Abstract:
A substrate is provided with: a stretchable sheet; a plurality of members located on the sheet; a plurality of strips that are stretchable, and that connect the plurality of members; and a plurality of fiber threads that sew the plurality of members and the sheet together.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a substrate including a stretchable sheet. 
         [0003]    2. Description of the Related Art 
         [0004]    Flexible substrates have often been used in recent years due to the miniaturization and/or thinning of electronic devices. The use of flexible substrates has been achieved in various fields besides the field of typical electronic devices. For example, flexible substrates have been used in mobile devices such as smartphones and also wearable devices. 
         [0005]    Wearable devices are required to be able to easily attach to movable parts of a measurement subject (a human body, for example), and to be able to perform sensing in close contact with the measurement subject. Consequently, flexible substrates are required to have sufficient stretchability. A flexible substrate having a serpentine structure is known as prior art (Japanese Unexamined Patent Application Publication No. 2000-294886). 
       SUMMARY 
       [0006]    In one general aspect, the techniques disclosed here feature a substrate that is provided with: a stretchable sheet; a plurality of members located on the sheet; a plurality of strips that are stretchable, and that connect the plurality of members; and a plurality of fiber threads that sew the plurality of members and the sheet together. 
         [0007]    Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a drawing schematically depicting a stretchable flexible substrate according to an embodiment; 
           [0009]      FIG. 2A  is a drawing schematically depicting an example of a stretchable flexible substrate according to an embodiment; 
           [0010]      FIG. 2B  is a drawing schematically depicting an example of a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 2A ; 
           [0011]      FIG. 2C  is a drawing schematically depicting an example of a stretchable flexible substrate according to an embodiment; 
           [0012]      FIG. 3A  is a drawing schematically depicting an example of a wiring layer of a stretchable flexible substrate according to an embodiment; 
           [0013]      FIG. 3B  is a drawing schematically depicting an example of a wiring layer of a stretchable flexible substrate according to an embodiment; 
           [0014]      FIG. 4  is a schematic drawing for illustrating an example of the relationship between a wiring layer and the direction of a force applied to the wiring layer; 
           [0015]      FIG. 5  is a drawing schematically depicting an example of a stretchable flexible substrate according to an embodiment; 
           [0016]      FIG. 6A  is a schematic drawing for illustrating the stretching behavior of a wiring layer of a stretchable flexible substrate according to an embodiment; 
           [0017]      FIG. 6B  is a schematic drawing for illustrating the stretching behavior of a wiring layer of a stretchable flexible substrate according to an embodiment; 
           [0018]      FIG. 7A  is a schematic drawing for depicting an example of a stretchable flexible substrate according to an embodiment; 
           [0019]      FIG. 7B  is a drawing schematically depicting an example of a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 7A ; 
           [0020]      FIG. 7C  is a drawing schematically depicting an example of a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 7A ; 
           [0021]      FIG. 8A  is a drawing schematically depicting a fiber knitted material having a knitted structure; 
           [0022]      FIG. 8B  is a schematic drawing for illustrating deformation of a fiber knitted material having a knitted structure; 
           [0023]      FIG. 9A  is a drawing schematically depicting a fiber knitted material having a net structure; 
           [0024]      FIG. 9B  is a schematic drawing for illustrating deformation of a fiber knitted material having a net structure; 
           [0025]      FIG. 10A  is a drawing schematically depicting a first modified example of a stretchable flexible substrate according to an embodiment; 
           [0026]      FIG. 10B  is a drawing depicting a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 10A ; 
           [0027]      FIG. 10C  is a drawing schematically depicting a second modified example of a stretchable flexible substrate according to an embodiment; 
           [0028]      FIG. 10D  is a drawing depicting an example of a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 10C ; 
           [0029]      FIG. 10E  is a drawing depicting another example of a cross-sectional structure of the stretchable flexible substrate depicted in  FIG. 10C ; 
           [0030]      FIG. 11A  is a cross-sectional drawing schematically depicting a third modified example of a stretchable flexible substrate according to an embodiment; 
           [0031]      FIG. 11B  is a cross-sectional drawing schematically depicting a fourth modified example of a stretchable flexible substrate according to an embodiment; 
           [0032]      FIG. 11C  is a cross-sectional drawing schematically depicting a fifth modified example of a stretchable flexible substrate according to an embodiment; and 
           [0033]      FIG. 11D  is a cross-sectional drawing schematically depicting a sixth modified example of a stretchable flexible substrate according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    First, the circumstances that led to the present inventors devising the stretchable flexible substrate of the present disclosure will be described. The present inventors discovered the following four problems. 
         [0035]    (1) With a conventional flexible substrate, stretching in the direction of extension of the flexible substrate is possible but stretching in a direction that is different from the direction of extension is difficult. Thus, it is difficult for sufficient stretchability of a level that meets market needs to be exhibited. 
         [0036]    (2) With a conventional flexible substrate, it is difficult to ensure high stretchability and also to prevent a breakage in wiring caused by lengthening. 
         [0037]    (3) With a conventional woven material into which an electrically conductive thread has been woven, it is difficult to ensure the stability of wiring resistance. 
         [0038]    (4) With a conventional woven material into which an electrically conductive thread has been woven, it is difficult to ensure reliability in the mounting of electronic components. 
         [0039]    The above mentioned point (2) will be described in detail. A conventional flexible substrate is provided with wiring that has curved sections. For example, in the case where a flexible substrate is attached to a movable part of a human body or a robot arm, the substrate extends in accordance with movement such as bending or extending of the movable part. However, when the amount of extension of the substrate exceeds a fixed level, the curved sections of the wiring extend, and there is a risk of a breakage occurring in a portion of the wiring where stress is likely to concentrate. Increasing the width of the wiring is feasible in order to avoid this problem. Thus, the cross-sectional area of a cross section that intersects the tensile direction increases, and the strength of the wiring increases. However, when the width of a wiring is increased, the space for the curving of the wiring is reduced, and sufficient stretchability can no longer be obtained. 
         [0040]    The above mentioned point (3) will be described in detail. A woven material into which an electrically conductive thread has been woven in order to impart a high degree of stretchability is proposed in Japanese Unexamined Patent Application Publication No. 2013-147767. In this woven material, the electrically conductive thread functions as wiring. However, wiring implemented by means of an electrically conductive thread exhibits a higher resistance value than typical metal wiring and large changes in wiring resistance when stretched. These tendencies become notable as the wiring lengthens. Therefore, this woven material is unsuitable for devices for large current applications, such as an LED matrix. 
         [0041]    The above mentioned point (4) will be described in detail. With a woven material into which an electrically conductive thread has been woven, flatness is inferior compared to a typical flexible substrate. It is therefore difficult for electronic components to be arranged with high density on this woven material. Furthermore, a woven material has inferior heat resistance compared to a typical flexible substrate. Therefore, mounting methods that require high heat such as solder mounting cannot be applied to this woven material. Consequently, with a woven material into which an electrically conductive thread has been woven, the mounting method is restricted, and it is difficult for a high degree of mounting reliability to be obtained. 
         [0042]    The present inventors carried out a diligent investigation in order to solve the aforementioned problems, which thereby led to the present inventors devising a stretchable flexible substrate in which non-stretchable portions of a wiring layer and a stretchable base material are sewed using fiber threads. 
         [0043]    In this stretchable flexible substrate, the wiring layer has non-stretchable portions and stretchable strips connected to the non-stretchable portions. The wiring layer has stretchability due to the stretchable strips extending and contracting. In the case where the wiring layer is provided with a flat sheet-like electrically conductive layer, for example, this electrically conductive layer exhibits low wiring resistance and also small changes in wiring resistance when stretched compared to an electrically conductive thread. Furthermore, with this kind of electrically conductive layer, the wiring layer has comparatively high heat resistance. In the case where the non-stretchable portions have a flat-sheet shape, it is easy for electronic components to be arranged. In addition, the wiring layer and the base material are sewed together using fiber threads, and therefore the wiring layer is able to move to an extent on the base material. Therefore, the sewing together of the wiring layer and the base material practically does not inhibit the extension and contraction of the stretchable strips. 
         [0044]    Hereinafter, a stretchable flexible substrate according to an embodiment will be described. The various kinds of elements depicted in the drawings are merely depicted in a schematic manner to aid understanding of the present disclosure, and the dimension ratios, the appearance, and the like may be different from actual elements. 
         [0045]    As depicted in  FIGS. 1 and 2A to 2C , a stretchable flexible substrate  100  according to an embodiment has a wiring layer  10  and a base material  50 . The wiring layer  10  has electrically conductive wiring. The wiring layer  10  includes non-stretchable portions  10 A and stretchable strips  10 B connected to the non-stretchable portions  10 A. The stretchable strips  10 B have a shape that is capable of stretching, and the wiring layer  10  is thereby able to stretch. It is desirable for the non-stretchable portions  10 A and the stretchable strips  10 B to be connected in an integral manner or a continuous manner, for example. That is, it is desirable for the non-stretchable portions  10 A and the stretchable strips  10 B to be integrated without joints. 
         [0046]    The base material  50  in the present embodiment is an example of a “sheet” in the present disclosure. The non-stretchable portions  10 A in the present embodiment are an example of a “non-stretchable member” in the present disclosure. The stretchable strips  10 B in the present embodiment are an example of a “strip” in the present disclosure. 
         [0047]      FIGS. 3A and 3B  depict only the wiring layer  10 . A depicted in the drawings, in the wiring layer  10 , a plurality of non-stretchable portions  10 A are provided, and adjacent non-stretchable portions  10 A are connected to each other by a stretchable strip  10 B. The plurality of non-stretchable portions  10 A may be arranged in a two-dimensional matrix form, and the stretchable strips  10 B may also be arranged in a two-dimensional matrix form in such a way as to connect the non-stretchable portions  10 A. It is desirable for the stretchable strips  10 B to have curved sections. In this case, the stretchable strips  10 B extend and contract due to changes in the curvature of the curved sections, and thus the wiring layer  10  overall exhibits stretchability. Two or more stretchable strips  10 B are provided for each non-stretchable portion  10 A. It is desirable for the plurality of stretchable strips  10 B to be separated from each other by gaps  15 . The degree of freedom of the changes in the curvature of the stretchable strips  10 B increases as the gaps  15  become larger, thereby facilitating stretching of the stretchable flexible substrate  100  overall. The stretchable flexible substrate  100  deforms and/or stretches in a three-dimensional manner, for example. 
         [0048]    The stretchable strips  10 B curve in a serpentine shape or a spiral shape, for example. In plan view, the stretchable strips  10 B depicted in  FIG. 3A  have a serpentine shape. In other words, the stretchable strips  10 B depicted in  FIG. 3A  have a meandering shape. Non-stretchable portions  10 A that are adjacent to each other are connected by way of a stretchable strip  10 B that curves in a serpentine shape therebetween. In plan view, the stretchable strips  10 B depicted in  FIG. 3B  are coiled in spirals. Non-stretchable portions  10 A that are adjacent to each other are connected by way of a stretchable strip  10 B that curves in a spiral shape therebetween. 
         [0049]    In the case where a plurality of non-stretchable portions  10 A are arranged with a predetermined pitch, a wiring layer  10  that has spiral-shaped stretchable strips  10 B is able to extend to a greater extent than a wiring layer  10  that has serpentine-shaped stretchable strips  10 B. This is due to the following two reasons. 
         [0050]    (1) The curved sections of a spiral-shaped stretchable strip  10 B curve with a greater radius of curvature than the curved sections of a serpentine-shaped stretchable strip  10 B. It is thereby possible to obtain a greater allowance in length for the stretchable strips  10 B. 
         [0051]    (2) A spiral-shaped stretchable strip  10 B displaces in such a way that the spirals loosen, and therefore this displacement assists the extension of the stretchable strip. 
         [0052]    Furthermore, a wiring layer  10  that has spiral-shaped stretchable strips  10 B is able to be extended by means of a smaller tensile force than a wiring layer  10  that has serpentine-shaped stretchable strips  10 B. 
         [0053]    For example, as depicted in  FIG. 4 , spiral-shaped stretchable strips  10 B are obtained by wiring that extends from a central portion (a non-stretchable portion  10 A, for example) being made to curve in a clockwise direction as indicated by the dashed arrows. The curvature of the spiral-shaped stretchable strips  10 B decreases as the stretchable flexible substrate  100  extends. Thus, the stretchable strips  10 B deform in such a way as to move away from the outer periphery of a non-stretchable portion  10 A, from the one end connected to the non-stretchable portion  10 A toward the other end. 
         [0054]    As depicted in  FIG. 4 , a plurality of spiral-shaped stretchable strips  10 B connected to one non-stretchable portion  10 A all curve along the outer periphery of that non-stretchable portion  10 A. Therefore, it is possible to decrease the margin between the stretchable strips  10 B, and it is possible to increase the housability of the stretchable strips  10 B and the wiring formed thereon. For example, in the case where sections that include a non-stretchable portion  10 A and a plurality of spiral-shaped stretchable strips  10 B are arranged in a matrix form, it is possible for the stretchability of the stretchable strips  10 B and the housability of the wiring thereon to be increased. 
         [0055]    The spiral-shaped stretchable strips  10 B desirably extend along at least half of a perimeter of a non-stretchable portion  10 A. For example, the spiral-shaped stretchable strips  10 B may extend along a perimeter of a non-stretchable portion  10 A one or more times, or may extend along a perimeter of a non-stretchable portion  10 A three or more times. It should be noted that the shape of the non-stretchable portions  10 A is not particularly restricted. The shape of the non-stretchable portions  10 A may be a circle or an ellipse, or may be a polygon such as a quadrilateral or a hexagon. The curved sections of the stretchable strips  10 B may be curved in a curved line shape, or may be bent in an angular manner. 
         [0056]    The wiring layer  10  includes electrically conductive wiring. For example, as depicted in the partial cross-sectional views in  FIGS. 3A and 3B , the wiring layer  10  includes an insulating base material  12  and electrically conductive wiring  16 . The electrically conductive wiring  16  is provided on the main surfaces of the insulating base material  12 , for example. In other words, the insulating base material  12  and the electrically conductive wiring  16  are layered on each another. In the case where the electrically conductive wiring  16  has bent sections, it is possible to increase the length of the electrically conductive wiring  16  that can be housed per unit area. 
         [0057]    The insulating base material  12  has an electrical insulating property. It is desirable for the insulating base material to have a sheet shape. It is desirable for the insulating base material  12  to be flexible. The material for the insulating base material  12  may be a resin material. A possible example of the material for the insulating base material  12  is at least one type of material selected from the group consisting of an acrylic resin, a urethane resin, a silicone resin, a fluororesin, a polyimide resin, an epoxy resin, and the like. 
         [0058]    The electrically conductive wiring  16  is electrically conductive. The electrically conductive wiring  16  may be in the form of a thin film. It is desirable for the electrically conductive wiring  16  to contain a metal material. A possible example of a metal material for the electrically conductive wiring  16  is at least one type selected from the group consisting of gold (Au), silver (Ag), copper (Cu), nickel (Ni), chromium (Cr), cobalt (Co), magnesium (Mg), calcium (Ca), platinum (Pt), molybdenum (Mo), iron (Fe), and zinc (Zn). The thickness of the electrically conductive wiring  16 , for example, may be of the order of 5 μm to 1000 μm, desirably of the order of 5 μm to 500 μm, and more desirably of the order of 5 μm to 250 μm. The electrically conductive wiring  16  may be a layer formed from metal foil. In this case, the metal foil may be subjected to patterning processing, for example. 
         [0059]    For example, as depicted in  FIG. 5 , electronic components  80  may be provided on the wiring layer  10 . The electronic components  80  are electrically connected to the wiring layer  10  (for example, the electrically conductive wiring  16 ). It is desirable for the electronic components  80  to be provided on the non-stretchable portions  10 A of the wiring layer  10 , as depicted in  FIG. 5 . The electronic components  80  are less affected by the stretching of the stretchable flexible substrate  100 . The electronic components  80  may be various electronic components used in the electronic mounting field, and are not particularly restricted. Possible examples of the electronic components  80  are a semiconductor element, a temperature sensor, a pressure sensor, an actuator, and the like. A semiconductor element is a light-emitting element, a light-receiving element, a diode, or a transistor, for example. Other possible examples of the electronic components  80  are an IC (a control IC, for example), an inductor, a capacitor, a power element, a chip resistor, a chip capacitor, a chip varistor, a chip thermistor, another chip-shaped laminated filter, a connection terminal, and the like. A plurality of types of electronic components  80  may be provided on the stretchable flexible substrate  100 . 
         [0060]    The manufacturer may mount the electronic components  80  on the non-stretchable portions  10 A of the wiring layer  10 , and thereafter sew the wiring layer  10  onto the base material  50 . A mounting method requiring high heat may be adopted in order to mount the electronic components  80  on the wiring layer  10 . 
         [0061]    The base material  50  supports the wiring layer  10 , for example. The base material  50  has an insulating property, for example. The base material  50  is provided in such a way as make contact with the wiring layer  10  in a direct or indirect manner. The wiring layer  10  and the base material  50  may be layered on each another, as depicted in  FIGS. 1 and 2B . A main surface of the wiring layer  10  and a main surface of the base material  50  face each other. A main surface of the wiring layer  10  is a surface that extends in the direction in which the non-stretchable portions  10 A and the stretchable strips  10 B are arranged. 
         [0062]    The base material  50  is a flexible sheet, for example. The stretchable flexible substrate  100  is thereby able to be flexible. The base material  50  may also be stretchable. The stretchable flexible substrate  100  is thereby able to be stretchable. The base material  50  may be a resin material (an elastomer material, for example), or a fiber fabric, for example. The base material  50  may be air-permeable and/or light-permeable. 
         [0063]    The wiring layer  10  and the base material  50  are sewed together by means of a fiber thread  70 , as depicted in  FIGS. 1 and 2A to 2C . The fiber thread  70  can attach the wiring layer  10  to the base material  50  without greatly inhibiting the extension and contraction of the wiring layer  10 . There are no particular restrictions regarding the way in which the sewing is carried out by means of the fiber thread  70 . For example, a method that is used when attaching a button to clothing by a thread may be adopted as the way in which the sewing is carried out. The wiring layer  10  and the base material  50  may be attached only by the fiber thread  70 . The locations of attachment by the fiber thread  70  are scattered, thereby ensuring the flexible stretchability of the stretchable flexible substrate  100 . 
         [0064]    The fiber thread  70  may be a fiber itself, or may be a thread obtained by processing a fiber. It is desirable for the fiber thread  70  to be flexible. The fiber included in the fiber thread  70  may be a short fiber or a long fiber, or may be a hollow fiber. The fiber thread  70  may be a twisted thread. In this case, the fiber thread  70  is able to have high strength. 
         [0065]    Although the non-stretchable portions  10 A are attached to the base material  50  by way of the fiber thread  70 , for example, it may be possible for the non-stretchable portions  10 A to rotate and/or displace with respect to the base material  50 . This can be realized by the non-stretchable portions  10 A and the base material  50  being sewed loosely with the fiber thread  70 , for example. Alternatively, this can be realized by the fiber thread  70  having elasticity. 
         [0066]    For example, when the wiring layer  10  stretches, the non-stretchable portions  10 A may rotate about the locations where attached by the fiber thread  70 , as depicted in  FIGS. 6A and 6B . Thus, it is possible to release some of the stress applied to the non-stretchable portions  10 A, and it is possible to improve the degree of freedom of the stretching of the stretchable flexible substrate  100 . 
         [0067]    For example, when the wiring layer  10  stretches, the non-stretchable portions  10 A may displace in a predetermined direction with respect to the base material  50 . For example, a design may be implemented in such a way that, when viewed from a direction perpendicular to a main surface of a non-stretchable portion  10 A, it is possible for the location where the fiber thread  70  passes through the non-stretchable portion  10 A and the location where the fiber thread  70  passes through the base material  50  to deviate. Thus, it is possible to release some of the stress applied to the non-stretchable portions  10 A, and it is possible to improve the degree of freedom of the stretching of the stretchable flexible substrate  100 . 
         [0068]    The fiber thread  70  may sew the centers of the non-stretchable portions  10 A and the base material  50  together. When a plurality of stretchable strips  10 B connected to a non-stretchable portion  10 A stretch, the non-stretchable portion  10 A may rotate about the fiber thread  70 . In other words, a plurality of stretchable strips  10 B connected to a certain non-stretchable portion  10 A may be arranged in a rotationally symmetrical manner about the fiber thread  70  attached to that non-stretchable portion  10 A. The rotational symmetry may be point symmetry, for example. Thus, when a rotational force is applied to the non-stretchable portion  10 A due to the plurality of stretchable strips  10 B stretching, for example, the non-stretchable portion  10 A rotates, and stress can thereby be efficiently released. As a result, it is possible to improve the degree of freedom of the stretching of the stretchable flexible substrate  100 . Here, the “center” is not restricted to the exact center. For example, when viewed from a direction perpendicular to a main surface of a non-stretchable portion  10 A, in the case where the fiber thread  70  is arranged in such a way as be applied in a predetermined region of the non-stretchable portion  10 A, this predetermined region corresponds to the “center”. 
         [0069]    The “plurality of stretchable strips  10 B being arranged in a rotationally symmetrical manner” is not restricted to strict rotational symmetry. For example, in the case where the shape of the non-stretchable portions  10 A does not have rotational symmetry, the plurality of stretchable strips  10 B may have rotational symmetry excluding the sections connecting with the non-stretchable portions  10 A. 
         [0070]    The fiber thread  70  may be electrically conductive. For example, an electrically conductive member on the front surface of the wiring layer  10  and an electrically conductive member on the rear surface may be electrically connected by way of the fiber thread  70 . Alternatively, an electrically conductive member within the wiring layer  10  and an electrically conductive member within the base material  50  may be electrically connected by way of the fiber thread  70 . Since a fiber thread  70  that is electrically conductive is a comparatively light conductor, the stretchable flexible substrate  100  can therefore be made lighter. Furthermore, with a fiber thread  70  that is electrically conductive, it is possible for electric resistance to be adjusted in a comparatively simple manner by changing, as appropriate, the way in which sewing is carried out (for example, the number of turns of the thread) or the like. 
         [0071]    A fiber thread that is electrically conductive may be, for example, a metal fiber, a coated fiber, an electrically conductive polymer fiber, or a thread that has been formed, configured, or processed from these. For example, a metal fiber may include at least one type of metal selected from the group consisting of gold (Au), silver (Ag), copper (Cu), nickel (Ni), chromium (Cr), cobalt (Co), magnesium (Mg), calcium (Ca), platinum (Pt), molybdenum (Mo), iron (Fe), and zinc (Zn). A coated fiber may be formed by coating a thread or fiber that includes at least one of a polymer, carbon, and cotton with the above mentioned metal. An electrically conductive polymer fiber may be polyacetylene, polyparaphenylene, polyaniline, polythiophene, polyparaphenylene vinylene, and/or polypyrrole, for example. 
         [0072]    One exemplary configuration of the stretchable flexible substrate  100  will be described in detail.  FIG. 7A  schematically depicts a stretchable flexible substrate  100  provided with a wiring layer  10  that includes curved stretchable strips  10 B, and a base material  50  configured from a fiber fabric.  FIGS. 7B and 7C  depict cross sections along VIIB and VIIC in  FIG. 7A .  FIG. 7B  is a cross-sectional drawing of when the stretchable flexible substrate  100  is not extended.  FIG. 7C  is a cross-sectional drawing of when the stretchable flexible substrate  100  is extended. 
         [0073]    In the wiring layer  10 , a plurality of non-stretchable portions  10 A are arranged in a two-dimensional matrix form, and a plurality of stretchable strips  10 B link the non-stretchable portions  10 A. In other words, the non-stretchable portions  10 A are arranged in positions corresponding to intersecting points of the plurality of stretchable strips  10 B. The plurality of non-stretchable portions  10 A are scattered in an island-like manner. Electronic components  80  may be mounted on the non-stretchable portions  10 A. The plurality of stretchable strips  10 B curve in a serpentine shape between the non-stretchable portions  10 A. 
         [0074]    As depicted in  FIG. 7B , the wiring layer  10  includes an insulating base material  12  and electrically conductive wiring  16 , and these are layered on each another. A polyimide film may be used as the insulating base material  12 , and pattern-formed copper foil may be used as the electrically conductive wiring  16 , for example. The fiber thread  70  may sew the non-stretchable portions  10 A of the wiring layer  10  and the base material  50  together. 
         [0075]    When an external tensile force is applied to the stretchable flexible substrate  100 , the stretchable strips  10 B of the wiring layer  10  extend and bend, thereby causing the stretchable flexible substrate  100  to stretch, as depicted in  FIG. 7C . At such time, if the base material  50  is a fiber fabric, plastic deformation of the wiring layer  10  is prevented by the elastic force (in other words, the reaction force) of the fiber fabric. As a result, a breakage or disconnection of the wiring layer  10  can be prevented. 
         [0076]    The base material  50  is a fiber fabric, for example. The fiber fabric is made of a chemical fiber and/or a natural fiber. 
         [0077]    The chemical fiber may be a synthetic fiber, a semisynthetic fiber, a regenerated fiber, and/or an inorganic fiber. Possible examples of the synthetic fiber are an aliphatic polyamide fiber (for example, a nylon  6  fiber and a nylon  66  fiber), an aromatic polyamide fiber, a polyvinyl alcohol fiber (for example, a vinylon fiber), a polyvinylidene chloride fiber, a polyvinyl chloride fiber, a polyester fiber (for example, a polyester fiber, a PET fiber, a PBT fiber, and a polyarylate fiber), a polyacrylonitrile fiber, a polyethylene fiber, a polypropylene fiber, a polyurethane fiber, a phenol fiber, a polyfluoroethylene fiber, and the like. Possible examples of the semisynthetic fiber are a cellulose fiber, a protein fiber, and the like. Possible examples of the regenerated fiber are a rayon fiber, a cupra fiber, a lyocell fiber, and the like. Also, possible examples of the inorganic fiber are a glass fiber, a carbon fiber, a ceramic fiber, a metal fiber, and the like. 
         [0078]    The natural fiber may be a plant fiber, an animal fiber, or a mixed fiber thereof. Possible examples of a plant fiber are cotton, hemp (for example, flax and ramie), and the like. Possible examples of an animal fiber are hair (for example, sheep wool, angora, cashmere, and mohair), silk, plumage (for example, down and feathers), and the like. 
         [0079]    The fiber itself that is used for the fiber fabric may be a short fiber or a long fiber, or also may be a hollow fiber. Furthermore, the fiber that is used for the fiber fabric may have a thread form, or a twisted thread form in which fibers are intertwined, for example. The fiber, or a thread made of the fiber, may itself have elastic characteristics. 
         [0080]    The fiber fabric may be any of a fiber woven material, a fiber knitted material, and a non-woven fabric. That is, the fiber fabric may be a woven material into which so-called warp threads and weft threads have been woven in such a way as to intersect, or may be a mesh material into which threads are woven in such a way as to bend. Alternatively, the fiber fabric may be a non-woven fabric (for example, a needle-punch fabric or a spunbond fabric). 
         [0081]    The base material  50  may be a material that deforms when pulled, practically returns to the original shape when deloaded, and when the amount of deformation caused by pulling exceeds a predetermined level, the reaction force (in other words, the elastic force) rapidly increases. Thus, it is possible to prevent the wiring layer  10  coming to plastically deform when the stretchable flexible substrate is extended, and it is possible to prevent a breakage and/or disconnection of the wiring layer  10 . This kind of material, for example, is configured from bent fiber threads and is able to flexibly extend due to the bending deformation, and the reaction force (in other words, the elastic force) rapidly increases when the bending is completely extended. 
         [0082]    The fiber fabric may have a knitted structure such as that depicted in  FIGS. 8A and 8B , for example. A material having a knitted structure is knitted while adjacent fiber threads are entwined together. In a knitted structure, when focusing on a single fiber thread, the fiber thread is entwined with adjacent fiber threads in an alternating manner while forming a serpentine shape as depicted in the drawings. Since the fiber thread has a serpentine shape, an extension allowance with respect to tension is sufficiently ensured. Knitted structures, for example, are used as material for sweaters, jerseys, stockinette stitch shirts, or the like. A material having this kind of knitted structure has abundant flexibility and stretchability in regions in which the amount of extension is comparatively small, and when extension advances and a state is entered in which the fiber threads are more or less completely extended, the reaction force rapidly increases and further extension becomes difficult. 
         [0083]    The fiber fabric may have a net structure such as that depicted in  FIGS. 9A and 9B , for example. In a material having a net structure, fiber threads are tied at intersecting points to form a lattice shape, and fiber threads linking lattice points form a serpentine shape having allowance. The fiber threads of the net structure have a serpentine shape when not extended, and when completely extended, the reaction force rapidly increases, and further extension becomes difficult. 
       MODIFIED EXAMPLES 
       [0084]      FIG. 10A  depicts a first modified example of the stretchable flexible substrate  100 , and  FIG. 10B  depicts a cross section near a non-stretchable portion  10 A depicted in  FIG. 10A . In the first modified example, the electrically conductive wiring  16  of the non-stretchable portion  10 A is constituted by an electrically conductive pad, and the fiber thread  70  passes through this electrically conductive pad. In the case where the electrically conductive pad is formed of a comparatively hard metal, sewing by means of the fiber thread  70  can be easily carried out. 
         [0085]      FIG. 10C  depicts a second modified example of the stretchable flexible substrate  100 , and  FIG. 10D  depicts a cross section near a non-stretchable portion  10 A depicted in  FIG. 10C . In the second modified example, an opening  17  that passes through an electrically conductive pad is provided in the non-stretchable portions  10 A. The fiber thread  70  passes through this opening  17 . The non-stretchable portions  10 A are able to displace to a small extent from a predetermined location on the base material  50  in accordance with the size of this opening  17 . Thus, it is possible to release some of the stress applied to the non-stretchable portions  10 A, and it is possible to improve the degree of freedom of the stretching of the stretchable flexible substrate  100 . Furthermore, in the case where the electrically conductive pad is formed of a comparatively hard metal, sewing by means of the fiber thread  70  can be easily carried out. It should be noted that the opening  17  may pass through the entirety of the wiring layer  10 , as depicted in  FIG. 10E . 
         [0086]      FIG. 11A  depicts a third modified example of the stretchable flexible substrate  100 . For convenience,  FIG. 11A  depicts a cross section that passes through the center of the non-stretchable portions  10 A and follows a direction in which the stretchable strips  10 B extend. In the third modified example, the wiring layer  10  has electrically conductive wiring  16  on both of the front surface side and rear surface side of the insulating base material  12 . The degree of freedom of the wiring pattern of the wiring layer  10  thereby increases. In addition, in the case where the fiber thread  70  is electrically conductive, the fiber thread  70  is able to electrically connect the electrically conductive wiring  16  on the front surface side and the electrically conductive wiring  16  on the rear surface side. 
         [0087]      FIG. 11B  depicts a fourth modified example of the stretchable flexible substrate  100 . For convenience,  FIG. 11B  depicts a cross section that passes through the center of the non-stretchable portions  10 A and follows a direction in which the stretchable strips  10 B extend. In the fourth modified example, a fiber thread  70  that is electrically conductive is wound around the base material  50 , and a portion of this wound fiber thread  70  that is exposed on the rear surface of the base material  50  functions as a rear surface electrode  70 A. The degree of design freedom of the stretchable flexible substrate  100  thereby increases. 
         [0088]      FIG. 11C  depicts a fifth modified example of the stretchable flexible substrate  100 . For convenience,  FIG. 11C  depicts a cross section that passes through the center of the non-stretchable portions  10 A and follows a direction in which the stretchable strips  10 B extend. In the fifth modified example, a plurality of the wiring layers  10  are layered on the base material  50 , and the plurality of wiring layers  10  are sewed to the base material  50  by the fiber thread  70  passing therethrough. Thus, the circuit density per unit area can be increased, and the degree of design freedom of the stretchable flexible substrate  100  increases. 
         [0089]      FIG. 11D  depicts a sixth modified example of the stretchable flexible substrate  100 . For convenience,  FIG. 11D  depicts a cross section that passes through the center of the non-stretchable portions  10 A and follows a direction in which the stretchable strips  10 B extend. In the sixth modified example, a fiber thread  70  that is electrically conductive passes through a plurality of separated adjacent wiring layers  10 , and sews the wiring layers  10  and the base material  50  together. Thus, the fiber thread  70  electrically connects the plurality of separated adjacent wiring layers  10 . 
         [0090]    The present disclosure is not restricted to a specific example described in the above mentioned embodiment or modified examples thereof, and also includes modes in which an alteration, substitution, addition, omission, combination, or the like has been implemented thereto as appropriate. 
         [0091]    A stretchable flexible substrate of the present disclosure is able to be used in the field of electronic devices, the field of wearable devices, the health care field, the medical field, and the nursing field.