JP7837052B2 - Wire-shaped circuit board, device, and method for manufacturing the same - Google Patents

Description

This invention relates to a stretchable wire-shaped circuit board, a device, and a method for manufacturing the same.

In applications such as health monitoring and sensory sharing systems, there is a demand for electronic devices that can be worn comfortably on the body. The central circuitry in these devices requires not only high functionality but also miniaturization and lightweight design.

For example, Patent Document 1 discloses a spiral-shaped circuit device in which a circuit layer is formed on a sheet material and then wound into a spiral shape. The spiral-wound circuit is said to be extremely advantageous in terms of volumetric and weight characteristics compared to conventional circuits, and can be applied to smaller, lighter, and more multifunctional circuit devices in aerospace technology and other fields.

Special Publication No. 2006-527484

To use the spiral circuit devices described above in wearable devices, a degree of freedom in deformation is necessary, particularly elasticity in the winding axis direction (length direction). Furthermore, to process the spiral circuit device into a thinner, wire-like form, it is necessary to minimize the use of adhesives, such as those used to bond the spiral layers, which increase volume and weight.

This invention has been made in view of the circumstances described above, and its objective is to provide a stretchable wire-shaped circuit board, a device, and a method for manufacturing the same, which are suitable for application to stretchable devices.

The circuit board according to the present invention is a stretchable wire-shaped circuit board, characterized by the winding of a thin-film substrate on which a circuit layer made of a thin film having conductive circuit portions is applied, covering an elastic film, and the formation of undulations on the surface of the circuit layer along the longitudinal direction, which flatten when stretched in the longitudinal direction. This characteristic allows for stretchability in the winding axis direction (length direction) without compromising compactness and light weight, making it suitable for application in stretchable devices.

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. A waviness is formed on the surface of the circuit layer along the longitudinal direction, and this waviness flattens when stretched in the longitudinal direction. This feature allows for miniaturization and lightweight construction without compromising stretchability in the winding axis direction (length direction), making it suitable for application to stretchable devices.

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.

Furthermore, the method for manufacturing a circuit board according to the present invention is a method for manufacturing a stretchable wire-shaped circuit board, characterized by 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 elastically deforming it in a uniaxial direction; applying a circuit layer made of a conductive thin film to cover the elastic film; and releasing the load to form undulations on the surface of the circuit layer along the uniaxial direction, while simultaneously winding the elastic film in opposite directions from its two long sides. According to these features, a circuit board suitable for application to stretchable devices can be easily obtained without compromising compactness and light weight, while possessing stretchability in the winding axis direction (length direction).

This is a perspective view of a wire-shaped circuit board as an embodiment of the present invention. This is a perspective view showing a cross-section of the circuit board along its longitudinal direction. This is a magnified view of the same cross-section. This is a perspective view showing the steps of the first manufacturing method for a circuit board. This is a perspective view showing the steps of the second manufacturing method for a circuit board. This is a photograph showing the third manufacturing process for a circuit board. This is a perspective view showing the dimensional symbols of a circuit board during manufacturing testing. This graph shows whether or not a scroll shape was formed based on the initial length and width in the first manufacturing test. This is a table listing the manufacturing conditions in the second manufacturing test and the resulting scroll width of the circuit board.

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

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

Referring to Figures 2 and 3(a) together, the winding sections R1 and R2 are multilayered structures made of the thin film substrate 2, and undulations 3 are formed on the inner surface of each layer along the winding axes A1 and A2. That is, the undulations 3 are formed so that their ridges 3a and valleys 3b circulate 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.

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 undulation 3 flattens, reducing the height difference between its ridges 3a and valleys 3b. Furthermore, 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.

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.

Furthermore, by integrating necessary functional elements into the circuit layer 4 with a predetermined configuration, the circuit board 1 can be transformed into a stretchable device such as a bending detection device, a photovoltaic power generation device, or a light-emitting device.

For example, the material used in the conductive circuit portion of the circuit layer 4 must be able to follow the deformation of the thin-film substrate 2. For instance, when a pressure sensor is constructed as a device using the circuit substrate 1, conductive polymer materials such as PEDOT:PSS, a polythiophene-based conductive polymer, are preferably used. Other materials that can be used for light-emitting devices include conductive polymer materials, luminescent elastic materials, and organic luminescent materials. Furthermore, liquid metal materials can be used for stretchable wiring. In addition, for photovoltaic elements, conductive polymer materials, gold, organic semiconductor materials for organic thin-film solar cells such as P3HT/PCBM, and liquid metal materials are considered.

Next, we will explain how to manufacture such a circuit board 1.

[First manufacturing method]
As shown in Figure 4(a), first, a rectangular elastic membrane 5 is prepared, and both ends in the longitudinal direction are fixed with jigs 11 so as to restrain the two opposing short sides in the width direction. For the elastic membrane 5, a silicone elastomer such as PDMS (polydimethylsiloxane) can be suitably used.

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 a multi-layer.

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 by cutting the circuit board between the winding sections R1 and R2 in the longitudinal direction, a wire-shaped circuit board with a single winding section can also be obtained.

In this manufacturing method, the amount of stretching can be relatively large because it is limited by the elastic limit of the elastic membrane 5, making it easy to adjust the conditions for forming the winding portion.

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. Therefore, as shown in Figure (c), the winding sections R1 and R1 spread out, making the entire thin film substrate 2 flat. Also, the waviness 3 decreases and disappears completely when sufficient load is applied.

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

First, as shown in Figure (a), a pre-stretched thin film substrate 2' is prepared by applying a pre-stretched circuit layer 4' 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 of the rectangular pre-stretched thin film substrate 2' in the longitudinal direction are fixed with jigs 11 so that the two opposing short sides are constrained in the width direction.

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' undergoes plastic deformation to stretch and become the circuit layer 4. The pre-stretched circuit layer 4' is sized to become the circuit layer 4 upon stretching and is formed using a material that can maintain its thin film shape even under plastic deformation. For example, 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, the conductive polymer materials, luminescent elastic materials, organic luminescent materials, liquid metal materials, gold, and organic semiconductor materials mentioned above can be suitably used.

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, which 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. 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.

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, due to the constraint on the short side by the jig 11, the winding portions 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.

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, since no load is required on the jig 11 when applying the pre-stretched circuit layer 4', manufacturing is easier.

[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.

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

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. In addition, 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.

Next, as shown in Figure (b), a portion of the pre-stretched thin film substrate 2' 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 sections R1 and R2 are formed on the peeled and stretched portion of the thin film substrate 2, resulting in a scroll-shaped circuit board 1. In this example, approximately 3 cm of the pre-stretched thin film substrate 2' was peeled off, stretched to approximately 5 cm to form the thin film substrate 2, and then the load was released.

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.

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

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.

[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.

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 Sylgard® 184 Elastomer kit (manufactured by The Dow Chemical Company), mixing the main agent and curing agent in a 5:1 ratio and depositing a film to a thickness of 55 μm. The pre-stretched circuit layer 4' was obtained by depositing Parylene C (PARYLENE is a registered trademark) to a thickness of 4 μm on the elastic film 5.

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. This caused plastic deformation of the pre-stretched circuit layer 4', obtaining the thin film substrate 2 (see Figure 5(b)). Furthermore, the load separating the jigs 11 was released, and it was observed whether the thin film substrate 2 exhibited a scroll shape.

Figure 8 shows the observed results. Here, "○" indicates a scroll shape, and "×" indicates a lack of a scroll shape. It can be seen that there are conditions regarding the combination of width and initial length required to exhibit a scroll shape.

[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 by the same manufacturing method as the second manufacturing method described above.

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

For samples No. 1 to 27, the following conditions were met. The elastic film 5 was prepared by mixing Sylgard 184 Elastomer kit in a 5:1 ratio of main component to hardener, resulting in a Young's modulus of 1.37 MPa. The pre-stretch circuit layer 4' was prepared using Parylene C with a thickness of 4 μm, as described above. The Young's modulus of the pre-stretch circuit layer 4' was 1.8 GPa.

Nos. 28 and 29 are examples where the elastic film 5 is used as 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 Sylgard 184 Elastomer 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). Parylene had a thickness of 0.2 μm in both layers, and its 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 its Young's modulus was 1.3 GPa.

As shown above, we were able to manufacture a circuit board 1 with a scroll shape under various conditions. The scroll width tended to be smaller when the thickness of the thin film substrate before stretching was thin, the width W of the thin film substrate before stretching was small, and the maximum strain ε was large.

Although embodiments and modifications based thereon have been described above, the present invention is not necessarily limited thereto. 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.

1 Circuit board 2 Thin film substrate 2' Thin film substrate before stretching 3 Wavy 4 Circuit layer 4' Circuit layer before stretching 5 Elastic film 11 Jig R1, R2 Winding section

Claims (5)

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. 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. 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. The device according to claim 3, characterized by including two parallel windings wound in opposite directions from two opposing sides of the rectangular thin-film substrate. 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.