Strain gauge

Abstract

To provide a strain gauge with an improved creep property.SOLUTION: A strain gauge provided herein comprises a substrate made of resin, a resistor formed on a flat surface of the substrate, and a pair of wiring lines formed on the flat surface to be connected to respective ends of the resistor. The resistor has a plurality of juxtaposed elongate portions. On the flat surface, at least one of the plurality of elongate portions has projecting protrusions at positions facing the other adjacent elongate portion and / or positions facing the wiring lines.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, a strain gauge that is attached to a measurement object and used is known. For example, the strain gauge may be used as a sensor for detecting the strain of a material or a sensor for detecting the ambient temperature (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the strain gauge as described above, a metal base material or a resin base material is used. However, in the strain gauge using a resin base material, creep may occur. "Creep" in the strain gauge is a phenomenon in which strain changes with time when a constant load acts on the strain gauge under a certain temperature condition. In a strain gauge, creep is a factor of measurement error. Therefore, it is required to improve the creep characteristics.

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

Means for Solving the Problems

[0006] A strain gauge according to one embodiment of the present disclosure comprises a resin substrate, a resistor formed on the plane of the substrate, and a pair of wires formed on the plane and connected to each end of the resistor, wherein the resistor includes a plurality of juxtaposed elongated portions, and in the plane, a protruding portion, or convex portion, is provided at a position where at least one of the plurality of elongated portions faces an adjacent elongated portion and / or faces the wires. In the plane, a recess is provided in the other elongated portion and / or the wiring adjacent to the at least one elongated portion, at a position facing the convex portion, and part or all of the convex portion protrudes toward the gap formed by the recess of the recess in the plane, where the resistor is not formed, so as to interlock with the recess. It is. [Effects of the Invention]

[0007] According to the disclosed technology, the creep characteristics of strain gauges can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 2] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 3] This is a diagram explaining trimming. [Figure 4] This diagram illustrates the method for measuring creep amount and creep recovery amount. [Figure 5] This figure shows the results of the investigation into creep amount and creep recovery amount. [Figure 6] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 7] This is a plan view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 8] This is a plan view illustrating a strain gauge according to a modified example 2 of the first embodiment. [Figure 9] This is a plan view illustrating a strain gauge according to the second 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, identical components may be denoted by the same reference numeral. In each drawing, mutually orthogonal X, Y, and Z directions may be defined. In this case, in the X direction, the starting point (root) of the arrow may be referred to as the X- side, and the ending point (arrowhead) of the arrow may be referred to as the X+ side. The same applies to the Y and Z directions. In addition, in the description of each drawing, the description of components that are the same as those already described may be omitted.

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

[0011] Referring to Figures 1 and 2, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. The cover layer 60 can be provided as needed. For convenience, in Figures 1 and 2, only the outer edge of the cover layer 60 is shown with a dashed line. First, the various parts constituting the strain gauge 1 will be described in detail.

[0012] In this embodiment, for convenience, the side of the base material 10 on which the resistor 30 is provided in the strain gauge 1 is referred to as the "upper side," and the side on which the resistor 30 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 1 can also be used upside down. Furthermore, the strain gauge 1 can be positioned at any angle. Moreover, a planar view refers to viewing the object in the direction normal to the upper surface 10a of the base material 10 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 10 is a member serving as a base layer for forming a resistor 30 or the like. The base material 10 has flexibility. The thickness of the base material 10 is not particularly limited and may be appropriately determined according to the purpose of use of the strain gauge 1 or the like. For example, the thickness of the base material 10 may be about 5 μm to 500 μm. On the lower surface side of the strain gauge 1, a strained body may be joined via an adhesive layer or the like. In view of the strain transmission from the surface of the strained body to the sensing part and the dimensional stability against environmental changes, the thickness of the base material 10 is preferably within the range of 5 μm to 200 μm. Also, from the viewpoint of insulation, the thickness of the base material 10 is preferably 10 μm or more.

[0014] The base material 10 is made of resin. The base material 10 is formed from an insulating resin film such as, for example, a PI (polyimide) resin, an epoxy resin, a PEEK (polyetheretherketone) resin, a PEN (polyethylene naphthalate) resin, a PET (polyethylene terephthalate) resin, a PPS (polyphenylene sulfide) resin, an LCP (liquid crystal polymer) resin, or a polyolefin resin. Here, a film refers to a member having a thickness of about 500 μm or less and having flexibility.

[0015] When the base material 10 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, or the like. For example, the base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0016] The resistor 30 is a thin film formed in a predetermined pattern on the upper side of the base material 10. In the strain gauge 1, the resistor 30 is a sensing part that receives strain and causes a resistance change. The resistor 30 may be formed directly on the upper surface 10a of the planar base material 10, or may be formed on the upper surface 10a of the base material 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown as a densely textured pattern.

[0017] The resistor 30 includes a plurality of elongated portions and a plurality of folded portions. In the resistor 30, the plurality of elongated portions are juxtaposed with their longitudinal directions oriented in the first direction (the X-axis direction in the example of FIG. 1). And the plurality of folded portions alternately connect the ends of adjacent elongated portions among the plurality of elongated portions to connect each elongated portion in series. Thereby, the resistor 30 has a structure that is folded in a zigzag as a whole. The longitudinal direction of the plurality of elongated portions becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the Y-axis direction in the example of FIG. 1).

[0018] In the resistor 30, the X-side end of the elongated portion located on the most Y+ side bends in the Y+ direction and reaches one end 30e1 of the resistor 30 in the grid width direction. Also, the X-side end of the elongated portion located on the most Y- side bends in the Y- direction and reaches the other end 30e2 of the resistor 30 in the grid direction. Each of the ends 30e1 and 30e2 is electrically connected to the electrode 50 via the wiring 40. In other words, the wiring 40 electrically connects each of the ends 30e1 and 30e2 of the resistor 30 in the grid width direction to each electrode 50.

[0019] A part of the portion where the elongated portions are adjacent in the width direction of the resistor 30 has a convex shape with a protruding width. Hereinafter, such a protruding portion of the resistor 30 is referred to as a convex portion 30a. Also, the width of the elongated portion facing the convex portion 30a (that is, the elongated portion in the direction in which the convex portion 30a protrudes) becomes narrow and is recessed. Hereinafter, this recessed portion of the elongated portion is referred to as a concave portion 30b. A part or all of the convex portion 30a protrudes toward the portion of the gap where the resistor 30 is not formed due to the recess of the concave portion 30b so as to engage with the concave portion 30b on the upper surface 10a of the base material 10.

[0020] On the upper surface 10a of the base material 10, at least one protrusion 30a is provided at a position on at least one of the multiple elongated portions of the resistor 30 that faces an adjacent elongated portion. Alternatively, at least one pair of protrusions 30a and recesses 30b is provided at a position on at least one of the multiple elongated portions that faces an adjacent elongated portion.

[0021] More preferably, the resistor 30 is provided with at least one pair of convex portions 30a and concave portions 30b in the interlocking arrangement described above. For example, in the example shown in Figure 1, a total of four pairs of convex portions 30a and concave portions 30b are provided for the entire resistor 30. Specifically, in the first elongated portion counting from the Y-side, two concave portions 30b are provided at positions opposite to the second elongated portion. In addition, in the second elongated portion counting from the Y-side, two convex portions 30a are provided at positions opposite to the first elongated portion, and two more convex portions 30a are provided at positions opposite to the third elongated portion. Furthermore, in the third elongated portion counting from the Y-side, two concave portions 30b are provided at positions opposite to the two elongated portions.

[0022] In the example shown in Figure 1, the protrusion 30a is shaped to project from the upper surface 10a of the base material 10 in a direction perpendicular to the longitudinal direction of the elongated portion (Y-axis direction). However, the protrusion 30a may also project in a direction inclined with respect to the Y-axis direction. In addition, although the protrusion 30a is rectangular in the example shown in Figure 1, the protrusion 30a may be any shape such as a semicircle, semiellipse, trapezoid, or polygon. From the viewpoint of ease of manufacturing, it is preferable that the protrusion 30a is rectangular and projects in a direction perpendicular to the longitudinal direction of the elongated portion.

[0023] The length of the protrusion of the convex portion 30a (in Figure 1, the increase in the width of the elongated portion due to the protrusion) may be, for example, about 1 / 3 or less of the width W of the elongated portion. Here, the width W is the width of the portion of the elongated portion where neither the convex portion 30a nor the concave portion 30b is provided. Also, the length of the recess of the concave portion 30b (in Figure 1, the decrease in the width of the elongated portion due to the recess) may also be about 1 / 3 or less of the width W.

[0024] Furthermore, the protrusions 30a and recesses 30b may be provided on all elongated sections, or only on some of the elongated sections. The width W of each elongated section may be constant. On the other hand, the length of the protrusion of the protrusion 30a and / or the length of the recess of the recess 30b may differ for each protrusion 30a and / or recess 30b.

[0025] By providing a protrusion 30a in the resistor 30, or by arranging the protrusion 30a and recess 30b in the interlocking configuration described above, the resistor 30 can be efficiently arranged within the limited area of ​​the base material 10. As a result, the width of the elongated portion of the resistor 30 is partially widened, increasing the rigidity of the resistor 30 and suppressing expansion and contraction of the resistor 30. Therefore, the creep characteristics can be improved.

[0026] In this specification, "creep" refers to the phenomenon in which, under constant temperature conditions and with a constant load applied to a strain gauge, the amount of strain on the surface of the substrate 10 to which the resistor 30 is provided changes over time (in most cases, the amount of strain increases). Furthermore, "creep characteristics" refers to, for example, the amount of creep and the amount of recovery. Furthermore, "improving creep characteristics" means reducing the absolute value of the amount of creep and the absolute value of the amount of recovery. Improvement of creep characteristics will be described in detail separately.

[0027] Furthermore, in the strain gauge 1, the protrusions 30a can also be used as resistance adjustment regions for trimming. For example, as shown in part B of Figure 3, the resistance value of the resistor 30 can be increased by reducing the area of ​​the conductor by cutting off part or all of the protrusions 30a with a laser or the like. Also, as shown in part C of Figure 3, the resistance value of the resistor 30 can be increased by reducing the area of ​​the conductor by cutting off part or all of the protrusions 30a with a laser or the like. In addition, the amount of change in the resistance value of the resistor 30 can be adjusted by selecting how many of the multiple protrusions 30a to reduce the area of ​​the conductor and by how much.

[0028] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0029] 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.

[0030] The thickness of the resistor 30 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 1. For example, the thickness of the resistor 30 may be approximately 0.05 μm to 2 μm. In particular, when the thickness of the resistor 30 is 0.1 μm or more, the crystallinity of the crystal constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 30 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 10, caused by internal stress in the film constituting the resistor 30, are reduced.

[0031] For example, if the resistor 30 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Also, for example, if the resistor 30 is a Cr multiphase film, by making α-Cr the main component of the resistor 30, the gauge factor of strain gauge 1 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 30 contains 80% by weight or more of α-Cr. Furthermore, from the same viewpoint, it is even more preferable that the resistor 30 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0032] Furthermore, if the resistor 30 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less, the decrease in the gauge factor of the strain gauge 1 can be suppressed.

[0033] 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 30 is reduced, making brittle fracture of the resistor 30 less likely to occur.

[0034] 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.

[0035] In strain gauge 1, using a Cr multiphase film as the material for the resistor 30 enables higher sensitivity and miniaturization. For example, while the output of a conventional strain gauge was approximately 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 30 allows for an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was approximately 3mm × 3mm, using a Cr multiphase film as the material for the resistor 30 allows for miniaturization to approximately 0.3mm × 0.3mm.

[0036] The wiring 40 is provided on the base material 10. One end of the wiring 40 is electrically connected to both ends of the resistor 30, and the other end is electrically connected to the electrode 50. The wiring 40 is not limited to a straight line and can be in any pattern. Also, the wiring 40 can have any width and any length. For convenience, in Figure 1, the wiring 40 is shown with a matte pattern that is less dense than the resistor 30.

[0037] The electrode 50 is provided on the substrate 10. The electrode 50 is electrically connected to the resistor 30 via the wiring 40. In a plan view, the electrode 50 is wider than the wiring 40 and is formed in a substantially rectangular shape. The electrode 50 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 30 caused by strain. For example, lead wires for external connection are joined to the electrode 50. A low-resistance metal layer such as copper, or a metal layer with good solderability such as gold, may be laminated on the upper surface of the electrode 50. For convenience, the resistor 30, wiring 40, and electrode 50 are given different reference numerals, but both can be formed integrally from the same material in the same process. In Figure 1, for convenience, the electrode 50 is shown with a textured pattern of the same density as the wiring 40.

[0038] The cover layer 60 (insulating resin layer) is provided on the upper surface 10a of the substrate 10 as needed, covering the resistor 30 and wiring 40 and exposing the electrodes 50. Examples of materials for the cover layer 60 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 60 may also contain fillers and pigments. The thickness of the cover layer 60 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 60 can be about 2 μm to 30 μm. By providing the cover layer 60, mechanical damage to the resistor 30 can be suppressed. In addition, by providing the cover layer 60, the resistor 30 can be protected from moisture and other elements.

[0039] [Improved creep characteristics] The strain gauge 1 preferably has excellent creep characteristics. That is, it is preferable that the amount of creep and the amount of creep recovery of the strain gauge 1 are small. For example, if the amount of creep and the amount of creep recovery can be reduced to below a predetermined value, the strain gauge 1 can be used not only for sensor applications but also for weighing applications.

[0040] The creep amount and creep recovery amount of a strain gauge are affected by the viscoelasticity of the constituent material. Generally, creep hardly occurs in metal materials, which are elastic materials, but creep does occur in resins, which are viscous materials. Since strain gauge 1 uses a resin base material 10, the viscosity of the base material 10 cannot be ignored.

[0041] The creep amount and creep recovery amount are determined by the change in the amount of elastic deformation (strain) of the surface of the base material 10 on which the resistor 30 is provided, over time in the strain gauge 1. Therefore, the creep amount and creep recovery amount can be measured by monitoring the strain voltage calculated based on the output between the pair of electrodes 50 of the strain gauge 1. This will be explained in detail with reference to Figure 4.

[0042] Figure 4 illustrates the method for measuring creep and creep recovery. In Figure 4, the horizontal axis represents time, and the vertical axis represents strain voltage [mV].

[0043] First, after powering on the measuring device for 10 seconds, a 150% load is applied to strain gauge 1 attached to the strain generating body for 10 seconds, and then the load is removed. After 20 minutes have passed since the load was removed, a 100% load is applied to strain gauge 1 attached to the strain generating body for 20 minutes, and then the load is removed. Then, wait for another 20 minutes to pass after the load has been removed.

[0044] The strain voltage changes as shown in Figure 4, for example. In Figure 4, the absolute value B of the difference in strain voltage is measured between 20 minutes after the 150% load is removed and immediately after the 100% load is applied. Also, the absolute value ΔA of the difference in strain voltage is measured between immediately after the 100% load is applied and 20 minutes after the 100% load is applied. In this case, ΔA / B is the creep amount. Next, the absolute value ΔC of the difference in strain voltage is measured between immediately after the 100% load is removed and 20 minutes after the 100% load is removed. In this case, ΔC / B is the creep recovery amount.

[0045] Note that 100% load is 3 kg, and 150% load is 1.5 times the load of 100% load.

[0046] Figure 5 shows the results of the investigation into creep amount and creep recovery amount, and summarizes the measured results as follows.

[0047] First, four types of measurement samples, A to D, were prepared as measurement samples with the same structure as strain gauge 1 shown in Figures 1 and 2. In measurement sample A, a polyimide resin film with a thickness of 25 μm was used as the base material. A Cr multiphase film was used as the resistor, and the width of each elongated part was kept constant at 50 μm. In addition, a polyimide resin film with a thickness of 15 μm was used as the cover layer.

[0048] Measurement sample B was the same as measurement sample A, except that the width of each elongated part of the resistor was set to 100 μm. Measurement sample C was the same as measurement sample A, except that the width of each elongated part of the resistor was set to 200 μm. Measurement sample D was the same as measurement sample A, except that the width of each elongated part of the resistor was set to 500 μm.

[0049] Next, measurement samples A to D were attached to separate strain-generating bodies made of SUS304, and the creep amount and creep recovery amount were measured using the measurement method shown in Figure 4. The results shown in Figure 5 were obtained. In Figure 5, the horizontal axis represents the width of the elongated portion, and the vertical axis represents the creep amount and creep recovery amount.

[0050] As shown in Figure 5, the creep amount and creep recovery amount decrease as the width of the elongated portion of the resistor increases. In particular, when the width of the elongated portion is 200 μm or more, the creep amount and creep recovery amount fall within ±0.25% or less. When strain gauges are used for sensor applications, the required creep amount and creep recovery amount are approximately ±0.5%. If the width of the elongated portion is 200 μm or more, this requirement can be met with sufficient margin. Furthermore, when the width of the elongated portion is around 350 μm, the creep amount becomes zero%, and even when the width of the elongated portion is 350 μm or more, the creep amount and creep recovery amount remain within the range of 0 to 0.25%. Thus, in strain gauges, the creep characteristics are improved by increasing the width of the elongated portion of the resistor. This is because increasing the width of the elongated portion of the resistor increases the rigidity of the resistor, thereby suppressing the expansion and contraction of the resistor.

[0051] Therefore, in the strain gauge 1, in addition to having a structure with a convex portion 30a and a concave portion 30b, it is preferable that the width W of each elongated portion is 200 μm or more. This can further improve the creep characteristics. Furthermore, it is even more preferable that the width W of each elongated portion is 350 μm or more. This can further improve the creep characteristics. The distance between the opposing regions of adjacent elongated portions of the resistor 30 can be narrowed to about 5 μm to 10 μm. By narrowing this distance as much as possible, it becomes easier to widen the width W of each elongated portion.

[0052] Furthermore, in the case of highly sensitive strain gauges with a gauge factor of 10 or higher (for example, when a Cr multiphase film is used for the resistor 30), the high sensitivity makes them highly susceptible to the influence of material properties, and the creep characteristics may be significantly reduced. Therefore, in highly sensitive strain gauges with a gauge factor of 10 or higher, it is extremely important to improve the creep characteristics by providing irregularities in the opposing regions of adjacent elongated parts.

[0053] [Method of manufacturing strain gauges] In the strain gauge 1 according to this embodiment, a resistor 30, wiring 40, electrodes 50, and a cover layer 60 are formed on a base material 10. Note that another layer (such as a functional layer, described later) may be formed between the base material 10 and these layers.

[0054] The manufacturing method of the strain gauge 1 is described below. To manufacture the strain gauge 1, first, a base material 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the base material 10. Metal layer A is the layer that will ultimately be patterned to become the resistor 30, wiring 40, and electrode 50. Therefore, the material and thickness of metal layer A are the same as the material and thickness of the resistor 30, etc., mentioned above.

[0055] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, or pulsed laser deposition instead of magnetron sputtering.

[0056] After forming a metal layer A on the upper surface 10a of the substrate 10, the metal layer A is patterned into a planar shape similar to the resistor 30, wiring 40, and electrode 50 in Figure 1 by a well-known photolithography method. The resistor 30 includes a plurality of elongated parts arranged side by side, with a convex portion on one of the opposing regions of adjacent elongated parts and a concave portion on the other, and a portion of the convex portion located within the concave portion.

[0057] Alternatively, a base layer may be formed on the upper surface 10a of the substrate 10 before forming the metal layer A. For example, a functional layer of a predetermined thickness may be vacuum-deposited on the upper surface 10a of the substrate 10 by conventional sputtering. By providing a base layer in this way, the gauge characteristics of the strain gauge 1 can be stabilized.

[0058] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 30). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen or moisture contained in the substrate 10, and / or the function of improving the adhesion between the substrate 10 and the metal layer A. The functional layer may further have other functions.

[0059] The insulating resin film constituting the base material 10 may contain oxygen and moisture, and Cr may form an oxidized film. Therefore, especially when metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of metal layer A.

[0060] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics in the strain gauge 1 is improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A improves the gauge characteristics in the strain gauge 1.

[0061] Examples of materials for the functional layer 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.

[0062] Figure 6 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 6 shows the cross-sectional shape of the strain gauge 1 when a functional layer 20 is provided as a base layer for the resistor 30, wiring 40, and electrode 50.

[0063] The planar shape of the functional layer 20 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 30, the wiring 40, and the electrodes 50. However, the planar shapes of the functional layer 20 and the resistor 30, the wiring 40, and the electrodes 50 do not have to be substantially the same. For example, if the functional layer 20 is formed from an insulating material, the functional layer 20 may be patterned to be different from the planar shapes of the resistor 30, the wiring 40, and the electrodes 50. In this case, the functional layer 20 may be formed as a solid in the region where the resistor 30, the wiring 40, and the electrodes 50 are formed. Alternatively, the functional layer 20 may be formed as a solid over the entire upper surface of the substrate 10.

[0064] After forming the resistor 30, wiring 40, and electrode 50, a cover layer 60 is formed on the upper surface 10a of the base material 10 as needed. The cover layer 60 covers the resistor 30 and wiring 40, but the electrode 50 may be exposed from the cover layer 60. For example, the cover layer 60 can be formed by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the base material 10 so as to cover the resistor 30 and wiring 40 and expose the electrode 50, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 1 is completed.

[0065] <Variation 1 of the First Embodiment> Modification 1 of the first embodiment shows an example in which the positions of the convex and concave portions of the strain gauge differ from those of the first embodiment. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0066] Figure 7 is a plan view illustrating a strain gauge according to Modification 1 of the First Embodiment. Referring to Figure 7, in strain gauge 1A, two protrusions 30a are provided in the region facing the wiring 40 in the first elongated section counting from the Y-side, and two more protrusions 30a are provided in the region facing the second elongated section. In addition, two recesses 30b are provided in the region facing the first elongated section of the wiring 40 on the Y-side. In addition, two recesses 30b are provided in the region facing the first elongated section in the second elongated section counting from the Y-side. A portion of each protrusion 30a is located within the corresponding recess 30b.

[0067] Thus, in the strain gauge, the convex portion 30a and the concave portion 30b may be provided in opposing regions of adjacent elongated portions, or in opposing regions of the elongated portion and the wiring. In either case, the same effect is achieved.

[0068] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows an example in which the strain gauge includes convex portions with different lengths in the X direction. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0069] Figure 8 is a plan view illustrating a strain gauge according to a modification 2 of the first embodiment. Referring to Figure 8, in strain gauge 1B, the multiple protrusions 30a include two or more types of protrusions 30a whose lengths in the direction parallel to the longitudinal direction of the elongated portion (the X direction in Figure 8) are different from each other. In the example in Figure 8, all four protrusions 30a have different lengths in the direction parallel to the longitudinal direction of the elongated portion.

[0070] As with strain gauge 1B, the multiple protrusions 30a may include two or more types of protrusions 30a whose lengths in the direction parallel to the longitudinal direction of the elongated portion differ from each other. This allows the resistance value of the resistor 30 to be adjusted to different values ​​depending on which protrusion 30a is cut during trimming.

[0071] <Second Embodiment> The second embodiment shows an example in which the electrode area is increased. In the second embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0072] Figure 9 is a plan view illustrating a strain gauge according to the second embodiment. Referring to Figure 9, in strain gauge 2, the area of ​​the pair of electrodes 50 is larger than that of strain gauge 1.

[0073] In the strain gauge 2, it is preferable to make the distance between the opposing regions of adjacent elongated parts of the resistor 30 as narrow as possible given the manufacturing constraints. Furthermore, it is preferable to make the distance between the opposing regions of each electrode 50 and the folded portion of the resistor 30, and the distance between the opposing regions of each electrode 50, as narrow as possible given the manufacturing constraints. The manufacturing limits for the distance between the opposing regions of adjacent elongated parts of the resistor 30 are approximately 5 μm to 10 μm.

[0074] By setting the distance between opposing regions of adjacent elongated parts of the resistor 30 to a value that limits manufacturing constraints, and by making the distance between opposing regions of each electrode 50 and the folded portion of the resistor 30, and the distance between opposing regions of each electrode 50 equal to the distance between opposing regions of the elongated parts, the area of ​​each elongated part of the resistor 30 can be increased, as can the area of ​​the electrodes 50. As a result, the rigidity of the electrodes 50 is increased and expansion and contraction are suppressed, so the expansion and contraction of the resistor 30 placed adjacent to the electrodes 50 is further suppressed, and the creep characteristics of the strain gauge 2 can be further improved. Here, "equal" means that the distance between opposing regions of each electrode 50 and the folded portion of the resistor 30, and the distance between opposing regions of each electrode 50 are within ±2 μm of the average value of the distance between opposing regions of adjacent elongated parts of the resistor 30.

[0075] Preferred embodiments have been described in detail above. However, the strain gauges relating to this disclosure are not limited to the embodiments and modifications described above. For example, various modifications and substitutions can be made to the strain gauges relating to the embodiments described above without departing from the scope described in the claims. [Explanation of Symbols]

[0076] 1,1A,1B,2 Strain gauge, 10 Substrate, 10a Top surface, 20 Functional layer, 30 Resistor, 30a Convex part, 30b Recessed part, 40 Wiring, 50 Electrode, 60 Cover layer

Claims

1. A resin base material, A resistor formed on the plane of the substrate, It has a pair of wires formed on the plane and connected to each end of the resistor, The resistor includes a plurality of elongated parts arranged side by side, In the plane, a protruding portion, or convex portion, is provided at a position on at least one of the plurality of elongated portions that faces an adjacent elongated portion, and / or faces the wiring. In the plane, a recess is provided in the other elongated portion and / or the wiring adjacent to the at least one elongated portion, at a position facing the convex portion. A strain gauge wherein part or all of the convex portion protrudes toward the portion of the gap formed by the recess in the recess, where the resistive element is not formed, so as to engage with the recess on the plane.

2. The convex portion is a part that protrudes so as to widen the width of the at least one elongated portion, The strain gauge according to claim 1, wherein the recess is a recessed portion that narrows the width of the other elongated portion and / or the wiring.

3. The strain gauge according to claim 1 or 2, wherein the width of the region in each of the elongated portions that does not have either the convex portion or the concave portion is 200 μm or more.

4. The strain gauge according to claim 3, wherein the width of the region in each of the elongated portions that does not have either the convex portion or the concave portion is 350 μm or more.

5. The strain gauge according to any one of claims 1 to 4, wherein the convex portion has a shape that protrudes in the plane in a direction perpendicular to the longitudinal direction of the elongated portion.

6. The strain gauge according to any one of claims 1 to 5, wherein the plurality of protrusions include two or more types of protrusions whose lengths in a direction parallel to the longitudinal direction of the elongated portion differ from each other.

7. Having a first electrode and a second electrode, The wiring includes a first wiring and a second wiring arranged alongside the elongated portions on both sides of the plurality of elongated portions, The first wiring connects one end of the elongated portion to the first electrode, The second wiring connects the other end of the elongated portion to the second electrode. The resistor includes a folded portion which connects the ends of adjacent elongated portions in a series by alternating them among a plurality of elongated portions, The strain gauge according to any one of claims 1 to 6, wherein the distance between the first electrode and the second electrode and the opposing region of the folded portion, and the distance between the mutually opposing regions of the first electrode and the second electrode are equal to the distance between the mutually opposing regions of adjacent elongated portions.

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

9. A strain gauge according to any one of claims 1 to 8, wherein the gauge factor is 10 or more.

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