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, and wiring formed on the substrate and electrically connected with the resistor; and a step of irradiating the wiring with a laser beam. The wiring has a first metal layer, and a second metal layer laminated on the first metal layer. In the step of irradiating with the laser beam, the irradiation with the laser beam forms a high resistance part where a material forming the first metal layer and a material forming the second metal layer are diffused to each other.SELECTED DRAWING: Figure 4

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 is known which is attached to a measurement object to detect the strain of the measurement object. The strain gauge includes a resistor for detecting 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 on the base material for covering the resistor and wiring, for example (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 a protective layer, but the resistance value may vary 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, and wiring formed on the base material and electrically connected to the resistor; and irradiating the wiring with laser light, wherein the wiring has a first metal layer and a second metal layer laminated on the first metal layer, and in the step of irradiating with laser light, a high-resistance portion is formed in which the material constituting the first metal layer and the material constituting the second metal layer are mutually diffused by the irradiation of the laser light. [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 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 4] This diagram illustrates a method for adjusting the resistance value of a strain gauge according to the first embodiment. [Figure 5] This is a cross-sectional view (part 3) illustrating a strain gauge according to the first embodiment. [Figure 6] This is a plan view illustrating a strain gauge according to a modified example 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. Figure 3 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 1.

[0011] Referring to Figures 1 to 3, the strain gauge 1 comprises a base material 10, a resistor 30, wiring 40, electrodes 50, and a cover layer 60. The cover layer 60 is provided as needed. In Figure 1, for convenience, only the outer edge of the cover layer 60 is shown with a dashed line. First, we will explain in detail each part that makes up 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 component that serves as a base layer for forming the resistor 30, etc. The base material 10 is flexible. A strain-generating body may be joined to the lower surface 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 intended use of the strain gauge 1, etc. For example, the thickness of the base material 10 may be about 5 μm to 500 μm. However, from the viewpoint of strain transmission from the surface of the strain-generating body to the sensing part and dimensional stability against environmental changes, the thickness of the base material 10 is preferably in 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 PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, or polyolefin resin. Note that "film" refers to a flexible material with a thickness of approximately 500 μm or less.

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

[0016] Other materials for the substrate 10 besides resin include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3). In addition to the aforementioned crystalline materials, amorphous glass or the like may also be used as the material for the substrate 10. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 10. When a metal is used, an insulating film is provided on the metallic substrate 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 change in resistance. 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 has a structure in which a plurality of elongated portions are arranged at a predetermined interval with their longitudinal directions facing the same direction (the X direction in the example of FIG. 1), and the ends of adjacent elongated portions are alternately connected to form a zigzag shape as a whole when folded back. 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 most 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 most 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 to each electrode 50.

[0020] [[ID=XI]] 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). <H

[0021] Here, the Cr mixed - phase film is a film in which Cr, CrN, Cr2N, etc. are in a mixed phase. The Cr mixed - phase film may contain inevitable 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 substrate 10. The wiring 40 is electrically connected to the resistor 30 and the electrode 50. The wiring 40 has a first metal layer 41 and a second metal layer 42 laminated on the upper surface of the first metal layer 41. A high-resistance section 45 is formed in a part of the wiring 40. The wiring 40 is not limited to a straight line and can be in any pattern. The wiring 40 can also have any width and length. For convenience, in Figure 1, 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.

[0031] The electrode 50 has a first metal layer 51 and a second metal layer 52 laminated on the upper surface of the first metal layer 51. The first metal layer 51 is electrically connected to the ends 30e1 and 30e2 of the resistor 30 via the first metal layer 41 of the wiring 40. In plan view, the first metal layer 51 is formed in a substantially rectangular shape. The first metal layer 51 may be formed to the same width as the wiring 40.

[0032] Although the resistor 30, the first metal layer 41, and the first metal layer 51 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 30, the first metal layer 41, and the first metal layer 51 have approximately the same thickness. Similarly, although the second metal layer 42 and the second metal layer 52 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 42 and the second metal layer 52 have approximately the same thickness.

[0033] The second metal layer 42 and the second metal layer 52 may be formed integrally from the same material, or they may be formed from different materials. The material of the second metal layer 42 can be selected to have a lower volume resistivity than the resistor 30 (first metal layers 41 and 51). Examples of such materials include Cu, Ni, Al, Ag, Au, Pt, etc., or alloys of any of these metals, compounds of any of these metals, or laminated films obtained by appropriately stacking any of these metals, alloys, or compounds. In particular, it is preferable to use Cu, Cu alloys, Al, Ag, Au, CrMn, etc. as the material for the second metal layer 42. The thickness of the second metal layer 42 is not particularly limited and can be appropriately selected depending on the purpose. The thickness of the second metal layer 42 can be, for example, about 0.5 μm to 5 μm.

[0034] The second metal layer 52 is formed from a material with a lower volume resistivity than the resistor 30 (first metal layers 41 and 51). The material of the second metal layer 52 is not particularly limited as long as it has a lower volume resistivity than the resistor 30, and can be appropriately selected according to the purpose. For example, if the resistor 30 is a Cr multiphase film, the material of the second metal layer 52 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately stacked. The thickness of the second metal layer 52 is not particularly limited and may be appropriately determined according to the purpose of use of the strain gauge 1. For example, although it can be appropriately selected according to the purpose, the thickness of the second metal layer 52 can be about 0.5 μm to 5 μm.

[0035] The second metal layers 42 and 52 may be formed on a part of the upper surface of the first metal layers 41 and 51, or on the entire upper surface of the first metal layers 41 and 51. One or more other metal layers may be laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be a copper layer, and a gold layer may be laminated on top of the copper layer. Alternatively, the second metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on top of the copper layer. By making the uppermost layer of the electrode 50 a gold layer, the solder wettability of the electrode 50 can be improved. The high-resistance portion 45 constituting the wiring 40 will be described later.

[0036] Thus, the wiring 40 has a structure in which a second metal layer 42, made of a material with a lower volume resistivity than the first metal layer 41, is laminated on a first metal layer 41 made of the same material as the resistor 30. Therefore, the wiring 40 has lower resistance than the resistor 30, which prevents the wiring 40 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

[0037] In other words, by forming the wiring 40 using a material with a lower volume resistivity than the resistor 30, 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.

[0038] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 30, reducing the resistance of the wiring 40 to that of the resistor 30 and limiting the effective sensing area to the local region where the resistor 30 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 40 to that of the resistor 30 also has the effect of reducing lateral sensitivity.

[0039] Note that the stacking order of the first metal layers 41 and 51 and the second metal layers 42 and 52 may be reversed. For example, the second metal layers 42 and 52 may be formed on the upper surface 10a of the substrate 10, and the first metal layers 41 and 51, which are made of a material with a higher volume resistivity than the second metal layers 42 and 52, may be stacked on top of the second metal layers 42 and 52. In other words, the wiring 40 only needs to have the first metal layers 41 and 51 and the second metal layers 42 and 52 stacked on the first metal layers 41 and 51, and the stacking order of the first and second metal layers is arbitrary.

[0040] The cover layer 60 is a protective layer formed on the substrate 10. The cover layer 60 is provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and wiring 40 and expose 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 or pigments. Alternatively, inorganic materials such as SiO2 or water glass may be used as the material for the cover layer 60. 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.

[0041] [High resistance part] 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 second metal layer 42. The high-resistance section 45 may have a lower volume resistivity than the first metal layer 41. The high-resistance section 45 is an interdiffusion region formed near the boundary between the first metal layer 41 and the second metal layer 42. Here, the interdiffusion region is a region in which the material constituting the first metal layer 41 and the material constituting the second metal layer 42 have diffused with each other. In the interdiffusion region, the boundary between the first metal layer 41 and the second metal layer 42 does not need to be clearly defined.

[0042] The high-resistance portion 45 includes, for example, an alloy of the first metal layer 41 and the second metal layer 42. In other words, the high-resistance portion 45 is formed from, for example, an alloy of the first metal layer 41 and the second metal layer 42. For example, if the first metal layer 41 is a Cr multiphase film and the second metal layer 42 is Cu, the high-resistance portion 45 may include a chromium-copper alloy (CrCu), which is an alloy of these.

[0043] However, in the high-resistivity section 45, the first metal layer 41 and the second metal layer 42 do not need to be alloyed if the materials constituting the first metal layer 41 and the materials constituting the second metal layer 42 diffuse with each other and the volume resistivity becomes higher than that of the second metal layer 42.

[0044] By forming a high-resistance section 45 in a part of the wiring 40, the resistance value of the resistor 30 and the wiring 40 connecting the electrodes 50 can be increased compared to before the high-resistance section 45 was formed. In the wiring 40, the more the volume of the high-resistance section 45 increases, the higher the resistance value of the resistor 30 and the wiring 40 connected between the pair of electrodes 50 becomes.

[0045] Figure 4 illustrates a method for adjusting the resistance value of a strain gauge according to the first embodiment. 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, and a cover layer 60 formed on the base material 10 that covers the resistor 30 and the wiring 40 (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.

[0046] After preparing the strain gauge 1, a laser beam is shone onto a predetermined area of ​​the wiring 40 through the cover layer 60 (the laser beam shone step). Specifically, as shown above the arrow in Figure 4, the laser beam L is shone onto the second metal layer 42 of the wiring 40 through the cover layer 60 from above the cover layer 60.

[0047] 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 60 in order to avoid damaging the cover layer 60. Furthermore, in order to efficiently heat the second metal layer 42, 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 wiring 40 (i.e., the upper surface of the second metal layer 42).

[0048] By scanning with the laser beam L, the first metal layer 41 and the second metal layer 42 are heated in the scanned area. As a result, as shown below the arrow in Figure 4, a high-resistance region 45 is formed near the boundary between the first metal layer 41 and the second metal layer 42, where the materials constituting the first metal layer 41 and the materials constituting the second metal layer 42 are mutually diffused. The thickness of the high-resistance region 45 can be adjusted by the irradiation time of the laser beam.

[0049] The laser used to form the high-resistance portion 45 is preferably capable of irradiating laser light with a wavelength that easily penetrates the resin cover layer 60 and is easily absorbed by the second metal layer 42. An example of such a laser is a YAG laser with a near-infrared wavelength.

[0050] In the process of irradiating with laser light, an oxide film of the metal constituting the wiring 40 may form on a portion of the wiring 40 due to the irradiation of the laser light. If the formation of such an oxide film is a problem, it is preferable to perform the laser light irradiation process 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 of the metal constituting the wiring 40 on a portion of the wiring 40 due to the irradiation of laser light.

[0051] Thus, in the strain gauge 1, even after forming the cover layer 60 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 60, the resistance value can be adjusted to a higher value by forming a high-resistance section 45 in a part of the wiring 40 by irradiating it with laser light through the cover layer 60. At that time, the desired resistance value can be obtained by adjusting the volume of the high-resistance section 45.

[0052] 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 60. However, by using the method shown in Figure 4, 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 60, 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.

[0053] 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 60. Therefore, being able to adjust the resistance after forming the cover layer 60 is extremely useful.

[0054] Although the resistance of the wiring 40 increases by forming the high-resistance section 45, the overall resistance of the wiring 40 is lower than that of the resistor 30 because the high-resistance section 45 is formed only partially. Therefore, the effect of providing wiring 40 with lower resistance than the resistor 30 is not lost.

[0055] The above describes an example in which the strain gauge 1 has a cover layer 60. However, since the cover layer 60 is provided as needed, in the process of preparing the strain gauge, the strain gauge 1 may be prepared 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. In this case, after preparing the strain gauge 1, in the process of irradiating it with laser light, the laser light is irradiated directly onto the wiring 40 without going through other layers.

[0056] Alternatively, even if the strain gauge 1 has a cover layer 60, the resistance value may be adjusted before the cover layer 60 is formed. In this case as well, in the laser irradiation process, the laser light is irradiated directly onto the wiring 40 without going through any other layers. After the cover layer 60 is formed, if the resistance value deviates from the desired value, it is possible to adjust it again in the direction of increasing the resistance value by irradiating the wiring 40 with laser light through the cover layer 60.

[0057] Thus, in strain gauge 1, the resistance value can be adjusted before and / or after the process of forming the cover layer 60. Of course, even if the manufacturing process of strain gauge 1 does not include the process of forming the cover layer 60, the resistance value can be adjusted by directly irradiating the wiring 40 with laser light. In other words, the method for adjusting the resistance value of strain gauge 1 allows for resistance adjustment regardless of the presence or absence of the cover layer 60.

[0058] [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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Figure 5 is a cross-sectional view (part 3) illustrating a strain gauge according to the first embodiment. Figure 5 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.

[0065] 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.

[0066] Next, a second metal layer 42 and a second metal layer 52 are formed on the upper surface of metal layer A. The second metal layer 42 and the second metal layer 52 can be formed in a predetermined pattern, for example, by a well-known photolithography method.

[0067] Next, a photosensitive resist is formed on the upper surface of metal layer A, the upper surface of the second metal layer 42, and the upper surface of the second metal layer 52. The resist is then exposed and developed to pattern it into a planar shape similar to the resistor 30, wiring 40, and electrode 50 shown in Figure 1. The resist is then used as an etching mask, and 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.

[0068] After forming the resistor 30, wiring 40, and electrodes 50, a cover layer 60 is formed on the upper surface 10a of the substrate 10. The cover layer 60 covers the resistor 30 and wiring 40, but the electrodes 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 substrate 10 so as to cover the resistor 30 and wiring 40 and expose the electrodes 50, and then heating and curing the insulating resin film. Alternatively, if the cover layer 60 is made of an inorganic material, it may be formed using dipping, screen printing, sputtering, CVD, or the like.

[0069] After forming the cover layer 60, a high-resistance section 45 is formed in a part of the wiring 40 using the method shown in Figure 4, and the resistance values ​​of the resistor 30 between the electrodes 50 and the wiring 40 are adjusted to the desired value. Through these steps, the strain gauge 1 is completed. As mentioned above, the resistance value may be adjusted before the cover layer 60 is formed, or it may be adjusted before and after the cover layer 60 is formed. Also, as mentioned above, even if the manufacturing process of the strain gauge 1 does not include the step of forming the cover layer 60, the resistance value can still be adjusted.

[0070] The above description shows an example in which the wiring 40 connected to one of the pair of electrodes 50 has a high-resistance section 45, but it is not limited to this. For example, as shown in the strain gauge 1A in Figure 6, the wiring 40 connected to one of the pair of electrodes 50 may have a high-resistance section 45, and the wiring 40 connected to the other of the pair of electrodes 50 may have a high-resistance section 46. Alternatively, multiple high-resistance sections may be provided in the wiring 40 connected to one and / or the other of the pair of electrodes 50. By increasing the number of locations where high-resistance sections are provided in the wiring 40, it is possible to widen the range of resistance adjustment.

[0071] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of symbols]

[0072] 1,1A Strain gauge, 10 Base material, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1, 30e2 Termination, 40 Wiring, 50 Electrode, 41, 51 First metal layer, 42, 52 Second metal layer, 45, 46 High resistance section, 60 Cover layer

Claims

1. A step of preparing a strain gauge having a base material, a resistor formed on the base material, and wiring formed on the base material and electrically connected to the resistor, The process includes the step of irradiating the wiring with laser light, The wiring comprises a first metal layer and a second metal layer laminated on the first metal layer. A method for adjusting the resistance value of a strain gauge, wherein, in the step of irradiating with laser light, a high-resistance portion is formed in which the material constituting the first metal layer and the material constituting the second metal layer are mutually diffused by the irradiation of the laser light.

2. The method for adjusting the resistance value of a strain gauge according to claim 1, wherein in the step of irradiating with laser light, the laser light is irradiated directly onto the wiring without passing through any other layers.

3. The process includes forming a protective layer that covers the resistor and the wiring, The method for adjusting the resistance value of a strain gauge according to claim 1, wherein in the step of irradiating with laser light, the laser light is irradiated onto the wiring through the protective layer.

4. The method for adjusting the resistance value of a strain gauge according to claim 3, 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.

5. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 4, 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 wiring.

6. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 5, wherein the high-resistance portion includes an alloy of the first metal layer and the second metal layer.

7. The method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 6, wherein the metal constituting the second metal layer is copper or a copper alloy.

8. The resistor and the first metal layer 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 7, wherein the strain gauge is formed from a film containing N.

9. Substrate and A resistor formed on the aforementioned substrate, The substrate has a wire formed thereon and electrically connected to the resistor, The wiring comprises a first metal layer and a second metal layer laminated on the first metal layer. A strain gauge in which a high-resistance region is formed in a part of the wiring in which the material constituting the first metal layer and the material constituting the second metal layer are mutually diffused.

10. The strain gauge according to claim 9, comprising a protective layer formed on the substrate and covering the resistor and the wiring.

11. The strain gauge according to claim 9 or 10, wherein the high-resistance portion includes an alloy of the first metal layer and the second metal layer.

12. The strain gauge according to any one of claims 9 to 11, wherein the metal constituting the second metal layer is copper or a copper alloy.

13. The resistor and the first metal layer are made of Cr, CrN, and Cr ２ A strain gauge according to any one of claims 9 to 12, which is formed from a film containing N.

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