Stretchable substrate

Abstract

Provided is a stretchable substrate having improved mounting strength while solder wettability is further improved. Stretchable substrates 1A-1E according to the present disclosure each have a solder layer SD disposed on a base material 10. Each of the stretchable substrates comprises: a conductive layer 20 that is positioned on one main surface side of the base material 10; and a first layer 30 that contains a first metal and is in contact with the conductive layer 20. In a cross-sectional view of the conductive layer SD, the first layer 30, and the solder layer SD, a second layer 40 that contains the first metal and a solder is disposed at least partially between the first layer 30 and the conductive layer 20 in the thickness direction. The content density of the first metal in the second layer 40 is lower than the content density of the first metal in the first layer 30. The first layer 30 has protrusions PT in which the surface protrudes in the thickness direction due to the second layer 40.

Description

Stretchable substrate 【0001】 This disclosure relates to a stretchable substrate. 【0002】 In Patent Document 1, as a conductor surface treatment method for a circuit board that improves the wetting spreadability of solder when melting lead-free solder, an electroless plating layer is formed on the conductor exposed surface of the circuit board, and lead-free solder is adhered onto this electroless plating layer, and the lead-free solder is melted to form a lead-free solder layer. 【0003】 Japanese Patent Application Laid-Open No. 2001-291950 【0004】 In a substrate on which solder is disposed on a base material, it is required to further improve the wetting spreadability of the solder. On the other hand, when improving the wettability of the solder, a phenomenon such as the solder reacting with a conductive member having good wettability with the solder and the solder being eaten away occurs. Therefore, a conductive member having good wettability with the solder is likely to break as a whole, and as a result, the mounting strength is likely to decrease. Further, when performing component mounting with solder on a stretchable substrate, since the substrate stretches and shrinks, the difficulty of mounting with solder becomes high. 【0005】 This disclosure has been made in view of such problems. That is, the main object of this disclosure is to provide a stretchable substrate that further improves the wetting spreadability of solder and further improves the mounting strength. 【0006】 The stretchable substrate of this disclosure is a stretchable substrate on which a solder layer is disposed on a base material, and includes a conductive layer located on one main surface side of the base material, and a first layer containing a first metal and contacting the conductive layer. When the conductive layer, the first layer, and the solder layer are viewed in cross section, in the thickness direction, at least a part between the first layer and the conductive layer is provided with a second layer containing a first metal and solder, and the content density of the first metal in the second layer is smaller than the content density of the first metal in the first layer, and the first layer has a convex portion whose surface protrudes in the thickness direction by the second layer. 【0007】The stretchable substrate of this disclosure can improve solder wetting and spreading properties while also improving mounting strength. 【0008】 Figure 1 is a schematic plan view of the stretchable substrate of the first embodiment. Figure 2 is a schematic cross-sectional view taken along the line II-II in Figure 1. Figure 3 is an analysis photograph taken when the composition of the stretchable substrate of the first embodiment was analyzed. Figure 4 is a schematic plan view of a modified example of the stretchable substrate of the first embodiment. Figure 5 is a schematic cross-sectional view of the stretchable substrate of the second embodiment. Figure 6 is a schematic cross-sectional view of the stretchable substrate of the third embodiment. Figure 7 is a schematic plan view of the stretchable substrate of the fourth embodiment. Figure 8 is a schematic cross-sectional view taken along the line VIII-VIII in Figure 7. Figure 9 is a schematic plan view of the stretchable substrate of the fifth embodiment. 【0009】 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. 【0010】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" shown in Figure 2. The Z direction is intended to be the direction normal to the main surface of the substrate. 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 viewing an object along the positive direction (or negative direction) in the "X direction" shown in Figure 1. The X direction may be intended to be the direction perpendicular to the Z direction mentioned above and the Y direction described below. 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 viewing an object along the negative direction (- direction) in the "Y direction" shown in Figure 1. The Y direction may refer to the direction in which wiring is drawn out from the electronic component and extends. The "positive direction" mentioned above refers to the direction of the X, Y, and Z arrows shown in the drawing, while the "negative direction" refers to the direction opposite to the direction of the X, Y, and Z arrows shown in the drawing. The X, Y, and Z directions are mutually orthogonal. Furthermore, the "cross-sectional view" as used herein refers to the state when a cross-section cut by a plane parallel to the Z direction is viewed from a direction perpendicular to the Z direction (the Y direction in Figure 2). 【0011】 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. 【0012】 <Stretchable Substrate of the First Embodiment> The stretchable substrate 1 of the first embodiment according to this disclosure will be described with reference to Figures 1 to 3. Figure 1 is a schematic plan view of the stretchable substrate of the first embodiment, Figure 2 is a schematic cross-sectional view taken along the line II-II in Figure 1, Figure 3 is an analysis photograph taken when the stretchable substrate of the first embodiment was subjected to compositional analysis, and Figure 4 is a schematic plan view of a modified example of the stretchable substrate of the first embodiment. 【0013】The stretchable substrate 1A of this embodiment comprises a base material 10, and on one main surface side of the base material 10, a conductive layer 20, a first layer 30, and a second layer 40, with a solder layer SD disposed on the first layer 30. Each component will be described in detail below. 【0014】 The substrate 10 supports the electronic components 50 (see Figure 1) 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. 【0015】 The substrate 10 can be any substrate as long as it can support the electronic components 50 in a connectable manner. Examples include PCBs (Printed Circuit Boards) or FPCs (Flexible Printed Circuits). 【0016】 A suitable example of a substrate 10 may be one that is stretchable. The wiring 60, described later, may also be 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 1A of this disclosure comprises a stretchable substrate 10, the entire stretchable substrate 1A can be stretched or compressed. 【0017】 As an example of the material for the stretchable base material 10, it may include at least one resin selected from the group consisting of urethane resins, silicone resins, acrylic resins, and olefin resins. Examples of urethane resins include 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. 【0018】A conductive layer 20 is provided on one main surface side of the conductive layer substrate 10 to prevent solder erosion. In this specification, "solder erosion" refers to the phenomenon caused by the diffusion of solder into the conductive layer. Therefore, the conductive layer 20 that prevents solder erosion contains a material with low compatibility with flux (soldering accelerator) in the solder. 【0019】 The conductive layer 20 is provided by applying a conductive layer paste to one main surface of the substrate 10 and curing it. The curing after application of the conductive layer paste is referred to as the first curing. The conductive layer paste may contain a conductive layer filler containing a second metal 40, a thermosetting resin, a solvent, and additives. In this embodiment, the conductive layer paste contains a thermosetting resin, and the thermosetting resin, through thermal curing, has resistance to dissolution by flux, thus preventing "solder erosion." More specifically, if the conductive layer 20 that prevents solder erosion is not provided, a single first layer paste cured layer with high wettability, described later, will be provided on one main surface of the substrate 10. In this case, the first layer paste cured layer will be eroded by the solder, making it difficult to maintain the electrode shape. Therefore, in this embodiment, the electrode shape is maintained by combining the first layer 30 and the conductive layer 20, described later. 【0020】 Examples of fillers for the conductive layer include metal fillers such as silver fillers, copper fillers, and nickel fillers. Among these, silver fillers are preferred for the conductive layer. Examples of shapes for the conductive layer fillers include plate-like and spherical shapes. Examples of thermosetting resins include thermosetting ester resins, epoxy resins, and urethane resins. Examples of solvents include diethylene glycol monoethyl ether acetate, N-methylpyrrolidone, dimethylformamide, and toluene. Examples of additives include fine silica powder. The conductive layer 20 mainly contains the second metal 40 and a thermosetting resin. The conductive layer 20 is largely maintained even after the third curing process described later, although at least a portion of the surface may alloy with the molten solder. 【0021】- On one main surface side of the first layer substrate 10, the first layer 30 is provided so as to be in contact with the conductive layer 20 in cross-sectional view. More preferably, as shown in Figure 2, the first layer 30 may cover the conductive layer 20. In this specification, "covering" means that, in cross-sectional view, as shown in Figure 2, the width dimension W2 of the first layer 30 is larger than the width dimension W1 of the conductive layer 20, and the conductive layer 20 is covered by the first layer 30. It may also mean that there is a portion where the first layer 30 and the substrate 10 are in contact. Furthermore, it may also mean that, in plan view, the conductive layer 20 is overlapped and hidden by the first layer 30. In this embodiment, the embodiment in which the first layer 30 covers the conductive layer 20 as shown in Figure 2 will be described in detail below. 【0022】 The first layer 30 has higher wettability to the solder SD than the conductive layer 20. In this specification, "high wettability" means that the contact angle, which is one of the indicators of wettability, is relatively small. More specifically, it means that the contact angle between the first layer 30 and the solder SD is smaller than the contact angle between the conductive layer and the solder SD. 【0023】 The first layer 30 is provided by applying a paste for the first layer so as to be in contact with the conductive layer 20 and curing it, followed by the application of a solder paste described later, and a third curing process. The curing after the application of the paste for the first layer is referred to as the second curing. The cured layer of the paste for the first layer after the second curing is referred to as the first layer paste cured layer. The paste for the first layer may contain a filler for the first layer containing a first metal, a thermoplastic resin, and a solvent. 【0024】Examples of fillers for the first layer include metal fillers such as silver fillers, copper fillers, and nickel fillers. Among these, silver fillers are preferred for the first layer. The first layer filler may be made of the same metal as the conductive layer filler mentioned above, or it may be made of a different metal. Examples of shapes for the first layer filler include plate-like and spherical shapes. The shape of the first layer filler may be the same as the shape of the conductive layer filler mentioned above, or it may be a different shape. Examples of thermoplastic resins include thermoplastic acrylic resins, thermoplastic urethane resins (e.g., thermoplastic polyurethane), and silicone rubber. Examples of solvents include diethylene glycol monoethyl ether acetate, N-methylpyrrolidone, dimethylformamide, and toluene. 【0025】 In this embodiment, at least a portion of the first layer 30 is separated from the conductive layer 20. Specifically, as shown in Figure 2 when viewed in cross-section, if the first layer 30 is divided into three equal parts in the X direction, a central region Ri and an end region Ro, the central region Ri may be in contact with the first layer 30 and the conductive layer 20. On the other hand, at least a portion of the end region Ro is separated from the first layer 30 and the conductive layer 20, without contact. In other words, as shown in Figure 2, at least a portion of the end region Ro has a separation point SP. Due to this separation point SP, the surface of the first layer 30 is provided with a convex portion PT that protrudes in the thickness direction (Z direction). 【0026】 One method for separating the first layer 30 and the conductive layer 20 to form separation points SP is to use a paste for the first layer containing a thermoplastic resin that is easily soluble in flux, thereby increasing the fluidity of the molten solder and forming separation points SP. Alternatively, the fluidity of the molten solder can be increased by increasing the amount of solder, thereby forming separation points SP. In other words, separation points SP may be formed by controlling the fluidity of the molten solder. Furthermore, it is also possible to form the paste for the first layer wider than the conductive layer 20, and then perform second and third curing. 【0027】The solder layer SD is formed by applying solder paste so as to be in contact with the first layer paste curing layer and then curing it. The curing after the application of the solder paste is referred to as the third curing. The solder paste may contain solder constituent metals such as tin and bismuth, and a solvent. It is preferable that it be a so-called low-temperature solder. By using such a low-temperature solder, even if the heat resistance temperature of the substrate 10 and the electronic component 50 is low, damage to them can be reduced and electrical connection can be made by the solder layer SD. 【0028】 During the third curing process by heat, the solder melts and flows, diffusing into the paste-cured layer for the first layer. Subsequently, solidification forms the first layer 30 and the solder layer SD spread out on top of it, as shown in Figure 2, enabling the mounting of electronic components 50. The first layer 30, which mainly contains an alloy of solder and the first metal, is then formed. 【0029】 - At the second layer separation point SP, the solder of the solder paste placed above the paste hardening layer for the first layer flows due to the heat of the third hardening, flows between the conductive layer 20 and the paste hardening layer for the first layer, and solidifies to form the second layer 40. Here, the second layer 40 has a lower content density of the first metal than the first layer 30. Lower content density of the first metal than the first layer 30 includes embodiments in which the first metal is not present. Figure 3 shows measurement results showing that the second layer has a relatively lower content density of the first metal compared to the first layer. It is preferable that the content density of the first metal in each layer, both the first and second layers, is approximately constant, as shown in Figure 3. Similarly, it is preferable that the content density of the second metal in the conductive layer is approximately constant. 【0030】 In this way, the third hardening by heat forms the first layer 30 and the second layer 40, in which the solder and the first metal are alloyed. As used herein, "alloying" refers to a state in which the solder and the first metal and the second metal are mixed together and become a single integrated entity. 【0031】In this embodiment, the content density of the first metal can be determined by performing a compositional analysis (compositional analysis of the elements of the first metal) on the cross-section of the stretchable substrate 1A, as shown in Figure 3. An example is shown in Figure 3. Figure 3 shows the result of elemental mapping of the silver element as the first metal element on the cross-section of the stretchable substrate 1A (energy-dispersive X-ray spectrometer, Hitachi High-Technologies Corporation, serial number: 166080-10, and Hitachi Miniscope™3030Plus desktop microscope). The second metal in this sample is also silver. In Figure 3, the content density of the first metal is determined as follows: (1) In the observation field, black and white image data of the cross-section including the first and second layers is acquired. The range of the observation field is the range that includes the entire second layer, or the range that includes the entire edge region Ro. This range is then used as the analysis range. (2) Within the observation field, the total number of pixels in the image constituting the first layer and the total number of pixels in the image constituting the second layer are counted. (3) Measure the number of pixels of the first metal element. In the image shown in Figure 3, the first metal element is displayed as white pixels, so count the number of white pixels. (4) Calculate the number of white pixels / total number of pixels in the first layer, and calculate the number of white pixels / total number of pixels in the second layer. The calculated values ​​correspond to the content density of the first metal in the first layer and the occupancy density of the first metal in the second layer. In this embodiment, the content density of silver (first metal) in the second layer of the stretchable substrate 1A is smaller than the content density of silver (first metal) in the first layer. In this embodiment, the content density is calculated by counting the number of pixels, but the method of calculation is not limited to this, and for example, the proportion of white pixels constituting the first layer and the proportion of white pixels constituting the second layer may be determined by visual inspection. In other words, the occupancy density of the first metal in the second layer in Figure 3 is clearly less than the occupancy density of the first metal in the first layer. Therefore, the image data shown in Figure 3 indicates that the content density of the first metal in the second layer is lower than that of the first metal in the first layer. 【0032】Thus, in this embodiment, the stretchable substrate 1A forms a first layer on top of a conductive layer 20 that does not mix with molten solder, in which the solder and the first metal are alloyed. This allows for the formation of a solder layer SD over a wide area, thereby increasing the mounting strength (more specifically, the bonding strength between the solder layer SD and the substrate 10) compared to conventional methods. Furthermore, the protrusions PT formed by the separated areas SP exert an anchoring effect, enabling even stronger mounting strength. 【0033】 As described above, the stretchable substrate 1A of this embodiment includes a conductive layer 20 located on one main surface side of the base material 10 to prevent solder erosion, and a first layer 30 containing a first layer filler, covering the conductive layer 20 in cross-sectional view, and having higher solder wettability than the conductive layer 20. Therefore, it is possible to further improve solder wettability while further improving the mounting strength using solder. Furthermore, in the stretchable substrate 1A of this embodiment, at least a part of the first layer 30 is separated from the conductive layer 20, and a second layer 40 is provided at the separated area SP. In addition, at least in the first layer 30, the solder and the first metal of the first layer filler are alloyed. Therefore, this alloying can further increase the mounting strength (more specifically, the bonding strength between the solder layer SD and the base material 10). 【0034】 Furthermore, in the stretchable substrate 1A of this embodiment, the first metal of the first layer filler may be silver. By using silver for the first layer filler, it can be suitably alloyed with solder, and the mounting strength can be further improved. 【0035】 In a preferred embodiment of the stretchable substrate 1A, the conductive layer 20 contains a conductive layer filler containing a second metal, and within the first layer 30, the solder, the first metal, and the second metal may be alloyed. Providing a conductive layer filler on the conductive layer 20 side in this way allows for more favorable alloying with the solder, thereby further improving mounting strength. The second metal of the conductive layer filler may be silver, similar to the first metal of the first layer filler, but it may also be a metal other than silver (for example, copper). 【0036】Furthermore, the position of the separation point SP (second layer 40) is not particularly limited, but it is preferable that it be provided on the end side of the conductive layer 20 in a cross-sectional view, as in this embodiment. In this specification, "end side" means that, as shown in Figure 2, when the stretchable substrate is viewed in cross-section, the first layer 30 is divided into three equal parts in the X direction, and the separation point is provided in the end region Ro. In this way, when the separation point SP is provided on the end side of the conductive layer 20 in a cross-sectional view, the bonding strength between the solder SD and the conductive layer 20 can be more favorably increased on the end side. 【0037】 Furthermore, the separation points SP (second layer 40) in this embodiment may be partially provided at the interface with the conductive layer 20 in a cross-sectional view. In this specification, "partially" means that the separation points SP are provided only in a portion of the entire interface between the conductive layer 20 and the first layer 30. When the separation points SP are provided partially in this way, the solder SD and the conductive layer 20 are in direct contact in a partial manner, and this acts like a so-called anchoring effect, further suitably increasing the bonding strength between the solder layer SD and the conductive layer 20. 【0038】 In the first embodiment of the stretchable substrate 1A described above, the description has mainly focused on the configuration in which the first layer 30 covers the conductive layer 20, as shown in Figure 2. However, the invention is not limited to this configuration, and the first layer 30 may partially cover the conductive layer 20. Specifically, the width dimension W2 of the first layer 30 may be the same as the width dimension W1 of the conductive layer 20. Furthermore, as shown in Figure 4, the width dimension W2 of the first layer 30 may be smaller than the width dimension W1 of the conductive layer 20. 【0039】 <Stretchable Substrate of the Second Embodiment> Next, the stretchable substrate 1B of the second embodiment according to this disclosure will be described with reference to Figure 5. Figure 5 is a schematic cross-sectional view of the stretchable substrate of the second embodiment. When describing the stretchable substrate 1B of the second embodiment, configurations common to the stretchable substrate 1A of the first embodiment will be omitted from the explanation as appropriate. In other words, the configurations that differ from the stretchable substrate 1A of the first embodiment will be described below. 【0040】In the second embodiment of the stretchable substrate 1B, separation points SP, where the first layer 30 and the conductive layer 20 are separated, may be provided across the entire outer surface of the conductive layer 20. In this specification, "outer surface" refers to the surface of the conductive layer 20 that is not in contact with the substrate 10. As an example of a method for creating a structure like the stretchable substrate 1B of the second embodiment, one method is to make the first layer 30 larger than in the first embodiment, thereby making the first layer 30 more flexible and increasing the size of the separation points SP, and allowing solder to flow into these separation points SP. Another method is to use a larger amount of solder than in the stretchable substrate of the first embodiment and allow the solder to flow into the separation points SP. 【0041】 As in this embodiment, if the separation points SP between the first layer 30 and the conductive layer 20 are provided across the entire outer surface of the conductive layer 20, the solder layer SD can be brought into contact with the entire outer surface of the conductive layer 20, thereby further improving the wettability of the solder and enhancing the mounting strength. 【0042】 Furthermore, as a further method for providing the separated areas SP across the entire outer surface of the conductive layer 20, as in the stretchable substrate 1B of the second embodiment, the fluidity of the solder may be increased even further than that of the stretchable substrate 1A of the first embodiment, thereby allowing the solder to flow across the entire outer surface of the conductive layer 20 and providing the separated areas SP. 【0043】 <Stretchable Substrate of the Third Embodiment> Next, the stretchable substrate 1C of the third embodiment according to this disclosure will be described with reference to Figure 6. Figure 6 is a schematic cross-sectional view of the stretchable substrate of the third embodiment. When describing the stretchable substrate 1C of the third embodiment, configurations common to the stretchable substrates 1A and 1B of the first and second embodiments will be omitted from the explanation as appropriate. In other words, the configurations that differ from the stretchable substrates 1A and 1B of the first and second embodiments will be described below. 【0044】In the stretchable substrate 1C of the third embodiment, the separation location SP (second layer 40) is provided such that the separation distance SL (thickness of the second layer 40) increases toward the end side of the conductive layer 20. Referring to FIG. 6, in the separation location SP between the conductive layer 20 and the first layer 30, the separation distance SL along the Z direction increases as it goes in the +X direction. As a result, the solder flowed between the conductive layer 20 and the first layer 30 may become thicker as it goes toward the end side (the +X direction in the separation location SP on the right side of FIG. 6). Therefore, by giving the end side of the solder layer SD a thickness, cracking of the solder layer SD can be prevented. In this embodiment, since the conductive layer 20 overlaps and is hidden by the first layer 30 in plan view, it can be said that the first layer 30 covers the conductive layer 20. 【0045】 <Stretchable Substrate of the Fourth Embodiment> Next, the stretchable substrate 1D of the fourth embodiment according to the present disclosure will be described with reference to FIGS. 7 and 8. FIG. 7 is a schematic plan view of the stretchable substrate of the fourth embodiment, and FIG. 8 is a schematic cross-sectional view taken along line VIII-VIII of FIG. 7. In describing the stretchable substrate 1D of the fourth embodiment, the description of the configurations common to the stretchable substrates 1A to 1C of the first to third embodiments will be omitted as appropriate. That is, the configurations different from the stretchable substrates 1A to 1C of the first to third embodiments will be described below. 【0046】 In the stretchable substrate 1D of the fourth embodiment, the solder layer SD is covered with the first resin material R1. The first resin material R1 may be a member for protecting the electrical connection position with the electronic component 50, and specifically may be an insulating material. As an example, acrylic resin, urethane resin, epoxy resin, silicone resin, olefin resin, etc. can be mentioned. With such a covering mode by the first resin material R1, since the solder layer SD is covered by the first resin material R1, the electrical connection position by the solder layer SD can be protected. 【0047】Furthermore, as shown in FIG. 7, in the stretchable substrate 1D of the fourth embodiment, the conductive layer 20 and the wiring 60 may be electrically connected. Then, the first resin material R1 may cover the solder layer SD so as to expose the wiring 60. According to such a covering mode by the first resin material R1, the covering by the first resin material R1 can be minimized, and it is possible to reduce the inhibition of the bending and / or stretching of the stretchable substrate 1D by the first resin material R1. 【0048】 As a preferable stretchable substrate 1D of the fourth embodiment, the Young's modulus of the first resin material R1 is higher than the Young's modulus of the base material 10. In other words, the first resin material R1 has higher rigidity than the base material 10 and is difficult to deform. In such an aspect of the first resin material R1, even if the stretchable substrate 1D bends and / or stretches, deformation of the first resin material R1 can be reduced, and the dropping of the mounted electronic components 50 and the like can be prevented. 【0049】 <Stretchable Substrate of the Fifth Embodiment> Next, the stretchable substrate 1E of the fifth embodiment according to the present disclosure will be described with reference to FIG. 9. FIG. 9 is a schematic plan view of the stretchable substrate of the fifth embodiment. In describing the stretchable substrate 1E of the fifth embodiment, the description of the configuration common to the stretchable substrates 1A to 1D of the first to fourth embodiments will be omitted as appropriate. That is, the configuration different from the stretchable substrates 1A to 1D of the first to fourth embodiments will be described below. 【0050】The stretchable substrate 1E of the fifth embodiment is provided with a second resin material R2 that covers the wiring 60 on the stretchable substrate 1E, and the Young's modulus of the second resin material R2 is lower than that of the first resin material R1. In other words, the second resin material R2 may be an insulating material that is less rigid and more easily deformed than the first resin material R1. For example, it may be at least one resin selected from the group consisting of urethane resins, silicone resins, acrylic resins, and olefin resins. As shown in Figure 9, the first resin material R1 may cover a part of the wiring 60 portion on the stretchable substrate 1E, or it may cover the area excluding the wiring 60 portion. The second resin material R2, which has a Young's modulus lower than that of the first resin material R1, may cover the wiring 60 on the stretchable substrate 1E. Note that if the second resin material R2 covers the conductive layer 20, the conductive layer 20 has poor elasticity, and therefore may break at the interface of the conductive layer 20. Therefore, it is preferable that the second resin material R2 does not cover the conductive layer 20. Also, if the wiring 60 is exposed from the first resin material R1 and / or the second resin material R2, stress may concentrate during elongation, potentially causing disconnection. Therefore, it is preferable that the wiring 60 is reliably covered by the first resin material R1 and / or the second resin material R2. 【0051】 In the fifth embodiment, the coating is provided by a first resin material R1 and a second resin material R2. This reduces deformation of the first resin material R1 even when the stretchable substrate 1E is bent and / or stretched, preventing the mounted electronic components 50 from falling off. In addition, the second resin material R2 protects the wiring on the stretchable substrate 1E. Furthermore, since the Young's modulus of the second resin material R2 is lower than that of the first resin material R1, the stretchable substrate 1E can be protected without impairing its stretchability. 【0052】 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. 【0053】 The stretchable substrate of this disclosure can be suitably used as an electronic component that further improves solder wettability while also improving mounting strength. 【0054】 1A-1E Stretchable substrate 10 Base material 20 Conductive layer 30 First layer 40 Second layer 50 Electronic components 60 Wiring SD Solder layer SP Separation point SL Separation distance Ri Central region Ro Edge region W1, W2 Width R1 First resin material R2 Second resin material PT Protrusion

Claims

1. A stretchable substrate having a solder layer disposed on a substrate, comprising: a conductive layer located on one main surface side of the substrate; and a first layer containing a first metal and in contact with the conductive layer, wherein when the conductive layer, the first layer, and the solder layer are viewed in cross-section, a second layer containing solder and the first metal is disposed in the thickness direction, at least a portion between the first layer and the conductive layer, the content density of the first metal in the second layer is smaller than the content density of the first metal in the first layer, and the first layer has a convex portion whose surface protrudes in the thickness direction due to the second layer.

2. The stretchable substrate according to claim 1, wherein the first layer covers the conductive layer.

3. The stretchable substrate according to claim 1 or 2, wherein the first metal is silver.

4. The stretchable substrate according to any one of claims 1 to 3, wherein the second layer is provided on the end side of the conductive layer in a cross-sectional view.

5. The stretchable substrate according to any one of claims 1 to 4, wherein the second layer is partially provided at the interface with the conductive layer in a cross-sectional view.

6. The stretchable substrate according to any one of claims 1 to 5, wherein the second layer is provided over the entire outer edge of the conductive layer.

7. The stretchable substrate according to any one of claims 1 to 6, wherein the second layer is provided such that its thickness increases toward the edge side of the conductive layer.

8. The stretchable substrate according to any one of claims 1 to 7, wherein the conductive layer contains a filler containing a second metal, and at least on the surface of the conductive layer, the solder and the second metal are alloyed.

9. The stretchable substrate according to any one of claims 1 to 8, wherein the solder layer is covered with a first resin material.

10. The stretchable substrate according to claim 9, wherein the Young's modulus of the first resin material is higher than that of the substrate.

11. The stretchable substrate according to claim 9 or 10, wherein a second resin material is provided to cover the wiring on the mounting substrate, and the Young's modulus of the second resin material is lower than that of the first resin material.

12. The stretchable substrate according to any one of claims 1 to 11, wherein the substrate is stretchable.

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