Strain gauges, sensor structures

Abstract

To provide a strain gauge capable of easily reducing an effect of an electromagnetic noise.SOLUTION: This strain guage is a strain guage that is mounted to a measuring object and detects a strain generated in the measuring object, includes a base material, a resistor formed on an upper surface of the base material, and a penetration electrode penetrating the base material from the upper surface to a lower surface. When the strain guage is mounted to the measuring object, the lower surface of the base material and the lower surface of the penetration electrode become a surface abutted to the measuring object.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, a strain gauge that is attached to a measurement object and used is known. The strain gauge includes a resistor that detects strain, and the resistor is formed on, for example, an insulating resin. The resistor is connected to an electrode via wiring (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] By the way, the resistor of the strain gauge may be affected by electromagnetic noise, and when affected by electromagnetic noise, it becomes difficult to obtain a normal signal from the strain gauge.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a strain gauge that can easily reduce the influence of electromagnetic noise.

Means for Solving the Problems

[0006] The present strain gauge is a strain gauge that is attached to a measurement object and detects strain generated in the measurement object, and includes a base material and a resistor formed on the upper surface of the base material , wiring, and terminal section and a through electrode that penetrates the base material from the upper surface to the lower surface. The through-electrode is provided at a distance from the resistor, the wiring, and the terminal portion, and the lower surface of the through-electrode is flush with the lower surface of the substrate or protrudes from the lower surface of the substrate. .

Effects of the Invention

[0007] According to the disclosed technology, it is possible to provide strain gauges that can easily reduce the effects of electromagnetic noise. [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 illustrating a strain gauge according to the first embodiment. [Figure 3] This is a diagram illustrating how to use strain gauges. [Figure 4] This is a cross-sectional view illustrating a sensor structure. [Figure 5] This is a cross-sectional view (part 1) showing an example where the object being measured by the sensor structure is a rolling bearing. [Figure 6] This is a cross-sectional view (part 2) showing an example where the object being measured by the sensor structure is a rolling bearing. [Figure 7] This is a cross-sectional view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 8] This is a cross-sectional view illustrating a strain gauge according to a modified example 2 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> (Strain gauge) Figure 1 is a plan view illustrating a strain gauge according to the first embodiment. Figure 2 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 1.

[0011] Referring to Figures 1 and 2, the strain gauge 100 includes a base material 101, a functional layer 102, a resistor 103, wiring 104, a terminal portion 105, and a through electrode 106. However, the functional layer 102 may be provided as needed.

[0012] In this embodiment, for convenience, the side of the strain gauge 100 on which the resistor 103 is provided on the base material 101 is referred to as the "upper side," and the side on which the resistor 103 is not provided is referred to as the "lower side." Furthermore, the surface located above each part is referred to as the "upper surface," and the surface located below each part is referred to as the "lower surface." However, the strain gauge 100 can also be used upside down. Furthermore, the strain gauge 100 can be positioned at any angle. Moreover, a planar view refers to viewing the object in the direction normal to the upper surface 101a of the base material 101 from top to bottom. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0013] The base material 101 is a component that serves as a base layer for forming the resistor 103, etc. The base material 101 is flexible. The thickness of the base material 101 is not particularly limited and may be appropriately determined according to the intended use of the strain gauge 100. For example, the thickness of the base material 101 may be about 5 μm to 500 μm. However, from the viewpoint of strain transmission from the surface of the object to be measured to the sensing part, and dimensional stability against environmental changes, the thickness of the base material 101 is preferably in the range of 5 μm to 200 μm. Furthermore, from the viewpoint of insulation, the thickness of the base material 101 is preferably 10 μm or more.

[0014] The base material 101 is 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. Note that "film" refers to a flexible material with a thickness of approximately 500 μm or less.

[0015] When the base material 101 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the base material 101 may be formed from an insulating resin film containing fillers such as silica and alumina.

[0016] Examples of materials other than the resin of the base material 101 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, perovskite-based ceramics (CaTiO3, BaTiO3), etc. Also, in addition to the aforementioned crystalline materials, amorphous glass or the like may be used as the material of the base material 101. Also, as the material of the base material 101, metals such as aluminum, aluminum alloy (duralumin), and titanium may be used. When a metal is used, an insulating film is provided between the metal base material 101 and the functional layer 102, and between the metal base material 101 and the through electrode 106.

[0017] The functional layer 102 is formed as a lower layer of the resistor 103 on the upper surface 101a of the base material 101. 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 resistor 103. The functional layer 102 preferably further has a function of preventing the oxidation of the resistor 103 by oxygen or moisture contained in the base material 101, and / or a function of improving the adhesion between the base material 101 and the resistor 103. The functional layer 102 may further have other functions.

[0018] The insulating resin film constituting the base material 101 may contain oxygen or moisture, and Cr may form a self-oxidized film. Therefore, particularly when the resistor 103 contains Cr, it is preferable to form the functional layer 102 having a function of preventing the oxidation of the resistor 103.

[0019] In this way, by providing a functional layer 102 in the lower layer of the resistor 103, crystal growth of the resistor 103 can be promoted, and a resistor 103 consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the strain gauge 100 is improved. Furthermore, the material constituting the functional layer 102 diffuses into the resistor 103, improving the gauge characteristics of the strain gauge 100.

[0020] Examples of materials for the functional layer 102 include one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of these metals, or a compound of any of these metals.

[0021] The planar shape of the functional layer 102 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 103, the wiring 104, and the terminal portion 105. However, the planar shapes of the functional layer 102 and the resistor 103, the wiring 104, and the terminal portion 105 do not have to be substantially the same. For example, if the functional layer 102 is formed from an insulating material, the functional layer 102 may be patterned to be a different shape from the planar shapes of the resistor 103, the wiring 104, and the terminal portion 105. In this case, the functional layer 102 may be formed as a solid block in the region where the resistor 103, the wiring 104, and the terminal portion 105 are formed. Alternatively, the functional layer 102 may be formed as a solid block over the entire upper surface 101a of the base material 101.

[0022] The resistor 103 is formed on the upper surface 101a of the substrate 101. The resistor 103 is a thin film formed on the upper surface 101a of the substrate 101 in a predetermined pattern. In the strain gauge 100, the resistor 103 is a sensitive part that receives strain and causes a change in resistance. The resistor 103 may be formed directly on the upper surface 101a of the substrate 101, or it may be formed on the upper surface 101a of the substrate 101 via another layer.

[0023] The resistor 103 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 103 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).

[0024] Here, a Cr multiphase film is a film in which Cr, CrN, and Cr2N are mixed together. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0025] The thickness of the resistor 103 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 100. For example, the thickness of the resistor 103 may be approximately 0.05 μm to 2 μm. In particular, when the thickness of the resistor 103 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 103 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 103 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 101 caused by internal stress in the film constituting the resistor 103 are reduced.

[0026] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of the resistor 103 is preferably 5 μm or more and 100 μm or less. More specifically, the width of the resistor 103 is preferably 5 μm or more and 70 μm or less, and more preferably 5 μm or more and 50 μm or less.

[0027] For example, if the resistor 103 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. Also, for example, if the resistor 103 is a Cr multiphase film, by making α-Cr the main component of the resistor 103, the gauge factor of the strain gauge 100 can be set to 10 or more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means a component that accounts for 50% by weight or more of the total material constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 103 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is even more preferable that the resistor 103 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0028] Furthermore, if the resistor 103 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 be 20% by weight or less, the decrease in the gauge factor of the strain gauge 100 can be suppressed.

[0029] Furthermore, in the Cr multiphase film, it is preferable that the ratio of CrN to Cr2N is such that the proportion of Cr2N is 80% or more and less than 90% by weight relative to the total weight of CrN and Cr2N. More preferably, the ratio is such that the proportion of Cr2N is 90% or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the decrease in TCR (negative TCR) becomes even more pronounced. Moreover, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the ceramicization of the resistor 103 is reduced, making brittle fracture of the resistor 103 less likely to occur.

[0030] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of unstable nitrogen generation can be reduced, thus enabling the creation of a stable strain gauge. Here, "unstable nitrogen" refers to trace amounts of N2 or atomic nitrogen that may be present in the Cr multiphase film. These unstable nitrogen atoms may escape from the film depending on the external environment (e.g., high temperature environment). When unstable nitrogen atoms escape from the film, the film stress of the Cr multiphase film may change.

[0031] In strain gauge 100, using a Cr multiphase film as the material for the resistor 103 makes it possible to achieve both high sensitivity and miniaturization. For example, while the output of a conventional strain gauge was about 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 103 makes it possible to obtain an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was about 3mm × 3mm, using a Cr multiphase film as the material for the resistor 103 makes it possible to miniaturize the size (gauge length × gauge width) to about 0.3mm × 0.3mm.

[0032] The terminal portion 105 extends from both ends of the resistor 103 via the wiring 104, and in a plan view, it is wider than the resistor 103 and the wiring 104 and is formed in a substantially rectangular shape. The terminal portion 105 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 103 caused by strain. The resistor 103 extends from one of the terminal portion 105 and the wiring 104, for example, by folding back in a zigzag pattern, and is connected to the other wiring 104 and terminal portion 105. The upper surface of the terminal portion 105 may be covered with a metal that has better solderability than the terminal portion 105.

[0033] Although the resistor 103, wiring 104, and terminal portion 105 are given different reference numerals for convenience, they can be formed integrally from the same material in the same process.

[0034] The through electrode 106 penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The through electrode 106 is positioned within a through hole 101x that penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The upper surface 106a of the through electrode 106 is flush with, for example, the upper surface 101a of the substrate 101. Similarly, the lower surface 106b of the through electrode 106 is flush with, for example, the lower surface 101b of the substrate 101.

[0035] The planar shape of the through electrode 106 is, for example, rectangular. However, it is not limited to this, and the planar shape of the through electrode 106 may be circular, elliptical, or any other arbitrary shape. Also, in the example of Figure 1, the through electrode 106 is provided in the region sandwiched between the two terminal portions 105, but the through electrode 106 can be provided at any position on the base material 101 as long as it is separated from the resistor 103, the wiring 104, and the terminal portions 105.

[0036] It is preferable to select a material for the through-electrode 106 that has a lower volume resistivity than the resistor 103. Examples of such materials include Cu, Ni, Al, Ag, Au, Pt, alloys of any of these metals, compounds of any of these metals, or laminated films obtained by appropriately stacking any of these metals, alloys, or compounds.

[0037] The cover layer 107 is provided on the upper surface 101a of the substrate 101, as needed, to cover the resistor 103 and wiring 104, while exposing the terminal portion 105 and through electrode 106. Examples of materials for the cover layer 107 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The cover layer 107 may also contain fillers and pigments. The thickness of the cover layer 107 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 107 can be approximately 2 μm to 30 μm. By providing the cover layer 107, mechanical damage to the resistor 103 can be suppressed. Furthermore, by providing the cover layer 107, the resistor 103 can be protected from moisture and other elements.

[0038] (Method of manufacturing strain gauges) In the strain gauge 100 according to this embodiment, a resistor 103, wiring 104, and terminal portion 105 are formed on the base material 101. A functional layer 102 and a cover layer 107 may be formed as needed.

[0039] The manufacturing method for the strain gauge 100 is described below. To manufacture the strain gauge 100, first, a base material 101 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 101a of the base material 101. Metal layer A is the layer that will ultimately be patterned to form the resistor 103, the wiring 104, and the terminal portion 105. Therefore, the material and thickness of metal layer A are the same as those of the resistor 103 and other components mentioned above.

[0040] The metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming the metal layer A. Alternatively, the metal layer A may be deposited using reactive sputtering, vapor deposition, arc ion plating, or pulsed laser deposition instead of magnetron sputtering. After depositing the metal layer A on the upper surface 101a of the substrate 101, the metal layer A is patterned into a planar shape similar to the resistor 103, wiring 104, and terminal portion 105 in Figure 1 using a well-known photolithography method.

[0041] Alternatively, a functional layer 102 may be formed as an underlayer on the upper surface 101a of the substrate 101 before forming the metal layer A. For example, a functional layer 102 of a predetermined thickness may be vacuum-deposited on the upper surface 101a of the substrate 101 by conventional sputtering. By providing the functional layer 102 in this way, the gauge characteristics of the strain gauge 100 can be stabilized.

[0042] To form the through-electrode 106, for example, a through-hole 101x is formed in the base material 101 by press working, and then the through-electrode 106 is formed within the through-hole 101x. The through-electrode 106 can be formed, for example, by preparing a metal foil of approximately the same size as the through-hole 101x and fixing this metal foil within the through-hole 101x. Alternatively, the through-electrode 106 that fills the through-hole 101x may be formed by a plating method or the like.

[0043] After forming the resistor 103, wiring 104, terminal portion 105, and through electrode 106, a cover layer 107 is formed on the upper surface 101a of the base material 101 as needed. The cover layer 107 covers the resistor 103 and wiring 104, but the terminal portion 105 and through electrode 106 are exposed from the cover layer 107. For example, a semi-cured thermosetting insulating resin film is laminated onto the upper surface 101a of the base material 101 so as to cover the resistor 103 and wiring 104 and expose the terminal portion 105 and through electrode 106. Then, the cover layer 107 can be formed by heating and curing the insulating resin film. Through the above steps, the strain gauge 100 is completed.

[0044] (Examples of strain gauge usage) Figure 3 illustrates how to use a strain gauge. As shown in Figure 3, the strain gauge 100 is attached to the object to be measured 200 and detects the strain occurring in the object to be measured 200. The strain gauge 100 is placed directly on the first surface 200a of the object to be measured 200 without an adhesive layer or the like on the lower surface 101b side of the base material 101.

[0045] When the strain gauge 100 is placed on the first surface 200a of the object to be measured 200, the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 come into contact with the first surface 200a of the object to be measured 200. In other words, when the strain gauge 100 is attached to the object to be measured 200, the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 become surfaces that come into contact with the object to be measured 200.

[0046] In the object to be measured 200, at least the portion in contact with the lower surface 106b of the through electrode 106 is made of a conductive material. For example, if a wire or the like is connected to the upper surface 106a of the through electrode 106, and the through electrode 106 is brought to the same potential as the GND potential of the circuit to which the strain gauge 100 is connected, the object to be measured 200 will also be at the GND potential.

[0047] The strain gauge 100 is susceptible to interference from electromagnetic noise present in the vicinity of the object being measured 200. However, by making the object being measured 200 equal to the GND potential of the circuit to which the strain gauge 100 is connected, the influence of electromagnetic noise can be reduced. As a result, the strain gauge 100 can detect strain with a good signal-to-noise ratio. In particular, when a high gauge factor Cr multiphase film is used as the material for the resistor 103 in the strain gauge 100, the resistor 103 is very susceptible to interference from electromagnetic noise, so the effect of making the object being measured 200 equal to the GND potential of the circuit to which the strain gauge 100 is connected is significant.

[0048] Figure 4 is a cross-sectional view illustrating a sensor structure. As shown in Figure 4, the sensor structure 10 includes a strain gauge 100, an object to be measured 200, an opposing part 300, and an elastic body 400. The object to be measured 200 has a first surface 200a to which the lower surface 101b of the base material 101 of the strain gauge 100 and the lower surface 106b of the through electrode 106 come into contact.

[0049] The opposing portion 300 has a second surface 300b that faces the first surface 200a of the object to be measured 200. The opposing portion 300 is positioned relative to the object to be measured 200. The opposing portion 300 is positioned, for example, by being fixed to the object to be measured 200. Any method can be used to fix the opposing portion 300 to the object to be measured 200, such as adhesive, screw fastening, press-fitting, or crimping.

[0050] Alternatively, the opposing portion 300 may be indirectly fixed to the object to be measured 200 via other members, thereby positioning it relative to the object to be measured 200. Alternatively, the opposing portion 300 may be formed integrally with the object to be measured 200. In other words, the opposing portion 300 may be part of the object to be measured 200.

[0051] The strain gauge 100 is mounted on the object to be measured 200 such that the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 are in contact with the first surface 200a. A wire 112 is joined to the upper surface 106a of the through electrode 106 of the strain gauge 100 using a bonding material 111 such as solder.

[0052] The elastic body 400 is positioned between the first surface 200a and the second surface 300b, pressing the strain gauge 100 toward the first surface 200a. A portion of the wire 112 protrudes from the elastic body 400, enabling electrical connection to the outside of the sensor structure 10.

[0053] As the elastic body 400 presses the strain gauge 100 toward the first surface 200a, the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 come into firm contact with the first surface 200a of the object to be measured 200, and the through electrode 106 and the object to be measured 200 become at the same potential.

[0054] The elastic body 400 is formed from an insulating material. Preferably, the elastic body 400 is formed from a low-anisotropy material. By forming the elastic body 400 from a low-anisotropy material, the elastic body 400 can press the strain gauge 100 against the first surface 200a with a substantially uniform force. As a result, the lower surface 106b of the through electrode 106 can more reliably contact the first surface 200a of the object to be measured 200. Low anisotropy here refers to the fact that, in the cross-section shown in Figure 5, the Young's modulus and Poisson's ratio in the direction perpendicular to the first surface 200a are within ±30% of the direction parallel to the first surface 200a. However, in the cross-section shown in Figure 5, the Young's modulus and Poisson's ratio in the direction perpendicular to the first surface 200a are preferably within ±20%, more preferably within ±10%, and even more preferably within ±5% of the direction parallel to the first surface 200a.

[0055] Examples of low-anisotropy materials include foaming materials in which bubbles are discontinuous during molding. Examples of such foaming materials include foamed silicone. Low-anisotropy materials do not have to be foaming materials. Examples of such materials include silicone rubber, ethylene propylene rubber (EPDM), fluororubber, nitrile butadiene rubber (NBR), and urethane rubber.

[0056] To fabricate the sensor structure 10, first prepare a strain gauge 100, and then join a wire 112 to the upper surface 106a of the through electrode 106 of the strain gauge using a bonding material 111 such as solder. Also, prepare a measuring object 200 with the opposing portion 300 positioned.

[0057] Next, the strain gauge 100 is placed in the gap between the first surface 200a and the second surface 300b such that the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 are in contact with the first surface 200a. At this time, the side surface of the base material 101 and the first surface 200a of the object to be measured 200 may be temporarily fixed with adhesive, tape, or the like.

[0058] Next, a fluid material, such as an elastic body 400, is poured into the gap between the first surface 200a and the second surface 300b. The fluid material is then heated and foamed to create the elastic body 400. As a result, the elastic body 400 expands and fills the gap between the first surface 200a and the second surface 300b, and the strain gauge 100 is pressed towards the first surface 200a.

[0059] By connecting the wire 112 protruding from the elastic body 400 to the GND of the circuit to which the strain gauge 100 is connected, the potential of the object to be measured 200 can be made equal to the GND potential of the circuit to which the strain gauge 100 is connected. This reduces the influence of electromagnetic noise, and as a result, the strain gauge 100 can detect strain with a good signal-to-noise ratio.

[0060] As described above, since the strain gauge 100 has a through electrode 106, simply by placing it on the first surface 200a of the object to be measured 200, the object to be measured 200 can be easily brought to GND potential via the through electrode 106, thereby reducing the influence of electromagnetic noise. For example, even in a relatively narrow area sandwiched between the first surface 200a and the second surface 300b, as shown in Figure 4, the object to be measured 200 can be easily brought to GND potential. Furthermore, even when it is difficult to directly connect GND wiring to the object to be measured 200 using solder or screws due to mechanical strength considerations, the object to be measured 200 can be easily brought to GND potential simply by contacting it with the through electrode 106.

[0061] It is also conceivable to apply a conductive adhesive to the lower surface 101b of the base material 101 and connect the through electrode 106 and the object to be measured 200 via the conductive adhesive, but this is undesirable for the following reasons. Specifically, conductive particles (for example, metal powder such as aluminum or silver) contained in the conductive adhesive may cause irregularities on the strain gauge 100 or damage to the resistor 103. Furthermore, if the conductive particles in the conductive adhesive are made finer as a countermeasure, the conductivity between the through electrode 106 and the object to be measured 200 may become unstable. In addition, if the conductive particles are made finer, the amount of insulating material contained in the conductive adhesive increases, which may increase the viscosity of the conductive adhesive and reduce the sensitivity of strain detection. Furthermore, the conductive particles contained in the conductive adhesive may cause migration.

[0062] In the strain gauge 100, the through electrode 106 contacts the object being measured 200, thereby establishing electrical conductivity between the through electrode 106 and the object being measured 200. Therefore, in the strain gauge 100, there is no need to provide a conductive adhesive on the lower surface 101b of the base material 101, thus avoiding the various problems mentioned above. Furthermore, by pressing the strain gauge 100 toward the object being measured 200 with the elastic body 400, stable electrical conductivity can be established between the through electrode 106 and the object being measured 200.

[0063] In Figure 4, the object to be measured 200 is not particularly limited, but as a more specific example, an example in which the object to be measured in the sensor structure is a rolling bearing is shown. Figure 5 is a cross-sectional view (1) showing an example in which the object to be measured in the sensor structure is a rolling bearing, and shows a cross-section in a direction parallel to the axis m. Figure 6 is a cross-sectional view (2) showing an example in which the object to be measured in the sensor structure is a rolling bearing, and shows a cross-section in a direction perpendicular to the axis m.

[0064] As shown in Figures 5 and 6, the sensor structure 20 includes a strain gauge 100, a rolling bearing 200R, a bearing housing 300R, and an elastic body 400. The rolling bearing 200R corresponds to the object to be measured 200 in Figure 4, and the bearing housing 300R corresponds to the opposing part 300 in Figure 4.

[0065] The rolling bearing 200R has an outer ring 210, an inner ring 220, and a plurality of rolling elements 230. The outer ring 210 is a cylindrical structure with axis m as its central axis. The inner ring 220 is a cylindrical structure arranged coaxially with the outer ring 210 on its inner circumference. Each of the plurality of rolling elements 230 is a sphere placed in a raceway formed between the outer ring 210 and the inner ring 220. A lubricant such as grease is sealed in the raceway.

[0066] The bearing housing 300R is a substantially cylindrical member and is positioned to contact the outer circumferential surface of the outer ring 210, i.e., the first surface 200a of the rolling bearing 200R. The bearing housing 300R presses against the outer circumferential surface of the outer ring 210 around its entire circumference, except for the portion where the strain gauge 100 is positioned. Here, contact with the first surface 200a of the rolling bearing 200R includes not only cases where the bearing housing 300R directly contacts the first surface 200a without the use of other members, but also cases where it indirectly contacts the first surface 200a via other members such as adhesive.

[0067] The bearing housing 300R is, for example, press-fitted onto the outer ring 210. Alternatively, the bearing housing 300R may be bonded to the outer ring 210. The bearing housing 300R has a cavity for arranging the strain gauge 100, and the top surface of the cavity becomes a second surface 300b facing the first surface 200a (outer circumference surface of the outer ring 210) of the rolling bearing 200R. The bearing housing 300R can be formed from, for example, a metal such as brass, aluminum, or stainless steel, or from a resin or the like.

[0068] The strain gauge 100 is mounted on the rolling bearing 200R such that the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 are in contact with the first surface 200a of the rolling bearing 200R. Although not shown in the figure, a wire 112 is joined to the upper surface 106a of the through electrode 106 of the strain gauge 100 using a bonding material 111 such as solder, similar to Figure 4.

[0069] The elastic body 400 is positioned between the first surface 200a and the second surface 300b, pressing the strain gauge 100 toward the first surface 200a. Similar to Figure 4, a portion of the wire 112 protrudes from the elastic body 400, enabling electrical connection to the outside of the sensor structure 20.

[0070] As the elastic body 400 presses the strain gauge 100 toward the first surface 200a, the lower surface 101b of the base material 101 and the lower surface 106b of the through electrode 106 come into firm contact with the first surface 200a of the rolling bearing 200R. As a result, the through electrode 106 and the outer ring 210 of the rolling bearing 200R are at the same potential.

[0071] By connecting the wire 112 protruding from the elastic body 400 to the GND of the circuit to which the strain gauge 100 is connected, the outer ring 210 of the rolling bearing 200R can be made equal in potential to the GND of the circuit to which the strain gauge 100 is connected. This reduces the influence of electromagnetic noise, and as a result, the strain gauge 100 can detect strain with a good signal-to-noise ratio.

[0072] <Variations of the first embodiment> A modified example of the first embodiment shows a strain gauge having a through electrode with a different cross-sectional shape than that of the first embodiment. In the modified example of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0073] Figure 7 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the First Embodiment. Note that the plan view of the strain gauge according to Modification 1 of the First Embodiment is the same as that of Figure 1 and is therefore omitted from the illustration. Figure 7 shows a cross-section corresponding to the cross-section along line AA in Figure 1.

[0074] The strain gauge 100A shown in Figure 7 differs from the strain gauge 100 (see Figure 2, etc.) in that the through electrode 106 is replaced with a through electrode 116.

[0075] The through electrode 116 penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The through electrode 116 is positioned within a through hole 101x that penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The upper surface 116a of the through electrode 116 is, for example, flush with the upper surface 101a of the substrate 101.

[0076] On the other hand, the lower surface 116b of the through electrode 116 protrudes downward from the lower surface 101b of the base material 101. In cross-sectional view, the lower surface 116b of the through electrode 116 has a shape in which, for example, the amount of protrusion is greatest in the center and decreases towards the periphery, but is not limited to this.

[0077] Any material exemplified for the material of the through electrode 106 can be used for the through electrode 116.

[0078] In this way, because the lower surface 116b of the through electrode 116 protrudes from the lower surface 101b of the base material 101, the lower surface 116b of the through electrode 116 can be reliably brought into contact with the object to be measured when the strain gauge 100A is attached to the object to be measured. As a result, it becomes easy to establish electrical conductivity between the through electrode 116 and the object to be measured.

[0079] Figure 8 is a cross-sectional view illustrating a strain gauge according to Modification 2 of the First Embodiment. Note that the plan view of the strain gauge according to Modification 2 of the First Embodiment is the same as that of Figure 1 and is therefore omitted from the illustration. Figure 8 shows a cross-section corresponding to the cross-section along line AA in Figure 1.

[0080] The strain gauge 100B shown in Figure 8 differs from the strain gauge 100 (see Figure 2, etc.) in that the through electrode 106 is replaced with a through electrode 126.

[0081] The through electrode 126 penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The through electrode 126 is positioned within a through hole 101x that penetrates the substrate 101 from the upper surface 101a to the lower surface 101b. The upper surface 126a of the through electrode 126 is flush with, for example, the upper surface 101a of the substrate 101. Similarly, the lower surface 126b of the through electrode 106 is flush with, for example, the lower surface 101b of the substrate 101.

[0082] The area of ​​the opening of the through-hole 101x on the lower surface 101b side of the base material 101 is larger than the area of ​​the opening of the through-hole 101x on the upper surface 101a side of the base material 101. Furthermore, if the lower surface 126b of the through-electrode 126 is flush with the lower surface 101b of the base material 101, the area of ​​the opening of the through-hole 101x on the lower surface 101b side of the base material 101 is equal to the area of ​​the lower surface 126b of the through-electrode 126. Also, if the upper surface 126a of the through-electrode 126 is flush with the upper surface 101a of the base material 101, the area of ​​the opening of the through-hole 101x on the upper surface 101a side of the base material 101 is equal to the area of ​​the upper surface 126a of the through-electrode 126.

[0083] The shape of the through electrode 126 is, for example, a figurines. That is, the shape of the through electrode 126 is, for example, a trapezoid in cross-section. However, it is not limited to this, and for example, the side surface of the through electrode 126 does not have to be inclined in a straight line in cross-section, but may be curved in a convex or concave shape, for example. Alternatively, the side surface of the through electrode 126 may be stepped in cross-section.

[0084] Any material exemplified for the material of the through electrode 106 can be used for the through electrode 126.

[0085] Thus, in the strain gauge 100B, the area of ​​the opening of the through hole 101x on the lower surface 101b side of the base material 101 is larger than the area of ​​the opening of the through hole 101x on the upper surface 101a side of the base material 101. This makes it possible to suppress the through electrode 126 from coming out to the upper surface 101a side of the base material 101 when joining a wire or the like to the upper surface 126a of the through electrode 126 or after joining.

[0086] Furthermore, the lower surface 126b of the through electrode 126 may protrude downward from the lower surface 101b of the base material 101, similar to the through electrode 116 shown in Figure 7.

[0087] 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]

[0088] 10,20 Sensor structure, 100,100A,100B Strain gauge, 101 Base material, 101a,106a,116a,126a Top surface, 101b,106b,116b,126b Bottom surface, 101x Through hole, 102 Functional layer, 103 Resistor, 104 Wiring, 105 Terminal section, 106,116,126 Through electrode, 107 Cover layer, 111 Bonding material, 112 Wire, 200 Object to be measured, 200a First surface, 200R Rolling bearing, 210 Outer ring, 220 Inner ring, 230 Rolling element, 300 Opposing part, 300b Second surface, 300R Bearing housing, 400 Elastic body

Claims

1. A strain gauge that is attached to an object to be measured and detects the strain occurring in the object to be measured, Substrate and A resistor, wiring, and terminal portion formed on the upper surface of the substrate, The substrate has a through electrode that penetrates from the top surface to the bottom surface, The through electrode is provided at a distance from the resistor, the wiring, and the terminal portion. A strain gauge wherein the lower surface of the through electrode is flush with the lower surface of the substrate or protrudes from the lower surface of the substrate.

2. The through electrode is positioned in a through hole that penetrates the substrate from the top surface to the bottom surface. The strain gauge according to claim 1, wherein the area of ​​the opening on the lower surface side of the substrate of the through hole is larger than the area of ​​the opening on the upper surface side of the substrate of the through hole.

3. The strain gauge according to claim 1, wherein the resistor is formed from a Cr multiphase film.

4. A strain gauge according to any one of claims 1 to 3, A measurement target having a first surface in which the lower surface of the substrate and the lower surface of the through electrode come into contact, A second surface facing the first surface, and a facing portion positioned relative to the object to be measured, A sensor structure comprising: an elastic body positioned between the first surface and the second surface, which presses the strain gauge toward the first surface.

5. The sensor structure according to claim 4, wherein the elastic body is formed from a low-anisotropy material.

6. The sensor structure according to claim 5, wherein the elastic body is formed from a foamed material.

7. The sensor structure according to claim 4, wherein the object to be measured is a rolling bearing.

8. The sensor structure according to claim 7, wherein the opposing portion is a bearing housing.

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