Stretchable device

Abstract

This stretchable device (1) comprises: a stretchable base material (11) having a main surface (111); an electronic component (30) provided on the main surface (111) of the stretchable base material (11); first stretchable wiring (21) connected to the electronic component (30); and second stretchable wiring (22) connected to the first stretchable wiring (21), wherein a first end section (211) in the extending direction of the first stretchable wiring (21) is connected to the electronic component (30), and a second end section (212) in the extending direction of the first stretchable wiring (21) is connected to the first end section (221) in the extending direction of the second stretchable wiring (22).

Description

Stretchable Device

[0001] The present disclosure relates to stretchable devices.

[0002] A conventional stretchable device is described in International Publication No. 2009 / 081929 (Patent Document 1). This stretchable device includes an insulating substrate, a first conductor having a land provided on the insulating substrate, a second conductor provided on the land, solder individually provided on the second conductor, and an electronic component having electrode portions independently contacting the solder.

[0003] International Publication No. 2009 / 081929

[0004] In prior art devices, the end of the electronic component is positioned over the overlapping area of ​​the first conductor and the second conductor, and the solder on the second conductor is also positioned over the overlapping area.

[0005] However, when a conventional device having the above structure was evaluated, it was found that the conventional device had low mechanical strength. A detailed study revealed that when a stretchable substrate is used as the substrate, stress during stretching is most likely to be concentrated near the interface between the wiring and a connecting member such as solder. Therefore, it was found that the conventional device may suffer from breakage of the wiring or interfacial peeling between the substrate and the wiring.

[0006] Therefore, an object of the present disclosure is to provide a stretchable device that can improve mechanical strength.

[0007] In order to achieve the above object, a stretchable device according to one aspect of the present disclosure includes: a stretchable base material having a main surface; an electronic component provided on the main surface of the stretchable base material; a first stretchable wire connected to the electronic component; and a second stretchable wire connected to the first stretchable wire, wherein a first end in an extension direction of the first stretchable wire is connected to the electronic component; and a second end in an extension direction of the first stretchable wire is connected to a first end in an extension direction of the second stretchable wire.

[0008] According to the stretchable device according to one aspect of the present disclosure, it is possible to improve mechanical strength.

[0009] FIG. 1 is a schematic perspective view partially showing a stretchable device according to a first embodiment of the present disclosure. FIG. 2 is a cross-sectional view taken along II-II of FIG. 1. FIG. 3 is a schematic perspective view partially showing a stretchable device according to a second embodiment of the present disclosure. FIG. 4 is a schematic plan view partially showing a stretchable device according to the second embodiment of the present disclosure. FIG. 5 is a graph showing the relationship between stress and elongation of a stretchable wiring according to an example. FIG. 6 is a graph showing thickness dependency of the relationship between the stretch rate and resistance value of a stretchable wiring according to an example. FIG. 7 is a schematic perspective view partially showing a stretchable device according to an example. FIG. 8A is a diagram showing the shape of an applied paste. FIG. 8B is a diagram showing the shape of an applied paste.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each embodiment, differences from those previously described will be mainly described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment. Among the components in the following embodiments, components not recited in independent claims will be described as optional components. Furthermore, the size and size ratios of components shown in the drawings are not necessarily strict. Furthermore, in each figure, substantially identical components are assigned the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0011] [First embodiment] (Overall configuration) The overall configuration of a stretchable device 1 according to a first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a schematic perspective view partially showing the stretchable device 1. Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Note that the coating layer is omitted from Fig. 1.

[0012] In the drawings of this specification, the thickness direction of the stretchable substrate is indicated by an arrow T. The "direction perpendicular to the main surface of the stretchable substrate" described in the claims corresponds to the T direction. In this specification, the direction from the main surface of the stretchable substrate on which no stretchable wires are provided to the main surface of the stretchable substrate on which stretchable wires are provided is defined as the upper side.

[0013] The stretchable device 1 includes a stretchable base material 11 having a main surface 111, an electronic component 30 provided on the main surface 111 of the stretchable base material 11, a first stretchable wiring 21 connected to the electronic component 30, a second stretchable wiring 22 connected to the first stretchable wiring 21, and a covering layer 50 provided so as to cover the first stretchable wiring 21 and the second stretchable wiring 22. The stretchable device 1 is used, for example, to be attached to a living body and to measure a biological signal.

[0014] Here, "on the main surface of the stretchable substrate" does not refer to an absolute direction such as vertically upward as determined by the direction of gravity, but rather refers to the direction toward the outside of the outside and inside of the stretchable substrate, with the main surface of the stretchable substrate as the boundary. Therefore, "on the main surface of the stretchable substrate" is a relative direction determined by the orientation of the main surface of the stretchable substrate. Furthermore, "above" an element includes not only a position directly above the element (on), but also a position above the element, i.e., a position above another object on the element or a position above the element with a gap (above).

[0015] The stretchable substrate 11 is a sheet-like or film-like substrate made of a stretchable resin material. Examples of the resin material include thermoplastic polyurethane (TPU). The thickness of the stretchable substrate 11 is not particularly limited, but from the viewpoint of not inhibiting the stretching of the surface of the living body when attached to the living body, it is preferably 1 mm or less, more preferably 100 μm or less, and even more preferably 50 μm or less. Furthermore, the thickness of the stretchable substrate 11 is preferably 1 μm or more. The shape of the stretchable substrate 11 is not particularly limited. In this embodiment, the stretchable substrate 10 is shaped to extend in one direction A when viewed from the thickness direction T.

[0016] The electronic component 30 is, for example, a capacitor component, an inductor component, or an IC (semiconductor integrated circuit). The type of electronic component 30 is not particularly limited. The shape of the electronic component 30 is not particularly limited, but in this embodiment it is a rectangular parallelepiped. The electronic component 30 is arranged so that its longitudinal direction is parallel to the extension direction of the extensible base material 11 (hereinafter referred to as "direction A"). External electrodes 31 are provided on both ends of the electronic component 30 in direction A.

[0017] The first expandable wire 21 is a member having a function such as alleviating stress applied to the stretchable device 1. The first expandable wire 21 is formed of a conductive material having stretchability. The conductive material may be, for example, a metal foil such as silver, copper, or nickel, or a mixture of a metal powder such as silver, copper, or nickel and an elastomer resin such as epoxy resin, urethane resin, acrylic resin, or silicone resin. The first expandable wire 21 preferably has a larger Young's modulus than the second expandable wire 22. The shape of the first expandable wire 21 is not particularly limited, but in this embodiment, it is formed into a shape extending in one direction. Specifically, the first expandable wire 21 is formed so that the extension direction is parallel to the A direction.

[0018] A first end 211 in the extension direction of the first elastic wire 21 is connected to the electronic component 30. Specifically, the first end 211 in the extension direction of the first elastic wire 21 is connected to an external electrode 31 on one side of the electronic component 30 via a connection member 40. The connection member 40 is, for example, solder, a conductive adhesive, or the like.

[0019] The length L1 of the first elastic wire 21 in the extension direction is preferably, for example, 0.2 mm or more and 5 mm or less. In this specification, the length L1 does not include the overlapping portion with the second elastic wire 22. The width W1 of the first elastic wire 21 in the direction perpendicular to the extension direction is preferably, for example, 0.2 mm or more and 3.2 mm or less. The thickness t1 of the first elastic wire 21 in the T direction is preferably, for example, 10 μm or more and 30 μm or less.

[0020] The second expandable wire 22 is a wire that is mainly responsible for transmitting and receiving biosignals and the like. The second expandable wire 22 is formed of a stretchable conductive material. For example, a metal foil such as silver, copper, or nickel may be used as the conductive material, or a mixture of a metal powder such as silver, copper, or nickel and an elastomer resin such as epoxy resin, urethane resin, acrylic resin, or silicone resin may be used. The shape of the second expandable wire 22 is not particularly limited, but in this embodiment, the second expandable wire 22 is formed to extend in one direction. Specifically, the extension direction of the second expandable wire 22 is parallel to the A direction. That is, the extension direction of the second expandable wire 22 is parallel to the extension direction of the first expandable wire 21. In this application, "parallel" is not limited to a strict parallel relationship, but also includes a substantial parallel relationship, taking into account the range of realistic variation.

[0021] A first end 221 in the extension direction of the second expandable wire 22 is connected to a second end 212 in the extension direction of the first expandable wire 21. Specifically, the first end 221 in the extension direction of the second expandable wire 22 is stacked on the second end 212 in the extension direction of the first expandable wire 21 and connected to the second end 212 in the extension direction of the first expandable wire 21. However, without being limited thereto, the second end 212 in the extension direction of the first expandable wire 21 may be stacked on the first end 221 in the extension direction of the second expandable wire 22 and connected to the first end 221 in the extension direction of the second expandable wire 22. The length L3 in the A direction of a portion 22P of the second expandable wire 22 that overlaps with the first expandable wire 21 (overlapping portion) is preferably, for example, 0.1 mm or more and 1 mm or less.

[0022] The length L2 of the second expandable wire 22 in the extension direction is preferably, for example, three times or more the length L1. In this specification, the length L2 does not include the overlapping portion with the first expandable wire 21. Furthermore, as shown in FIG. 7 described later, when there are multiple electronic components 30 and one second expandable wire 22 is connected to multiple electronic components 30, L2 is the length to the midpoint between adjacent electronic components 30 in the extension direction of the second expandable wire 22. The width W2 of the second expandable wire 22 in the direction perpendicular to the extension direction is preferably, for example, 0.2 mm or more and 3.2 mm or less. The thickness t2 of the second expandable wire 22 in the T direction is preferably, for example, 10 μm or more and 30 μm or less.

[0023] In this embodiment, there are two sets of expandable wires each consisting of a first expandable wire 21 connected to an external electrode 31 of the electronic component 30 and a second expandable wire 22 connected to the first expandable wire 21, one set corresponding to each of the two external electrodes 31 provided at both ends of the electronic component 30 in the A direction.

[0024] The covering layer 50 protects the first expandable wiring 21 and the second expandable wiring 22 from the external environment. The covering layer 50 is, for example, a potting resin. The covering layer 50 is preferably an expandable resin material, and is preferably, for example, an ionomer resin, a polyester resin, a styrene resin, an olefin resin, an epoxy resin, a urethane resin, an acrylic resin, or a silicone resin, and is more preferably a urethane resin. Note that the covering layer 50 does not need to be provided, but it is preferable that it covers at least the connection portion between the first expandable wiring 21 and the electronic component 30.

[0025] According to the stretchable device 1, the first end 211 in the extension direction of the first expandable wire 21 is connected to the electronic component 30, and the second end 212 in the extension direction of the first expandable wire 21 is connected to the first end 221 in the extension direction of the second expandable wire 22. Therefore, when viewed from a direction perpendicular to the main surface 111 of the stretchable base material 11, the end of the electronic component 30 does not overlap the connection portion between the first expandable wire 21 and the second expandable wire 22. Furthermore, the connection member 40 connecting the electronic component 30 and the first expandable wire 21 can also be arranged so as not to overlap the connection portion between the first expandable wire 21 and the second expandable wire 22. This allows different members to be arranged in stages from the end of the electronic component 30 toward the second expandable wire 22. As a result, stress that may concentrate at the connection portion between the electronic component 30 and the first expandable wire 21 can be dispersed from the end of the electronic component 30 toward the second expandable wire 22, thereby alleviating the concentration of the stress. As a result, the mechanical strength of the stretchable device 1 can be improved.

[0026] (Tensile Load Ratio) In the stretchable device 1, it is preferable to satisfy the following formulas (1) and (2). In the following description, the stretching direction is assumed to be parallel to the A direction. σ1≦allowable stress σ1 of the first stretchable wiring ｍａｘ ... (1) σ2≦allowable stress σ2 of second expandable wiring ｍａｘ ... (2) where, σ1 = (δ x E1 x S2 x E2) / (L1 x S2 x E2 + L2 x S1 x E1) ... (3) σ2 = (δ x E1 x S1 x E2) / (L1 x S2 x E2 + L2 x S1 x E1) ... (4) δ: total displacement amount of the first elastic wire 21 and the second elastic wire 22 L1: length of the first elastic wire 21 in the expansion / contraction direction (direction A) L2: length of the second elastic wire 22 in the expansion / contraction direction S1: cross-sectional area of ​​the first elastic wire 21 in a cross section perpendicular to the expansion / contraction direction (width W1 x thickness t1 of the first elastic wire 21) S2: cross-sectional area of ​​the second elastic wire 22 in a cross section perpendicular to the expansion / contraction direction (width W2 x thickness t2 of the second elastic wire 22) E1: elastic modulus of the first elastic wire 21 E2: elastic modulus of the second elastic wire 22

[0027] The above σ1 means the tensile load acting on the first expandable wire 21 when a displacement amount δ is applied to the entire first expandable wire 21 and the second expandable wire 22. The above σ2 means the tensile load acting on the second expandable wire 22 when a displacement amount δ is applied to the entire first expandable wire 21 and the second expandable wire 22. In other words, satisfying the above formulas (1) and (2) means that each of the first tensile load ratio and the second tensile load ratio calculated by the following formula is 1 or less. First tensile load ratio = (tensile load σ1 acting on the first expandable wire 21) / (allowable stress σ1 of the first expandable wire 21) ｍａｘ Second tensile load ratio = (tensile load σ2 acting on the second expandable wire 22) / (allowable stress σ2 of the second expandable wire 22) ｍａｘ )

[0028] Here, the derivation of the above formulas (3) and (4), which are formulas for calculating the tensile load σ1 and the tensile load σ2, will be explained. When a displacement δ is applied to the entire first expandable wire 21 and the second expandable wire 22, the load F applied to the first expandable wire 21 and the second expandable wire 22 is expressed by the following formula: F = δ / [{L1 / (E1 × S1)} + {L2 / (E2 × S2)}]

[0029] The tensile loads σ1 and σ2 are calculated using the above load F according to the following formulas: σ1=F / S1=(δ / S1)×{(E1×S1×E2×S2) / (L1×S2×E2+L2×S1×E1)}=(δ×E1×S2×E2) / (L1×S2×E2+L2×S1×E1) σ2=F / S2=(δ / S2)×{(E1×S1×E2×S2) / (L1×S2×E2+L2×S1×E1)}=(δ×E1×S1×E2) / (L1×S2×E2+L2×S1×E1)

[0030] As can be seen from the above formulas (3) and (4), the tensile load σ1 and the tensile load σ2 can be adjusted by adjusting the elastic moduli E1, E2, lengths L1, L2 in the expansion and contraction directions, cross-sectional areas S1, S2, and length L3 of the overlapping portions of the first expandable wiring 21 and the second expandable wiring 22 of the first expandable wiring 21 and the second expandable wiring 22. Note that when the lengths of the first expandable wiring 21 and the second expandable wiring 22 in the extension directions of the members are predetermined lengths, the lengths L1, L2 of the first expandable wiring 21 and the second expandable wiring 22 in the expansion and contraction directions can be adjusted by adjusting the lengths of the overlapping portions of the first expandable wiring 21 and the second expandable wiring 22.

[0031] The calculation of the tensile load σ1 and the calculation of the tensile load σ2 are shown for one of the two sets of expandable wires, but the same applies to the other set. That is, δ, L1, L2, S1, S2, E1, and E2 can be defined for each of the two sets of expandable wires.

[0032] The allowable stress σ1 of the first elastic wiring 21 in the above formula (1) ｍａｘ is the stress at the maximum elongation of the first elastic wire 21. ｍａｘ For example, after cutting out the first expandable wire 21 to a predetermined length in the extension direction, the relationship between the elongation and stress of the first expandable wire 21 (stress-strain diagram) may be measured, and the stress at which the first expandable wire 21 breaks may be determined. ｍａｘ is the stress at the maximum elongation of the second elastic wire 22. ｍａｘ For example, after cutting out the second expandable wiring 22 to a predetermined length in the extension direction, the relationship between the elongation and stress of the second expandable wiring 22 can be measured, and this can be the stress at which the second expandable wiring 22 breaks.

[0033] The first tensile load ratio being 1 or less means that the tensile load σ1 acting on the first expandable wiring 21 is less than the allowable stress σ1 of the first expandable wiring 21. ｍａｘIn other words, with the selected configuration of the first expandable wire 21, the first expandable wire 21 will not break and the mechanical strength of the first expandable wire 21 will be sufficient. Similarly, the second tensile load ratio being 1 or less means that the tensile load σ2 acting on the second expandable wire 22 is smaller than the allowable stress σ2 of the second expandable wire 22. ｍａｘ That is, with the selected configuration of the second expandable wire 22, the second expandable wire 22 will not break and the mechanical strength of the second expandable wire 22 will be sufficient.

[0034] By satisfying the above formulas (1) and (2), the first tensile load ratio and the second tensile load ratio are each equal to or less than 1, and therefore it is possible to prevent each of the first expandable wires 21 and the second expandable wires 22 from breaking. Furthermore, by satisfying the above formulas (1) and (2), it is possible to determine the shapes and materials of the first expandable wires 21 and the second expandable wires 22 corresponding to the displacement amount δ. Therefore, the displacement amount δ falls within a range in which the stretchable device 1 does not break.

[0035] More preferably, the following formula is satisfied: σ1≦0.80×allowable stress σ1 of the first elastic wire 21 ｍａｘ σ2≦0.80×allowable stress σ2 of the second elastic wiring 22 ｍａｘ According to this configuration, breakage of the first expandable wires 21 and the second expandable wires 22 can be more reliably suppressed.

[0036] Even more preferably, the following formula is satisfied: σ1≦0.50×allowable stress σ1 of the first elastic wire 21 ｍａｘ σ2≦0.50×allowable stress σ2 of the second elastic wiring 22 ｍａｘ According to this configuration, breakage of the first expandable wires 21 and the second expandable wires 22 can be suppressed even more reliably.

[0037] (Other Preferred Configurations) Preferably, the electronic component 30 is further provided with a connecting member 40 that connects the first expandable wire 21 to the electronic component 30, and the connecting member 40 does not overlap with the first end 221 in the extension direction of the second expandable wire 22 when viewed from the direction (T direction) perpendicular to the main surface 111 of the expandable base material 11. According to this configuration, for example, when the connecting member 40 is solder, it is possible to suppress the thermal influence on the second expandable wire 22 when the connecting member 40 is formed.

[0038] Preferably, the solder leach resistance of the first expandable wiring 21 is higher than the solder leach resistance of the second expandable wiring 22. Solder leach is a phenomenon in which metal or the like in the expandable wiring dissolves into solder, causing a reduction in the volume of the expandable wiring. According to this configuration, when the connection member 40 is solder, it is possible to improve the connection reliability between the first expandable wiring 21 and the connection member 40.

[0039] As an example of a method for evaluating solder leach resistance, for example, an expandable wiring is immersed in molten solder, and a graph showing the relationship between the immersion time and the amount of dissolved metal in the expandable wiring is created. Then, the greater the slope of the graph, the more susceptible to solder leach, i.e., the lower the solder leach resistance can be evaluated.

[0040] Preferably, the solubility (chemical attack) of the first expandable wire 21 in the resin is smaller than the solubility (chemical attack) of the second expandable wire 22 in the resin. According to this configuration, even if the covering layer 50 is, for example, a potting resin and covers at least the connection portion between the electronic component 30 and the first expandable wire 21, it is possible to prevent the material of the first expandable wire 21 from dissolving in the covering layer 50.

[0041] The solubility of the expandable wiring in the resin can be evaluated based on, for example, JIS K 7114:2001 (ISO 175:1999). In this test method, a test piece is completely immersed in a test solution at a specified temperature for a specified time. The mass of the test piece is measured before immersion and after removal from the test solution and drying, if necessary. The greater the change in mass, the greater the solubility in the test solution (the greater the chemical attack).

[0042] Preferably, the length L1 in the extension direction of the first expandable wire 21 is shorter than the length L2 in the extension direction of the second expandable wire 22. According to this configuration, even if the first expandable wire 21 is harder than the second expandable wire 22, the influence on the stretchability of the stretchable device 1 can be suppressed.

[0043] Preferably, the Young's modulus (elastic modulus) of the first expandable wire 21 is greater than the Young's modulus (elastic modulus) of the second expandable wire 22. According to this configuration, the first expandable wire 21 can be made harder than the second expandable wire 22. Therefore, the hardness can be softened stepwise from the end of the electronic component 30 toward the second expandable wire 22. As a result, stress that can concentrate on the connection portion between the electronic component 30 and the first expandable wire 21 can be further alleviated.

[0044] Preferably, the thickness t1 of the first elastic wire 21 is greater than the thickness t2 of the second elastic wire 22. According to this configuration, it is possible to further improve the solder leach resistance of the first elastic wire 21. In addition, the allowable stress σ1 of the first elastic wire 21 ｍａｘ In addition, since the clearance between the electronic component 30 and the extensible base material 11 can be increased, the filling of the coating layer 50 into the clearance can be improved.

[0045] Preferably, the viscosity of the material of the first expandable wire 21 is greater than the viscosity of the material of the second expandable wire 22. According to this configuration, the thickness t1 of the first expandable wire 21 can be made greater than the thickness t2 of the second expandable wire 22 more reliably.

[0046] Preferably, the first expandable wire 21 is made of a thermosetting material, the second expandable wire 22 is made of a thermoplastic material, and a first end 221 in the extension direction of the second expandable wire 22 is laminated on a second end 212 in the extension direction of the first expandable wire 21. According to this configuration, even when stress is applied to the stretchable device 1, interfacial peeling between the first expandable wire 21 and the second expandable wire 22 can be suppressed, and the mechanical strength of the stretchable device 1 can be further improved.

[0047] Second Embodiment A stretchable device 1A according to a second embodiment will be described below with reference to Fig. 3 and Fig. 4. Fig. 3 is a schematic perspective view of the stretchable device 1A. Fig. 4 is a schematic plan view partially showing the stretchable device 1A. Specifically, Fig. 4 is a view of the lower right part of the page of Fig. 3 as seen from above. The stretchable device 1A differs from the stretchable device 1 according to the first embodiment in the configurations of the electronic components, the first stretchable wiring, and the second stretchable wiring.

[0048] 3 and 4, in this embodiment, the electronic component 30A has a square prism shape. A plurality of external electrodes 32 are provided on the outer periphery of the lower surface of the electronic component 30A.

[0049] There are a plurality of first expandable wires 21 and a plurality of second expandable wires 22, and there are a plurality of sets of expandable wires each composed of a first expandable wire 21 connected to the electronic component 30A and a second expandable wire 22 connected to the first expandable wire 21. Specifically, one first expandable wire 21 is connected to one external electrode 32 of the electronic component 30A, and one second expandable wire 22 is connected to the one first expandable wire 21. There are a plurality of sets of expandable wires each composed of the one first expandable wire 21 and the one second expandable wire 22 corresponding to each external electrode 32.

[0050] According to the above configuration, since there are multiple sets of the stretchable wirings, it is possible to further alleviate stress that may be concentrated at the connection portion between the electronic component 30A and the first stretchable wiring 21, and it is possible to further improve the mechanical strength of the stretchable device 1A.

[0051] Preferably, when viewed from a direction (T direction) perpendicular to the main surface 111 of the stretchable base material 11, each of the first stretchable wires 21 in the plurality of sets of stretchable wires is arranged on the periphery of the electronic component 30A so as to be radial with respect to the center C of the electronic component 30A, and in two sets of stretchable wires adjacent along the periphery of the electronic component 30A, the angle formed between the extension direction of the first stretchable wires 21 in one set of stretchable wires and the extension direction of the first stretchable wires 21 in the other set of stretchable wires is greater than 0° and not greater than 90°.

[0052] 4, the first expandable wires 21 in the first expandable wire set P1, the second expandable wire set P2, and the third expandable wire set P3 are arranged on the outer periphery of the electronic component 30A so as to radiate from the center C of the electronic component 30A. In the first expandable wire set P1 and the second expandable wire set P2 adjacent to each other along the outer periphery of the electronic component 30A, the angle θ1 formed between the extension direction of the first expandable wires 21 in the first expandable wire set P1 and the extension direction of the first expandable wires 21 in the second expandable wire set P2 is greater than 0° and equal to or less than 90°. In a set P2 of second expandable wires and a set P3 of third expandable wires that are adjacent along the outer periphery of the electronic component 30A, the angle θ2 between the extension direction of the first expandable wires 21 in the set P2 of second expandable wires and the extension direction of the first expandable wires 21 in the set P3 of third expandable wires is greater than 0° and less than or equal to 90°.

[0053] In this embodiment, in the multiple second expandable wires 22 connected to the external electrode 32 provided on one side of the outer periphery of the electronic component 30A when viewed from the T direction, the extension directions of each second expandable wire 22 are parallel to each other, but may also be arranged at an angle to each other.

[0054] According to the above configuration, each of the first expandable wires 21 in the set of multiple expandable wires is disposed on the outer periphery of the electronic component 30A so as to be radially aligned with the center C of the electronic component 30A, and therefore the inter-wire pitch WP can be made different from the inter-electrode pitch EP. Furthermore, the periphery of the electronic component 30A can be covered with the first expandable wires 21, which are softer than the electronic component 30A. Therefore, even when tensile stress is applied to the stretchable device 1A, stress that may concentrate at the connection portion between the electronic component 30A and the first expandable wires 21 can be further alleviated. Furthermore, even when tensile stress is applied to the stretchable device 1A from any direction, shear deformation at the most affected location can be reduced, and the durability of the stretchable device 1A can be improved.

[0055] It should be noted that each embodiment is an example, and the present disclosure is not limited to each embodiment. Also, each drawing is an example of components, and does not limit the shape. Furthermore, partial substitution or combination of configurations shown in different embodiments is possible.

[0056] In the above embodiment, there are multiple pairs of first expandable wirings connected to electronic components and second expandable wirings connected to the first expandable wirings, but it is sufficient that there is at least one pair of expandable wirings.

[0057] (Example 1) The elongation with respect to stress was measured for the first expandable wire and the second expandable wire. Fig. 5 is a graph showing the relationship of the elongation with respect to stress for the first expandable wire and the second expandable wire. Graph G1 shows the results for the first expandable wire. Graph G2 shows the results for the second expandable wire.

[0058] As shown in Fig. 5, the first expandable wire broke at an elongation of about 7%. The stress at this time was about 16 MPa. That is, the allowable stress of the first expandable wire was about 16 MPa. The second expandable wire broke at an elongation of about 17%. The stress at this time was about 3 MPa. That is, the allowable stress of the second expandable wire was about 3 MPa.

[0059] The relationship between the thickness of the first expandable wire and the expansion rate until the first expandable wire breaks was measured. Fig. 6 is a graph showing the thickness dependency of the relationship between the expansion rate and resistance value of the first expandable wire.

[0060] 6, it was found that the expansion rate until breakage increases as the thickness of the first expandable wire increases. This is thought to be because the tensile load acting on the first expandable wire decreases as the thickness of the first expandable wire increases, and the first tensile load ratio decreases.

[0061] Example 2 The range of tensile load F that can be used without breaking the stretchable device was calculated. Note that the following calculation is an example, and the range of tensile load F that can be used without breaking the stretchable device may vary depending on the material and shape of the stretchable base material, the material and shape of the first and second stretchable wirings, the number and arrangement of electronic components, etc.

[0062] Assuming that the stretch rate is ε%, the tensile load F that the stretchable device 1 can use without breaking can be calculated using the following formula. The stretch rate ε can be defined, for example, as the ratio of the above-mentioned displacement δ to the overall length of the stretchable base material before stretching. Tensile load F that the stretchable device 1 can use without breaking = E × (ε / 100) × S where, E: combined elastic modulus (composite elastic coefficient) of the stretchable base material 11, the first stretchable wiring 21, and the second stretchable wiring 22 S: cross-sectional area of ​​the stretchable base material 11 in a cross section perpendicular to the stretching direction

[0063] Fig. 7 is a schematic perspective view partially showing a stretchable device 1B according to Example 2. As shown in Fig. 7, in the stretchable device 1B, a group of wirings / components, in which a second stretchable wiring 22, a first stretchable wiring 21, an electronic component 30, and the first stretchable wiring 21 are connected in this order, are repeatedly connected along the direction A. A plurality of such repeatedly connected wirings / component groups exist in a direction perpendicular to the direction A. In Fig. 7, the stretchable direction is indicated by an arrow.

[0064] The dashed line of the region AR in Fig. 7 indicates a virtual line connecting the midpoints between adjacent electronic components 30. Although the region AR is depicted as a square in Fig. 7, the region AR is not necessarily a square. The center of gravity of the region AR overlaps with the electronic component 30 when viewed from the T direction. The area of ​​the region AR is the value obtained by dividing the area of ​​the entire substrate by the number of electronic components 30. When the region AR is ε EX When stretched at a stretch rate of , the composite elastic modulus of this occupied range is E EX , the cross-sectional area of ​​the cross section perpendicular to the expansion and contraction direction is S EX Then, the load dF of this occupied range is calculated by the following formula: dF = E EX ×ε EX ×S EX

[0065] The area of ​​the area AR is 10 mm ２ , expansion / contraction ratio ε EXwas assumed to be 20%. The elastic modulus (elastic modulus, Young's modulus), cross-sectional area of ​​a cross section perpendicular to the stretching direction, length in the stretching direction, and composite elastic modulus of the stretchable substrate, first stretchable wire, and second stretchable wire in the region AR are shown in Table 1. The composite elastic modulus was roughly calculated from the elastic modulus, cross-sectional area, and length of each member. The stretchable substrate was assumed to be thermoplastic polyurethane (TPU). In FIG. 7, the length in the stretching direction of the first stretchable wire 21 is the sum of lengths L1a and L1b. The length in the stretching direction of the second stretchable wire 22 is the sum of lengths L2a and L2b. The length in the stretching direction of the stretchable substrate is the sum of lengths L1a, L1b, L2a, and L2b.

[0066]

[0067] Cross-sectional area S EX When approximating the cross-sectional area of ​​the elastic substrate, the load dF is calculated as follows: dF = E ＥＸ ×ε ＥＸ ×S ＥＸ = 14 MPa × 0.2 × (4 × 10 －１ mm ２ ) = 1.12 N The total area of ​​the stretchable device 1B is 100 mm ２ In this case, the load is 10 times larger, so the maximum tensile load F that the stretchable device can use without breaking is calculated to be 10 N.

[0068] (Example 3) A paste was used as the material for the first expandable wire, and the relationship between the viscosity of the paste and the thickness of the formed first expandable wire was investigated. Since the shape of the first expandable wire is island-shaped, it can be printed using a metal mask, and a paste with increased thixotropy, i.e., paste viscosity, can be used by adding a thixotropic agent. The paste was printed using a metal mask to form the first expandable wire.

[0069] Fig. 8A is a diagram showing the applied shape of paste M1 to which no thixotropic agent was added. Fig. 8B is a diagram showing the applied shape of paste M2 to which a thixotropic agent was added. As shown in Fig. 8A, in the case of paste M1 to which no thixotropic agent was added, the paste spread and had a thickness of about 25 µm. As shown in Fig. 8B, in the case of paste M2 to which a thixotropic agent was added, the paste did not spread and had a thickness of about 50 µm. It was found that the thickness of the first expandable wiring could be increased in the case of paste M2 to which a thixotropic agent was added and whose viscosity was increased.

[0070] Furthermore, a sample having a first expandable wiring thickness of 10 μm and a sample having a first expandable wiring thickness of 50 μm were prepared. Then, for each sample, the solder thickness and the number of reflows were variously changed, and the solder leaching resistance was evaluated. The solder thickness was changed to 20 μm, 50 μm, 80 μm, 110 μm, and 140 μm. The number of reflows was changed to 1 time, 2 times, 3 times, 4 times, and 5 times. Solder leaching was observed in the sample having a first expandable wiring thickness of 10 μm, but no solder leaching was observed in the sample having a first expandable wiring thickness of 50 μm. It was found that solder leaching resistance was improved by increasing the thickness of the first expandable wiring.

[0071] Example 4 The relationship between the stacking order of the first and second expandable wires and interfacial peeling was investigated. Specifically, an investigation was conducted to determine whether the behavior of interfacial peeling differs between a case in which the first end of the second expandable wire is stacked on the second end of the first expandable wire, as shown in FIG. 2 , and a case in which the second end of the first expandable wire is stacked on the first end of the second expandable wire. A thermosetting material was used as the material of the first expandable wire. A thermoplastic material was used as the material of the second expandable wire. Table 2 shows the results when the first end of the second expandable wire was stacked on the second end of the first expandable wire. Table 3 shows the results when the second end of the first expandable wire was stacked on the first end of the second expandable wire. In Tables 2 and 3, for example, a numerical value such as "0.16 N / mm" means the tensile load per unit width at the time of interfacial peeling.

[0072]

[0073]

[0074] As shown in Tables 2 and 3, when a thermosetting material was used as the material for the first expandable wire and a thermoplastic material was used as the material for the second expandable wire, cohesive failure occurred when the first end of the second expandable wire was laminated on the second end of the first expandable wire, and interfacial delamination occurred when the second end of the first expandable wire was laminated on the first end of the second expandable wire. Cohesive failure is a state in which failure occurs inside either the first expandable wire or the second expandable wire, rather than peeling at the interface between the first expandable wire and the second expandable wire. It was found that when a thermosetting material was used as the material for the first expandable wire and a thermoplastic material was used as the material for the second expandable wire, laminating the first end of the second expandable wire on the second end of the first expandable wire suppresses interfacial delamination and improves mechanical strength.

[0075] The present disclosure includes the following aspects. <1> A stretchable device comprising: a stretchable base material having a main surface; an electronic component provided on the main surface of the stretchable base material; a first stretchable wire connected to the electronic component; and a second stretchable wire connected to the first stretchable wire, wherein a first end in an extension direction of the first stretchable wire is connected to the electronic component, and a second end in an extension direction of the first stretchable wire is connected to a first end in an extension direction of the second stretchable wire. <2> The stretchable device according to <1>, which satisfies the following formula: σ1≦allowable stress of first expandable wiring σ2≦allowable stress of second expandable wiring where σ1=(δ×E1×S2×E2) / (L1×S2×E2+L2×S1×E1) σ2=(δ×E1×S1×E2) / (L2×S1×E1+L1×S2×E2) δ: total displacement amount of the first expandable wiring and the second expandable wiring L1: length of the first expandable wiring in the expansion / contraction direction L2: length of the second expandable wiring in the expansion / contraction direction S1: cross-sectional area of ​​the first expandable wiring in a cross section orthogonal to the expansion / contraction direction S2: cross-sectional area of ​​the second expandable wiring in a cross section orthogonal to the expansion / contraction direction E1: elastic modulus of the first expandable wiring E2: elastic modulus of the second expandable wiring <3> The stretchable device according to <2>, further satisfying the following formula: <4> The stretchable device according to <2>, further satisfying the following formulas: σ1≦0.80×allowable stress of first stretchable wiring σ2≦0.80×allowable stress of second stretchable wiring <5> The stretchable device according to any one of <1> to <4>, further comprising a connection member that connects the electronic component and the first stretchable wiring, wherein when viewed from a direction orthogonal to the main surface of the stretchable base material, the connection member does not overlap a first end of the second stretchable wiring in an extending direction. <6> The stretchable device according to any one of <1> to <5>, wherein there are a plurality of the first stretchable wirings and a plurality of the second stretchable wirings, and wherein there are a plurality of pairs of stretchable wirings each composed of the first stretchable wiring connected to the electronic component and the second stretchable wiring connected to the first stretchable wiring.<7> The stretchable device according to <6>, wherein, when viewed from a direction orthogonal to the main surface of the stretchable base material, each of the first stretchable wires in the plurality of sets of stretchable wires is arranged on the periphery of the electronic component so as to radiate from a center of the electronic component, and in two sets of the stretchable wires adjacent along the periphery of the electronic component, an angle formed between an extension direction of the first stretchable wire in one set of stretchable wires and an extension direction of the first stretchable wire in the other set of stretchable wires is greater than 0° and not more than 90°. <8> The stretchable device according to any one of <1> to <7>, wherein a solder erosion resistance of the first stretchable wire is higher than a solder erosion resistance of the second stretchable wire. <9> The stretchable device according to any one of <1> to <8>, wherein a solubility of the first stretchable wire in a resin is lower than a solubility of the second stretchable wire in a resin. <10> The stretchable device according to any one of <1> to <9>, wherein a length in the extension direction of the first stretchable wire is shorter than a length in the extension direction of the second stretchable wire. <11> The stretchable device according to any one of <1> to <10>, wherein a Young's modulus of the first stretchable wire is larger than a Young's modulus of the second stretchable wire. <12> The stretchable device according to any one of <1> to <11>, wherein a thickness of the first stretchable wire is larger than a thickness of the second stretchable wire. <13> The stretchable device according to any one of <1> to <12>, wherein a viscosity of a material of the first stretchable wire is larger than a viscosity of a material of the second stretchable wire. <14> The stretchable device according to any one of <1> to <13>, wherein the first stretchable wire is made of a thermosetting material, the second stretchable wire is made of a thermoplastic material, and a first end portion in the extension direction of the second stretchable wire is stacked on a second end portion in the extension direction of the first stretchable wire.

[0076] 1, 1A, 1B: Stretchable device 11: Stretchable base material 111: Main surface 21: First stretchable wire 211: First end of first stretchable wire 212: Second end of first stretchable wire 22: Second stretchable wire 221: First end of second stretchable wire 222: Second end of second stretchable wire 30, 30A: Electronic component 31, 32: External electrode 40: Connection member 50: Covering layer C: Center L1: Length of first stretchable wire L2: Length of second stretchable wire P1, P2, P3: Set of stretchable wires t1: Thickness of first stretchable wire t2: Thickness of second stretchable wire W1: Width of first stretchable wire W2: Width of second stretchable wire

Claims

1. A stretchable substrate having a main surface; An electronic component provided on the main surface of the stretchable base material; A first elastic wiring connected to the electronic component; A second elastic wire connected to the first elastic wire, A first end portion in an extension direction of the first elastic wire is connected to the electronic component, A second end portion in an extension direction of the first expandable wire is connected to a first end portion in an extension direction of the second expandable wire, A stretchable device that satisfies the following formula: σ1≦Allowable stress of first elastic wiring σ2≦Allowable stress of second elastic wiring however, σ1=(δ×E1×S2×E2) / (L1×S2×E2+L2×S1×E1) σ2=(δ×E1×S1×E2) / (L2×S1×E1+L1×S2×E2) δ: Total displacement of the first elastic wire and the second elastic wire L1: Length of the first elastic wire in the elastic direction L2: Length of the second elastic wire in the elastic direction S1: Cross-sectional area of ​​the first elastic wire in a cross section perpendicular to the elastic direction S2: Cross-sectional area of ​​the second elastic wire in a cross section perpendicular to the elastic direction E1: Elastic modulus of the first elastic wiring E2: Elastic modulus of the second elastic wiring

2. The stretchable device according to claim 1 , further satisfying the following formula: σ1≦0.80×allowable stress of the first elastic wiring σ2≦0.80×allowable stress of second elastic wiring

3. The stretchable device according to claim 1 , further satisfying the following formula: σ1≦0.50×allowable stress of the first elastic wiring σ2≦0.50×allowable stress of second elastic wiring

4. Further comprising a connection member that connects the electronic component and the first elastic wiring, The stretchable device according to claim 1 , wherein the connection member does not overlap with a first end portion of the second stretchable wire in an extension direction when viewed from a direction perpendicular to the main surface of the stretchable base material.

5. There are a plurality of the first elastic wires and a plurality of the second elastic wires, The stretchable device according to claim 1, wherein there are a plurality of sets of stretchable wirings each including the first stretchable wiring connected to the electronic component and the second stretchable wiring connected to the first stretchable wiring.

6. When viewed from a direction perpendicular to the main surface of the stretchable base material, each of the first stretchable wires in the set of the plurality of stretchable wires is disposed on the outer periphery of the electronic component so as to be radial with respect to the center of the electronic component; 6. The stretchable device according to claim 5, wherein an angle between an extension direction of the first stretchable wire in one set of stretchable wires and an extension direction of the first stretchable wire in the other set of stretchable wires is greater than 0° and less than 90°.

7. The stretchable device according to claim 1 , wherein a solder leach resistance of the first stretchable wiring is higher than a solder leach resistance of the second stretchable wiring.

8. The stretchable device according to claim 1 , wherein a solubility of the first stretchable wiring in a resin is lower than a solubility of the second stretchable wiring in a resin.

9. The stretchable device according to claim 1 , wherein a length of the first stretchable wire in an extension direction is shorter than a length of the second stretchable wire in an extension direction.

10. The stretchable device according to claim 1 , wherein a Young's modulus of the first stretchable wire is greater than a Young's modulus of the second stretchable wire.

11. The stretchable device according to claim 1 , wherein a thickness of the first stretchable wire is greater than a thickness of the second stretchable wire.

12. The stretchable device according to claim 1 , wherein a viscosity of a material of the first stretchable wire is greater than a viscosity of a material of the second stretchable wire.

13. The first elastic wire is made of a thermosetting material, The second elastic wire is made of a thermoplastic material, The stretchable device according to claim 1 , wherein a first end portion in an extension direction of the second stretchable wire is stacked on a second end portion in an extension direction of the first stretchable wire.