Circuit substrate and method of manufacturing the same

Abstract

To provide a circuit base material which improves thinning, chemical resistance and followability, heat-treats a conductive material at high temperature and can improve a function of a conductive pattern layer, and can prevent positional deviation to cause hindrance of mounting, and a manufacturing method of the same.SOLUTION: A circuit base material includes a peeling layer 1 having flexibility, an insulation layer 3 which is peelably formed on the peeling layer 1, a conductive pattern layer 4 which is laminated and formed on the insulation layer 3 by a silver-containing paste, an adhesive layer 8 which is bonded to a part of the conductive pattern layer 4, and a plurality of deformation suppression layers 9 which are laminated and formed in the residual part of the conductive pattern layer 4, wherein Shore A hardness when the peeling layer 1 is measured as a silicone elastomer 2 having thickness of 10 μm or more and 250 μm or less according to JIS K 6253 is set to 10 or more and 60 or less, the insulation layer 3 is laminated and formed by a resin, its thickness is set to 10 μm or more and 20 μm or less, and the silver-containing paste is any one of a silver complex paste ink and a silver nano paste ink whose volume resistivities are lowered by heat treatment of 160°C or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a circuit board used in in-vehicle electronic devices, industrial electronic devices, information terminal devices, home appliances, etc., and a method for manufacturing the same. [Background technology]

[0002] Although not shown, a conventional circuit substrate is formed into a self-capacitance type capacitance sensor that includes, for example, a bendable substrate, a conductive pattern on the surface of the substrate on which multiple electrodes and the like are arranged, and a protective sheet that is laminated on the surface of the substrate and covers the conductive pattern.After being placed opposite the back side of an operation panel, when a finger, which is a conductor, selectively approaches multiple electrodes of the conductive pattern through the operation panel, the capacitance between the electrode and the finger changes and the touch coordinate is detected (see Patent Documents 1 and 2).

[0003] The substrate is formed, for example, from a thick resin film made of polyethylene terephthalate (PET) resin, which has high chemical and physical functionality as well as stable and uniform quality. The conductive pattern is formed by printing a pattern of a predetermined conductive material, such as silver ink or carbon nanotubes, on the surface of the substrate, followed by heat treatment to dry and harden it. The protective sheet is not particularly limited, but may be formed, for example, from a transparent sheet made of silicone with weak adhesiveness, which adheres to the surface of the substrate and effectively prevents external dust and other particles from adhering to the conductive pattern. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-201272 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-244776 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional capacitance sensors are constructed as described above, and when the substrate is a thick resin film, it is difficult to achieve the thinning that has been strongly desired in recent years. Furthermore, when the substrate is a resin film of polyethylene terephthalate resin, it is not easy to not only thin the sensor, but also to improve its chemical resistance. Moreover, the resin film becomes brittle and may require reinforcement.

[0006] Furthermore, when the substrate is a polyethylene terephthalate resin film, the specified conductive material pattern is printed on the surface of the substrate and then heat-treated at a temperature of 150°C or less, taking into consideration the heat resistance of the polyethylene terephthalate resin. However, if the conductive material is heat-treated at a temperature below 150°C, the conductive material may not be able to fully function. For example, if the conductive material is a conductive ink that requires high-temperature heating of 160°C or more to metallize, heat treatment at a temperature below 150°C cannot prevent high resistance due to residual organic matter, making it extremely difficult to achieve a volume resistivity of 20 μΩ·cm or less for the conductive pattern.

[0007] Furthermore, if the protective sheet for the capacitance sensor is simply a transparent silicone sheet, when the operation panel is curved like a bow and has a high curvature, the protective sheet may not properly conform to the curved surface of the operation panel and fit tightly, or it may become misaligned, causing problems with the attachment of the capacitance sensor.

[0008] The present invention has been made in consideration of the above, and aims to provide a circuit substrate and a manufacturing method thereof that can be made thinner, have improved chemical resistance and conformability, can heat-treat conductive materials at high temperatures to improve the functionality of the conductive pattern layer, and can eliminate the risk of misalignment causing problems with installation. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a flexible adhesive sheet including a flexible release layer, an insulating layer releasably formed on the release layer, a conductive pattern layer formed on the insulating layer using at least a silver-containing paste, an adhesive layer adhered to a portion of the conductive pattern layer, and a deformation suppressing layer formed on the remaining portion of the conductive pattern layer, the release layer is made of a silicone elastomer having a thickness of 10 μm or more and 250 μm or less, and the silicone elastomer has a Shore A hardness of 10 or more and 60 or less when measured in accordance with JIS K 6253, a breaking elongation of 100% or more and 1000% or less when measured in accordance with JIS K 6251, and a tensile strength of 4 MPa or more and 12 MPa or less when measured in accordance with JIS K 6251; The insulating layer is formed by laminating resin to a thickness of 10 μm or more, The silver-containing paste is characterized by being either a silver complex paste ink or a silver nanopaste ink, the volume resistivity of which decreases when heat-treated at 160°C or higher.

[0010] The insulating layer is formed by laminating a thermosetting polyol-based resin, and the Shore D hardness of this resin, measured in accordance with JIS K 6253, can be 60 or more and 75 or less, and the flexural modulus, measured in accordance with JIS K 7171, can be 500 MPa or more and 2500 MPa or less.

[0011] In addition, the silver complex paste ink of the silver-containing paste can be a paste ink having a thixotropy index of 1.7 or more and 1.8 or less, a solid content of 30% wt or more and 33% wt or less, and a volume resistivity of the conductive pattern layer of 10 μΩ·cm or less when heat-treated at 160°C or higher. In addition, the silver nanopaste ink of the silver-containing paste can also be a paste ink having a silver concentration of 50 wt% or more as measured by thermogravimetric differential thermal analysis, and a solvent composition of a non-water-soluble solvent or an alcohol-glycol mixed solvent.

[0012] The adhesive layer is made of a hot melt adhesive, a thermosetting adhesive, a light curing adhesive, an ultraviolet curing adhesive, or a room temperature curing adhesive, and preferably has a thickness of 12 μm or more. The deformation suppression layer is preferably made of a resin film having a thickness of 12 μm or more, a Shore A hardness of 10 or more and 60 or less when measured in accordance with JIS K 6253, a breaking elongation of 100% or more and 1000% or less when measured in accordance with JIS K 6251, and a tensile strength of 4 MPa or more and 12 MPa or less when measured in accordance with JIS K 6251.

[0013] In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a circuit substrate as described in claim 1 or 2, which comprises: forming a resin insulating layer having a thickness of 10 μm or more on a flexible release layer in a releasable manner; printing at least a silver-containing paste on the insulating layer and heat-treating the printed insulating layer to form a conductive pattern layer; applying an adhesive to a portion of the conductive pattern layer and curing the adhesive to form an adhesive layer; and forming a deformation suppressing layer on the remaining portion of the conductive pattern layer, the release layer is made of a silicone elastomer having a thickness of 10 μm or more and 250 μm or less, and the silicone elastomer has a Shore A hardness of 10 or more and 60 or less when measured in accordance with JIS K 6253, a breaking elongation of 100% or more and 1000% or less when measured in accordance with JIS K 6251, and a tensile strength of 4 MPa or more and 12 MPa or less when measured in accordance with JIS K 6251; The silver-containing paste is characterized by being either a silver complex paste ink or a silver nanopaste ink, the volume resistivity of which decreases when heat-treated at 160°C or higher.

[0014] Here, the silver-containing paste in the claims has a volume resistance of 10 when measured by a four-terminal four-probe method. -5If the resistance is Ω or less, a silver complex paste ink or a silver nanopaste ink may be used. Furthermore, the multiple electrodes of the conductive pattern layer are appropriately arranged in the XY direction, X direction, and Y direction of the insulating layer. When the conductive pattern layer is laminated by heat treatment, it is preferable to heat the silver-containing paste to at least 160°C. Furthermore, the circuit substrate may be, for example, a capacitance sensor, a printed wiring board, a flexible substrate, a high-frequency substrate, an antenna, an RFID tag, or the like, and may be built into the housing of various electrical and electronic devices or attached to the back side of an operation panel, for example.

[0015] According to the present invention, since no thick substrate is used for the insulating layer, the circuit substrate can be made thinner and lighter, thereby improving the design freedom of the capacitance sensor. Furthermore, since the release layer is made of a silicone elastomer with excellent heat resistance of 200°C or higher, high-temperature drying processing is possible. Furthermore, since this silicone elastomer has excellent flexibility, the circuit substrate can be appropriately bent and fitted closely to a three-dimensional surface. [Effects of the Invention]

[0016] The present invention has the advantages of enabling a circuit substrate to be made thinner and having improved chemical resistance and conformability, and also of improving the functionality of the conductive pattern layer by heat-treating the conductive material at a high temperature exceeding 150°C, while eliminating the risk of misalignment causing problems when mounting the circuit substrate.

[0017] According to the invention of claim 2, the insulating layer is formed by laminating a thermosetting polyol-based resin, which is expected to have excellent heat resistance, chemical resistance, weather resistance, etc. Furthermore, the Shore D hardness of the insulating layer measured in accordance with JIS K 6253 is 60 or more and 75 or less, which ensures the flexibility and pliability of the insulating layer when applied to complex or curved surfaces.

[0018] According to the invention described in claim 3, the silver complex paste ink of the silver-containing paste is a paste ink that has a thixotropy index of 1.7 or more and 1.8 or less, a solids content of 30% wt or more and 33% wt or less, and a volume resistivity of the conductive pattern layer of 10 μΩ·cm or less when heat-treated at 160°C or higher, so that the volume resistivity of the conductive pattern layer can be lower than conventional.

[0019] According to the invention described in claim 4, the silver nanopaste ink, which is a silver-containing paste, has a silver concentration of 50 wt% or more when measured by thermogravimetric differential thermal analysis, and is a paste ink whose solvent composition is a non-water-soluble solvent or an alcohol-glycol mixed solvent, so that the volume resistivity of the conductive pattern layer can be made lower than before, and furthermore, the surface of the conductive pattern layer can be made smooth, making it possible to stabilize the quality. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an overall perspective view schematically illustrating a capacitance sensor in an embodiment of a circuit board according to the present invention. [Figure 2] 1 is a cross-sectional view illustrating a capacitance sensor according to an embodiment of a circuit board according to the present invention; [Figure 3] 1 is an exploded perspective view schematically illustrating a capacitance sensor in an embodiment of a circuit board according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] A preferred embodiment of the present invention will now be described with reference to the drawings. As shown in Figures 1 to 3, the circuit substrate in this embodiment is a self-capacitance type capacitance sensor comprising a flexible release layer 1, a flexible insulating layer 3 removably formed on this release layer 1, a light-transmitting conductive pattern layer 4 formed on this insulating layer 3 by laminating it with a silver-containing paste, a light-transmitting adhesive layer 8 covering part of this conductive pattern layer 4, and a plurality of deformation suppression layers 9 covering the remainder of the conductive pattern layer 4, and contributes to the achievement of Goal 9 of the SDGs (the United Nations' international goals for sustainable development, consisting of 17 global goals and 169 targets (achievement criteria)) adopted at the United Nations Summit.

[0022] The release layer 1 is formed into a flat rectangular shape or the like from a silicone elastomer 2 that is flexible and has excellent heat resistance of 200°C to 250°C, weather resistance, flame retardancy, dielectric properties, and electrical insulation properties, and the surface facing the insulating layer 3 is subjected to a mirror finish or release treatment as necessary, and is peeled off from the insulating layer 3 when the capacitance sensor is in use. From the viewpoint of ease of handling and workability, this silicone elastomer 2 has a thickness of 10 μm to 250 μm, preferably 50 μm to 250 μm, and a density of 1.21 g / cm when measured at 23°C in accordance with JIS K 6268. 3 More than 1.25g / cm 3 or less, preferably 1.24 g / cm 3 The Shore A hardness measured in accordance with JIS K 6253 is set to a range of 10 to 60, preferably 30 to 60, to ensure flexibility on curved surfaces.

[0023] The elongation at break of the silicone elastomer 2, as measured in accordance with JIS K 6251, is preferably 100% to 1000%, and more preferably 500% to 800%, in order to improve mechanical properties. Furthermore, the tensile strength, as measured in accordance with JIS K 6251, is preferably 4 MPa to 12 MPa, and more preferably 6 MPa to 12 MPa, in order to achieve both flexibility and strength. Furthermore, the tear strength (crescent type), as measured in accordance with JIS K 6252, is preferably 8 kN / m to 28 kN / m, and more preferably 13 kN / m to 18 kN / m, in order to prevent warping and deformation. These measurements can be performed using measuring instruments and testing machines from M&K Corporation, ITS Japan Co., Ltd., etc.

[0024] A specific example of such a silicone elastomer 2 is KE-153U (product name, manufactured by Shin-Etsu Chemical Co., Ltd.).

[0025] The insulating layer 3 is formed by laminating a predetermined resin, for example, a thermosetting polyol-based resin such as a UV-curable acrylic resin, onto the surface of the release layer 1 by printing or the like, into a flat rectangular thin film, and has flexibility for use on complex uneven or curved surfaces. The reason for using a thermosetting polyol-based resin for the insulating layer 3 is that it is expected to have excellent heat resistance, chemical resistance, weather resistance, heat insulation, etc. The thickness of the insulating layer 3 is 10 μm or more, preferably 10 μm to 20 μm, more preferably 15 μm to 20 μm, from the perspective of thinning the capacitance sensor.

[0026] The Shore D hardness of the insulating layer 3, measured in accordance with JIS K 6253, is preferably 60 to 75, and more preferably 65 to 75, in order to ensure flexibility to curved surfaces. The flexural modulus, measured in accordance with JIS K 7171, is preferably 500 MPa to 2500 MPa, and more preferably 1500 MPa to 2500 MPa.

[0027] The conductive pattern layer 4 is formed by directly screen printing a silver-containing paste onto the surface of the insulating layer 3, and then drying and hardening it by heat treatment at a high temperature of 160°C or higher, exceeding 150°C. The silver-containing paste is not silver ink, but a paste with a volume resistivity of 20 μΩ·cm or less due to high-temperature treatment, and a volume resistivity of 10 μΩ·cm or less when measured by the four-terminal four-probe method. -5 A silver complex paste ink or silver nanopaste ink with a volume resistivity of Ω or less is used because, if such a paste ink is heat-treated, the volume resistivity finally obtained becomes about 1 / 8 or less of that of silver ink.

[0028] The viscosity characteristics of the silver complex paste ink measured with a viscometer (product name: CPA-52Z) are as follows: -1 An inexpensive paste ink is preferably used that has a viscosity of about 32,000 cPs to about 33,000 cPs, a thixotropy index of about 1.7 to about 1.8, a solids content of about 30% wt to about 33% wt, and a volume resistivity of the conductive pattern layer 4 of 10 μΩ cm or less, preferably 7.5 μΩ cm or less, when heat-treated at a high temperature of 160° C. or more. Specific examples of such silver complex paste inks include El-904 (product name, manufactured by Electronix, Inc., USA) and El-909 (product name, manufactured by Electronix, Inc., USA).

[0029] In contrast, silver nanopaste inks with a silver concentration of 50 wt% or more as measured by thermogravimetric differential thermal analysis (TG-DTA) and solvent composition of a non-aqueous solvent or an alcohol-glycol mixed solvent are suitable. To minimize volume resistivity, the silver concentration of silver nanopaste inks measured by thermogravimetric differential thermal analysis should be 50 wt% to 70 wt%, preferably 60 wt% to 70 wt%. Furthermore, the volume resistivity of silver nanopaste inks measured by the four-point probe method after baking at 120°C for 30 minutes should be 6.0 μΩ·cm to 6.3 μΩ·cm, preferably 6.1 μΩ·cm to 6.25 μΩ·cm.

[0030] A specific example of such a silver nanopaste ink is DNS409 (DNS409S) (manufactured by Daicel Corporation: product name Picosil (registered trademark) series), which can provide a conductive pattern layer 4 similar to a metal foil.

[0031] The conductive pattern layer 4 includes, for example, a plurality of electrodes 5 laminated in the center of the insulating layer 3 and covered with an adhesive layer 8, a GND electrode laminated on the insulating layer 3, a plurality of conductive lines 6 connected to the plurality of electrodes 5 and covered with a plurality of deformation suppression layers 9, and a plurality of connection terminals 7 formed at the end portions of at least some of the plurality of conductive lines 6 and connected to the rigid substrate, and the thickness of these is set in the range of 1 μm or more and 20 μm or less.

[0032] The electrodes 5 are arranged at predetermined intervals in the longitudinal direction of the insulating layer 3, for example, and each electrode 5 is formed in a transparent, planar rectangular, diamond, circular, or other shape so as to be able to come into close proximity with a conductor such as an operator's finger via the adhesive layer 8, forming a capacitance between the electrode 5 and the conductor and detecting a change in that capacitance. Each conductive line 6 is formed to extend in at least either the longitudinal direction of the insulating layer 3, and has a line width of 30 μm to 1000 μm, preferably 30 μm to 500 μm.

[0033] The volume resistivity of such a conductive pattern layer 4 is 19 Ω or less, preferably 17 Ω or less, and more preferably 15 Ω or less, when a pattern having a width of 100 μm, a length of 10 cm, and a thickness of 5 μm is measured in accordance with JIS H 0505. Furthermore, the surface roughness Ra of the conductive pattern layer 4 is 0.1 μm or more and 0.9 μm or less, and preferably about 0.1 μm, when measured in accordance with JIS B 0651.

[0034] The adhesive layer 8 is made of a predetermined adhesive, such as a hot melt adhesive, a thermosetting adhesive, a light curing adhesive, an ultraviolet curing adhesive, or a room temperature curing adhesive, and is laminated and bonded into a flat rectangular shape by screen printing the predetermined adhesive onto at least a plurality of electrodes 5 of the conductive pattern layer 4, and is then attached to the back side of the operation panel, etc. The thickness of this adhesive layer 8 is not particularly limited, but from the perspective of making the capacitance sensor thinner, it is preferable that it be in the range of 12 μm to 100 μm.

[0035] The plurality of deformation suppression layers 9 are formed into a planar rectangular shape using an unstretched resin film such as polyethylene terephthalate resin or polycarbonate resin, and are laminated and bonded onto at least the plurality of conductive lines 6 of the conductive pattern layer 4 via an acrylic adhesive or the like, and are arranged to sandwich the adhesive layer 8, thereby preventing defects during bonding of the capacitance sensor. Each deformation suppression layer 9 preferably has a thickness of 12 μm or more, preferably 12 μm to 250 μm, a Shore A hardness measured in accordance with JIS K 6253 of 10 to 60, an elongation at break measured in accordance with JIS K 6251 of 100% to 1000%, preferably 500% to 800%, and a tensile strength measured in accordance with JIS K 6251 of 4 MPa to 12 MPa.

[0036] When manufacturing a capacitance sensor with the above configuration, first prepare a silicone elastomer 2 of a predetermined size as the release layer 1. Then, a thermosetting polyol resin is printed on most of the surface of the silicone elastomer 2, excluding the peripheral edge, and then the insulating layer 3 is laminated by irradiating it with ultraviolet light, drying, or curing it. The thermosetting polyol resin is automatically screen-printed using a screen printing device. This is because screen printing is ideal for achieving high-quality insulating layer 3 and speeding up the process. Since the resin is screen-printed rather than laminating a commercially available thermosetting polyol resin film on the surface of the silicone elastomer 2, it is expected that the insulating layer 3 will be significantly thinner.

[0037] After the insulating layer 3 is laminated and formed, a silver-containing paste is directly printed on the surface of the insulating layer 3, and then heat-treated at a high temperature of 160°C or higher to dry and harden, thereby metallizing and forming an array of multiple conductive pattern layers 4. The silver-containing paste is automatically screen-printed using a screen printing device. This is because screen printing is ideal for achieving high quality conductive pattern layers 4 and accelerating work. The screen-printed silver-containing paste is then heat-treated, and the heat treatment temperature is adjusted to a high temperature of 160°C or higher, preferably 180°C or higher, more preferably 190°C or higher, and even more preferably around 200°C, in order to reduce the resistance of the conductive pattern layers 4.

[0038] Next, a predetermined adhesive is screen-printed onto the multiple electrodes 5 of the multiple conductive pattern layers 4 in the same manner as above to laminate and bond a light-transmitting adhesive layer 8, and a resin film of a deformation suppression layer 9 is laminated and bonded onto the multiple conductive lines 6 of each conductive pattern layer 4 via an adhesive.After that, the peel layer 1, insulating layer 3, multiple conductive pattern layers 4, adhesive layer 8, and pair of deformation suppression layers 9 are cut to adjust the appearance, thereby manufacturing a capacitance sensor.

[0039] Next, when the capacitance sensor is to be attached to a curved operation panel for use, the capacitance sensor is bent onto the back surface of the operation panel, and its adhesive layer 8 and the pair of deformation suppressing layers 9 are brought into contact while being positioned, and the multiple connection terminals 7 of the conductive pattern layer 4 are connected to the rigid substrate, and then the release layer 1 is peeled off and removed from the insulating layer 3 of the capacitance sensor, and the capacitance sensor is ready for use. At this time, the insulating layer 3 alone is thin, brittle, and prone to tearing, but because the insulating layer 3 and the pair of deformation suppressing layers 9 are integrated, not only is handling improved but damage to the insulating layer 3 can be prevented extremely effectively.

[0040] According to the above configuration, the insulating layer 3 is formed as a thin film by resin printing, eliminating the need for a thick substrate for the insulating layer 3. This allows for a thinner and lighter capacitance sensor, improving the design flexibility of the capacitance sensor. Furthermore, if the insulating layer 3 is made of a thermosetting polyol-based resin rather than a polyethylene terephthalate resin film, excellent chemical resistance, weather resistance, heat insulation, and the like can be expected. Furthermore, since the release layer 1 is made of a silicone elastomer 2 with excellent heat resistance of 200°C or higher, high-temperature drying processing is possible, and the conductive pattern layer 4 can be formed by heat-treating a silver-containing paste at a high temperature of 160°C or higher, for example, around 200°C.

[0041] Therefore, high resistance due to remaining organic matter can be prevented, and the volume resistivity of the conductive pattern layer 4 can be made 20 μΩ·cm or less, preferably 19 μΩ·cm or less, more preferably 18 μΩ·cm or less, and even more preferably 16 μΩ·cm or less.

[0042] Furthermore, because the release layer 1 is made of a silicone elastomer 2 with excellent flexibility and a Shore A hardness of 10 to 60, the capacitance sensor can be properly conformed to the curved surface of the operation panel, even when the operation panel has a complex three-dimensional curve with a high curvature (e.g., a hollow hemisphere or hemispherical shape). This effectively eliminates the risk of misalignment interfering with the attachment of the capacitance sensor, and also improves design flexibility. Furthermore, because the conductive pattern layer 4 is covered and protected by the adhesive layer 8 and the pair of deformation suppression layers 9, it is possible to effectively prevent dust from adhering to the conductive pattern layer 4 and degrading its performance.

[0043] In the above embodiment, the insulating layer 3 is formed by laminating a thin film of a thermosetting polyol-based resin, but this is not limited to this, and the insulating layer 3 may be formed by laminating a thin film of a resin other than a thermosetting polyol-based resin as long as it provides approximately the same function. [Industrial Applicability]

[0044] The circuit board and its manufacturing method according to the present invention are used in the manufacturing fields of in-vehicle electronic devices, industrial electronic devices, information terminal devices, home appliances, and the like. [Explanation of symbols]

[0045] 1. Peel layer 2. Silicone elastomer 3. Insulation layer 4 Conductive pattern layer 5 electrodes 6 Conductive Lines 7 Connection terminal 8 Adhesive layer 9 Deformation suppression layer

Claims

1. The adhesive tape includes a flexible release layer, an insulating layer releasably formed on the release layer, a conductive pattern layer formed on the insulating layer by laminating at least a silver-containing paste, an adhesive layer adhered to a portion of the conductive pattern layer, and a deformation suppressing layer formed on the remaining portion of the conductive pattern layer, the release layer is made of a silicone elastomer having a thickness of 10 μm or more and 250 μm or less, the silicone elastomer having a Shore A hardness of 10 or more and 60 or less when measured in accordance with JIS K 6253, a breaking elongation of 100% or more and 1000% or less when measured in accordance with JIS K 6251, and a tensile strength of 4 MPa or more and 12 MPa or less when measured in accordance with JIS K 6251; The insulating layer is formed by laminating resin to a thickness of 10 μm or more, A circuit substrate characterized in that the silver-containing paste is either a silver complex paste ink or a silver nanopaste ink whose volume resistivity decreases when heat-treated at 160°C or higher.

2. 2. The circuit board according to claim 1, wherein the insulating layer is formed by laminating a thermosetting polyol-based resin, and the resin has a Shore D hardness of 60 to 75 when measured in accordance with JIS K 6253 and a flexural modulus of 500 MPa to 2500 MPa when measured in accordance with JIS K 7171.

3. 3. The circuit substrate according to claim 1, wherein the silver complex paste ink of the silver-containing paste is a paste ink having a thixotropy index of 1.7 or more and 1.8 or less, a solid content of 30% wt or more and 33% wt or less, and a volume resistivity of the conductive pattern layer of 10 μΩ cm or less when heat-treated at 160°C or more.

4. The circuit substrate according to claim 1 or 2, wherein the silver nanopaste ink of the silver-containing paste is a paste ink having a silver concentration of 50 wt% or more as measured by thermogravimetric differential thermal analysis and a solvent composition of a non-water-soluble solvent or an alcohol / glycol mixed solvent.

5. 3. A method for manufacturing a circuit substrate according to claim 1 or 2, comprising the steps of: forming a resin insulating layer having a thickness of 10 μm or more on a flexible release layer in a releasable manner; printing at least a silver-containing paste on the insulating layer and heat-treating the printed insulating layer to form a conductive pattern layer; applying an adhesive to a portion of the conductive pattern layer and curing the adhesive to form an adhesive layer; and forming a deformation suppressing layer on the remaining portion of the conductive pattern layer, the release layer is made of a silicone elastomer having a thickness of 10 μm or more and 250 μm or less, the silicone elastomer having a Shore A hardness of 10 or more and 60 or less when measured in accordance with JIS K 6253, a breaking elongation of 100% or more and 1000% or less when measured in accordance with JIS K 6251, and a tensile strength of 4 MPa or more and 12 MPa or less when measured in accordance with JIS K 6251; A method for manufacturing a circuit substrate, characterized in that the silver-containing paste is either a silver complex paste ink or a silver nanopaste ink whose volume resistivity decreases when heat-treated at 160°C or higher.

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