Wiring board and method for manufacturing wiring board

A wiring board on which electronic components are mountable includes a stretchable portion having stretchability and having a first surface and a second surface opposite to the first surface, and an interconnection wire electrically connected to the electronic components mounted on the wiring board. The stretchable portion includes first regions lined up in each of a first direction and a second direction, a second region including first portions and second portions, and a third region surrounded by the second region. The first regions overlap the electronic components. The first portion extends from one of two first regions neighboring each other in the first direction to the other thereof. The second portion extends from one of two first regions neighboring each other in the second direction to the other thereof. The second region has a lower modulus of elasticity than the first region. The interconnection wire overlaps the second region.

BACKGROUND OF THE INVENTION

Technical Field

Embodiments of the present disclosure relate to a wiring board including a stretchable portion having stretchability and an interconnection wire and a method for manufacturing the wiring board.

Background Art

In recent years, research has been conducted on electronic devices having deformability, such as stretchability. For example, PTL1describes a wiring board including a substrate and an interconnection wire provided on the substrate and having stretchability. In PTL 1, a manufacturing method is employed in which circuitry is provided on a substrate that has been stretched in advance and, after the circuitry is formed, the substrate is relaxed.

CITATION LIST

Patent Literature

SUMMARY OF THE INVENTION

When the substrate is stretched by applying tensile stress to the substrate in first and second directions and, thereafter, the substrate is relaxed after the interconnection wire is disposed on the substrate, a plurality of wrinkles aligned in the first and second directions are generated on the wiring board having the substrate and the interconnection wire. In this case, the wrinkles extending in the first direction interfere with the wrinkles extending in the second direction, making it difficult to control the wrinkles.

Accordingly, the embodiments of the present disclosure provide a wiring board and a method for manufacturing the wiring board capable of effectively solving the problem.

According to an embodiment of the present disclosure, a wiring board on which electronic components are mountable is provided. The wiring board includes a stretchable portion having stretchability and having a first surface and a second surface opposite to the first surface and an interconnection wire that is located adjacent to the first surface of the stretchable portion and that is electrically connected to the electronic components mounted on the wiring board. The stretchable portion includes a plurality of first regions lined up in each of a first direction and a second direction that intersects the first direction, where each of the first region overlaps an electronic component mounted on the wiring board when viewed in a direction normal to the first surface of the stretchable portion, a plurality of second regions including first portions and second portions, where the first portion extends from one of two first regions neighboring each other in the first direction to the other thereof among the plurality of first regions, where the second portion extends from one of two first regions neighboring each other in the second direction to the other thereof among the plurality of first regions, where the second region has a lower modulus of elasticity than the first region, and a third region surrounded by the second regions. The interconnection wire overlaps the second region when viewed in the direction normal to the first surface of the stretchable portion.

In the wiring board according to an embodiment of the present disclosure, the stretchable portion may include a first member located in the first region and a second member that overlaps the first member in the first region and extends over the first regions and the second regions. The second member may have a lower modulus of elasticity than the first member.

According to an embodiment of the present disclosure, a wiring board including a stretchable portion and an interconnection wire is provided. The stretchable portion has stretchability. The stretchable portion has a first surface and a second surface opposite to the first surface. The stretchable portion includes a plurality of first regions lined up in each of a first direction and a second direction that intersects the first direction and each including a first member, a plurality of second regions including first portions and second portions and including a second member having a lower modulus of elasticity than the first member, where the first portion extends from one of two first regions neighboring each other in the first direction to the other thereof among the plurality of first regions, where the second portion extends from one of two first regions neighboring each other in the second direction to the other thereof among the plurality of first regions, and a third region surrounded by the second regions. The interconnection wire is located adjacent to the first surface of the stretchable portion and overlaps at least the second region when viewed in a direction normal to the first surface of the stretchable portion.

In the wiring board according to an embodiment of the present disclosure, the first member of the stretchable portion may be located adjacent to the first surface of the stretchable portion. The first member of the stretchable portion may be disposed so as to appear on neither the first surface nor the second surface of the stretchable portion. The first member of the stretchable portion may be located adjacent to the second surface of the stretchable portion. The first member of the stretchable portion may be disposed on a surface of the second member.

In the wiring board according to an embodiment of the present disclosure, the second member of the stretchable portion may contain thermoplastic elastomer, silicone rubber, urethane gel, or silicone gel.

According to an embodiment of the present disclosure, the wiring board may further include a support portion located between the interconnection wire and the first surface of the stretchable portion. The support portion may have a crest portion and a valley portion respectively corresponding to a crest portion and a valley portion of an undulating portion of the interconnection wire, and the support portion may support the interconnection wire. In this case, the wiring board may further include an adhesive layer that joins the stretchable portion to the support portion. The first member of the stretchable portion may be in contact with the adhesive layer in an in-plane direction of the wiring board.

In the wiring board according to an embodiment of the present disclosure, the stretchable portion may further include an adhesive layer located between the interconnection wire and the second member. The first member of the stretchable portion may be located closer to the interconnection wire than a surface of the second member adjacent to the interconnection wire and may be in contact with the adhesive layer in an in-plane direction of the wiring board.

The wiring board according to an embodiment of the present disclosure may further include a support portion located between the interconnection wire and the adhesive layer. The support portion may have a crest portion and a valley portion respectively corresponding to a crest portion and a valley portion of an undulating portion of the interconnection wire, and the support portion may support the interconnection wire. The first member of the stretchable portion may be in contact with the support portion.

In the wiring board according to an embodiment of the present disclosure, the first member of the stretchable portion may contain polyimide, polyethylene naphthalate, polycarbonate, acrylic resin, or polyethylene terephthalate.

The wiring board according to an embodiment of the present disclosure may further include a plurality of stretch control portions lined up along at least one of the first portion and the second portion of the second region when viewed in the direction normal to the first surface of the stretchable portion, and the stretch control portions may have a higher modulus of elasticity than the second region.

In the wiring board according to an embodiment of the present disclosure, the third region of the stretchable portion may have a hole that penetrates the stretchable portion.

The wiring board according to an embodiment of the present disclosure may further include an insulating layer that overlaps the second region when viewed in the direction normal to the first surface of the stretchable portion, and the insulating layer may be located on the interconnection wire.

According to an embodiment of the present disclosure, a wiring board includes a stretchable portion having stretchability, where the stretchable portion has a first surface and a second surface opposite to the first surface, and an interconnection wire. The interconnection wire includes a plurality of first interconnection wires located adjacent to the first surface of the stretchable portion and extending in a first direction and a plurality of second interconnection wires located adjacent to the first surface of the stretchable portion and extending in a second direction that intersects the first direction, and the second interconnection wires intersect the first interconnection wires.

In the wiring board according to an embodiment of the present disclosure, the interconnection wire may include an undulating portion in which a crest portion and a valley portion in a direction normal to the first surface of the stretchable portion repeatedly appear in an in-plane direction of the first surface of the stretchable portion.

In the wiring board according to an embodiment of the present disclosure, the undulating portion of the interconnection wire may have an amplitude greater than or equal to 1 μm.

The wiring board according to an embodiment of the present disclosure may further include a support portion located between the interconnection wire and the first surface of the stretchable portion. The support portion may have a crest portion and a valley portion respectively corresponding to the crest portion and the valley portion of the undulating portion of the interconnection wire, and the support portion may support the interconnection wire.

In the wiring board according to an embodiment of the present disclosure, the support portion may have a thickness of less than or equal to 10 μm.

In a wiring board according to an embodiment of the present disclosure, the stretchable portion may have a thickness greater than a thickness of the support portion.

The wiring board according to an embodiment of the present disclosure may further include an electronic component electrically connected to the interconnection wire.

According to an embodiment of the present disclosure, a method for manufacturing a wiring board on which electronic components are mountable is provided. The method includes a step of preparing a stretchable portion having stretchability and having a first surface and a second surface opposite to the first surface, a stretch step of stretching the stretchable portion, a wiring step, and a contraction step. The stretchable portion includes a plurality of first regions lined up in each of a first direction and a second direction that intersects the first direction, a plurality of second regions including first portions and second portions, and a third region surrounded by the second regions. The first regions overlap the electronic components mounted on the wiring board when viewed in a direction normal to the first surface of the stretchable portion The second region has a lower modulus of elasticity than the first region. The first portion extends from one of two first regions neighboring each other in the first direction to the other of the two first regions among the plurality of first regions. The second portion extends from one of two first regions neighboring each other in the second direction to the other of the two first regions among the plurality of first regions. In the stretch step, the stretchable portion is stretched by applying tensile stress to the stretchable portion in at least two of in-plane directions of the first surface of the stretchable portion. In the wiring step, an interconnection wire to be electrically connected to the electronic components mounted on the wiring board is disposed on the first surface of the stretchable portion that is stretched so as to overlap the second region when viewed in the direction normal to the first surface of the stretchable portion. In the contraction step, the tensile stress is removed from the stretchable portion.

According to an embodiment of the present disclosure a method for manufacturing a wiring board includes a step of preparing a stretchable portion having stretchability and having a first surface and a second surface opposite to the first surface, a stretch step of stretching the stretchable portion, a wiring step, and a contraction step. The stretchable portion includes a plurality of first regions lined up in each of a first direction and a second direction that intersects the first direction and each having a first member, a plurality of second regions including first portions and second portions and including a second member having a lower modulus of elasticity than the first member, and a third region surrounded by the first regions and the second regions. The first portion extends from one of two first regions neighboring each other in the first direction to the other thereof among the plurality of first regions. The second portion extends from one of two first regions neighboring each other in the second direction to the other thereof among the plurality of first regions. In the stretch step, the stretchable portion is stretched by applying tensile stress to the stretchable portion in at least two of in-plane directions of the first surface of the stretchable portion. In the wiring step, the interconnection wire is disposed on the first surface of the stretchable portion that is stretched so as to overlap the second region when viewed in a direction normal to the first surface of the stretchable portion. In the contraction step the tensile stress is removed from the stretchable portion.

In the method for manufacturing a wiring board according to an embodiment of the present disclosure, the stretch step may be performed with the first regions clamped in a thickness direction of the stretchable portion.

According to an embodiment of the present disclosure, a method for manufacturing a wiring board includes a step of preparing a stretchable portion having stretchability and having a first surface and a second surface opposite to the first surface, a stretch step of stretching the stretchable portion by applying tensile stress to the stretchable portion in at least two of in-plane directions of the first surface of the stretchable portion, a wiring step of disposing, on the first surface of the stretchable portion that is stretched, an interconnection wire including a plurality of first interconnection wires each extending in a first direction and a plurality of second interconnection wires each extending in a second direction that intersects the first direction and intersecting the first interconnection wires, and a contraction step of removing the tensile stress from the stretchable portion.

The method for manufacturing a wiring board according to an embodiment of the present disclosure may further include a wiring preparation of disposing the interconnection wire on the support portion, and the wiring step may include a joint step of joining the support portion, on which the interconnection wire is disposed, to the first surface of the stretchable portion that is stretched.

According to the embodiments of the present disclosure, the interference between wrinkles extending in the first direction and wrinkles extending in the second direction can be removed.

DETAILED DESCRIPTION OF THE INVENTION

The structure of a wiring board and a method for manufacturing the wiring board according to an embodiment of the present disclosure are described in detail below with reference to the accompanying drawings. Note that the embodiments illustrated below are only examples of the embodiments of the present disclosure, and the present disclosure is not to be construed as limited to these embodiments. In addition, terms such as “board”, “base material”, “sheet” and “film” as used herein are not distinguished from each other based solely on differences in address term usage. For example, “board” is a concept that includes members that can be referred to as a base material, a sheet, or a film. Furthermore, the terms as used herein to identify the shape, the geometric conditions, or their degree, such as “parallel” and “orthogonal”, and the numerical values of, for example, a length and angle are not used in a strict sense, and shall be interpreted to include the extent to which similar functions can be expected, without being bound by the strict meaning. In the drawings referred to in the present embodiment, the same or similar reference signs are attached to the same parts or parts having similar functions, and descriptions of the parts may not be repeated. In addition, the dimensional proportions in the drawings may differ from the actual proportions for convenience of description, and some of the configurations may be removed from the drawings.

An embodiment of the present disclosure is described below with reference toFIGS.1to10.

A wiring board10according to the present embodiment is described first.FIG.1andFIG.2Aare a cross-sectional view and a plan view of the wiring board10, respectively. The cross-sectional view illustrated inFIG.1is a cutaway view of the wiring board10taken along line A-A ofFIG.2A.

The wiring board10illustrated inFIG.1has a support portion40provided with a plurality of electronic components51and a plurality of interconnection wires52, a stretchable portion20having stretchability, and an adhesive layer60that joins the stretchable portion20and the support portion40. Each of the constituent elements of the wiring board10is described below.

The stretchability of the support portion40is lower than that of the stretchable portion20. The support portion40has a first surface41located adjacent to the electronic components51and the interconnection wires52and a second surface42located opposite to the first surface41. In the example illustrated inFIG.1, the adhesive layer60and the stretchable portion20are located adjacent to the second surface42of the support portion40.

As described below, when the tensile stress is removed from the stretchable portion20joined to the support portion40and, thus, the stretchable portion20contracts, an undulating portion is formed in the support portion40. The characteristics and dimensions of the support portion40are set so as to facilitate the formation of such an undulating portion. For example, the thickness of the support portion40is less than the thickness of the stretchable portion20. For example, the thickness of the support portion40is less than or equal to 10 μm, and more preferably less than or equal to 5 μm. By reducing the thickness of the support portion40, the undulating portion is more easily formed in the support portion40when the stretchable portion20contracts. The support portion40may have a greater modulus of elasticity than a second region (described below) of the stretchable portion20. For example, the modulus of elasticity of the support portion40is higher than or equal to 100 MPa, and more preferably higher than or equal to 1 GPa. The modulus of elasticity of the support portion40may be 100 times or more, or 1000 times or more, than the modulus of elasticity of the second region of the stretchable portion20. By increasing the modulus of elasticity of the support portion40, the support portion40is suppressed from stretching due to a tensile force or other forces applied to the support portion40during the process of forming the electronic components51or the interconnection wires52on the support portion40or the process of joining the support portion40to the stretchable portion20. This facilitates handling of the support portion40, such as alignment of the support portion40.

For example, as the material for the support portion40, polyethylene naphthalate, polyimide, polycarbonate, acrylic resin, or polyethylene terephthalate is usable.

The modulus of elasticity of the support portion40may be less than 100 times the modulus of elasticity of the second region of the stretchable portion20. The thickness of the support portion40may be greater than or equal to 500 nm.

In the example illustrated inFIG.1, each of the plurality of electronic components51has at least an electrode that is connected to an interconnection wire52. As illustrated inFIG.1, the electronic components51may be covered by a sealing portion58made of resin or the like.

Alternatively, the electronic component51does not necessarily have to have an electrode that is connected to the interconnection wire52. For example, the electronic component51may include a member that is integrated with at least one of the plurality of constituent elements of the wiring board10. Examples of such an electronic component51include one that includes a conductive layer integrated with a conductive layer constituting an interconnection wire52of the wiring board10and one that includes a conductive layer located in a layer different from the conductive layer constituting the interconnection wire52. For example, the electronic component51may be a pad composed of a conductive layer having a wider width in plan view than the conductive layer constituting the interconnection wire52. A probe for inspection, a terminal for software rewriting, or the like is connected to the pad. Alternatively, the electronic component51may be a wiring pattern patterned to have a predetermined function. For example, the electronic component51may be a wiring pattern composed of a conductive layer extending in a spiral shape in plan view. Alternatively, the electronic component51may be a wiring pattern that extends in a meandering shape. The shape of the meandering wiring pattern is not limited to a particular shape. For example, the wiring pattern may change direction at an angle of 90°. As described above, a portion of the conductive layer that has been patterned and given a predetermined function can also be an electronic component51.

The electronic component51having an electrode may be an active component, a passive component, or a mechanical component. Examples of an electronic component51with an electrode include a transistor, an LSI (Large-Scale Integration), MEMS (Micro Electro Mechanical Systems), a relay, a light-emitting device, such as an LED, an OLED, and an LCD, a sensor, a sound-emitting component, such as a buzzer, a vibration component that emits vibration, a cooling/heating component, such as a Peltier device that controls cooling and heating or a heating wire, a resistor, a capacitor, an inductor, a piezoelectric device, a switch, and a connector. Among the above-mentioned examples of an electronic component51, a sensor is preferably used. Examples of a sensor include a temperature sensor, a pressure sensor, an optical sensor, a photoelectric sensor, a proximity sensor, a shear force sensor, a biometric sensor, a laser sensor, a microwave sensor, a humidity sensor, a strain sensor, a gyro sensor, an acceleration sensor, a displacement sensor, a magnetic sensor, a gas sensor, a GPS sensor, an ultrasonic sensor, an odor sensor, an electroencephalographic sensor, a current sensor, a vibration sensor, a pulse wave sensor, an electrocardiographic sensor, and a photometric sensor. Of these sensors, a biometric sensor is particularly desirable. Biometric sensors can measure biometric information, such as heartbeat, pulse, electrocardiogram, blood pressure, body temperature, and a blood oxygen level.

The applications of an electronic component51that does not have an electrode are described below. For example, the pad described above can function as a part to which a probe for inspection, a terminal for software rewriting, or the like is to be connected. In addition, the wiring pattern patterned to have a predetermined function can function as an antenna or the like.

As illustrated inFIG.2A, the plurality of electronic components51are lined up in each of a first direction D1and a second direction D2that intersects the first direction D1. According to the present embodiment, the first direction D1and the second direction D2are orthogonal to each other.

Each of the interconnection wires52is an electrically conductive member connected to the electrodes of the electronic components51. As illustrated inFIGS.1and2A, each of the plurality of interconnection wires52extends from one of two neighboring electronic components51to the other. According to the present embodiment, the plurality of the interconnection wires52include a first interconnection wire521extending from one of the two neighboring electronic components51to the other in the first direction D1and a second interconnection wire522extending from one of the two neighboring electronic components51to the other in the second direction D2.

As described below, when the tensile stress is removed from the stretchable portion20joined to the support portion40and, thus, the stretchable portion20contracts, the interconnection wire52deforms into an accordion shape. Accordingly, it is desirable that the interconnection wire52have a structure that is resistant to deformation. The material itself for the interconnection wire52may or may not have stretchability. Examples of a material usable for the interconnection wire52and not having stretchability by itself include metals, such as gold, silver, copper, aluminum, platinum, and chromium, and alloys containing these metals. If the material for the interconnection wire52itself does not have stretchability, a metal film is usable for the interconnection wire52. If the material used for the interconnection wire52itself has stretchability, the stretchability of the material is the same as that of the stretchable portion20, for example. For example, the interconnection wire52has a base material and a plurality of electrically conductive particles dispersed in the base material. In this case, by using a deformable material, such as resin, as the base material, the interconnection wire52can also deform in accordance with stretching and contracting of the stretchable portion20. In addition, even when deformation occurs, the conductivity of the interconnection wire52can be maintained by setting the distribution and shape of the plurality of conductive particles such that contact between the conductive particles is maintained.

For example, as a material that serves as the base material for the interconnection wire52, widely used thermoplastic elastomers and thermosetting elastomers are usable. For example, styrene elastomer, acrylic elastomer, olefin elastomer, urethane elastomer, silicone rubber, urethane rubber, fluorine rubber, nitrile rubber, polybutadiene, polychloroprene, or the like is usable. Among these, resins and rubbers containing an urethane or silicone structure is preferably used due to their stretchability and durability. In addition, as a material for the conductive particles in the interconnection wire52, particles of silver, copper, gold, nickel, palladium, platinum, carbon, or the like is usable, for example. Among others, silver particles are preferably used due to its price and conductivity.

The thickness of the interconnection wire52having the base material and the plurality of conductive particles dispersed in the base material is less than the thickness of the electronic component51. For example, the thickness is less than or equal to 50 μm. The width of the interconnection wire52having the base material and the plurality of conductive particles dispersed in the base material is, for example, greater than or equal to 50 μm and less than or equal to 10 mm.

An example of a method for forming a material that is usable for the interconnection wire52and that itself does not have stretchability is a vapor deposition method or a plating method for forming a thin metal film. The thickness of the interconnection wire52including a metal film is, for example, less than or equal to 50 μm. The width of the interconnection wire52including the metal film is, for example, greater than or equal to 10 μm.

The adhesive layer60is a layer located between the second surface42of the support portion40and the first surface21of the stretchable portion20. The adhesive layer60contains an adhesive. As the adhesive of the adhesive layer60, an acrylic adhesive or a silicone adhesive is usable, for example. The thickness of the adhesive layer60is, for example, greater than or equal to 5 μm and less than or equal to 200 μm. The second surface42of the support portion40may be joined to the first surface21of the stretchable portion20by room temperature bonding or molecular bonding. In this case, for example, as illustrated inFIG.6C, an adhesive layer does not necessarily have to be provided between the stretchable portion20and the support portion40. In this case, the first member35may be buried in the second member36. That is, the first member35may be disposed so as to appear on neither the first surface21nor the second surface22of the stretchable portion20. In addition, a primer layer may be provided on at least one of the first surface21of the stretchable portion20and the second surface42of the support portion40in order to improve the adhesiveness of room temperature bonding or molecular bonding.

The stretchable portion20is a member configured to have stretchability. The stretchable portion20includes the first surface21located adjacent to the electronic component51and the interconnection wires52and the second surface22located opposite to the first surface21. The thickness of the stretchable portion20is, for example, less than or equal to 10 mm, and more preferably less than or equal to 1 mm. By reducing the thickness of the stretchable portion20, the force required to stretch or contract the stretchable portion20can be reduced. In addition, by reducing the thickness of the stretchable portion20, the thickness of the entire body of a product using the wiring board10can be reduced. For example, if the product including the wiring board10is a sensor to be attached to a part of the body, such as a human arm, this can reduce the uncomfortableness that a person experiences when wearing the product. The thickness of the stretchable portion20may be greater than or equal to 50 μm.

Referring toFIGS.3and4Ain addition toFIGS.1and2A, the stretchable portion20is described in detail below.FIG.3is a plan view of the stretchable portion20of the wiring board10as viewed from the first surface21.FIG.4Ais a cutaway view of the wiring board10taken along line B-B ofFIG.2A. Note that line A-A and line B-B inFIG.3are illustrated in the same positions as line A-A and line B-B inFIG.2A, respectively.

As illustrated inFIG.3, the stretchable portion20has a plurality of first regions31, a plurality of second regions32, and a plurality of third regions33. The plurality of first regions31are lined up in each of the first direction D1and the second direction D2. In the example illustrated inFIG.3, the first region31has a rectangular shape with four sides and four corners.

Each of the plurality of second regions32extends from one of two neighboring first regions31to the other. According to the present embodiment, the plurality of second regions32include a first portion321extending from one of two neighboring first regions31to the other in the first direction D1and a second portion322extending from one of two neighboring first regions31to the other in the second direction D2. In the example illustrated inFIG.3, one end of the second region32is connected to one side of one of two neighboring rectangular-shaped first regions31, and the other end of the second region32is connected to one side of the other rectangular-shaped first region31. Each of the plurality of second regions32has a lower modulus of elasticity than the first region31. Note that in terms of the second region32located at an end portion of the wiring board10, one of one end and the other end of the second region32may be connected to the first region31, and the other may be a free end.

As illustrated inFIG.3, the third region33is the region surrounded by a plurality of second regions32. According to the present embodiment, the third region33is a hole37that penetrates the stretchable portion20, as illustrated inFIG.4A. Note that the contour enclosing the third region33may be partially composed of the first region31instead of entirely composed of the second region32. Note that in terms of the third region33located at the end portion of the wiring board10, two or three of the four sides are enclosed by the second region32. At this time, one or two sides may be free ends.

FIGS.4B to4Eare cross-sectional views illustrating other examples of the third region33. As illustrated inFIGS.4B and4C, in terms of the third region33, holes37may also be formed in the support portion40and the adhesive layer60. By providing, in the support portion40and the adhesive layer60, holes37that communicate with the holes37in the stretchable portion20, the wiring board itself can have air permeability. This allows the wiring board10to exhibit the effect of suppress sweaty feeling when the wiring board10is affixed to a living body.

As illustrated inFIGS.4D and4E, the second member36may also be present in the third region33. Even in this case, by forming holes in the support portion40and the adhesive layer60located in the third region33, the third region33stretches and contracts more easily than the second region32.

As illustrated inFIGS.4B and4D, each of the third regions33may be provided with a single support portion40of the third region33and a single hole37of the adhesive layer60. Alternatively, as illustrated inFIGS.4C and4E, each of the third regions33may be provided with a plurality of support portions40and a plurality of holes.

FIG.2Bis a plan view illustrating an example of the wiring board10in which a plurality of holes37are provided in one third region33as illustrated inFIGS.4C and4E. Each ofFIGS.4C and4Ecorresponds to a cutaway view of the wiring board10taken along line B-B ofFIG.2B. As illustrated inFIG.2B, the plurality of holes37in the third region33may be lined up in the first direction D1and the second direction D2.

In the case where a plurality of holes37are provided in one third region33, crest portions P1(described below) that appear on the surface of the interconnection wire52may appear at positions each overlapping one of the plurality of holes37lined up in the first direction D1when viewed in the first direction D1, as illustrated inFIG.2B. In addition, the crest portions P1may also appear at positions each overlapping one of the plurality of holes37lined up in the second direction D2when viewed in the second direction D2.

The structures of the first region31and the second region32of the stretchable portion20are described below. As illustrated inFIGS.1and2A, the stretchable portion20has a plurality of first members35each located in one of the plurality of first regions31and the second member36that overlaps the first members35in the first regions31and that extends across the first regions31and the second regions32. That is, each of the first regions31includes the first member35and the second member36stacked on top of each other, and each of the second regions32includes the second member36. In the example illustrated inFIG.1, the thickness of the second member36located in the second region32is equal to the sum of the thicknesses of the first member35and the second member36located in the first region31.

The second member36has a lower modulus of elasticity than the first member35. Therefore, the modulus of elasticity of the second region32including the second member36is lower than that of the first region31including the first member35and the second member36. For this reason, when tensile stress is applied to the stretchable portion20, the second region32stretches more easily than the first region31.

The modulus of elasticity of the first member35is, for example, greater than or equal to 100 MPa, and more preferably greater than or equal to 1 GPa. The thickness of the first member35is, for example, greater than or equal to 25 μm, and may be greater than or equal to 100 μm. In addition, the thickness of the first member35is, for example, less than or equal to 10 mm, and may be less than or equal to 1 mm. The ratio of a thickness T1of the first member35to a thickness T0of the entire first region31is, for example, greater than or equal to 5%, and may be greater than or equal to 10%. In addition, the ratio of the thickness T1of the first member35to the thickness T0of the entire first region31may be, for example, less than or equal to 100%, and may be less than or equal to 50%.

Examples of the material used for the first member35include a film material, such as polyimide, polyethylene naphthalate, polycarbonate, acrylic resin, or polyethylene terephthalate, an insulating inorganic material, such as ceramic and glass, and a metal, such as copper or aluminum.

The modulus of elasticity of the second member36is, for example, less than or equal to 10 MPa, and more preferably less than or equal to 1 MPa. The modulus of elasticity of the second member36may be greater than or equal to 1 kPa. The thickness T2of the second member36located in the second region32is, for example, greater than or equal to 25 μm, and may be greater than or equal to 100 mm. In addition, the thickness T2of the second member36located in the second region32may be, for example, less than or equal to 10 mm, and may be less than or equal to 1 mm.

Examples of the material used for the second member36include thermoplastic elastomers, silicone rubber, urethane gel, and silicone gel. As thermoplastic elastomer, one of polyurethane elastomer, styrene thermoplastic elastomer, olefin thermoplastic elastomer, vinyl chloride thermoplastic elastomer, ester thermoplastic elastomer, amide thermoplastic elastomer, 1,2-BR thermoplastic elastomer, and fluorinated thermoplastic elastomer is usable, for example. In view of the mechanical strength and abrasion resistance, it is desirable that urethane-based elastomer to be used. Furthermore, because silicone rubber has excellent heat resistance, chemical resistance, and flame retardance, silicone rubber is desirable as the material used for the stretchable portion20. In addition, in consideration of the case where the wiring board10is disposed in clothing, a fabric or non-woven fabric made of acrylic, polyester or urethane material in fiber form, woven or interwoven, is usable as the second member36. This increases the affinity between the wiring board10and clothing.

The modulus of elasticity of the first region31including the stacked first member35and second member36is, for example, greater than or equal to 100 MPa, and more preferably greater than or equal to 1 GPa. The thickness of the first region31is, for example, greater than or equal to 50 μm, and may be greater than or equal to 100 μm. In addition, the thickness of the first region31is, for example, less than or equal to 10 mm, and may be less than or equal to 1 mm.

The desirable range of the elastic modulus of the second region32is the same as the desirable range of the elastic modulus of the second member36described above. In addition, the desirable range of the thickness of the second region32is the same as the desirable range of the thickness of the second member36described above located in the second region32.

As a method for calculating the modulus of elasticity, the method for conducting a tensile test using a sample extracted from a target member can be employed. The standard of the tensile test may be selected appropriately in accordance with the target member. For example, the tensile test of samples extracted from the first member35and the support portion40may be conducted in accordance with ASTM D882. In addition, the tensile test of a sample extracted from the second member36may be conducted in accordance with JIS K6251. Alternatively, the method for measuring the modulus of elasticity of a sample by the nanoindentation technique in accordance with ISO 14577 may be employed. As a measuring instrument used in the nanoindentation technique, a nanoindenter is usable. As a method for preparing samples of the first region31and the second region32, the method for taking, as a sample, part of the first region31and the second region32of the stretchable portion20of the wiring board10or a method for taking, as a sample, a part of the first region31and the second region32before the wiring board10is configured can be employed. As a method for taking a sample of the first member35, the first member35can be separated from the second member36in a sample of the first region31, or part of the first member35can be taken as a sample before the first member35is stacked on the second member36. As another method for calculating the modulus of elasticity, the material for the target member can be analyzed and, thereafter, the modulus of elasticity can be calculated on the basis of an existing database of materials.

Another example of a parameter representing the stretchability of the stretchable portion20is the bending stiffness of the stretchable portion20. The bending stiffness is the product of the second moment of area of a target member and the modulus of elasticity of the material that forms the target member, and the unit of bending stiffness is given by N·m2or Pa·m4. The second moment of area of each region or each member of the stretchable portion20is calculated on the basis of the cross section of the stretchable portion20when the stretchable portion20is cut by a plane perpendicular to the stretching direction of the wiring board10. It is desirable that the each of the plurality of second regions32have a lower bending stiffness than the first region31.

The arrangement of the first regions31and the second regions32of the stretchable portion20is described below.

As illustrated inFIGS.1and2A, the first region31of the stretchable portion20at least overlaps the electronic component51mounted on the wiring board10. The first region31includes the first member35that has a higher modulus of elasticity than the second member36that forms the second region32. Therefore, the modulus of elasticity of the first region31is higher than that of the second region32. For this reason, when a force, such as tensile stress, is applied to the wiring board10, the first region31is less likely to undergo deformation, such as stretch or contraction, than the second region32. As a result, it is possible to suppress the stress caused by the deformation of the stretchable portion20from being applied to the electronic component51and, thus, the electronic component51is suppressed from being deformed or damaged. Note that the term “overlap” as used herein means that two constituent elements overlap when viewed in the direction normal to the first surface21of the stretchable portion20.

As illustrated inFIGS.1and4A, the second region32of the stretchable portion20overlaps the interconnection wire52. More specifically, the first portion321of the second region32overlaps the first interconnection wire521of the interconnection wire52, and the second portion322of the second region32overlaps the second interconnection wire522of the interconnection wire52.

Subsequently, the cross-sectional structure of the interconnection wire52is described in detail with reference toFIG.5.FIG.5is an enlarged cross-sectional view illustrating an example of the interconnection wire52, such as the first interconnection wire521and second interconnection wire522, and its surrounding constituent elements.

As described above, the interconnection wire52overlaps the second region32of the stretchable portion20. Consequently, the stress generated in the stretchable portion20due to stretch and construction of the second region32of the stretchable portion20is transferred to the support portion40and the interconnection wire52on the support portion40. For example, when tensile stress is removed from the stretchable portion20that is stretched and, thus, the second region32of the stretchable portion20is relaxed, compressive stress is generated in the stretchable portion20, and the compressive stress is transferred to the support portion40and the interconnection wire52on the support portion40that overlap the second region32of the stretchable portion20. As a result, as illustrated inFIG.5, an undulating portion57is generated in the interconnection wire52.

The undulating portion57includes crest portions and valley portions in the direction normal to the first surface21of the stretchable portion20. InFIG.5, a reference sign P1represents a crest portion appearing on the front surface of the interconnection wire52, and a reference sign P2represents a crest portion appearing on the back surface of the interconnection wire52. A reference sign B1represents a valley portion appearing on a front surface of the interconnection wire52, and a reference sign B2represents a valley portion appearing on a back surface of the interconnection wire52. Note that the term “front surface” refers to a surface of interconnection wire52that is located remote from the stretchable portion20, and the term “back surface” refers to a surface of interconnection wire52that is located adjacent to the stretchable portion20.

The crest portions P1and P2and valley portions B1and B2appear repeatedly in an in-plane direction of the first surface21of the stretchable portion20. For example, the crest portions P1and P2and the valley portions B1and B2of the first interconnection wire521of the interconnection wire52appear repeatedly in the first direction D1. In addition, the crest portion P1and P2and the valley portions B1and B2of the second interconnection wire522of interconnection wire52appear repeatedly in the second direction D2. A cycle F in which each of the crest portions P1and P2and each of the valley portions B1or B2repeatedly appear is, for example, greater than or equal to 10 μm and less than or equal to 100 mm.

InFIG.5, a reference sign S1represents the amplitude of the undulating portion57on the surface of the interconnection wire52. The amplitude S1is, for example, greater than or equal to 1 μm, and more preferably greater than or equal to 10 μm. By setting the amplitude S1to a value greater than or equal to 10 μm, deformation of the interconnection wire52is facilitated in accordance with stretch or contraction of the stretchable portion20. Note that the amplitude S1may be less than or equal to 500 μm, for example.

The amplitude S1is calculated by, for example, measuring the distance in the direction normal to the first surface21between every neighboring crest portion P1and valley portion B1over a certain range in the length direction of the interconnection wire52and finding their average. For example, the amplitude S1of the undulating portion57of the first interconnection wire521is calculated by measuring the distance in the direction normal to the first surface21between every neighboring crest portion P1and valley portion B1over a certain range in the first direction D1and, thereafter, finding their average. The same applies to the amplitude of the second interconnection wire522. The term “certain range” refers to, for example, a 10-mm range. As a measuring instrument for measuring the distance between neighboring crest portion P1and valley portion B1, a non-contact measuring instrument using a laser microscope or the like is usable. Alternatively, a contact measuring instrument is usable. The distance between neighboring crest portion P1and valley portion B1may be measured on the basis of an image, such as a tomographic image.

InFIG.5, a reference sign S2represents the amplitude of the undulating portion57on the back surface of the interconnection wire52. Like the amplitude S1, the amplitude S2is, for example, greater than or equal to 1 μm, and more preferably greater than or equal to 10 μm. The amplitude S2may be, for example, less than or equal to 500 μm.

As illustrated inFIG.5, the support portion40, the adhesive layer60, and the first surface21of the stretchable portion20may also have an undulating portion similar to that of the interconnection wire52. InFIG.5, a reference sign S3represents the amplitude of an undulating portion on the first surface21of the second member36of the stretchable portion20. The amplitude S3is, for example, greater than or equal to 1 μm, and more preferably greater than or equal to 10 μm. In addition, the amplitude S3may be, for example, less than or equal to 500 μm.

FIG.6Ais an enlarged cross-sectional view illustrating another example of the interconnection wire52and surrounding constituent elements of the wiring board10illustrated inFIG.1. As illustrated inFIG.6A, the undulating portion does not necessarily have to be formed on the first surface21of the second member36of the stretchable portion20.

FIG.6Bis an enlarged cross-sectional view illustrating another example of the interconnection wire52and surrounding components of the wiring board10illustrated inFIG.1. As illustrated inFIG.6B, the cycle F1of the undulating portion57on the front surface of the interconnection wire52may differ from a cycle F2of an undulating portion on the second surface22of the second member36of the stretchable portion20. For example, as illustrated inFIG.6B, the cycle F2at the second surface22of the second member36of the stretchable portion20may be greater than the cycle F1at the front surface of the interconnection wire52. Alternatively, the cycle F2may be less than the cycle F1(not illustrated).

FIG.36is an enlarged cross-sectional view of an example of the undulating portion57. InFIG.36, the reference signs M1and M2respectively represent the width of the crest portion P1and the width of the valley portion B1in the direction in which the interconnection wire52extends, when no tensile force is applied to the wiring board10. In the example illustrated inFIG.36, the width M1of the crest portion P1and the width M2of the valley portion B1are substantially the same. The ratio for the crest portion P1in the undulating portion57in the state where no tensile force is applied to the wiring board10is denoted as X1. The ratio X1is calculated by X1=M1/(M1+M2). For example, the ratio X1is greater than or equal to 0.40 and less than or equal to 0.60.

The advantage of the undulating portion57formed in the interconnection wire52illustrated inFIG.5or6is described below.

If tensile stress is applied to the wiring board10, the elastic deformation of the stretchable portion20, especially, the second region32stretches. When the stretchable portion20is stretched, the interconnection wire52deforms to reduce the undulation of the undulating portion57, that is, to flatten the accordion shape. Thus, the interconnection wire52can follow the stretching of the stretchable portion20. As a result, it is possible to suppress an increase in the total length of interconnection wire52and a decrease in the cross-sectional area of the interconnection wire52caused by the stretching of the stretchable portion20. This can suppress an increase in the resistance value of the interconnection wire52caused by the stretching of wiring board10. In addition, damage of the interconnection wire52, such as cracks, can be suppressed.

As an example, the effect of the undulating portion57of the interconnection wire52on the resistance value of the interconnection wire52is described below. As used herein, the term “first resistance value” refers to the resistance value of the interconnection wire52in a first state in which no tensile stress is applied to the stretchable portion20in the in-plane direction of the first surface21of the stretchable portion20. In addition, the term “second resistance value” refers to the resistance value of the interconnection wire52in a second state in which tensile stress is applied to the stretchable portion20to stretch the length of the stretchable portion20in the in-plane direction of the first surface21by 30% of the length in the first state. According to the present embodiment, by forming the undulating portion57in the interconnection wire52, the ratio of the absolute value of the difference between the first resistance value and the second resistance value to the first resistance value can be less than or equal to 20%, more preferably less than or equal to 10%, and even more preferably less than or equal to 5%.

FIG.37is an enlarged cross-sectional view of the wiring board10stretched by 25% when a tensile force is applied to the wiring board10in the first state in an in-plane direction of the first surface21(e.g., the first direction D1). InFIG.37, the reference sign S10represents the amplitude of the undulating portion57when the wiring board10is stretched by 25%. In addition, a reference sign F10represents the cycle of the undulating portion57when the length of the wiring board10is stretched by 25%. The amplitude S10of the undulating portion57of the 25% stretched wiring board10is, for example, less than or equal to 0.8 times the amplitude S1of the undulating portion57of the unstretched wiring board10. The amplitude S10may be less than or equal to 0.7 times or 0.6 times the amplitude S1. The amplitude S10is, for example, 0.2 times or more the amplitude S1. The amplitude S10may be 0.3 times or more, or 0.4 times or more the amplitude S1.

InFIG.37, the reference signs M10and M20respectively represent the width of the crest portion P1and the width of the valley portion B1of the undulating portion57of the 25% stretched wiring board10in the direction in which the interconnection wire52is stretched. As illustrated inFIG.37, the width M10of the crest portion P1and the width M20of the valley portion B1in the 25% stretched wiring board10are greater than the width M1of the crest portion P1and the width M2of the valley portion B1in the unstretched wiring board10, respectively.

When the wiring board10is stretched, the widths of the crest portion P1and the valley portion B1in the undulating portion57may be increased while maintaining the ratio between the widths. The ratio for the crest portion P1in the accordion-shape portion57when no tensile force is applied to the wiring board10is denoted by X2. The ratio X2is calculated by X2=M10/(M10+M20). The ratio X2is equivalent to the ratio X1described above when no tensile force is applied to the wiring board10and is, for example, greater than or equal to 0.40 and less than or equal to 0.60. In addition, the absolute value of the difference between the ratio X1and the ratio X2is, for example, less than or equal to 0.20, and may be less than or equal to 0.15, less than or equal to 0.10, less than or equal to 0.08, less than or equal to 0.06, or less than or equal to 0.04.

Examples of the measured amplitudes of the undulating portion57of the wiring board10and the measured width change ratio of each of the crest portion P1and the valley portion B1before and after the tensile force is applied are described below. In each of examples 1 and 2 described below, the material of the interconnection wire52is copper, the thickness of the interconnection wire52is 1 μm, and the width of the interconnection wire52is 200 μm. The stretch ratio of the stretchable portion20during the wiring process (described below) is 1.6. In addition, the stretch ratio of the stretchable portion20is 1.25 when measuring the amplitude of the undulating portion57and the widths of the crest portion P1and the valley portion B1with a tensile force applied to the wiring board10.

In the case where no tensile force is applied to the wiring board10

Amplitude S1of the undulating portion: 192 μmWidth M1of the crest portion P1: 254 μmWidth M2of the valley portion B1: 286 μmRatio X1for the crest portion: 254/(254+286)=0.47
In the case where a tensile force is applied to the wiring board10to stretch the wiring board10to 1.25 times its original lengthAmplitude S10of the undulating portion: 108 μmWidth M10of the crest portion P1: 296 μmWidth M20of the valley portion B1: 370 μmRatio X2for the crest portion: 296/(296+370)=0.44S10/S1=0.56

In the case where no tensile force is applied to the wiring board10

Amplitude S1of the undulating portion: 256 μmWidth M1of the crest portion P1: 322 μmWidth M2of the valley portion B1: 318 μmRatio X1of the crest portion: 322/(322+318)=0.50
In the case where a tensile force is applied to the wiring board10to stretch the wiring board10to 1.25 times its original lengthAmplitude S10of the undulating portion: 140 μmWidth M10of the crest portion P1: 386 μmWidth M20of the valley portion B1: 418 μmRatio X2of the crest portion: 386/(386+418)=0.48S10/S1=0.54

FIG.43Ais an enlarged cross-sectional view of an example of the undulating portion57. InFIG.43A, the reference signs M1and M2respectively represent the width of the crest portion P1and the width of the valley portion B1in the direction in which the interconnection wire52extends, when no tensile force is applied to the wiring board10. As illustrated inFIG.43A, the width M1of the crest portion P1may be less than the width M2of the valley portion B1. The width M1of the crest portion P1may be 0.3 times or more, 0.4 times or more, 0.5 times or more, or 0.6 times or more the width M2of the valley portion B1. In addition, the width M1of the crest portion P1may be less than or equal to 0.9 times, less than or equal to 0.8 times, or less than or equal to 0.7 times the width M2of the valley portion B1. The width M1of the crest portion P1and the width M2of the valley portion B1are calculated by separating the crest portion P1from the valley portion B1using the midpoint of the amplitude S1of the undulating portion57as the boundary.

In addition, as illustrated inFIG.43B, the width M2of the valley portion B1in the direction in which the interconnection wire52extends when no tensile force is applied to the wiring board10may be less than the width M1of the crest portion P1. The width M2of the valley portion B1may be greater than or equal to 0.05 times or more, 0.1 times or more, 0.2 times or more, or 0.3 times or more the width M1of the crest portion P1. The width M2of the valley portion B1may be less than or equal to 0.9 times, less than or equal to 0.8 times, or less than or equal to 0.7 times the width M1of the crest portion P1.

The ratio of the width M2of the valley portion B1to the width M1of the crest portion P1decreases with increasing sum of the stiffness values of the constituent elements, such as the interconnection wire52and the support portion40, located adjacent to the first surface21of the stretchable portion20. Thus, the undulating portion57tends to have the shape illustrated inFIG.43B. In contrast, the ratio of the width M1of the crest portion P1to the width M2of the valley portion B1decreases with decreasing sum of the stiffness values of the constituent elements, such as the interconnection wire52and the support portion40, located adjacent to the first surface21of the stretchable portion20. Thus, the undulating portion57tends to have the shape illustrated inFIG.43A.

The applications of the wiring board10include the healthcare field, the medical field, the nursing care field, the electronics field, the sports and fitness field, the beauty field, the mobility field, the livestock and pet field, the amusement field, the fashion and apparel field, the security field, the military field, the distribution field, the education field, the construction material/furniture/decoration field, the environmental energy field, the agricultural, the forestry or fishery field, and the robotics field. For example, a product that is to be attached to a part of the human body, such as an arm, is configured using the wiring board10according to the present embodiment. Since the wiring board10can be stretched or contracted, the wiring board10can be in tight contact with the part of the human body by attaching the wiring board10to the human body with the wiring board10being stretched. For this reason, comfortable wearability can be provided. In addition, a decrease in resistance value of the interconnection wire52can be suppressed when the wiring board10is stretched, excellent electrical characteristics of the wiring board10can be achieved. In addition, since the wiring board10can be stretched or contracted, the wiring board10can be installed or assembled not only in a living body, such as the human body, but also along a curved surface or a three-dimensional shape. Examples of such a product include a vital sensor, a mask, a hearing aid, a toothbrush, an adhesive plaster, a poultice, contact lenses, an artificial arm, an artificial leg, an artificial eye, a catheter, a gauze, a medicine pack, a bandage, a disposable bioelectrode, a diaper, rehabilitation equipment, a home appliance, a display, a signage, a personal computer, a cell phone, a mouse, a loudspeaker, sportswear, a wristband, a cloth headband, a glove, a swimwear, a jockstrap, a ball, a baseball glove, a racket, a golf club, a bat, a fishing rod, a relay baton, gymnastics equipment and its grip, physical training equipment, an inner tube, a tent, swimwear, a saddlecloth, a goal net, a goal tape, an osmotic medicinal beauty mask, an electro stimulation weight loss equipment product, a pocket body warmer, an artificial nail, a tattoo, seats of an automobile, an airplane, a railway train, a boat, a bicycle, a baby buggy, a drone, and a wheelchair, an instrument panel, a tire, an interior package, an exterior package, a saddle, a steering wheel, a road, a rail, a bridge, a tunnel, a gas or water pipe, an electric wire, a tetrapod, a rope collar, a leash, a harness, an animal tag, a bracelet, a belt, etc., a haptic device (such as a game device or a controller), a luncheon mat, a ticket, a doll, a stuffed animal, cheering goods, a hat, clothes, glasses, shoes, insoles, socks/stockings, slippers, inner wear, a muffler/scarf, earmuffs, a bag, an accessory, a ring, a watch, a tie, a personal ID recognition device, a helmet, a package, an IC tag, a plastic bottle, stationery, a book, a pen, a carpet, a sofa, bedclothes, an illumination lamp, a doorknob, an arm rail, a vase, a bed, a mattress, a cushion, a curtain, a door, a window, a ceiling, a wall, a floor, a wireless power transfer antenna, a battery, plastic greenhouses, a net, a robot hand, and a robot exterior.

A method for manufacturing the wiring board10is described below. Referring toFIGS.7A to9B, a method for manufacturing the stretchable portion20of the wiring board10is described first.

A mold70for molding the stretchable portion20is prepared first.FIGS.7A and7Bare a cross-sectional view and a plan view of the mold70, respectively.

As illustrated inFIGS.7A and7B, the mold70has a base material71and a groove72formed in the base material71. As illustrated inFIG.7B, the groove72has first grooves721each extending in the first direction D1and second grooves722each extending in the second direction D2. The first groove721and the second groove722intersect with each other.

Subsequently, as illustrated inFIGS.8A and8B, the first member35is disposed in the groove72of the mold70at each of the intersections of the first grooves721and the second grooves722. Thereafter, as illustrated inFIGS.9A and9B, the grooves72of the mold70are filled with the second member36. For example, the second member36dispersed in a solvent is poured into the grooves72of the mold70. At this time, as illustrated inFIG.9A, the second member36may be poured in the grooves72until the first member35is covered by the second member36. Thereafter, the solvent is evaporated and, thus, the second member36can be set in the grooves72. Subsequently, the first member35and the second member36are removed from the grooves72of the mold70. In this manner, a stretchable portion20can be obtained having the first region31including the stacked first member35and second member36, the second region32extending between two neighboring first regions31in the first direction D1or the second direction D2, and the third region33including the hole37surrounded by the second regions32.

(Method for Manufacturing Wiring Board)

A method for manufacturing the wiring board10is described below with reference toFIGS.10(a) to10(d).

The support portion40is prepared first. Subsequently, as illustrated inFIG.10A, the electronic components51and the interconnection wires52are disposed on the first surface41of the support portion40. As a technique for disposing the interconnection wires52, a technique of printing, on the first surface41of the support portion40, a conductive paste containing the base material and conductive particles can be employed, for example.

In addition, as illustrated inFIG.10B, a stretching process is performed to stretch the stretchable portion20by applying tensile stress to the stretchable portion20. In the stretching process, first tensile stress T1is applied to the stretchable portion20. In addition, although not illustrated, second tensile stress acting in a direction that differs from the direction of the first tensile stress T1is applied to the stretchable portion20. The first tensile stress T1is a force exerted, for example, in the first direction D1, and the second tensile stress is a force exerted, for example, in the second direction D2.

The extension percentage of the stretchable portion20in the direction in which the first tensile stress T1is applied and in the direction in which the second tensile stress is applied is, for example, greater than or equal to 10% and less than or equal to 200%. The stretching process may be carried out with the stretchable portion20being heated or at room temperature. When the stretchable portion20is heated, the temperature of the stretchable portion20is, for example, higher than or equal to 50° C. and lower than or equal to 100° C.

Subsequently, as illustrated inFIG.10C, a wiring process is performed to dispose the interconnection wires52on the first surface21of the stretchable portion20that is stretched. According to the present embodiment, the wiring process includes a joining process in which the support portion40having the electronic components51and the interconnection wires52disposed therein is joined to the first surface21of the stretchable portion20that is stretched. The joining process is performed such that the electronic components51provided on the support portion40overlap the first region31of the stretchable portion20and, in addition, the interconnection wires52overlap the second region32of the stretchable portion20. In the joining process, the adhesive layer60may be provided between the stretchable portion20and the support portion40.

Thereafter, a contracting process is performed to remove the tensile stress from the stretchable portion20. This causes the stretchable portion20to contract in the first direction D1, as indicated by arrow Cl inFIG.10D. Although not illustrated, the stretchable portion20also contracts in the second direction D2. As a result, deformation also occurs in the support portion40and the interconnection wires52supported by the support portion40. For example, the undulating portion57described above is formed in the support portion40and the interconnection wires52.

When as described above, the stretchable portion20is stretched due to application of tensile stress to the stretchable portion20in the first directions D1and second direction D2and, thereafter, the stretchable portion20contracts due to removal of the tensile stress from the stretchable portion20, the undulating portion57appears in each of the first direction D1and the second direction D2. If the undulating portions57appear randomly in the support portion40and the interconnection wires52, the undulating portion57that appears in the first direction D1and the undulating portion57that appears in the second direction D2may interfere with each other at some locations of the support portion40and the interconnection wires52. In this case, due to the interference between the undulating portions57, the amplitude of the undulating portions57may be locally increased, or the cycle of the undulating portions57may be locally disordered.

Note that according to the present embodiment, the second region32of the stretchable portion20that is stretched in each of the first direction D1and the second direction D2has the first portion321extending in the first direction D1and the second portion322extending in the second direction D2. In this case, the stretching caused by the first tensile stress T1acting in the first direction D1occurs mainly in the first portion321of the stretchable portion20. Accordingly, the contraction caused by the removal of the first tensile stress T1occurs mainly in the first portion321of the stretchable portion20. In addition, the stretching caused by the first tensile stress acting in the second direction D2occurs mainly in the second portion322of the stretchable portion20. Accordingly, the contraction caused by the removal of the second tensile stress occurs mainly in the second portion322of the stretchable portion20.

As described above, according to the present embodiment, since contraction in the first portion321of the stretchable portion20mainly occurs in the first direction D1, the undulating portion57extending in the first direction D1is likely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. However, the undulating portion57extending in the second direction D2is unlikely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. Similarly, since the second portion322of the stretchable portion20contracts mainly in the second direction D2, the undulating portion57that extends in the second direction D2is likely to appear in the support portion40overlapping the second portion322and in the second interconnection wire522. However, the undulating portion57that extends in the first direction D1is unlikely to appear in the support portion40overlapping the second portion322and in the second interconnection wire522. As described above, according to the present embodiment, it is possible to control the direction of the undulating portion57that preferentially appears in each of the first interconnection wire521and the second interconnection wire522. As a result, it is possible to control the occurrence of interference between the undulating portions57that appear in different directions. Therefore, it is possible to suppress the amplitude of the undulating portion57from being locally increased or the cycle of the undulating portion57from being locally disordered. For example, as can be seen from Examples described below, the standard deviation of the cycles of the undulating portions57can be controlled to a value less than ¾ of the average value of the cycles, and more preferably less than ½ of the average value. Note that according to the present embodiment, since the undulating portion57is generated by contraction of the stretchable portion20, it is not easy to set the standard deviation of the cycles of the undulating portion57to zero. The standard deviation of the cycles of the undulating portion57is, for example, greater than or equal to 1/50 of the average value of the cycles, which may be greater than or equal to 1/10 or greater than or equal to ¼.

In addition, according to the present embodiment, the first region31having a higher modulus of elasticity than the second region32is located between the first portion321and the second portion322in the second region32. As a result, when the stretchable portion20is stretched or when the wiring board10having the stretchable portion20and the support portion40therein is stretched, transfer of the stress generated in the first portion321to the second portion322can be suppressed. In addition, transfer of the stress generated in the second portion322to the first portion321can be suppressed. This can also contribute to controlling the direction of the undulating portion57that appears in each of the first interconnection wire521and the second interconnection wire522.

It should be noted that various changes can be made to the above-described embodiment. Modifications are described below with reference to the accompanying drawings as needed. In the following description and the drawings used in the following description, parts that can be configured in the same manner as in the above-described embodiment are identified by the same reference signs as those used for the corresponding parts in the above-mentioned embodiment, and duplicated description is not provided. In addition, if it is clear that the effect obtained in the above-mentioned embodiment can also be obtained in the modification, description of the effect may not be provided herein.

FIGS.11and12are a cross-sectional view and a plan view of a wiring board10according to the first modification, respectively. The cross-sectional view illustrated inFIG.11is a cutaway view of the wiring board10taken along line A-A ofFIG.12. The wiring board10may further include a plurality of stretch control portions39that line up along at least one of the first portion321and the second portion322in the second region32when viewed in the direction normal to the first surface21of the stretchable portion20. In the example illustrated inFIG.12, the stretch control portions39have a plurality of first control portions391that line up in the first direction D1in which the first portion321extends and that overlap the first portion321and a plurality of second control portions392that line up in the second direction D2in which the second portion322extends and that overlap the second portion322. Each of the stretch control portions39, such as the first control portions391and the second control portions392, is a member for controlling the cycle of the undulating portion57that appears in the interconnection wire52.

According to the present modification, the stretch control portion39is part of the stretchable portion20. For example, like the first member35, the stretch control portion39constitutes part of the first surface21of the stretchable portion20.

The stretch control portion39may have a higher modulus of elasticity than the second region32, such as the first portion321or the second portion322. The modulus of elasticity of the stretch control portion39is, for example, greater than or equal to 100 MPa and less than or equal to 500 GPa, and more preferably greater than or equal to 1 GPa and less than or equal to 300 GPa. By providing such stretch control portions39in the wiring board10, it is possible to suppress a portion of the wiring board10that overlaps the stretch control portions39from stretching or contracting. In this manner, the wiring board10can be divided into portions in which stretching and contracting are likely to occur and portions in which expansion and contraction are less likely to occur. As a result, the cycle and amplitude of the undulating portion57that appears on the wiring board10can be controlled.

If a second modulus of elasticity of the stretch control portion39is higher than the modulus of elasticity of the second region32, a metallic material, for example, is usable as a material for the stretch control portion39. Examples of the metallic material include copper, aluminum, and stainless steel. Alternatively, as the material used for the stretch control portion39, any one of the following materials is usable: widely used thermoplastic elastomer, acrylic oligomer or polymer, urethane oligomer or polymer, epoxy oligomer or polymer, polyester oligomer or polymer, vinyl ether oligomer or polymer, polyene/thiol oligomer or polymer, and silicone oligomer or polymer. Alternatively, as the material of the stretch control portion39, the same material as that of the first member35of the first region31is usable. The thickness of the stretch control portion39is, for example, greater than or equal to 1 μm and less than or equal to 100 μm.

However, the modulus of elasticity of the stretch control portion39may be less than or equal to the modulus of elasticity of the second region32. For example, the modulus of elasticity of the stretch control portion39may be less than or equal to 10 MPa and may be less than or equal to 1 MPa. The modulus of elasticity of the stretch control portion39may be less than or equal to 1 times the elastic modulus of the second region32or may be less than or equal to 0.8 times the elastic modulus of the second region32. In this case, as compared with the case where the second elastic modulus of the stretch control portion39is greater than the modulus of elasticity of the second region32, the amplitude of the undulating portion that appears in the interconnection wire52overlapping the second region32is increased and, thus, the stretchability of the wiring board10is increased. Even when the modulus of elasticity of the stretch control portion39is less than or equal to that of the second region32, a difference in stretchability is generated between part of the stretchable portion20that overlaps the stretch control portion39and part of the stretchable portion20that does not overlap the stretch control portion39. That is, the stretchable portion20can be partitioned into part that is easily stretched and contracted and part that is not easily stretched and contracted. As a result, the cycle and amplitude, for example, of the undulating portion that appears in the interconnection wire52overlapping the stretchable portion20can be controlled.

If the second modulus of elasticity of the stretch control portion39is less than or equal to the modulus of elasticity of the second region32, widely used thermoplastic elastomer and thermosetting elastomer are usable as the material of the stretch control portion39. Examples of the material include styrene elastomer, acrylic elastomer, olefinic elastomer, urethane elastomer, silicone rubber, urethane rubber, fluorine-contained rubber, nitrile rubber, polybutadiene, and polychloroprene. The thickness of the stretch control portion39is, for example, greater than or equal to 1 μm and less than or equal to 100 μm.

FIG.13is an enlarged cross-sectional view illustrating an example of the interconnection wire52, such as the first interconnection wire521and second interconnection wire522, and its surrounding constituent elements. According to the present modification, the second region32of the stretchable portion20can be partitioned into a portion that is likely to stretch and contract and a portion that is less likely to stretch and contract in the direction in which the second region32extends. In this case, when the second region32is relaxed, the undulating portion57having a cycle F corresponding to the cycle of the stretch control portion39is easily generated in the interconnection wire52, as illustrated inFIG.13. That is, the cycle F of the undulating portion57can be controlled by the stretch control portion39.

While the first modification has been described with reference to the example of the stretch control portion39being part of the stretchable portion20, the structure and the location of the stretch control portion39are not limited thereto. For example, as illustrated inFIG.14, the plurality of stretch control portions39may be provided on the interconnection wire52.

While the embodiment and the modifications above have been described with reference to the example in which the first member35included in the first region31of the stretchable portion20partially constitutes the first surface21of the stretchable portion20, the structure is not limited thereto. As illustrated inFIG.15A, the first member35included in the first region31of the stretchable portion20may be disposed so as to partially constitute the second surface22of the stretchable portion20. Alternatively, as illustrated inFIG.15B, the first member35included in the first region31of the stretchable portion20may be disposed so as to appear on neither the first surface21nor the second surface22of the stretchable portion20. In addition, although not illustrated, the first member35included in the first region31of the stretchable portion20may extend throughout the entire thickness of the stretchable portion20, from the first surface21to the second surface22of the stretchable portion20. The first member35included in the first region31of the stretchable portion20may be disposed on a surface of the second member36. For example, as illustrated inFIG.15C, the first member35included in the first region31of the stretchable portion20may be disposed on the surface of the second member36adjacent to the interconnection wire52and may be in contact with the adhesive layer60in the in-plane direction of the wiring board10. In this case, as illustrated inFIG.15C, the surface of the first member35adjacent to the interconnection wire52may be covered by the adhesive layer60or, although not illustrated, may be in contact with the second surface42of the support portion40. In addition, as illustrated inFIG.15D, the first member35included in the first region31of the stretchable portion20may be disposed on a surface of the second member36remote from the interconnection wire52.

In addition, as illustrated inFIG.15E, the first member35of the first region31may be located closer to the interconnection wire52than a surface of the second members36adjacent to the interconnection wire52and may be in contact with the adhesive layer60in the in-plane direction of the wiring board10. In this case, the adhesive layer60is thought to be a constituent element of the stretchable portion20. In the example illustrated inFIG.15E, the stretchable portion20includes the second member36, the adhesive layer60located on a surface of the second member36adjacent to the interconnection wire52, and the first members35disposed in the adhesive layer60at positions each corresponding to one of the first regions31.

In addition, as illustrated inFIG.16, the stretchable portion20may include two stacked second members36. In this case, of the two second members36, the second member36located adjacent to the interconnection wire52may be provided with the first member35having a higher modulus of elasticity than the second member36. As long as the two second members36all have a lower modulus of elasticity than the first member35, the modulus of elasticity of the two second members36may be set to any value. In the example illustrated inFIG.16, the interconnection wire52is provided on the second member36located adjacent to the interconnection wire52. An adhesive layer61and the like may be interposed between the two second members36.

FIG.17is a plan view of a wiring board10according to the present modification. As illustrated inFIG.17, a plurality of interconnection wires52may be provided between two neighboring electronic components51in the first direction D1or the second direction D2so as to extend from one of the electronic components51to the other. In this case, it is desirable that the plurality of the interconnection wires52be all disposed so as to overlap the second region32of the stretchable portion20when viewed in the direction normal to the first surface21of the stretchable portion20.

FIG.18is a plan view of the stretchable portion20of the wiring board10according to the present modification. As illustrated inFIG.18, each of corners31cof the first region31may include a portion that extends in a direction that is inclined to both the first direction D1and second direction D2.

FIG.19is a plan view of the stretchable portion20of the wiring board10according to the present modification. As illustrated inFIG.19, a corner31cof the first region31may include a curved shape.

FIG.20is a plan view of the stretchable portion20of the wiring board10according to the present modification. As illustrated inFIG.20, the third region33surrounded by the plurality of second regions32may have a shape that is at least partially curved. For example, the third region33may have a circular shape. In this case, the second region32may include a pair of end portions32eeach in contact with one of the first regions31and a central portion32clocated between the pair of end portions32e, and the width of the central portion32cmay be less than the width of the end portion32e. For example, the first portion321of the second region32includes a pair of end portions32eeach in contact with one of two first regions31lined up in the first direction D1and a central portion32clocated between the pair of end portions32e. In the second direction D2orthogonal to the first direction D1, the dimension of the central portion32cof the first portion321is less than the dimension of the end portion32eof the first portion321.

FIG.21is a plan view of a stretchable portion20of the wiring board10according to the present modification. As illustrated inFIG.21, the third region33surrounded by the plurality of second regions32may have an elliptical shape. In the example illustrated inFIG.21, the elliptical third region33has a major axis parallel to the first direction D1and a minor axis parallel to the second direction D2.

Like the seventh modification, according to the present modification, the second region32includes a pair of end portions32eeach in contact with one of the first regions31and a central portion32clocated between the pair of end portions32e, and the width of the central portion32cmay be less than the width of the end portion32e.

FIG.22is a plan view illustrating an example of a stretchable portion20of a wiring board10according to the present modification. As illustrated inFIG.22, a plurality of first regions31of the stretchable portion20are lined up in each of a first direction D1, a second direction D2, and a third direction D3. The first direction D1, the second direction D2, and the third direction D3are different directions from one another. In the example illustrated inFIG.22, the angle formed by the first direction D1and the second direction D2and the angle formed by the second direction D2and the third direction D3are each 60 degrees. In the example illustrated inFIG.22, the first region31has a hexagonal shape with six sides and six corners.

As illustrated inFIG.22, the plurality of second regions32of the stretchable portion20include a first portions321each extending from one of two neighboring first regions31to the other in the first direction D1, a second portions322each extending from one of two neighboring first regions31to the other in the second direction D2, and a third portions323each extending from one of two neighboring first regions31to the other in the third direction D3. In the example illustrated inFIG.22, one end of the second region32is connected to one side of a hexagonal shape of one of the two neighboring first regions31, and the other end of the second region32is connected to one side of a hexagon shape of the other of the first regions31. In the example illustrated inFIG.22, the third region33surrounded by the plurality of second regions32has a triangular shape.

Although not illustrated, according to the present modification, the interconnection wires52may include a first interconnection wire extending in the first direction D1so as to overlap the first portion321of the second region32, a second interconnection wire extending in the second direction D2so as to overlap the second portion322of the second region32, and a third interconnection wire extending in the third direction D3so as to overlap the third portion323of the second region32.

FIG.23is a plan view illustrating an example of a stretchable portion20of a wiring board10according to the present modification. As illustrated inFIG.23, the plurality of first regions31of the stretchable portion20are lined up in each of a first direction D1, a second direction D2, a third direction D3, and a fourth direction D4. The first direction D1, the second direction D2, the third direction D3and the fourth direction D4are different directions from one another. In the example illustrated inFIG.23, the angle formed by the first direction D1and the second direction D2and the angle formed by the third direction D3and the fourth direction D4are each 90 degrees. In addition, the angle formed by the first direction D1and the third direction D3and the angle formed by the second direction D2and the fourth direction D4are each 45 degrees. The first region31has an octagonal shape with eight sides and eight corners. Each of the spacing between two neighboring first regions31in the first direction D1and the spacing between two neighboring first regions31in the second direction D2is smaller than each of the spacing between two neighboring first regions31in the third direction D3and the spacing between two neighboring first regions31in the fourth direction D4.

As illustrated inFIG.23, the plurality of second regions32of the stretchable portion20include first portions321each extending from one of two neighboring first regions31to the other in the first direction D1, second portions322each extending from one of two neighboring first regions31to the other in the second direction D2, third portions323each extending from one of two neighboring first regions31to the other in the third direction D3, and fourth portions324each extending from one of two neighboring first regions31to the other in the fourth direction D4.

In the example illustrated inFIG.23, one end of the second region32is connected to one side of an octagonal shape of one of two neighboring first regions31, and the other end is connected to one side of an octagonal shape of the other first region31. Each of the length of the first portion321and the length of the second portion322is less than each of the length of the third portion323and the length of the fourth portion324. In addition, for one of two neighboring first regions31in each of the first and second directions D1and D2, two first portions321, two second portions322, two third portions323, and two fourth portions324are connected to the eight sides of the octagonal shape. For the other of the two neighboring first regions31in each of the first and second directions D1and D2, two first portions321and two second portions322are connected to four of the eight sides of the octagonal shape. However, the third portion323and the fourth portion324are not connected.

Although not illustrated, according to the present modification, the interconnection wires52may include a first interconnection wire extending in the first direction D1so as to overlap the first portion321of the second region32, a second interconnection wire extending in the second direction D2so as to overlap the second portion322of the second region32, a third interconnection wire extending in the third direction D3so as to overlap the third portion323of the second region32, and a fourth interconnection wire extending in the fourth direction D4so as to overlap the fourth portion324of the second region32.

FIG.24is a plan view illustrating an example of a stretchable portion20of a wiring board10according to the present modification. As illustrated inFIG.24, one first region31is surrounded by three other neighboring first regions31. A first one of the three first regions31neighbors the first region31in the first direction D1, the second one neighbors the first region31in the second direction D2, and the third one neighbors the first region31in the third direction D3. In the example illustrated inFIG.24, the angle formed by the first direction D1and the second direction D2, the angle formed by the second direction D2and the third direction D3, and the angle formed by the third direction D3and the first direction D1are each 120 degrees. The first region31has a hexagonal shape with six sides and six corners.

As illustrated inFIG.24, a plurality of second regions32of the stretchable portion20include first portions321each extending from one of two neighboring first regions31to the other in the first direction D1, second portions322each extending from one of two neighboring first regions31to the other in the second direction D2, and third portions323each extending from one of two neighboring first regions31to the other in the third direction D3.

In the example illustrated inFIG.23, one end of the second region32is connected to one side of a hexagon shape of one of two neighboring first regions31, and the other end is connected to one side of a hexagon shape of the other first region31. In the first region31, one first portion321, one second portion322, and one third portion323are connected to three of the six sides of the hexagonal shape.

Although not illustrated, according to the present modification, the interconnection wires52may include a first interconnection wire extending in the first direction D1so as to overlap the first portion321of the second region32, a second interconnection wire extending in the second direction D2so as to overlap the second portion322of the second region32, and a third interconnection wire extending in the third direction D3so as to overlap the third portion323of the second region32.

According to the above-described embodiment and each of the modifications, an example has been described in which the third region33of the stretchable portion20includes the hole37that penetrates the stretchable portion20. However, the structure of the third region33is not particularly limited provided that the stress generated in the first portion321can be suppressed from being transferred to the second portion322and, in addition, the stress generated in the second portion322can be suppressed from being transferred to the first portion321. For example, as illustrated inFIG.25, the third region33may include a third member38.FIG.26is a cross-sectional view of the stretchable portion20taken along line C-C ofFIG.25. The third region33including the third member38has a lower bending stiffness than the second region32. For example, the third member38of the third region33is a member that is integrated into the second member36by using the same material as the second member36and that has a smaller thickness than the second member36.

The twelfth modification above has been described with reference to an example in which the third member38of the third region33has a smaller thickness than the second member36of the second region32. However, in the wiring board10provided with the stretchable portion20, the second region32and the third region33of the stretchable portion20may have any configuration, provided that the portion that overlaps the second region32has a higher bending stiffness than the portion that overlaps the third region. For example, the third member38of the third region33is a member that is integrated into the second member36by using the same material as the second member36and that has the same thickness as the second member36.

FIG.27is a cross-sectional view of the wiring board10including the stretchable portion20taken along line D-D ofFIG.25.FIG.28is a cross-sectional view of the wiring board10including the stretchable portion20taken along line E-E ofFIG.25. As illustrated inFIGS.27and28, the third member38of the third region33is a member that is integrated into the second member36by using the same material as the second member36and that has the same thickness as the second member36. In addition, an insulating layer59is provided on the interconnection wire52that overlaps the first portion321of the second region32. This allows the bending stiffness of a portion of the wiring board10that overlaps the second region32to be higher than the bending stiffness of a portion of the wiring board10that overlaps the third region33.

Examples of a material used for the insulating layer59include widely used thermoplastic elastomer, acrylic oligomer or polymer, urethane oligomer or polymer, epoxy oligomer or polymer, polyester oligomer or polymer, vinyl ether oligomer or polymer, polyene/thiol oligomer or polymer, and silicone oligomer or polymer. The thickness of the insulating layer59is, for example, greater than or equal to 1 μm and less than or equal to 100 μm.

The stretching process, in which tensile stress is applied to the stretchable portion20to stretch the stretchable portion20, may be performed with the first region31clamped in the thickness direction of the stretchable portion20. This facilitates stretching of the second region32that neighbors the first region31in a uniform manner in the stretching process.

The embodiment and each of the modifications above have been described with reference to an example in which the wiring board10has the electronic components51mounted on the first surface21of the support portion40. However, the configuration is not limited thereto. The wiring board10does not necessarily have to have the electronic components51. For example, the support portion40having no electronic components51mounted thereon may be joined to the stretchable portion20. In addition, the wiring board10may be shipped without electronic components51mounted therein. Furthermore, the wiring board10may be used without the electronic components51mounted therein.FIGS.29A and30are a cross-sectional view and a plan view illustrating an example of a wiring board10without an electronic component51mounted therein. The cross-sectional view illustrated inFIG.29Ais a cutaway view of the wiring board10taken along line E-E ofFIG.30.

As illustrated inFIGS.29A and30, when an electronic component51is not mounted in the wiring board10, a portion of the wiring board10that includes the first member35constitutes the first region31, and a portion of the wiring board10that is located between two neighboring first regions31and that includes the second member36having a lower modulus of elasticity than the first member35and does not include the first member35constitutes the second region32. In addition, a portion surrounded by the second regions32constitutes the third region33. In this case, the interconnection wire52may be located in both the first region31and second region32. The third region33does not have any interconnection wire52located therein.

Like the embodiment described above, according to the present modification, since the first portion321of the second region32of the wiring board10contracts mainly in the first direction D1, the undulating portion57extending in the first direction D1is likely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. However, the undulating portion57extending in the second direction D2is less likely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. Similarly, since the second portion322of the second region32of the wiring board10mainly contracts mainly in the second direction D2, the undulating portion57extending in the second direction D2is likely to appear in the support portion40overlapping the second portion322and the second interconnection wire522. However, the undulating portion57extending in the first direction D1is less likely to appear in the support portion40overlapping the second portion322and the second interconnection wire522. In addition, the undulating portion57is less likely to appear in the first region31of the wiring board10. As described above, according to the present embodiment, it is possible to control the direction of the undulating portion57that preferentially appears in each of the first interconnection wire521and the second interconnection wire522. As a result, it is possible to control the interference between the undulating portions57appearing in different directions. Consequently, it is possible to suppress the amplitude of the undulating portion57from being locally increased and suppress the cycle of the undulating portions57from being locally disordered.

FIG.29Bis a cross-sectional view illustrating another example of the wiring board10according to the present modification. As illustrated inFIG.29B, in a portion in which the first interconnection wire521extending in the first direction D1and the second interconnection wire522extending in the second direction D2intersect in plan view, an insulating layer59A may be interposed between the first interconnection wire521and the second interconnection wire522in the thickness direction of the wiring board10. This allows the first interconnection wire521and the second interconnection wire522to intersect with each other in plan view without electrical connection therebetween.

The embodiment and each of the modifications above have been described with reference to an example in which the first region31, the second region32, and the third region33of the wiring board10are defined on the basis of the modulus of elasticity of the electronic component51or the stretchable portion20. However, the structures of the first region31, the second region32, and the third region33are not particularly limited provided that the first region31is more difficult to stretch and contract than the second region32and, in addition, the second region32is more difficult to stretch and contract than the third region33. For example, as illustrated inFIGS.31to33, the first region31need not include the first member35.

FIG.31is a plan view of a wiring board10according to the present modification.FIGS.32and33are cross-sectional views of the wiring board10taken along line F-F and line G-G ofFIG.31, respectively. According to the present modification, as illustrated inFIGS.32and33, the stretchable portion20is configured by a member having a uniform thickness over the entire area, for example, by the second member36described above. The interconnection wire52has a plurality of first interconnection wires521that are located adjacent to the first surface21of the stretchable portion20and that extend in the first direction D1and a plurality of second interconnection wires522that are located adjacent to the first surface21of the stretchable portion20and that extend in the second direction D2and intersect with the first interconnection wires521. In this case, the portions of the wiring board10in which the first interconnection wire521and the second interconnection wire522intersect with each other is less likely to stretch and contract than the other portions of the interconnection wire52. In addition, a portion of the wiring board10in which the interconnection wire52is present is less likely to stretch and contract than a portion of the wiring board10in which the interconnection wire52is not present. Therefore, according to the present modification, the region that overlaps the portion of the wiring board10in which the first interconnection wire521and the second interconnection wire522intersect with each other defines the first region31. In addition, a region of the wiring board10that overlaps the first interconnection wire521or the second interconnection wire522but that is not the intersection of the first interconnection wire521and the second interconnection wire522defines the second region32. Furthermore, the portion of the wiring board10that overlaps neither the first interconnection wire521nor the second interconnection wire522defines the third region33.

Like the above-described embodiment, according to the present modification, since the first portion321of the second region32of the wiring board10contracts mainly in the first direction D1, the undulating portion57extending in the first direction D1is likely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. However, the undulating portion57extending in the second direction D2is less likely to appear in the support portion40overlapping the first portion321and in the first interconnection wire521. Similarly, since the second portion322of the second region32of the wiring board10contracts mainly in the second direction D2, the undulating portion57extending in the second direction D2is likely to appear in the support portion40overlapping the second portion322and in the second interconnection wire522. However, the undulating portion57extending in the first direction D1is less likely to appear in the support portion40overlapping the second portion322and in the second interconnection wire522. In addition, the undulating portion57is less likely to appear in the first region31of the wiring board10. As described above, according to the present embodiment, it is possible to control the direction of the undulating portion57that preferentially appears in each of the first interconnection wire521and the second interconnection wire522. As a result, it is possible to control the interference between the undulating portions57that appear in different directions. Therefore, it is possible to suppress the amplitude of the undulating portions57from being locally increased and suppress the cycle of the undulating portions57from being locally disordered.

Note thatFIG.33illustrates an example in which a member the same as the member (the second member36) of the stretchable portion20located in each of the first and second regions31and32is also present in the third region33. However, the configuration is not limited thereto. As illustrated inFIG.34, the third region33may include a hole formed in the stretchable portion20.

FIG.35is a cross-sectional view of another example of the wiring board10according to the present modification. Similar toFIG.32, FIG.35is a cross-sectional view of the wiring board10taken along line F-F ofFIG.31. As illustrated inFIG.35, in a portion in which the first interconnection wire521extending in the first direction D1and the second interconnection wire522extending in the second direction D2intersect with each other in plan view, an insulating layer59A may be interposed between the first interconnection wire521and the second interconnection wire522in the thickness direction of the wiring board10. This enables the first interconnection wire521and the second interconnection wire522to intersect with each other in plan view without electrical connection therebetween.

In addition, in the example illustrated inFIG.35, the first region31, which is a portion in which the first interconnection wire521and the second interconnection wire522intersect with each other in plan view, includes a conductive layer that constitutes the first interconnection wire521, the insulating layer59A, and a conductive layer that constitutes the second interconnection wire522. For this reason, the first region31is more difficult to stretch and contract than the second region32.

The embodiment and each of the modifications above have been described with reference to an example in which the interconnection wire52is supported by the support portion40located between the interconnection wire52and the stretchable portion20. However, the configuration is not limited thereto. The wiring board10does not necessarily have to include the support portion40. For example, the interconnection wire52and the electronic component51may be directly provided in the stretchable portion20.

The embodiment above has been described with reference to an example in which the first member35that has a higher modulus of elasticity than the second member36constituting the second region32is disposed over the entire area of the first region31in plan view. However, the configuration is not limited thereto. As illustrated inFIG.38, the first member35may have a shape of a picture frame. In this case, when the stretchable portion20is stretched, a portion of the stretchable portion20that is located inside the frame-shaped first member35is rarely subject to the tensile force and is less likely to deform. Therefore, in the example illustrated inFIG.38, a portion of the stretchable portion20in which the frame-shaped first member35is located and the portion located inside the first member35can function as the first region31having a higher elastic modulus than the second region32.

As illustrated inFIG.38, the electronic component51may be located inside the frame-shaped first member35in plan view. In addition, the second member36may be present inside the frame-shaped first member35of the stretchable portion20. Furthermore, as illustrated inFIG.38, the frame-shaped first member35may extend orthogonally to the direction in which the interconnection wire52extends at a position at which the first members35overlaps the interconnection wire52in plan view.

While the eighteenth modification illustrated inFIG.38has been described with reference to an example in which the frame-shaped first member35is applied to a wiring board10including the electronic components51, the configuration is not limited thereto. The frame-shaped first member35may be applied to the wiring board10without the electronic component51, as in the above-described fifteenth modification illustrated inFIG.30. In this case, as illustrated inFIGS.39to42, a portion in which the interconnection wires extending in different directions intersect to form a cross-intersection or a merge intersection may be located inside the frame-shaped first member35in plan view.

InFIGS.39and40, a portion in which the interconnection wires extending in two different directions intersect to form a cross-intersection or a merge intersection is located inside the frame-shaped first member35in plan view. InFIGS.41and42, a portion in which the interconnection wires extending in three different directions intersect to form a cross-intersection or a merge intersection is located inside the frame-shaped first member35in plan view. As illustrated inFIGS.39to42, the frame-shaped first member35may extend orthogonally to the direction in which the interconnection wire52extends at a position at which the first member35overlaps the interconnection wire52in plan view.

While several modifications of the embodiment described above have been described, it should be appreciated that the plurality of modifications can be combined in an appropriate way and be applied.

EXAMPLES

The present invention is described in more detail below with reference to examples and comparative examples. Note that the invention should not be construed as being limited to the examples described below unless the invention departs from the scope thereof.

As a mold for molding the stretchable portion20, a mold70having a base material71and grooves72formed in a grid pattern on the base material71was prepared, as illustrated inFIGS.7A and7B. The width of the groove72was 10 mm. Each of the spacing between two neighboring second grooves722in the first direction D1and the spacing between two neighboring first grooves721in the second direction D2was 10 mm.

Subsequently, an adhesive sheet was placed on the bottom surfaces of the first groove721and the second groove722as the adhesive layer60. “8146” available from 3M Company was used for the adhesive layer60. Thereafter, the first member35was placed on the adhesive layer60at the intersection of the first groove721extending in the first direction D1and the second groove722extending in the second direction D2. As the first member35, a polyimide film cut into a square having a side of 10 mm was used. As the polyimide film, Upilex (available from UBE Industries, Ltd.) having a thickness of 125 μm was used. In addition, the modulus of elasticity of the polyimide film was measured by a tensile test in accordance with ASTM D882. As a result of the test, the modulus of elasticity was 7 Gpa.

Subsequently, the groove72of the mold70was filled with polydimethylsiloxane (hereinafter referred to as PDMS) of two-component addition-condensation so that the thickness of the PDMS was about 1 mm. At this time, the first member35lay buried in the PDMS. Thereafter, the PDMS was cured to form the second member36. In this manner, a grid-shaped stretchable portion20was obtained. The stretchable portion20included a second member36that spreads in a grid shape and a first member35made from polyimide film buried in the PDMS at the intersection region of the grid of the second member36. The modulus of elasticity of the PDMS was measured by a tensile test in accordance with JIS K6251. As a result of the test, the modulus of elasticity was 0.05 MPa.

<<Preparation of Support Portion>>

A polyethylene naphthalate (PEN) film having a thickness of 2.5 μm was prepared to serve as the support portion40. Thereafter, a copper layer having a thickness of 1 μm was formed on the first surface41of the support portion40by the vapor deposition technique. Subsequently, the copper layer was processed using the photolithography and etching techniques. As a result, a plurality of the first interconnection wires521each extending in the first direction D1and having a width of 200 μm were obtained. The modulus of elasticity of the support portion40was measured by a tensile test in accordance with ASTM D882. As a result, the modulus of elasticity of the support portion40was 2.2 GPa.

Subsequently, ink containing dissolved urethane resin was applied to the first interconnection wire521by the screen printing technique so as to cover the first interconnection wire521. More specifically, printing was performed such that a plurality of ink layers each with a square shape having a side of 10 mm were formed at intervals in the direction in which the first interconnection wire521extended. Subsequently, a drying process was carried out using an oven of 120° C. for 30 minutes. In this manner, a plurality of insulating layers each having a thickness of 10 μm were formed on the first interconnection wire521so as to be lined up in the direction in which the first interconnection wire521extended. Each of the insulating layers was disposed so as to overlap one of the first regions31of the stretchable portion20, which was joined to the support portion40in a subsequent process.

Subsequently, conductive paste containing silver particles was patterned onto the support portion40by screen printing. In this manner, a plurality of second interconnection wires522were obtained. Each of the second interconnection wire522extended in the second direction D1orthogonal to the first interconnection wire521and had a width of 200 μm. At this time, printing was performed such that the insulating layer was positioned at an intersection of the first interconnection wire521and the second interconnection wire522.

Subsequently, an LED chip was disposed in the vicinity of the location at which the first interconnection wire521and the second interconnection wire522intersected. In addition, the anode electrode of the LED chip was connected to the first interconnection wire521, and the cathode electrode was connected to the second interconnection wire522by using conductive adhesive. CL-3160 available from KAKEN TECH Co., Ltd. was used as the conductive adhesive. Thereafter, a silicone potting agent was applied around the LED chip, and the silicone potting agent was cured to obtain the sealing portion58that covered the LED chip. TB1220G available from ThreeBond Co., Ltd. was used as the silicone potting agent.

Subsequently, the stretchable portion20was stretched to 1.5 times the original length in each of the two axes extending in the first direction D1and the second direction D2. The stretchable portion20that was stretched to 1.5 times the original length was joined to the support portion40having the interconnection wire52and the LED chip mounted thereon. More specifically, the adhesive layer60provided on the stretchable portion20was bonded to the surface of the support portion40on which the interconnection wire52and LED chip were not provided. At this time, the stretchable portion20and the support portion40were aligned so that the following conditions were satisfied:The first region31including the first member35of the stretchable portion20overlaps the LED chip and the intersection of the first interconnection wire521and the second interconnection wire522on the support portion40.The first interconnection wire521and the second interconnection wire522on the support40overlap the second region32located between the two neighboring first regions31in the first direction D1or the second direction D2.The direction in which the second region32of the stretchable portion20extends is parallel to the direction in which the interconnection wire52on the support portion40extends.

Subsequently, a portion of the support40that was not joined to the second member36of the stretchable portion20, that is, a portion that overlapped the hole37of the stretchable portion20, was cut and removed. Thereafter, the tensile stress was removed from the stretchable portion20to contract the stretchable portion20and the support portion40joined to the stretchable portion20. As a result, an undulating portion57was formed on each of the first interconnection wire521and the second interconnection wire522on the support portion40. The undulating portion57included crest portions and valley portions that were orthogonal to the direction in which each of the first interconnection wire521and the second interconnection wire522extended.

An adhesive sheet serving as an adhesive layer60was placed on a suitable support stand first. Subsequently, a plurality of first members35were placed on the adhesive layer60in each of the first direction D1and the second direction D2. A polyimide film cut into a square shape having a side of 10 mm was used as the first member35. As the polyimide film, Upilex (available from UBE Industries, Ltd.) having a thickness of 125 μm was used. The distance between two neighboring first members35in the first direction D1or the second direction D2was 10 mm.

Subsequently, PDMS of two-component addition-condensation was applied so as to cover the adhesive layer60and the first member35. Thereafter, a mold form having a concave-convex shape was pressed against the PDMS to cure the PDMS. The mold form was selected such that a convex portion of the mold form pressed the PDMS located in the third region33illustrated inFIG.25while a concave portion of the mold form pressed the PDMS located in the first region31and the second region32illustrated inFIG.25. As a result, the thickness of the first region31including the first member35and PDMS pressed by the concave portion of the mold form was about 1 mm, the thickness of the second region32containing PDMS pressed by the concave portion of the mold form was about 1 mm, and the thickness of the third region33containing PDMS pressed by the convex portion of the mold form was about 100 μm. In this way, as illustrated inFIG.25, the stretchable portion20having the third region33containing PDMS, which is thinner than the first region31and the second region32, was prepared.

<<Preparation of Support Portion>>

In the same way as in Example 1, the support portion40was prepared, the interconnection wire52was formed on the support portion40, and the LED chip was disposed on the support portion40.

In the same way as in Example 1, the stretchable portion20was stretched to 1.5 times the original length along each of the two axes extending in the first direction D1and the second direction D2. The stretchable portion20that is stretched to 1.5 times the original length was joined to the support portion40having the interconnection wire52and LED chip mounted thereon. Thereafter, the tensile stress was removed from the stretchable portion20to contract the stretchable portion20and the support portion40joined to the stretchable portion20. As a result, as in Example 1, an undulating portion57was formed on each of the first interconnection wire521and the second interconnection wire522on the support portion40. The undulating portion57included crest portions and valley portions orthogonal to the direction in which each of the first interconnection wire521and the second interconnection wire522extended.

An adhesive sheet was placed on a suitable support stand as an adhesive layer60. Thereafter, a plurality of first members35were placed on the adhesive layer60so as to be aligned in the first direction D1and the second direction D2. A polyimide film cut into a square shape having a side of 10 mm was used as the first member35. As the polyimide film, Upilex (available from UBE Industries, Ltd.) having a thickness of 125 μm was used. The distance between two neighboring first members35in the first direction D1or the second direction D2was 10 mm.

Subsequently, PDMS of two-component addition-condensation was applied so as to cover the adhesive layer60and the first member35. Thereafter, the PDMS was cured to form the second member36. The thickness of a portion of the second member36that did not overlap the first member35was 1.5 mm. In this way, as illustrated inFIG.4Ddescribed above, a stretchable portion20was prepared that includes the second member36located in the first region31, the second region32, and the third region33and the first member35located in the first region31.

<<Preparation of Support Portion>>

In the same way as in Example 1, the support portion40was prepared, the interconnection wire52was formed on the support portion40, and the LED chip was disposed on the support portion40. Subsequently, the support portion40was cut to remove a portion of the support portion40that overlapped the third region33of the stretchable portion20. As a result, the support portion40has a grid-like shape that overlaps the first regions31and second regions32of the stretchable portion20.

In the same way as in Example 1, the stretchable portion20was stretched to 1.5 times the original length along each of the two axes extending in the first direction D1and the second direction D2. The stretchable portion20that was stretched to 1.5 times the original length was joined to the support portion40having the interconnection wire52and the LED chip mounted thereon. Thereafter, the tensile stress was removed from the stretchable portion20to contract the stretchable portion20and the support portion40joined to the stretchable portion20. As a result, as in Example 1, an undulating portion57was formed on each of the first interconnection wire521and the second interconnection wire522on the support portion40. The undulating portion57included crest portions and valley portions orthogonal to the direction in which each of the first interconnection wire521and the second interconnection wire522extended.FIG.44is a plan view of a wiring board10obtained in this manner.FIG.45is a cutaway view of the wiring board10taken along line B-B ofFIG.44. Note that the cutaway view of the wiring board10taken along line A-A ofFIG.44is the same as the view illustrated inFIG.1.

The average value and the standard deviation of the cycles of the undulating portion57of the first interconnection wire521and the second interconnection wire522were calculated. More specifically, at each of 20 locations of the undulating portion57of the first interconnection wire521, the distance between two neighboring crest portions in the first direction D1was measured. In addition, at each of 20 locations of the undulating portion57of the second interconnection wire522, the distance between two neighboring crest portions in the second direction D2was measured. Thereafter, the average value and the standard deviation of the distance between the crest portions at 40 locations were calculated. As a result, the average value of the distances was 660 μm, and the standard deviation was 230 μm. As a measuring instrument, CNC image measuring system NEXIV VMZ-H3030 available from Nikon Corporation is usable. The specifications of the measuring instrument are as follows:Magnification: 81×Field of view: 3 mm×3 mm

Comparative Example

In the same manner as in Example 2, a stretchable portion20was produced, except that PDMS was applied onto the adhesive layer60without placing the plurality of first members35on an adhesive sheet disposed as the adhesive layer60. In addition, in the same manner as in Example 1, the support portion40was prepared, the interconnection wire52was formed on the support portion40, and an LED chip was disposed on the support portion40.

Subsequently, in the same way as in Example 1, the stretchable portion20was stretched to 1.5 times the original length along each of the two axes extending in the first direction D1and second direction D2. The stretchable portion20that is stretched to 1.5 times the original length was joined to the support portion40having the interconnection wire52and the LED chip mounted thereon. Thereafter, the tensile stress was removed from the stretchable portion20to contract the stretchable portion20and the support portion40joined to the stretchable portion20. As a result, an undulating portion57was formed on each of the first interconnection wire521and the second interconnection wire522on the support portion40. The crest portion and the valley portions of the undulating portion57extended in random directions. That is, the direction of the undulating portion57was unable to be controlled.

REFERENCE SIGNS LIST