Strain gauge and method for manufacturing a 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 Art]

[0002] As a conventional strain gauge, one described in, for example, Patent Document 1 is known. The strain gauge described in Patent Document 1 includes: a measurement grid (resistor) arranged on a supporting foil; and a cover arranged on the measurement grid and having a first layer of an insulating material and a second layer of a metal material. The measurement grid includes a wavy strip (sensing portion) and an exchange region (connection portion) provided at an end of the strip. [Prior Art Literature] [Patent Literature]

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

[0004] In a strain gauge, when moisture (such as humidity) infiltrates a base material or the infiltrated moisture is released from the base material, expansion and / or contraction may occur in the base material. In this case, since the resistor arranged on the base material expands and contracts due to the expansion and / or contraction of the base material, a change occurs in the output of the strain gauge, which may reduce the reliability of the strain gauge. In conventional strain gauges, a cover is arranged to cover the strip so as to suppress the infiltration of moisture into the base material. However, in conventional strain gauges, although the strip of the measurement grid is covered with a sheet, the base material between the exchange region and the measurement grid is exposed. Therefore, in conventional strain gauges, there is a risk that the infiltration of moisture into the base material cannot be sufficiently suppressed.

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

[0006] A strain gauge according to one aspect of the present invention comprises an insulating base material, a conductive resistor disposed on one main surface of the base material and expanding and contracting with deformation of the base material, a metal sheet covering one main surface of the base material, and an insulating sheet located between the resistor and the metal sheet, wherein the resistor comprises a sensing portion formed to extend along a first direction while folding back, a first connection portion connected to one end of the sensing portion and having a connection point to which wiring to an external circuit is connected, and a second connection portion connected to the other end of the sensing portion and having a connection point to which wiring to an external circuit is connected, wherein the sensing portion and the two connection points are first The components are spaced apart in the direction, and 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 and second connection parts has an extended portion that extends inward beyond both ends of the second direction of the sensing part. 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 extended portions of the first and second connection parts. The ends of the metal sheet on the two connection point sides are located in front of the edges of the first and second openings on the sensing part side, as viewed from the sensing part in the first direction.

[0007] In a strain gauge according to one aspect of the present invention, the metal sheet extends to a position overlapping the extended portions of the first and second connection parts, and the ends of the metal sheet on the two connection parts side are located in front of the edges of the first and second openings on the sensing part side, as viewed from the sensing part in the first direction. Since the metal sheet, made of a metallic material, does not allow moisture to penetrate, it can suppress the intrusion of moisture into the substrate. Therefore, in the strain gauge, in addition to the sensing part, the substrate exposed between the two connection parts and the sensing part is also covered with the metal sheet, thereby reducing the area of ​​the substrate exposed around the resistor. As a result, in the strain gauge, it is possible to suppress the expansion of the substrate due to the intrusion of moisture into the substrate, and / or the contraction of the substrate due to the release of the intruded moisture. Consequently, in the strain gauge, it is possible to suppress the expansion and contraction of the resistor due to the expansion and / or contraction of the substrate. As a result, the strain gauge can suppress a decrease in reliability.

[0008] In one embodiment, the metal sheet is arranged across the first and second connection portions and the sensing portion, and may also cover a portion of the first and second connection portions beyond the substrate exposed between the two connection points and the sensing portion, as viewed from the sensing portion. This configuration can suppress the intrusion of moisture from the region between the sensing portion and the first and second connection portions.

[0009] In one embodiment, an insulating portion is provided between the resistor and the metal sheet, and the insulating portion has openings that expose two connection points, and the metal sheet may be positioned so as not to overlap the openings. In this configuration, the resistor and the metal sheet are electrically insulated by the insulating portion. The two connection points to which the wiring is connected are not covered by the metal sheet. Therefore, it is possible to connect the wiring to the connection points while avoiding short circuits between the metal sheet and the wiring.

[0010] In one embodiment, the sensing part and the two connection points are spaced apart in a first direction, the connection point of the first connection part and the connection point of the second connection part are placed side by side in a second direction intersecting the first direction, and the ends of the metal sheet on the two connection point side may be located in front of the edge of the opening on the sensing part side, as viewed from the sensing part in the first direction. In this configuration, the wiring connected to the connection points is not covered by the metal sheet. Therefore, short circuits between the wiring and the metal sheet can be reliably avoided. In addition, in this configuration, since the wiring is not covered by the metal sheet, the wiring can not be constrained by the metal sheet.

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

[0012] In one embodiment, the sensing portion and the two connection points are spaced apart in a first direction, the connection point of the first connection part and the connection point of the second connection part are placed side by side in a second direction intersecting the first direction, and the metal sheet may cover 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. This configuration can further suppress the penetration of moisture into the substrate.

[0013] In one embodiment, the metal sheet may protrude outward beyond 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, since the metal sheet protrudes outward beyond the substrate, it can completely cover one main surface of the substrate. Furthermore, since the strain gauge can completely cover the side surface of the substrate (the end surface of one main surface), it can suppress the intrusion of moisture from the end surface of the substrate. As a result, the strain gauge can further suppress the intrusion of moisture into the substrate.

[0014] In one embodiment, the first and second directions are orthogonal, and the metal sheet may protrude from the base material by a length of more than half the length between the end of the resistor and the outer edge of the base material in the first direction and on the side opposite to where the two connection points are located, and on the side of one end of the resistor in the second direction by a length of more than half the length between one end of the resistor and the outer edge of the base material, and on the side of the other end of the resistor in the second direction by a length of more than half the length between the other end of the resistor and the outer edge of the base material. In this configuration, the side surface of the base material (the end surface of one main surface) can be completely covered, so that moisture can not penetrate from the end surface of the base material.

[0015] In one embodiment, the first and second directions are orthogonal, and the distance between the sensing portion and the two connection points may be greater than the distance between the sensing portion and the two outer edges of the base material in the second direction, and the distance between the sensing portion and the outer edge of the base material on the side opposite to where the two connection points are located in the first direction. In this configuration, because the distance between the sensing portion and the two connection points is large, the area of ​​the base material exposed between the two connection points and the sensing portion may be large. Therefore, in this configuration, it is particularly effective to cover the base material exposed between the two connection points and the sensing portion 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 waterproofing effect and protect the metal sheet.

[0017] In one embodiment, the strain gauge includes a covering portion made of a metal material, which is electrically insulated from the resistor on one main surface of the substrate and covers at least a portion of the main surface to suppress the penetration of moisture into the substrate. The covering portion may cover at least a portion of the substrate that is not covered by the metal sheet. Since the covering portion made of a metal material does not allow moisture to penetrate, it can suppress the penetration of moisture into the substrate. Therefore, in the strain gauge, by covering the substrate with a covering portion that is directly placed on one main surface of the substrate, the penetration of moisture into the substrate can be further suppressed.

[0018] In one embodiment, the covering portion may be arranged around at least the first connection portion and the second connection portion. This configuration further suppresses the penetration of moisture into the substrate around the first and second connection portions.

[0019] In one embodiment, a rubber sheet may be further provided to cover the metal sheet and the covering from above. In this configuration, the waterproofing effect can be improved by the rubber sheet, and the metal sheet and the covering can be protected by the rubber sheet.

[0020] In one embodiment, each of the first and second connecting portions may extend to the outer edge of one main surface of the substrate, viewed in a second direction intersecting the first direction, at least in areas where the metal sheet does not cover the substrate. In this configuration, since one main surface of the substrate is covered by the first and second connecting portions, the penetration of moisture into the substrate can be suppressed by the first and second connecting portions.

[0021] A method for manufacturing a strain gauge according to one aspect of the present invention is a conductive resistor comprising: a sensing portion formed to extend along a first direction while being folded back; a first connection portion connected to one end of the sensing portion and having a connection point for wiring to an external circuit; and a second connection portion connected to the other end of the sensing portion and having a connection point for wiring to an external circuit, wherein the sensing portion and the two connection points are arranged separately in the first direction, and the connection point of the first connection portion and the connection point of the second connection portion are arranged side by side in a second direction intersecting the first direction, and the first connection portion and the second connection The process includes the steps of forming a resistor on one main surface of an insulating substrate, wherein at least one of the connecting portion has an extended portion that extends inward beyond both ends of the second direction of the sensing portion; forming an insulating sheet having a first opening that exposes the first connecting portion and a second opening that exposes the second connecting portion; and arranging a metal sheet that covers one main surface of the substrate, wherein the metal sheet is arranged such that it extends to a position overlapping the extended portions of the first and second connecting portions, and the ends of the metal sheet on the two connection points are positioned in front of the edges of the first and second openings on the sensing portion side, as viewed from the sensing portion in the first direction.

[0022] In a method for manufacturing a strain gauge according to one aspect of the present invention, in the step of arranging a metal sheet, the metal sheet extends to a position overlapping the extending portions of the first connection portion and the second connection portion, and ends of the metal sheet on the two connection portion sides are positioned closer to the sensing portion than edges of the first opening and the second opening on the sensing portion side as viewed from the sensing portion in the first direction. The metal sheet formed of a metal material does not allow moisture to permeate, so that ingress of moisture into the base material can be suppressed. Therefore, in the strain gauge, by covering, with at least the metal sheet, the base material exposed between the two connection portions and the sensing portion in addition to the sensing portion, the area where the base material is exposed around the resistor can be reduced. Accordingly, in the strain gauge, expansion of the base material caused by moisture ingress into the base material, and / or contraction of the base material caused by release of the ingressed moisture can be suppressed. Therefore, in the strain gauge, expansion and contraction of the resistor caused by expansion and / or contraction of the base material can be suppressed. As a result, a decrease in reliability of the strain gauge can be suppressed. Effects of the Invention

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

[0024] [Figure 1] FIG. 1 is a perspective view showing a state where a strain gauge according to an embodiment is installed on a strain-generating body. [Figure 2] FIG. 2 is an exploded perspective view of the strain gauge shown in FIG. 1. [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. Mode for Carrying Out the Invention

[0025] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. In the following description, "X" in each figure will be the first direction, and "Y" will be the second direction. The first direction X and the second direction Y are orthogonal (intersecting) to each other.

[0026] As shown in Figure 1, the strain gauge 1 is installed on the strain generating body 100 of a load cell, for example, which is provided in a weighing device (not shown). Wiring L1 and wiring L2 are connected to the strain gauge 1. Wiring L1 and wiring L2 are connected to an external circuit (not shown). The external circuit is, for example, a bridge circuit. Wiring L1 is connected to the first connection part 31 (described later) of the resistor 3 by solder F1. Wiring L2 is connected to the second connection part 32 (described later) of the resistor 3 by solder F2.

[0027] As shown in Figures 2 and 3, the strain gauge 1 comprises a base material 2, a resistor 3, an insulating sheet (insulating part) 4, a metal sheet 5, and a rubber sheet 6. In Figure 3, the insulating sheet 4 is not shown.

[0028] The base material 2 supports the resistor 3. The base material 2 is, for example, rectangular in shape. The base material 2 has a main surface (one main surface) 2a and a main surface 2b. The base material 2 is insulating. The base material 2 is made of, for example, resin. As the resin, for example, polyimide (PI), polyamide-imide (PAI), polyethylene (PE), polyetheretherketone, etc. can be used. The base material 2 is flexible. The thickness of the base material 2 is, for example, 10 μm to 50 μm. The base material 2 is provided with a plurality of marks T around the resistor 3. The marks T are used as markers (references) when attaching the base material 2 to the strain generator 100.

[0029] The resistor 3 is placed on the main surface 2a of the substrate 2. The resistor 3 is fixed (adhered) 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 the expansion and contraction. The resistor 3 is electrically conductive. The resistor 3 is made of a metallic material. For example, Cu-Ni can be used as the metallic material. The resistor 3 can be formed on the main surface 2a of the substrate 2 by, for example, photolithography. The thickness of the resistor 3 is, 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 portion 30 is the part whose resistance value changes primarily in accordance with the deformation of the substrate. As shown in Figure 3, the sensing portion 30 has a straight portion 30a and a folded portion 30b. Multiple straight portions 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 portions 30b connect the ends of adjacent straight portions 30a. The sensing portion 30 exhibits a meandering shape due to the multiple straight portions 30a and multiple folded portions 30b.

[0032] The first connection portion 31 is connected to one end 30c of the sensing portion 30. The wiring L1 to the external circuit is connected to the first connection portion 31. The first connection portion 31 has a connection portion 31a and a connecting portion 31b. The connection portion 31a is the portion to which the wiring L1 is connected. The connection portion 31a is, for example, substantially rectangular in shape. In this embodiment, each side of the connection portion 31a is aligned along 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 (solder F1 is formed). The connection point 33 is a part of the region of the connection portion 31a.

[0033] The connecting portion 31b connects one end 30c of the sensing portion 30 to 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 portion 30. The connecting portion 31b may extend with a certain 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 portion 30. The wiring L2 to the external circuit is connected to the second connection portion 32. The second connection portion 32 has a connection portion 32a and a connecting portion 32b. The connection portion 32a is the portion to which the wiring L2 is connected. The connection portion 32a is, for example, substantially rectangular in shape. In this embodiment, each side of the connection portion 32a is aligned along 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 (solder F2 is formed). The connection point 34 is a part of the area of ​​the connection portion 32a.

[0035] The connecting portion 32b connects the other end 30d of the sensing portion 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 portion 30. The connecting portion 32b may extend with a certain width between the connecting portion 32a and the other end 30d.

[0036] The sensing portion 30 and the connection portion 31a (connection point 33) of the first connection portion 31 and the connection portion 32a (connection point 34) of the second connection portion 32 are arranged at a predetermined distance apart in the first direction X. The connection portion 31a of the first connection portion 31 and the connection portion 32a of the second connection portion 32 are arranged side by side at a predetermined distance apart in the second direction Y. In the resistor 3, the distance D1 between the sensing portion 30 and the two connection points 33 and 34 is greater than the distances D2 and D3 between the sensing portion 30 and the two outer edges 2e3 and 2e4 of the base material 2 in the second direction Y, and the distance D4 between the sensing portion 30 and the outer edge 2e2 of the base material 2 on the side opposite to where the sensing portion 30 and the two connection points 33 and 34 are located 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 Figures 1 and 2, the insulating sheet 4 is placed 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. As the resin, polyimide (PI), polyamide-imide (PAI), polyethylene (PE), polyetheretherketone, etc. can be used. The thickness of the insulating sheet 4 is, 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 allowing it to solidify, or by adhering the insulating sheet 4 to the resistor 3. As a method of adhering the insulating sheet 4 to the resistor 3, an epoxy adhesive may be used, or the surface of the insulating sheet 4 may be dissolved with a solvent and pressed onto the resistor 3. The insulating sheet 4 may have a shape corresponding to the shape of the resistor 3.

[0038] As shown in Figure 2, the insulating sheet 4 covers the resistor 3. The insulating sheet 4 is, for example, roughly rectangular in shape. The insulating sheet 4 is large enough to cover the entire resistor 3. The insulating sheet 4 is provided with a first opening 4a and a second opening 4b.

[0039] The first opening 4a is, for example, rectangular in 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 corresponding 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 is, for example, rectangular in 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 corresponding to the connection point 34 of the second connection part 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 substrate 2. The metal sheet 5 is, for example, rectangular in 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) formed from a metal material. As the metal material, Al, Ni, Cu, Cr, Au, or alloys thereof (e.g., Ni-Cr) can be used. The thickness of the metal sheet 5 is, for example, 2 μm to 10 μm. The metal sheet 5 is bonded to the substrate 2 by an adhesive. As the adhesive, for example, an epoxy adhesive can be used.

[0042] As shown in Figure 2, the metal sheet 5 is positioned such that its main surface 5b faces the main surface 2a of the base material 2. As shown in Figure 3, the metal sheet 5 covers at least the portion of the base material 2 exposed between the two connection points 33, 34 to which the wiring L1, L2 to the external circuit, each of the first connection point 31 and second connection point 32 of the resistor 3 is connected, and the sensing portion 30. In this embodiment, the metal sheet 5 covers region A, which includes the portion of the base material 2 exposed between the two connection points 33, 34 and the sensing portion 30, and a portion of the portion of the base material 2 exposed between the two connection points 33, 34.

[0043] In this embodiment, the metal sheet 5 is positioned over the first connection portion 31 and the second connection portion 32 and the sensing portion 30, and, as viewed from the sensing portion 30, it covers a portion of the connection portion 31a of the first connection portion 31 and a portion of the connection portion 32a of the second connection portion 32, beyond the base material 2 exposed between the two connection points 33 and 34 and the sensing portion 30. In detail, the metal sheet 5 is positioned so as not to overlap with 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 side of the two connection points 33 and 34 are positioned in front of the edges of the first opening 41a and the second opening 42a on the sensing portion 30 side, as viewed from the sensing portion 30, in the first direction X.

[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 in the first direction X opposite to the side where the two connection points 33 and 34 are located, and protrudes outward from the two outer edges 2e3 and 2e4 and the outer edge 2e2. In the first direction X, and on the side opposite to where the two connection points 33 and 34 are located, the length of the metal sheet 5 protrudes from the base material 2 by more than half the length between the end of the resistor 3 and the outer edge 2e2 of the base material 2. Specifically, if the distance D6 is the distance between the outer edge 2e2 of the base material 2 and the outer edge 5e2 of the metal sheet 5, then the distance D6 is greater than or equal to half the distance D4 (D6 > 1 / 2D4).

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

[0046] The rubber sheet 6 covers the metal sheet 5 from above. The rubber sheet 6 is, for example, rectangular in 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 surface area) than the metal sheet 5. The main surface 6b of the rubber sheet 6 is positioned opposite the main surface 5a of the metal sheet 5. On the rubber sheet 6, the outer edge opposite to the side where the two connection points 33 and 34 are located in the first direction X, and both outer edges in the second direction Y, protrude outward from 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, we will explain the manufacturing method (assembly method) of strain gauge 1.

[0049] First, a resistor 3 is formed on the main surface 2a of the substrate 2 (step for 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, a photoresist is formed on the metal layer, and then a mask is placed and exposed to form the pattern of the resistor 3. Subsequently, the resistor 3 is formed on the substrate 2 by etching and removal of the photoresist. 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 for forming the resistor 3 and 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, an 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 onto the resistor 3 and drying and solidifying the liquid agent. Subsequently, a chemical is applied to the parts that will form the first opening 4a and the second opening 4b, and they are exposed to light to form the first opening 4a and the second opening 4b. The first opening 4a and the second opening 4b may also be formed by applying a chemical to the parts other than the first opening 4a and the second opening 4b and exposing them to light. After that, the insulating sheet 4 is formed by washing off the chemical. The insulating sheet 4 may also be formed by attaching a sheet with the first opening 4a and the second opening 4b already formed to the resistor 3. Alternatively, the first opening 4a and the second opening 4b may be formed after attaching an insulating sheet 4 without openings to the resistor 3.

[0051] Next, the 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 area A of the base material 2 that is exposed between the two connection points 33, 34 of the first connection part 31 and the second connection part 32 and the sensing part 30. Finally, the 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 strain generating body 100.

[0052] When attaching the strain gauge 1 to the strain generating body 100, first, the strain generating body 100 to be attached is cleaned to remove any oil from its surface. Next, an epoxy adhesive, for example, is applied to the strain generating body 100, and the strain gauge 1 is placed on the strain generating body 100 based on mark T. Subsequently, pressure is applied using a jig, and the body is heated in an oven for a predetermined time (for example, 3 hours). After that, the wires L1 and L2 are connected to 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 base material 2 exposed between the two connection points 33, 34 to which the wiring L1, L2 to the external circuit, each of the first connection part 31 and the second connection part 32, is connected, and the sensing part 30. Since the metal sheet 5, which is made of a metallic material, does not allow moisture to penetrate, it can suppress the intrusion of moisture into the base material 2. Therefore, in the strain gauge 1, in addition to the sensing part 30, the base material 2 exposed between the two connection points 33, 34 and the sensing part 30 is also covered with the metal sheet 5, thereby reducing the area of ​​the base material 2 exposed around the resistor 3. As a result, in the strain gauge 1, it is possible to suppress the expansion of the base material 2 due to the intrusion of moisture into the base material 2, and / or the contraction of the base material 2 due to the release of the intruded moisture. Consequently, in the strain gauge 1, it is possible to suppress the expansion and contraction of the resistor 3 due to the expansion and / or contraction of the base material 2. As a result, the strain gauge 1 can suppress a decrease in reliability.

[0054] In this embodiment, the metal sheet 5 covers region A, which includes the portion of the base material 2 exposed between the two connection points 33 and 34 and the sensing portion 30, as well as a portion of the portion of the base material 2 exposed between the two connection points 33 and 34. Therefore, in the strain gauge 1, the expansion and contraction of the resistor 3 due to the expansion and / or contraction of the base material 2 can be further suppressed.

[0055] The moisture mentioned above refers to the moisture (humidity) contained in the air in the environment where the strain gauge 1 is placed. Therefore, the strain gauge 1 can suppress the expansion of the substrate 2 due to moisture in the air penetrating it, 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 arranged across the first connection portion 31 and the second connection portion 32 and the sensing portion 30, and as viewed from the sensing portion 30, it covers a portion of the first connection portion 31 and the second connection portion 32 beyond the base material 2 exposed between the two connection points 33 and 34 and the sensing portion 30. With this configuration, it is possible to suppress the intrusion of moisture from the region between the sensing portion 30 and the two first connection portions 31 and the second connection portion 32.

[0057] The strain gauge 1 according to this embodiment includes an insulating sheet 4 that is placed 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 two connection points 33 and 34. The metal sheet 5 is positioned so as not to overlap with the first opening 41a and the second opening 42a. In this configuration, the resistor 3 and the metal sheet 5 are electrically insulated by the insulating sheet 4. Furthermore, the two connection points 33 and 34 to which the wirings L1 and L2 are connected are not covered by the metal sheet 5. Therefore, it is possible to connect the wirings L1 and L2 to the connection points 33 and 34 while avoiding a short circuit between the metal sheet 5 and the wirings L1 and L2.

[0058] In the strain gauge 1 according to this embodiment, the sensing part 30 and the two connection points 33 and 34 are spaced 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 placed side by side in the second direction Y. The ends of the metal sheet 5 on the side of the two connection points 33 and 34 are located in front of the edges of the first opening 41a and the second opening 42a on the sensing part 30 side, as viewed from the sensing part 30 in the first direction X. In this configuration, the wirings L1 and L2 connected to the connection points 33 and 34 are not covered by the metal sheet 5. Therefore, short circuits between the wirings L1 and L2 and the metal sheet 5 can be reliably avoided. In addition, in this configuration, since the wirings L1 and L2 are not covered by the metal sheet 5, it is possible to avoid the wirings L1 and L2 being constrained by the metal sheet 5.

[0059] In the strain gauge 1 according to this embodiment, the sensing part 30 and the two connection points 33 and 34 are spaced 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 placed side by side in the second direction Y. 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 where the two connection points 33 and 34 are located in the first direction X. With this configuration, the penetration of moisture into the base material 2 can be further suppressed.

[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 base material 2, which is 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, since the metal sheet 5 protrudes outward from the base material 2, it can completely cover the main surface 2a of the base material 2. Furthermore, since the strain gauge 1 can completely cover the side surface of the base material 2 (the end side surface of the main surface 2a), it is possible to suppress the intrusion of moisture from the end side surface of the base material 2. As a result, the strain gauge 1 can further suppress the intrusion of moisture into the base material 2.

[0061] In the strain gauge 1 according to this embodiment, the metal sheet 5 protrudes from the base material 2 by a length of more than half the length between the end of the resistor 3 and the outer edge 2e2 of the base material 2 in the first direction X, and on the side opposite to where the two connection points 33 and 34 are located. In the second direction Y, on the side of one end 30c of the resistor 3, more than half the length between the one end 30c of the resistor 3 and the outer edge 2e3 of the base material 2 protrudes from the base material 2. In the second direction Y, on the side of the other end 30d of the resistor 3, more than half the length between the other end 30d of the resistor 3 and the outer edge 2e4 of the base material 2 protrudes from the base material 2. With this configuration, the side surface of the base material 2 (the end surface of the main surface 2a) can be completely covered, so that moisture can not penetrate from the end surface of the base material 2.

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

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

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

[0065] In the above embodiment, a configuration in which the first connecting portion 31 and the second connecting portion 32 are arranged at a distance from the outer edges 2e1, 2e3, and 2e4 of the base material 2 was described as an example. However, the configuration of the first connecting portion 31 and the second connecting portion 32 is not limited to this. As shown in Figure 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 connecting portion 31Ab. The second connecting portion 32A has a connecting portion 32Aa and a connecting 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, each of the connection portion 31Aa of the first connection portion 31A and the connection portion 32Aa of the second connection portion 32A extends to the outer edges 2e3, 2e4 of the main surface 2a of the base material 2 when 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, since the main surface 2a of the base material 2 is covered by the first connection portion 31A and the second connection portion 32A, the penetration of moisture into the base material 2 can be suppressed by the first connection portion 31 (connection portion 31Aa) and the second connection portion 32A (connection portion 32Aa).

[0067] In addition to the embodiments described above, the strain gauge 1B may also include a covering portion 7, as shown in Figure 5. The covering portion 7 is made of a metallic material and is arranged on the main surface 2a of the substrate 2 so as to be electrically insulated from the resistor 3. As the metallic material, for example, Cu-Ni can be used. The covering portion 7 can be formed on the main surface 2a of the substrate 2 by, for example, photolithography. The covering portion 7 covers at least a part of the main surface 2a of the substrate 2 to suppress the penetration of moisture into the substrate 2. The covering portion 7 covers a part of the substrate 2 that is not covered by the metal sheet 5. Specifically, the covering portion 7 is formed on the substrate 2 around the first connection portion 31 and the second connection portion 32 that are not covered by the metal sheet 5. The metal sheet 5 and the covering portion 7 may or may not overlap in some parts, as shown in Figure 5. In other words, the metal sheet 5 extends from the sensing portion 30A in the first direction X to just before the first connection portion 31 and the second connection portion 32, covering the area between the sensing portion 30A and the first and second connection portions 31 and 32, and may be configured not to overlap with the first and second connection portions 31 and 32. Even in this case, the exposure of the base material 2 between the sensing portion 30A and the first and second connection portions 31 and 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 sensing portion 30A and the first and second connection portions 31 and 32.

[0068] The coating portion 7, made of metal, prevents moisture from penetrating, thus suppressing the intrusion of moisture into the base material 2. Therefore, in the strain gauge 1A, by covering the base material 2 with the coating portion 7 which is directly positioned on the main surface 2a of the base material 2, the intrusion of moisture into the base material 2 can be further suppressed.

[0069] Furthermore, as shown in Figure 6, the covering portion 7C may be arranged to surround the resistor 3C. In the strain gauge 1C, the resistor 3C has a sensing portion 30C, a first connection portion 31C, and a second connection portion 32C. The first connection portion 31C has a connecting portion 31Ca and a connecting portion 31Cb. The second connection portion 32C has a connecting portion 32Ca and a connecting portion 32Cb. The first connection portion 31C is provided with a connection point 33C. The second connection portion 32C is provided with a connection point 34C. The connection portion 31Ca and the connection portion 32Ca are arranged in close proximity.

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

[0071] In the above embodiment, the metal sheet 5 is positioned so as not to overlap with 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 and 34 are positioned in front of the edges of the first opening 41a and the second opening 42a on the receiving point 30 side, as viewed from the receiving point 30 in the first direction X. However, an insulating layer may be formed on top of the wiring L1 and L2 at connection points 33 and 34 of the first connection point 31 and the second connection point 32, and the metal sheet 5 may cover the receiving point 30 and the first connection point 31 and the second connection point 32, and at least a portion of the wiring L1 and L2 may be covered from above the insulating layer at the first connection point 31 and the second connection point 32. In this configuration, the resistor and the metal sheet are electrically insulated by the insulating layer. The metal sheet covers the entire area of ​​the receiving point of the resistor and the first and second connection points. This allows the strain gauge to further reduce the area where the substrate is exposed. Therefore, the strain gauge can further suppress the penetration of moisture into the substrate.

[0072] Furthermore, the metal sheet 5 may have openings corresponding to two connection points 33 and 34. In this configuration, the metal sheet 5 covers the entire area of ​​the resistor's sensing portion, the first connection point, and the second connection point. This further reduces the area of ​​the substrate exposed in the strain gauge. Therefore, the penetration of moisture into the substrate can be further suppressed in the strain gauge.

[0073] In the above embodiment, an example was described in which the insulating portion is an insulating sheet 4. However, the insulating portion may also be formed, for example, by coating the resistor 3 with resin. [Explanation of symbols]

[0074] 1, 1A, 1B, 1C... Strain gauge, 2... Base material, 2a... Main surface (one main surface), 2e1, 2e2, 2e3, 2e4... Outer edge, 3, 3A, 3C... Resistor, 4... Insulating sheet (insulating part), 5... Metal sheet, 6... Rubber sheet, 7, 7C... Covering part, 30, 30A, 30C... Sensing part, 30c, 30d... End, 31, 31A, 31C... First connection part, 32, 32A, 32C... Second connection part, 33, 33A, 33C, 34, 34A, 34C... Connection point, L1, L2... Wiring, X... First direction, Y... Second direction.

Claims

1. An insulating substrate, A resistor is disposed on one main surface of the substrate and is conductive, and expands and contracts in accordance with the deformation of the substrate. A metal sheet covering one main surface of the substrate, The system comprises an insulating sheet positioned between the resistor and the metal sheet, The resistor is A sensing part is formed to extend along the first direction while folding back, A first connection part is connected to one end of the aforementioned sensing part and has a connection point to which wiring to an external circuit is connected, The device comprises a second connection part which is connected to the other end of the aforementioned sensing part and has a connection point to which wiring to the external circuit is connected, The sensing portion and the two connection points are arranged to be separated in the first direction. The connection point of the first connection part and the connection point of the second connection part are arranged side by side in a second direction that intersects with the first direction. At least one of the first connecting portion and the second connecting portion has an extended portion that extends inward beyond both ends of the sensing portion in the second direction, The insulating sheet has a first opening that exposes the first connection portion and a second opening that exposes the second connection portion. The metal sheet extends to a position where it overlaps the extended portions of the first and second connecting portions. A strain gauge wherein the two ends of the metal sheet on the connection side are located in front of the edges of the first opening and the second opening on the sensing side, as viewed from the sensing part in the first direction.

2. The strain gauge according to claim 1, wherein the metal sheet is arranged across the first connection portion and the second connection portion and the sensing portion, and as seen from the sensing portion, it covers a portion of the first connection portion and the second connection portion beyond the base material exposed between the two connection portions and the sensing portion.

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

4. The strain gauge according to claim 1, wherein the metal sheet protrudes 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 the main surface of the base material.

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

6. The first direction and the second direction are orthogonal to each other. The strain gauge according to claim 4 or 5, wherein the distance between the sensing portion and the two connection points is greater than the distance between the sensing portion and the two outer edges of the base material in the second direction, and the distance between the sensing portion and the outer edge of the base material on the side opposite to the side where 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. It is made of a metallic material and is arranged on one main surface of the substrate in an electrically insulated manner from the resistor, and includes a covering portion that covers at least a part of the one main surface to suppress the penetration of moisture into the substrate, The covering portion covers at least a part of the substrate that is not covered by the metal sheet. A strain gauge according to any one of claims 1 to 7.

9. The strain gauge according to claim 8, wherein the covering portion is arranged around at least the first connection portion and the second connection portion, respectively.

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 connecting portion and the second connecting portion extends to the outer edge of one main surface of the base material when viewed in the second direction intersecting the first direction, at least in the region where the metal sheet does not cover the base material.

12. A resistor having conductivity, comprising: a sensing portion formed to extend along a first direction while being folded back; a first connection portion connected to one end of the sensing portion and having a connection point for wiring to an external circuit; and a second connection portion connected to the other end of the sensing portion and having a connection point for wiring to the external circuit, wherein the sensing portion and the two connection points are spaced apart 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, and at least one of the first connection portion and the second connection portion has an extended portion that extends inward beyond both ends of the sensing portion in the second direction, the resistor being formed on one main surface of an insulating substrate, A step of forming an insulating sheet having a first opening that exposes the first connection portion and a second opening that exposes the second connection portion, The step includes arranging a metal sheet that covers one main surface of the substrate, A method for manufacturing a strain gauge, comprising the step of arranging the metal sheet, wherein the metal sheet extends to a position overlapping the extended portions of the first and second connection portions, and the ends of the metal sheet on the connection portion side are positioned in front of the edges of the first and second openings on the sensing portion side, as viewed from the sensing portion in the first direction.

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