Strain gauge

Abstract

To provide a strain gauge that is excellent in solder wettability of an electrode even when it is used over time.SOLUTION: The strain gauge has a base material, a resistor formed on the base material, and an electrode formed on the base material and electrically connected to the resistor. The electrode has a metal layer, and at least a top face of the metal layer has an alloy of conductive metal and added metal having higher corrosion resistance than the conductive metal. The electrode includes, in its thickness direction, a portion different in the content of the added metal in the alloy.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to strain gauges. [Background technology]

[0002] Strain gauges are known that are attached to a measurement object to detect strain on the object. A strain gauge includes a substrate and electrodes formed on the substrate. The substrate may be, for example, an insulator or an insulating film. Also disclosed as electrodes are electrodes in which titanium (Ti), nickel (Ni), and gold (Au) are sequentially layered from the substrate side (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 06-300649 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a strain gauge that has excellent solder wettability of the electrodes even when used over time. [Means for solving the problem]

[0005] This strain gauge includes a substrate, a resistor formed on the substrate, and an electrode formed on the substrate and electrically connected to the resistor, the electrode having a metal layer, and at least an upper surface of the metal layer having an alloy of a conductive metal and an additive metal having higher corrosion resistance than the conductive metal, The electrode includes portions in the thickness direction where the content of the additive metal in the alloy varies. [Effects of the Invention]

[0006] According to the disclosed technology, it is possible to provide a strain gauge in which the solder wettability of the electrodes is excellent even when used over time. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 3] 3A to 3C are diagrams (part 1) illustrating a manufacturing process of the strain gauge according to the first embodiment; [Figure 4] 5A to 5C are diagrams (part 2) illustrating the manufacturing process of the strain gauge according to the first embodiment; [Figure 5] 1 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0009] First Embodiment Fig. 1 is a plan view illustrating a strain gauge according to a first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, taken along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, and an electrode 40A.

[0010] In this embodiment, for convenience, in each component shown in the cross-sectional view of the strain gauge 1 in Fig. 2, the side facing the same direction as the side on which the resistor 30 is provided as viewed from the substrate 10 may be referred to as the upper side, and the side facing the same direction as the side of the substrate 10 on which the resistor 30 is not provided may be referred to as the lower side. Also, the upper surface of each part may be referred to as the upper surface, and the lower surface may be referred to as the lower surface. However, the strain gauge 1 can be used upside down or placed at any angle.

[0011] In this embodiment, the "thickness direction" refers to the same direction as the direction in which the substrate 10 of the strain gauge 1 has a thickness. For example, if the substrate 10 is flat, the thickness direction is the surface normal to the top surface 10a of the substrate 10. Furthermore, a planar view refers to viewing the entire strain gauge 1 from the side where the top surface 10a is located, and a planar shape refers to the shape of the object when viewed from above.

[0012] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transferability of strain from the surface of the strain generator bonded to the lower surface of the substrate 10 via an adhesive layer or the like and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation properties.

[0013] The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0014] Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina, for example.

[0015] The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strain is applied. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 with a matte finish.

[0016] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr mixed phase film. An example of a material containing Ni is Ni-Cu (nickel copper). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0017] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0019] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0020] The electrodes 40A extend from both ends of the resistor 30. The shape of the electrodes 40A is not particularly limited, but for example, the electrodes 40A are formed in a generally rectangular shape wider than the resistor 30 in a plan view. The electrodes 40A are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and are connected to, for example, a lead wire for external connection. For example, the resistor 30 extends from one of the electrodes 40A while folding back in a zigzag pattern and is electrically connected to the other electrode 40A. In the example of FIG. 1 , this zigzag folding back portion is the sensitive portion of the strain gauge 1, and its grid direction is parallel to the AA direction in a plan view. Furthermore, both ends of the resistor 30 can also be considered as wiring portions that electrically connect the sensitive portion of the resistor 30 and the electrodes 40A.

[0021] The electrode 40A has terminal portions 41 extending from both ends of the resistor 30, and a metal layer 43 formed on the upper surface of the terminal portion 41. Although the resistor 30 and the terminal portion 41 are denoted by different reference numerals for convenience, they can be integrally formed from the same material in the same process.

[0022] The metal layer 43 of the electrode 40A contains a conductive metal. At least the upper surface of the metal layer 43 contains an alloy of the conductive metal and an additive metal that is more corrosion-resistant than the conductive metal. For example, when the strain gauge 1 has the shape shown in FIG. 1, at least a portion of the upper surface of the metal layer 43 formed on the upper surface of the terminal portion 41 is made of the alloy. Here, "corrosion resistance" refers to the resistance of the metal to rust, and "more corrosion-resistant than conductive metals" refers to a metal that has a lower ionization tendency than conductive metals, or a metal that has a higher ionization tendency than conductive metals but forms a passivation film on the surface by bonding with oxygen.

[0023] Because metal layer 43 contains a conductive metal, electrode 40A is conductive. Furthermore, because at least a portion of the upper surface of metal layer 43 is made of the above-mentioned alloy, the alloy portion on the upper surface is less likely to oxidize, even when strain gauge 1 is used over time. Therefore, the strain gauge 1 according to this embodiment is less likely to experience a decrease in the solder wettability of electrode 40A, even when strain gauge 1 is used over time, and therefore can be said to have excellent solder wettability.

[0024] The conductive metal is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include Cu and Ni. The thickness of the metal layer 43 may be determined taking into consideration the solderability to the electrode 40A. The thickness of the metal layer 43 is preferably 1 μm or more. For example, by using Cu, a Cu alloy, Ni, or a Ni alloy as the material for the metal layer 43 and setting the thickness of the metal layer 43 to 1 μm or more, solder erosion of the electrode 40A is improved.

[0025] Here, solder erosion refers to the material that constitutes electrode 40A dissolving in the solder that is joined to electrode 40A, causing a decrease in the thickness of electrode 40A or even the disappearance of electrode 40A. If solder erosion occurs, there is a risk that the adhesive strength and tensile strength of the lead wire or the like joined to electrode 40A will decrease, so it is preferable that solder erosion does not occur (or that there is little solder erosion).

[0026] The additive metal can be appropriately selected depending on the purpose. For example, examples of the additive metal include Ag, Pt, Au, Fe, Cr, Co, Zn, and Sn. When the conductive metal is Cu, Ni can also be suitably used as the additive metal.

[0027] In the first embodiment, one type of additive metal is used as an example. When forming a metal layer of an alloy using a method such as electroless plating, which will be described later, a film of concentrated additive metal (a so-called "rich film") may be formed between the metal layer and other layers. However, the rich film is very thin and has almost no effect on the function and effect of the strain gauge according to the present disclosure. Therefore, this specification and drawings do not specifically mention the presence or absence of a rich film in the strain gauge, or the configuration when a rich film is present. Furthermore, in this disclosure, the term "metal layer" does not include a rich film.

[0028] The content of the additive metal in the alloy is not particularly limited and can be selected appropriately depending on the purpose, but is preferably 20% by mass or more and 40% by mass or less. This results in excellent solder wettability of the strain gauge due to the high content of additive metal on the upper surface side, and excellent conductivity due to the high content of conductive metal inside the electrode. Furthermore, it is preferable that the content of the additive metal in the alloy in the portion of the electrode that contains the alloy increases from the substrate side to the upper surface side.

[0029] Metal layer 43 of electrode 40A includes portions in its thickness direction where the content of the additive metal in the alloy of the conductive metal and the additive metal varies.

[0030] Here, "including portions with different contents of added metal" means, for example, that multiple layers with different contents of added metal are stacked, or that the contents of added metal form a gradation structure in which the contents of added metal differ stepwise within the alloy.

[0031] Although the terminal portion 41 is exposed around the metal layer 43 in a plan view, the terminal portion 41 may have the same planar shape as the metal layer 43 .

[0032] Furthermore, a cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrodes 40A. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture and the like. Note that the cover layer 60 may be provided so as to cover the entire portion except for the electrodes 40A.

[0033] The cover layer 60 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0034] 3 and 4 are diagrams illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section corresponding to FIG. 2. To manufacture the strain gauge 1, first, in the step shown in FIG. 3(a), a substrate 10 is prepared, and a resistor precursor layer 300 is formed on the upper surface 10a of the substrate 10. The resistor precursor layer 300 is a layer that will eventually be patterned to become the resistor element 30 and the terminal portion 41. Therefore, the material and thickness of the resistor precursor layer 300 are the same as those of the resistor element 30 and the terminal portion 41 described above.

[0035] The resistor precursor layer 300 can be formed by, for example, magnetron sputtering using as a target a raw material capable of forming the resistor precursor layer 300. Instead of magnetron sputtering, the resistor precursor layer 300 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0036] From the viewpoint of stabilizing the gauge characteristics, a base layer may be formed on the upper surface 10a of the substrate 10 before forming the resistor precursor layer 300. This base layer may be, for example, a functional layer having a film thickness of about 1 nm to 100 nm. The functional layer can be formed in a vacuum by conventional sputtering.

[0037] In the present disclosure, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper layer, the resistor precursor layer 300 (resistor 30, etc.). The functional layer preferably further has a function of preventing oxidation of the resistor precursor layer 300 due to oxygen or moisture contained in the substrate 10, and / or a function of improving adhesion between the substrate 10 and the resistor precursor layer 300. The functional layer may further have other functions.

[0038] Since the insulating resin film that constitutes the substrate 10 contains oxygen and moisture, it is effective for the functional layer to have the function of preventing oxidation of the resistor precursor layer 300, especially when the resistor precursor layer 300 contains Cr, since Cr forms a self-oxidized film.

[0039] The material of the functional layer is not particularly limited as long as it has the function of promoting crystal growth of at least the upper layer, the resistor precursor layer 300 (resistor 30), and can be appropriately selected depending on the purpose. For example, the material of the functional layer may be one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group.

[0040] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0041] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0042] However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

[0043] There are no particular limitations on the combination of the material of the functional layer and the material of the resistor precursor layer 300, and they can be selected appropriately depending on the purpose. For example, it is possible to use Ti for the functional layer and form a Cr mixed phase film containing α-Cr (alpha chromium) as the main component for the resistor precursor layer 300.

[0044] In this case, for example, the resistor precursor layer 300 can be formed by magnetron sputtering using a target made of a material capable of forming a Cr mixed phase film and introducing Ar gas into a chamber. Alternatively, the resistor precursor layer 300 can be formed by reactive sputtering using a target made of pure Cr and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber.

[0045] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0046] When the resistor precursor layer 300 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the resistor precursor layer 300, preventing oxidation of the resistor precursor layer 300 due to oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and the resistor precursor layer 300. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0047] In this way, by providing a functional layer below the resistor precursor layer 300, it is possible to promote crystal growth in the resistor precursor layer 300, and to produce a resistor precursor layer 300 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material constituting the functional layer into the resistor precursor layer 300, it is possible to improve the gauge characteristics of the strain gauge 1.

[0048] 3(b), a photosensitive resist 800 is formed on the entire upper surface of the resistor precursor layer 300, and is exposed and developed to form openings 800x that expose regions where the metal layer 43 will be formed. As the resist 800, for example, a dry film resist or the like can be used.

[0049] 3(c), a metal layer 43 is formed on the resistor precursor layer 300 exposed in the opening 800x by, for example, electroless plating. When forming the metal layer 43 by electroless plating, electroless plating is performed in a single plating bath while changing the concentration ratio of the conductive metal to the additive metal in the plating solution. As a result, the formed electrode has a configuration including portions in its thickness direction where the content of the additive metal in the alloy of the conductive metal and the additive metal varies.

[0050] Next, in the step shown in Fig. 4(a), the resist 800 shown in Fig. 3(c) is removed. The resist 800 can be removed, for example, by immersing it in a solution that can dissolve the material of the resist 800.

[0051] 4(b), a photosensitive resist 810 is formed on the entire upper surface of the resistor precursor layer 300, and is then exposed and developed to be patterned into a planar shape similar to that of the resistor element 30 and the terminal portion 41 in FIG. 1. For example, a dry film resist or the like can be used as the resist 810.

[0052] Next, in the step shown in FIG. 4(c), the resist 810 is used as an etching mask to remove the resistor precursor layer 300 exposed from the resist 810, thereby forming the resistor 30 and terminal portions 41 having the planar shape shown in FIG. 1. For example, unnecessary portions of the resistor precursor layer 300 can be removed by wet etching. If a functional layer is formed below the resistor precursor layer 300, the functional layer is patterned by etching into the planar shape shown in FIG. 1, similar to the resistor 30 and terminal portions 41. At this point, a seed layer 420 has been formed on the resistor 30.

[0053] The strain gauge 1 is completed by the step shown in FIG. 4(c). After the step shown in FIG. 4(c), a cover layer 60 that covers the resistor 30 and exposes the electrode 40A may be provided on the upper surface 10a of the substrate 10. The strain gauge 1 is completed. The cover layer 60 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrode 40A, and then heating and curing the film. The cover layer 60 may also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrode 40A, and then heating and curing the film.

[0054] In this way, by forming metal layer 43 having a thick film (1 μm or more) of an alloy of a conductive metal and an additive metal on terminal portion 41, it is possible to prevent solder erosion of electrode 40A and improve solder wettability.

[0055] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example of an electrode having a layer structure different from that of Embodiment 1 is shown. Note that in Modification 1 of the first embodiment, the description of the same components as those of the already described embodiments may be omitted.

[0056] Fig. 5 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the first embodiment, showing a cross section corresponding to Fig. 2. Referring to Fig. 5, strain gauge 1A differs from strain gauge 1 (see Fig. 2, etc.) in that electrode 40A is replaced with electrode 40B. Note that cover layer 60 may be provided so as to cover the entire portion excluding electrode 40B.

[0057] Electrode 40B has a laminated structure in which multiple metal layers are stacked. Specifically, electrode 40B has terminal portions 41 extending from both ends of resistor 30, a metal layer 43 formed on the upper surface of terminal portion 41, and a metal layer 44 formed on the upper surface of metal layer 43.

[0058] In Figure 5, the multiple metal layers are shown as a two-layer structure of metal layer 43 and metal layer 44, but the number of metal layers is not particularly limited as long as the total number is two or more layers, and can be determined appropriately depending on the purpose.

[0059] The material of the metal layer 44 is not particularly limited and can be selected appropriately depending on the purpose. For example, the same material as that of the metal layer 43 can be used as the material of the metal layer 44. The thickness of the metal layer 44 is not particularly limited and can be selected appropriately depending on the purpose. For example, the thickness of the metal layer 44 can be about 1 μm to 2 μm.

[0060] The metal layer 43 and the metal layer 44 can be formed by, for example, electroless plating in the step shown in FIG. 3(c).

[0061] When forming metal layer 43 and metal layer 44 by electroless plating, electroless plating is performed using multiple electroless plating baths in sequence. For example, metal layer 43 can be formed by electroless plating in a first plating bath having a desired concentration ratio of conductive metal to additive metal, and then metal layer 44 can be formed by electroless plating in a second plating bath having a different concentration ratio. As a result, the formed electrode has a configuration including multiple layers in its thickness direction, each layer having a different content of additive metal in the alloy of conductive metal and additive metal.

[0062] The portion containing the alloy can be formed into a structure in which three or more layers are laminated by performing electroless plating using three or more plating baths.

[0063] It is preferable that the content of the additive metal in the alloy of the multiple metal layers (metal layer 43, metal layer 44, etc.) increases from the layer on the substrate side toward the layer on the upper surface side. As a result, the layer on the upper surface side has a higher content of additive metal than the layer on the substrate side, and therefore has the property of excellent solder wettability for the strain gauge. On the other hand, the layer on the substrate side has a higher content of conductive metal than the layer on the upper surface side, and therefore has the property of excellent conductivity.

[0064] The thickness of each of the plurality of metal layers is not particularly limited and can be determined appropriately depending on the purpose. For example, when determining the thickness from the viewpoint of reducing the resistance value of the electrode and improving conductivity, it is preferable that metal layer 44 on the top surface of electrode 40A be thinner than the other metal layers that are not on the top surface.

[0065] The above describes the embodiments and modifications. However, the configuration of the strain gauge according to the present disclosure is not limited to the above-described embodiments and modifications. The strain gauge according to the present disclosure can be realized by adding various modifications and substitutions to the above-described embodiments, etc., without departing from the scope of the claims. [Explanation of symbols]

[0066] 1, 1A, 1B strain gauge, 10 substrate, 10a upper surface, 30 resistor, 41 terminal portion, 40A, 40B electrodes, 43, 44 metal layer, 60 cover layer

Claims

1. A substrate; a resistor formed on the substrate; an electrode formed on the substrate and electrically connected to the resistor; the electrode has a metal layer, and at least a top surface of the metal layer has an alloy of a conductive metal and an additive metal having higher corrosion resistance than the conductive metal; A strain gauge characterized in that the electrode includes a portion in the thickness direction thereof where the content of the additive metal in the alloy varies.

2. 2. The strain gauge according to claim 1, wherein the portion of the electrode containing the alloy has a higher content of the additive metal in the alloy from the substrate side toward the upper surface side.

3. The strain gauge according to claim 1 , wherein the portion having the alloy has a structure in which a plurality of layers are laminated.

4. 4. The strain gauge according to claim 3, wherein the plurality of layers have a higher content of the additive metal in the alloy from the layer closest to the substrate toward the layer closest to the upper surface.

5. 5. The strain gauge according to claim 1, wherein the additive metal is nickel or silver.

6. The additive metal is nickel, 6. The strain gauge according to claim 5, wherein the content of the additive metal in the alloy is 20% by mass or more and 40% by mass or less.

Images