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 a resistance adjustment part formed on the substrate; and a step of irradiating the resistance adjustment part with a laser beam. The resistance adjustment part includes a plurality of grid resistances connected in series with the resistor, and a trim resistance connected in parallel with a series circuit including the adjacent two grid resistances. The trim resistance includes a first resistance part, and a second resistance part laminated on a part of the first resistance part. The grid resistances and the first resistance part are formed of the same material as the resistor, and the second resistance part is formed of a material having a lower volume resistivity than the first resistance part.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 is known that 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 a wiring, for example. Further, the strain gauge includes a protective layer on the base material that covers the resistor and the 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 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, and a resistance adjustment section formed on the base material; and irradiating the resistance adjustment section with laser light, wherein the resistance adjustment section includes a plurality of grid resistors connected in series with the resistor, and a trim resistor connected in parallel to a series circuit including two adjacent grid resistors, the trim resistor includes a first resistance section and a second resistance section laminated on a part of the first resistance section, the grid resistor and the first resistance section are formed from the same material as the resistor, and the second resistance section is formed from a material with a lower volume resistivity than the first resistance section. re , In the step of irradiating with laser light, the irradiation of the second resistive portion with laser light causes the material constituting the first resistive portion and the material constituting the second resistive portion to diffuse with each other, forming a high-resistance portion. . [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 first method for adjusting the resistance value of a strain gauge. [Figure 5] This diagram illustrates a second method for adjusting the resistance value of a strain gauge. [Figure 6] This is a cross-sectional view (part 3) illustrating a strain gauge according to 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. Figures 1 to 3 show strain gauge 1 before the resistance value is adjusted.

[0011] Referring to Figures 1 to 3, 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 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 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 as a fine-patterned texture with high density.

[0018] The resistor 30 includes a plurality of elongated portions and a plurality of folded portions. In the resistor 30, the plurality of elongated portions are juxtaposed with their longitudinal directions oriented in the first direction (the X direction in the example of FIG. 1). And the plurality of folded portions connect the ends of the adjacent elongated portions among the plurality of elongated portions alternately to connect each elongated portion in series. Thereby, the resistor 30 has a structure that is folded in a zigzag as a whole. The longitudinal direction of the plurality of elongated portions becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the Y direction in the example of FIG. 1). However, as will be described later, a resistance adjusting portion 60 is inserted between the resistors 30.

[0019] In the resistor 30, the end portion 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 portion 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 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. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[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 substrate 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 be arranged in any pattern. In the example in Figure 1, the width of the wiring 40 is narrower on the resistor 30 side and wider towards the electrode 50 side, but this is just an example, and for example, the width of the wiring 40 may be constant.

[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 inserted into the pattern of the resistor 30. The resistance adjustment section 60 includes grid resistors R1, R2, R3, and R4 connected in series with the resistor 30. The resistance adjustment section 60 also includes trim resistors Ra, Rb, and Rc. The grid resistors R1 to R4 have different resistance values. The trim resistors Ra to Rc also have different resistance values. Furthermore, the resistance adjustment section 60 includes connecting sections x1, x2, x3, x4, and x5 that connect two or more of the resistor 30, each grid resistor, and / or each trim resistor. Thus, the resistance adjustment section 60 includes multiple grid resistors and multiple trim resistors. Note that the number of grid resistors and trim resistors in the resistance adjustment section 60, and the way in which the grid resistors and trim resistors are connected, are not limited to the example in Figure 1.

[0033] The connecting sections x1 and x5 are the ends of the resistance adjustment section 60, and a pattern connecting connecting section x1 and connecting section x5 is inserted into the resistor 30 to constitute the resistance adjustment section 60. The grid resistor R1 connects connecting section x1 and connecting section x2. The grid resistor R2 connects connecting section x2 and connecting section x3. The grid resistor R3 connects connecting section x3 and connecting section x4. The grid resistor R4 connects connecting section x4 and connecting section x5. The trim resistor Ra connects connecting section x1 and connecting section x3. The trim resistor Rb connects connecting section x2 and connecting section x4. The trim resistor Rc connects connecting section x3 and connecting section x5.

[0034] In other words, the grid resistors R1 to R4 and the connecting parts x1 to x5 are connected in series with the resistor 30. The trim resistor Ra is connected in parallel with the series circuit including the adjacent grid resistors R1 and R2. The trim resistor Rb is connected in parallel with the series circuit including the two adjacent grid resistors R2 and R3. The trim resistor Rc is connected in parallel with the series circuit including the adjacent grid resistors R3 and R4.

[0035] As shown in Figure 3, the grid resistors R1 to R4 and the connecting portions x1 to x5 are formed from the first resistor portion 31. In contrast, the trim resistors Ra to Rc have a laminated structure that includes the first resistor portion 31 and a second resistor portion 32 laminated on a part of the first resistor portion 31. Specifically, the trim resistors Ra to Rc include a folded portion and a connecting portion that connects the folded portion and the connecting portion, with the second resistor portion 32 laminated on the first resistor portion 31 that constitutes the folded portion. The first resistor portion 31 is formed from the same material as the resistor 30 and has the same layer structure as the resistor 30.

[0036] The material for the second resistive section 32 can be selected to have a lower volume resistivity than the resistor 30 and the first resistive section 31. Examples of such materials include Cu, Ni, Al, Ag, Au, Pt, alloys of any of these metals, compounds of any of these metals, or laminated films obtained by appropriately stacking any of these metals, alloys, or compounds. In particular, it is preferable to use Cu, Cu alloys, Al, Ag, Au, CrMn, etc. as the material for the second resistive section 32. The thickness of the second resistive section 32 is not particularly limited and can be appropriately selected according to the purpose. The thickness of the second resistive section 32 can be, for example, about 0.5 μm to 5 μm.

[0037] Note that the stacking order of the first resistive section 31 and the second resistive section 32 may be reversed. For example, the second resistive section 32 may be formed on the upper surface 10a of the base material 10, and the first resistive section 31, which is made of a material with a higher volume resistivity than the second resistive section 32, may be stacked on top of the second resistive section 32.

[0038] 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 section 60 and expose at least a portion of the electrode 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 and the resistance adjustment section 60 can be suppressed. Furthermore, by providing the cover layer 70, the resistor 30 and the resistance adjustment unit 60 can be protected from moisture and other elements.

[0039] [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 section is formed by irradiating the second resistance section 32 with laser light, and a second method in which one or more of the trim sections Ra to Rc are cut by irradiating them with laser light. Either the first method or the second method may be performed, or both may be performed.

[0040] (Method 1) First, let's describe the first method. Figure 4 illustrates the first method for adjusting the resistance value of a strain gauge.

[0041] 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 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.

[0042] After preparing the strain gauge 1, as shown above the arrow in Figure 4, a laser beam L is irradiated from above the cover layer 70, through the cover layer 70, onto one or more of the second resistance sections 32 of the trim resistors Ra~Rc of the resistance adjustment section 60 (laser beam irradiation step). In Figure 4, as an example, the irradiation of the second resistance section 32 of the trim resistor Rb with laser beam L is shown.

[0043] In the process of irradiating with laser light, it is preferable to irradiate the 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 the 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.

[0044] By scanning with the laser beam L, the second resistive portion 32 of the trim resistor Rb is heated in the scanned area. As a result, as shown below the arrow in Figure 4, a high-resistance portion 35 is formed near the boundary between the first resistive portion 31 and the second resistive portion 32 of the trim resistor Rb, where the materials constituting the first resistive portion 31 and the materials constituting the second resistive portion 32 are mutually diffused. The thickness of the high-resistance portion 35 can be adjusted by the irradiation time of the laser beam.

[0045] The laser used to form the high-resistance portion 35 is preferably capable of irradiating laser light with a wavelength that easily penetrates the resin cover layer 70 and is easily absorbed by the second resistance portion 32. An example of such a laser is a YAG laser with a near-infrared wavelength.

[0046] The high-resistance section 35 is provided to adjust the resistance value of the resistor 30 and wiring 40 connected between the pair of electrodes 50. The high-resistance section 35 has a higher volume resistivity than the second resistance section 32. The high-resistance section 35 may have a lower volume resistivity than the first resistance section 31. The high-resistance section 35 is an interdiffusion region formed near the boundary between the first resistance section 31 and the second resistance section 32. Here, the interdiffusion region is a region in which the material constituting the first resistance section 31 and the material constituting the second resistance section 32 have diffused with each other. In the interdiffusion region, the boundary between the first resistance section 31 and the second resistance section 32 does not need to be clearly defined.

[0047] The high-resistance section 35 includes, for example, an alloy of the first resistance section 31 and the second resistance section 32. In other words, the high-resistance section 35 is formed from, for example, an alloy of the first resistance section 31 and the second resistance section 32. For example, if the first resistance section 31 is a Cr multiphase film and the second resistance section 32 is Cu, the high-resistance section 35 can include an alloy of these, which is a chromium-copper alloy (CrCu).

[0048] However, in the high-resistance section 35, if the material constituting the first resistance section 31 and the material constituting the second resistance section 32 diffuse with each other and the volume resistivity becomes higher than that of the second resistance section 32, then the first resistance section 31 and the second resistance section 32 do not need to be alloyed.

[0049] By forming the high-resistance section 35, the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50 can be increased compared to before the high-resistance section 35 was formed. The larger the volume of the high-resistance section 35, the higher the resistance value of the resistor 30 and wiring 40 connected between the pair of electrodes 50.

[0050] Thus, in the first method, by irradiating the second resistance section 32 of the resistance adjustment section 60 with laser light, a high-resistance section is formed in a part of the first resistance section 31 and the second resistance section 32, where the material constituting the first resistance section 31 and the material constituting the second resistance section 32 are mutually diffused, thereby adjusting the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50.

[0051] (Second method) Next, the second method will be explained. Figure 5 illustrates the second method for adjusting the resistance value of the strain gauge. Note that Figure 5 shows strain gauge 1 after the resistance value has been adjusted.

[0052] 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 L is irradiated from above the cover layer 70, through the cover layer 70, onto one or more of the first resistance portions 31 of the trim resistance Ra~Rc of the resistance adjustment portion 60 (the step of irradiating with laser beam). The preferred focal position of the laser beam L and the preferred wavelength of the laser beam are as described above.

[0053] By irradiating one or more first resistance portions 31 of the trim resistors Ra~Rc of the resistance adjustment unit 60 with laser light L, the first resistance portions 31 are heated and cut. Figure 5 shows, as an example, the cutting of region C of the first resistance portion 31 of the trim resistor Rc by irradiating it with laser light L. This makes it possible to increase the resistance value of the resistor 30 and wiring 40 connecting the electrodes 50 compared to before the trim resistor Rc was cut. In addition, in the trim resistor Rc, the stacked portion of the first resistance portion 31 and the second resistance portion 32 may be cut instead of region C. In this case, after a high-resistance portion is formed near the boundary between the first resistance portion 31 and the second resistance portion 32 by laser light irradiation, the stacked portion of the first resistance portion 31 and the second resistance portion 32 can be cut by continuing to irradiate with laser light.

[0054] If you want to further increase the resistance of the resistor 30 and wiring 40 connecting the electrodes 50, you can do so by irradiating them with laser light L in the same manner as described above and disconnecting one or more trim resistors other than trim resistor Rc. You can also disconnect all trim resistors Ra to Rc.

[0055] Thus, in the second method, by irradiating one or more of the trim resistors Ra to Rc included in the resistance adjustment unit 60 with laser light, the trim resistor irradiated with laser light is disconnected, thereby adjusting the resistance values ​​of the resistor 30 and wiring 40 connecting the electrodes 50.

[0056] In the first and second methods, the step of irradiating with laser light may cause an oxide film to form on a portion of the metal constituting the second resistive part 32 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 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 second resistive part 32 due to the irradiation of laser light.

[0057] (Adjustment pattern) The adjustment patterns for the resistance adjustment unit 60, when combining the first method and the second method, are as follows: (1) to (4) are adjustment patterns when using only the second method. (5) to (8) are adjustment patterns when using only the first method. (9) and (10) are adjustment patterns when using the first method and the second method in combination.

[0058] (1) Do not disconnect any of the trim resistors Ra, Rb, and Rc (1 way) (2) Disconnect one of the trim resistors Ra, Rb, and Rc (3 ways) (3) Disconnect any two of the trim resistors Ra, Rb, and Rc (3 ways) (4) Disconnect all trim resistors Ra, Rb, and Rc (1 way) (5) Form a high-resistance section in one of the trim resistors Ra, Rb, and Rc (3 ways) (6) Form high-resistance sections in any two of the trim resistors Ra, Rb, and Rc (3 ways) (7) Form high-resistance sections in all trim resistors Ra, Rb, and Rc (1 way) (8) Disconnect one of the trim resistors Ra, Rb, and Rc, and create a high-resistance section in one of the trim resistors Ra, Rb, and Rc (6 ways) (9) Disconnect one of the trim resistors Ra, Rb, and Rc, and create high-resistance sections in any two of the trim resistors Ra, Rb, and Rc (3 ways) (10) Cut any two of the trim resistors Ra, Rb, and Rc, and form a high-resistance section in any one of the trim resistors Ra, Rb, and Rc (3 ways).

[0059] Thus, by using either or both of the first and second methods, 27 different adjustment patterns can be achieved.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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 a resistance adjustment part 60 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 to the trim resistor of the resistance adjustment part 60 without going through other layers.

[0065] 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.

[0066] 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.

[0067] [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, the first resistive part 31, the wiring 40, and the electrode 50. Therefore, the material and thickness of metal layer A are the same as the material and thickness of the resistor 30, etc., as described above.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Figure 6 is a cross-sectional view (part 3) illustrating a strain gauge according to the first embodiment. Figure 6 shows the cross-sectional shape of the strain gauge 1 when a functional layer 20 is provided as a base layer for the resistor 30, first resistance section 31, wiring 40, and electrode 50.

[0074] 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 first resistive section 31, the wiring 40, and the electrodes 50. However, the planar shapes of the functional layer 20 and the resistor 30, the first resistive section 31, 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 a different shape from the planar shapes of the resistor 30, the first resistive section 31, the wiring 40, and the electrodes 50. In this case, the functional layer 20 may be formed as a solid layer over the region where the resistor 30, the first resistive section 31, the wiring 40, and the electrodes 50 are formed. Alternatively, the functional layer 20 may be formed as a solid layer over the entire upper surface of the substrate 10.

[0075] Next, a second resistance section 32 is formed on the upper surface of the metal layer A, and a resistance adjustment section 60 is formed. The second resistance section 32 can be formed, for example, by photolithography.

[0076] Specifically, first, a seed layer is formed to cover the upper surface of the metal layer A, for example, by sputtering or electroless plating. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and exposure and development are performed to create an opening that exposes the region in which the second resistive section 32 will be formed. As the resist, for example, a dry film resist can be used.

[0077] Next, for example, a second resistive portion 32 is formed on the seed layer exposed within the opening by an electroplating method using the seed layer as the power supply path. The electroplating method is preferable because it has a high cycle time and can form a low-stress electroplated layer as the second resistive portion 32. By making the thick electroplated layer low-stress, warping of the strain gauge 1 can be prevented. The second resistive portion 32 may also be formed by an electroless plating method.

[0078] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0079] 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, first resistor 31, 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, first resistor 31, wiring 40, and electrode 50 with the planar shape shown in Figure 1 can be formed. In addition, a resistance adjustment section 60 can be formed by stacking the second resistor 32 on the folded portion of the first resistor 31.

[0080] 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, wiring 40, and resistance adjustment section 60, but the 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.

[0081] 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 4 and 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.

[0082] 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]

[0083] 1 Strain gauge, 10 Substrate, 10a Top surface, 20 Functional layer, 30 Resistor, 30e1, 30e2 Termination, 31 First resistance section, 32 Second resistance section, 35 High resistance section, 40 Wiring, 50 Electrode, 60 Resistance adjustment section, 70 Cover layer, R1~R4 Grid resistors, Ra~Rc Trim resistors, x1~x5 Connecting section

Claims

1. A step of preparing a strain gauge having a base material, a resistor formed on the base material, and a resistance adjustment part formed on the base material, The process includes the step of irradiating the resistance adjustment section with laser light, The resistance adjustment section includes a plurality of grid resistors connected in series with the resistor, and a trim resistor connected in parallel to a series circuit including two adjacent grid resistors. The trim resistor includes a first resistive section and a second resistive section laminated on a part of the first resistive section. The grid resistor and the first resistor are formed from the same material as the resistor. The second resistive portion is formed from a material with a lower volume resistivity than the first resistive portion. A method for adjusting the resistance value of a strain gauge, wherein in the step of irradiating the second resistance portion with laser light, a high-resistance portion is formed in which the material constituting the first resistance portion and the material constituting the second resistance portion are mutually diffused by the irradiation of the second resistance portion with laser light.

2. A step of preparing a strain gauge having a base material, a resistor formed on the base material, and a resistance adjustment part formed on the base material, The process includes the step of irradiating the resistance adjustment section with laser light, The resistance adjustment section includes a plurality of grid resistors connected in series with the resistor, and a trim resistor connected in parallel to a series circuit including two adjacent grid resistors. The trim resistor includes a first resistive section and a second resistive section laminated on a part of the first resistive section. The grid resistor and the first resistor are formed from the same material as the resistor. The second resistive portion is formed from a material with a lower volume resistivity than the first resistive portion. A method for adjusting the resistance value of a strain gauge, wherein in the step of irradiating the trim resistor with laser light, the trim resistor is cut by irradiating the trim resistor with laser light.

3. The method for adjusting the resistance value of a strain gauge according to claim 1, wherein the high-resistance portion includes an alloy of the first resistance portion and the second resistance portion.

4. The 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 with laser light, the laser light is irradiated directly onto the trim resistor without passing through any other layers.

5. 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 3, wherein in the step of irradiating with laser light, the laser light is irradiated onto the trim resistor through the protective layer.

6. The method for adjusting the resistance value of a strain gauge according to claim 5, 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.

7. A method for adjusting the resistance value of a strain gauge according to any one of claims 1 to 6, 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 trim resistor.

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

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

10. Substrate and A resistor formed on the aforementioned substrate, The substrate has a resistance adjustment section formed on it, The resistance adjustment section includes a plurality of grid resistors connected in series with the resistor, and a trim resistor connected in parallel to a series circuit including two adjacent grid resistors. The trim resistor includes a first resistive section and a second resistive section laminated on a part of the first resistive section. The grid resistor and the first resistor are formed from the same material as the resistor. The second resistive portion is formed from a material with a lower volume resistivity than the first resistive portion. A strain gauge in which a high-resistance portion is formed in the trim resistor, where the material constituting the first resistance portion and the material constituting the second resistance portion are mutually diffused.

11. Substrate and A resistor formed on the aforementioned substrate, The substrate has a resistance adjustment section formed on it, The resistance adjustment unit includes a plurality of grid resistors connected in series with the resistor, a trim resistor connected in parallel to a series circuit including two adjacent grid resistors, and one or more disconnected trim resistors. The trim resistor and the cut trim resistor include a first resistive portion and a second resistive portion laminated on a part of the first resistive portion. The cut trim resistor has the first resistance portion cut off. The grid resistor and the first resistor are formed from the same material as the resistor. A strain gauge wherein the second resistive portion is formed from a material having a lower volume resistivity than the first resistive portion.

12. The strain gauge according to claim 10, wherein the high-resistance portion includes an alloy of the first resistance portion and the second resistance portion.

13. A strain gauge according to any one of claims 10 to 12, comprising a protective layer formed on the substrate and covering the resistor and the resistance adjustment portion.

14. The strain gauge according to any one of claims 10 to 13, wherein the metal constituting the second resistive portion is copper or a copper alloy.

15. The resistor and the first resistor are made of Cr, CrN, and Cr ２ A strain gauge according to any one of claims 10 to 14, formed from a film containing N.

Images