fillers, it is possible to have sufficient flexibility. Further, in the thin film conductive film provided with the deposited metal thin film layer, since the metal thin film layer is formed by deposition, the thickness thereof is significantly thinner than that of the solid layers 61 and 71, which is sufficient. Flexibility can be provided.

  Further, in the present embodiment, as described in the first configuration example, soft ground layers 62 and 72 are alternately present on the front side and the back side of signal line 20 in pleated portion PL. It is arranged on the outer peripheral side. Therefore, the flexible printed circuit 10 can be easily expanded and contracted. That is, in the flexible printed circuit board 10 of the first configuration example, the stretchability can be improved.

  Furthermore, in the present embodiment, as described in the second configuration example, in the pleated portion PL, the soft ground layers 62 and 72 are curved in a state where they exist on either the front surface side or the rear surface side of the signal line 20. It is arrange | positioned at the outer peripheral side of PL2. Therefore, the stress acting on the signal line 20 at the time of operation can be reduced by using the flexible printed circuit board 10 of the second configuration example for the rotation part of an external device such as a joint of an arm such as a robot. It becomes a structure that withstands repeated operation.

  Further, in the present embodiment, one end side of solid ground layers 61, 71 (hard ground layer) and the other end side of soft ground layers 62, 72 are electrically conducted to ground layers 60, 70. Overlapping overlapping portions 64 are provided. The presence of the overlapping portions 64 and 74 allows the solid ground layers 61 and 71 and the soft ground layers 62 and 72 to form an integral ground layer.

  Further, in the present embodiment, the insulating layers 30 and 40 and the insulating resin layers 81 and 91 are formed of LCP (Liquid Crystal Polymer), which is a thermoplastic resin, as a material. For this reason, when heat molding is performed on the flexible printed circuit board 10 before heat molding, it is possible to easily form the pleat portion PL having the plurality of curved portions PL2.

  Furthermore, in the present embodiment, the ground layers 60 and 70 located at the curved portion PL2 have a configuration in which the plating film for interlayer connection is not formed. For this reason, the bending portion PL2 is in a state of being easily bent.

  Further, in the present embodiment, the flexible printed circuit board 10 before the thermoforming is thermoformed using the jig 400. Therefore, a flexible print having a good pleated portion PL without positional deviation is achieved by positioning the tip end side of the flexible printed circuit board 10 with the tip fixing member 410 and further performing heat forming in a state where the flexible printed board 10 is tensioned. The substrate 10 can be formed.

<Modification>
As mentioned above, although one embodiment of the present invention was described, the present invention can be variously deformed besides this. Below, we will discuss that.

  In the above embodiment, only one signal line 20 is shown. However, the number of signal lines 20 is not limited to one, and two or more may be present as long as they constitute a stripline transmission line.

  Further, in the second configuration example in the above-described embodiment, the flexible ground layer 72 is provided to the bending portion PL2 on the inner diameter side of the rotation portion of the rotation portion of the external device such as a joint of an arm of a robot or the like. Is located. That is, the soft ground layer 62 located in the curved portion PL2 on the outer diameter side of the rotation portion does not exist. However, a configuration may be adopted in which the soft ground layer 62 is disposed in the curved portion PL2 on the outer diameter side of the rotation portion. When configured in this way, the curved portion PL2 on the outer diameter side is deformed so as to be largely closed, but even in that case, it is easier to bend than in the conventional configuration, and it is possible to make a configuration in which a break does not easily occur in the signal line .

  In the first configuration example and the second configuration example, the soft ground layers 62 and 72 are disposed on the inner peripheral side of the curved portion PL2, and the solid ground layers 61 and 71 are disposed on the outer peripheral side of the curved portion PL2. You may. Also in this case, it is easier to bend than the conventional configuration, and it is possible to make the configuration in which disconnection of the signal line 20 is less likely to occur.

  Further, in the first configuration example and the second configuration example, a configuration in which soft ground layers 62 and 72 are disposed on both the inner and outer peripheral sides of curved portion PL2 is adopted, and straight portion PL1 is solid ground layer 61, A configuration in which 71 is arranged may be adopted. In this case, it becomes easier to bend than the first configuration example and the second configuration example, and it is possible to make the configuration in which the signal line 20 is not easily disconnected. In addition, even when such a configuration is adopted, the transmission loss can be reduced as compared with the configuration in which all of the ground layers 60 and 70 as in the comparative example described above are the soft ground layers 62 and 72.

  Moreover, in the above-mentioned embodiment, the flexible printed circuit board 10 has pleat part PL by which curved part PL2 of the same magnitude | size is arrange | positioned with the same pitch. However, the pitches at which the bending portions PL2 are disposed may not be the same, and the bending portions PL2 may be disposed such that they have different pitches or partially different pitches. Further, the size (radius or the like) of a certain curved portion PL2 may be different from the size (radius or the like) of another curved portion PL2. Further, a combination of a plurality of curved portions PL2 arranged at another pitch or size may be combined with a combination of a plurality of curved portions PL2 arranged at a certain pitch or size.

10, 10F: flexible printed circuit board, 11: signal pad, 12: conductive through hole, 12a: through hole, 12b: conductive film, 13: GND pad, 14: conductive through hole, 14a: through hole, 14b: conductive film, 15: conductive coating layer, 20: signal line, 21: receiving land, 30, 40: insulating layer, 50: adhesive layer, 60, 70: ground layer, 61, 71: solid ground layer (corresponds to hard ground layer) , 62, 72: soft ground layer, 63: removed portion, 64: overlapping portion, 80, 90: cover layer, 81, 91: insulating resin layer, 82, 92: adhesive layer, 100: double-sided copper-clad laminate, DESCRIPTION OF SYMBOLS 101 ... Base copper foil layer, 200 ... single-sided copper clad laminated board, 201 ... base copper foil layer, 300 ... lamination adhesive material, 400 ... jig, 410 ... tip fixing member, 411 ... tip receiving part, 412 ... latching Down, 420 ... jig pins, C1 -C6 ... intermediate product, PL ... pleated portion, PL1 ... straight portion, PL2 ... curved portion

Claims (8)

A signal line, an insulating layer made of thermoplastic resin and covering the signal line from both sides, and a pair of ground layers facing the signal line with the insulating layer interposed therebetween A flexible printed circuit board having a stripline transmission line of
A curved portion is formed at a plurality of points, and the pleat includes a pleated portion curved so as to open or close the curved portion;
The ground layer is a hard ground layer provided with a metal surface to shield electromagnetic waves, and a soft ground layer that is more flexible than the hard ground layers and inferior to electromagnetic shields than the hard ground layers. , Have,
The ground layer is provided with an overlapping portion in which the one end side of the hard ground layer and the other end side of the soft ground layer are electrically connected to each other.
The soft ground layer is disposed on at least one of an outer peripheral side and an inner peripheral side of the curved portion.
Flexible printed circuit board characterized by The flexible printed circuit board according to claim 1, wherein
The soft ground layer has at least one of a conductive paste obtained by mixing a conductive filler with a binder resin composition, and a thin film conductive film provided with a metal thin film layer formed by vapor deposition.
Flexible printed circuit board characterized by The flexible printed circuit board according to claim 1 or 2, wherein
The soft ground layer is disposed on the outer peripheral side of the curved portion, and the hard ground layer is disposed on the inner peripheral side of the curved portion.
Flexible printed circuit board characterized by The flexible printed circuit board according to claim 3, wherein
The pleated portion is provided in a bellows shape by alternately switching the direction of the curve of the curved portion,
The soft ground layer is disposed on an outer peripheral side of the curved portion in a state of being alternately present on the front side and the back side of the signal line.
Flexible printed circuit board characterized by The flexible printed circuit board according to claim 3, wherein
The pleated portion is provided in a bellows shape by alternately switching the direction of the curve of the curved portion,
The soft ground layer is disposed on an outer peripheral side of the curved portion in a state of being present on either the front side or the back side of the signal line.
Flexible printed circuit board characterized by The flexible printed circuit board according to any one of claims 1 to 5, wherein
The insulating layer is made of LCP (Liquid Crystal Polymer), which is a thermoplastic resin, as a material.
Flexible printed circuit board characterized by The flexible printed circuit board according to any one of claims 1 to 6, wherein
The ground layer located in the curved portion is not formed with a plating film for interlayer connection.
Flexible printed circuit board characterized by A signal line, an insulating layer made of thermoplastic resin and covering the signal line from both sides, and a pair of ground layers facing the signal line with the insulating layer interposed therebetween A method of manufacturing a flexible printed circuit board having a stripline transmission line of
A first step of forming at least one of the signal lines of the double-sided copper-clad laminate having a base copper foil layer on both sides of the insulating layer, on the one side of the base copper foil layer;
The double-sided copper-clad laminate in a state in which the said insulating layer of the single-sided copper clad laminate having a base copper foil layer on one surface of the insulating layer, covering the insulating layer constituting the double-sided copper-clad laminate through a laminating adhesive A second step of laminating on the one surface side on which the signal line of the plate is formed ;
A third step of forming a through hole at a predetermined portion of the intermediate product formed in the second step;
Forming a conductive film around the through hole and the opening thereof to form a conductive through hole;
In the intermediate product formed in the fourth step, by patterning the base copper foil layer facing the signal line, the base copper foil layer is formed from a predetermined portion on one of the surfaces. A fifth step of forming a removed removed portion and forming a hard ground layer having a conductive portion provided in a planar shape on the opposite surface side;
A sixth step of forming the removal portion so as to cover a soft ground layer that is more flexible than the hard ground layer and inferior to electromagnetic wave shielding properties than the hard ground layer;
A seventh step of covering the soft ground layer and the hard ground layer with an insulating resin layer via an adhesive layer;
The flexible printed circuit board before heat forming formed in the seventh step is subjected to heat forming in a state where a plurality of portions are curved, and after the heat forming, a plurality of soft ground layers are positioned on the outer peripheral side An eighth step of forming a pleated portion in which a curved portion is present;
A method of manufacturing a flexible printed circuit board, comprising:

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