Strain gauges, sensor modules, and strain bodies

Abstract

To provide a strain gage that suppresses reduction of strain detection accuracy.SOLUTION: A strain gage comprises a base material, a resistive element formed on one side of the base material, and a plurality of recesses opening on the other side of the base material. The plurality of recesses includes a first recess and a second recess. When a virtual line segment connecting the center of gravity of the first recess and the center of gravity of the second recess is considered in plan view, the first recess and the second recess are arranged so that the virtual line segment crosses the longitudinal direction of the resistive element at an angle.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a strain gauge and a sensor module. , and a strain-generating body Regarding. [Background technology]

[0002] The strain gauge includes a resistor for detecting strain, and the resistor is made of a material containing, for example, Cr (chromium) or Ni (nickel). The resistor is formed on a base material made of, for example, insulating resin (see, for example, Patent Document 1).

[0003] Strain gauges are used by, for example, attaching them to a flexure body via an adhesive layer. When attaching a strain gauge to a flexure body, for example, first, tiny grooves that intersect vertically and horizontally are scribed at predetermined positions on the top surface of the flexure body to indicate the positions and directions for fixing the strain gauges. Then, an adhesive layer is formed on the top surface of the flexure body, and the strain gauges are attached so that they align with the tiny grooves scribed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-74934 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, there are cases where stress concentration occurs in the minute grooves formed by the marking, which can become a cause of error in strain detection and reduce the accuracy of strain detection.

[0006] The present invention has been made in consideration of the above-mentioned points, and has an object to provide a strain gauge in which a decrease in the detection accuracy of strain is suppressed. [Means for solving the problem]

[0007] This strain gauge has a substrate, a resistor formed on one surface of the substrate, and a plurality of recesses opening to the other surface of the substrate, the recesses including a first recess and a second recess, and the first recess and the second recess are arranged such that, when a virtual line segment connecting a center of gravity of the first recess and a center of gravity of the second recess is considered in a plan view, the virtual line segment intersects obliquely with a longitudinal direction of the resistor. The first recess and the second recess are disposed in a region that does not overlap with a region in which the resistor is formed in a plan view. is. Effect of the Invention

[0008] According to the disclosed technique, it is possible to provide a strain gauge in which deterioration of strain detection accuracy is suppressed. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Diagram 3] FIG. 2 is a perspective view illustrating a flexure body. [Figure 4] FIG. 4 is a cross-sectional view for explaining the positioning of a strain body and a strain gauge. [Diagram 5] FIG. 4 is a plan view illustrating the arrangement of recesses. [Figure 6] 4 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. FIG. [Figure 7] FIG. 2 is a cross-sectional view illustrating a functional layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations may be omitted.

[0011] First embodiment [Structure of strain gauge] Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, showing a cross section along the line AA in Fig. 1.

[0012] 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. For convenience, only the outer edge of the cover layer 60 is shown by a dashed line in Fig. 1 and Fig. 2. The cover layer 60 may be provided as necessary.

[0013] In this embodiment, for convenience, in the strain gauge 1, the side of the substrate 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. In addition, the surface on which the resistor 30 is provided in each part is referred to as one side or upper surface, and the surface on which the resistor 30 is not provided is referred to as the other side or lower surface. However, the strain gauge 1 can be used upside down or placed at any angle. In addition, the planar view refers to the object being viewed from the normal direction of the upper surface 10a of the substrate 10, and the planar shape refers to the shape of the object being viewed from the normal direction of the upper surface 10a of the substrate 10.

[0014] 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, and 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 joined to the lower surface 10b 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.

[0015] 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, LCP (liquid crystal polymer) resin, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0016] 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.

[0017] Examples of materials other than resin for the substrate 10 include SiO 2 , ZrO 2 (including YSZ), Si, Si 2 N 3 , Al 2 O 3 (including sapphire), ZnO, perovskite ceramics (CaTiO 3 , BaTiO 3 ) and other crystalline materials, and furthermore, amorphous glass and the like can be used. Metals such as aluminum, aluminum alloys (duralumin), and titanium can also be used as the material for the base material 10. In this case, for example, an insulating film is formed on the metal base material 10.

[0018] 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 strained. 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 dark matte pattern.

[0019] The resistor 30 has a structure in which multiple elongated portions are arranged at regular intervals with their longitudinal direction in the same direction (the long side direction of the substrate 10 in FIG. 1), and the ends of adjacent elongated portions are alternately connected, folding back in a zigzag pattern as a whole. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the short side direction of the substrate 10 in FIG. 1).

[0020] One end of the two elongated portions located on the outermost sides in the grid width direction in the longitudinal direction is bent in the grid width direction, and each end 30e of the resistor 30 in the grid width direction is 1 and 30e 2 Each end 30e of the resistor 30 in the grid width direction is formed. 1 and 30e 2 are electrically connected to the electrodes 50 via the wiring 40. In other words, the wiring 40 is 1 and 30e 2 and each of the electrodes 50 are electrically connected.

[0021] The resistor 30 can be made of, 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 made of 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 Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0022] Here, the Cr mixed phase film is composed of Cr, CrN, Cr 2 It is a film containing a mixed phase of N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0023] The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 0.05 μm to 2 μm. In particular, it is preferable that the thickness of the resistor 30 is 0.1 μm or more in order to improve the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr). It is further preferable that the thickness of the resistor 30 is 1 μm or less in order to reduce cracks in the film and warping from the substrate 10 caused by the internal stress of the film constituting the resistor 30. The width of the resistor 30 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be, for example, about 10 μm to 100 μm in consideration of measures against disconnection.

[0024] For example, when the resistor 30 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha chromium) which is a stable crystal phase the main component. Furthermore, by making the resistor 30 mainly of α-Cr, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / °C to +1000 ppm / °C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, the resistor 30 preferably contains 80% by weight or more of α-Cr, and more preferably contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0025] In addition, when the resistor 30 is a Cr mixed phase film, CrN and Cr contained in the Cr mixed phase film 2 The N content is preferably 20% by weight or less. 2 By controlling the N content to 20% by weight or less, the decrease in the gauge factor can be suppressed.

[0026] In addition, CrN and Cr 2 Cr in N 2 The proportion of N 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. 2 Cr in N 2The N ratio is 90% by weight or more and less than 95% by weight, so Cr has semiconducting properties. 2 The decrease in TCR (negative TCR) becomes more pronounced due to the addition of N. Furthermore, the reduction in ceramic formation reduces brittle fracture.

[0027] On the other hand, trace amounts of N 2 Or, if atomic N is mixed in or present, it will escape from the film due to the external environment (for example, a high temperature environment), causing a change in film stress.By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

[0028] The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrodes 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 have any pattern. The wiring 40 can have any width and any length. For convenience, the wiring 40 and the electrodes 50 are shown in FIG. 1 with a matte finish that is thinner than the resistor 30.

[0029] The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40, and are formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting to the outside a change in the resistance value of the resistor 30 caused by strain, and for example, a lead wire for external connection is joined to the electrodes 50.

[0030] The electrode 50 has a pair of first metal layers 51 and a second metal layer 52 laminated on the upper surface of each of the first metal layers 51. The first metal layer 51 is connected to the end 30e of the resistor 30 via the first metal layer 41 of the wiring 40. 1 and 30e 2 The first metal layer 51 is electrically connected to the wiring 40. The first metal layer 51 is formed in a substantially rectangular shape in a plan view. The first metal layer 51 may be formed to have the same width as the wiring 40.

[0031] Although the resistor 30, the first metal layer 41, and the first metal layer 51 are given different reference numbers for convenience, they can be integrally formed in the same process using the same material. Therefore, the resistor 30, the first metal layer 41, and the first metal layer 51 have approximately the same thickness. Moreover, although the second metal layer 42 and the second metal layer 52 are given different reference numbers for convenience, they can be integrally formed in the same process using the same material. Therefore, the second metal layer 42 and the second metal layer 52 have approximately the same thickness.

[0032] The second metal layers 42 and 52 are formed of a material having a lower resistance than the resistor 30 (the first metal layers 41 and 51). The material of the second metal layers 42 and 52 is not particularly limited as long as it is a material having a lower resistance than the resistor 30, and can be appropriately selected according to the purpose. For example, when the resistor 30 is a Cr mixed phase film, the material of the second metal layers 42 and 52 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, and compounds are appropriately laminated. The thickness of the second metal layers 42 and 52 is not particularly limited and can be appropriately selected according to the purpose, and can be, for example, about 3 μm to 5 μm.

[0033] The second metal layers 42 and 52 may be formed on a part of the upper surface of the first metal layers 41 and 51, or may be formed on the entire upper surface of the first metal layers 41 and 51. One or more other 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 the upper surface 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 the upper surface of the copper layer. By forming the top layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 can be improved.

[0034] In this way, the wiring 40 has a structure in which the second metal layer 42 is laminated on the first metal layer 41 made of the same material as the resistor 30. Therefore, the resistance of the wiring 40 is lower than that of the resistor 30, and it is possible to prevent the wiring 40 from functioning as a resistor. As a result, it is possible to improve the accuracy of strain detection by the resistor 30.

[0035] In other words, by providing the wiring 40 having a lower resistance than the resistor 30, the actual sensing portion 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.

[0036] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed phase film as the resistor 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensing part to the local region where the resistor 30 is formed has a significant effect on improving the strain detection accuracy. Making the wiring 40 lower in resistance than the resistor 30 also has the effect of reducing the lateral sensitivity.

[0037] The cover layer 60 is formed on the substrate 10, covers the resistor 30 and the wiring 40, and exposes the electrodes 50. A part of the wiring 40 may be exposed from the cover layer 60. By providing the cover layer 60 that covers the resistor 30 and the wiring 40, it is possible to prevent mechanical damage, etc. from occurring to the resistor 30 and the wiring 40. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 and the wiring 40 from moisture, etc. The cover layer 60 may be provided so as to cover the entire portion except for the electrodes 50.

[0038] 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, polyolefin resin). The cover layer 60 may contain a filler or a pigment. There is no particular limit to 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.

[0039] [Structure for positioning strain gauge and strain body] The strain gauge 1 has a first recess 15 and a second recess 16 that open to the lower surface 10b side of the substrate 10. The first recess 15 and the second recess 16 are recesses that are recessed from the lower surface 10b of the substrate 10 toward the upper surface 10a side. The first recess 15 and the second recess 16 can be formed, for example, by etching the substrate 10 from the lower surface 10b side. Since the first recess 15 and the second recess 16 do not penetrate the substrate 10, it is necessary to adjust the etching depth when etching the substrate 10.

[0040] The strain gauge 1 is used by being attached to the flexure body via, for example, an adhesive layer. The adhesive layer is not particularly limited as long as it is a material that has the function of fixing the strain gauge 1 to the flexure body and can be appropriately selected depending on the purpose, and for example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used. Also, materials such as a bonding sheet can be used. The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, about 0.1 μm to 50 μm.

[0041] The shape of the flexure body is arbitrary, but an example is shown in Fig. 3. The flexure body 100 shown in Fig. 3 is a rectangular plate-like body with an upper surface 100a and a lower surface 100b. The upper surface 100a and the lower surface 100b are flat surfaces. The flexure body 100 has a first convex portion 150 and a second convex portion 160 protruding from the upper surface 100a.

[0042] In a plan view, the positions of the first convex portion 150 and the second convex portion 160 of the flexure body 100 correspond to the positions of the first concave portion 15 and the second concave portion 16 of the strain gauge 1. Moreover, the first convex portion 150 and the second convex portion 160 of the flexure body 100 are sized to be able to fit into the first concave portion 15 and the second concave portion 16 of the strain gauge 1.

[0043] 4, the first convex portion 150 fits into the first concave portion 15, and the second convex portion 160 fits into the second concave portion 16. This makes it possible to realize a sensor module 5 having the strain gauge 1 and the strain body 100 having the strain gauge 1 attached to the upper surface 100a side.

[0044] In this way, by configuring the first convex portion 150 and the second convex portion 160 of the flexure body 100 so as to be able to fit into the first concave portion 15 and the second concave portion 16 of the strain gauge 1, the strain gauge 1 can be easily positioned on the upper surface 100a of the flexure body 100. Also, marking work for positioning the strain gauge 1 on the flexure body 100 is no longer necessary, and stress concentration caused by marking can be avoided. Therefore, error factors are eliminated, deterioration of strain detection accuracy can be suppressed, and accurate strain detection by the strain gauge 1 becomes possible.

[0045] The planar shape of the first recess 15 and the second recess 16 is, for example, rectangular, but may be any shape such as circular, elliptical, or polygonal other than rectangular. When the planar shape of the first recess 15 and the second recess 16 is rectangular, for example, in a plan view, two opposing sides of the first recess 15 and the second recess 16 are parallel to the grid direction, and the other two opposing sides are perpendicular to the grid direction. When the planar shape of the first recess 15 and the second recess 16 is rectangular, the size of the first recess 15 and the second recess 16 can be, for example, 500 to 1000 μm in length × 500 to 1000 μm in width × 10 to 100 μm in depth. Here, the length is the grid direction, the width is the grid width direction, and the depth is the thickness direction of the substrate 10. The upper limit value of the size of the first recess 15 and the second recess 16 is determined by the size of the strain gauge 1, and may be large enough not to overlap the area where the resistor 30 is formed in a plan view. Moreover, the upper limit of the depth of the first recess 15 and the second recess 16 is naturally within a range in which the recess does not penetrate through the base material 10 .

[0046] 5, when considering an imaginary line segment L1 connecting the center of gravity of the first recess 15 and the center of gravity of the second recess 16 in a plan view, it is preferable that the first recess 15 and the second recess 16 are arranged so that the imaginary line segment L1 diagonally intersects with the longitudinal direction of the resistor 30. By arranging the first recess 15 and the second recess 16 in this way, it is possible to effectively suppress positional deviation of the strain gauge 1 in the rotational direction, and it becomes easy to position the strain gauge 1 at a correct position on the upper surface 100a of the strain gauge 100 in both the grid direction and the grid width direction.

[0047] Moreover, it is preferable that the first recess 15 and the second recess 16 are disposed in a region that does not overlap in a plan view with the region in which the resistor 30 is formed. This makes it possible to prevent the presence of the first recess 15 and the second recess 16 from affecting strain detection.

[0048] Furthermore, the first recess 15 and the second recess 16 are disposed outside both ends of the resistor 30 in the grid direction and are disposed between both ends (terminations 30e 1 and 30e 2 5. That is, the first recess 15 and the second recess 16 are preferably arranged outside the area E1 and E2 in Fig. 5. Alternatively, the first recess 15 and the second recess 16 may be arranged in the areas E3 and E4 in Fig. 5. This makes it possible to prevent the presence of the first recess 15 and the second recess 16 from affecting strain detection, and also makes it possible to increase the distance between the first recess 15 and the second recess 16. Therefore, the positioning accuracy of the strain gauge 1 with respect to the strain generating body 100 can be improved.

[0049] For example, if the planar shape of the substrate 10 is rectangular, the first recess 15 and the second recess 16 can be disposed at positions that pass through the diagonal line of the rectangle. In this case, the first recess 15 and the second recess 16 are also disposed outside both ends of the resistor 30 in the grid direction and are located between both ends (terminals 30e 1 and 30e 2 ) is preferably arranged outside.

[0050] In addition to the first recess 15 and the second recess 16, other recesses may be provided. That is, the strain gauge 1 may have three or more recesses used for positioning with the flexure body 100. In this case, the flexure body 100 is also provided with protrusions in a number corresponding to the number of recesses of the strain gauge 1, at positions where the recesses of the strain gauge 1 can be fitted into them.

[0051] Fig. 6 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the first embodiment, and shows a cross section corresponding to Fig. 2. As in the strain gauge 1A shown in Fig. 6, a base layer 70 may be formed on the lower surface 10b side of the substrate 10, and a first recess 75 and a second recess 76 may be provided in the base layer 70. The first recess 75 and the second recess 76 are formed by the inner side surface of a through hole penetrating the base layer 70 and the lower surface 10b of the substrate 10 exposed in the through hole of the base layer 70.

[0052] The first recess 75 and the second recess 76 are formed at the same positions as the first recess 15 and the second recess 16 in a plan view, and have the same shapes as the first recess 15 and the second recess 16. Therefore, the first recess 75 and the second recess 76 can be fitted with the first convex portion 150 and the second convex portion 160 of the strain body 100, similar to the first recess 15 and the second recess 16 shown in Fig. 4. In other words, the strain gauge 1A can be easily positioned on the upper surface 100a of the strain body 100.

[0053] The first recess 75 and the second recess 76 can be formed, for example, by forming through-holes penetrating the base layer 70 by etching, and attaching the base layer 70 with the through-holes formed therein to the lower surface 10b of the substrate 10 via an adhesive layer. With this method, when etching the base layer 70 to form the through-holes, adjustment of the etching depth as with the first recess 15 and the second recess 16 is not required, improving processability.

[0054] The underlayer 70 can be formed using any material, but may have a specific function selected from the materials as described below. The underlayer 70 may also have a multi-layer structure.

[0055] For example, the underlayer 70 may be a barrier layer that improves the weather resistance of the substrate 10 and the resistor 30. The barrier layer is, for example, a moisture-proof layer made of a material less permeable to moisture than the substrate 10, or a layer that is resistant to temperature changes. For example, when the substrate 10 is polyimide, the barrier layer can be made of a fluororesin, an epoxy resin, or an acrylic resin. Alternatively, a hybrid resin that combines these resins may be used.

[0056] The underlayer 70 may be a conductive layer formed of a material having a higher electrical conductivity than the substrate 10. The conductive layer may be formed of, for example, a metal, an alloy, or a laminated film in which metals and / or alloys are laminated. More specifically, examples of the material for the conductive layer include Cu, Ni, Al, Ag, Au, Pt, Pd, Sn, Cr, and the like, an alloy of any of these metals, or a laminated film in which any of these metals or alloys are appropriately laminated. The material for the conductive layer may be the same as that of the resistor 30 (for example, a Cr mixed phase film).

[0057] Alternatively, as the material for the conductive layer, an oxide film such as tin-doped indium oxide (ITO), fluorine-doped tin oxide (FTO), or antimony-doped tin oxide (ATO), or a resin film containing a conductive filler may be used as long as the material is conductive.

[0058] By forming the base layer 70 as a conductive layer, it is possible to reduce noise superimposed on the resistor. By forming a conductive layer on the lower surface 10b of the substrate 10 to reduce noise superimposed on the resistor, it is possible to suppress a decrease in the measurement accuracy of the strain gauge 1A. Furthermore, when the base layer 70 is made of a metal, the base layer 70 can also function as a barrier layer that improves the weather resistance of the substrate 10 and the resistor 30.

[0059] By forming a conductive layer on the lower surface 10b of the substrate 10, for example, in measurements in environments where noise such as static electricity is likely to occur (e.g., low humidity), effects such as reduced variation in the TCR value and the output voltage when strain is applied can be obtained. In particular, highly sensitive strain gauges using Cr mixed phase film and having a gauge factor of 10 or more are susceptible to the effects of static electricity generated from a measurement target such as a motor due to their high sensitivity, and the accumulation of static electricity in the substrate 10 is likely to cause measurement errors and variations in the output voltage. Therefore, the effect of forming a conductive layer is particularly remarkable in highly sensitive strain gauges using Cr mixed phase film and having a gauge factor of 10 or more.

[0060] It is preferable that the conductive layer is electrically connected to a reference potential (GND). Alternatively, when attaching the strain gauge 1A to the flexure body 100, the conductive layer may be set to the same potential as the flexure body 100. Either case is advantageous for reducing noise. For example, the strain gauge 1A may be attached to the metallic flexure body 100 via a conductive adhesive. This is advantageous for reducing noise because the conductive layer of the strain gauge 1A is electrically connected to the flexure body 100 via the conductive adhesive.

[0061] [Strain gauge manufacturing method] 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 an upper surface 10a of the base material 10. Metal layer A is a layer that is finally patterned to become resistor 30, first metal layer 41, and first metal layer 51. Therefore, the material and thickness of metal layer A are similar to the material and thickness of resistor 30, first metal layer 41, and first metal layer 51 described above.

[0062] The metal layer A can be formed by, for example, a magnetron sputtering method using a target made of a raw material capable of forming the metal layer A. The metal layer A may be formed by a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulsed laser deposition method, or the like instead of the magnetron sputtering method.

[0063] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the base material 10 by, for example, conventional sputtering, before depositing the metal layer A.

[0064] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 30). The functional layer preferably further has a function of preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and a function of improving adhesion between the base material 10 and the metal layer A. The functional layer may further have other functions.

[0065] 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 metal layer A, particularly when the metal layer A contains Cr, since Cr forms a self-oxidized film.

[0066] The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper layer, the metal layer A (resistor 30), and can be appropriately selected depending on 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 (bismuth), and the like can be used. Examples of the metal include one or more metals selected from the group consisting of ruthenium (Ru), 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.

[0067] Examples of the alloy include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compound include TiN, TaN, and Si 3 N 4 , TiO 2 , Ta 2 O 5 , SiO 2 etc.

[0068] When the functional layer is made of 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. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which reduces the detection sensitivity of strain.

[0069] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and the strain detection sensitivity can be further prevented from being reduced due to a part of the current flowing through the resistor flowing through the functional layer.

[0070] When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is more preferably 1 / 100 or less of the thickness of the resistor, which can further prevent a part of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

[0071] When the functional layer is made of an insulating material such as an oxide or a nitride, the thickness of the functional layer is preferably 1 nm to 1 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0072] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 0.8 μm, which can promote the crystal growth of α-Cr and can be easily formed without cracking the functional layer.

[0073] When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.5 μm, which can promote the crystal growth of α-Cr and can be more easily formed without cracking the functional layer.

[0074] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in FIG. 1, for example. 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 made of an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the region where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape on the entire upper surface of the substrate 10.

[0075] Furthermore, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, so that the thickness and surface area of ​​the functional layer are increased, and the heat generated by the resistor can be dissipated to the substrate 10. As a result, the deterioration of the measurement accuracy of the strain gauge 1 due to self-heating of the resistor can be suppressed.

[0076] The functional layer can be formed in vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target 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, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

[0077] 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 a 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.

[0078] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A and 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 with α-Cr (alpha chromium) as the main component for the metal layer A.

[0079] In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into the chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into the chamber. In this case, the CrN and Cr contained in the Cr mixed phase film can be formed by changing the amount and pressure of the nitrogen gas introduced (nitrogen partial pressure) or by adjusting the heating temperature by providing a heating process. 2 The proportion of N, CrN and Cr 2 Cr in N 2 The ratio of N can be adjusted.

[0080] In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film containing α-Cr, which has a stable crystal structure, as a main component, can be formed. Furthermore, the Ti constituting the functional layer is diffused into the Cr mixed-phase film, thereby improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

[0081] When the metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting the crystal growth of the metal layer A, preventing oxidation of the metal layer A due to oxygen and moisture contained in the base material 10, and improving the adhesion between the base material 10 and the metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0082] In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystal phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

[0083] Next, the second metal layer 42 and the second metal layer 52 are formed on the upper surface of the metal layer A. The second metal layer 42 and the second metal layer 52 can be formed by, for example, a photolithography method.

[0084] Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of the metal layer A. Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to form openings that expose the regions in which the second metal layer 42 and the second metal layer 52 are to be formed. At this time, the pattern of the second metal layer 42 can be formed into any shape by adjusting the shape of the openings in the resist. For example, a dry film resist can be used as the resist.

[0085] Next, for example, the second metal layer 42 and the second metal layer 52 are formed on the seed layer exposed in the opening by electrolytic plating using the seed layer as a power supply path. The electrolytic plating method is preferable in that it has high tact and can form low-stress electrolytic plating layers as the second metal layer 42 and the second metal layer 52. By making the electrolytic plating layer thick and low-stress, it is possible to prevent warping of the strain gauge 1. The second metal layer 42 and the second metal layer 52 may be formed by electroless plating.

[0086] Next, the resist is removed. For example, the resist can be removed by immersing the resist in a solution that can dissolve the resist material.

[0087] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to be patterned into a planar shape similar to that of the resistor 30, the wiring 40, and the electrode 50 in Fig. 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 the seed layer exposed from the resist, thereby forming the resistor 30, the wiring 40, and the electrode 50 in the planar shape of Fig. 1.

[0088] For example, unnecessary portions of the metal layer A and the seed layer can be removed by wet etching. If a functional layer is formed below the metal layer A, the functional layer is patterned by etching into the planar shape shown in Fig. 1, similar to the resistor 30, the wiring 40, and the electrode 50. At this point, a seed layer is formed on the resistor 30, the first metal layer 41, and the first metal layer 51.

[0089] Next, the second metal layer 42 and the second metal layer 52 are used as an etching mask to remove unnecessary seed layer exposed from the second metal layer 42 and the second metal layer 52, thereby forming the second metal layer 42 and the second metal layer 52. Note that the seed layer directly below the second metal layer 42 and the second metal layer 52 remains. For example, the unnecessary seed layer can be removed by wet etching using an etching solution that etches the seed layer but does not etch the functional layer, the resistor 30, the wiring 40, and the electrodes 50.

[0090] Next, the base material 10 is etched from the lower surface 10b side to form the first recess 15 and the second recess 16. Alternatively, a base layer 70 made of resin, metal, or the like is prepared, and through holes penetrating the base layer 70 are formed by etching. Then, the base layer 70 with the through holes formed therein is attached to the lower surface 10b of the base material 10 via an adhesive layer. When forming the through holes in the base layer 70, a press processing method, a laser processing method, or the like may be used. The first recess 15 and the second recess 16 may be formed in the base material 10 at any other timing.

[0091] Thereafter, as necessary, a cover layer 60 that covers the resistor 30 and the wiring 40 and exposes the electrodes 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. 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 the wiring 40 and expose the electrodes 50, 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 the wiring 40 and expose the electrodes 50, and then heating and curing the resin.

[0092] When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the resistor 30, the first metal layer 41, and the first metal layer 51, the strain gauge 1 has a cross-sectional shape as shown in Fig. 7. The layer indicated by reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is, for example, the same as that shown in Fig. 1. However, as described above, the functional layer 20 may be formed solidly on a part or all of the upper surface 10a of the substrate 10.

[0093] Although preferred embodiments have been described above in detail, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims. [Explanation of symbols]

[0094] 1, 1A strain gauge, 5 sensor module, 10 substrate, 10a upper surface, 10b lower surface, 15, 75 first recess, 16, 76 second recess, 20 functional layer, 30 resistor, 30e 1 ,30e 2 Termination, 40 wiring, 41, 51 first metal layer, 42, 52 second metal layer, 50 electrode, 60 cover layer, 70 underlayer, 100 strain body, 100a upper surface, 100b lower surface, 150 first convex portion, 160 second convex portion

Claims

1. A substrate; A resistor formed on one surface of the substrate; A plurality of recesses opening to the other surface side of the base material, The plurality of recesses include a first recess and a second recess, the first recess and the second recess are arranged such that, when a virtual line segment connecting a center of gravity of the first recess and a center of gravity of the second recess is considered in a plan view, the virtual line segment obliquely intersects with a longitudinal direction of the resistor; The strain gauge, wherein the first recess and the second recess are disposed in an area that does not overlap an area in which the resistor is formed in a plan view.

2. 2. The strain gauge according to claim 1, wherein the first recess and the second recess are disposed outward from both ends of the resistor in the grid direction and outward from both ends of the resistor in the grid width direction.

3. The planar shape of the substrate is rectangular, The strain gauge according to claim 1 , wherein the first recess and the second recess are disposed at positions passing through a diagonal line of the rectangle.

4. A base layer is formed on the other surface side of the base material, A plurality of through holes are provided through the underlayer, The strain gauge according to claim 1 , wherein the first recess and the second recess are formed by an inner surface of the through hole and another surface of the substrate exposed in the through hole.

5. The strain gauge according to claim 4 , wherein the underlayer is a barrier layer that improves weather resistance of the substrate and the resistor.

6. The strain gauge according to claim 4 or 5, wherein the underlayer is a conductive layer made of a material having a higher electrical conductivity than the base material.

7. The resistor is made of Cr, CrN, and Cr. ２ The strain gauge according to claim 1 , which is formed from a film containing N.

8. A strain gauge, a strain generating body having a first surface and a second surface, the strain gauge being attached to the first surface side; The strain body has a plurality of protrusions protruding from the first surface, The plurality of protruding portions include a first protruding portion and a second protruding portion, The strain gauge comprises: A substrate; A resistor formed on one surface of the substrate; A plurality of recesses opening to the other surface side of the base material, The plurality of recesses include a first recess and a second recess, the first recess engages with the first protrusion among the plurality of protrusions protruding from the first surface of the strain generating body, The second recess is engaged with the second convex portion of the plurality of convex portions protruding from the first surface of the strain generating body.

9. A strain gauge and a strain generating body having a first surface and a second surface, the strain gauge being attached to the first surface side; The strain gauge comprises: A substrate; A resistor formed on one surface of the substrate; A plurality of recesses opening to the other surface side of the base material; having The plurality of recesses include a first recess and a second recess, the first recess and the second recess are arranged such that, when a virtual line segment connecting a center of gravity of the first recess and a center of gravity of the second recess is considered in a plan view, the virtual line segment obliquely intersects with a longitudinal direction of the resistor; The strain body has a plurality of protrusions protruding from the first surface, The plurality of protruding portions include a first protruding portion and a second protruding portion, The first convex portion fits into the first concave portion, and the second convex portion fits into the second concave portion.

10. A strain gauge, a metallic strain generating body having a first surface and a second surface, the strain gauge being attached to the first surface side via a conductive adhesive; The strain body has a plurality of protrusions protruding from the first surface, The plurality of protruding portions include a first protruding portion and a second protruding portion, The strain gauge comprises: A substrate; A resistor formed on one surface of the substrate; A plurality of recesses opening to the other surface side of the base material; A base layer formed on the other surface side of the base material; having The plurality of recesses include a first recess and a second recess, the first recess engages with the first protrusion among the plurality of protrusions protruding from the first surface of the strain generating body, the second recess engages with the second protrusion among the plurality of protrusions protruding from the first surface of the strain body, A plurality of through holes are provided through the underlayer, the first recess and the second recess are formed by an inner surface of the through hole and another surface of the base material exposed in the through hole, the underlayer is a conductive layer formed of a material having a higher electrical conductivity than the base material, The conductive layer is electrically connected to the strain body via the conductive adhesive.

11. A strain gauge and a metallic strain generating body having a first surface and a second surface, the strain gauge being attached to the first surface side via a conductive adhesive; The strain gauge comprises: A substrate; A resistor formed on one surface of the substrate; A plurality of recesses opening to the other surface side of the base material; A base layer formed on the other surface side of the base material; having The plurality of recesses include a first recess and a second recess, the first recess and the second recess are arranged such that, when a virtual line segment connecting a center of gravity of the first recess and a center of gravity of the second recess is considered in a plan view, the virtual line segment obliquely intersects with a longitudinal direction of the resistor; A plurality of through holes are provided through the underlayer, the first recess and the second recess are formed by an inner surface of the through hole and another surface of the base material exposed in the through hole, the underlayer is a conductive layer formed of a material having a higher electrical conductivity than the base material, The strain body has a plurality of protrusions protruding from the first surface, The plurality of protruding portions include a first protruding portion and a second protruding portion, the first protrusion fits into the first recess, and the second protrusion fits into the second recess, The conductive layer is electrically connected to the strain body via the conductive adhesive.

12. A strain-generating body, A first protrusion that mates with the first recess of the strain gauge according to any one of claims 1 to 7; a second protrusion that mates with the second recess of the strain gauge; The first convex portion and the second convex portion protrude from a first surface of the flexure body.

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