WO2016113942A1

WO2016113942A1 - Flexible printed circuit board and method for manufacturing flexible printed circuit board

Info

Publication number: WO2016113942A1
Application number: PCT/JP2015/073869
Authority: WO
Inventors: 松田　文彦
Original assignee: 日本メクトロン株式会社
Priority date: 2015-01-16
Filing date: 2015-08-25
Publication date: 2016-07-21
Also published as: CN106031309B; JP2016134438A; JP6504828B2; CN106031309A

Abstract

The present invention provides a flexible printed circuit board that is not easily subjected to line breakage while still retaining the electrical characteristics thereof and a method for manufacturing such a flexible printed circuit board. Provided is a flexible printed circuit board 10 having at least one set of strip-line transmission paths by providing a signal line 20 and a pair of ground layers 60 and 70 facing the signal line 20 with insulating layers 30 and 40 interposed therebetween, the insulating layers 30 and 40 covering the signal line 20 from both sides and being formed of a thermoplastic resin. The flexible printed circuit board 10 is provided with a pleat portion PL that bends so as to open or close a plurality of bending sections PL2. The ground layers 60 and 70 have hard ground layers 61 and 71 that have a metal surface and that have electromagnetic-wave shielding performance and soft ground layers 62 and 72 that have a higher flexibility and a lower electromagnetic-wave shielding performance than the hard ground layers 61 and 71. The soft ground layers 62 and 72 are disposed on at least one of an outer circumferential side and an inner circumferential side of the bending section PL2.

Description

Flexible printed circuit board and method for manufacturing flexible printed circuit board

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

In recent years, the development of robots has become remarkable, such as the appearance of robots with various movements. In addition, wearable electronic devices that can be worn on the human body and clothes have been developed and put into practical use with various devices. These robots and wearable electronic devices use a large number of electric wires for power supply and electric signal transmission. Generally, the electric wires have a structure in which a copper wire is the core and the outer periphery is covered with an insulator. Therefore, there is almost no elasticity in the electric wire itself. For this reason, for example, in a robot or the like, it is necessary to allow a sufficient wire length so as not to hinder the movement of the joints, and this is a practical problem in designing for miniaturization and weight reduction. Become.

Especially 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, wires for moving the terminal motor via multi-degree-of-freedom joints and terminals are arranged. Many wires for transmitting electrical signals from various sensors are wired. And in order to raise the freedom degree of these wiring in a multi-degree-of-freedom joint, the request | requirement with respect to the electric wire comprised so that expansion-contraction is possible is increasing.

On the other hand, in recent years, arm robots are often used as industrial robots. In this type of arm robot, depending on the end effector attached to the tip side of the robot arm (equivalent to a hand in the human body) or the driving method of the joint part of the robot arm, from the base side to the tip side of the robot arm In addition to the electric cable, it may be necessary to wire an air hose or a hydraulic hose for applying air pressure. When such cables and hoses are wired to the joints, the cables may be bent or disconnected. For this reason, the cables and hoses are temporarily extended outward at positions closer to the base end than the joints of the robot arms, and the cables are arranged in the outer space of the joints, and again inside the arm at positions closer to the tip than the joints. A wiring method such as introduction into the network is adopted. However, in the method of arranging the cable in the outer space of the robot arm, a space for loosening the cable is required around the joint portion of the robot arm.

Further, for example, in Patent Document 1, a support rod is provided at the joint rotation center position in the joint portion of the robot arm, a cable is wound around the support rod, and the support rod on which the cable is wound is stored in the robot arm. Thus, a structure that prevents the cable from being bent or disconnected is disclosed. However, there is a possibility that functional deterioration (operation speed, accuracy, etc.) due to weight increase due to the separate provision of the support rod may occur. In some cases, a high-spec motor or the like is used in order to compensate for the deterioration of the function or the number of necessary members increases. In this case, the manufacturing cost increases. Furthermore, since the structure of the cable storage portion becomes complicated, there is a problem that it becomes very complicated when the cable is taken out and replaced when it is disassembled during wiring and maintenance of the robot arm during assembly. For this reason, even in the robot arm, there is an increasing demand for a telescopic electric transmission member that can avoid such a problem.

For example, there is a technique disclosed in Patent Document 2 as a response to the demand for such an electric transmission member. In Patent Document 2, a plurality of pins formed with a desired R are arranged in a jig at intervals that allow the flexible printed circuit board to pass, and heating is performed by passing the flexible printed circuit board while applying a constant tension to the jig. A method of molding is described.

Patent Document 2 also discloses a three-layer flexible printed board having three conductor layers in addition to a single-sided flexible printed board having a conductor layer only on one side with respect to the structure of the flexible printed board. Yes. As an application using a three-layer flexible printed circuit board, there is generally a so-called stripline transmission line in which a signal line whose characteristic impedance is matched is arranged on the inner layer and the outer layer is GND (ground). For example, an image sensor is attached to the tip of the movable part described above, and is required when transmitting large-capacity data such as high-definition video data via a flexible printed circuit board that can be expanded and contracted. The aim is to cut off and achieve both high-quality signal transmission and elasticity.

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

Japanese Patent Laid-Open No. 8-57772 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 hard as a flexible printed circuit board. Therefore, the followability with respect to a jig | tool is also bad, and it is difficult to shape | mold into the pleat shape in which a some bending part exists. In particular, the outer layer side has a large bending stress during molding into a pleated shape, and the bent portion in the pleated shape is highly likely to be disconnected by expansion and contraction within 1000 times. For this reason, it is necessary to frequently replace the disconnected flexible printed circuit board, which increases 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 a 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 shielding performance as compared to solid GND, it has been found that high-frequency current is less likely to flow, and transmission loss increases compared to 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 in the pleated shape, so that electrical interference is likely to occur and transmission loss increases. End up.

The present invention has been made on the basis of the above circumstances, and the object of the present invention is to provide a flexible printed circuit board capable of high-quality signal transmission with little transmission loss while the pleat portion has stretch resistance, and flexible printing. An object is to provide a method for 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 that covers the signal line from both sides and is made of a thermoplastic resin, and a signal line sandwiching each insulating layer And a pair of ground layers facing each other, a flexible printed circuit board having at least one pair of stripline transmission lines, wherein a curved portion curved at a plurality of locations is formed, and the curved portion opens. Alternatively, the ground layer has a pleated portion that curves so as to be closed, and the ground layer is provided with a metal surface and has a shielding property against electromagnetic waves, and is more flexible than the hard ground layer and more electromagnetic than the hard ground layer. A soft ground layer inferior in shielding property, and the soft ground layer is disposed on at least one of the outer peripheral side and the inner peripheral side of the curved portion. That, the flexible printed circuit board is provided, characterized in that.

According to another aspect of the present invention, in the above-described invention, the soft ground layer includes a conductive paste obtained by mixing a conductive filler in a binder resin composition, and a thin film conductive film including a metal thin film layer formed by vapor deposition. It is preferable to have at least one of them.

Furthermore, in another aspect of the present invention, in the above-described 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-described 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 that they are arranged on the outer peripheral side of the bending portion in a state where they alternately exist on the back side.

Further, according to another aspect of the present invention, in the above-described 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 that it is arranged on the outer peripheral side of the bending portion in a state of being present on either one of the back side.

Further, according to another aspect of the present invention, in the above-described invention, 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. It is preferable that

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

Further, in 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.

According to a second aspect of the present invention, a signal line, an insulating layer that covers the signal line from both sides and is made of a thermoplastic resin, and a pair of grounds that face the signal line with each insulating layer interposed therebetween A flexible printed circuit board having at least one set of stripline transmission lines, wherein at least one of the double-sided copper-clad laminates having base copper foil layers on both sides of the insulating layer. A first step of forming a signal line on a base copper foil layer on one surface side; and a second step of laminating a single-sided copper-clad laminate having a base copper-clad laminate on one side of the insulating layer via a laminated adhesive. A third step of forming a through-hole for a predetermined portion of the intermediate product formed by the step and the second step, and forming a conductive film around the through-hole and its opening to form a conductive through-hole Of the intermediate product formed in the fourth step and the fourth step, by patterning the base copper foil layer facing the signal line, the base copper foil from a predetermined part on either surface side 5th process of forming the removal part which removed the layer, and forming the hard ground layer in which the conductive part is provided in the shape of the surface on the opposite surface side, and the removal part is more flexible than the hard ground layer And covering the soft ground layer and the hard ground layer with an insulating resin layer via an adhesive layer. The sixth step is to cover the soft ground layer which is rich in properties and inferior to electromagnetic shielding than the hard ground layer. And the flexible printed circuit board formed in the seventh step before the heat forming is subjected to heat forming in a state where a plurality of portions are curved, and after the heat forming, the soft ground layer is placed on the outer peripheral side. To position Method of manufacturing a flexible printed circuit board, characterized in that it comprises an eighth step of forming a pleated portion curved portion of the number is present, is provided.

According to the present invention, the flexible printed circuit board enables high-quality signal transmission with little transmission loss while the pleat portion has stretch resistance.

It is a top view which shows the structure of the flexible printed circuit board of the 1st structural example before shaping | molding concerning one embodiment of this invention. FIG. 2 is a cross-sectional view of the flexible printed circuit board before and after molding, and shows a state cut along line AA in FIG. FIG. 2 is a cross-sectional view of the flexible printed circuit board before and after molding, showing a state cut along the line BB in 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 CC line of FIG. FIG. 2 is a cross-sectional view of the flexible printed circuit board before and after molding, and shows a state cut along line DD in 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 | wire 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 the 2nd structural example. It is a figure which shows the image which applied the flexible printed circuit board which concerns on a 2nd structural example to the rotation site | parts of external devices, such as a joint of arms, such as a robot, and shows the state where two arms are maintaining a horizontal state FIG. It is a figure which shows the state which the two arms in FIG. 10 rotated. FIG. 9 is a diagram showing a state in which signal lines and receiving lands are formed in the AA cross section of FIGS. 1 and 8 in the first step. FIG. 9 is a diagram showing a state in which signal lines are formed in the BB, CC, and DD sections of FIGS. 1 and 8 in the first step. FIG. 9 is a diagram showing a state where a single-sided copper-clad laminate is laminated on a double-sided copper-clad laminate in the AA cross section of FIGS. 1 and 8 in the second step. FIG. 9 is a diagram showing a state in which a single-sided copper-clad laminate is laminated on a double-sided copper-clad laminate in the BB cross section, CC cross-section, and DD cross-section of FIGS. 1 and 8 in the second step. FIG. 9 is a diagram showing a state in which through holes are formed in the AA cross section of FIGS. 1 and 8 in the third step. FIG. 9 is a side sectional view showing a configuration in a BB section, a CC section, and a DD section in FIGS. 1 and 8 in the third step. FIG. 9 is a diagram showing a state in which a conductive coating layer for forming a conductive coating is formed in the through hole in the AA cross section of FIGS. 1 and 8 according to the fourth step. FIG. 9 is a diagram showing a state in which patterning is performed in the AA cross section of FIGS. 1 and 8 in the fifth step. FIG. 9 is a diagram showing a state in which patterning is performed in the BB cross section of FIGS. 1 and 8 in the fifth step. FIG. 10 is a diagram showing a state in which patterning is performed in the CC section of FIG. 1 in the fifth step. FIG. 9 is a diagram showing a state in which patterning is performed in the DD section of FIGS. 1 and 8 in the fifth step. FIG. 10 is a diagram showing a state in which patterning is performed in the EE cross section of FIG. 1 in the fifth step. FIG. 10 is a diagram showing a configuration in a CC section of FIG. 1 when a soft ground layer is formed in the sixth step. FIG. 10 is a diagram showing a state in which a soft ground layer is formed in the DD cross section of FIGS. 1 and 8 according to a sixth step. FIG. 10 is a diagram showing a state in which a soft ground layer is formed in the EE cross section of FIG. 1 in connection with a sixth step. FIG. 9 is a diagram showing a configuration in the AA cross section of FIGS. 1 and 8 when a cover layer is formed in the seventh step. FIG. 9 is a diagram showing a state in which a cover layer is formed in the BB cross section of FIGS. 1 and 8 according to a seventh step. FIG. 10 is a diagram showing a state in which a cover layer is formed in the CC section of FIG. 1 in the seventh step. FIG. 10 is a diagram showing a state in which a cover layer is formed in the DD cross section of FIGS. 1 and 8 according to a seventh step. It is a figure which shows the state which concerns on the 8th process and set the flexible printed circuit board before shaping | molding to the jig | tool. It is a top view which shows the structure of the flexible printed circuit board of a conventional structure. FIG. 29 is a cross-sectional view of a conventional flexible printed circuit board, showing a state cut along the line AA in FIG. 28. It is sectional drawing of the flexible printed circuit board of a conventional structure, and is a figure which shows the state cut | disconnected along the BB line of FIG.

Hereinafter, the flexible printed circuit board 10 according to an embodiment of the present invention will be described below. In the following description, an XYZ orthogonal coordinate system may be used for explanation. Of these, the X direction is the longitudinal direction of the flexible printed circuit board 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 board 10, the Y1 side is the front side of the paper in FIG. 1, and the Y2 side is the back side of the paper. The Z direction is the thickness direction of the flexible printed circuit board 10, Z1 is the back side of the paper in FIG. 2, and Z2 is the front side of the paper.

<Regarding the first configuration example of the 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, and shows a state cut along the line AA in FIG. 3 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and shows a state cut along the line BB of FIG. FIG. 4 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and shows a state cut along the line CC in FIG. 5 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and shows a state cut along the line DD in FIG. 6 is a cross-sectional view of the flexible printed circuit board 10 before and after molding, and shows a state cut along the line EE 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 that is a kind of multilayer flexible printed circuit board, and has a structure in which three conductor portions exist. Specifically, the flexible printed circuit board 10 has a signal line 20 on the inner layer side. The signal line 20 is a portion formed by removing a copper foil portion that transmits a signal by etching or the like so that the characteristic impedance is matched for high-speed transmission by a manufacturing method as described later.

In addition, as shown in FIG. 1, the flexible printed circuit board 10 is provided in the elongate shape. In the present embodiment, for example, the flexible printed circuit board 10 has 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 formed into a pleated shape (bellows shape) so that the radius of the curved portion PL2 is 1 mm. However, the dimension example is not limited to this, and various dimensions can be set (the same applies to the 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 sides. That is, the signal pad 11 is not covered with

cover layers

80 and 90 described later, and is exposed to the outside on the front surface side and the back surface side. The signal pad 11 is a part that is electrically connected to the signal line 20 with respect to the signal line 20 and inputs or outputs a signal to the signal line 20. Therefore, the conductive through hole 12 is electrically connected to the signal pad 11. The conductive through hole 12 has a through hole 12a penetrating the flexible printed board 10 and a conductive film 12b such as plating formed on the inner wall side of the through hole 12a. The signal pad 11 is electrically connected to the signal line 20.

The flexible printed circuit board 10 is also provided with a GND pad 13 that is exposed without being covered with

cover layers

80 and 90 described later on the front and back surfaces of the flexible printed circuit board 10 in the same manner as the signal pad 11 described above. . The GND pad 13 is also electrically connected to the two

ground layers

60 and 70 on the front and back sides through the conductive through holes 14. As with the conductive through hole 12, the conductive through hole 14 also includes a through hole 14a penetrating the flexible printed circuit board 10 and a conductive coating 14b such as plating formed on the inner wall side of the through hole 14a. In addition, 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 laminated on the insulating layer 30. Furthermore, an insulating layer 40 is laminated on the upper surfaces of the signal line 20 and the insulating layer 30 with an adhesive layer 50 interposed therebetween. In the present embodiment, the insulating

layers

30 and 40 are made of thermoplastic resin such as LCP (Liquid Crystal Polymer: LCP). The adhesive layer 50 is a portion having adhesiveness and electrical insulation. The thickness of the insulating

layers

30 and 40 is, for example, 25 μm. The thickness of the adhesive layer 50 is, for example, 15 μm.

Further, as shown in FIG. 3, a solid ground layer 61 (corresponding to a hard ground layer) constituting a part of the ground layer 60 is provided on the upper surface side of the insulating layer 40. Further, a solid ground layer 71 constituting 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 a so-called solid GND (a solid portion (solid coating; planar shape with a large copper foil area)).

As shown in FIG. 3, the solid ground layers 61 and 71 are portions having a uniform thickness in the width direction (Y direction). The solid ground layers 61 and 71 are present on both the 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, a strip transmission path that propagates electromagnetic waves with a small transmission loss while suppressing interference from external electromagnetic waves is configured.

The thickness of the signal line 20 and the solid ground layers 61 and 71 is, 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 constituting 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, a solid ground layer 71 is provided on the lower surface side of the insulating layer 30. In the configuration shown in FIG. 5, a soft ground layer 72 constituting a part of the ground layer 70 is provided on the lower surface side of the insulating layer 30. In the configuration shown in FIG. 5, a 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 provided with metal surfaces and have electromagnetic wave shielding properties, and the soft ground layers 62 and 72 are possible than the solid ground layers 61 and 71. It is a portion that is excellent in flexibility and inferior in electromagnetic wave shielding properties than the solid ground layers 61 and 71. Details of the soft ground layers 62 and 72 will be described later.

Further, the cover layers 80 and 90 are arranged so as to cover the ground layers 60 and 70 having the solid ground layers 61 and 71 and the 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. 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 include insulating resin layers 81 and 91 made of a thermoplastic resin such as LCP (Liquid Crystal Polymer: LCP), for example, and an adhesive layer 82 having adhesiveness and electrical insulation. 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, for example, and the

adhesive layers

82 and 92 have a thickness of, for example, 15 μm. There is something. In this case, there is no problem of delamination or the like, so that the bonding can be performed.

<Details of Configuration of Soft Ground Layers 62 and 72 (First Configuration Example)>
Next, the 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 circuit board 10 after molding. As shown in FIG. 7, the flexible printed circuit board 10 after molding has a pleat portion PL formed in a pleat shape (bellows shape). The pleat portion PL is provided with a straight portion PL1 and a curved portion PL2. And by deform | transforming the curved part PL2, in the flexible printed circuit board 10 after a shaping | molding, it is possible to fold short and to expand | deploy long in the pleat part PL. That is, in the flexible printed circuit board 10 after molding, the entire length of the flexible printed circuit board 10 is provided so as to be expandable and contractible due to the presence of the pleat portion PL. Further, the flexible printed circuit board 10 after molding can be easily deformed to bend in each direction due to the presence of the pleat portion PL.

The above-mentioned soft ground layers 62 and 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2 among the curved portions PL2 of the pleat portion PL. In other words, the soft ground layers 62 and 72 are provided on the outer peripheral side of the curve drawn by the curved portion PL2 as shown in FIG. It is not done. In addition, the direction of the curve drawn by the curved portion PL2 is alternately switched when proceeding along the molded flexible printed board 10 shown in FIG. 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 line portion PL1 as shown in FIG. 3, but in the curved portion PL2 of the pleat portion PL, Located on the circumferential side.

7 corresponds to FIG. 3, the CC line corresponds to FIG. 4, and the DD 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. As the soft ground layers 62 and 72 having such flexibility, a conductive paste and / or a thin film conductive film can be used.

A typical example of the conductive paste is a silver paste containing silver as a conductive filler, such as SW1600C manufactured by Asahi Kaken. However, the silver paste is not limited to such products, and various materials can be used as long as they contain silver as a conductive filler. In addition, the conductive filler of the conductive paste may be any conductive particles other than silver, but examples of conductive fillers other than silver include copper, nickel, solder, aluminum, and copper powder. Examples thereof include a silver-coated copper filler subjected to silver plating, a filler obtained by performing metal plating on a resin ball or glass bead, or a mixture of these fillers. The diameter of the conductive filler particles is, for example, in the range of 10 nm to 5 μm. However, any diameter may be used as long as the loss when transmitting a high-frequency signal is lower than a specified value. .

Note that the thickness of the silver paste is, for example, 10 μm to 15 μm, but the thickness of the conductive paste containing conductive particles other than silver can also be made equal.

Also, the binder resin composition of the conductive paste can use various resins, and the material is not particularly limited. For example, acrylic, polystyrene, vinyl acetate, polyester, polyethylene, polypropylene , Polyamide-based, rubber-based, and other thermoplastic resins can be used, and epoxy-based, urethane-based, phenol-based, melamine-based, alkyd-based thermosetting resins can also be used. Mixtures can be used. Among various resins, epoxy-based, urethane-based, and acrylic-based resins are preferable in that they have a small coefficient of thermal expansion.

As the thin film conductive film, for example, SF-PC5500 manufactured by Tatsuta Electric Co., Ltd., one side of the metal thin film layer is covered with a protective layer and the other side is covered with a conductive adhesive layer. Something covered. The metal thin film layer is a portion where the metal is formed in a thin film, and the thickness thereof is very thin, for example, 0.1 μm. In addition, the thickness of the metal thin film layer is not limited to 0.1 μm, and various thicknesses can be used as long as the electromagnetic wave shielding property is maintained while maintaining flexibility. Practically, it can be appropriately selected within the range of 0.05 μm to 2 μm, for example.

Such thin metal thin film layers are generally formed by physical vapor deposition (PVD), such as vacuum deposition, sputtering, ion plating, or chemical vapor deposition (CVD). ) And the like. The overall thickness of the conductive film is set to a thickness of, for example, 5 to 20 μm. As a metal material constituting the metal thin film layer, various metal materials such as silver, aluminum, copper, gold, nickel, chromium and zinc can be used. Among these, 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 inside the adhesive made of resin, and the conductive fillers are brought into contact with each other by applying pressure. By doing so, what uses the anisotropic conductive adhesive layer which expresses the electroconductivity to a pressurization direction is mentioned. However, it may be configured to have anisotropic conductivity, for example, by self-condensing conductive fillers without applying pressure. The adhesive for the anisotropic conductive adhesive layer may be an adhesive layer formed of the same material as the conductive paste as described above. Moreover, as a conductive adhesive layer, the thing which does not express the anisotropy (directionality) in electroconductivity may be sufficient.

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

The arrangement of the soft ground layers 62 and 72 in the flexible printed board 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 each other. Hereinafter, this portion will be referred to as overlapping portions 64 and 74 (only the overlapping portion 64 is shown in FIG. 6; the overlapping portion 74 is not shown but is present). The overlapping portions 64 and 74 are, for example, in a range of about 0.5 mm to 1 mm in length, and conduction between the solid ground layers 61 and 71 and the soft ground layers 62 and 72 is secured by the overlapping portions 64 and 74. Yes. As a result, the solid ground layers 61 and 71 and the soft ground layers 62 and 72 constitute an integral ground layer.

Further, by adopting such a configuration in which conduction is ensured between the solid ground layers 61 and 71 and the soft ground layers 62 and 72, the distance between the signal line 20 and the soft ground layer 62 can be set to be equal to the signal line 20 and the solid ground layer 62. It does not change with the distance of the layer 61. Therefore, the line width of the signal line 20 matched so that the characteristic impedance is 50Ω can be 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 various line widths can be set.

In general, when the soft ground layers 62 and 72 are provided, the transmission loss during high-frequency transmission tends to increase. However, the soft ground layers 62 and 72 are provided in the curved portion PL2 of the pleat portion PL, and are provided in the minimum necessary portion, and the soft ground layers 62 and 72 are provided on the outer peripheral side of the curve drawn by the curved portion PL2. positioned. For this reason, there is little influence on characteristics such as transmission loss. In addition, the soft ground layers 62 and 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, and are so provided that the signal lines 20 do not directly face each other. The influence of general interference can be reduced.

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

On the other hand, when the soft ground layers 62 and 72 are present on the inner peripheral side of the curve drawn by the curved portion PL2, there is some electrical interference at the portion where the signal lines 20 face each other in the pleat portion PL. It may happen. This is because the shield functions of the soft ground layers 62 and 72 are generally inferior to the solid ground layers 61 and 71. Therefore, when a high-frequency current flows in the state where the soft ground layers 62 and 72 facing each other are inferior to the solid ground layers 61 and 71, there is a possibility that electrical interference occurs.

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

<Configuration of Soft Ground Layers 62 and 72 (Second Configuration Example)>
Next, a second configuration example of the arrangement of the soft ground layer 62 (soft ground layer 72) in the flexible printed board 10 will be described. FIG. 8 is a plan view showing a second configuration example of the flexible printed circuit board 10 before molding corresponding to the modification of FIG. In the description of the flexible printed circuit board 10 in the second configuration example below, the description of the portions common to the flexible printed circuit board 10 in the first configuration example is 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. 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 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 bent to the right or the curved portion PL2 bent to the left. Soft ground layers 62 and 72 are disposed on the outer peripheral side. Therefore, every other soft ground layer 62 (soft ground layer 72) is provided in a certain curved portion PL2, but not provided in the adjacent curved portion PL2. Is provided on the outer peripheral side of the bending portion PL2.

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 not 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 significantly different from the configuration in which the soft ground layers 62 and 72 are alternately present on the front surface side and the back surface side of the flexible printed circuit board 10 as in the first configuration example. 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 board 10 or is soft only on the back surface side (lower surface side) of the flexible printed circuit board 10. Either the ground layer 72 is 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 configuration other than FIG. 9; the same applies hereinafter) is a curve drawn by the curved portion PL2. It exists on the outer peripheral side. Therefore, there is no portion in which the opening 72b (opening 72b) of the soft ground layer 72 (soft ground layer 62) is in a positional relationship facing each other. Thereby, electrical interference between the signal lines 20 can be prevented, and fluctuations in characteristic impedance in 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 soft ground layers 72 (soft ground layer 62) provided in comparison with the first configuration example is smaller. It is halved. For this reason, the influence on characteristics such as transmission loss is further reduced. In addition, the soft ground layers 62 and 72 are located on the outer peripheral side of the curve drawn by the curved portion PL2, and are so provided that the signal lines 20 do not directly face each other. The influence of general interference can be reduced.

Also in the second configuration example, the soft ground layer 72 (soft ground layer 62) is still located on the outer peripheral side of the curve drawn by the curved portion PL2, so the bending stress during molding is reduced. be able to. In addition, since the bending stress is reduced, it is possible to ensure durability when the flexible printed circuit board 10 is repeatedly expanded and contracted.

FIG. 10 is a diagram 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 maintain a horizontal state. FIG. FIG. 11 is a diagram illustrating a state in which the two arms in FIG. 10 are rotated. In the application example shown in FIGS. 10 and 11, the soft ground layer 72 is located in the curved portion PL <b> 2 on the inner diameter side of the rotating portion. That is, the soft ground layer 62 located in the curved portion PL2 on the outer diameter side of the rotating 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 rotating portion, the flexible printed circuit board 10 is deformed so that the curved portion PL <b> 2 positioned on the inner diameter side (inner side) is greatly opened. Therefore, by disposing the soft ground layer 72 on the outer peripheral side (that is, the side located closest to the inner diameter) of the inner diameter side (inner side) bending part PL2, the bending part PL2 positioned on the inner diameter side (inner side) It deforms so that it can be easily opened wide.

At this time, in the bending portion PL2 on the inner diameter side, the soft ground layer 72 on the outer peripheral side is greatly deformed by the action of compressive stress, but the tensile ground acts on the solid ground layer 61 on the inner peripheral side. The circumferential solid ground layer 61 is more difficult to deform than the outer circumferential soft ground layer 72. Therefore, the neutral axis of the stress moves to the outer peripheral side and moves away from the inner peripheral side. Thereby, compressive stress acts on the signal line 20 instead of tensile stress.

In addition, as shown in FIG. 11, the bending part PL2 located in the outer diameter side (outer side) deform | transforms so that it may close. However, in the curved part PL2 located on the outer diameter side (outer side), the solid ground layer 61 is provided on both the inner peripheral side and the outer peripheral side. Therefore, in the curved portion PL <b> 2 located on the outer diameter side (outer side), the deformation in the closing direction is smaller than the deformation that opens in the soft ground layer 72. That is, as shown in FIG. 11, due to the presence or absence of the soft ground layer 72, the curved portion PL <b> 2 positioned on the inner diameter side (inner side) is selectively deformed so as to open widely, but the outer diameter side (outer side) The bending portion PL2 located at () is deformed only small.

With the configuration as described above, the stress that acts on the signal line 20 during operation is reduced by using the flexible printed circuit board 10 of the second configuration example at the rotation part of the external device such as the joint of an arm of a robot or the like. And can withstand repeated operations.

<About the manufacturing method of the flexible printed circuit board 10>
Then, the manufacturing method of the flexible printed circuit board 10 in a 1st structural example and a 2nd structural example is demonstrated below. In the following description, the first step to the eighth step will be sequentially described. However, in the method for manufacturing the flexible printed circuit board 10 in each embodiment, various other steps may exist. 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 AA cross section of FIGS. 1 and 8 in the first step. . 13 is a diagram showing a state in which the signal line 20 is formed in the BB cross section, the CC cross section (existing only in FIG. 1), and the DD cross section of FIGS. 1 and 8 in the first step. . 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 an insulating layer 30 is prepared. Then, the signal line 20 that will be positioned later on the inner layer side and the receiving lands 21 of the conductive through

holes

12 and 14 are formed using a normal photofabrication technique 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 FIG. 1 and FIG. It is a figure which shows a mode that is laminated | stacked. FIG. 15 relates to the second step, and the single-sided copper-clad laminate is added to the double-sided copper-clad laminate 100 in the BB cross section, CC cross-section (only FIG. 1 exists), and DD cross-section of FIG. 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 laminate adhesive 300 are prepared. Then, the laminated adhesive 300 is attached so as to cover the upper surface side of the insulating layer 30, and then the single-sided copper clad laminate 200 is attached to the upper surface side 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 one surface (upper surface) thereof. In addition, let the product after sticking be the intermediate product C2.

The laminated adhesive 300 is a portion that becomes the adhesive layer 50 after being stuck. Such a laminated adhesive 300 is preferably a low-elasticity material so as not to hinder subsequent molding. Specifically, since the elastic coefficient of the LCP film is about 3 to 4 GPa, the lamination adhesive 300 having an elastic coefficient of 2 GPa or less, which is less than half of this, can be used for bonding without affecting the formability. Is possible. Moreover, at the time of shaping | molding, it heats at about 200 degreeC for about 30 minutes. Therefore, as the laminated adhesive 300, an adhesive whose adhesiveness and electrical insulation characteristics are not significantly deteriorated by such a heat history is preferable.

(3) Third Step: Formation of Through

Holes

12a and 14a FIG. 16 is a diagram showing a state in which the through

holes

12a and 14a are formed in the AA cross section of FIGS. 1 and 8 according to the third step. . FIG. 17 is a side cross-sectional view showing a configuration in the BB cross section, CC cross section (existing only in FIG. 1), and DD cross section of FIGS. 1 and 8 in the third step. As shown in FIG. 16, through-

holes

12a and 14a for interlayer connection with the signal pad 11 and the GND pad 13 later are formed in the intermediate product C2. Such drilling may be performed by NC drilling, or may be interlayer connection at a non-through 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 and forms

conductive coatings

12b and 14b in the through

holes

12a and 14a in the AA cross section of FIGS. It is a figure which shows the state in which the conductive film layer 15 for this was formed. As shown in FIG. 18, in the intermediate product C3 after the drilling process, the portion corresponding to the AA cross section is subjected to partial plating to form the conductive coating layer 15 that is the basis of the

conductive coatings

12b and 14b. . Thereby, interlayer conduction in which the three layers are electrically connected is obtained. In addition, let the product by partial plating be the intermediate product C4.

(5) Fifth Step: Patterning of Base Copper Foil Layers 101 and 102 FIG. 19 is a diagram showing a state in which patterning is performed in the AA section of FIGS. 1 and 8 in the fifth step. FIG. 20 is a diagram showing a state in which patterning is performed in the BB cross section of FIGS. 1 and 8 in the fifth step. FIG. 21 is a diagram showing a state in which patterning is performed in the CC section of FIG. 1 in the fifth step. FIG. 22 is a diagram showing a state in which patterning is performed in the DD section of FIGS. 1 and 8 in the fifth step. FIG. 23 is a diagram showing a state in which patterning is performed in the EE cross section of FIG. 1 in the fifth step.

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

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

(6) Sixth Step: Formation of Soft Ground Layers 62 and 72 FIG. 24 is a diagram showing a configuration in the CC section of FIG. 1 when the soft ground layer 62 is formed in the sixth step. FIG. 25 is a diagram showing a state in which the soft ground layer 72 is formed in the DD section of FIGS. 1 and 8 in the sixth step. FIG. 26 is a diagram showing a state in which the soft ground layer 62 is formed in the section EE of FIG. 1 in connection with the sixth step.

24 to 26, soft ground layers 62 and 72 are formed for the intermediate product C5. When the soft ground layers 62 and 72 are formed of a conductive paste such as silver paste, for example, the conductive paste is printed so as to cover the

removal portions

63 and 73, and the printed portions are heated or irradiated with ultraviolet rays. Cured by etc. At this time, as shown in FIG. 26, the solid ground layer 61 and the conductive paste (soft ground layer 62) are partially overlapped with each other, and the conduction between the solid ground layer 61 and the conductive paste (soft ground layer 62) is achieved. Secure. Although not shown, a similar overlapping portion is provided between the solid ground layer 71 and the conductive paste (soft ground layer 72), so that 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 in a strip shape by cutting or the like so as to have a length that can cover the

removal portions

63 and 73. To do. Thereafter, the strip-shaped thin film conductive film is pasted so as to cover the

removal portions

63 and 73. Even in such affixing, the solid ground layer 61 and the thin-film conductive film (soft ground layer 62) are partially overlapped to ensure conduction between the solid ground layer 61 and the thin-film conductive film (soft ground layer 62). To 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), and the solid ground layer 71 and the thin film conductive film (soft ground layer) are provided. 72) is ensured.

In the formation of the soft ground layers 62 and 72 described above, the solid ground layers 61 and 71 and the portions that become the contact points of the soft ground layers 62 and 72 are partially plated such as electroless gold plating. You may make it surface-treat by a process. In such a partial plating treatment, a portion not subjected to the plating treatment may be masked using a photosensitive dry film resist having resistance to the plating solution 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 diagram showing a configuration in the 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 is a diagram showing a state in which cover layers 80 and 90 are formed in the BB cross section of FIGS. 1 and 8 in the seventh step. FIG. 29 is a diagram showing a state in which cover layers 80 and 90 are formed in the CC section of FIG. 18 in connection with the seventh step. FIG. 30 is a diagram showing a state in which cover layers 80 and 90 are formed in the DD section of FIGS. 1 and 8 in the seventh step.

27 to 30, cover layers 80 and 90 including insulating resin layers 81 and 91 and

adhesive layers

82 and 92 are formed on the intermediate product C6. The cover layers 80 and 90 are formed by attaching the

adhesive layers

82 and 92 to the intermediate product C6. It is necessary to prevent the signal pad 11 and the GND pad 13 from being covered with the cover layers 80 and 90. Therefore, in 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 technique 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.

29 and 30, soft ground layers 62 and 72 formed using a conductive paste such as a silver paste and a thin film conductive film are also covered with

cover layers

80 and 90, respectively. Protected. That is, the curved portion (curved portion PL2) of the flexible printed circuit board 10 is also covered with the cover layers 80 and 90. For this reason, the top coat which protects a curved part and becomes a surface protective layer is unnecessary.

It should be noted that surface treatment such as electroless gold plating can be performed on the portions not covered with the cover layers 80 and 90 as necessary. Through the steps as described above, the flexible printed circuit board 10 before molding is obtained.

(8) Eighth Step: Heat Molding of Flexible Printed Circuit Board 10 FIG. 31 is a diagram showing a state in which the flexible printed circuit board 10 before molding is set on the jig 400 in the eighth process. As shown in FIG. 31, the flexible printed circuit board 10 before molding is set on the jig 400 in a state in which it is 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 board 10 and a latch pin 412 to be inserted into a hole portion on the front end side of the flexible printed circuit board 10 (not shown). Is provided.

A hole on the distal end side of the flexible printed circuit board 10 is inserted into the latch pin 412, and the flexible printed circuit board 10 is meandered along the jig pin 420 disposed at a predetermined position of the jig 400 in that state. The setting of the flexible printed circuit board 10 to the jig 400 is completed. After the setting, a certain tension is applied to the rear end side of the flexible printed circuit board 10. In this state, by heating in an oven or the like, the flexible printed circuit board 10 having a three-layer structure containing the LCP material that is thermoplastic is formed in a pleated shape (bellows shape). It will be in the state which has pleat part PL as shown in these.

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

Further, after this molding, unnecessary parts such as the front end side positioned by the front end fixing member 410 or the like are cut out of the flexible printed circuit board 10 as necessary to complete the final product. As a method for cutting such unnecessary portions, a hole portion into which the latch pin 412 is inserted is diverted in the flexible printed circuit board 10, the starting point side is positioned, and the opposite side is positioned by abutment or the like. Then, it can be cut using a cutting jig such as a pinnacle or a mold. However, methods other than those described above may be used for cutting unnecessary portions. Examples of such methods include laser cutting using a laser and router cutting using a router bit.

<About test results>
Table 1 shows the result of the expansion / contraction test performed on the flexible printed circuit board 10 having the pleated portion PL formed as described above. In this expansion / contraction test, the flexible printed circuit board 10 is repeatedly expanded and contracted, whether or not the signal line 20 is disconnected during the test, the amount of extension of the flexible printed circuit board 10 before and after the test, and the flexible printed circuit board 10 before and after the test. DC resistance fluctuation, transmission loss before test, and change in transmission loss before and after the test were evaluated.

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

Also, the comparative example corresponds to a configuration in which the ground layers 60 and 70 are all 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 surfaces sandwiching the signal line 20 corresponds to the comparative example (not shown).

In this expansion / contraction test, the length of the flexible printed

circuit board

10 and 10F was increased by 50%, and the test was performed up to 5 million times. Also, after this test, if the elongation was within 10%, the test for elongation was accepted. In addition, the test was performed using 10 of 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 stretch test resistance, and the elongation rate after 5 million stretch tests is 5 %, And no disconnection was observed. In addition, the rate of change in DC resistance and transmission loss was 3% or less, and it was confirmed that the change in electrical characteristics was not seen so much. Regarding the transmission loss, the first and second flexible printed

circuit boards

10 and 10 are provided with solid ground layers 61 and 71 over the entire length of both surfaces having the lowest loss. It was confirmed that there was only a loss of 5% or less compared to the conventional configuration, and that there was only a loss within a range not causing any problem in signal transmission.

On the other hand, in the conventional configuration, the signal line 20 was disconnected for all of the 10 tested in 1000 times. In the evaluation of the conventional configuration, although it is in a disconnected state, the elongation is 5% or less, the resistance value is OPEN, and therefore the transmission loss is 0.22 dB / 10 mm, which is the lowest, and the change in transmission loss. The measurement was impossible due to the disconnection. In the configuration of the comparative example, the signal line 20 was not disconnected, the DC resistance change rate was 3% or less, and the transmission loss change rate was 3% or less. However, it was confirmed that the transmission loss was large, and in particular, there was about twice the transmission loss with respect to the flexible printed circuit board 10 of the first configuration example. From the above results, it was confirmed that the conventional configuration could not be used due to disconnection, and the comparative example also had a large transmission loss, and the performance was inferior to the flexible printed circuit board 10 of the first configuration example and the second configuration example. .

From the above results, it is found 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 elasticity. did.

<About effect>
According to the flexible printed circuit board 10 and the method for manufacturing the flexible printed circuit board 10 configured as described above, the following effects are produced.

That is, the curved portions PL2 at a plurality of places in the pleated portion PL of the flexible printed circuit board 10 having the stripline transmission line are deformed so as to open or close. On the other hand, the ground layers 60 and 70 are provided with metal surfaces and have a solid ground layer 61 and 71 (hard ground layer) having electromagnetic wave shielding properties, and are more flexible than the solid ground layers 61 and 71. In addition, it has soft ground layers 62 and 72 which are inferior in electromagnetic wave shielding properties than the solid ground layers 61 and 71. The soft 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.

For this reason, in the bending part PL2, since the soft ground layers 62 and 72 exist in the outer peripheral side of the bending part PL2, the bending stress at the time of shape | molding the flexible printed circuit board 10 in a pleat shape (bellows shape) is made small. be able to. And since bending stress becomes small, it becomes a structure where durability in the case of extending and contracting the flexible printed circuit board 10 repeatedly was ensured. In particular, the flexible printed circuit board 10 is formed by adopting a configuration in which the soft 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 ground layers 62 and 72 are easily deformed to be compressed. Thereby, compressive stress can be generated in the signal line 20, and the signal line 20 is difficult to be disconnected.

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

In the present embodiment, the soft ground layers 62 and 72 include at least one of a thin film conductive film including a conductive paste obtained by mixing a conductive filler in a binder resin composition and a metal thin film layer formed by vapor deposition. Have one. Here, in an electrically conductive paste, since an electroconductive filler can move in the state isolate | separated from the other electroconductive filler inside the binder resin composition, it can be set as the structure provided with sufficient flexibility. In addition, in a thin film conductive film having a deposited metal thin film layer, the thickness of the metal thin film layer is significantly reduced compared to the solid ground layers 61 and 71 because the metal thin film layer is formed by vapor deposition. It can be set as the structure provided with flexible.

In the present embodiment, as described in the first configuration example, the soft ground layers 62 and 72 in the pleat portion PL are alternately provided on the front surface side and the back surface side of the signal line 20 in the curved portion PL2. It is arranged on the outer peripheral side. Therefore, the flexible printed circuit board 10 can easily expand and contract. That is, in the flexible printed circuit board 10 of the first configuration example, the stretchability can be improved.

Further, 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 portions in a state where they are present on either the front surface side or the back surface side of the signal line 20. It arrange | positions at the outer peripheral side of PL2. Therefore, by using the flexible printed circuit board 10 of the second configuration example at the rotation part of an external device such as a joint of an arm such as a robot, the stress acting on the signal line 20 during operation can be reduced. The structure can withstand repeated operations.

In the present embodiment, the ground layers 60 and 70 are electrically connected to one end side of the solid ground layers 61 and 71 (hard ground layer) and the other end side of the soft ground layers 62 and 72. An overlapped portion 64 is provided. Due to the presence of the overlapping portions 64 and 74, the solid ground layers 61 and 71 and the soft ground layers 62 and 72 can form an integral ground layer.

In the present embodiment, the insulating

layers

30 and 40 and the insulating resin layers 81 and 91 are made of LCP (Liquid Crystal Polymer) which is a thermoplastic resin. For this reason, when heat forming is performed on the flexible printed circuit board 10 before heat forming, a pleated portion PL having a plurality of curved portions PL2 can be easily formed.

Furthermore, in the present embodiment, the ground layers 60 and 70 located in the curved portion PL2 are configured such that a plating film for interlayer connection is not formed. For this reason, the bending part PL2 is in a state where it is easy to bend.

In the present embodiment, the flexible printed circuit board 10 before heat forming is heat formed using the jig 400. For this reason, the flexible printed board 10 is positioned with the tip fixing member 410, and further, the flexible printed board 10 is heat-molded in a state where a tension is applied to the flexible printed board 10 so that a flexible print having a good pleated portion PL without misalignment is obtained. The substrate 10 can be formed.

<Modification>
Although one embodiment of the present invention has been described above, the present invention can be variously modified in addition to this. This will be described below.

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

Further, in the second configuration example in the above-described embodiment, the soft ground layer 72 is provided on the curved portion PL2 on the inner diameter side of the rotation portion with respect to the rotation portion of the external device such as an arm joint 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 rotating portion does not exist. However, a configuration in which the soft ground layer 62 is disposed on the curved portion PL2 on the outer diameter side of the rotating portion may be employed. When configured in this manner, the outer diameter side curved portion PL2 is deformed so as to be largely closed, but even in that case, it can be configured to be easier to bend than the conventional configuration and to prevent the signal line 20 from being broken. .

In the first configuration example and the second configuration example, a configuration in which 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 is adopted. You may do it. Also in this case, the signal line 20 can be bent more easily than the conventional structure, and the signal line 20 is less likely to be disconnected.

Further, in the first configuration example and the second configuration example, a configuration in which the soft ground layers 62 and 72 are disposed on both the inner peripheral side and the outer peripheral side of the curved portion PL2 is adopted, and the straight portion PL1 is a solid ground layer 61, A configuration in which 71 is arranged may be adopted. In this case, it is easier to bend than the first configuration example and the second configuration example, and the signal line 20 is less likely to be disconnected. Even when such a configuration is adopted, transmission loss can be reduced as compared with a 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.

Further, in the above-described embodiment, the flexible printed board 10 has the pleat portion PL in which the curved portions PL2 having the same size are arranged at the same pitch. However, the pitches at which the curved portions PL2 are arranged may not be the same, and the curved portions PL2 may be arranged so that the pitches are different from each other or partially different. Further, the size (radius etc.) of a certain curved portion PL2 may be different from the size (radius etc.) of another curved portion PL2. Moreover, you may combine what has several bending part PL2 arrange | positioned by another pitch and magnitude | size with respect to what has arranged several bending part PL2 with a certain pitch and magnitude | size.

DESCRIPTION OF

SYMBOLS

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, DESCRIPTION OF SYMBOLS 15 ... Conductive film layer, 20 ... Signal line, 21 ... Receiving land, 30, 40 ... Insulating layer, 50 ... Adhesive layer, 60, 70 ... Ground layer, 61, 71 ... Solid ground layer (corresponding to hard ground layer) 62, 72 ... soft ground layer, 63 ... removal part, 64 ... overlapping part, 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 ... Laminate adhesive, 400 ... Jig, 410 ... Tip fixing member, 411 ... Tip receiving part, 412 ... Latch Down, 420 ... jig pins, C1 ~ C6 ... intermediate product, PL ... pleated portion, PL1 ... straight portion, PL2 ... curved portion

Claims

A signal line; an insulating layer that covers the signal line from both sides and is made of a thermoplastic resin; and a pair of ground layers that face the signal line across the insulating layer, so that at least one set is provided. A flexible printed circuit board having a stripline transmission line of
A curved portion that is curved in a plurality of places is formed, and includes a pleat portion that curves so that the curved portion opens or closes,
The ground layer includes a hard ground layer provided with a metal surface and having electromagnetic wave shielding properties, and a soft ground layer that is superior in flexibility than the hard ground layer and inferior in electromagnetic wave shielding properties than the hard ground layer, and Have
The soft ground layer is disposed on at least one of the outer peripheral side and the inner peripheral side of the curved portion,
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to claim 1,
The soft ground layer has at least one of a conductive paste obtained by mixing a conductive filler in a binder resin composition and a thin film conductive film including a metal thin film layer formed by vapor deposition.
A flexible printed circuit board characterized by that.
A flexible printed circuit board according to claim 1 or 2,
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.
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to claim 3,
The pleat portion is provided in a bellows shape by alternately switching the direction of the curve of the curved portion,
The soft ground layer is arranged on the outer peripheral side of the curved portion in a state alternately present on the front side and the back side of the signal line,
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to claim 3,
The pleat 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 the 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.
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to any one of claims 1 to 5,
The ground layer is provided with an overlapping portion in which one end side of the hard ground layer and the other end side of the soft ground layer are electrically connected to each other.
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to any one of claims 1 to 6,
The insulating layer is made of LCP (Liquid Crystal Polymer), which is a thermoplastic resin,
A flexible printed circuit board characterized by that.
The flexible printed circuit board according to any one of claims 1 to 7,
In the ground layer located in the curved portion, a plating film for interlayer connection is not formed,
A flexible printed circuit board characterized by that.
A signal line; an insulating layer that covers the signal line from both sides and is made of a thermoplastic resin; and a pair of ground layers that face the signal line across the insulating layer, so that at least one set is provided. A method of manufacturing a flexible printed circuit board having a stripline transmission line of
Of the double-sided copper clad laminate having a base copper foil layer on both sides of the insulating layer, a first step of forming at least one of the signal lines on the base copper foil layer on one side;
A second step of laminating a single-sided copper-clad laminate having a base copper-clad laminate on one side of the insulating layer via a laminated adhesive;
A third step of forming a through hole for a predetermined portion of the intermediate product formed by the second step;
A fourth step of forming a conductive coating around the through hole and the opening thereof to form a conductive through hole;
Of 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 removed from a predetermined portion on either side. Forming a removed removed portion, and forming a hard ground layer in which a conductive portion is provided in a planar shape on the opposite surface side; and
A sixth step of forming a soft ground layer which is richer in flexibility than the hard ground layer and inferior to the hard ground layer in shielding electromagnetic waves with respect to the removal portion;
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 formed by the seventh step is subjected to heat forming in a state where a plurality of portions are curved, and after the heat forming, the plurality of soft ground layers positioned on the outer peripheral side. An eighth step of forming a pleated portion having a curved portion;
The manufacturing method of the flexible printed circuit board characterized by the above-mentioned.