Scalable mounting substrate and method for manufacturing the same

Abstract

The present invention relates to a stretchable mounting substrate and a method for manufacturing the stretchable mounting substrate. The stretchable mounting substrate (1) includes: a stretchable base material (10); a mounting electrode portion (30a) located on one main surface side of the stretchable base material (10) and including a conductive filler and a resin; a solder portion (40a) connected to the mounting electrode portion (30a); and an electronic component (50) electrically connected to the mounting electrode portion (30a) via the solder portion (40a). The mounting electrode portion (30a) has a first main surface (31a) on the side of the stretchable base material (10) and a second main surface (32a) on the side of the solder portion (40a). In the mounting electrode portion (30a), there are a first region (E1) including the first main surface (31a) and a second region (E2) including the second main surface (32a). In the mounting electrode portion (30a), when observing a cross-section including the first region (E1) and the second region (E2), the cross-sectional area of the conductive filler present in the second region (E2) is larger than the cross-sectional area of the conductive filler present in the first region (E1).

Description

Technical Field

[0001] The present invention relates to a stretchable mounting substrate and a method for manufacturing the stretchable mounting substrate. Background Art

[0002] In recent years, by using a wiring substrate to acquire and analyze biological information, the state of a living organism (for example, a human body) is managed.

[0003] In such a wiring substrate, electronic components are sometimes mounted. For example, Patent Document 1 discloses a substrate including: a flexible base material, a flexible wiring pattern formed on the base material, a conductive member formed on the wiring pattern, an electronic component, and a joining member that joins the conductive member and the electronic component.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-14381

[0005] In the substrate described in Patent Document 1, solder is used as the joining member. On the other hand, in order to improve the wettability of the solder, a metal foil, a metal plating, or metal powder is used as the conductive member. However, when a conductive member with good solder wettability and an electronic component are joined via solder, a phenomenon called solder erosion occurs in which the conductive member reacts with the solder to form a brittle metal compound. In the substrate described in Patent Document 1, it is considered that such solder erosion easily occurs in the entire conductive member, so the conductive member is likely to break as a whole, and as a result, the mounting strength of the electronic component is likely to decrease.

[0006] In addition, in the substrate described in Patent Document 1, when a metal foil or metal powder is used as the conductive member, in order to ensure the flexibility of the entire substrate, it is necessary to reduce the area where the metal foil or metal powder is provided within the range in contact with the solder, and a special device is required. In contrast, when a metal plating is used as the conductive member, flexibility is easily ensured, but in order to prevent short circuits between the wiring patterns, it is necessary to protect the base material so that no metal plating is formed between the wiring patterns, and the process becomes complicated. In addition, in this case, a base material resistant to the plating solution needs to be used. Thus, in the substrate described in Patent Document 1, there is room for improvement in terms of being able to be manufactured by a simple process. Summary of the Invention

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide a stretchable mounting substrate that can ensure the mounting strength of an electronic component and can be manufactured by a simple process. Another object of the present invention is to provide a method for manufacturing the above stretchable mounting substrate.

[0008] The stretchable mounting substrate of the present invention is characterized by comprising: a stretchable base material; a mounting electrode portion located on one main surface side of the stretchable base material and containing a conductive filler and a resin; a solder portion connected to the mounting electrode portion; and an electronic component electrically connected to the mounting electrode portion via the solder portion. The mounting electrode portion has a first main surface on the side of the stretchable base material and a second main surface on the side of the solder portion. In the mounting electrode portion, there is a first region including the first main surface and a second region including the second main surface. When observing a cross-section including the first region and the second region in the mounting electrode portion, the cross-sectional area of the conductive filler present in the second region is larger than the cross-sectional area of the conductive filler present in the first region.

[0009] The manufacturing method of the stretchable mounting substrate of the present invention is characterized by comprising: a first electrode layer forming step of applying a first conductive paste containing a first conductive filler and a thermosetting resin to one main surface side of a stretchable base material and then performing heat treatment to form a first electrode layer; a second electrode layer forming step of applying a second conductive paste containing a second conductive filler and a thermoplastic resin to the opposite side of the stretchable base material with respect to the first electrode layer and then performing heat treatment to form a second electrode layer; and an electronic component mounting step of applying a solder paste onto the second electrode layer, then mounting an electronic component on the solder paste, and then performing heat treatment to melt and solidify the solder paste to form a solder portion and joining the electronic component to the first electrode layer via the solder portion.

[0010] According to the present invention, it is possible to provide a stretchable mounting substrate that can ensure the mounting strength of an electronic component and can be manufactured by a simple process. In addition, according to the present invention, it is possible to provide a manufacturing method of the above stretchable mounting substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a plan view showing an example of the stretchable mounting substrate of the present invention.

[0012] Figure 2 is showing the corresponding part of the line segment A1 - A2 in Figure 1 in a cross-sectional view.

[0013] Figure 3 is a plan view showing another example of the stretchable mounting substrate of the present invention.

[0014] Figure 4 is showing the corresponding part of the line segment A1' - A2' in Figure 3 in a cross-sectional view.

[0015] Figure 5This is an example of a method for manufacturing a stretchable mounting substrate of the present invention, and is a cross-sectional schematic view showing a first electrode layer forming process.

[0016] Figure 6 This is an example of a method for manufacturing a stretchable mounting substrate of the present invention, and is a cross-sectional schematic view showing a second electrode layer forming process.

[0017] Figure 7 This is an example of a method for manufacturing a stretchable mounting substrate of the present invention, and is a plan schematic view showing an electronic component mounting process.

[0018] Figure 8 This is a cross-sectional schematic view showing a part corresponding to the line segment B1 - B2 in Figure 7 ...

[0019] Figure 9 This is Figure 8 an enlarged view of the region enclosed by a dashed line in..., and is a cross-sectional schematic view showing the state before heat treatment of the solder paste.

[0020] Figure 10 This is a cross-sectional schematic view showing the state during heat treatment of the solder paste with respect to the state shown in Figure 9 ...

[0021] Figure 11 This is a cross-sectional schematic view showing the state after heat treatment of the solder paste with respect to the state shown in Figure 9 ...

[0022] Figure 12 This is a cross-sectional schematic view showing an enlarged view of the region enclosed by a dashed line in Figure 2 ...

[0023] Figure 13 This is a cross-sectional photograph showing the state at the completion of the second electrode layer forming process during the manufacturing process of the stretchable mounting substrate of Example 1.

[0024] Figure 14 This is a cross-sectional photograph showing the state at the completion of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Example 1.

[0025] Figure 15 This is a cross-sectional photograph showing the state at the completion of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Comparative Example 1. Detailed Description

[0026] Hereinafter, the stretchable mounting substrate of the present invention and the method for manufacturing the stretchable mounting substrate of the present invention will be described. In addition, the present invention is not limited to the following structures and can be appropriately changed without departing from the gist of the present invention. In addition, a scheme in which a plurality of the following described preferred structures are combined is also the present invention.

[0027] Figure 1 It is a plan schematic view showing an example of the stretchable mounting substrate of the present invention. Figure 2 It is shown as Figure 1 a cross-sectional schematic view of a portion corresponding to the line segment A1 - A2 in

[0028] As shown in Figure 1 and Figure 2 the stretchable mounting substrate 1 includes a stretchable base material 10, stretchable wirings 20a, 20b, mounting electrode portions 30a, 30b, solder portions 40a, 40b, and an electronic component 50.

[0029] Preferably, the stretchable base material 10 contains at least one resin selected from polyurethane resins, silicone resins, acrylic resins, and olefin resins. As the polyurethane resin, for example, thermoplastic polyurethane (TPU) can be cited.

[0030] When the stretchable mounting substrate 1 is attached to a living body, from the viewpoint of not hindering the stretching of the living body surface, the thickness of the stretchable base material 10 is preferably 100 μm or less, more preferably 50 μm or less. In addition, the thickness of the stretchable base material 10 is preferably 10 μm or more.

[0031] In this specification, the thickness of each member and each layer means the length in the thickness direction orthogonal to the main surface of the stretchable base material (the up - down direction in Figure 2 ) when viewed in cross - section. In addition, unless otherwise specified, this thickness represents the thickness in a state where the stretchable mounting substrate does not stretch.

[0032] The stretchable wiring 20a is provided on one main surface 11a of the stretchable base material 10 and is arranged such that its end portion sandwiches the end portion of the mounting electrode portion 30a in the thickness direction between it and the stretchable base material 10. In this way, the stretchable wiring 20a and the mounting electrode portion 30a are connected to each other at the end portions.

[0033] The stretchable wiring 20b is provided on one main surface 11a of the stretchable base material 10 and is arranged such that its end portion sandwiches the end portion of the mounting electrode portion 30b in the thickness direction between it and the stretchable base material 10. In this way, the stretchable wiring 20b and the mounting electrode portion 30b are connected to each other at the end portions.

[0034] The stretchable wirings 20a and 20b include, for example, a conductive filler and a resin.

[0035] Examples of the conductive filler included in the stretchable wirings 20a and 20b include metal fillers such as silver fillers, copper fillers, and nickel fillers. Among them, the conductive filler included in the stretchable wirings 20a and 20b is preferably a silver filler.

[0036] Preferably, the types of metals of the conductive filler included in the stretchable wiring 20a and the conductive filler included in the stretchable wiring 20b are the same as each other, but the types of metals may also be different from each other.

[0037] Examples of the shape of the conductive filler included in the stretchable wirings 20a and 20b include a plate shape, a spherical shape, and the like.

[0038] Preferably, the shapes of the conductive filler included in the stretchable wiring 20a and the conductive filler included in the stretchable wiring 20b are the same as each other, but the shapes may also be different from each other.

[0039] The particle diameter of the conductive filler included in the stretchable wirings 20a and 20b is preferably 0.01 μm or more and 10 μm or less. The particle diameter of the conductive filler refers to the length of the maximum side in the case where the conductive filler is in a plate shape, and refers to the diameter in the case where the conductive filler is in a spherical shape.

[0040] Preferably, the particle diameters of the conductive filler included in the stretchable wiring 20a and the conductive filler included in the stretchable wiring 20b are the same as each other, but the particle diameters may also be different from each other.

[0041] Preferably, the resin included in the stretchable wirings 20a and 20b is at least one elastomeric resin selected from acrylic resins, epoxy resins, polyurethane resins, and silicone resins.

[0042] Preferably, the types of resins of the resin included in the stretchable wiring 20a and the resin included in the stretchable wiring 20b are the same as each other, but the types of resins may also be different from each other.

[0043] The thicknesses of the stretchable wirings 20a and 20b are preferably 100 μm or less, more preferably 50 μm or less. In addition, the thicknesses of the stretchable wirings 20a and 20b are preferably 1 μm or more.

[0044] Preferably, the thicknesses of the stretchable wirings 20a and 20b are the same as each other, but they may also be different from each other.

[0045] The mounting electrode portion 30a and the mounting electrode portion 30b are located on the side of one main surface 11a of the stretchable base material 10, and are provided on one main surface 11a of the stretchable base material 10 here. The mounting electrode portion 30a and the mounting electrode portion 30b are provided at positions separated from each other.

[0046] The mounting electrode portion 30a and the mounting electrode portion 30b contain a conductive filler and a resin.

[0047] Examples of the conductive filler contained in the mounting electrode portion 30a and the mounting electrode portion 30b include metal fillers such as silver filler, copper filler, and nickel filler. Among them, the conductive filler contained in the mounting electrode portion 30a and the mounting electrode portion 30b is preferably silver filler.

[0048] The conductive filler contained in the mounting electrode portion 30a and the conductive filler contained in the mounting electrode portion 30b preferably have the same type of metal, but the types of metal can also be different from each other.

[0049] Examples of the shape of the conductive filler contained in the mounting electrode portion 30a and the mounting electrode portion 30b include plate shape, spherical shape, etc. Among them, the conductive filler contained in the mounting electrode portion 30a and the mounting electrode portion 30b is preferably plate-shaped.

[0050] The conductive filler contained in the mounting electrode portion 30a and the conductive filler contained in the mounting electrode portion 30b preferably have the same shape, but the shapes can also be different from each other.

[0051] The resin contained in the mounting electrode portion 30a and the mounting electrode portion 30b is preferably a thermosetting resin such as a thermosetting polyester resin.

[0052] The resin contained in the mounting electrode portion 30a and the resin contained in the mounting electrode portion 30b preferably have the same type of resin, but the types of resin can also be different from each other.

[0053] The mounting electrode portion 30a has a first main surface 31a and a second main surface 32a.

[0054] The first main surface 31a of the mounting electrode portion 30a is the main surface located on the side of the stretchable base material 10. More specifically, the first main surface 31a of the mounting electrode portion 30a faces one main surface 11a of the stretchable base material 10, and is in contact with one main surface 11a of the stretchable base material 10 here.

[0055] The second main surface 32a of the mounting electrode portion 30a is the main surface located on the side of the solder portion 40a.

[0056] The mounting electrode portion 30b has a first main surface 31b and a second main surface 32b.

[0057] The first main surface 31b of the mounting electrode portion 30b is the main surface located on the side of the stretchable base material 10. More specifically, the first main surface 31b of the mounting electrode portion 30b faces one main surface 11a of the stretchable base material 10, and here, it is in contact with one main surface 11a of the stretchable base material 10.

[0058] The second main surface 32b of the mounting electrode portion 30b is the main surface located on the side of the solder portion 40b.

[0059] Details of the mounting electrode portion 30a and the mounting electrode portion 30b, which are characteristic portions of the stretchable mounting substrate of the present invention, will be described later.

[0060] The solder portion 40a is connected to the mounting electrode portion 30a.

[0061] The solder portion 40b is connected to the mounting electrode portion 30b.

[0062] The solder portion 40a and the solder portion 40b are provided at positions separated from each other.

[0063] The solder portion 40a and the solder portion 40b preferably contain tin and bismuth as metal components and are preferably so-called low-temperature solders. By using such low-temperature solders as the solder portion 40a and the solder portion 40b, even when the heat-resistant temperatures of the stretchable base material 10, the stretchable wirings 20a, 20b, and the electronic component 50 are low, the electronic component 50 can be mounted without damaging them.

[0064] The metal components of the solder portion 40a and the metal components of the solder portion 40b preferably have the same metal types as each other, but the metal types can also be different from each other.

[0065] The electronic component 50 is electrically connected to the mounting electrode portion 30a via the solder portion 40a. In addition, the electronic component 50 is electrically connected to the mounting electrode portion 30b via the solder portion 40b.

[0066] Examples of the electronic component 50 include an amplifier (operational amplifier, transistor, etc.), a diode, an integrated circuit (IC), a capacitor, a resistor, an inductor, and the like.

[0067] The stretchable mounting substrate 1 may also have electrodes connected to the stretchable wiring 20a at positions different from the mounting electrode portion 30a and the mounting electrode portion 30b. In addition, the stretchable mounting substrate 1 may also have electrodes connected to the stretchable wiring 20b at positions different from the mounting electrode portion 30a and the mounting electrode portion 30b. By attaching the stretchable mounting substrate 1 to a living body via such electrodes, it can function as a sensor.

[0068] Such an electrode is preferably a gel electrode. By using a gel electrode, the attachment of the stretchable mounting substrate 1 to the living body becomes easy. The gel electrode is composed of, for example, a conductive gel material containing water, ethanol, a humectant, an electrolyte, etc. As such a gel material, for example, hydrogel etc. can be cited.

[0069] Figure 3 It is a plan schematic view showing another example of the stretchable mounting substrate of the present invention. Figure 4 It is shown with Figure 3 a cross-sectional schematic view of a part corresponding to the line segment A1'-A2' in.

[0070] As Figure 3 and Figure 4 shown by the stretchable mounting substrate 1', the end of the stretchable wiring 20a can also be provided between the stretchable base material 10 and the mounting electrode part 30a. In addition, the end of the stretchable wiring 20b can also be provided between the stretchable base material 10 and the mounting electrode part 30b.

[0071] Regarding the mounting electrode part 30a and the mounting electrode part 30b, a manufacturing method of the stretchable mounting substrate 1 which is an example of the manufacturing method of the stretchable mounting substrate of the present invention is shown, and will be described below.

[0072] <First electrode layer forming process>

[0073] Figure 5 It is a cross-sectional schematic view showing the first electrode layer forming process, which is an example of the manufacturing method of the stretchable mounting substrate of the present invention.

[0074] The first conductive paste containing the first conductive filler and the thermosetting resin is coated on one main surface 11a side of the stretchable base material 10, here it is one main surface 11a of the stretchable base material 10, and then heat treatment is performed, thereby forming Figure 5 the first electrode layer 35a and the first electrode layer 35b shown. The first electrode layer 35a and the first electrode layer 35b thus formed are composed of the first conductive paste. More specifically, the first electrode layer 35a and the first electrode layer 35b contain the first conductive filler and the thermosetting resin.

[0075] Since the first conductive paste contains the thermosetting resin, the wettability of the solder paste described later with respect to the first conductive paste is poor. That is, the wettability of the solder paste described later with respect to the first electrode layer 35a and the first electrode layer 35b composed of the first conductive paste becomes poor.

[0076] The coating of the first conductive paste is preferably performed by the screen printing method. Thereby, the coating of the first conductive paste can be easily performed.

[0077] Preferably, the coating of the first conductive paste for forming the first electrode layer 35a and the coating of the first conductive paste for forming the first electrode layer 35b are performed at the same timing. Thereby, the coating of both first conductive pastes can be effectively performed. Then, by performing the heat treatment of the first conductive paste for forming the first electrode layer 35a and the heat treatment of the first conductive paste for forming the first electrode layer 35b at the same timing, the first electrode layer 35a and the first electrode layer 35b can be effectively formed at the same timing.

[0078] The coating of the first conductive paste for forming the first electrode layer 35a and the coating of the first conductive paste for forming the first electrode layer 35b may also be performed at different timings. For example, the coating and heat treatment of the first conductive paste for forming the first electrode layer 35a may be performed to form the first electrode layer 35a, and then the coating and heat treatment of the first conductive paste for forming the first electrode layer 35b may be performed to form the first electrode layer 35b.

[0079] Examples of the first conductive filler include metal fillers such as silver filler, copper filler, and nickel filler. Among them, the first conductive filler is preferably silver filler.

[0080] The first conductive filler contained in the first conductive paste for forming the first electrode layer 35a and the first conductive filler contained in the first conductive paste for forming the first electrode layer 35b preferably have the same metal type, but the metal types may also be different from each other.

[0081] Examples of the shape of the first conductive filler include plate shape, spherical shape, etc. Among them, the first conductive filler is preferably plate shape.

[0082] The first conductive filler contained in the first conductive paste for forming the first electrode layer 35a and the first conductive filler contained in the first conductive paste for forming the first electrode layer 35b preferably have the same shape, but the shapes may also be different from each other.

[0083] Examples of the thermosetting resin include thermosetting polyester resins and the like.

[0084] The thermosetting resin contained in the first conductive paste for forming the first electrode layer 35a and the thermosetting resin contained in the first conductive paste for forming the first electrode layer 35b preferably have the same resin type, but the resin types may also be different from each other.

[0085] The first conductive paste may also contain a solvent. Examples of such a solvent include diethylene glycol monoethyl ether acetate and the like.

[0086] When the first conductive paste contains a solvent, the solvents contained in the first conductive paste for forming the first electrode layer 35a and the solvents contained in the first conductive paste for forming the first electrode layer 35b are preferably the same in terms of the type of solvent, but the types of solvents may also be different from each other.

[0087] The first conductive paste may also contain additives such as fine powder silica.

[0088] <Second Electrode Layer Forming Step>

[0089] Figure 6 It is an example of a method for manufacturing a stretchable mounting substrate of the present invention and is a cross-sectional schematic diagram showing the second electrode layer forming step.

[0090] For the first electrode layer 35a and the first electrode layer 35b, a second conductive paste containing a second conductive filler and a thermoplastic resin is coated on the side opposite to the stretchable substrate 10, and then heat treatment is performed, thereby forming at positions separated from each other Figure 6 the second electrode layer 36a and the second electrode layer 36b shown. The second electrode layer 36a and the second electrode layer 36b thus formed are composed of the second conductive paste. More specifically, the second electrode layer 36a and the second electrode layer 36b contain a second conductive filler and a thermoplastic resin.

[0091] Since the second conductive paste contains a thermoplastic resin, the wettability of a solder paste described later with respect to the second conductive paste is good. That is, the wettability of the solder paste described later with respect to the second electrode layer 36a and the second electrode layer 36b composed of the second conductive paste is improved.

[0092] The coating of the second conductive paste is preferably performed by a screen printing method. Thereby, the coating of the second conductive paste can be easily performed.

[0093] It is preferable that the coating of the first conductive paste in the first electrode layer forming step and the coating of the second conductive paste in the second electrode layer forming step are both performed by the screen printing method. Thereby, not only can the coating of the first conductive paste in the first electrode layer forming step and the coating of the second conductive paste in the second electrode layer forming step be easily performed, but also the same device can be used, so that the manufacturing efficiency of the stretchable mounting substrate 1 obtained later is improved.

[0094] Preferably, the coating of the second conductive paste for forming the second electrode layer 36a and the coating of the second conductive paste for forming the second electrode layer 36b are performed at the same timing. Thereby, the coating of both second conductive pastes can be effectively performed. Then, by performing the heat treatment for the second conductive paste for forming the second electrode layer 36a and the heat treatment for the second conductive paste for forming the second electrode layer 36b at the same timing, the second electrode layer 36a and the second electrode layer 36b can be effectively formed at the same timing.

[0095] The coating of the second conductive paste for forming the second electrode layer 36a and the coating of the second conductive paste for forming the second electrode layer 36b may also be performed at different timings. For example, the coating and heat treatment of the second conductive paste for forming the second electrode layer 36a may be performed to form the second electrode layer 36a, and then the coating and heat treatment of the second conductive paste for forming the second electrode layer 36b may be performed to form the second electrode layer 36b.

[0096] Examples of the second conductive filler include metal fillers such as silver fillers, copper fillers, and nickel fillers. Among them, the second conductive filler is preferably a silver filler.

[0097] The second conductive fillers contained in the second conductive paste for forming the second electrode layer 36a and the second conductive fillers contained in the second conductive paste for forming the second electrode layer 36b preferably have the same metal type, but the metal types may also be different from each other.

[0098] The first conductive filler and the second conductive filler preferably have the same metal type, but the metal types may also be different from each other.

[0099] Examples of the shape of the second conductive filler include plate shape, spherical shape, etc.

[0100] The second conductive fillers contained in the second conductive paste for forming the second electrode layer 36a and the second conductive fillers contained in the second conductive paste for forming the second electrode layer 36b preferably have the same shape, but the shapes may also be different from each other.

[0101] The first conductive filler and the second conductive filler preferably have the same shape, but the shapes may also be different from each other.

[0102] Examples of the thermoplastic resin include thermoplastic acrylic resins, thermoplastic polyurethane resins (e.g., thermoplastic polyurethane), etc.

[0103] The thermoplastic resins contained in the second conductive paste for forming the second electrode layer 36a and the thermoplastic resins contained in the second conductive paste for forming the second electrode layer 36b are preferably the same in terms of resin type, but the resin types may also be different from each other.

[0104] The second conductive paste may also contain a solvent. Examples of such a solvent include diethylene glycol monoethyl ether acetate.

[0105] When the second conductive paste contains a solvent, the solvents contained in the second conductive paste for forming the second electrode layer 36a and the solvents contained in the second conductive paste for forming the second electrode layer 36b are preferably the same in terms of solvent type, but the solvent types may also be different from each other.

[0106] In this step, the second conductive paste is applied to one main surface 11a of the stretchable substrate 10 and to a position where the ends of the first electrode layer 35a and the first electrode layer 35b are sandwiched between the stretchable substrate 10 in the thickness direction by a screen printing method or the like, and then heat treatment is performed, thereby further forming Figure 6 the stretchable wirings 20a and 20b shown.

[0107] The application of the second conductive paste for forming the stretchable wiring 20a and the application of the second conductive paste for forming the stretchable wiring 20b are preferably performed at the same timing, but may also be performed at different timings.

[0108] Preferably, the application of the second conductive paste for forming the stretchable wirings 20a and 20b and the application of the second conductive paste for forming the second electrode layers 36a and 36b are performed at the same timing. Thereby, the application of these second conductive pastes can be effectively performed. Then, by performing the heat treatment for the second conductive paste for forming the stretchable wirings 20a and 20b and the heat treatment for the second conductive paste for forming the second electrode layers 36a and 36b at the same timing, the stretchable wirings 20a, the stretchable wiring 20b, the second electrode layer 36a, and the second electrode layer 36b can be effectively formed at the same timing.

[0109] The coating of the second conductive paste for forming the stretchable wirings 20a and 20b and the coating of the second conductive paste for forming the second electrode layers 36a and 36b can also be performed at different timings. For example, the coating of the second conductive paste for forming the stretchable wirings 20a and 20b can be performed, followed by heat treatment to form the stretchable wirings 20a and 20b, and then the coating of the second conductive paste for forming the second electrode layers 36a and 36b can be performed, followed by heat treatment to form the second electrode layers 36a and 36b. Alternatively, the coating of the second conductive paste for forming the second electrode layers 36a and 36b can be performed, followed by heat treatment to form the second electrode layers 36a and 36b, and then the coating of the second conductive paste for forming the stretchable wirings 20a and 20b can be performed, followed by heat treatment to form the stretchable wirings 20a and 20b.

[0110] The conductive paste for forming the stretchable wirings 20a and 20b is preferably the second conductive paste as described above, but it can also be other than the second conductive paste.

[0111] <Electronic component mounting process>

[0112] Figure 7 It is a schematic plan view showing an example of the method for manufacturing the stretchable mounting substrate of the present invention and representing the electronic component mounting process. Figure 8 It represents the Figure 7 cross-sectional schematic view of the portion corresponding to the line segment B1 - B2 in

[0113] The solder paste 45a is coated on the second electrode layer 36a. More specifically, the solder paste 45a is coated on the second electrode layer 36a on the side opposite to the first electrode layer 35a so as not to contact the first electrode layer 35a.

[0114] In addition, the solder paste 45b is coated on the second electrode layer 36b. More specifically, the solder paste 45b is coated on the second electrode layer 36b on the side opposite to the first electrode layer 35b so as not to contact the first electrode layer 35b.

[0115] The coating of the solder paste 45a and the solder paste 45b is performed, for example, by printing using a metal mask or the like.

[0116] The solder paste 45a and the solder paste 45b preferably contain tin and bismuth as metal components and are preferably so-called low-temperature solder pastes. By using such low-temperature solder pastes, even when the heat-resistant temperatures of the stretchable substrate 10, the stretchable wirings 20a, the stretchable wirings 20b, and the electronic component 50 are relatively low, the electronic component 50 can be mounted without damaging them.

[0117] The metal components of the solder paste 45a and the metal components of the solder paste 45b preferably have the same type of metal, but the types of metal may also be different from each other.

[0118] In addition to the metal components, the solder paste 45a and the solder paste 45b may also contain a flux component.

[0119] Examples of the flux component include rosin-based fluxes and the like.

[0120] When the solder paste 45a and the solder paste 45b contain a flux component, the flux components of the solder paste 45a and the solder paste 45b preferably have the same type of flux, but the types of flux may also be different from each other.

[0121] Next, as Figure 7 and Figure 8 shown, the electronic component 50 is mounted on the solder paste 45a and the solder paste 45b, and then heat treatment is performed in a reflow soldering furnace. Thereby, the solder paste 45a is melted and solidified to form a solder portion 40a (see Figure 2 ), and the electronic component 50 is joined to the first electrode layer 35a via the solder portion 40a. In addition, the solder paste 45b is melted and solidified to form a solder portion 40b (see Figure 2 ), and the electronic component 50 is joined to the first electrode layer 35b via the solder portion 40b. At this time, the obtained first electrode layer 35a and the first electrode layer 35b respectively become the mounting electrode portions 30a and 30b (see Figure 2 ) respectively.

[0122] When performing heat treatment in a reflow soldering furnace, the maximum temperature of the heat treatment is preferably 150°C or higher and 190°C or lower.

[0123] The formation process of the mounting electrode portion 30a will be described below.

[0124] Figure 9 is Figure 8 an enlarged view of the area enclosed by the dashed line in Figure 10 and is a cross-sectional schematic diagram showing the state before heat treatment of the solder paste. Figure 9 is a cross-sectional schematic diagram showing the state in the middle of heat treatment of the solder paste with respect to the state shown in Figure 11 and is a cross-sectional schematic diagram showing the state after heat treatment of the solder paste with respect to the state shown in Figure 9 .

[0125] As Figure 9As shown, in the state before the heat treatment of the solder paste 45a, the conductive filler 60a is included in the first electrode layer 35a (plate-shaped in Figure 9 ), and the conductive filler 61a is included in the second electrode layer 36a (spherical in Figure 9 ).

[0126] If the heat treatment of the solder paste 45a is performed with respect to the state shown in Figure 9 , since the solder paste 45a has good wettability with respect to the second electrode layer 36a, as shown in Figure 10 , the solder paste 45a wets and spreads in a molten state toward the second electrode layer 36a, and thus the second electrode layer 36a enters the solder paste 45a. In addition, the solder paste 45a wets and spreads from the side of the second electrode layer 36a across the interface between the two layers toward the first electrode layer 35a side. Therefore, the metal components of the conductive filler 60a and the solder paste 45a in the region D2 existing near the interface between the first electrode layer 35a and the second electrode layer 36a in the first electrode layer 35a react with each other, thereby ensuring the connection between the first electrode layer 35a and the solder paste 45a. In such a state, the cross-sectional area of the conductive filler 60a existing in the region D2 increases due to the reaction with the metal component of the solder paste 45a.

[0127] On the other hand, since the solder paste 45a has poor wettability with respect to the first electrode layer 35a, as shown in Figure 10 , the solder paste 45a does not wet and spread excessively on the first electrode layer 35a. More specifically, it is not easy to wet and spread to the interface between the first electrode layer 35a and the stretchable substrate 10. Therefore, the connection between the stretchable substrate 10 and the first electrode layer 35a can be ensured. In such a state, in the first electrode layer 35a, the cross-sectional area of the conductive filler 60a existing in the region D1 near the interface between the first electrode layer 35a and the stretchable substrate 10 almost maintains the cross-sectional area at the time of the first electrode layer formation process, and is smaller than the cross-sectional area of the conductive filler 60a existing in the region D2.

[0128] Then, if the heat treatment of the solder paste 45a is completed and the solder paste 45a is solidified, as shown in Figure 11 , the solder portion 40a is formed at the position including the second electrode layer 36a, and the electronic component 50 is joined to the first electrode layer 35a via the solder portion 40a. At this time, by using the obtained first electrode layer 35a as the mounting electrode portion 30a, the states shown in Figure 1 and Figure 2 are obtained.

[0129] The formation process of the mounting electrode portion 30b is the same as that of the mounting electrode portion 30a.

[0130] Thus, the manufacturingFigure 1 and Figure 2 the flexible mounting substrate 1 shown in Figure 2 .

[0131] As described above, the flexible mounting substrate 1 can use both the first conductive paste with poor wettability of the solder paste and the second conductive paste with good wettability of the solder paste, and can be manufactured by a simple process.

[0132] As Figure 2 and Figure 11 shown in Figure 11 , in the mounting electrode portion 30a, there are a first region E1 including the first main surface 31a and a second region E2 including the second main surface 32a. More specifically, when the mounting electrode portion 30a is divided into four parts in the thickness direction, the first region E1 refers to the region including the first main surface 31a, and the second region E2 refers to the region including the second main surface 32a.

[0133] The first region E1 of the mounting electrode portion 30a is derived from Figure 10 the region D1 shown in Figure 10 . In addition, the second region E2 of the mounting electrode portion 30a is derived from Figure 10 the region D2 shown in Figure 10 . Therefore, as Figure 11 shown in Figure 11 , in the mounting electrode portion 30a, when observing the cross section including the first region E1 and the second region E2, the cross-sectional area of the conductive filler 60a existing in the second region E2 is larger than the cross-sectional area of the conductive filler 60a existing in the first region E1.

[0134] Since it can also be said that the second region E2 of the mounting electrode portion 30a is derived from Figure 10 the region D2 shown in Figure 10 , that is, the region where the solder paste 45a wets and spreads on the first electrode layer 35a side, it can be said that the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a is ensured.

[0135] Since it can also be said that the first region E1 of the mounting electrode portion 30a is derived from Figure 10 the region D1 shown in Figure 10 , that is, the region where the solder paste 45a is not easily wetted and spreads on the first electrode layer 35a side, it can be said that the connection between the flexible substrate 10 and the first region E1 of the mounting electrode portion 30a is ensured.

[0136] In this way, in the mounting electrode portion 30a, the fact that the cross-sectional area of the conductive filler 60a existing in the second region E2 is larger than the cross-sectional area of the conductive filler 60a existing in the first region E1 can be said to ensure the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a, and to ensure the connection between the flexible substrate 10 and the first region E1 of the mounting electrode portion 30a, and as a result, the mounting strength of the electronic component 50 is ensured.

[0137] As Figure 2As shown, in the mounting electrode portion 30b, there are a first region F1 including the first main surface 31b and a second region F2 including the second main surface 32b. The first region F1 and the second region F2 of the mounting electrode portion 30b can also be said to be the same as the first region E1 and the second region E2 of the mounting electrode portion 30a. That is, in the mounting electrode portion 30b, when observing a cross-section including the first region F1 and the second region F2, the cross-sectional area of the conductive filler present in the second region F2 is larger than the cross-sectional area of the conductive filler present in the first region F1. In this way, in the mounting electrode portion 30b, the fact that the cross-sectional area of the conductive filler present in the second region F2 is larger than the cross-sectional area of the conductive filler present in the first region F1 can be said to ensure the connection between the second region F2 of the mounting electrode portion 30b and the solder portion 40b, and to ensure the connection between the stretchable base material 10 and the first region F1 of the mounting electrode portion 30b, and as a result, to ensure the mounting strength of the electronic component 50.

[0138] The cross-sectional areas of the conductive filler present in the first region and the second region in the mounting electrode portion are determined as follows.

[0139] Figure 12 It is for Figure 2 a cross-sectional schematic diagram showing an enlarged view of the region enclosed by the dashed line in

[0140] First, by grinding the stretchable mounting substrate or the like, Figure 12 a cross-section along the thickness direction as shown, that is, a cross-section including the stretchable base material 10, the mounting electrode portion 30a, and the solder portion 40a, is exposed. Then, a cross-sectional photograph of the exposed cross-section is taken using a scanning electron microscope (SEM).

[0141] Next, by confirming the obtained cross-sectional photograph, a region where resin (excluding voids) exists outside the stretchable substrate 10 is determined as the mounting electrode portion 30a. Then, in the mounting electrode portion 30a, a first end point P1 that is closest to the stretchable substrate 10 in the thickness direction and a second end point P2 that is closest to the solder portion 40a in the thickness direction are determined. Then, a first straight line L1 that passes through the first end point P1 and extends in a direction orthogonal to the thickness direction, and a second straight line L2 that passes through the second end point P2 and is parallel to the first straight line L1 are determined. It can also be said that the first straight line L1 and the second straight line L2 thus determined correspond to the first main surface 31a and the second main surface 32a of the mounting electrode portion 30a, respectively. Then, a third straight line L3, a fourth straight line L4, and a fifth straight line L5 are further determined in order from the first straight line L1 side so that the distance between the first straight line L1 and the second straight line L2 in the thickness direction is divided into four parts. In this way, in the mounting electrode portion 30a, the region between the first straight line L1 and the third straight line L3 is determined as the first region E1, and the region between the second straight line L2 and the fifth straight line L5 is determined as the second region E2.

[0142] Next, 10 straight lines are drawn at 5-μm intervals in the thickness direction in such a way that the first region E1 and the second region E2 are longitudinally cut in the mounting electrode portion 30a. Then, for each of the 10 straight lines, the number of intersections with the conductive filler 60a existing in the first region E1 is counted. In addition, for each of the 10 straight lines, the number of intersections with the conductive filler 60a existing in the second region E2 is counted. At this time, the conductive filler 60a that entirely exists in the first region E1 of course exists in the first region E1, and for a part of the conductive filler 60a that exists in the first region E1, it also exists in the first region E1. In addition, the conductive filler 60a that entirely exists in the second region E2 of course exists in the second region E2, and for a part of the conductive filler 60a that exists in the second region E2, it also exists in the second region E2.

[0143] In Figure 12 as an example of two of such 10 straight lines, straight lines M1 and M2 with an interval of 5 μm are shown. For each of the straight lines M1 and M2, the number of intersections with the conductive filler 60a existing in the first region E1 is 4, and the number of intersections with the conductive filler 60a existing in the second region E2 is 2. Similarly, for each of the remaining 8 straight lines, the intersections with the conductive filler 60a existing in the first region E1 and the intersections with the conductive filler 60a existing in the second region E2 are counted.

[0144] Then, calculate the average value G1 of the 10 count values obtained for the first region E1. Additionally, calculate the average value G2 of the 10 count values obtained for the second region E2. Moreover, consider the case where the average value G1 is greater than the average value G2 as the case where the cross-sectional area of the conductive filler 60a present in the second region E2 is larger than the cross-sectional area of the conductive filler 60a present in the first region E1.

[0145] For the cross-sectional areas of the conductive fillers present in the first region F1 and the second region F2 in the mounting electrode portion 30b, they are also determined using the same method as the above method.

[0146] As Figure 11 shown, it is preferable that the solder portion 40a extends in the second region E2 of the mounting electrode portion 30a. In this case, from the formation process of the above-mentioned mounting electrode portion 30a, it can be said that in the Figure 10 shown state, the conductive filler 60a present in the region D2 easily reacts with the metal component of the solder paste 45a. As a result, it is easy to ensure the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a. Additionally, in this case, the mounting electrode portion 30a also contains the component of the solder portion 40a in the second region E2.

[0147] Regarding whether the solder portion extends in the second region of the mounting electrode portion, it can be confirmed as follows. First, by grinding the stretchable mounting substrate or the like, the cross-section along the thickness direction is exposed. Next, elemental mapping of the exposed cross-section is performed by scanning electron microscopy - energy dispersive X-ray analysis (SEM-EDX). Then, in the obtained elemental mapping image, it is confirmed whether the metal component of the solder portion exists in the second region of the mounting electrode portion.

[0148] In the mounting electrode portion 30a, it is preferable that the conductive filler present in the second region E2 is integrated with the solder portion 40a. In this case, from the formation process of the above-mentioned mounting electrode portion 30a, it can be said that in the Figure 10 shown state, the conductive filler 60a present in the region D2 reacts with the metal component of the solder paste 45a, and as a result, the cross-sectional area of the conductive filler 60a becomes quite large. As a result, the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a is sufficiently ensured.

[0149] The thickness of the mounting electrode portion 30a is preferably 10 μm or more. In this case, from the formation process of the mounting electrode portion 30a described above, it can be said that the thickness of the first electrode layer 35a is large enough, so that in the thickness direction, the stretchable substrate 10 and the solder paste 45a are sufficiently separated. Therefore, the influence of the metal component of the solder paste 45a is less likely to affect the interface between the stretchable substrate 10 and the first electrode layer 35a. As a result, the connection between the stretchable substrate 10 and the first electrode layer 35a is ensured sufficiently. That is, by setting the thickness of the mounting electrode portion 30a to 10 μm or more, the connection between the stretchable substrate 10 and the first region E1 of the mounting electrode portion 30a is ensured sufficiently.

[0150] On the other hand, if the thickness of the mounting electrode portion 30a is too large, from the formation process of the stretchable wiring 20a described above, the second conductive paste is applied by a screen printing method or the like to a position where the end portion of the first electrode layer 35a is sandwiched in the thickness direction between the stretchable substrate 10, that is, to a position with a large step. Therefore, the applied second conductive paste is likely to ooze out, and as a result, the stretchable wiring 20a is easily disconnected by this step. In addition, if the thickness of the mounting electrode portion 30a is too large, during the formation process of the stretchable wiring 20a described above, it becomes difficult to dry the coating film of the second conductive paste, so the manufacturing efficiency is reduced, or the deviation of the thickness of the coating film of the second conductive paste becomes large, so the uniformity of the coating film becomes poor. In addition to such viewpoints, from the viewpoint of reducing the height of the stretchable mounting substrate 1, the thickness of the mounting electrode portion 30a is preferably 40 μm or less.

[0151] The thicknesses of the mounting electrode portion 30a and the mounting electrode portion 30b are preferably the same as each other, but they may also be different from each other.

[0152] As Figure 2 shown, preferably in a direction parallel to one main surface 11a of the stretchable substrate 10, that is, in a direction orthogonal to the thickness direction, the length R1 of the region of the second region E2 of the mounting electrode portion 30a that is in contact with the solder portion 40a is smaller than the overall length R2 of the second region E2 of the mounting electrode portion 30a. In this case, the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a is ensured to be the minimum. On the other hand, from the formation process of the mounting electrode portion 30a described above, in the Figure 10 state shown, the influence of the metal component of the solder paste 45a is less likely to affect the entire second region D2 of the first electrode layer 35a, and as a result, it is easy to ensure the strength of the mounting electrode portion 30a itself.

[0153] In the direction parallel to one main surface 11a of the stretchable substrate 10, the length R1 of the region in the second region E2 of the mounting electrode portion 30a that is in contact with the solder portion 40a may also be the same as the length R2 of the entire second region E2 of the mounting electrode portion 30a. In this case, since the contact area between the second region E2 of the mounting electrode portion 30a and the solder portion 40a becomes larger, the connection between the second region E2 of the mounting electrode portion 30a and the solder portion 40a can be sufficiently ensured.

[0154] It can be said that the above-described preferred features of the mounting electrode portion 30a are the same for the mounting electrode portion 30b.

[0155] As described above, in the stretchable mounting substrate 1, the connection between the mounting electrode portion 30a and the solder portion 40a and the connection between the stretchable substrate 10 and the mounting electrode portion 30a are both ensured, and the connection between the mounting electrode portion 30b and the solder portion 40b and the connection between the stretchable substrate 10 and the mounting electrode portion 30b are both ensured. Therefore, the mounting strength of the electronic component 50 can be ensured.

[0156] As described above, a preferred mode is shown in which the cross-sectional area of the conductive filler existing in the second region is larger than the cross-sectional area of the conductive filler existing in the first region in both the mounting electrode portion 30a and the mounting electrode portion 30b. On the other hand, it may also be a mode in which the cross-sectional area of the conductive filler existing in the second region is larger than the cross-sectional area of the conductive filler existing in the first region in one of the mounting electrode portion 30a and the mounting electrode portion 30b. In such a case, the mounting strength of the electronic component 50 can also be ensured to a minimum. That is, in the stretchable mounting substrate 1, it is sufficient that the cross-sectional area of the conductive filler existing in the second region is larger than the cross-sectional area of the conductive filler existing in the first region in at least one of the mounting electrode portion 30a and the mounting electrode portion 30b.

[0157] Examples

[0158] Hereinafter, examples more specifically disclosing the stretchable mounting substrate of the present invention and the manufacturing method of the stretchable mounting substrate of the present invention are shown. In addition, the present invention is not limited to this example.

[0159] [Example 1]

[0160] The stretchable mounting substrate of Example 1 was manufactured using the following method.

[0161] <First electrode layer forming step>

[0162] The first conductive paste was applied to one main surface of the stretchable substrate by screen printing, and then heat treatment was performed at 140 ° C for 30 minutes in an atmospheric air environment to form a Figure 5The first electrode layer of the structure shown. Measurement was performed using an image measurement system having a laser autofocus mechanism, and the thickness of the first electrode layer was approximately 12 μm.

[0163] As the first conductive paste, a paste containing plate-like silver fillers, a thermosetting polyester resin, blocked isocyanate, diethylene glycol monoethyl ether acetate, and fine powder silica was used.

[0164] Here, the first conductive paste contains blocked isocyanate, but in this step, a polymerization reaction is generated by performing heat treatment at 140 °C, which is above the decomposition temperature of the blocking agent. Therefore, the obtained first electrode layer contains plate-like silver fillers, a polyester resin, and a cured product of isocyanate. In addition, in order to cause the above polymerization reaction, heat treatment may be performed at a temperature above the decomposition temperature of the blocking agent (for example, 140 °C or higher) not in this step but in the subsequent second electrode layer formation step.

[0165] As the stretchable substrate, a material containing thermoplastic polyurethane was used.

[0166] <Second Electrode Layer Formation Step>

[0167] Using the screen printing method, the second conductive paste was applied to the first electrode layer on the side opposite to the stretchable substrate. At the same time, the second conductive paste was applied to one main surface of the stretchable substrate and at a position where the end portion of the first electrode layer in the thickness direction was sandwiched between the stretchable substrate. Then, in an atmospheric air environment, the applied second conductive paste was heat-treated at 140 °C for 30 minutes, thereby forming the second electrode layer and the stretchable wiring having the Figure 6 structure shown.

[0168] As the second conductive paste, a paste containing spherical silver fillers, a thermoplastic acrylic copolymer resin, and diethylene glycol monoethyl ether acetate was used. Therefore, the obtained second electrode layer and stretchable wiring contain spherical silver fillers and an acrylic copolymer resin.

[0169] <Electronic Component Mounting Step>

[0170] By printing using a metal mask, the solder paste was applied to the second electrode layer on the side opposite to the first electrode layer so as not to contact the first electrode layer.

[0171] As the solder paste, a paste containing tin, bismuth, a solvent, and a rosin-based solder flux was used.

[0172] Next, as shown in Figure 7 and Figure 8As shown, an electronic component with a size of 1005M is mounted on a solder paste, and then heat treatment is performed at a maximum temperature of 180°C in a reflow soldering furnace. Thereby, the solder paste is melted and solidified to form a solder portion, and the electronic component is joined to the first electrode layer via the solder portion. Here, the first electrode layer thus obtained is used as the mounting electrode portion.

[0173] Thereby, a stretchable mounting substrate of Example 1 having a Figure 1 and Figure 2 structure as shown is manufactured.

[0174] [Comparative Example 1]

[0175] A stretchable mounting substrate of Comparative Example 1 is manufactured in the same manner as the stretchable mounting substrate of Example 1, except that the first electrode layer is formed thinner at about 8 μm in the first electrode layer forming process.

[0176] [Evaluation 1]

[0177] Cross-sectional photographs are taken using a scanning electron microscope of the state at the completion of the second electrode layer forming process and the state at the completion of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Example 1.

[0178] Figure 13 is a cross-sectional photograph showing the state at the completion of the second electrode layer forming process during the manufacturing process of the stretchable mounting substrate of Example 1. Figure 14 is a cross-sectional photograph showing the state at the completion of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Example 1.

[0179] As Figure 13 shown, it was confirmed that in the state at the completion of the second electrode layer forming process during the manufacturing process of the stretchable mounting substrate of Example 1, plate-shaped silver fillers 70a are included in the first electrode layer 35a, and spherical silver fillers 71a are included in the second electrode layer 36a.

[0180] In contrast, as Figure 14 shown, it was confirmed that in the state at the completion of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Example 1, the second electrode layer 36a enters the solder portion 40a. In addition, it was confirmed that in the first electrode layer 35a, that is, the mounting electrode portion 30a, the cross-sectional area of the silver fillers 70a existing in the second region E2 is larger than the cross-sectional area at the completion of the second electrode layer forming process as Figure 13 shown. In addition, in the mounting electrode portion 30a, the cross-sectional area of the silver fillers 70a existing in the first region E1 is maintained Figure 13The cross-sectional area at the completion time of the second electrode layer forming process shown was also confirmed to be smaller than the cross-sectional area of the silver filler 70a present in the second region E2 by the above method.

[0181] Next, a cross-sectional photograph was taken of the state at the completion time of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Comparative Example 1 using a scanning electron microscope.

[0182] Figure 15 It is a cross-sectional photograph showing the state at the completion time of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Comparative Example 1.

[0183] As Figure 15 shown, it was confirmed that in the state at the completion time of the electronic component mounting process during the manufacturing process of the stretchable mounting substrate of Comparative Example 1, the solder portion 40a reached the interface between the stretchable base material 10 and the mounting electrode portion 30a, and the entire mounting electrode portion 30a entered the solder portion 40a. Therefore, the cross-sectional area of the silver filler 70a became larger at any part of the mounting electrode portion 30a, and it was also confirmed by the above method that the cross-sectional area of the silver filler 70a present in the second region E2 was not larger than the cross-sectional area of the silver filler 70a present in the first region E1. It is considered that this is because the first electrode layer was formed thinner compared to the manufacturing process of the stretchable mounting substrate of Example 1, and the solder paste constituting the solder portion 40a was likely to wet and spread on the first electrode layer. In addition, in the first electrode layer forming process, a first conductive paste containing a blocked isocyanate was used, but it is considered that if heat treatment is performed at a temperature lower than the decomposition temperature of the blocking agent or under curing conditions where the polymerization reaction is insufficient to form the first electrode layer, then in the electronic component mounting process, the resin contained in the first electrode layer is dissolved in the flux component of the solder paste, resulting in the same state as the stretchable mounting substrate of Comparative Example 1.

[0184] [Evaluation 2]

[0185] For the stretchable mounting substrate of Example 1 and the stretchable mounting substrate of Comparative Example 1, the shear strength (also referred to as the shear-off strength) was measured as follows. First, for the stretchable mounting substrate of each example, three samples with a rigid body bonded to the other main surface (the main surface opposite to the side of the electronic component) of the stretchable base material were fabricated. Next, for the stretchable mounting substrate of each example, the shear strength in the long side direction of the three samples was measured using a shear testing machine. For the stretchable mounting substrate of each example, the average value and the minimum value of the shear strength of the three samples are shown in Table 1.

[0186] [Table 1]

[0187]

[0188] As shown in Table 1, in the flexible mounting substrate of Example 1, the average value and the minimum value of the shear strength are higher than those of the flexible mounting substrate of Comparative Example 1. That is, it can be seen that in the flexible mounting substrate of Example 1, the mounting strength of the electronic component is higher than that of the flexible mounting substrate of Comparative Example 1.

[0189] In the flexible mounting substrate of each example, the failure site generated when measuring the shear strength is the interface between the flexible substrate and the mounting electrode portion. From this, it can be seen that, like the flexible mounting substrate of Comparative Example 1, when the solder portion reaches the interface between the flexible substrate and the mounting electrode portion, that is, in the mounting electrode portion, when the cross-sectional area of the conductive filler existing in the second region is not larger than the cross-sectional area of the conductive filler existing in the first region, the connection between the flexible substrate and the mounting electrode portion cannot be ensured. As a result, the mounting strength of the electronic component is reduced. That is, it can be seen that, like the flexible mounting substrate of Example 1, when the cross-sectional area of the conductive filler existing in the second region in the mounting electrode portion is larger than the cross-sectional area of the conductive filler existing in the first region, the connection between the flexible substrate and the mounting electrode portion can be ensured. As a result, the mounting strength of the electronic component is increased.

[0190] Description of Reference Numerals

[0191] 1, 1’... Flexible mounting substrate; 10... Flexible substrate; 11a... One main surface of the flexible substrate; 20a, 20b... Flexible wiring; 30a, 30b... Mounting electrode portion; 31a, 31b... First main surface of the mounting electrode portion; 32a, 32b... Second main surface of the mounting electrode portion; 35a, 35b... First electrode layer; 36a, 36b... Second electrode layer; 40a, 40b... Solder portion; 45a, 45b... Solder paste; 50... Electronic component; 60a, 61a... Conductive filler; 70a, 71a... Silver filler; D1... Region near the interface between the first electrode layer and the flexible substrate in the first electrode layer; D2... Region near the interface between the first electrode layer and the second electrode layer in the first electrode layer; E1, F1... First region of the mounting electrode portion; E2, F2... Second region of the mounting electrode portion; L1... First straight line; L2... Second straight line; L3... Third straight line; L4... Fourth straight line; L5... Fifth straight line; M1, M2... Straight line; P1... First end point; P2... Second end point; R1... Length of the region in the second region of the mounting electrode portion that is in contact with the solder portion; R2... Total length of the second region of the mounting electrode portion.

Claims

1. A stretchable mounting substrate, characterized in that, it comprises: a stretchable base material; a mounting electrode portion located on one main surface side of the stretchable base material and including a conductive filler and a resin; a solder portion connected to the mounting electrode portion; and an electronic component electrically connected to the mounting electrode portion via the solder portion, the mounting electrode portion has a first main surface on the stretchable base material side and a second main surface on the solder portion side, in the mounting electrode portion, there is a first region including the first main surface and a second region including the second main surface, in the mounting electrode portion, when observing a cross-section including the first region and the second region, the cross-sectional area of the conductive filler existing in the second region is larger than the cross-sectional area of the conductive filler existing in the first region, in each unit volume, the proportion of the conductive filler in the second region is larger than the proportion of the conductive filler in the first region, in the mounting electrode portion, the conductive filler existing in the second region is integrated with the solder portion.

2. The stretchable mounting substrate according to claim 1, wherein, the solder portion extends in the second region of the mounting electrode portion.

3. The stretchable mounting substrate according to claim 1 or 2, wherein, the thickness of the mounting electrode portion is 10 μm or more.

4. The stretchable mounting substrate according to claim 1 or 2, wherein, the stretchable mounting substrate further comprises a stretchable wiring whose end portion is provided to sandwich the end portion of the mounting electrode portion between the stretchable base material.

5. The stretchable mounting substrate according to claim 1 or 2, wherein, the stretchable mounting substrate further comprises a stretchable wiring whose end portion is provided between the stretchable base material and the mounting electrode portion.

6. A manufacturing method of a stretchable mounting substrate, characterized in that, it comprises: a first electrode layer forming step of coating a first conductive paste containing a first conductive filler and a thermosetting resin on one main surface side of a stretchable base material and then performing heat treatment to form a first electrode layer; a second electrode layer forming step of coating a second conductive paste containing a second conductive filler and a thermoplastic resin on the side opposite to the stretchable base material for the first electrode layer and then performing heat treatment to form a second electrode layer; and an electronic component mounting step of coating a solder paste on the second electrode layer, then mounting an electronic component on the solder paste, and then performing heat treatment to melt and solidify the solder paste to form a solder portion, and joining the electronic component and the first electrode layer via the solder portion, the mounting electrode portion obtained from the first electrode layer has a first main surface on the stretchable base material side and a second main surface on the solder portion side, in the mounting electrode portion, there is a first region including the first main surface and a second region including the second main surface, In the mounting electrode portion, when observing a cross section including the first region and the second region, the cross-sectional area of the conductive filler present in the second region is larger than the cross-sectional area of the conductive filler present in the first region. In each unit volume, the proportion of the conductive filler in the second region is larger than the proportion of the conductive filler in the first region. In the mounting electrode portion, the conductive filler present in the second region is integrated with the solder portion.

7. The method for manufacturing a stretchable mounting substrate according to claim 6, wherein, The coating of the first conductive paste in the first electrode layer forming process and the coating of the second conductive paste in the second electrode layer forming process are both performed by a screen printing method.

8. The method for manufacturing a stretchable mounting substrate according to claim 6 or 7, wherein, The solder paste contains tin and bismuth as metal components.

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