Wire-shaped circuit board, device, and method for manufacturing the same

Abstract

To provide a wire-like circuit board which is appropriate to be applied to a stretchable device and has flexibility, a device and a manufacturing method thereof.SOLUTION: A circuit board is configured by winding a thin film substrate to which a circuit layer consisting of a thin film covering an elastic body film and including a conductive circuit portion is applied, swell is formed on a surface of the circuit layer in a length direction in such a manner that the swell is flattened when the circuit board is stretched in the length direction, and a device using the circuit board is also provided. A manufacturing method of the circuit board includes the steps of: applying a load so as to separate opposed two short sides of the rectangular elastic body film from each other while restricting them in a width direction and performing elastic deformation in a uniaxial direction; applying the circuit layer consisting of the conductive thin film while covering the elastic body film; and forming the swell on the surface of the circuit layer in the uniaxial direction by cancelling the load, and performing winding in mutually reverse directions from two long sides of the elastic body film.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wire-shaped circuit board having elasticity, a device, and a manufacturing method thereof.

Background Art

[0002] In health monitoring and sensory sharing systems, etc., there is a demand for electronic devices that can be worn without discomfort on the body, and in this central circuit part, miniaturization and weight reduction are required along with high functionality.

[0003] For example, Patent Document 1 discloses a spiral circuit device formed by forming a circuit layer on a sheet material and then winding it in a spiral shape. The spiral-wound circuit is extremely advantageous in terms of volume characteristics and weight characteristics compared to conventional circuits, and it is said that it can be applied to smaller, lighter, and more multifunctional circuit devices in aerospace technology, etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to use the spiral circuit device as described above in a wearable device, freedom in deformation is required, and in particular, elasticity in the winding axis direction (length direction) is required. Further, in order to process it into a thinner wire shape as a deformable spiral circuit device, it is also required to limit as much as possible the use of, for example, an adhesive for adhering between spiral layers, which causes an increase in its volume and weight.

[0006] The present invention has been made in view of the above-described circumstances, and its object is to provide a stretchable wire-shaped circuit board, a device, and a method for manufacturing the same that are suitable for application to stretchable devices. [Means for solving the problem]

[0007] The circuit board according to the present invention is a stretchable wire-shaped circuit board, characterized in that a thin-film substrate, on which a circuit layer made of a thin film having a conductive circuit portion is provided by covering an elastic film, is wound, and undulations are formed on the surface of the circuit layer along the longitudinal direction, and the undulations flatten when stretched in the longitudinal direction. With these features, it is possible to have stretchability in the winding axis direction (length direction) without compromising small size and light weight, making it suitable for application to stretchable devices.

[0008] Furthermore, the device according to the present invention is a device using a stretchable wire-shaped circuit board, wherein a thin film substrate, on which functional elements are attached, is wound around a circuit layer made of a thin film covering an elastic film and having a conductive circuit portion, and undulations are formed on the surface of the circuit layer along the longitudinal direction, and the undulations flatten when stretched in the longitudinal direction. With these features, it is possible to have stretchability in the winding axis direction (length direction) without compromising small size and light weight, making it suitable for application to stretchable devices.

[0009] The invention described above may be characterized by including two parallel windings wound in opposite directions from two opposing sides of the rectangular elastic film. This feature allows for increased circuit density and is suitable for application to stretchable devices.

[0010] Furthermore, the present invention relates to a method for manufacturing a circuit board, which is a method for manufacturing a stretchable wire-shaped circuit board, and is characterized by including the steps of: applying a load to a rectangular elastic film so as to restrain two opposing short sides in the width direction and separate them from each other, thereby causing elastic deformation in a uniaxial direction; covering the elastic film with a circuit layer made of a conductive thin film; and releasing the load to form undulations on the surface of the circuit layer along the uniaxial direction, and winding the elastic film in opposite directions from its two long sides. With these features, a circuit board suitable for application to stretchable devices can be easily obtained without compromising compactness and light weight, and which can have stretchability in the winding axis direction (length direction). [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of a wire-shaped circuit board as an embodiment of the present invention. [Figure 2] This is a perspective view showing a cross-section of the circuit board along its longitudinal direction. [Figure 3] This is a magnified view of the same cross-section. [Figure 4] This is a perspective view showing the steps of the first manufacturing method for a circuit board. [Figure 5] This is a perspective view showing the steps of the second manufacturing method for a circuit board. [Figure 6] This is a photograph showing the third manufacturing process for a circuit board. [Figure 7] This is a perspective view showing the dimensional symbols of a circuit board during manufacturing testing. [Figure 8] This graph shows whether or not a scroll shape was formed based on the initial length and width in the first manufacturing test. [Figure 9] This is a table listing the manufacturing conditions in the second manufacturing test and the resulting scroll width of the circuit board. [Modes for carrying out the invention]

[0012] Below, an embodiment of the present invention, a wire-shaped circuit board, a device using the same, and a method for manufacturing them, will be described with reference to Figures 1 to 6.

[0013] As shown in Figure 1, the circuit board 1 is wire-like (linear) overall, formed by winding a thin film substrate 2 around a winding axis oriented in the longitudinal direction. In this embodiment, there are two winding axes, A1 and A2, which form two parallel winding sections R1 and R2.

[0014] Referring to Figures 2 and 3(a) together, the winding sections R1 and R2 are multilayered structures made of thin film substrate 2, and undulations 3 are formed on the inner surface of each layer along the winding axes A1 and A2. In other words, the undulations 3 are formed so that their ridges 3a and valleys 3b are routed around the winding axes A1 and A2 on a plane perpendicular to the winding axes A1 and A2. The thin film substrate 2 has a two-layer structure consisting of an elastic film 5 and a circuit layer 4 covering it. The circuit layer 4 is formed of a thin film having a conductive circuit portion.

[0015] Here, as shown in Figure 3(b), when the circuit board 1 is stretched in the longitudinal direction (left-right direction on the paper), the undulations 3 flatten out, reducing the height difference between their ridges 3a and valleys 3b. When the stretching force is released, the circuit board 1 returns to its original shape with a large height difference between the undulations 3, as shown in Figure 3(a), due to the elasticity of the elastic membrane 5.

[0016] In other words, even if the circuit layer 4 does not possess the excellent elasticity of an elastic membrane 5, it can follow longitudinal stretching by flattening the undulations 3 formed along its longitudinal direction. Therefore, the circuit board 1 can be stretched by applying a load in the longitudinal direction, and furthermore, it can return to its original shape by releasing the load. For example, a wire-shaped circuit board 1 can be made into stretchable wiring.

[0017] In addition, the circuit board 1 can be a stretchable device such as a bending detection device, a photovoltaic device, a light-emitting device, etc. by incorporating functional elements necessary for the circuit layer 4 into a predetermined configuration.

[0018] For example, as the material used for the conductive circuit portion of the circuit layer 4, a material that can follow the deformation of the thin film substrate 2 is required. For example, when a pressure sensor is configured as a device using the circuit board 1, a conductive polymer material such as PEDOT:PSS, which is a polythiophene-based conductive polymer, is preferably used. In addition, when a light-emitting element is used, a conductive polymer material, a light-emitting elastomer material, an organic light-emitting material, etc. can be used. Also, when stretchable wiring is used, a liquid metal material, etc. can be used. Furthermore, when a photovoltaic element is used, the application of a conductive polymer material, gold, an organic semiconductor material for an organic thin film solar cell such as P3HT / PCBM, a liquid metal material, etc. is considered.

[0019] Next, a method for manufacturing such a circuit board 1 will be described.

[0020] [First manufacturing method] As shown in Fig. 4(a), first, a rectangular elastic body film 5 is prepared, and both ends in the longitudinal direction are fixed with jigs 11 respectively so as to restrain the two opposite short sides in the width direction. As the elastic body film 5, for example, a silicone elastomer such as PDMS (polydimethylsiloxane) can be preferably used.

[0021] As shown in Figure (b), a load is applied to the two jigs 11 so as to separate them from each other while constraining the short side of the elastic film 5 in the width direction with the jig 11, causing the elastic film 5 to be elastically deformed so as to stretch in the longitudinal direction (elastic deformation step). Then, while maintaining this elastic deformation, a circuit layer 4 is applied so as to cover the elastic film 5 (circuit layer application step). The circuit layer 4 is a film body that can form undulations 3 by having flexibility, and is, for example, a conductive thin film in which a conductive circuit portion is applied to an insulating film such as parylene (registered trademark) or fluororesin. A thin film substrate 2 is obtained by applying the circuit layer 4 to the elastic film 5. It is preferable to apply O2 plasma before forming the circuit layer 4 to improve the bonding between each layer. It is also preferable to perform plasma treatment in the same way when the circuit layer 4 is multilayered.

[0022] As shown in Figure (c), the load applied to the jig 11 is maintained, and then, as shown in Figure (d), the load applied to the jig 11 is released (load release step). This forms winding sections R1 and R2 in the central longitudinal portion of the thin film substrate 2, which is not constrained by the jig 11. The winding sections R1 and R2 are wound in opposite directions from two opposing sides (long sides) of the rectangular elastic film 5, with the elastic film 5 of the thin film substrate 2 facing outwards. This shape, including the winding sections wound in opposite directions from the two long sides, will hereafter be referred to as a "scroll shape." Furthermore, undulations 3 are formed on the surface of the circuit layer 4 along the long sides of the elastic film 5. In this way, the circuit board 1 can be obtained. Note that a wire-shaped circuit board with a single winding section can also be obtained by cutting the section between the winding sections R1 and R2 in the longitudinal direction.

[0023] In this manufacturing method, the amount of stretching can be relatively large because it is limited by the elasticity of the elastic membrane 5, and the conditions for forming the winding portion can be easily adjusted.

[0024] Furthermore, as shown in Figure (d), when a load is applied to the two parts of the jig 11 in a direction that separates them from each other, the short side is constrained by the jig 11, causing the winding parts R1 and R1 to spread out and flatten the entire thin film substrate 2, as shown in Figure (c). Also, the waviness 3 becomes smaller and disappears when sufficient load is applied.

[0025] [Second manufacturing method] As shown in Figure 5, a circuit board 1 having a scroll shape can also be obtained by other manufacturing methods.

[0026] First, as shown in Figure (a), a pre-stretched thin film substrate 2' is prepared, on which a pre-stretched circuit layer 4' is applied so as to cover the rectangular elastic film 5. At this time, no load is applied to the elastic film 5. Then, similar to the first manufacturing method, both ends in the longitudinal direction of the rectangular pre-stretched thin film substrate 2' are fixed with jigs 11 so as to restrain the two opposing short sides in the width direction.

[0027] Next, as shown in Figure (b), a load is applied to the two jigs 11 so as to separate them while constraining the short side of the pre-stretched thin film substrate 2' in the width direction, thereby deforming the pre-stretched thin film substrate 2' by stretching it in the longitudinal direction to form the thin film substrate 2. At this time, the elastic film 5 undergoes elastic deformation, and the pre-stretched circuit layer 4' is stretched by plastic deformation to become the circuit layer 4. The pre-stretched circuit layer 4' is sized to become the circuit layer 4 when stretched, and is formed using a material that can maintain its thin film shape even under plastic deformation. Parylene can be suitably used as the material for the pre-stretched circuit layer 4'. Furthermore, the material used for the conductive circuit portion of the pre-stretched circuit layer 4' must also be able to follow the deformation of the pre-stretched thin film substrate 2'. For example, conductive polymer materials, luminescent elastic materials, organic luminescent materials, liquid metal materials, gold, and organic semiconductor materials can be suitably used.

[0028] Finally, as shown in Figure (c), when the load applied to the jig 11 is released, winding portions R1 and R2 are formed in the central longitudinal portion of the thin film substrate 2 that is not constrained by the jig 11. The winding portions R1 and R2 are wound in opposite directions from two opposing sides (long sides) of the rectangular elastic film 5, with the elastic film 5 of the thin film substrate 2 facing outwards, thereby obtaining a scroll shape. In addition, undulations 3 are formed on the surface of the circuit layer 4 along the long sides of the elastic film 5. In this way, the circuit board 1 can be obtained.

[0029] Furthermore, as shown in Figure (c), when a load is applied to the two parts of the jig 11 in a direction that separates them from each other, starting from a state where no load is applied to the jig 11, the thin film substrate 2 is stretched, as shown in Figure (b). At this time, because the short side is constrained by the jig 11, the winding parts R1 and R1 are spread out, making the entire thin film substrate 2 flat. Also, the waviness 3 becomes smaller and disappears when sufficient load is applied.

[0030] In this manufacturing method, the amount of plastic deformation is determined by the plastic deformability of the pre-stretched circuit layer 4', and therefore tends to be smaller compared to the first manufacturing method described above. On the other hand, no load is required on the jig 11 when applying the pre-stretched circuit layer 4', making manufacturing easier.

[0031] [Third manufacturing method] As shown in Figure 6, for example, it is also possible to manufacture a circuit board 1 having a length exceeding 1 meter.

[0032] First, as shown in Figure (a), a release agent is deposited on the surface of a disc-shaped base, and a pre-stretched thin film substrate 2' is deposited on top of it in the same manner as in the second manufacturing method. Furthermore, spiral-shaped cuts are made in the pre-stretched thin film substrate 2'.

[0033] Here, an 8-inch diameter silicon wafer was used as the substrate, and Cytop 809M was deposited as a release agent by spin coating. Furthermore, as the elastic film 5 of the pre-stretched thin film substrate 2', a mixture of the main component and curing agent of Sylgard 184 in a 5:1 ratio was applied to a thickness of approximately 50 μm and cured. Additionally, parylene C was deposited to a thickness of 4 μm as the pre-stretched circuit layer 4' of the pre-stretched thin film substrate 2'. The width of the spiral-shaped cutouts was approximately 5 mm.

[0034] Next, as shown in Figure (b), a portion of the thin film substrate 2' before stretching is peeled off from the outer periphery, and a tensile load is applied to stretch it. When the load is released from the stretched portion, winding portions R1 and R2 are formed on the thin film substrate 2 in the peeled and stretched portion, resulting in a circuit board 1 having a scroll shape. In this case, a length of approximately 3 cm of the thin film substrate 2' before stretching was peeled off, stretched to a length of approximately 5 cm to form the thin film substrate 2, and then the load was released.

[0035] Furthermore, as shown in Figure (c), peeling and stretching were repeatedly performed sequentially from the outside of the spiral to obtain a circuit board 1 having a long, continuous scroll shape.

[0036] As described above, by winding the thin film substrate 2, a circuit board 1 can be obtained that is small and lightweight, and has stretchability in the winding axis direction (length direction). Furthermore, since such a circuit board 1 is wire-shaped and stretchable in the length direction, it is suitable for application to stretchable devices and can be obtained relatively easily.

[0037] Next, the results of actually manufacturing a circuit board using the second manufacturing method described above will be explained with reference to Figures 7 to 9.

[0038] [First Manufacturing Test] We investigated whether a wire-shaped circuit board 1 having a scroll shape could be obtained by manufacturing the thin film substrate 2 using the same manufacturing method as the second manufacturing method described above, under multiple manufacturing conditions.

[0039] First, as shown in Figure 7, a rectangular pre-stretched thin film substrate 2' with an initial length L and width W between the jigs 11 was prepared. That is, both short sides of the pre-stretched thin film substrate 2', which had an elastic film 5 and a pre-stretched circuit layer 4' covering it, were restrained by the jigs 11. The elastic film 5 was obtained by using the Sylgard® 184 Erastomer kit (manufactured by The Dow Chemical Company) and mixing the main agent and curing agent in a 5:1 ratio to form a film with a thickness of 55 μm. The pre-stretched circuit layer 4' was obtained by forming a 4 μm thick Parylene C (PARYLENE is a registered trademark) film on top of the elastic film 5.

[0040] Next, a load was applied to separate the two jigs 11 from each other, and the pre-stretched thin film substrate 2' was stretched until the distance between the jigs 11 became 1.8 times the initial length L, causing plastic deformation of the pre-stretched circuit layer 4' and obtaining the thin film substrate 2 (see Figure 5(b)). Furthermore, the load that separated the jigs 11 was released, and it was observed whether the thin film substrate 2 exhibited a scroll shape.

[0041] Figure 8 shows the observed results. Here, "○" indicates a scroll shape, and "×" indicates a scroll shape was not obtained. It can be seen that there are conditions for the combination of width and initial length that produce a scroll shape.

[0042] [Second Manufacturing Test] The width of the scroll-shaped portion (scroll width) was measured when a circuit board 1 having a scroll shape was manufactured using the same manufacturing method as the second manufacturing method described above.

[0043] Figure 9 shows the scroll width when the thickness of the elastic film 5, the thickness of the pre-stretch circuit layer 4', the length and width of the pre-stretch thin film substrate 2', and the degree of stretching (maximum strain) of the pre-stretch thin film substrate 2' are varied. The maximum strain ε indicates that the total length is stretched to L × (1 + ε / 100%) relative to the initial length L. For example, if the maximum strain ε is 100%, the stretched dimension is 2 × L relative to the initial length L.

[0044] For samples No. 1 to 27, the following conditions were met. For the elastic film 5, Sylgard 184 Erastomer kit was mixed with the main agent and hardener in a 5:1 ratio, as described above, resulting in a Young's modulus of 1.37 MPa. For the pre-stretch circuit layer 4', Parylene C was used with a thickness of 4 μm, as described above. The Young's modulus of the pre-stretch circuit layer 4' was 1.8 GPa.

[0045] Examples No. 28 and 29 show cases where the elastic film 5 is a mixed material and the pre-stretched thin film substrate 2' is multilayered. The elastic film 5 was prepared by mixing the main component (a) and curing agent (b) of the Sylgard 184 Erastomer kit with component A (c) and component B (d) of Ecoflex 00-30 (manufactured by Smoothon). The mixing ratio was (a):(b):(c):(d) = 40:1:82:82. The Young's modulus was 86 kPa. The pre-stretched thin film substrate 2' had a four-layer structure of Parylene C → diX-SR (diX is a registered trademark: manufactured by KISCO Corporation) → Parylene C → Cytop 809M (Cytop is a registered trademark: manufactured by AGC Chemicals Company). Both Parylene layers had a thickness of 0.2 μm, and the Young's modulus was 1.8 GPa. diX-SR had a thickness of 1 μm in No. 28 and a thickness of 0.8 μm in No. 29, with a Young's modulus of 4.0 GPa. Cytop 809M had a thickness of 0.3 μm and a Young's modulus of 1.3 GPa.

[0046] As shown above, we were able to manufacture a circuit board 1 having a scroll shape under various conditions. The thinner the thickness of the thin film substrate before stretching, the smaller the width W of the thin film substrate before stretching, and the larger the maximum strain ε, the smaller the scroll width tended to be.

[0047] Although embodiments and modifications based thereon have been described above, the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the invention or the scope of the attached claims. [Explanation of Symbols]

[0048] 1 Circuit board 2 Thin-film substrate 2' Thin film substrate before stretching 3. Swell 4 circuit layers 4' circuit layer before stretching 5. Elastic membrane 11. Jig R1, R2 winding section

Claims

1. A wire-shaped circuit board that is stretchable, A wire-shaped circuit board is formed by winding a thin-film substrate onto which a circuit layer made of a thin film having a conductive circuit portion is provided, covering an elastic film, wherein undulations are formed on the surface of the circuit layer along the longitudinal direction, and the undulations flatten out when the wire is stretched in the longitudinal direction.

2. The wire-shaped circuit board according to claim 1, characterized in that it includes two parallel windings wound in opposite directions from two opposing sides of the rectangular elastic film.

3. A device using a wire-shaped circuit board that is stretchable, A device using a wire-shaped circuit board, characterized in that a thin film substrate, on which a functional element is attached, is wound around a circuit layer made of a thin film covering an elastic film and having a conductive circuit portion, and undulations are formed on the surface of the circuit layer along the longitudinal direction, and the undulations become flat when stretched in the longitudinal direction.

4. The device according to claim 3, characterized in that it includes two parallel windings wound in opposite directions from two opposing sides of the rectangular thin film substrate.

5. A method for manufacturing a stretchable wire-shaped circuit board, A step of elastically deforming a rectangular elastic membrane in one axis direction by applying a load to restrict two opposing short sides in the width direction and move them apart from each other, The steps include: providing a circuit layer made of a conductive thin film by covering the elastic film; A method for manufacturing a wire-shaped circuit board, comprising the steps of releasing the load to form undulations on the surface of the circuit layer along the uniaxial direction, and winding the elastic film in opposite directions from its two long sides.

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