Strain gauge and method for manufacturing strain gauge

Abstract

To provide a strain gauge capable of suppressing deterioration of reliability, and a manufacturing method of the strain gauge.SOLUTION: The strain gauge includes a substrate, a resistor, and an insulating sheet, at least one of the first connection portion and the second connection portion has an extending portion extending inward from both ends of the sensing portion in the second direction, the insulating sheet has a first opening portion exposing the first connection portion and a second opening portion exposing the second connection portion, and the metal sheet extends to a position overlapping the extending portions of the first connection portion and the second connection portion. The end portions of the metal sheet on the two connection site sides are positioned in front of the edges of the first opening portion and the second opening portion on the sensing portion side when viewed from the sensing portion in the first direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a strain gauge and a method for manufacturing a strain gauge. [Background technology]

[0002] A known conventional strain gauge is described in, for example, Patent Document 1. The strain gauge described in Patent Document 1 includes a measurement grid (resistive element) arranged on a carrier foil, and a cover arranged on the measurement grid and having a first layer of insulating material and a second layer of metallic material. The measurement grid has a strip (sensitive part) with a wave-like shape and an exchange area (connection part) provided at the end of the strip. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-35808 Summary of the Invention [Problem to be solved by the invention]

[0004] In a strain gauge, if moisture (such as humidity) penetrates the substrate or is released from the substrate, the substrate may expand and / or contract. In this case, the resistor disposed on the substrate expands and contracts due to the expansion and / or contraction of the substrate, causing a change in the output of the strain gauge and potentially reducing the reliability of the strain gauge. Conventional strain gauges are designed to prevent moisture from penetrating the substrate by placing a cover over the strip. However, in conventional strain gauges, although the measurement grid strip is covered with a sheet, the substrate between the exchange area and the measurement grid is exposed. Therefore, conventional strain gauges may not be able to adequately prevent moisture from penetrating the substrate.

[0005] An object of one aspect of the present invention is to provide a strain gauge and a method for manufacturing the strain gauge that can suppress a decrease in reliability. [Means for solving the problem]

[0006] A strain gauge according to one aspect of the present invention comprises an insulating substrate, a resistor that is disposed on one main surface of the substrate and is conductive, and expands and contracts as the substrate deforms, a metal sheet that covers the one main surface of the substrate, and an insulating sheet that is located between the resistor and the metal sheet, wherein the resistor comprises a sensing portion that is formed to extend in a first direction while folding back, a first connection portion that is connected to one end of the sensing portion and has a connection point to which wiring to an external circuit is connected, and a second connection portion that is connected to the other end of the sensing portion and has a connection point to which wiring to an external circuit is connected, and the sensing portion and the two connection points are the first and second connection parts are arranged apart in the first direction, the connection point of the first connection part and the connection point of the second connection part are juxtaposed in a second direction intersecting the first direction, at least one of the first connection part and the second connection part has an extension part that extends inward beyond both ends of the sensing part in the second direction, the insulating sheet has a first opening that exposes the first connection part and a second opening that exposes the second connection part, the metal sheet extends to a position that overlaps the extension parts of the first and second connection parts, and the ends of the metal sheet on the two connection part sides are located in front of the edges of the first opening and the second opening on the sensing part side in the first direction when viewed from the sensing part.

[0007] In a strain gauge according to one aspect of the present invention, the metal sheet extends to a position overlapping the extending portions of the first and second connection portions, and the ends of the metal sheet on the two connection side are located in front of the edges of the first and second openings on the sensing part side in the first direction, as viewed from the sensing part. A metal sheet made of a metallic material is impermeable to moisture and can therefore prevent moisture from penetrating into the substrate. Therefore, in a strain gauge, by covering not only the sensing part but also the exposed substrate between the two connection points and the sensing part with a metal sheet, the exposed area of ​​the substrate around the resistor can be reduced. This prevents the strain gauge from expanding due to moisture penetration into the substrate and / or shrinking due to the release of the penetrated moisture. Therefore, in a strain gauge, expansion and contraction of the resistor caused by expansion and / or contraction of the substrate can be prevented. As a result, a decrease in reliability can be prevented.

[0008] In one embodiment, the metal sheet may be disposed across the first and second connecting portions and the sensing portion, and may cover a portion of the first and second connecting portions beyond the substrate exposed between the two connecting points and the sensing portion, as viewed from the sensing portion. This configuration can prevent moisture from penetrating through the region between the sensing portion and the first and second connecting portions.

[0009] In one embodiment, the resistor includes an insulating portion disposed between the resistor and the metal sheet, the insulating portion having openings that expose the two connection points, and the metal sheet may be disposed so as not to overlap the openings. In this configuration, the insulating portion electrically insulates the resistor from the metal sheet. Furthermore, the two connection points where the wiring is connected are not covered by the metal sheet. Therefore, the wiring can be connected to the connection points while avoiding short circuits between the metal sheet and the wiring.

[0010] In one embodiment, the sensing unit and the two connection points are spaced apart in a first direction, the connection point of the first connection unit and the connection point of the second connection unit are juxtaposed in a second direction intersecting the first direction, and the end of the metal sheet on the two connection points side may be located in front of the edge of the opening on the sensing unit side in the first direction, as viewed from the sensing unit. In this configuration, the wiring connected to the connection points is not covered by the metal sheet. This reliably prevents short circuits between the wiring and the metal sheet. Furthermore, in this configuration, because the wiring is not covered by the metal sheet, the wiring is prevented from being restrained by the metal sheet.

[0011] In one embodiment, an insulating layer may be formed on top of the wiring at the connection point of each of the first and second connection parts, and the metal sheet may cover the sensing part and the first and second connection parts, and may also cover at least a portion of the wiring in the first and second connection parts from above the insulating layer. In this configuration, the insulating layer electrically insulates the resistor from the metal sheet. The metal sheet then covers the entire sensing part of the resistor and the first and second connection parts. This further reduces the area of ​​the exposed substrate in the strain gauge. Therefore, the strain gauge can further prevent moisture from penetrating the substrate.

[0012] In one embodiment, the sensing unit and the two connection points may be spaced apart in a first direction, the connection point of the first connection part and the connection point of the second connection part may be juxtaposed in a second direction intersecting the first direction, and the metal sheet may cover two outer edges of one main surface of the base material in the second direction and an outer edge on the side opposite to the side on which the two connection points are located in the first direction. This configuration can further prevent moisture from penetrating the base material.

[0013] In one embodiment, the metal sheet may protrude outward from the two outer edges in the second direction and the outer edge in the first direction opposite to the side where the two connection points are located on one main surface of the substrate. In this configuration, the metal sheet protrudes outward from the substrate, so that the one main surface of the substrate can be completely covered. Furthermore, since the strain gauge can completely cover the side surface of the substrate (the end side surface of the one main surface), it is possible to prevent moisture from penetrating from the end side surface of the substrate. As a result, the strain gauge can further prevent moisture from penetrating the substrate.

[0014] In one embodiment, the first direction and the second direction are orthogonal, and the metal sheet may protrude from the substrate in the first direction on the side opposite to the side where the two connection points are located by at least half the length between the end of the resistor and the outer edge of the substrate, and may protrude from the substrate on one end side of the resistor in the second direction by at least half the length between one end of the resistor and the outer edge of the substrate, and may protrude from the substrate on the other end side of the resistor in the second direction by at least half the length between the other end of the resistor and the outer edge of the substrate. With this configuration, the side surface of the substrate (the end side surface of one main surface) can be completely covered, thereby preventing moisture from entering from the end side surface of the substrate.

[0015] In one embodiment, the first direction and the second direction are perpendicular to each other, and the distance between the sensing unit and the two connection points may be greater than each of the distances between the sensing unit and the two outer edges of the substrate in the second direction and the distance between the sensing unit and the outer edge of the substrate opposite the side on which the two connection points are located in the first direction. In this configuration, the greater the distance between the sensing unit and the two connection points, the greater the area of ​​the substrate exposed between the two connection points and the sensing unit. Therefore, in this configuration, it is particularly effective to cover the exposed portion of the substrate between the two connection points and the sensing unit with a metal sheet.

[0016] In one embodiment, a rubber sheet may be further provided to cover the metal sheet from above. In this configuration, the rubber sheet can improve the waterproof effect and also protect the metal sheet.

[0017] In one embodiment, the strain gauge includes a covering portion formed of a metallic material and disposed on one principal surface of the substrate so as to be electrically insulated from the resistor, the covering portion covering at least a portion of the principal surface to suppress moisture penetration into the substrate, and the covering portion may cover at least a portion of the substrate not covered by the metal sheet. The covering portion formed of a metallic material does not allow moisture to penetrate, thereby suppressing moisture penetration into the substrate. Therefore, in the strain gauge, by covering the substrate with the covering portion disposed directly on one principal surface of the substrate, moisture penetration into the substrate can be further suppressed.

[0018] In one embodiment, the covering portion may be disposed around at least the first connecting portion and the second connecting portion, which can further prevent moisture from penetrating into the base material around the first connecting portion and the second connecting portion.

[0019] In one embodiment, the device may further include a rubber sheet covering the metal sheet and the covering portion from above. In this configuration, the rubber sheet improves the waterproof effect and protects the metal sheet and the covering portion.

[0020] In one embodiment, each of the first connecting portion and the second connecting portion may extend to an outer edge of one main surface of the substrate as viewed in a second direction intersecting the first direction, at least in an area where the metal sheet does not cover the substrate. In this configuration, the one main surface of the substrate is covered by the first connecting portion and the second connecting portion, and therefore the first connecting portion and the second connecting portion can suppress moisture from penetrating the substrate.

[0021] A method of manufacturing a strain gauge according to one aspect of the present invention is a method of manufacturing a strain gauge comprising: a conductive resistor having a sensitive portion formed so as to extend along a first direction while folding back; a first connection portion connected to one end of the sensitive portion and having a connection portion to which wiring to an external circuit is connected; and a second connection portion connected to the other end of the sensitive portion and having a connection portion to which wiring to an external circuit is connected, wherein the sensitive portion and the two connection portions are arranged apart from each other in the first direction, and the connection portion of the first connection portion and the connection portion of the second connection portion are juxtaposed in a second direction intersecting the first direction, and the first connection portion and the second connection portion are arranged apart from each other in the first direction. The method includes the steps of: forming the resistor on one main surface of an insulating substrate, the resistor having an extension portion in which at least one of the connection portions extends further inward than both ends of the sensing part in the second direction; forming an insulating sheet having a first opening that exposes the first connection portion and a second opening that exposes the second connection portion; and arranging a metal sheet that covers one main surface of the substrate, wherein in the step of arranging the metal sheet, the metal sheet is arranged so that it extends to a position that overlaps the extension portions of the first connection portion and the second connection portion, and the ends of the metal sheet on the two connection point side are located in front of the edges of the first opening and the second opening on the sensing part side in the first direction, as viewed from the sensing part.

[0022] In a strain gauge manufacturing method according to one aspect of the present invention, the step of arranging a metal sheet includes arranging the metal sheet so that the metal sheet extends to a position overlapping the extending portions of the first and second connection portions and so that the ends of the metal sheet on the two connection locations are located in front of the edges of the first and second openings on the sensing unit side in the first direction, as viewed from the sensing unit. A metal sheet made of a metal material is impermeable to moisture and can therefore prevent moisture from penetrating into the substrate. Therefore, in a strain gauge, by covering at least the substrate exposed between the two connection locations and the sensing unit with the metal sheet, in addition to the sensing unit, the exposed area of ​​the substrate around the resistor can be reduced. This prevents moisture from penetrating into the substrate, causing expansion, and / or shrinking of the substrate due to the release of the moisture. Therefore, in a strain gauge, expansion and contraction of the resistor due to expansion and / or contraction of the substrate can be prevented. As a result, a decrease in the reliability of the strain gauge can be prevented. [Effects of the Invention]

[0023] According to one aspect of the present invention, a decrease in reliability can be suppressed. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a perspective view showing a state in which a strain gauge according to one embodiment is installed on a strain generating body. [Figure 2] FIG. 2 is an exploded perspective view of the strain gauge shown in FIG. [Figure 3] FIG. 3 is a plan view of the strain gauge. [Figure 4] FIG. 4 is a plan view of a strain gauge according to another embodiment. [Figure 5] FIG. 5 is a plan view of a strain gauge according to another embodiment. [Figure 6] FIG. 6 is a plan view of a strain gauge according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the description of the drawings, identical or corresponding elements are designated by the same reference numerals, and duplicated explanations will be omitted. In the following description, "X" in each drawing indicates a first direction, and "Y" indicates a second direction. The first direction X and the second direction Y are perpendicular to each other (intersect).

[0026] As shown in FIG. 1, the strain gauge 1 is installed on a strain element 100 of a load cell provided in, for example, a weighing device (not shown). Wires L1 and L2 are connected to the strain gauge 1. The wires L1 and L2 are connected to an external circuit (not shown). The external circuit is, for example, a bridge circuit. The wire L1 is connected to a first connection portion 31 (described below) of the resistor 3 by solder F1. The wire L2 is connected to a second connection portion 32 (described below) of the resistor 3 by solder F2.

[0027] 2 and 3, the strain gauge 1 includes a substrate 2, a resistor 3, an insulating sheet (insulating portion) 4, a metal sheet 5, and a rubber sheet 6. The insulating sheet 4 is not shown in FIG.

[0028] The substrate 2 supports the resistor 3. The substrate 2 has, for example, a rectangular shape. The substrate 2 has a main surface (one main surface) 2a and a main surface 2b. The substrate 2 has insulating properties. The substrate 2 is made of, for example, a resin. Examples of resin that can be used include polyimide (PI), polyamideimide (PAI), polyethylene (PE), and polyether ether ketone. The substrate 2 has flexibility. The thickness of the substrate 2 is, for example, 10 μm to 50 μm. The substrate 2 has a plurality of marks T provided around the resistor 3. The marks T are used as markers (references) when attaching the substrate 2 to the strain generating element 100.

[0029] The resistor 3 is disposed on the main surface 2a of the substrate 2. The resistor 3 is fixed (anchored) to the substrate 2. The resistor 3 expands and contracts in accordance with the deformation of the substrate 2. The resistance value of the resistor 3 changes due to expansion and contraction. The resistor 3 is conductive. The resistor 3 is made of a metal material. For example, Cu-Ni can be used as the metal material. The resistor 3 can be formed on the main surface 2a of the substrate 2 by, for example, photolithography. The resistor 3 has a thickness of, for example, 2 μm to 5 μm.

[0030] The resistor 3 has a sensing portion 30, a first connecting portion 31, and a second connecting portion 32. In the resistor 3, the sensing portion 30, the first connecting portion 31, and the second connecting portion 32 are integrally formed.

[0031] The sensing part 30 is the part whose resistance value mainly changes as the substrate deforms. As shown in FIG. 3, the sensing part 30 has straight parts 30a and folded parts 30b. The straight parts 30a extend in a first direction X and are arranged side by side in a second direction Y that intersects with the first direction X. The folded parts 30b connect the ends of adjacent straight parts 30a. The straight parts 30a and folded parts 30b give the sensing part 30 a serpentine shape.

[0032] The first connection portion 31 is connected to one end 30c of the sensing portion 30. A wiring L1 is connected to the first connection portion 31 to an external circuit. The first connection portion 31 has a connection portion 31a and a linking portion 31b. The connection portion 31a is the portion to which the wiring L1 is connected. The connection portion 31a has, for example, a substantially rectangular shape. In this embodiment, each side of the connection portion 31a is aligned with the first direction X or the second direction Y. The connection portion 31a has a connection point 33 to which the wiring L1 is connected (where solder F1 is formed). The connection point 33 is a partial area of ​​the connection portion 31a.

[0033] The connecting portion 31b connects one end 30c of the sensing unit 30 and the connecting portion 31a. The connecting portion 31b extends in the first direction X. In this embodiment, the connecting portion 31b tapers from the connecting portion 31a toward one end 30c of the sensing unit 30. Note that the connecting portion 31b may extend with a constant width between the connecting portion 31a and one end 30c.

[0034] The second connection portion 32 is connected to the other end 30d of the sensing unit 30. A wiring L2 to an external circuit is connected to the second connection portion 32. The second connection portion 32 has a connection portion 32a and a linking portion 32b. The connection portion 32a is a portion to which the wiring L2 is connected. The connection portion 32a has, for example, a substantially rectangular shape. In this embodiment, each side of the connection portion 32a is aligned with the first direction X or the second direction Y. The connection portion 32a has a connection point 34 to which the wiring L2 is connected (where solder F2 is formed). The connection point 34 is a partial region of the connection portion 32a.

[0035] The connecting portion 32b connects the other end 30d of the sensing unit 30 to the connecting portion 32a. The connecting portion 32b extends in the first direction X. In this embodiment, the connecting portion 32b tapers from the connecting portion 32a toward the other end 30d of the sensing unit 30. Note that the connecting portion 32b may extend with a constant width between the connecting portion 32a and the other end 30d.

[0036] The sensitive part 30, the connection portion 31a (connection point 33) of the first connection part 31, and the connection portion 32a (connection point 34) of the second connection part 32 are arranged at a predetermined distance apart in the first direction X. The connection portion 31a of the first connection part 31 and the connection portion 32a of the second connection part 32 are arranged juxtaposed at a predetermined distance apart in the second direction Y. In the resistor 3, the distance D1 between the sensitive part 30 and the two connection points 33, 34 is greater than each of the distances D2, D3 between the sensitive part 30 and the two outer edges 2e3, 2e4 of the substrate 2 in the second direction Y, and the distance D4 between the sensitive part 30 and the outer edge 2e2 of the substrate 2 opposite to the side where the two connection points 33, 34 are arranged in the first direction X (D1>D2, D3, D4). Furthermore, the distance D1 is greater than the distance D5 between the connection portion 31a of the first connection portion 31 and the connection portion 32a of the second connection portion 32 in the second direction Y.

[0037] As shown in FIGS. 1 and 2, the insulating sheet 4 is disposed on the resistor 3. The insulating sheet 4 is located between the resistor 3 and the metal sheet 5. The insulating sheet 4 has insulating properties. The insulating sheet 4 is formed of, for example, a resin. Examples of resin that can be used include polyimide (PI), polyamideimide (PAI), polyethylene (PE), and polyether ether ketone. The insulating sheet 4 has a thickness of, for example, 10 μm to 50 μm. The insulating sheet 4 may be formed by applying a liquid agent for forming the insulating sheet 4 onto the resistor 3 and solidifying it, or by adhering the insulating sheet 4 to the resistor 3. The insulating sheet 4 may be adhered to the resistor 3 using an epoxy adhesive, or by dissolving the surface of the insulating sheet 4 in a solvent and then pressing it onto the resistor 3. The insulating sheet 4 may have a shape corresponding to the shape of the resistor 3.

[0038] 2, the insulating sheet 4 covers the resistor 3. The insulating sheet 4 has, for example, a substantially rectangular shape. The insulating sheet 4 has a size that allows it to cover the entire resistor 3. The insulating sheet 4 has a first opening 4a and a second opening 4b.

[0039] The first opening 4a has, for example, a rectangular shape. The first opening 4a is a through-hole that penetrates the insulating sheet 4 in the thickness direction. The first opening 4a is formed to correspond to the connection point 33 of the first connection portion 31 of the resistor 3. The first opening 4a exposes the connection point 33 when the insulating sheet 4 covers the resistor 3.

[0040] The second opening 4b has, for example, a rectangular shape. The second opening 4b is a through-hole that penetrates the insulating sheet 4 in the thickness direction. The second opening 4b is formed to correspond to the connection point 34 of the second connection portion 32 of the resistor 3. The second opening 4b exposes the connection point 34 when the insulating sheet 4 covers the resistor 3.

[0041] The metal sheet 5 covers the main surface 2a of the base material 2. The metal sheet 5 has, for example, a rectangular shape. The metal sheet 5 has a main surface 5a and a main surface 5b. The metal sheet 5 is a metal foil (rolled foil) made of a metal material. Examples of the metal material that can be used include Al, Ni, Cu, Cr, Au, and alloys thereof (for example, Ni-Cr). The thickness of the metal sheet 5 is, for example, 2 μm to 10 μm. The metal sheet 5 is bonded to the base material 2 with an adhesive. For example, an epoxy adhesive can be used as the adhesive.

[0042] 2, the metal sheet 5 is disposed so that the main surface 5b faces the main surface 2a of the substrate 2. As shown in Fig. 3, the metal sheet 5 covers at least the substrate 2 exposed between the sensing unit 30 and two connection points 33, 34 to which wirings L1, L2 to an external circuit, which wirings L1, L2 have in the first connection portion 31 and the second connection portion 32 of the resistor 3, respectively, are connected. In this embodiment, the metal sheet 5 covers an area A including a portion of the substrate 2 exposed between the two connection points 33, 34 and the sensing unit 30 and a part of a portion of the substrate 2 exposed between the two connection points 33, 34.

[0043] In this embodiment, the metal sheet 5 is disposed across the first connecting portion 31, the second connecting portion 32, and the sensory unit 30, and covers a portion of the connecting portion 31a of the first connecting portion 31 and the connecting portion 32a of the second connecting portion 32 beyond the substrate 2 exposed between the two connecting points 33, 34 and the sensory unit 30, as viewed from the sensory unit 30. In detail, the metal sheet 5 is disposed so as not to overlap the first opening 41a and the second opening 42a of the insulating sheet 4, and the end portion (outer edge 5e1) of the metal sheet 5 on the two connecting points 33, 34 side is located in front of the edges of the first opening 41a and the second opening 42a on the sensory unit 30 side in the first direction X, as viewed from the sensory unit 30.

[0044] The metal sheet 5 covers the two outer edges 2e3 and 2e4 of the main surface 2a of the base material 2 in the second direction Y and the outer edge 2e2 on the side opposite to the side on which the two connection points 33 and 34 are located in the first direction X, and protrudes outward beyond the two outer edges 2e3 and 2e4 and the outer edge 2e2. The metal sheet 5 protrudes from the base material 2 in the first direction X on the side opposite to the side on which the two connection points 33 and 34 are located by a length equal to or greater than half the length between the end of the resistor 3 and the outer edge 2e2 of the base material 2. Specifically, when the distance between the outer edge 2e2 of the base material 2 and the outer edge 5e2 of the metal sheet 5 is defined as D6, the distance D6 is equal to or greater than ½ of the distance D4 (D6>½D4).

[0045] The metal sheet 5 protrudes from the base 2 at one end of the resistor 3 in the second direction Y by a length equal to or greater than half the length between the one end of the resistor 3 and the outer edge 2e3 of the base 2. Specifically, when the distance between the outer edge 2e3 of the base 2 and the outer edge 5e3 of the metal sheet 5 is defined as D7, the distance D7 is equal to or greater than half the distance D2 (D7 > 1 / 2D2). Furthermore, the metal sheet 5 protrudes from the base 2 at the other end of the resistor 3 in the second direction Y by a length equal to or greater than half the length between the other end of the resistor 3 and the outer edge 2e4 of the base 2. Specifically, when the distance between the outer edge 2e4 of the base 2 and the outer edge 5e4 of the metal sheet 5 is defined as D8, the distance D8 is equal to or greater than half the distance D3 (D8 > 1 / 2D3).

[0046] The rubber sheet 6 covers the metal sheet 5 from above. The rubber sheet 6 has, for example, a rectangular shape. The rubber sheet 6 has a main surface 6a and a main surface 6b. The rubber sheet 6 is made of, for example, butyl rubber or urethane rubber. The thickness of the rubber sheet 6 is, for example, 0.5 mm to 2.0 mm.

[0047] The rubber sheet 6 is larger (has a larger area) than the metal sheet 5. The rubber sheet 6 is arranged so that the main surface 6b faces the main surface 5a of the metal sheet 5. The outer edge of the rubber sheet 6 on the side opposite to the side on which the two connection points 33, 34 are arranged in the first direction X, and both outer edges in the second direction Y protrude outward beyond the metal sheet 5. The rubber sheet 6 is adhered to the metal sheet 5 by the adhesive force of the rubber sheet 6.

[0048] Next, a manufacturing method (assembly method) of the strain gauge 1 will be described.

[0049] First, the resistor 3 is formed on the main surface 2a of the substrate 2 (step of forming the resistor 3). The resistor 3 is formed on the substrate 2 by photolithography. Specifically, a metal layer (metal film) is formed on the substrate 2, and a photoresist is formed on the metal layer. After that, a mask is placed and the photoresist is exposed to light to form a pattern of the resistor 3. Thereafter, an etching process and removal of the photoresist are performed to form the resistor 3 on the substrate 2. In addition, the mark T is also formed on the main surface 2a of the substrate 2 by photolithography at the same time as the resistor 3. Note that the method of forming the resistor 3 and the mark T is not limited to photolithography, and they may be formed by other methods (such as forming only the resistor 3 and adhering it to the substrate 2).

[0050] Next, the insulating sheet 4 is formed on the resistor 3. The insulating sheet 4 is formed by applying a liquid agent for forming the insulating sheet 4 in a rectangular shape on the resistor 3 and then drying and solidifying the liquid agent. Subsequently, a chemical agent is applied to the areas where the first openings 4a and the second openings 4b are to be formed, and the sheet is exposed to light to form the first openings 4a and the second openings 4b. The first openings 4a and the second openings 4b may also be formed by applying a chemical agent to areas other than the first openings 4a and the second openings 4b and exposing the chemical agent to light. The insulating sheet 4 is then formed by washing away the chemical agent. The insulating sheet 4 may also be formed by attaching a sheet in which the first openings 4a and the second openings 4b are pre-formed to the resistor 3. Alternatively, the first openings 4a and the second openings 4b may be formed after attaching an insulating sheet 4 without openings to the resistor 3.

[0051] Next, a metal sheet 5 is placed so as to cover the main surface 2a of the base material 2 (step of placing the metal sheet 5). The metal sheet 5 is placed on the base material 2 so as to cover the region A of the base material 2 that is exposed between the sensing unit 30 and the two connection points 33, 34 of each of the first connection portion 31 and the second connection portion 32. Finally, a rubber sheet 6 is placed on the metal sheet 5. The rubber sheet 6 may be provided after the strain gauge 1 is attached to the flexure element 100.

[0052] When attaching the strain gauge 1 to the flexure body 100, first clean the flexure body 100 to be attached and remove any oil from its surface. Next, an epoxy adhesive, for example, is applied to the flexure body 100, and the strain gauge 1 is placed on the flexure body 100 based on the mark T. Next, pressure is applied using a jig and the body is heated in an oven for a predetermined time (for example, 3 hours). Thereafter, the wires L1 and L2 are connected to the connection points 33 and 34, respectively, with solder F1 and F2.

[0053] As described above, in the strain gauge 1 according to this embodiment, the metal sheet 5 covers at least the exposed portion of the substrate 2 between the sensing unit 30 and the two connection points 33, 34, to which the wiring lines L1, L2 of the first connection unit 31 and the second connection unit 32, respectively, are connected to external circuits. The metal sheet 5, formed of a metallic material, is impermeable to moisture and thus can prevent moisture from penetrating into the substrate 2. Therefore, in the strain gauge 1, the metal sheet 5 covers not only the sensing unit 30 but also the exposed portion of the substrate 2 between the two connection points 33, 34 and the sensing unit 30, thereby reducing the exposed area of ​​the substrate 2 around the resistor 3. This prevents moisture from penetrating the substrate 2 and causing expansion, and / or shrinkage of the substrate 2 due to the release of the moisture. Therefore, in the strain gauge 1, the expansion and / or contraction of the resistor 3 due to the expansion and / or contraction of the substrate 2 can be prevented. As a result, the strain gauge 1 can prevent a decrease in reliability.

[0054] In this embodiment, the metal sheet 5 covers the area A including not only the exposed portion of the base material 2 between the two connection points 33, 34 and the sensing part 30, but also a part of the exposed portion of the base material 2 between the two connection points 33, 34. Therefore, in the strain gauge 1, the expansion and / or contraction of the base material 2 can be further suppressed.

[0055] The moisture mentioned above is moisture (humidity) contained in the air in the environment in which the strain gauge 1 is placed. Therefore, the strain gauge 1 can prevent the expansion of the substrate 2 due to moisture contained in the air penetrating into the substrate 2, and / or the contraction of the substrate 2 due to the release of the penetrating moisture into the air. Of course, the moisture is not limited to that contained in the air.

[0056] In the strain gauge 1 according to this embodiment, the metal sheet 5 is disposed across the first connecting portion 31 and the second connecting portion 32 and the sensing portion 30, and also covers a portion of the first connecting portion 31 and the second connecting portion 32 beyond the two connection points 33, 34 and the substrate 2 exposed between the sensing portion 30, as viewed from the sensing portion 30. With this configuration, it is possible to prevent moisture from penetrating from the region between the sensing portion 30 and the two first connecting portions 31 and the second connecting portions 32.

[0057] The strain gauge 1 according to this embodiment includes an insulating sheet 4 that is disposed between the resistor 3 and the metal sheet 5 and has insulating properties. The insulating sheet 4 has a first opening 41a and a second opening 42a that expose the two connection points 33, 34. The metal sheet 5 is disposed so as not to overlap the first opening 41a and the second opening 42a. In this configuration, the insulating sheet 4 electrically insulates the resistor 3 from the metal sheet 5. Furthermore, the two connection points 33, 34 where the wiring lines L1, L2 are connected are not covered by the metal sheet 5. Therefore, the wiring lines L1, L2 can be connected to the connection points 33, 34 while avoiding short-circuiting between the metal sheet 5 and the wiring lines L1, L2.

[0058] In the strain gauge 1 according to this embodiment, the sensing unit 30 and the two connection points 33, 34 are spaced apart in the first direction X. The connection point 33 of the first connection unit 31 and the connection point 34 of the second connection unit 32 are juxtaposed in the second direction Y. The ends of the metal sheet 5 on the two connection points 33, 34 side are located in front of the edges of the first opening 41a and the second opening 42a on the sensing unit 30 side in the first direction X, as viewed from the sensing unit 30. In this configuration, the wirings L1, L2 connected to the connection points 33, 34 are not covered by the metal sheet 5. This reliably prevents a short circuit between the wirings L1, L2 and the metal sheet 5. Furthermore, in this configuration, because the wirings L1, L2 are not covered by the metal sheet 5, the wirings L1, L2 are prevented from being constrained by the metal sheet 5.

[0059] In the strain gauge 1 according to this embodiment, the sensing unit 30 and the two connection points 33, 34 are arranged apart in the first direction X. The connection point 33 of the first connection part 31 and the connection point 34 of the second connection part 32 are arranged side by side in the second direction Y. The metal sheet 5 covers the two outer edges 2e3, 2e4 of the main surface 2a of the base material 2 in the second direction Y and the outer edge 2e2 on the side opposite to the side where the two connection points 33, 34 are arranged in the first direction X. This configuration can further prevent moisture from penetrating the base material 2.

[0060] In the strain gauge 1 according to this embodiment, the metal sheet 5 protrudes outward from the outer edge 2e2 of the main surface 2a of the substrate 2, opposite to the side where the two outer edges 2e3, 2e4 in the second direction Y and the two connection points 33, 34 in the first direction X are located. In this configuration, the metal sheet 5 protrudes outward from the substrate 2, so that the main surface 2a of the substrate 2 is completely covered. Furthermore, in the strain gauge 1, the side surfaces of the substrate 2 (the end side surfaces of the main surface 2a) are completely covered, so that moisture penetration from the end side surfaces of the substrate 2 is suppressed. As a result, the strain gauge 1 can further suppress moisture penetration into the substrate 2.

[0061] In the strain gauge 1 according to this embodiment, the metal sheet 5 protrudes from the base 2 in the first direction X on the side opposite to the side where the two connection points 33, 34 are located by at least half the length between the end of the resistor 3 and the outer edge 2e2 of the base 2, and protrudes from the base 2 on the side of one end 30c of the resistor 3 in the second direction Y by at least half the length between one end 30c of the resistor 3 and the outer edge 2e3 of the base 2, and protrudes from the base 2 on the side of the other end 30d of the resistor 3 in the second direction Y by at least half the length between the other end 30d of the resistor 3 and the outer edge 2e4 of the base 2. With this configuration, the side surface of the base 2 (the end side surface of the main surface 2a) can be completely covered, thereby preventing moisture from entering from the end side surface of the base 2.

[0062] In the strain gauge 1 according to this embodiment, the distance D1 between the sensitive portion 30 and the two connection points 33, 34 is greater than each of the distances D2, D3 between the sensitive portion 30 and the two outer edges 2e3, 2e4 of the substrate 2 in the second direction Y, and the distance D4 between the sensitive portion 30 and the outer edge 2e2 of the substrate 2 opposite the side on which the two connection points 33, 34 are located in the first direction X. In this configuration, since the distance D1 between the sensitive portion 30 and the two connection points 33, 34 is large, the area of ​​the substrate 2 exposed between the two connection points 33, 34 and the sensitive portion 30 can be large. Therefore, in this configuration, it is particularly effective to cover the exposed portion of the substrate 2 between the two connection points 33, 34 and the sensitive portion 30 with a metal sheet 5.

[0063] The strain gauge 1 according to this embodiment further includes a rubber sheet 6 made of butyl rubber that covers the metal sheet 5 from above. In this configuration, the rubber sheet 6 improves the waterproof effect and also protects the metal sheet 5.

[0064] Although the embodiments of the present invention have been described above, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0065] In the above embodiment, an example has been described in which the first connecting portion 31 and the second connecting portion 32 are disposed apart from the outer edges 2e1, 2e3, and 2e4 of the substrate 2. However, the configuration of the first connecting portion 31 and the second connecting portion 32 is not limited to this. As shown in FIG. 4 , the resistor 3A of the strain gauge 1A has a sensing portion 30A, a first connecting portion 31A, and a second connecting portion 32A. The first connecting portion 31A has a connecting portion 31Aa and a linking portion 31Ab. The second connecting portion 32A has a connecting portion 32Aa and a linking portion 32Ab. The first connecting portion 31A is provided with a connection point 33A. The second connecting portion 32A is provided with a connection point 34A.

[0066] In the strain gauge 1A, the connection portion 31Aa of the first connection portion 31A and the connection portion 32Aa of the second connection portion 32A each extend to the outer edges 2e3, 2e4 of the main surface 2a of the base material 2 as viewed in the second direction Y, at least in the region where the metal sheet 5 does not cover the base material 2. In this configuration, the main surface 2a of the base material 2 is covered by the first connection portion 31A and the second connection portion 32A, and therefore, the first connection portion 31A (connection portion 31Aa) and the second connection portion 32A (connection portion 32Aa) can prevent moisture from penetrating the base material 2.

[0067] In addition to the above-described embodiments, as shown in FIG. 5, the strain gauge 1B may include a covering 7. The covering 7 is formed of a metal material and is disposed on the main surface 2a of the substrate 2 so as to be electrically insulated from the resistor 3. Examples of the metal material that can be used include Cu-Ni. The covering 7 may be formed on the main surface 2a of the substrate 2 by, for example, photolithography. The covering 7 covers at least a portion of the main surface 2a of the substrate 2 to prevent moisture from penetrating into the substrate 2. The covering 7 covers a portion of the substrate 2 that is not covered by the metal sheet 5. Specifically, the covering 7 is formed on the substrate 2 around the first connecting portion 31 and the second connecting portion 32 that are not covered by the metal sheet 5. Note that the metal sheet 5 and the covering 7 may or may not partially overlap as shown in FIG. 5. In other words, the metal sheet 5 may extend from the sensory sensing unit 30A to just before the first connecting portion 31 and the second connecting portion 32 when viewed in the first direction X, cover the area between the sensory sensing unit 30A and the first connecting portion 31 and the second connecting portion 32, and not overlap the first connecting portion 31 and the second connecting portion 32. Even in this case, exposure of the base material 2 between the sensory sensing unit 30A and the first connecting portion 31 and the second connecting portion 32 is reduced. However, from the viewpoint of moisture resistance, it is preferable that the metal sheet 5 and the covering portion 7 overlap. This is because the metal sheet 5 can completely cover the base material 2 located between the sensory sensing unit 30A and the first connecting portion 31 and the second connecting portion 32.

[0068] The covering 7 made of a metal material does not allow moisture to penetrate, and therefore can prevent moisture from entering the base material 2. Therefore, in the strain gauge 1A, by covering the base material 2 with the covering 7 that is directly disposed on the main surface 2a of the base material 2, it is possible to further prevent moisture from entering the base material 2.

[0069] 6, the covering portion 7C may be disposed so as to surround the periphery of the resistor 3C. In the strain gauge 1C, the resistor 3C has a sensing portion 30C, a first connecting portion 31C, and a second connecting portion 32C. The first connecting portion 31C has a connecting portion 31Ca and a linking portion 31Cb. The second connecting portion 32C has a connecting portion 32Ca and a linking portion 32Cb. The first connecting portion 31C is provided with a connecting point 33C. The second connecting portion 32C is provided with a connecting point 34C. The connecting portion 31Ca and the connecting portion 32Ca are disposed adjacent to each other.

[0070] The covering portion 7C is disposed so as to surround the periphery of the resistor 3C and is formed as a continuous piece. The covering portion 7C extends to the outer edges 2e1, 2e2, 2e3, and 2e4 of the substrate 2. In the strain gauge 1C, the mark T is formed in a portion where the covering portion 7C is not formed (a portion where the main surface 2a of the substrate 2 is exposed). In the strain gauge 1C, by covering the substrate 2 with the covering portion 7C disposed directly on the main surface 2a of the substrate 2, the penetration of moisture into the substrate 2 can be further suppressed.

[0071] In the above embodiment, the metal sheet 5 is arranged so as not to overlap the first opening 41a and the second opening 42a of the insulating sheet 4, and the ends (outer edges 5e1) of the metal sheet 5 on the two connection points 33, 34 sides are located in front of the edges of the first opening 41a and the second opening 42a on the sensing part 30 side in the first direction X, as viewed from the sensing part 30. However, an insulating layer may be formed on top of the wirings L1, L2 at the connection points 33, 34 of each of the first connection part 31 and the second connection part 32, and the metal sheet 5 may cover the sensing part 30 and the first connection part 31 and the second connection part 32, and may also cover at least a portion of the wirings L1, L2 in the first connection part 31 and the second connection part 32 from above the insulating layer. In this configuration, the insulating layer electrically insulates the resistor from the metal sheet. The metal sheet then covers the entire sensing part of the resistor and the first and second connection parts. This allows the area of ​​the strain gauge where the substrate is exposed to be further reduced, thereby further preventing moisture from penetrating into the substrate of the strain gauge.

[0072] Alternatively, openings corresponding to the two connection points 33 and 34 may be provided in the metal sheet 5. In this configuration, the metal sheet 5 covers the entire area of ​​the sensing part of the resistor and the first and second connection parts. This further reduces the area of ​​the exposed base material in the strain gauge. Therefore, the strain gauge can further prevent moisture from penetrating into the base material.

[0073] In the above embodiment, the insulating portion is the insulating sheet 4. However, the insulating portion may be formed by applying a resin to the resistor 3, for example. [Explanation of symbols]

[0074] 1, 1A, 1B, 1C... strain gauge, 2... substrate, 2a... main surface (one main surface), 2e1, 2e2, 2e3, 2e4... outer edge, 3, 3A, 3C... resistor, 4... insulating sheet (insulating portion), 5... metal sheet, 6... rubber sheet, 7, 7C... covering portion, 30, 30A, 30C... sensing portion, 30c, 30d... end portion, 31, 31A, 31C... first connecting portion, 32, 32A, 32C... second connecting portion, 33, 33A, 33C, 34, 34A, 34C... connection point, L1, L2... wiring, X... first direction, Y... second direction.

Claims

1. an insulating substrate; a resistor that is disposed on one main surface of the base material, has electrical conductivity, and expands and contracts in accordance with deformation of the base material; a metal sheet covering the one main surface of the base material; an insulating sheet positioned between the resistor and the metal sheet, The resistor is a sensing portion formed to extend along a first direction while folding back; a first connection part connected to one end of the sensing part and having a connection part to which wiring to an external circuit is connected; a second connection portion connected to the other end of the sensing portion and having a connection portion to which wiring to the external circuit is connected, The sensing unit and the two connection points are disposed apart from each other in the first direction, the connection point of the first connection portion and the connection point of the second connection portion are juxtaposed in a second direction intersecting the first direction, At least one of the first connecting portion and the second connecting portion has an extending portion that extends inward from both ends of the sensing portion in the second direction, the insulating sheet has a first opening through which the first connection portion is exposed and a second opening through which the second connection portion is exposed, the metal sheet extends to a position overlapping the extending portions of the first connection portion and the second connection portion, A strain gauge in which the ends of the metal sheet on the two connection points side are located in front of the edges of the first opening and the second opening on the sensing part side in the first direction, as viewed from the sensing part.

2. 2. The strain gauge of claim 1, wherein the metal sheet is arranged across the first connection portion, the second connection portion, and the sensing portion, and covers a portion of the first connection portion and the second connection portion beyond the substrate exposed between the two connection points and the sensing portion, as viewed from the sensing portion.

3. The strain gauge according to claim 2 , wherein the metal sheet is arranged so as not to overlap the first opening and the second opening.

4. 2. The strain gauge according to claim 1, wherein the metal sheet protrudes outward from two outer edges of the one main surface of the substrate in the second direction and from an outer edge opposite to a side on which the two connection points are located in the first direction.

5. the first direction and the second direction are perpendicular to each other, The metal sheet is In the first direction, on the side opposite to the side where the two connection points are arranged, the resistor protrudes from the base by a length equal to or greater than half of the length between the end of the resistor and the outer edge of the base, and 5. The strain gauge according to claim 4, wherein, at one end side of the resistor in the second direction, a length equal to or greater than half of the length between the one end of the resistor and the outer edge of the substrate protrudes from the substrate, and, at the other end side of the resistor in the second direction, a length equal to or greater than half of the length between the other end of the resistor and the outer edge of the substrate protrudes from the substrate.

6. the first direction and the second direction are perpendicular to each other, 6. A strain gauge as described in claim 4 or 5, wherein the distance between the sensing part and the two connection points is greater than each of the distances between the sensing part and the two outer edges of the substrate in the second direction and the distance between the sensing part and the outer edge of the substrate opposite to the side on which the two connection points are located in the first direction.

7. The strain gauge according to any one of claims 1 to 6, further comprising a rubber sheet covering the metal sheet from above.

8. a covering portion that is formed of a metal material and disposed on the one main surface of the base so as to be electrically insulated from the resistor, and that covers at least a portion of the one main surface to suppress moisture penetration into the base; The covering portion covers at least a part of the base material that is not covered by the metal sheet. The strain gauge according to any one of claims 1 to 7.

9. The strain gauge according to claim 8 , wherein the covering portion is disposed around at least each of the first connecting portion and the second connecting portion.

10. The strain gauge according to claim 8 or 9, further comprising a rubber sheet covering the metal sheet and the covering portion from above.

11. The strain gauge according to any one of claims 1 to 8, wherein each of the first connection portion and the second connection portion extends to an outer edge of the one main surface of the substrate when viewed in the second direction intersecting the first direction, at least in an area where the metal sheet does not cover the substrate.

12. a step of forming a conductive resistor on one main surface of an insulating substrate, the resistor having a sensing part formed so as to extend along a first direction while folding back, a first connection part connected to one end of the sensing part and having a connection part to which wiring to an external circuit is connected, and a second connection part connected to the other end of the sensing part and having a connection part to which wiring to the external circuit is connected, the sensing part and the two connection parts being arranged apart from each other in the first direction, the connection part of the first connection part and the connection part of the second connection part being juxtaposed in a second direction intersecting the first direction, and at least one of the first connection part and the second connection part having an extension part that extends inward beyond both ends of the sensing part in the second direction; forming an insulating sheet having a first opening exposing the first connection portion and a second opening exposing the second connection portion; and placing a metal sheet covering the one main surface of the base material, A method for manufacturing a strain gauge, wherein in the step of positioning the metal sheet, the metal sheet is positioned so that it extends to a position overlapping the extending portions of the first connection portion and the second connection portion, and so that the ends of the metal sheet on the two connection points side are located in front of the edges of the first opening and the second opening on the sensing portion side in the first direction, as viewed from the sensing portion.

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