Stretchable substrate and method for manufacturing stretchable substrate

Abstract

Provided is a stretchable substrate which enables more effective reduction of ion migration, and a method for manufacturing the stretchable substrate. A stretchable substrate (1) according to the present disclosure has a solder layer (40) disposed on a base material (10) and includes: a pair of electrodes (20) which is disposed on one main surface of the base material (10) and which contains Ag; and a solder layer (40) which is disposed on the electrodes (20) and which contains Sn. In a plan view, an alloy phase (30) of at least Ag and Sn is provided to edges (20e) of the pair of electrodes (20) which face each other.

Description

Stretchable substrate and method for manufacturing the same

[0001] The present disclosure relates to a stretchable substrate and a method for manufacturing the stretchable substrate.

[0002] In recent years, the development of stretchable substrates that can be stretched and contracted has been actively carried out. A stretchable substrate can stretch and contract itself or be bent. Therefore, according to such a stretchable substrate, the stretchable substrate can be disposed along a curved surface or an uneven surface.

[0003] In stretchable substrates, Ag electrodes are often used for stretchable wiring, but Ag electrodes are generally known as the metal most likely to cause ion migration. Therefore, when an electric field is applied in a high-humidity state, ion migration (also called electrochemical migration) may occur, posing a problem that the insulation function may deteriorate.

[0004] Here, Patent Document 1 discloses an adhesive sheet capable of reducing ion migration. Specifically, a double-sided adhesive sheet having a water vapor transmission rate of 400 g / m ２ / 24 h or less, a sulfur content of 50 mg / kg or less, and containing a colorant is disclosed in Patent Document 1.

[0005] Japanese Unexamined Patent Application Publication No. 2024-46444

[0006] The double-sided adhesive sheet disclosed in Patent Document 1 is insufficient for reducing ion migration and has room for further improvement.

[0007] The present disclosure has been made in view of the above problems. That is, the main object of the present disclosure is to provide a stretchable substrate and a method for manufacturing the stretchable substrate that can more effectively reduce ion migration.

[0008] The stretchable substrate of the present disclosure is a stretchable substrate in which solder is disposed on a base material, and includes a pair of electrodes containing Ag disposed on one main surface of the base material, and a solder layer containing Sn disposed on the electrodes. In a plan view, an alloy phase of at least Ag and Sn is provided at opposing edge portions of the pair of electrodes.

[0009] The method for manufacturing a stretchable substrate according to the present disclosure comprises a coating step of coating each of the opposing edges of a pair of electrodes with the solder.

[0010] This disclosure provides a stretchable substrate and a method for manufacturing a stretchable substrate that can more effectively reduce ion migration.

[0011] Figure 1A is a schematic plan view of a stretchable substrate according to an embodiment of the present disclosure. Figure 1B is a schematic cross-sectional view taken along the line IB-IB in Figure 1A. Figure 2A is a schematic process plan view of a method for manufacturing a stretchable substrate according to an embodiment of the present disclosure. Figure 2B is a schematic cross-sectional view taken along the line IIB-IIB in Figure 2A. Figure 3A is a schematic process plan view of a method for manufacturing a stretchable substrate according to an embodiment of the present disclosure. Figure 3B is a schematic cross-sectional view taken along the line IIIB-IIIB in Figure 3A. Figure 4A is a schematic process plan view of a method for manufacturing a stretchable substrate according to an embodiment of the present disclosure. Figure 4B is a schematic cross-sectional view taken along the line IVB-IVB in Figure 4A. Figure 5 is a schematic plan view of a stretchable substrate according to another embodiment of the present disclosure. Figure 6A is a schematic plan photograph showing reduced ion migration. Figure 6B is a schematic plan photograph showing ion migration occurring. Figure 7 is a graph showing the reliability test with resistance on the vertical axis and time on the horizontal axis. Figure 8 is a table showing the results of the verification test. Figure 9 is a table showing the results of the verification test.

[0012] The embodiments for implementing this disclosure will be described below with reference to the drawings. The stretchable substrate described below is intended to embody the technical concept of this disclosure, and unless otherwise specified, this disclosure is not limited to the following.

[0013] In this specification, "plan view" refers to the state when viewing an object (e.g., a stretchable substrate) from directly above in the height direction, and is synonymous with a plan view. For example, a plan view is the state when viewed along the negative direction (- direction) in the "Z direction" as shown in Figure 1B. In this specification, "side view" refers to the state when viewing an object from the side perpendicular to the height direction, unless otherwise specified, and is synonymous with a side view. For example, a side view is the state when viewed along the positive direction (or negative direction) in the "X direction" as shown in Figure 1A. In this specification, "front view" refers to the state when viewing an object from the front perpendicular to the height direction, unless otherwise specified, and is synonymous with a front view. For example, a front view is the state when viewed along the negative direction (- direction) in the "Y direction" as shown in Figure 1A. The "positive direction" mentioned above refers to the direction indicated by the X, Y, and Z arrows in the diagram, while the "negative direction" refers to the direction opposite to the direction indicated by the X, Y, and Z arrows in the diagram. Furthermore, the X, Y, and Z directions are mutually orthogonal.

[0014] In this specification, terms describing relationships between elements (e.g., "parallel," "orthogonal," etc.) and terms describing the shapes of elements mean not only their literal, exact forms, but also a range that is substantially equivalent, for example, a range that includes differences of a few percent.

[0015] <Description of the stretchable substrate of this disclosure> The stretchable substrate 1 of the embodiment of this disclosure will be described with reference to Figures 1A and 1B. Figure 1A is a schematic plan view of the stretchable substrate of the embodiment, and Figure 1B is a schematic cross-sectional view obtained by cutting along the line IB-IB in Figure 1A.

[0016] The stretchable substrate 1 of this embodiment comprises a base material 10, an electrode 20 on one main surface side of the base material 10, and a solder layer 40 arranged on the electrode 20. More preferably, it may also include stretchable wiring 60 that is electrically connected to a pair of electrodes 20 and wired so as to be separated from each other. Each component will be described in detail below.

[0017] The substrate 10 supports the electronic components 50 so that they can be electrically connected. Examples of electronic components 50 include amplifiers (operational amplifiers, transistors, etc.), diodes, integrated circuits (ICs), capacitors, resistors, inductors, etc.

[0018] The substrate 10 can be any substrate as long as it can support the electronic components in a connectable manner. Examples include PCB (Printed Circuit Board) or FPC (Flexible Printed Circuit).

[0019] A suitable example of a substrate 10 is one that is stretchable. In this specification, "stretchable" means that it is capable of elastic deformation (deformation that occurs when a force is applied to an object and returns to its original shape when the force is removed). Therefore, since the stretchable substrate 1 of this disclosure is equipped with a stretchable substrate 10, the entire stretchable substrate 1 can be stretched or compressed.

[0020] An example of the material for the stretchable base material 10 is a stretchable rubber or elastomer. Specifically, it may contain at least one resin selected from the group consisting of silicone resins, acrylic resins, olefin resins, and urethane resins. An example of a urethane resin is thermoplastic polyurethane (TPU). In order to ensure stretchability, the thickness of the base material 10 is preferably 100 μm or less when not stretched, and more preferably 50 μm or less. Alternatively, the thickness of the base material 10 may be 10 μm or more when not stretched.

[0021] A pair of electrodes 20 containing Ag are provided on one main surface side of the electrode substrate 10. For example, an anode 20a and a cathode 20b containing Ag are provided adjacent to each other in the X direction on one main surface side of the substrate 10 (see Figure 1A). More preferably, an expandable wiring 60a for the anode electrically connected to the anode 20a and an expandable wiring 60b for the cathode electrically connected to the cathode 20b extend away from each other along the X direction, and the anode 20a and cathode 20b are provided adjacent to each other in the extending direction (X direction) (see Figure 1A). The anode 20a and cathode 20b may basically be made of the same shape and material, but they may also be made of different shapes and materials.

[0022] The electrode 20 is provided by coating one main surface of the substrate 10 with silver paste. The silver paste may contain a silver filler, a resin, a solvent, and additives.

[0023] Examples of silver filler shapes include plate-like, spherical, and needle-like shapes. Among these, the silver filler is preferably of an irregular shape such as plate-like.

[0024] Examples of resins include thermosetting resins and / or thermoplastic resins. When a thermosetting resin is used, when a solder layer 40 is provided on the electrode 20, "solder erosion," in which the metal of the electrode diffuses into the solder layer 40, can be prevented. Suitable examples of thermosetting resins include thermosetting polyester resins. When a thermoplastic resin is used, when a solder layer 40 is provided on the electrode 20, the contact angle between the electrode 20 and the solder layer 40 can be made relatively small, thereby improving the wettability between the electrode 20 and the solder layer 40. Suitable examples of thermoplastic resins include thermoplastic acrylic resins and thermoplastic urethane resins (e.g., thermoplastic polyurethane). In this embodiment, both thermosetting resins and thermoplastic resins may be used, or only one of them may be used.

[0025] Examples of solvents include diethylene glycol monoethyl ether acetate. Examples of additives include fine silica powder, carbon filler, and metal powder.

[0026] - Stretchable Wiring The stretchable wiring 60 is electrically connected to a pair of electrodes 20 and arranged to be separated from each other. In the example shown in Figure 1A, the anode stretchable wiring 60a extending from the anode 20a extends along the +X direction, and the cathode stretchable wiring 60b extending from the cathode 20b extends along the -X direction. The anode stretchable wiring 60a and the cathode stretchable wiring 60b may be basically made of the same shape and material, but they may also be made of different shapes and materials.

[0027] The thickness of each stretchable wiring 60 is preferably 100 μm or less, and more preferably 50 μm or less. Alternatively, the thickness of each stretchable wiring 60 may be 1 μm or more.

[0028] The expandable wiring 60 includes, for example, a conductive filler and a resin. Examples of conductive fillers include metal fillers such as silver filler, copper filler, and nickel filler. Among these, the conductive filler included in the expandable wiring 60 is preferably a silver filler. The shape of the conductive filler in the expandable wiring 60 may be, for example, plate-shaped or spherical. The particle size of the conductive filler is preferably 0.01 μm or more and 10 μm or less. Here, the particle size of the conductive filler refers to the length of its longest side if the conductive filler is plate-shaped, and refers to its diameter if the conductive filler is spherical.

[0029] - The solder layer 40 preferably contains Sn as a metallic component. More preferably, it contains Bi in addition to Sn. In other words, it is preferable to use a so-called BiSn-based low-temperature solder. By using such a low-temperature solder, even when the heat resistance temperature of the substrate 10 and the electronic component 50 is low, damage to them can be reduced and electrical connections can be made by the solder layer 40.

[0030] The solder layer 40 may be made of a material that can be melted and made to flow by heat treatment. In other words, the solder layer 40 is in a non-flowing state before heat treatment. As will be described in detail in the <Explanation of the Method for Manufacturing a Stretchable Substrate> section below, when placing the solder layer 40 on the electrodes 20, the solder layer 40 is placed so as to cover each of the opposing edges 20e of the pair of electrodes 20 in a plan view. As shown in Figure 1A, in this specification, the edge 20e refers to the parts of the pair of electrodes 20 that face each other, but it may also refer to the entire edge area EG including the edge 20e of the electrode 20. When the solder layer 40 is melted by heat treatment with the solder layer 40 placed on the pair of electrodes 20 in this state, an alloy phase 30 of the electrode 20 and the solder layer 40 is formed on the opposing edges 20e of the pair of electrodes 20. The alloy phase 30 may be an alloy phase of at least Ag and Sn. In this specification, the term "alloy phase" refers to a state in which the solder layer 40 and the electrode 20, which have been melted by heat, are mixed together and become a single integrated entity. In this embodiment, the presence or absence of the "alloy phase" can be determined by performing a compositional analysis (compositional analysis of the metal elements of the filler for the intervening conductive layer) on a cross-section of the stretchable substrate 1. For example, the presence or absence of the alloy phase 30 can be confirmed by elemental mapping of the metal elements of the solder layer 40 and the electrode 20 (for example, measured using a wavelength-dispersive X-ray spectrometer: FE-WDX (JEOL Ltd.: JXA-8530F)). Specifically, for a sample with a solder cross-section, the measurement position can be identified using FE-WDX, and then an elemental mapping can be generated at the measurement position. This makes it possible to confirm the elements in the solder (specifically, whether Ag is dissolved). As a simpler way to determine the presence or absence of the alloy phase, as shown in Figures 6A and 6B, the presence or absence of discoloration on the edge 20e can be determined by microscopic observation of the electrode 20.

[0031] In this embodiment, the stretchable substrate 1, in a plan view, has an alloy phase 30 between the electrodes 20 and the solder layer 40 at the opposing edges 20e of a pair of electrodes 20 within the entire edge region EG. The alloy phase 30 may be an alloy of at least Ag and Sn. Therefore, compared to the conventional structure with electrodes without an alloy phase, when an alloy phase 30 containing at least Ag and Sn is provided as in this embodiment, ion migration at the edges 20e of the electrodes 20 is less likely to occur. Thus, the stretchable substrate 1 of this embodiment can suppress the deterioration of insulation function due to ion migration. Furthermore, by including Ag in the electrodes 20, a stretchable substrate with good stretchability can be made.

[0032] <Description of Preferred Stretchable Substrate Embodiments> In a preferred embodiment of the stretchable substrate 1, the alloy phase 30 of Ag and Sn may be provided over the entire edge EG of the pair of electrodes 20. In the embodiment shown in Figure 1A, the alloy phase 30 is provided over the entire outer circumference of the electrode 20, which is rectangular in shape in plan view. With such an embodiment of the alloy phase 30, the deterioration of the insulating function due to ion migration can be more effectively prevented, and by including Ag in the electrode 20, a stretchable substrate with good stretchability can be made.

[0033] Regarding the specific embodiment of the alloy phase 30, the alloy phase 30 of the electrode 20 containing Ag and the BiSn-based solder layer 40 may contain Ag3Sn. One way to determine whether or not the alloy phase 30 contains Ag3Sn is to check whether the diffraction angles of the profile obtained by an X-ray diffractometer have peaks around 2θ = 34.5°, 37.2°, and 52.8°, and this is determined in conjunction with the FE-WDX results described above. In this way, if the alloy phase 30 is Ag3Sn, the deterioration of the insulating function due to ion migration can be effectively prevented. The alloy phase 30 needs to be formed with an appropriate width and thickness, but this can be achieved by adjusting the thickness of the electrode 20, the reflow temperature, the Ag particle size, the flux, etc.

[0034] In a specific embodiment of the alloy phase 30, the alloy phase may have a width W (see Figures 1A and 1B) of 1 μm or more in a plan view. In this specification, "width" refers to the average of the width measurements taken at a total of five locations, two at equal intervals on both sides of the ±Y direction from the center position shown in Figure 1A, after observing the electrode 20. Thus, if the width W of the alloy phase is 1 μm or more, a deterioration of the insulating function due to ion migration can be suitably prevented.

[0035] Furthermore, as a specific embodiment of the electrode 20 that generates the alloy phase 30, the thickest part D20 of the electrode 20 (see Figure 1B) may be 10 μm or more. As will be described in detail in the <Explanation of Manufacturing Method of Stretchable Substrate> below, the electrode 20 may be formed by screen printing as an example. Therefore, the shape of the electrode 20 may be such that the thickness is greater in the center of the electrode 20 and thinner at the outer ends of the electrode 20 (see Figure 1B). In this specification, the "thickness of the electrode 20" is measured by observing the stretchable substrate 1 in cross-section with a scanning electron microscope (SEM) to measure the thickest part. Alternatively, the thickness of the electrode 20 may be confirmed using a microscope such as a microscope. As described above, if the thickest part D20 of the electrode 20 is 10 μm or more, the adhesion between the electrode 20 and the substrate 10 can be improved, as will be described in detail in the later examples (adhesion strength test results).

[0036] Furthermore, the thickness of the alloy phase 30 may be 5 μm or less. As described above, the thickness D30 of the alloy phase 30 (see Figure 1B) is measured by cross-sectional observation of the stretchable substrate 1 using a scanning electron microscope (SEM), but in this specification, "thickness of the alloy phase" refers to the thickness measured at the point where the alloy phase is thickest by cross-sectional observation. In this way, if the thickness D30 of the alloy phase 30 is 5 μm or less, the electrode 20 and the solder layer 40 can be properly alloyed, and the alloy phase 30 can suitably prevent a decrease in insulating function due to ion migration.

[0037] <Description of Other Embodiments of the Stretchable Substrate of the Disclosure> Next, other embodiments of the stretchable substrate of the Disclosure will be described with reference to Figure 5. In describing other embodiments of the stretchable substrate, configurations common to the stretchable substrate 1 described above will be omitted from the description as appropriate. In other words, the configurations that differ from the stretchable substrate 1 described above will be described below.

[0038] The stretchable substrate 1 shown in Figure 5 has a two-layer electrode 20. When the electrode 20 has a two-layer structure, the second electrode 22 may be printed by screen printing so as to overlap the first electrode 21. In this case, it is preferable to print the entire second electrode 22 so as to be positioned on top of the first electrode 21, but there may be some parts that do not overlap. In this case, the first electrode 21 may be formed relatively thin (for example, with a thickness of 5 μm or less) in order to form an alloy phase 30 at its edges. The second electrode 22 may be provided so as to overlap a part of the first electrode 21 and may be formed to be thicker than the first electrode 21. In this configuration, by making the first electrode 21 relatively thin, it is made easier to alloy with solder, preventing a decrease in insulating function due to ion migration, while by applying the second electrode 22, the central part of the electrode 20 can be made relatively thicker, improving the adhesion between the electrode 20 and the substrate 10. Furthermore, according to this embodiment, a configuration that facilitates alloying (for example, reducing the particle size of Ag) can be adopted for the first layer, and a configuration that is less prone to alloying than the first layer can be adopted for the second layer, allowing the configurations of the first and second layers to be changed as appropriate.

[0039] <Description of the manufacturing method of the stretchable substrate according to the present disclosure> Next, the manufacturing method of the stretchable substrate according to the present disclosure will be described with reference to Figures 1A to 4B. The manufacturing method of the stretchable substrate according to the present disclosure may include an electrode formation step, a solder printing step, and a reflow step. In particular, the manufacturing method of the stretchable substrate according to the present disclosure is characterized mainly by the solder printing step. The following will describe each step in detail.

[0040] - Electrode Formation Step First, a stretchable substrate 10 is prepared. A pair of electrodes 20 are screen-printed on one major surface of the substrate 10. After screen-printing the electrodes 20, they are heated and cured. In this heating, heating may be performed under conditions where a predetermined resistance value is obtained.

[0041] Next, stretchable wirings 60 are screen-printed on each of the pair of electrodes 20. In FIGS. 2A and 2B showing an example, the stretchable wiring 60a for the anode extending from the anode 20a extends along the +X direction, and the stretchable wiring 60b for the cathode extending from the cathode 20b extends along the -X direction. After screen-printing the electrodes 20, they may be heated and cured under conditions where a predetermined resistance value is obtained. In the electrode formation step of the present disclosure, although electrode formation by screen-printing has been described, the electrode formation method is not limited to the method by screen-printing. For example, electrodes may be formed by methods such as inkjet printing, dispense printing, flexographic printing, gravure printing, etc.

[0042] - Solder Printing Step The solder printing step of the present disclosure is a step of coating each of the opposing edge portions 20e of the pair of electrodes 20 by solder printing. First, a BiSn-based solder layer 40 is applied using a stencil. The applied solder layer 40 is melted, and the solder layer 40 is printed on at least the opposing edge portions 20e of the pair of electrodes 20. In FIGS. 3A and 3B showing an example, the entire peripheral edge of the electrode 20 is coated with solder. In this way, an electronic component 50 is disposed on the solder layer 40 (FIGS. 4A and 4B).

[0043] - Reflow Step After the coating step, the solder layer 40 is melted by heating (reflow). The solder layer 40 may aggregate to approximately the same size as the electrodes 20 by heating (FIGS. 1A and 1B). Also, in the case of a BiSn-based low-temperature solder, melting of the solder layer 40 occurs by heating to a temperature of 160°C or higher. By this heating step, an alloy phase 30 of the electrodes 20 and the solder layer 40 is formed at the edge portions 20e covered with the solder layer 40 in the coating step. More specifically, Ag3Sn is formed as the alloy phase 30.

[0044] The stretchable substrate of the present disclosure manufactured through the above steps has, in a plan view, an alloy phase 30 of the electrode 20 and the solder layer 40 provided at the opposite edges 20e of the pair of electrodes 20. Therefore, compared with an electrode made of only Ag where ion migration, which is the prior art, is most likely to occur, when an alloy phase 30 containing Ag and Sn is provided as in the present embodiment, ion migration at the edge 20e of the electrode 20 is less likely to occur. Thus, it is possible to prevent a decline in the insulating function due to ion migration and to obtain a stretchable substrate 1 with good stretchability by including Ag in the electrode.

[0045] <Explanation of a Preferred Method for Manufacturing a Stretchable Substrate> As a preferred electrode formation step, the electrode 20 may be formed such that the thickness of the edge of the electrode 20 is thinner than the thickness of the central portion of the electrode 20. For example, when the electrode 20 is formed by screen printing, the shape of the electrode 20 extruded from the screen mask by the squeegee has a thinner edge thickness and a thicker central portion thickness. When the thickness of the edge 20e of the electrode 20 is relatively thin, it becomes easier for the electrode 20 and the solder layer 40 to alloy, and the alloy phase 30 of the electrode 20 and the solder layer 40 can be preferably formed. Also, when the thickness of the central portion of the electrode 20 is relatively thick, the adhesion between the electrode 20 and the base material 10 can be improved.

[0046] In addition, as another aspect of forming the electrode 20 such that the thickness of the edge of the electrode 20 is thinner than the thickness of the central portion of the electrode 20, as illustrated in FIG. 5, the electrode 20 may have a two-layer structure. Specifically, the first-layer electrode 21 is formed relatively thin, and the second-layer electrode 22 is provided such that the first-layer electrode 21 is exposed in a plan view, and the thickness of the edge of the electrode 20 as a whole electrode may be formed to be thinner than the thickness of the central portion of the electrode 20.

[0047] The demonstration test regarding the stretchable substrate of the present disclosure will be described in detail. Specifically, the stretchable substrates described in the following examples and comparative examples were manufactured.

[0048] ・Stretchable substrate of Example 1 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, an electrode 20 containing Ag was formed. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 160°C to produce a stretchable substrate having Ag3Sn as the alloy phase 30 between the electrode 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20 in a plan view. The width of the alloy phase 30 was 1 to 5 μm.

[0049] ・Stretchable substrate of Example 2 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, an electrode 20 containing Ag was formed. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 170°C to produce a stretchable substrate having Ag3Sn as the alloy phase 30 between the electrode 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20 in a plan view. The width of the alloy phase 30 was 10 to 30 μm.

[0050] ・Stretchable substrate of Example 3 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, electrodes 20 containing Ag were formed so that the maximum electrode thickness was 8 μm. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 160°C, thereby producing a stretchable substrate in which, in a plan view, Ag3Sn was present as the alloy phase 30 between the electrodes 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20. In Example 3, the entire electrode 20 of the stretchable substrate 1 was the alloy phase 30 in a plan view.

[0051] ・Stretchable substrate of Example 4 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, electrodes 20 containing Ag were formed so that the maximum electrode thickness was 10 μm. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 160°C to produce a stretchable substrate having Ag3Sn as the alloy phase 30 between the electrodes 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20 in a plan view. The width of the alloy phase 30 was 15 to 32 μm.

[0052] ・Stretchable substrate of Example 5 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, electrodes 20 containing Ag were formed so that the maximum electrode thickness was 15 μm. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 160°C to produce a stretchable substrate having Ag3Sn as the alloy phase 30 between the electrodes 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20 in a plan view. The width of the alloy phase 30 was 3 to 19 μm.

[0053] ・Stretchable substrate of Example 6 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, electrodes 20 containing Ag were formed so that the maximum electrode thickness was 19 μm. In the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. In the reflow step, the solder layer 40 was heated at 160°C to produce a stretchable substrate having Ag3Sn as the alloy phase 30 between the electrodes 20 and the solder layer 40 at the opposing edges 20e of the pair of electrodes 20 in a plan view. The width of the alloy phase 30 was 3 to 13 μm.

[0054] ・Stretchable substrate of Comparative Example 1 In the electrode formation step described in the manufacturing method of the stretchable substrate described above, an electrode 20 containing Ag was formed, and in the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. Here, when the solder layer 40 was heated at 140°C in the reflow step, no alloy phase like that in the example was formed on the stretchable substrate.

[0055] ・Stretchable substrate of Comparative Example 2: In the electrode formation step described in the manufacturing method of the stretchable substrate described above, an electrode 20 containing Ag was formed, and in the solder printing step, each of the opposing edges 20e of the pair of electrodes 20 was covered with a solder layer 40 containing Bi and Sn. Here, when the solder layer 40 was heated to 150°C in the reflow step, no alloy phase like that in the example was formed on the stretchable substrate.

[0056] Comparative Example 3: Stretchable Substrate In the electrode formation step described in the manufacturing method of the stretchable substrate described above, after forming an electrode 20 containing Ag, a solder layer 40 containing Bi and Sn was placed so that the edges 20e of the pair of electrodes 20 were exposed. Then, in the reflow step, the solder layer 40 was heated at 160°C. No alloy phase like that in the example was formed on the stretchable substrate manufactured by this manufacturing method.

[0057] Comparative Example 4: Stretchable Substrate In the electrode formation step described in the above-mentioned method for manufacturing a stretchable substrate, after forming an electrode 20 containing Ag, a solder layer 40 containing Bi and Sn was placed so that the edges 20e of the pair of electrodes 20 were exposed. Then, in the reflow step, the solder layer 40 was heated at 170°C. No alloy phase like that in the example was formed on the stretchable substrate manufactured by this method.

[0058] <Evaluation of Stretchable Substrate 1: Observation Results of Alloy Phase> A stretchable substrate with an alloy phase formed according to the example and a stretchable substrate without an alloy phase formed according to the comparative example were observed under a microscope. The observation results are shown in Figures 6A and 6B. Figure 6A is a microscopic image of the stretchable substrate with an alloy phase formed, and Figure 6B is a microscopic image of the stretchable substrate without an alloy phase formed. According to Figures 6A and 6B, the stretchable substrate of the comparative example (Figure 6B) did not have an alloy phase formed, and ion migration occurred between the electrodes. On the other hand, it was confirmed that an alloy phase was formed at the edges of the electrodes in the stretchable substrate of the example, and ion migration was reduced.

[0059] <Evaluation of Stretchable Substrate 2: Insulation Test Results> An insulation test was performed on the stretchable substrate with an alloy phase formed according to the example and the stretchable substrate without an alloy phase formed according to the comparative example. In the insulation test, the stretchable substrate was placed in a constant temperature bath maintained at 40°C and 95% RH, and a voltage of 3V was applied between the electrodes. The insulation resistance between the electrodes was monitored. Monitoring was performed for 1000 hours, and when the insulation resistance was 10 ８ The test was deemed unsuccessful if the resistance value fell below Ω. Figure 7 shows an example of a graph related to reliability testing, with resistance on the vertical axis and time on the horizontal axis.

[0060] According to the graph in Figure 7, the stretchable substrate of the embodiment has an insulation resistance of 10 １０ While maintaining an ohm order of resistance, the stretchable substrate used in the comparative example showed an insulation resistance of 10 after about 70 hours. ８ The values ​​fell below Ω, confirming a decrease in insulation function due to ion migration. The above evaluation was performed on the stretchable substrates of Examples 1 to 6 and the stretchable substrates of Comparative Examples 1 to 4, respectively. As shown in the tables in Figures 8 and 9, the stretchable substrates of Examples 1 to 6 showed good results in the insulation test, while the stretchable substrates of Comparative Examples 1 to 4 obtained worse results in the insulation test than the examples.

[0061] <Evaluation of Stretchable Substrate 3: Bonding Strength Test Results> Bonding strength tests were conducted using the stretchable substrates of Examples 3 to 6. In the bonding strength test, a lateral shear strength test was performed based on JIS C-62137-1-2:2010. Specifically, stress was applied to a 1005 size capacitor at a predetermined speed, and the bonding strength was measured at the maximum load. A bonding strength of 2N or higher was considered acceptable (○), and 3N or higher was considered preferable (◎). According to the table shown in Figure 9, the stretchable substrates of Examples 4 to 6, in which the thickest part of the electrode was 10 μm or more, showed better bonding strength results than the stretchable substrate of Example 3, in which the thickest part of the electrode was less than 10 μm.

[0062] The embodiments disclosed herein are illustrative in all respects and do not constitute a limiting interpretation. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined based on the claims. Furthermore, the technical scope of this disclosure includes all modifications within the meaning and scope of equivalence to the claims.

[0063] The stretchable substrate of this disclosure can be suitably used as an electronic component that can more effectively reduce ion migration.

[0064] 1 Stretchable substrate 10 Base material 20, 21, 22 Electrodes 20a Anode 20b Cathode 20e Edge 30 Alloy phase 40 Solder layer 50 Electronic components 60 Stretchable wiring 60a Stretchable wiring for anode 60b Stretchable wiring for cathode W Width D20 Thickest part of electrode D30 Thickness of alloy phase

Claims

1. A stretchable substrate having solder arranged on a base material, comprising: a pair of electrodes containing Ag arranged on one main surface of the base material; and a solder layer containing Sn arranged on the electrodes, wherein, in a plan view, an alloy phase of at least Ag and Sn is provided at the opposing edges of the pair of electrodes.

2. The stretchable substrate according to claim 1, wherein the solder layer further comprises Bi.

3. The stretchable substrate according to claim 1 or 2, wherein the alloy phase is provided over the entire edge of the pair of electrodes.

4. The stretchable substrate according to any one of claims 1 to 3, wherein the alloy phase comprises Ag3Sn.

5. The stretchable substrate according to any one of claims 1 to 4, wherein, in a plan view, the width of the alloy phase is 1 μm or more.

6. The stretchable substrate according to any one of claims 1 to 5, wherein the thickest part of the electrode is 10 μm or more.

7. The stretchable substrate according to any one of claims 1 to 6, wherein the thickness of the alloy phase is 5 μm or less.

8. The stretchable substrate according to any one of claims 1 to 7, wherein the substrate is stretchable.

9. The stretchable substrate according to any one of claims 1 to 8, wherein the electrode is electrically connected to a stretchable wiring.

10. A method for manufacturing a stretchable substrate according to any one of claims 1 to 9, comprising a coating step of coating each of the opposing edges of a pair of electrodes with the solder.

11. A method for manufacturing a stretchable substrate according to claim 10, wherein the coating step comprises coating the entire peripheral area of ​​the electrode with the solder.

12. A method for manufacturing a stretchable substrate according to claim 11, comprising a heating step of heating the solder to a temperature of 160°C or higher after the coating step.

13. A method for manufacturing a stretchable substrate according to claim 11 or 12, comprising an electrode forming step of forming the pair of electrodes on one main surface of the substrate, wherein the electrode forming step makes the thickness of the edge portion of the electrodes thinner than the thickness of the central portion of the electrodes.

Images