Circuit board

Abstract

To provide a circuit board that is capable of maintaining stable electrical characteristics even under repeated stretching and / or bending over a long period of use, as compared to conventional ones based on stretchable conductive materials.SOLUTION: A circuit board 1 of the present invention comprises: a base member 101 having stretchability and / or flexibility; a conductive layer 110 formed on the base member 101 in a predetermined pattern and containing a liquid metal 110a; and a coating layer 120 laminated on the conductive layer 110.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a circuit board, and more particularly to a wiring structure used for a flexible circuit board having stretchability, flexibility, etc., and related to a structure containing liquid metal.

Background Art

[0002] In recent years, the development of flexible devices having stretchability or flexibility, such as wearable devices for detecting biological signals and devices used for movable parts of robots, has been actively carried out.

[0003] In such devices, a conductive material having high stretchability or flexibility is required so as not to break when the device stretches or bends. For example, organic conductive materials such as conductive polymers are known, but they have high resistance when used as wiring materials.

[0004] Therefore, a stretchable low-resistance wiring material is required. At present, metal paste is promising as a stretchable conductive material obtained by compounding metal particles and a polymer (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in stretchable conductive materials such as metal paste, there is a problem that the resistance value increases acceleratively as the frequency of deformation such as stretching and bending increases, so that stable accuracy and functions cannot be maintained for a long period of time.

[0007] An object of the present invention is to obtain a circuit board that can maintain stable electrical characteristics even under repeated stretching and / or bending due to long-term use, as compared with a conventional circuit board using a stretchable conductive material without liquid metal.

Means for Solving the Problems

[0008] The present invention provides the following items.

[0009] (Item 1) A base member having stretchability and / or bendability, A conductive layer containing liquid metal, formed on the base member so as to form a predetermined pattern, And a coating layer laminated on the conductive layer A circuit board comprising.

[0010] (Item 2) The circuit board according to Item 1, configured to have a space around the conductive layer.

[0011] (Item 3) The circuit board according to Item 1, wherein the liquid metal is directly laminated on the base member.

[0012] (Item 4) The conductive layer has a conductive base material different from the liquid metal, The circuit board according to Item 1, wherein the liquid metal is laminated on the base material.

[0013] (Item 5) The circuit board according to Item 3, wherein base materials having conductivity and different from the liquid metal are arranged on both sides in the wiring width direction of the liquid metal.

[0014] (Item 6) The circuit board according to Item 1, wherein the base material and the liquid metal are metallically bonded.

[0015] (Item 7) The circuit board according to item 1, wherein the coating layer has insulation properties and is formed by applying a resin material that solidifies by drying or attaching a film-like body.

[0016] (Item 8) A wiring terminal for connection to an external device, formed on the base member, and An electrode pad that contacts the human skin, formed on the base member and is provided with One end of the conductive layer is connected to the wiring terminal, and the other end of the conductive layer is connected to the electrode pad. The circuit board according to item 1.

[0017] (Item 9) The circuit board according to item 1, wherein the resistance value of the conductive layer after performing a test of stretching and contracting the circuit board by about 20% for 500 cycles to 1000 cycles is about 20 Ω or less.

Advantages of the Invention

[0018] According to the present invention, compared with a conventional circuit board using a stretchable conductive material without liquid metal, a circuit board can be obtained that can maintain stable electrical characteristics even against repeated stretching and / or bending due to long-term use.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiment for Carrying Out the Invention

[0020] Hereinafter, the present invention will be described. It should be understood that the terms used in this specification are used in the meanings commonly used in the art unless otherwise specified. Therefore, unless otherwise defined, all technical terms and scientific terms used in this specification have the same meaning as generally understood by those skilled in the art to which the present invention pertains. In case of contradiction, this specification (including definitions) shall prevail.

[0021] In this specification, "about" means within the range of ±10% of the following number.

[0022] An object of the present invention is to obtain a circuit board that can maintain stable electrical characteristics even under repeated stretching and / or bending due to long-term use, as compared with those using conventional stretchable conductive materials. A base member having stretchability and / or bendability; A conductive layer containing liquid metal, formed on the base member so as to form a predetermined pattern; A coating layer laminated on the conductive layer The above problems are solved by providing a circuit board including.

[0023] Therefore, the circuit board of the present invention is not particularly limited as long as the conductive layer formed on the base member having stretchability, bendability, etc. and covered with the coating layer contains liquid metal. Here, a circuit is a path through which electricity flows.

[0024] And a circuit board is one in which a conductive layer having a predetermined pattern containing liquid metal is formed on a base member and the conductive layer is covered with a coating layer, and other configurations are not limited.

[0025] (Base member) The base member can be any material as long as it has elasticity and / or flexibility. For example, it may be cloth, or it may be polyurethane, paper, rubber, cloth, or silicone, etc. In particular, when used as a circuit board directly attached to the skin, the base member is preferably polyurethane or silicone, and when used for a circuit board that makes the circuit board a wearable product, cloth is preferred.

[0026] (Liquid metal material) Liquid metal is a metal or alloy that becomes liquid near room temperature. The liquid metal material is not limited to a specific material. For example, it can be mercury or gallium, or an alloy of gallium and other metals, such as an alloy of gallium and indium, an alloy of gallium, indium, and tin, or an alloy of gallium, indium, and zinc. Since liquid metal is a metal with fluidity near room temperature, it can keep a low resistance against continuous stretching or bending, and disconnection can be suppressed.

[0027] Also, the thickness of the liquid metal layer can be arbitrary, but in order to prevent leakage, a thickness of about 2μm to about 50μm is preferred.

[0028] (Base material) The base material is included in the above conductive layer and serves as a base when arranging liquid metal in a predetermined pattern on the base member. The liquid metal may be laminated on the base material on the base member, or the liquid metal may be arranged between two base materials on the base member in a form of sandwiching.

[0029] The base material is not limited to a specific material, but those with high affinity (ease of metal bonding) with liquid metal are preferred. For example, it may be silver, copper, or carbon. However, the present invention is not limited thereto. Also, the base material is preferably in a paste form containing an adhesive or the like, but the present invention is not limited thereto.

[0030] For example, the metal bond between silver paste as the base material and gallium indium as the liquid metal is expected to have a high affinity between the base material and the liquid metal.

[0031] (Coating layer) The material of the coating layer is not limited to a specific material as long as it has insulating properties. For example, a resin material that solidifies by drying or a resin material formed in a film shape is used. Also, the coating layer may be, for example, a stretchable insulating ink. Generally, a specific material and formation method of the coating layer that are suitable for the manufacturer's manufacturing equipment are adopted.

[0032] Note that the method of forming the coating layer is not limited to printing, and a spray dispenser or jet method can be used. Furthermore, these methods are also applicable to the formation of the base material and the layer of liquid metal.

[0033] The liquid metal contained in the conductive layer of the present invention may be directly laminated on the base member, or may be laminated via the base material serving as its base. In the structure of the conductive layer in which the liquid metal is laminated on the base member via the base material, due to the effect of the metal bond, the liquid metal is held in a predetermined pattern without leaking from the base material.

[0034] Note that in the structure of the conductive layer in which the liquid metal is directly laminated on the base member, by making the layer of the liquid metal into a thin film, it is possible to prevent leakage from a predetermined pattern.

[0035] By providing the above configuration, it becomes possible to provide a space around the conductive layer, so there is no need to provide a groove, side wall, etc. for fixing the liquid metal in a predetermined pattern, which simplifies the structure and particularly reduces the man-hours. As a result, it is also possible to manufacture the circuit board at low cost.

[0036] In the structure of the conductive layer in which the liquid metal is directly laminated on the base member, a base material that forms a wall in the wiring width direction of the layer of the liquid metal disposed on the base member may be provided. By providing the wall, it becomes possible to reliably prevent leakage from a predetermined pattern of the liquid metal.

[0037] In the circuit board including the liquid metal in the conductive layer of the present invention, even when repeatedly stretched and contracted, the resistance value of the wiring is stable and it becomes possible to maintain accuracy and function in the long term.

[0038] Furthermore, in one embodiment, the circuit board includes a wiring terminal formed on the base member for connection to an external device and an electrode pad formed on the base member and contacting the skin of a human body. One end of the conductive layer is connected to the wiring terminal, and the other end of the conductive layer is connected to the electrode pad.

[0039] As described above, the circuit board of the present invention is not particularly limited as long as the conductive layer formed on the base member having stretchability, flexibility, etc. and covered with the coating layer contains the liquid metal. However, in the following Embodiment 1, the conductive layer has a liquid metal and a base material serving as its base, and the liquid metal is laminated on the base member via the base material. This is an example of a circuit board. In Embodiment 2, a circuit board in which the liquid metal is directly laminated on the base member is cited. In a modified example thereof, a circuit board in which the base material is disposed as a wall on both sides of the liquid metal in the circuit board of Embodiment 2 is cited.

[0040] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0041] (Embodiment 1) FIG. 1 is a diagram showing a circuit board 1 according to Embodiment 1 of the present invention, and shows a case where the liquid metal contained in the conductive layer is disposed on the circuit board via a base material serving as its base.

[0042] The circuit board 1 of this Embodiment 1 includes a base member 101 having stretchability and flexibility, a conductive layer 110 containing liquid metal formed on the base member 101 so as to form a predetermined pattern, and an insulating coating layer 120 laminated on the conductive layer 110. In FIG. 1, the coating layer 120 is shown in perspective to show the base material 110b and the liquid metal 110a constituting the conductive layer 110.

[0043] The conductive layer 110 has a structure in which a liquid metal 110a made of an alloy (here gallium indium) is laminated on a base material 110b made of silver paste formed on the base member 101. The silver base of the base material 110b and the mercury which is the liquid metal 110a exhibit a metallic bonding state. Here, the liquid metal 110a may be a metal (for example, mercury) made of a single metal element instead of an alloy.

[0044] And the upper surface and / or both side surfaces of the conductive layer 110 are covered by a coating layer 120 made of stretchable insulating ink, and a wiring 10 is formed by the conductive layer 110 and the coating layer 120, and both ends of the wiring 10 are connected to electrode pads or wiring terminals (see FIG. 7).

[0045] The thickness of the layer of the liquid metal 110a is made thin so that the highly fluid liquid metal 110a can be more reliably held on the base material 110b. For example, the thickness is in the range of about 2 μm to about 50 μm. If the layer of the liquid metal 110a is too thin compared to the above range, the resistance of the conductive layer 110 constituting the wiring 10 increases, and if the liquid metal 110a is too thick compared to the above range, there is a risk of leakage.

[0046] Such a circuit board 1 is manufactured by forming a metal paste layer with a predetermined pattern in a region where the conductive layer 110 is to be formed on its surface, laminating (arranging) the liquid metal 110a thereon, and then forming a coating layer 120 such as stretchable insulating ink.

[0047] (Embodiment 2) FIG. 2 is a diagram for explaining a circuit board according to Embodiment 2 of the present invention, showing a case where the liquid metal constituting the conductive layer is directly disposed on the circuit board. Also in FIG. 2, the liquid metal constituting the conductive layer 210a is shown through the coating layer 220.

[0048] The circuit board 2 of this Embodiment 2 includes a base member 101, a conductive layer 210a formed on the base member 101 so as to form a predetermined pattern, and an insulating coating layer 220 laminated on the conductive layer 210a. Here, the conductive layer 210a has a structure in which liquid metal is directly laminated on the base member 101.

[0049] The conductive layer 210a made of liquid metal is covered by the coating layer 220 on its upper surface and both side surfaces, and wiring 20 is formed by the conductive layer 210a and the coating layer 220. Both ends of the wiring 20 are connected to electrode pads and wiring terminals (see FIG. 7).

[0050] Here, the same materials as those shown in Embodiment 1 are used for the base member 101, the liquid metal constituting the conductive layer 210a, and the coating layer 220.

[0051] In the structure of the conductive layer 210a in which the liquid metal is directly laminated on the base member 101, it is preferable to dispose a base material serving as a wall on both sides in the wiring width direction of the layer of the liquid metal disposed on the base member. This is because the leakage of the liquid metal is suppressed by the base material positioned as a wall on both sides of the layer of the liquid metal.

[0052] (Modification of Embodiment 2) FIG. 3 is a diagram for explaining a modification of the circuit board shown in FIG. 2. Also in FIG. 3, the liquid metal 210a and the base material 210b constituting the conductive layer 210 are shown through the coating layer 220.

[0053] In the circuit board 2a of this modification example, in the circuit board 2 of the second embodiment, base materials 210b serving as walls are arranged on both sides of the liquid metal 210a that forms the conductive layer. Here, the liquid metal 210a and the base materials 210b on both sides thereof form the conductive layer 210, and the wiring 20a is formed by the conductive layer 210 and the coating layer 220. Note that the same material as the base material 110b of the first embodiment is used for the base material 210b.

[0054] In the circuit board 2a according to this modification example, compared with the circuit board 2 of the second embodiment, the leakage of the liquid metal is more suppressed by the base material 210b positioned as walls on both sides of the layer of the liquid metal 210a.

[0055] (Performance Test of the Circuit Board of the Present Invention) The test sample is as shown in FIG. 4. Here, the thickness of the base material constituting the conductive layer is about 25 μm. Here, the conductive layer is shown by dot display.

[0056] In addition, samples with the thickness of the liquid metal, which is an alloy of gallium and indium constituting the conductive layer, changed to three types (about 2 μm, about 25 μm, about 50 μm) were prepared, and the resistance value of the conductive layer was tested. The test conditions are that the expansion and contraction process, which includes a step of expanding the circuit board by about 20% of the total length of the circuit board (20% of the length of 85 mm in FIG. 4, that is, about 17 mm) from the steady state (without expansion and contraction) and a step of contracting it back to the original steady state length after expansion, is defined as one cycle, and after performing a plurality of set predetermined cycles, the electrical resistance value is measured respectively. Also, as a reference example, a test is also conducted on a circuit board of the prior art, where the conductive layer is made of silver paste without using liquid metal.

[0057] FIG. 5 is a diagram showing the test results of the continuous expansion and contraction test of the circuit board shown in the first embodiment. Also, FIG. 6 is a diagram showing the test results of the continuous expansion and contraction test of the circuit board shown in the modification example of the second embodiment.

[0058] In both FIGS. 5 and 6, the vertical axis represents the measured electrical resistance value, and the horizontal axis represents the number of cycles of continuous expansion and contraction. As shown in FIGS. 5 and 6, in all cases of thickness, the resistance value tends to increase as the number of cycles increases. However, compared to the prior art shown in the reference example, the increase in the resistance value with respect to the increase in the number of cycles is suppressed to a low level.

[0059] Specifically, in the case of the prior art, the resistance value before the test is about 5 Ω or less, and it remains within 10 Ω to 20 Ω until 350 cycles. However, after that, the resistance value increases rapidly, and exceeds about 40 Ω after 500 cycles. On the other hand, in the circuit board of the present invention, the increase rate of the resistance value is low even with the increase in the number of cycles, and even after 1000 cycles, it maintains a low value of about 20 Ω or less. In particular, when the thickness of the liquid metal is about 25 to about 50 μm, it is found that even after 1000 cycles, it is about 10 Ω or less, and the electrical characteristics are maintained stably with almost no change in the resistance value before the test.

[0060] Also, from another perspective, in the conventional circuit board, the resistance value exceeds about 10 times compared to before the test between 500 cycles and 1000 cycles, whereas in the circuit board of the present invention, between 500 cycles and 1000 cycles, the resistance value is suppressed to about 3 times or less compared to before the test.

[0061] Also, in the circuit board 2a which is a modified example of Embodiment 2, in which the liquid metal 210a is directly laminated on the base member 101 and the base material 210b is arranged as a wall on both sides of the liquid metal 210a, compared to the circuit board 1 of Embodiment 1 in which the liquid metal 110a is laminated on the base member 101 via the base material 110b, when the thickness of the liquid metal is about 50 μm and about 2 μm, there is no substantial difference in the increase in the resistance value. However, when the thickness of the liquid metal is about 25 μm, the resistance value maintains a low value regardless of the number of cycles.

[0062] From these results, the circuit board of the present invention has an excellent effect that cannot be achieved by the circuit boards of the prior art, namely, the electrical characteristics can be stabilized even under repeated expansion / contraction and / or bending during long-term use.

[0063] FIG. 7 is a diagram for explaining an application example of the circuit board of the present invention. FIG. 7(a) shows a case where the circuit board of the present invention is used as a circuit board directly attached to human skin, and FIG. 7(b) shows a case where the circuit board of the present invention is used as a circuit board constituting a wearable device.

[0064] First, a case where the circuit board of the present invention is directly attached to the human body skin as shown in FIG. 7(a) will be described.

[0065] For example, the base member 101 of the circuit board 1 of Embodiment 1 is attached to the human skin 50a.

[0066] In this case, specifically, the back surface of the base member 101 of the circuit board 1 of Embodiment 1 is attached to the human skin 50a with an adhesive material, an adhesive tape, etc. Here, this circuit board 1 is used to electrically connect the wiring terminal 12 and the electrode pad 11 attached to the human skin. Note that the electrode pad 11 is a member that contacts the human skin, and the wiring terminal 12 is a member for connection with an external device and is a member for connection with an external device.

[0067] Also, the circuit board may include, in addition to the wiring 10, the wiring terminal 12 and the electrode pad 11 connected by this wiring 10.

[0068] Next, a case where the circuit board of the present invention is used as a circuit board constituting a wearable device as shown in FIG. 7(b) will be described.

[0069] For example, when configuring the wearable device Wd using the circuit board 1 of Embodiment 1, the back surface of the base member 101 of the circuit board 1 is attached to the back surface of the fabric of the shirt 50b. In this case, the wiring 10 of the circuit board 1 electrically connects the wiring terminal 12 and the electrode pad 11 formed on the back surface of the fabric of the shirt. Note that the wiring 10 and the wiring terminal 12 may be attached to the front surface of the fabric of the shirt.

[0070] In addition, as the circuit board of the present invention applied in this way, instead of the circuit board 1 of Embodiment 1, the circuit board 2 of Embodiment 2 or the circuit board 2a of its modified example may be used.

[0071] Also, in FIG. 7(b), although the form of attaching the base member of the circuit board to the shirt was described, the base member of the circuit board may be the shirt.

[0072] As described above, the present invention has been illustrated using the preferred embodiments of the present invention. However, the present invention should not be construed as being limited to this embodiment. It is understood that the scope of the present invention should be construed only by the scope of the claims. Those skilled in the art will understand that an equivalent range can be implemented based on the description of the present invention and common technical knowledge from the description of the specific preferred embodiments of the present invention. It is understood that the documents cited in this specification should be incorporated by reference in the same way as if the content itself were specifically described in this specification.

Industrial Applicability

[0073] The present invention is useful as it can obtain a circuit board that can maintain stable electrical characteristics even under repeated stretching and / or bending due to long-term use, compared to those using conventional stretchable conductive materials.

Explanation of Signs

[0074] 1, 2, 2a Circuit board 10, 20, 20a Wiring 11 Electrode pad 12 Wiring terminal 101 Base member 110, 210 Conductive layer 110a, 210a Liquid metal 110b, 210b Base material 120, 220 Coating layer

Claims

[Claim 1] The invention described in this specification.

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