How to adjust the resistance value of a strain gauge, strain gauge

Abstract

To provide a method for adjusting a resistance value of a strain gauge with which a resistance value can be adjusted regardless of the presence or absence of a protective layer.SOLUTION: The present method for adjusting a resistance value of a strain gauge includes: a step of preparing a strain gauge having a substrate, a resistor formed on the substrate, wiring formed on the substrate and electrically connected with the resistor, and a resistance adjustment part electrically connected with the resistor and the wiring; and a step of irradiating the resistance adjustment part with a laser beam. The resistance adjustment part includes a first portion laminated on the wiring, and a second portion extending from the first portion and connected in parallel with a part of the resistor. The resistance adjustment part is formed of a material having a lower volume resistivity than the wiring.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for adjusting the resistance value of a strain gauge and a strain gauge.

Background Art

[0002] A strain gauge that is attached to a measurement object to detect the strain of the measurement object is known. The strain gauge includes a resistor that detects strain, and the resistor is formed on a base material, for example. The resistor is connected to an electrode via wiring, for example. Further, the strain gauge includes a protective layer that covers the resistor and wiring, for example, on the base material (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 manufacturing process of a strain gauge, resistance value adjustment (trimming) may be performed before forming the protective layer, but the resistance value may change in the process of forming the protective layer after the resistance value adjustment. In that case, the resistance value of the strain gauge deviates from the desired value. Therefore, it is preferable that the resistance value can be adjusted both before and after the process of forming the protective layer.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a method for adjusting the resistance value of a strain gauge that enables adjustment of the resistance value regardless of the presence or absence of a protective layer.

Means for Solving the Problems

[0006] A method for adjusting the resistance value of a strain gauge according to one embodiment of the present disclosure comprises the steps of: preparing a strain gauge having a base material, a resistor formed on the base material, wiring formed on the base material and electrically connected to the resistor, and a resistance adjustment section electrically connected to the resistor and the wiring; and irradiating the resistance adjustment section with laser light, wherein the resistance adjustment section includes a first portion laminated on the wiring and a second portion extending from the first portion and connected in parallel with a part of the resistor, and the resistance adjustment section is formed from a material having a lower volume resistivity than the wiring. [Effects of the Invention]

[0007] According to the disclosed technology, a method for adjusting the resistance value of a strain gauge can be provided, which allows for resistance adjustment with or without a protective layer. [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 diagram illustrates a first method for adjusting the resistance value of a strain gauge. [Figure 4] This is a diagram (part 1) illustrating a second method for adjusting the resistance value of a strain gauge. [Figure 5] This is a diagram (part 2) illustrating a second method for adjusting the resistance value of a strain gauge. [Figure 6] This diagram illustrates the adjustment patterns for adjusting the resistance value of a strain gauge. [Figure 7] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 8] This is a plan view illustrating a strain gauge according to a modified example 1 of the first embodiment. [Figure 9] This is a plan 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, 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. Note that Figures 1 and 2 show strain gauge 1 before adjusting the resistance value.

[0011] Referring to Figures 1 and 2, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, an electrode 50, a resistance adjustment section 60, and a cover layer 70. The cover layer 70 is provided as needed. In Figure 1, for convenience, only the outer edge of the cover layer 70 is shown with a dashed line. First, we will explain in detail each part that constitutes the strain gauge 1.

[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 that serves as a base layer for forming a resistor 30 or the like. The base material 10 has flexibility. A strain generating body may be joined to the lower surface side of the base material 10 via an adhesive layer or the like. 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. In view of the strain transmission from the surface of the strain generating body to the sensing portion 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 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] Examples of materials other than the resin of the base material 10 include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite-based ceramics (CaTiO3, BaTiO3). In addition to the above-mentioned crystalline materials, amorphous glass or the like may also be used as the material of the base material 10. Also, as the material of the base material 10, metals such as aluminum, aluminum alloy (duralumin), and titanium may be used. When a metal is used, an insulating film is provided on the metal base material 10.

[0017] The resistor 30 is a thin film formed in a predetermined pattern on 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 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 in a high-density matte pattern.

[0018] The resistor 30 includes a plurality of elongated portions and a plurality of folded-back portions. In the resistor 30, the plurality of elongated portions are juxtaposed with their longitudinal directions oriented in the first direction (the X direction in the example of FIG. 1). Then, the plurality of folded-back portions connect the ends of adjacent elongated portions among the plurality of elongated portions alternately to connect each elongated portion in series. As a result, the resistor 30 has a structure that is folded back 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 direction in the example of FIG. 1).

[0019] In the resistor 30, the end on the X− side of the elongated portion located on the far Y+ side is bent in the Y+ direction and reaches one end 30e1 in the grid width direction of the resistor 30. Also, the end on the X− side of the elongated portion located on the far Y− side is bent in the Y− direction and reaches the other end 30e2 in the grid direction of the resistor 30. 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 in the grid width direction of the resistor 30 and each electrode 50.

[0020] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. Examples of the material containing Cr include, for example, a Cr mixed-phase film. Examples of the material containing Ni include, for example, Cu-Ni (copper nickel). Examples of the material containing both Cr and Ni include, for example, Ni-Cr (nickel chromium).

[0021] 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.

[0022] 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.

[0023] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of the resistor 30 is preferably 10 μm or more and 100 μm or less. More specifically, the width of the resistor 30 is preferably 10 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0024] 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).

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The wiring 40 is provided on the base material 10. The wiring 40 is electrically connected to the resistor 30 and the electrode 50. The wiring 40 can have any width and any length. Furthermore, the wiring 40 is not limited to a straight line and can have any pattern. In Figure 1, for convenience, the wiring 40 and the electrode 50 are shown with a matte pattern that is less dense than the resistor 30.

[0030] 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 layer of metal with low resistance, such as copper, or a layer of metal with good solderability, such as gold, may be laminated on the upper surface of the electrode 50.

[0031] Although the resistor 30, wiring 40, and electrode 50 are given different designations for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, wiring 40, and electrode 50 have approximately the same thickness.

[0032] The resistance adjustment section 60 is electrically connected to the resistor 30 and the wiring 40. The resistance adjustment section 60 includes a first portion 61 laminated on the wiring 40 and a second portion 62 extending from the first portion 61 and connected in parallel with the resistor 30. The second portion 62 includes trim portions 62a to 62g for adjusting the resistance value of the resistor 30 by cutting it with a laser or the like. Each of the trim portions 62a to 62g is connected in parallel with one of the folded portions of the resistor 30. For convenience, in Figure 1, the resistance adjustment section 60 is shown with a denser textured surface than the resistor 30.

[0033] The material for the resistance adjustment section 60 can be selected to have a lower volume resistivity than the resistor 30 and the wiring 40. 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 layering any of these metals, alloys, or compounds. It is particularly preferable to use Cu, Cu alloys, Al, Ag, Au, CrMn, etc., as the material for the resistance adjustment section 60. The thickness of the resistance adjustment section 60 is not particularly limited and can be appropriately selected according to the purpose. The thickness of the resistance adjustment section 60 can be, for example, about 0.5 μm to 5 μm.

[0034] Note that the stacking order of the resistor 30 and wiring 40 and the resistance adjustment section 60 may be reversed. For example, the resistance adjustment section 60 may be formed on the upper surface 10a of the base material 10, and the resistor 30 or wiring 40, which is made of a material with a higher volume resistivity than the resistance adjustment section 60, may be stacked on top of a part of the resistance adjustment section 60.

[0035] The cover layer 70 is a protective layer formed on the substrate 10. The cover layer 70 is provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and the resistance adjustment part 60 and expose the electrodes 50. The cover layer 70 may also cover the wiring 40. Examples of materials for the cover layer 70 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 70 may also contain fillers or pigments. Alternatively, inorganic materials such as SiO2 or water glass may be used as the material for the cover layer 70. The thickness of the cover layer 70 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 70 can be about 2 μm to 30 μm. By providing the cover layer 70, mechanical damage to the resistor 30 can be suppressed. In addition, by providing the cover layer 70, the resistor 30 can be protected from moisture and the like.

[0036] [Method for adjusting resistance value] There are two methods for adjusting the resistance value of the strain gauge 1: a first method in which a high-resistance portion is formed by irradiating the first portion 61 with laser light, and a second method in which one or more of the trim portions 62a to 62g of the second portion 62 are cut by irradiating them with laser light. Either the first method or the second method may be performed, or both may be performed.

[0037] (Method 1) First, let's describe the first method. Figure 3 illustrates the first method for adjusting the resistance value of a strain gauge.

[0038] First, a strain gauge 1 is prepared, which includes a base material 10, a resistor 30 formed on the base material 10, wiring 40 formed on the base material 10 and electrically connected to the resistor 30, a resistance adjustment section 60 electrically connected to the resistor 30 and the wiring 40, and a cover layer 70 covering the resistor 30 and the resistance adjustment section 60 (step of preparing the strain gauge). The strain gauge 1 may be prepared by manufacturing part or all of it oneself, or by obtaining a finished product such as a commercially available product.

[0039] After preparing the strain gauge 1, a laser beam is shone onto a predetermined area of ​​the resistance adjustment section 60 through the cover layer 70 (the laser beam shone step). Specifically, as shown above the arrow in Figure 3, the laser beam L is shone onto the first portion 61 of the resistance adjustment section 60 through the cover layer 70 from above the cover layer 70.

[0040] In the step of irradiating with laser light, it is preferable to irradiate with laser light L such that the focal point of the laser light L is located deeper than the upper surface of the cover layer 70 in order to avoid damaging the cover layer 70. Furthermore, in order to efficiently heat the resistance adjustment section 60, it is preferable to irradiate with laser light L such that the focal point of the laser light L is located on the upper surface of the resistance adjustment section 60 (i.e., the upper surface of the first section 61).

[0041] By scanning with the laser beam L, the wiring 40 and the resistance adjustment section 60 are heated in the scanned area. As a result, as shown below the arrow in Figure 3, a high-resistance section 45 is formed near the boundary between the wiring 40 and the resistance adjustment section 60, where the materials constituting the wiring 40 and the materials constituting the resistance adjustment section 60 are mutually diffused. The thickness of the high-resistance section 45 can be adjusted by the irradiation time of the laser beam.

[0042] The laser used to form the high-resistance section 45 is preferably capable of irradiating laser light with a wavelength that easily penetrates the resin cover layer 70 and is easily absorbed by the resistance adjustment section 60. An example of such a laser is a YAG laser with a near-infrared wavelength.

[0043] The high-resistance section 45 is provided to adjust the resistance of the resistor 30 and wiring 40 connected between the pair of electrodes 50. The high-resistance section 45 has a higher volume resistivity than the resistance adjustment section 60. The high-resistance section 45 may have a lower volume resistivity than the wiring 40. The high-resistance section 45 is an interdiffusion region formed near the boundary between the wiring 40 and the resistance adjustment section 60. Here, the interdiffusion region is a region in which the material constituting the wiring 40 and the material constituting the resistance adjustment section 60 have diffused with each other. In the interdiffusion region, the boundary between the wiring 40 and the resistance adjustment section 60 does not need to be clearly defined.

[0044] The high-resistance section 45 includes, for example, an alloy of the wiring 40 and the resistance adjustment section 60. In other words, the high-resistance section 45 is formed from, for example, an alloy of the wiring 40 and the resistance adjustment section 60. For example, if the wiring 40 is a Cr multiphase film and the resistance adjustment section 60 is Cu, the high-resistance section 45 may include an alloy of these, which is a chromium-copper alloy (CrCu).

[0045] However, in the high-resistance section 45, if the materials constituting the wiring 40 and the materials constituting the resistance adjustment section 60 diffuse with each other and their volume resistivity becomes higher than that of the resistance adjustment section 60, then the wiring 40 and the resistance adjustment section 60 do not need to be alloyed.

[0046] By forming the high-resistance section 45, the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50 can be increased compared to before the high-resistance section 45 was formed. The larger the volume of the high-resistance section 45, the higher the resistance value of the resistor 30 and wiring 40 connected between the pair of electrodes 50.

[0047] Thus, in the first method, by irradiating the first part 61 with laser light, a high-resistance section 45 is formed in the wiring 40 and a part of the first part 61 in which the material constituting the wiring 40 and the material constituting the resistance adjustment section 60 are mutually diffused, thereby allowing the resistance values ​​of the resistor 30 and wiring 40 connecting the electrodes 50 to be adjusted.

[0048] (Second method) Next, the second method will be described. Figures 4 and 5 illustrate the second method for adjusting the resistance value of the strain gauge. Figures 4 and 5 show strain gauge 1 after the resistance value has been adjusted.

[0049] In the second method, the step of preparing the strain gauge is the same as in the first method. After preparing the strain gauge 1, a laser beam is shone onto a predetermined area of ​​the resistance adjustment unit 60 through the cover layer 70 (the step of irradiating with laser beam).

[0050] Specifically, similar to the upper side of the arrow in Figure 3, the laser beam L is irradiated from above the cover layer 70 through the cover layer 70 to one of the trim portions 62a to 62g of the second portion 62 of the resistance adjustment section 60. Here, as an example, the laser beam L is irradiated to the trim portion 62c. The preferred focal position of the laser beam L and the preferred wavelength of the laser beam are as described above.

[0051] When the trim portion 62c is irradiated with laser light L, the trim portion 62c is heated and cut. Figures 4 and 5 show the state after the trim portion 62c has been cut by laser irradiation. As a result, the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50 can be made higher than before the trim portion 62c was cut.

[0052] If you want to further increase the resistance of the resistor 30 and wiring 40 connecting the electrodes 50, you can irradiate them with laser light L in the same manner as described above and cut off one or more trim sections other than trim section 62c. Alternatively, you can cut off all of the trim sections 62a to 62g.

[0053] Furthermore, if all trim sections 62a to 62g are connected in parallel to the folded portion of the resistor 30, the strain gauge 1 will not be able to function as a strain gauge. Therefore, one of the trim sections 62a to 62g is always cut. In other words, in the strain gauge 1 after resistance adjustment, the second portion 62 of the resistance adjustment section 60 is connected in parallel to a part of the resistor 30, but not to the entirety of the resistor 30.

[0054] Thus, in the second method, by irradiating one or more of the trim portions 62a to 62g included in the second portion 62 with laser light, the trim portion irradiated with laser light is cut, thereby adjusting the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50.

[0055] In the first and second methods, the laser irradiation step may cause an oxide film to form on a portion of the metal constituting the resistance adjustment section 60. If the formation of such an oxide film is a problem, it is preferable to perform the laser irradiation step in an environment with a low oxygen concentration. For example, oxidation can be prevented by processing in an Ar atmosphere. This makes it possible to suppress the formation of an oxide film on a portion of the metal constituting the resistance adjustment section 60 due to laser irradiation.

[0056] (Adjustment pattern) The first method has three adjustment patterns: forming a high-resistance section in both of the two first parts 61, forming a high-resistance section in one of them, or not forming a high-resistance section in either.

[0057] The second method will be explained with reference to Figure 6. As shown in Figure 6, considering the symmetry of the resistor 30, the resistor 30 is divided into seven regions T1 to T7. Regions T1 and T7 have the same resistance, so they are combined into resistance region A. Regions T3 and T5 also have the same resistance, so they are combined into resistance region B. Regions T2, T4, and T6 also have the same resistance, so they are combined into resistance region C.

[0058] For example, in resistance region A, the resistance value of resistor 30 is the same whether the trim section 62a corresponding to region T1 is cut or the trim section 62g corresponding to region T7 is cut. Note that the corresponding trim section refers to one trim section connected in parallel with each region. Considering this, and organizing the adjustment patterns so that there are no overlapping adjustment patterns with the same resistance value, the adjustment patterns for the resistance value of resistor 30 that can be adjusted by cutting the trim sections are as follows.

[0059] (1) Cut one of the trim sections in each of the resistance ranges A, B, and C (3 ways) (2) Cut two or more trim sections in any one of the resistance ranges A, B, or C (4 ways) (3) Cut one trim section in each of the two resistance ranges A, B, and C (3 ways) (4) Cut one or more corresponding trim sections in any two of the resistance ranges A, B, and C, and cut two or more trim sections in at least one of the resistance ranges (12 ways) (5) Cut one or more trim sections in each of the resistance ranges A, B, and C (6 ways).

[0060] Thus, the adjustment patterns in the second method total 28, which is the sum of (1) to (5). By combining these with the three adjustment patterns available in the first method, it is possible to achieve even more adjustment patterns that allow for adjustment of the resistance value of the resistor 30.

[0061] Thus, in the strain gauge 1, even after forming the cover layer 70 that covers the resistor 30, the resistance values ​​of the resistor 30 and wiring 40 between the electrodes 50 can be adjusted. That is, the resistance values ​​of the resistor 30 and wiring 40 between the electrodes 50 can be designed in advance to be lower than the desired value, and then, in the manufacturing process of the strain gauge 1, after forming the cover layer 70, the resistance values ​​can be adjusted to a higher value by irradiating the cover layer 70 with laser light, using the first method and / or the second method.

[0062] In other words, the resistance values ​​of the resistors 30 and wiring 40 between the electrodes 50 may fluctuate during the formation process of the cover layer 70. However, by using the first method and / or the second method, even if the resistance values ​​of the resistors 30 and wiring 40 between the electrodes 50 fluctuate during the formation process of the cover layer 70, the resistance values ​​of the resistors 30 and wiring 40 between the electrodes 50 can be adjusted to a desired value. This improves the yield of the strain gauge 1.

[0063] In particular, in strain gauge 1, when the thickness of the resistor 30 is thin, the resistance value is prone to fluctuation due to physical factors such as the formation of the cover layer 70. Therefore, being able to adjust the resistance after forming the cover layer 70 is extremely useful.

[0064] Furthermore, with strain gauge 1, a greater number of adjustment patterns can be achieved by appropriately combining the first method and the second method for adjusting the resistance value of the resistor 30.

[0065] The above describes an example in which the strain gauge 1 has a cover layer 70. However, since the cover layer 70 is provided as needed, in the process of preparing the strain gauge, a strain gauge 1 having a base material 10, a resistor 30 formed on the base material 10, and wiring 40 formed on the base material 10 and electrically connected to the resistor 30 may be prepared. In this case, after preparing the strain gauge 1, in the process of irradiating with laser light in both the first method and the second method, the laser light is irradiated directly onto the resistance adjustment section 60 without going through other layers.

[0066] Alternatively, even if the strain gauge 1 has a cover layer 70, the resistance value may be adjusted before the cover layer 70 is formed. In this case as well, in both the first and second methods, the laser beam is irradiated directly onto the resistance adjustment section 60 without going through any other layers. After the cover layer 70 is formed, if the resistance value deviates from the desired value, in both the first and second methods, the resistance value can be adjusted again in the direction of increasing the resistance value by irradiating the resistance adjustment section 60 with laser beam through the cover layer 70.

[0067] Thus, in the strain gauge 1, the resistance value can be adjusted before and / or after the process of forming the cover layer 70. Of course, even if the manufacturing process of the strain gauge 1 does not include the process of forming the cover layer 70, the resistance value can be adjusted by directly irradiating the resistance adjustment unit 60 with laser light. In other words, the method for adjusting the resistance value of the strain gauge 1 allows for resistance adjustment regardless of the presence or absence of the cover layer 70.

[0068] [Method of manufacturing strain gauges] 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 those of the resistor 30, wiring 40, and electrode 50 described above.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Figure 7 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 7 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.

[0075] 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.

[0076] Next, a photosensitive resist is formed on the upper surface of metal layer A, and the resist is exposed and developed to pattern it into a planar shape similar to the resistor 30, wiring 40, and electrode 50 in Figure 1. Then, the resist is used as an etching mask, and the metal layer A exposed from the resist is removed by wet etching or the like. Next, by removing the resist, the resistor 30, wiring 40, and electrode 50 with the planar shape shown in Figure 1 can be formed.

[0077] Next, the resistance adjustment section 60 is formed. The resistance adjustment section 60 is formed to include a first portion 61 laminated on the wiring 40, and a second portion 62 extending from the first portion 61 and connected in parallel with a part of the resistor 30. The resistance adjustment section 60 can be formed by, for example, plating, sputtering, lift-off, or mask etching.

[0078] After forming the resistor 30, wiring 40, electrode 50, and resistance adjustment section 60, a cover layer 70 is formed on the upper surface 10a of the substrate 10. The cover layer 70 covers the resistor 30 and the resistance adjustment section 60, but the wiring 40 and electrode 50 may be exposed from the cover layer 70. For example, the cover layer 70 can be formed by laminating a semi-cured thermosetting insulating resin film onto the upper surface 10a of the substrate 10 so as to cover the wiring 40, electrode 50, and resistance adjustment section 60, while exposing the electrode 50, and then heating and curing the insulating resin film. Alternatively, if the cover layer 70 is made of an inorganic material, it may be formed using dipping, screen printing, sputtering, CVD, or the like.

[0079] After forming the cover layer 70, the resistance values ​​of the resistor 30 and wiring 40 between the electrodes 50 are adjusted to the desired value by the first method and / or the second method shown in Figures 3 to 5. The strain gauge 1 is completed through these steps. As mentioned above, the resistance values ​​may be adjusted before the cover layer 70 is formed, or both before and after the cover layer 70 is formed. Furthermore, as mentioned above, the resistance values ​​can be adjusted even if the manufacturing process of the strain gauge 1 does not include the step of forming the cover layer 70.

[0080] <Variations of the first embodiment> In the modified version of the first embodiment, an example is shown in which the region where the resistance adjustment unit is provided differs from that of the first embodiment. Note that in the modified version of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0081] Figure 8 is a plan view illustrating a strain gauge according to a modified example 1 of the first embodiment. As shown in the strain gauge 1A in Figure 8, in the resistance adjustment section 60, the first portion 61 may not be stacked on each of the two wires 40, but on only one of the wires 40. In this case, the second portion 62 of the resistance adjustment section 60 is connected in parallel with a part of the folded portion of the resistor 30. In the example of Figure 8, the second portion 62 includes three trim portions 62a, 62b, and 62c, but is not limited to this, and the second portion 62 can be formed to include one or more trim portions from the trim portions 62a to 62f shown in Figure 1, starting from the side closer to the first portion 61.

[0082] Figure 9 is a plan view illustrating a strain gauge according to a modified example 2 of the first embodiment. As shown in the strain gauge 1B in Figure 9, the first portion 61 of the resistance adjustment section 60 may be laminated with the entire wiring 40. This increases the area in which a high-resistance section can be formed by laser irradiation, thereby widening the adjustment range of the resistance value.

[0083] Furthermore, in strain gauge 1B, a resistance adjustment section 60, made of a material with a lower volume resistivity than the wiring 40, is laminated over the entire wiring 40. As a result, the laminated portion between the wiring 40 and the resistance adjustment section 60 has lower resistance than the resistor 30, which prevents the wiring 40 from functioning as a resistor. Consequently, the accuracy of strain detection by the resistor 30 can be improved.

[0084] In other words, by laminating a material with a lower volume resistivity than the resistor 30 onto the wiring 40, the effective sensing area of ​​the strain gauge 1 can be limited to the local region where the resistor 30 is formed. Therefore, the accuracy of strain detection by the resistor 30 can be improved.

[0085] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more using a Cr multiphase film as the resistor 30, reducing the resistance of the laminated portion between the wiring 40 and the resistance adjustment section 60 to be lower than that of the resistor 30, thereby limiting the effective sensitive area to the local region where the resistor 30 is formed, has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the laminated portion between the wiring 40 and the resistance adjustment section 60 to be lower than that of the resistor 30 also has the effect of reducing lateral sensitivity.

[0086] 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. For example, Modification 1 and Modification 2 of the first embodiment may be combined. [Explanation of symbols]

[0087] 1,1A,1B Strain gauge, 10 Base material, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1, 30e2 Termination, 40 Wiring, 45 High resistance section, 50 Electrode, 60 Resistance adjustment section, 61 First section, 62 Second section, 62a~62g Trim section, 70 Cover layer

Claims

1. A step of preparing a strain gauge having a base material, a resistor formed on the base material, wiring formed on the base material and electrically connected to the resistor, and a resistance adjustment part electrically connected to the resistor and the wiring, The process includes the step of irradiating the resistance adjustment section with laser light, The resistance adjustment section includes a first portion stacked on the wiring, and a second portion extending from the first portion and connected in parallel with a part of the resistor. A method for adjusting the resistance value of a strain gauge, wherein the resistance adjustment section is formed from a material with a lower volume resistivity than the wiring.

2. The method for adjusting the resistance value of a strain gauge according to claim 1, wherein in the step of irradiating the first portion with laser light, a high-resistance portion is formed in which the material constituting the wiring and the material constituting the resistance adjustment portion are mutually diffused by the irradiation of the first portion with laser light.

3. The method for adjusting the resistance value of a strain gauge according to claim 2, wherein the high-resistance section includes an alloy of the wiring and the resistance adjustment section.

4. A method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 3, wherein in the step of irradiating the second portion with laser light, the second portion is cut by irradiating the second portion with laser light.

5. The resistor includes a plurality of elongated portions arranged side by side with their longitudinal direction facing a first direction, and a folded portion that connects the ends of adjacent elongated portions in an alternating manner to connect each of the elongated portions in series. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 4, wherein the second part includes a trim portion connected in parallel with the folded portion.

6. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 5, wherein in the step of irradiating with laser light, the laser light is irradiated directly onto the resistance adjustment section without passing through any other layers.

7. The process includes forming a protective layer that covers the resistor and the resistance adjustment section. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 5, wherein in the step of irradiating with laser light, the laser light is irradiated to the resistance adjustment part through the protective layer.

8. The method for adjusting the resistance value of a strain gauge according to claim 7, wherein in the step of irradiating with laser light, the laser light is irradiated such that the focal point of the laser light is located deeper than the upper surface of the protective layer.

9. A method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 8, wherein in the step of irradiating with laser light, the laser light is irradiated such that the focal point of the laser light is located on the upper surface of the resistance adjustment part.

10. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 9, wherein the metal constituting the resistance adjustment section is copper or a copper alloy.

11. The resistor and the wiring are made of Cr, CrN, and Cr ２ A method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 10, wherein the strain gauge is formed from a film containing N.

12. Substrate and A resistor formed on the aforementioned substrate, Wiring formed on the substrate and electrically connected to the resistor, It has a resistance adjustment unit that is electrically connected to the resistor and the wiring, The resistance adjustment section includes a first portion stacked on the wiring, and a second portion extending from the first portion and connected in parallel with a part of the resistor. The resistance adjustment section is a strain gauge formed from a material with a lower volume resistivity than the wiring.

13. The strain gauge according to claim 12, wherein a high-resistance portion is formed in the wiring and a part of the first portion, in which the material constituting the wiring and the material constituting the resistance adjustment portion are mutually diffused.

14. The strain gauge according to claim 13, wherein the high-resistance section includes an alloy of the wiring and the resistance adjustment section.

15. The resistor includes a plurality of elongated portions arranged side by side with their longitudinal direction facing a first direction, and a folded portion that connects the ends of adjacent elongated portions in an alternating manner to connect each of the elongated portions in series. The strain gauge according to any one of claims 12 to 14, wherein the second portion includes a trim portion connected in parallel with the folded portion.

16. A strain gauge according to any one of claims 12 to 15, comprising a protective layer formed on the substrate and covering the resistor and the resistance adjustment portion.

17. The strain gauge according to any one of claims 12 to 16, wherein the metal constituting the resistance adjustment section is copper or a copper alloy.

18. The resistor and the wiring are made of Cr, CrN, and Cr ２ A strain gauge according to any one of claims 12 to 17, formed from a film containing N.

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