Strain gauge

Abstract

To provide a strain gauge with an improved creep characteristic.SOLUTION: The strain gauge includes: a base material; a resistor directly or indirectly provided on the base material; and a wire connected to an end part of the resistor. The wire includes: a first metal layer extending from the end part, the first metal being formed of the same material as that of the resistor; and a second metal layer on the first metal layer, the second metal layer being formed of a material with a lower resistance than that of the first metal layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a strain gauge.

Background Art

[0002] A strain gauge having a resistor on a base material, which is attached to a measurement object to detect the characteristics of the measurement object, is known. The strain gauge is used, for example, as a sensor for detecting the strain of a material, a sensor for detecting the ambient temperature, etc. (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a strain gauge, creep characteristics are important. By improving the creep characteristics, for example, the strain gauge may be used not only for sensor applications but also for weighing applications.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a strain gauge with improved creep characteristics.

Means for Solving the Problems

[0006] This strain gauge has a base material, a resistor provided directly or indirectly on the base material, a wiring connected to an end of the resistor, and an insulating resin layer covering the resistor and the wiring, and the insulating resin layer has an opening exposing at least a part of the wiring. The wiring includes a first metal layer formed of the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material with lower resistance than the first metal layer. .

Effects of the Invention

[0007] According to the disclosed technology, it is possible to provide strain gauges with improved creep characteristics. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 2] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 3] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 4] This is a cross-sectional view (part 3) illustrating a strain gauge according to the first embodiment. [Figure 5] This is a plan view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 6] This is a cross-sectional view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 7] This is a plan view illustrating a strain gauge according to a modified example 2 of the first embodiment. [Figure 8] This is a plan view illustrating a strain gauge according to a modified example 3 of the first embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> Figure 1 is a plan view illustrating a strain gauge according to the first embodiment. Figure 2 is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1. Figure 3 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 1.

[0011] Referring to Figures 1 to 3, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, an electrode 50, wiring 60, and a cover layer 70. For convenience, only the outer edge of the cover layer 70 is shown with a dashed line in Figures 1 to 3. The cover layer 70 may be provided as needed.

[0012] In this embodiment, for convenience, the side of the base material 10 on which the resistor 30 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 30 is provided at each part is referred to as one surface or the upper surface, and the surface on which the resistor 30 is not provided is referred to as the other surface or the lower surface. However, the strain gauge 1 can be used upside down or positioned at any angle. Moreover, a plan view refers to viewing the object from the direction normal to the upper surface 10a of the base material 10, and a planar shape refers to the shape of the object when viewed from the direction normal to the upper surface 10a of the base material 10.

[0013] The base material 10 is a member that serves as a base layer for forming the resistor 30, etc., and is flexible. The thickness of the base material 10 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm of the base material 10 is preferable in terms of the transmission of strain from the surface of the strain-generating body joined to the lower surface of the base material 10 via an adhesive layer, etc., and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0014] The base material 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, LCP (liquid crystal polymer) resin, or polyolefin resin. The term "film" refers to a flexible material with a thickness of approximately 500 μm or less.

[0015] 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, for example, an insulating resin film containing fillers such as silica and alumina.

[0016] Examples of materials other than the resin of the base material 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO3, BaTiO3), etc., and in addition, amorphous glass, etc. may be mentioned. Also, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), and titanium may be used. In this case, for example, an insulating film is formed on the metal base material 10.

[0017] The resistor 30 is a thin film formed on the base material 10 in a predetermined pattern and is a sensing part that undergoes strain and causes a resistance change. The resistor 30 may be formed directly on the upper surface 10a of the base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown as a dark embossed pattern.

[0018] The resistor 30 has a structure in which a plurality of elongated portions are arranged at a predetermined interval with their longitudinal directions facing the same direction (the direction of line A-A in FIG. 1), and the ends of adjacent elongated portions are alternately connected to form a folded portion 35, and the whole is folded back in a zigzag shape. The longitudinal direction of the plurality of elongated portions becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the direction perpendicular to line A-A in FIG. 1).

[0019] One end portion in the longitudinal direction of the two outermost elongated portions located in the grid width direction is bent in the grid width direction to form respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction. The respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction are electrically connected to the electrodes 50 via the wirings 40. In other words, the wirings 40 electrically connect the respective terminals 30e1 and 30e2 of the resistor 30 in the grid width direction to the respective electrodes 50.

[0020] 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 multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0021] Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0022] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more of the resistor 30 is preferable because it improves the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less of the resistor 30 is even preferable because it can reduce cracks in the film and warping from the substrate 10 caused by internal stress in the film constituting the resistor 30. The width of the resistor 30 can be optimized according to the required specifications such as resistance value and lateral sensitivity, and also takes into account measures to prevent wire breakage, for example, it can be about 10 μm to 100 μm.

[0023] For example, if the resistor 30 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Furthermore, by making α-Cr the main component of the resistor 30, the gauge factor of strain gauge 1 can be set to 10 or higher, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means that the substance in question accounts for 50% by weight or more of the total substances constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 30 contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0024] Furthermore, if the resistor 30 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0025] Furthermore, the proportion of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the proportion of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0026] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, and a stable strain gauge can be obtained.

[0027] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrode 50. The wiring 40 has a first metal layer 41 and a second metal layer 42 laminated on the upper surface of the first metal layer 41. The wiring 40 is not limited to a straight line and can be in any pattern. Also, the wiring 40 can have any width and any length. For convenience, in Figure 1, the wiring 40, electrode 50, and wiring 60 are shown with a matte finish that is thinner than the resistor 30.

[0028] The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40. For example, they are wider than the wiring 40 and are formed in a roughly rectangular shape. The electrodes 50 are a pair of electrodes for outputting the change in the resistance value of the resistor 30 caused by strain to the outside, and for example, lead wires for external connection are attached to them.

[0029] The electrode 50 has a pair of first metal layers 51 and a second metal layer 52 laminated on the upper surface of each first metal layer 51. The first metal layers 51 are electrically connected to the terminals 30e1 and 30e2 of the resistor 30 via the first metal layers 41 of the wiring 40. The first metal layers 51 are formed in a substantially rectangular shape in plan view. The first metal layers 51 may be formed to the same width as the wiring 40.

[0030] The wiring 60 is a dummy wire formed on the base material 10, with one end connected to one of the folded portions 35 of the resistor 30 and the other end open. In the example in Figure 1, the wiring 60 includes a circular portion in plan view on the other end, but is not limited to this, and may include any shape such as an ellipse or rectangle on the other end. Alternatively, the wiring 60 may have the same width from one end to the other.

[0031] The strain gauge 1 only needs to have one or more wires 60, but in the example in Figure 1, it has multiple wires 60 (specifically six). As shown in Figure 1, the multiple wires 60 may include wires 60 arranged on both sides of the resistor 30 in the direction of the AA line. Also, as shown in Figure 1, the multiple wires 60 may include two or more wires 60 arranged along a direction perpendicular to the AA line.

[0032] Furthermore, the strain gauge 1 may have one wire 60 at each folded portion 35. Each wire 60 is spaced apart and not connected to others. There are no particular restrictions on the area of ​​the wire 60, and it can be appropriately selected depending on the purpose, but for example, 0.07 mm². 2 The above is possible. A larger total area of ​​the wiring 60 is preferable in that it increases the rigidity of the strain gauge 1. The wiring 60 has a first metal layer 61 made of the same material as the resistor 30 and extending from the folded portion 35, and a second metal layer 62 laminated on the upper surface of the first metal layer 61.

[0033] Note that the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 are given different reference numerals for convenience, but they may be formed from the same material. In that case, the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 can be formed integrally from the same material in the same process. Therefore, the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 have approximately the same thickness.

[0034] Furthermore, although the second metal layer 42, the second metal layer 52, and the second metal layer 62 are given different reference numerals for convenience, they may be formed from the same material. In that case, the second metal layer 42, the second metal layer 52, and the second metal layer 62 can be formed integrally from the same material in the same process. Therefore, the second metal layer 42, the second metal layer 52, and the second metal layer 62 have approximately the same thickness.

[0035] The second metal layers 42, 52, and 62 are formed from a material with lower resistance than the resistor 30 (first metal layers 41, 51, and 61). The material of the second metal layers 42, 52, and 62 is not particularly limited as long as it has lower resistance than the resistor 30, and can be appropriately selected according to the purpose. For example, if the resistor 30 is a Cr multiphase film, the material of the second metal layers 42, 52, and 62 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately stacked. The thickness of the second metal layers 42, 52, and 62 is not particularly limited and can be appropriately selected according to the purpose, but for example it can be about 3 μm to 5 μm.

[0036] The second metal layers 42, 52, and 62 may be formed on a portion of the upper surface of the first metal layers 41, 51, and 61, or on the entire upper surface of the first metal layers 41, 51, and 61. One or more additional metal layers may be laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be a copper layer, and a gold layer may be laminated on top of the copper layer. Alternatively, the second metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on top of the copper layer. By making the uppermost layer of the electrode 50 a gold layer, the solder wettability of the electrode 50 can be improved.

[0037] Thus, the wiring 40 has a structure in which a second metal layer 42 is laminated on a first metal layer 41 made of the same material as the resistor 30. Therefore, since the wiring 40 has lower resistance than the resistor 30, it is possible to suppress the wiring 40 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

[0038] In other words, by providing wiring 40 with lower resistance than the resistor 30, the effective sensitive area of ​​the strain gauge 1 can be limited to the local region where the resistor 30 is formed. Therefore, the accuracy of strain detection by the resistor 30 can be improved.

[0039] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 30, reducing the resistance of the wiring 40 to that of the resistor 30 and limiting the effective sensing area to the local region where the resistor 30 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 40 to that of the resistor 30 also has the effect of reducing lateral sensitivity.

[0040] Furthermore, by providing wiring 60 connected to the folded portion 35 of the resistor 30, the rigidity of the strain gauge 1 is increased, thereby reducing the displacement of the resistor 30 and improving the creep characteristics. In other words, the amount of creep and creep recovery can be reduced in the strain gauge 1. The amount of creep and creep recovery are the amounts by which the amount of elastic deformation (strain) of the surface on which the resistor 30 is provided in the strain gauge 1 changes over time, and can be measured by processing the output of the pair of electrodes 50.

[0041] By reducing the amount of creep and creep recovery, strain gauge 1 can be used for weighing purposes. When strain gauge 1 is used for weighing purposes, it is necessary to satisfy the standards related to creep. Examples of standards related to creep include accuracy class C1 (hereinafter referred to as the C1 standard) based on OIML R60 and accuracy class C2 (hereinafter referred to as the C2 standard) based on OIML R60.

[0042] The C1 standard requires that the creep amount and creep recovery amount be ±0.0735% or less. The C2 standard requires that the creep amount and creep recovery amount be ±0.0368% or less. Note that when strain gauge 1 is used for sensor applications, the creep amount and creep recovery amount specifications are approximately ±0.5%.

[0043] The cover layer 70 (insulating resin layer) is formed on the substrate 10 and covers the resistor 30, wiring 40, and wiring 60, while exposing the electrode 50. The cover layer 70 has an opening 70x, and the electrode 50 is exposed within the opening 70x. Part of the electrode 50 may be covered by the cover layer 70. Also, part of the wiring 40 may be exposed from the cover layer 70. By providing the cover layer 70 that covers the resistor 30, wiring 40, and wiring 60, mechanical damage to the resistor 30, wiring 40, and wiring 60 can be prevented. In addition, by providing the cover layer 70, the resistor 30, wiring 40, and wiring 60 can be protected from moisture, etc. Note that the cover layer 70 may be provided to cover the entire portion excluding the electrode 50.

[0044] The cover layer 70 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, polyolefin resin). The cover layer 70 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 70, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0045] To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 10. Metal layer A is the layer that will ultimately be patterned to become the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61.

[0046] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0047] From the viewpoint of stabilizing gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as an underlayer on the upper surface 10a of the substrate 10, for example, by conventional sputtering, before depositing the metal layer A.

[0048] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 30). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen and moisture contained in the substrate 10, and the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer may further have other functions.

[0049] Since the insulating resin film that makes up the base material 10 contains oxygen and moisture, and especially when the metal layer A contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer A.

[0050] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of at least the upper metal layer A (resistor 30), and can be appropriately selected according to the purpose. For example, 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 (bismodium) Examples include one or more metals selected from the group consisting of (S), 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 these metals, or a compound of any of these metals.

[0051] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0052] When the functional layer is formed from a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor can flow into the functional layer, preventing a decrease in strain detection sensitivity.

[0053] When the functional layer is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer, further preventing a decrease in strain detection sensitivity.

[0054] When the functional layer is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to some of the current flowing through the resistor flowing into the functional layer.

[0055] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be easily formed without cracking.

[0056] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracking.

[0057] When the functional layer is formed from an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer.

[0058] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 1. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is formed from an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed as a solid block in at least the region where the resistor is formed. Alternatively, the functional layer may be formed as a solid block over the entire upper surface of the substrate 10.

[0059] Furthermore, when the functional layer is formed from an insulating material, forming the functional layer relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer, allowing the heat generated when the resistor is heated to be dissipated towards the substrate 10. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 1.

[0060] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 10a of the substrate 10 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0061] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 10a of the substrate 10 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

[0062] There are no particular restrictions on the combination of materials for the functional layer and the metal layer A, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer A.

[0063] In this case, for example, metal layer A can be formed by targeting a raw material capable of forming a Cr multiphase film and using a magnetron sputtering method with Ar gas introduced into the chamber. Alternatively, metal layer A may be formed by targeting pure Cr and using a reactive sputtering method with an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0064] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of strain gauge 1 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that when the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0065] Furthermore, when metal layer A is a Cr multiphase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A by oxygen and moisture contained in the substrate 10, and improving adhesion between the substrate 10 and metal layer A. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0066] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A can improve the gauge characteristics in the strain gauge 1.

[0067] Next, a second metal layer 42, a second metal layer 52, and a second metal layer 62 are formed on the upper surface of metal layer A. The second metal layer 42, the second metal layer 52, and the second metal layer 62 can be formed, for example, by photolithography.

[0068] Specifically, first, a seed layer is formed to cover the upper surface of metal layer A, for example, by sputtering or electroless plating. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and exposure and development are performed to create openings that expose the areas for forming the second metal layer 42, the second metal layer 52, and the second metal layer 62. At this time, by adjusting the shape of the openings in the resist, the second metal layer 42, the second metal layer 52, and the second metal layer 62 can be made into any shape. For example, a dry film resist can be used as the resist.

[0069] Next, for example, a second metal layer 42, a second metal layer 52, and a second metal layer 62 are formed on the seed layer exposed within the opening by an electroplating method using the seed layer as the power supply path. The electroplating method is preferable because it has a high cycle time and can form low-stress electroplated layers as the second metal layer 42, the second metal layer 52, and the second metal layer 62. By making the thick electroplated layers low-stress, warping of the strain gauge 1 can be prevented. The second metal layer 42, the second metal layer 52, and the second metal layer 62 may also be formed by an electroless plating method.

[0070] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0071] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, exposed and developed to pattern it into a planar shape similar to the resistor 30, wiring 40, electrode 50, and wiring 60 in Figure 1. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and seed layer exposed from the resist, forming the resistor 30, wiring 40, electrode 50, and wiring 60 in the planar shape of Figure 1.

[0072] For example, unwanted portions of metal layer A and seed layer can be removed by wet etching. If a functional layer is formed beneath metal layer A, etching will pattern the functional layer into the planar shape shown in Figure 1, similar to the resistor 30, wiring 40, electrode 50, and wiring 60. At this point, seed layers are formed on the resistor 30, first metal layer 41, first metal layer 51, and first metal layer 61.

[0073] Next, the second metal layers 42, 52, and 62 are used as etching masks, and the unwanted seed layers exposed from the second metal layers 42, 52, and 62 are removed to form the second metal layers 42, 52, and 62. Note that the seed layers directly beneath the second metal layers 42, 52, and 62 remain. For example, the unwanted seed layers can be removed by wet etching using an etching solution that etches the seed layers but not the functional layers, resistors 30, wiring 40, electrodes 50, and wiring 60.

[0074] Subsequently, if necessary, a cover layer 70 is provided on the upper surface 10a of the base material 10 to cover the resistor 30, wiring 40, and wiring 60 and expose the electrode 50, thereby completing the strain gauge 1. The cover layer 70 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the base material 10 to cover the resistor 30, wiring 40, and wiring 60 and expose the electrode 50, and then heating and curing it. Alternatively, the cover layer 70 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the base material 10 to cover the resistor 30, wiring 40, and wiring 60 and expose the electrode 50, and then heating and curing it. The opening 70x can be formed, for example, by photolithography.

[0075] Furthermore, when a functional layer is provided on the upper surface 10a of the substrate 10 as a base layer for the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61, the strain gauge 1 will have the cross-sectional shape shown in Figure 4. The layer indicated by reference numeral 20 is the functional layer. The planar shape of the strain gauge 1 when the functional layer 20 is provided will be the same as, for example, as shown in Figure 1. However, as mentioned above, the functional layer 20 may also be formed as a solid layer on part or all of the upper surface 10a of the substrate 10.

[0076] <Variation 1 of the First Embodiment> Modification 1 of the first embodiment shows an example in which a metal with a lower melting point than the second metal layer 62 is laminated on the wiring 60. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0077] Figure 5 is a plan view illustrating a strain gauge according to Modification 1 of the First Embodiment. Figure 6 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the First Embodiment, showing a cross-section along line CC in Figure 5. Referring to Figures 5 and 6, strain gauge 1A differs from strain gauge 1 (see Figures 1 to 3, etc.) in that a metal 80 with a lower melting point than the second metal layer 62 is added on the wiring 60.

[0078] In strain gauge 1A, the cover layer 70 has an opening 70y that exposes at least a portion of the wiring 60. A metal 80 with a lower melting point than the second metal layer 62 is laminated on the second metal layer 62 of the wiring 60 exposed within the opening 70y. The metal 80 is, for example, solder or metal paste.

[0079] In this way, by laminating a metal 80 with a lower melting point than the second metal layer 62 on the wiring 60, the rigidity of strain gauge 1A can be made even higher than that of strain gauge 1. As a result, the creep characteristics of strain gauge 1A can be further improved compared to strain gauge 1.

[0080] Furthermore, considering the thermal damage to the resistor 30, it is preferable to select lead-free solder or metal paste as the material for the metal 80. High-temperature solder and high-melting-point solder are not preferred.

[0081] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows an example in which a third metal layer is arranged around the resistor 30. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0082] Figure 7 is a plan view illustrating a strain gauge according to a modified example 2 of the first embodiment. Referring to Figure 7, strain gauge 1B differs from strain gauge 1 (see Figures 1 to 3, etc.) in that it has a third metal layer 90 positioned around the resistor 30, spaced apart from the resistor 30 and the wiring 60.

[0083] The third metal layer 90 is made of the same material as the resistor 30. The third metal layer 90 can be formed in the same process as the resistor 30 and the first metal layer 41. It is preferable to place the third metal layer 90 in the surplus space around the resistor 30 so as large an area as possible. A metal layer made of the same material as the second metal layer 62 may be laminated on the third metal layer 90.

[0084] In this way, by arranging the third metal layer 90 around the resistor 30, the rigidity of the strain gauge 1B can be made even higher than that of the strain gauge 1. As a result, the creep characteristics of the strain gauge 1B can be further improved compared to those of the strain gauge 1. It should be noted that the modification 2 of the first embodiment can also be combined with the modification 1 of the first embodiment. In that case, the creep characteristics will be further improved.

[0085] <Modification 3 of the First Embodiment> Modification 3 of the first embodiment shows an example in which the arrangement of electrodes is changed. In Modification 3 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0086] Figure 8 is a plan view illustrating a strain gauge according to modification 3 of the first embodiment. Referring to Figure 8, strain gauge 1C differs from strain gauge 1 (see Figures 1 to 3, etc.) in that electrode 50 is replaced by electrode 50A. The laminated structure of electrode 50A is the same as that of electrode 50.

[0087] The pair of electrodes 50A are positioned on either side of the resistor 30, in the longitudinal direction (direction of line AA in Figure 1) of each elongated portion of the resistor 30. For example, the electrodes 50A have a width in the direction perpendicular to the longitudinal direction that is greater than the width in the longitudinal direction (direction of line AA in Figure 1) of each elongated portion of the resistor 30. It is preferable to arrange the electrodes 50A in the surplus space around the resistor 30 so as to cover as large an area as possible.

[0088] In this way, by arranging electrodes 50A on both sides of the resistor 30 in the longitudinal direction (direction of line AA in Figure 1) of each elongated part of the resistor 30, the rigidity of the strain gauge 1C can be made even higher than that of the strain gauge 1. As a result, the creep characteristics of the strain gauge 1C can be further improved compared to the strain gauge 1. Note that the modification 3 of the first embodiment can also be combined with the modification 1 and / or 2 of the first embodiment. In that case, the creep characteristics will be further improved.

[0089] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of Symbols]

[0090] 1,1A,1B,1C Strain gauges, 10 Substrate, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1,30e2 Termination, 35 Folded section, 40,60 Wiring, 41,51,61 First metal layer, 42,52,62 Second metal layer, 50,50A Electrode, 70 Cover layer, 70x,70y Opening, 80 Metal, 90 Third metal layer

Claims

1. Substrate and A resistor provided directly or indirectly on the substrate, Wiring connected to the end of the resistor, The resistor and the insulating resin layer covering the wiring are included. The insulating resin layer has an opening that exposes at least a portion of the wiring, The strain gauge comprises a wiring that includes a first metal layer formed of the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material with lower resistance than the first metal layer.

2. Substrate and A resistor provided directly or indirectly on the substrate, comprising a plurality of elongated portions arranged at predetermined intervals with their longitudinal directions in the same direction, and folded portions connecting adjacent elongated portions, The resistor has a wiring connected to the end of the elongated portion via the aforementioned folded portion, The strain gauge comprises a wiring that includes a first metal layer formed of the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material with lower resistance than the first metal layer.

3. The strain gauge according to any one of claims 1 or 2, wherein the resistor is formed from a material containing Cr, a material containing Ni, or a material containing at least one of Cr and Ni.

4. A strain gauge according to any one of claims 1 to 3, wherein one end of the wiring is connected to both ends of the resistor, and the other end of the wiring is left open.

5. The strain gauge according to claim 1, wherein a metal having a lower melting point than the second metal layer is laminated on the wiring exposed in the opening.

6. The resistor has a third metal layer positioned around it, spaced apart from the resistor and the wiring. The strain gauge according to any one of claims 1 to 5, wherein the third metal layer is formed of the same material as the resistor.

7. Having a pair of electrodes formed on the substrate and electrically connected to the resistor, The strain gauge according to any one of claims 1 to 6, wherein the electrodes are arranged on both sides in the grid direction with respect to the resistor.

8. The strain gauge according to claim 7, wherein the electrode has a width in the direction perpendicular to the grid direction that is greater than the width in the grid direction.

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