JP2024177526A - Strain gauges - Google Patents

Abstract

A strain gauge with improved creep characteristics is provided.
[Solution] The strain gauge has a substrate, a resistor directly or indirectly disposed on the substrate, and wiring connected to an end of the resistor, the wiring including a first metal layer formed from the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material having a lower resistance than the first metal layer.
[Selected Figure] Figure 1

Description

The present invention relates to a strain gauge.

Strain gauges are known that have a resistor on a substrate and are attached to an object to be measured to detect the characteristics of the object. Strain gauges are used in sensor applications such as sensors that detect the strain of materials and sensors that detect ambient temperature (see, for example, Patent Document 1).

JP 2001-221696 A

Creep properties are important for strain gauges, and by improving the creep properties, for example, it may be possible to use strain gauges not only for sensor applications, but also for weighing applications.

The present invention was made in consideration of the above points, and aims to provide a strain gauge with improved creep characteristics.

This strain gauge has a substrate, a resistor directly or indirectly provided on the substrate, and wiring connected to an end of the resistor, the wiring including a first metal layer formed of the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material having a lower resistance than the first metal layer.

The disclosed technology makes it possible to provide a strain gauge with improved creep characteristics.

FIG. 2 is a plan view illustrating the strain gauge according to the first embodiment. FIG. 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment. FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. 4 is a cross-sectional view (part 3) illustrating the strain gauge according to the first embodiment; FIG. 4 is a plan view illustrating a strain gauge according to a first modified example of the first embodiment. FIG. 2 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. FIG. 11 is a plan view illustrating a strain gauge according to a second modified example of the first embodiment. FIG. 11 is a plan view illustrating a strain gauge according to a third modified example of the first embodiment.

Below, a description will be given of a mode for carrying out the invention with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated explanations may be omitted.

First Embodiment
Fig. 1 is a plan view illustrating the strain gauge according to the first embodiment. Fig. 2 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line A-A in Fig. 1. Fig. 3 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment, showing a cross section along line B-B in Fig. 1.

Referring to Figures 1 to 3, the strain gauge 1 has a substrate 10, a resistor 30, wiring 40, electrodes 50, wiring 60, and a cover layer 70. For convenience, only the outer edge of the cover layer 70 is shown by a dashed line in Figures 1 to 3. The cover layer 70 may be provided as needed.

In this embodiment, for convenience, in the strain gauge 1, the side of the substrate 10 on which the resistor 30 is provided is referred to as the upper side or one side, and the side on which the resistor 30 is not provided is referred to as the lower side or the other side. Also, the surface on which the resistor 30 is provided in each portion is referred to as the one side or upper surface, and the surface on which the resistor 30 is not provided is referred to as the other side or lower surface. However, the strain gauge 1 can be used upside down or placed at any angle. Also, a planar view refers to viewing an object from the normal direction of the upper surface 10a of the substrate 10, and a planar shape refers to the shape of the object viewed from the normal direction of the upper surface 10a of the substrate 10.

The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. There are no particular limitations on the thickness of the substrate 10, and it can be selected appropriately depending on the purpose, but it can be, for example, about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm is preferable in terms of the transmission of strain from the surface of the strain generator that is joined to the underside of the substrate 10 via an adhesive layer or the like, and dimensional stability against the environment, and a thickness of 10 μm or more is even more preferable in terms of insulation.

The substrate 10 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, polyolefin resin, etc. Note that a film refers to a flexible material with a thickness of about 500 μm or less.

Here, "formed from an insulating resin film" does not prevent the base material 10 from containing fillers, impurities, etc. in the insulating resin film. The base material 10 may be formed from an insulating resin film containing fillers such as silica or alumina.

Examples of materials other than _resin for the substrate 10 include crystalline materials such _{as SiO2} , _ZrO2 (including YSZ), Si, _Si2N3 , _Al2O3 (including sapphire), ZnO, perovskite ceramics ( _CaTiO3 , _BaTiO3 ), and amorphous glass. Metals such as aluminum, aluminum alloys (duralumin), and titanium may also be used as the material for the substrate 10. In this case, for example, an insulating film is formed on the metal substrate 10.

The resistor 30 is a thin film formed in a predetermined pattern on the substrate 10, and is a sensing part that generates a resistance change when strained. The resistor 30 may be formed directly on the upper surface 10a of the substrate 10, or may be formed on the upper surface 10a of the substrate 10 via another layer. For convenience, the resistor 30 is shown in FIG. 1 with a dark matte pattern.

The resistor 30 has multiple elongated portions arranged at regular intervals with their longitudinal direction in the same direction (the direction of line A-A in FIG. 1), and the ends of adjacent elongated portions are alternately connected to form folded-back portions 35, resulting in a zigzag folded-back structure overall. The longitudinal direction of the multiple elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the direction perpendicular to line A-A in FIG. 1).

One end in the longitudinal direction of the two elongated portions located at the outermost sides in the grid width direction is bent in the grid width direction to form respective ends _30e1 and _30e2 in the grid width direction of the resistor 30. The respective ends _30e1 and _30e2 in the grid width direction of the resistor 30 are electrically connected to the electrodes 50 via the wiring 40. In other words, the wiring 40 electrically connects the respective ends _30e1 and _30e2 in the grid width direction of the resistor 30 to the respective electrodes 50.

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

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N, etc. are mixed together. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

The thickness of the resistor 30 is not particularly limited and can be appropriately selected depending on the purpose, but can be, for example, about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more is preferable in that the crystallinity of the crystals constituting the resistor 30 (for example, the crystallinity of α-Cr) is improved. Furthermore, a thickness of 1 μm or less is even more preferable in that film cracks caused by internal stress in the film constituting the resistor 30 and warping from the substrate 10 can be reduced. The width of the resistor 30 can be optimized for the required specifications such as resistance value and lateral sensitivity, and can be, for example, about 10 μm to 100 μm, taking into consideration measures against disconnection.

For example, when the resistor 30 is a Cr mixed phase film, the stability of the gauge characteristics can be improved by making the main component α-Cr (alpha chromium), which is a stable crystal phase. In addition, by making the resistor 30 mainly composed of α-Cr, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. Here, the main component means that the target substance accounts for 50% by weight or more of the total substance constituting the resistor, but from the viewpoint of improving the gauge characteristics, it is preferable that the resistor 30 contains α-Cr at 80% by weight or more, and more preferably at 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

Furthermore, when the resistor 30 is a Cr mixed-phase film, the Cr mixed-phase film preferably contains 20% by weight or less of CrN and Cr ₂ N. By containing the Cr mixed-phase film with 20% by weight or less of CrN and Cr ₂ N, a decrease in the gauge factor can be suppressed.

In addition, the ratio of _Cr2N in CrN and _Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the ratio of _Cr2N in CrN and _Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes more significant due to the _Cr2N having semiconducting properties. Furthermore, by reducing the ceramicization, brittle fracture is reduced.

On the other hand, if a small amount of _N2 or atomic N is mixed in or present in the film, it will escape to the outside of the film due to the external environment (for example, a high temperature environment), causing a change in the film stress. By creating chemically stable CrN, it is possible to obtain a stable strain gauge without generating the unstable N mentioned above.

The wiring 40 is formed on the substrate 10 and is electrically connected to the resistor 30 and the electrode 50. The wiring 40 has a first metal layer 41 and a second metal layer 42 laminated on the upper surface of the first metal layer 41. The wiring 40 is not limited to being linear, and can be in any pattern. The wiring 40 can also be of any width and length. For convenience, in FIG. 1, the wiring 40, the electrode 50, and the wiring 60 are shown with a matte pattern that is thinner than the resistor 30.

The electrodes 50 are formed on the substrate 10 and are electrically connected to the resistor 30 via the wiring 40, and are formed, for example, in a substantially rectangular shape wider than the wiring 40. The electrodes 50 are a pair of electrodes for outputting the change in resistance value of the resistor 30 caused by distortion to the outside, and for example, lead wires for external connection are joined to the electrodes 50.

The electrode 50 has a pair of first metal layers 51 and a second metal layer 52 laminated on the upper surface of each of the first metal layers 51. The first metal layers 51 are electrically connected to the ends _30e1 and _30e2 of the resistor 30 via the first metal layers 41 of the wiring 40. The first metal layers 51 are formed in a substantially rectangular shape in a plan view. The first metal layers 51 may be formed to have the same width as the wiring 40.

The wiring 60 is a dummy wiring formed on the substrate 10, one end of which is connected to one of the folded portions 35 of the resistor 30, and the other end of which is open. In the example of FIG. 1, the wiring 60 includes a circular portion in a plan view on the other end side, but is not limited to this, and the other end side may include any shape such as an ellipse or a rectangle. Alternatively, the wiring 60 may have the same width from one end side to the other end side.

The strain gauge 1 may have one or more wirings 60, but in the example of FIG. 1, it has multiple wirings 60 (specifically, six). As shown in FIG. 1, the multiple wirings 60 may include wirings 60 arranged on both sides of the resistor 30 in the direction of line A-A. Also, as shown in FIG. 1, the multiple wirings 60 may include two or more wirings 60 arranged along a direction perpendicular to line A-A.

The strain gauge 1 may also include one wiring 60 for each of the folded portions 35. The wirings 60 are separated from each other and are not connected to each other. The area of the wiring 60 is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, 0.07 ^mm2 or more. The larger the total area of the wirings 60, the higher the rigidity of the strain gauge 1, which is preferable. The wiring 60 includes a first metal layer 61 formed of the same material as the resistor 30 and extending from the folded portion 35, and a second metal layer 62 laminated on the upper surface of the first metal layer 61.

Note that the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 are given different reference numbers for convenience, but may be formed from the same material. In that case, the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 can be integrally formed from the same material in the same process. Therefore, the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 have approximately the same thickness.

Although the second metal layer 42, the second metal layer 52, and the second metal layer 62 are given different reference numbers for convenience, they may be formed from the same material. In that case, the second metal layer 42, the second metal layer 52, and the second metal layer 62 can be integrally formed from the same material in the same process. Therefore, the second metal layer 42, the second metal layer 52, and the second metal layer 62 have approximately the same thickness.

The second metal layers 42, 52, and 62 are formed from a material with a lower resistance than the resistor 30 (the first metal layers 41, 51, and 61). There is no particular restriction on the material of the second metal layers 42, 52, and 62, as long as it is a material with a lower resistance than the resistor 30, and it can be appropriately selected according to the purpose. For example, when the resistor 30 is a Cr mixed phase film, the material of the second metal layers 42, 52, and 62 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, and compounds are appropriately laminated. There is no particular restriction on the thickness of the second metal layers 42, 52, and 62, and it can be appropriately selected according to the purpose, but it can be, for example, about 3 μm to 5 μm.

The second metal layers 42, 52, and 62 may be formed on a portion of the upper surface of the first metal layers 41, 51, and 61, or may be formed on the entire upper surface of the first metal layers 41, 51, and 61. One or more other metal layers may be laminated on the upper surface of the second metal layer 52. For example, the second metal layer 52 may be a copper layer, and a gold layer may be laminated on the upper surface of the copper layer. Alternatively, the second metal layer 52 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on the upper surface of the copper layer. By forming the top layer of the electrode 50 as a gold layer, the solder wettability of the electrode 50 can be improved.

In this way, the wiring 40 has a structure in which the second metal layer 42 is laminated on the first metal layer 41 made of the same material as the resistor 30. Therefore, the resistance of the wiring 40 is lower than that of the resistor 30, and the wiring 40 can be prevented from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 30 can be improved.

In other words, by providing wiring 40 with a lower resistance than resistor 30, the actual sensing area of strain gauge 1 can be limited to the local area where resistor 30 is formed. This improves the accuracy of strain detection by resistor 30.

In particular, in a highly sensitive strain gauge with a gauge factor of 10 or more that uses a Cr mixed-phase film as the resistor 30, making the wiring 40 lower in resistance than the resistor 30 and limiting the actual sensing area to the local area where the resistor 30 is formed has a significant effect on improving strain detection accuracy. Making the wiring 40 lower in resistance than the resistor 30 also has the effect of reducing lateral sensitivity.

In addition, by providing wiring 60 connected to the folded portion 35 of the resistor 30, the rigidity of the strain gauge 1 is increased, so that the displacement of the resistor 30 can be reduced and the creep characteristics can be improved. In other words, the creep amount and creep recovery amount can be reduced in the strain gauge 1. The creep amount and creep recovery amount are the amount of elastic deformation (strain amount) of the surface on which the resistor 30 is provided in the strain gauge 1 that changes over time, and can be measured by calculating the output of the pair of electrodes 50.

By reducing the amount of creep and the amount of creep recovery, it becomes possible to use the strain gauge 1 for weighing purposes. When using the strain gauge 1 for weighing purposes, it is necessary to satisfy the standards related to creep. Examples of standards related to creep include precision class C1 based on OIML R60 (hereinafter referred to as C1 standard) and precision class C2 based on OIML R60 (hereinafter referred to as C2 standard).

The C1 standard requires that the creep amount and creep recovery amount be ±0.0735% or less. The C2 standard requires that the creep amount and creep recovery amount be ±0.0368% or less. When the strain gauge 1 is used for sensor applications, the standard for the creep amount and creep recovery amount is approximately ±0.5%.

The cover layer 70 (insulating resin layer) is formed on the substrate 10, covers the resistor 30, the wiring 40, and the wiring 60, and exposes the electrode 50. The cover layer 70 has an opening 70x, and the electrode 50 is exposed in the opening 70x. A part of the electrode 50 may be covered by the cover layer 70. Also, a part of the wiring 40 may be exposed from the cover layer 70. By providing the cover layer 70 that covers the resistor 30, the wiring 40, and the wiring 60, it is possible to prevent mechanical damage, etc. from occurring to the resistor 30, the wiring 40, and the wiring 60. Also, by providing the cover layer 70, it is possible to protect the resistor 30, the wiring 40, and the wiring 60 from moisture, etc. The cover layer 70 may be provided so as to cover the entire portion except the electrode 50.

The cover layer 70 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 70 may contain a filler or pigment. There is no particular limit to the thickness of the cover layer 70 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

To manufacture the strain gauge 1, first, a substrate 10 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 10a of the substrate 10. Metal layer A is a layer that is ultimately patterned to become the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61. Therefore, the material and thickness of metal layer A are the same as those of the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61 described above.

Metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming metal layer A as a target. Instead of magnetron sputtering, metal layer A may also be formed using reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as a base layer on the upper surface 10a of the substrate 10, for example, by conventional sputtering, before depositing the metal layer A.

In this application, the functional layer refers to a layer that has the function of promoting the crystal growth of at least the upper layer, metal layer A (resistor 30). The functional layer preferably also has the function of preventing oxidation of metal layer A due to oxygen and moisture contained in the substrate 10, and the function of improving adhesion between the substrate 10 and metal layer A. The functional layer may also have other functions.

The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, particularly when the metal layer A contains Cr, it is effective for the functional layer to have the function of preventing oxidation of the metal layer A.

The material of the functional layer is not particularly limited as long as it has the function of promoting the crystal growth of at least the upper metal layer A (resistor 30), and can be appropriately selected according to the purpose. For example, one or more metals selected from the group consisting of Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of the metals in this group, or a compound of any of the metals in this group can be mentioned.

Examples of the alloy include FeCr, TiAl, FeNi, NiCr, CrCu, _etc. Examples of the compound include TiN, TaN, _Si3N4 , _TiO2 , _Ta2O5 , _{SiO2 ,} etc.

When the functional layer is made of a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1/20 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and a part of the current flowing through the resistor can be prevented from flowing through the functional layer, which would reduce the sensitivity of strain detection.

When the functional layer is made of a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer is 1/50 or less of the thickness of the resistor. In this range, the crystal growth of α-Cr can be promoted, and it is also possible to further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby reducing the sensitivity of strain detection.

When the functional layer is made of a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer is 1/100 or less of the thickness of the resistor. In this range, it is possible to further prevent a portion of the current flowing through the resistor from flowing through the functional layer, thereby preventing a decrease in the strain detection sensitivity.

When the functional layer is made of an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. This range promotes the crystal growth of α-Cr and allows the functional layer to be easily formed without cracking.

When the functional layer is made of an insulating material such as an oxide or nitride, it is more preferable that the thickness of the functional layer is 1 nm to 0.8 μm. This range promotes the crystal growth of α-Cr and makes it easier to form the functional layer without cracking.

When the functional layer is made of an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer is 1 nm to 0.5 μm. This range promotes the crystal growth of α-Cr and makes it easier to form the functional layer without cracking.

The planar shape of the functional layer is patterned, for example, to be substantially the same as the planar shape of the resistor shown in FIG. 1. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. If the functional layer is formed from an insulating material, it does not have to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed in a solid shape at least in the area where the resistor is formed. Alternatively, the functional layer may be formed in a solid shape over the entire top surface of the substrate 10.

In addition, when the functional layer is made of an insulating material, the functional layer is formed relatively thick, at a thickness of 50 nm to 1 μm, and formed in a solid shape, thereby increasing the thickness and surface area of the functional layer, and therefore heat generated by the resistor can be dissipated to the substrate 10. As a result, the deterioration of measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 1.

The functional layer can be formed in a vacuum by conventional sputtering, for example, using a raw material capable of forming the functional layer as a target and introducing Ar (argon) gas into a chamber. By using conventional sputtering, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, so that the amount of the functional layer formed can be minimized and the effect of improving adhesion can be obtained.

However, this is just one example of a method for forming the functional layer, and the functional layer may be formed by other methods. For example, a method may be used in which the upper surface 10a of the substrate 10 is activated by plasma treatment using Ar or the like before forming the functional layer, thereby improving adhesion, and then the functional layer is vacuum-formed by magnetron sputtering.

There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer A, and they can be selected appropriately depending on the purpose. For example, it is possible to use Ti as the functional layer and form a Cr mixed phase film with α-Cr (alpha chromium) as the main component as the metal layer A.

In this case, for example, the metal layer A can be formed by magnetron sputtering using a raw material capable of forming a Cr mixed phase film as a target and introducing Ar gas into a chamber. Alternatively, the metal layer A can be formed by reactive sputtering using pure Cr as a target and introducing an appropriate amount of nitrogen gas together with Ar gas into a chamber. In this case, the ratio of CrN and Cr ₂ N contained in the Cr mixed phase film and the ratio of Cr ₂ N in CrN and Cr ₂ N can be adjusted by changing the amount and pressure (nitrogen partial pressure) of the nitrogen gas introduced or by adjusting the heating temperature by providing a heating process.

In these methods, the growth surface of the Cr mixed-phase film is determined by the functional layer made of Ti, and a Cr mixed-phase film can be formed that is mainly composed of α-Cr, which has a stable crystal structure. In addition, the Ti that constitutes the functional layer diffuses into the Cr mixed-phase film, improving the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be set to 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be set within the range of -1000 ppm/°C to +1000 ppm/°C. Note that when the functional layer is formed from Ti, the Cr mixed-phase film may contain Ti and TiN (titanium nitride).

When metal layer A is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A due to oxygen and moisture contained in substrate 10, and improving adhesion between substrate 10 and metal layer A. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

In this way, by providing a functional layer below the metal layer A, it is possible to promote crystal growth in the metal layer A, and to produce a metal layer A consisting of a stable crystalline phase. As a result, the stability of the gauge characteristics of the strain gauge 1 can be improved. In addition, the material constituting the functional layer diffuses into the metal layer A, thereby improving the gauge characteristics of the strain gauge 1.

Next, a second metal layer 42, a second metal layer 52, and a second metal layer 62 are formed on the upper surface of the metal layer A. The second metal layer 42, the second metal layer 52, and the second metal layer 62 can be formed, for example, by a photolithography method.

Specifically, first, a seed layer is formed by, for example, sputtering or electroless plating so as to cover the upper surface of metal layer A. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and is exposed and developed to form openings that expose the areas in which second metal layer 42, second metal layer 52, and second metal layer 62 will be formed. At this time, by adjusting the shape of the openings in the resist, second metal layer 42, second metal layer 52, and second metal layer 62 can be formed into any shape. For example, a dry film resist can be used as the resist.

Next, for example, the second metal layer 42, the second metal layer 52, and the second metal layer 62 are formed on the seed layer exposed in the opening by electrolytic plating using the seed layer as a power supply path. The electrolytic plating method is advantageous in that it has a high tact time and can form low-stress electrolytic plating layers as the second metal layer 42, the second metal layer 52, and the second metal layer 62. By making the thick electrolytic plating layer low-stress, it is possible to prevent warping of the strain gauge 1. The second metal layer 42, the second metal layer 52, and the second metal layer 62 may also be formed by electroless plating.

Next, the resist is removed. For example, the resist can be removed by immersing it in a solution that can dissolve the resist material.

Next, a photosensitive resist is formed on the entire upper surface of the seed layer, and is exposed and developed to be patterned into a planar shape similar to the resistor 30, wiring 40, electrode 50, and wiring 60 in FIG. 1. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and the seed layer exposed from the resist, forming the resistor 30, wiring 40, electrode 50, and wiring 60 in the planar shape of FIG. 1.

For example, unnecessary portions of the metal layer A and the seed layer can be removed by wet etching. If a functional layer is formed below the metal layer A, the functional layer is patterned by etching into the planar shape shown in FIG. 1, similar to the resistor 30, the wiring 40, the electrode 50, and the wiring 60. At this point, a seed layer is formed on the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61.

Next, the second metal layer 42, the second metal layer 52, and the second metal layer 62 are used as an etching mask to remove the unnecessary seed layer exposed from the second metal layer 42, the second metal layer 52, and the second metal layer 62, thereby forming the second metal layer 42, the second metal layer 52, and the second metal layer 62. Note that the seed layer directly below the second metal layer 42, the second metal layer 52, and the second metal layer 62 remains. For example, the unnecessary seed layer can be removed by wet etching using an etching solution that etches the seed layer but does not etch the functional layer, resistor 30, wiring 40, electrode 50, and wiring 60.

Then, as necessary, a cover layer 70 that covers the resistor 30, the wiring 40, and the wiring 60 and exposes the electrode 50 is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer 70 can be produced, for example, by laminating a semi-cured thermosetting insulating resin film on the upper surface 10a of the substrate 10 so as to cover the resistor 30, the wiring 40, and the wiring 60 and expose the electrode 50, and then heating and curing the film. The cover layer 70 can also be produced by applying a liquid or paste-like thermosetting insulating resin to the upper surface 10a of the substrate 10 so as to cover the resistor 30, the wiring 40, and the wiring 60 and expose the electrode 50, and then heating and curing the resin. The opening 70x can be formed, for example, by photolithography.

When a functional layer is provided on the upper surface 10a of the substrate 10 as an underlayer for the resistor 30, the first metal layer 41, the first metal layer 51, and the first metal layer 61, the strain gauge 1 has a cross-sectional shape as shown in FIG. 4. The layer indicated by the reference numeral 20 is the functional layer. When the functional layer 20 is provided, the planar shape of the strain gauge 1 is, for example, the same as that shown in FIG. 1. However, as described above, the functional layer 20 may be formed in a solid shape on part or all of the upper surface 10a of the substrate 10.

First Modification of the First Embodiment
In the first modification of the first embodiment, an example is shown in which a metal having a lower melting point than the second metal layer 62 is laminated on the wiring 60. Note that in the first modification of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

Figure 5 is a plan view illustrating a strain gauge according to Variation 1 of the first embodiment. Figure 6 is a cross-sectional view illustrating a strain gauge according to Variation 1 of the first embodiment, showing a cross section along line CC in Figure 5. With reference to Figures 5 and 6, strain gauge 1A differs from strain gauge 1 (see Figures 1 to 3, etc.) in that metal 80 with a lower melting point than second metal layer 62 is added onto wiring 60.

In the strain gauge 1A, the cover layer 70 has an opening 70y that exposes at least a portion of the wiring 60. A metal 80 having a lower melting point than the second metal layer 62 is laminated on the second metal layer 62 of the wiring 60 exposed in the opening 70y. The metal 80 is, for example, solder or metal paste.

In this way, by laminating metal 80, which has a lower melting point than second metal layer 62, on wiring 60, the rigidity of strain gauge 1A can be made even higher than that of strain gauge 1. As a result, the creep characteristics of strain gauge 1A can be improved even more than that of strain gauge 1.

In addition, taking into consideration the thermal damage to the resistor 30, it is preferable to select lead-free solder or metal paste as the material for the metal 80. High temperature solder and high melting point solder are not preferable.

<Modification 2 of the First Embodiment>
In the second modification of the first embodiment, an example is shown in which a third metal layer is disposed around the resistor 30. Note that in the second modification of the first embodiment, the description of the same components as those in the already described embodiment may be omitted.

Figure 7 is a plan view illustrating a strain gauge according to the second modification of the first embodiment. Referring to Figure 7, the strain gauge 1B differs from the strain gauge 1 (see Figures 1 to 3, etc.) in that it has a third metal layer 90 arranged around the resistor 30 and spaced apart from the resistor 30 and the wiring 60.

The third metal layer 90 is formed of the same material as the resistor 30. The third metal layer 90 can be formed in the same process as the resistor 30 and the first metal layer 41. It is preferable to arrange the third metal layer 90 in the excess space around the resistor 30 so that it has as large an area as possible. A metal layer made of the same material as the second metal layer 62 may be laminated on the third metal layer 90.

In this way, by disposing the third metal layer 90 around the resistor 30, the rigidity of the strain gauge 1B can be made even higher than that of the strain gauge 1. As a result, the creep characteristics of the strain gauge 1B can be improved even more than that of the strain gauge 1. Note that the modified example 2 of the first embodiment can also be combined with the modified example 1 of the first embodiment. In that case, the creep characteristics are further improved.

<Modification 3 of the First Embodiment>
In the third modification of the first embodiment, an example in which the arrangement of electrodes is changed will be described. Note that in the third modification of the first embodiment, the description of the same components as those in the embodiments already described may be omitted.

Figure 8 is a plan view illustrating a strain gauge according to the third modified example of the first embodiment. Referring to Figure 8, strain gauge 1C differs from strain gauge 1 (see Figures 1 to 3, etc.) in that electrode 50 is replaced with electrode 50A. The layered structure of electrode 50A is similar to the layered structure of electrode 50.

The pair of electrodes 50A are arranged on either side of the resistor 30 in the longitudinal direction (direction of line A-A in FIG. 1) of each elongated portion of the resistor 30. For example, the width of the electrode 50A in the direction perpendicular to the longitudinal direction is wider than the width of each elongated portion of the resistor 30 in the longitudinal direction (direction of line A-A in FIG. 1). It is preferable to arrange the electrode 50A in the excess space around the resistor 30 so that it occupies as large an area as possible.

In this way, by sandwiching the resistor 30 and arranging the electrodes 50A on both sides of the longitudinal direction of each elongated portion of the resistor 30 (the direction of line A-A in FIG. 1), the rigidity of the strain gauge 1C can be made even higher than that of the strain gauge 1. As a result, the creep characteristics of the strain gauge 1C can be improved even more than those of the strain gauge 1. Note that the modified example 3 of the first embodiment can also be combined with the modified examples 1 and/or 2 of the first embodiment. In that case, the creep characteristics are further improved.

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

1, 1A, 1B, 1C strain gauge, 10 substrate, 10a upper surface, 20 functional layer, 30 resistor, 30e ₁ , 30e ₂ termination, 35 folded portion, 40, 60 wiring, 41, 51, 61 first metal layer, 42, 52, 62 second metal layer, 50, 50A electrode, 70 cover layer, 70x, 70y opening, 80 metal, 90 third metal layer

Claims (9)

A substrate;
A resistor provided directly or indirectly on the substrate;
a wiring connected to an end of the resistor,
A strain gauge, wherein the wiring includes a first metal layer formed from the same material as the resistor and extending from the end, and a second metal layer formed on the first metal layer from a material having a lower resistance than the first metal layer. The strain gauge according to claim 1, wherein the resistor is formed from a material containing Cr, a material containing Ni, or a material containing at least one of Cr and Ni. The strain gauge according to claim 1 or 2, wherein one end of the wiring is connected to each of both ends of the resistor, and the other end of the wiring is open. an insulating resin layer that covers the resistor and the wiring;
The strain gauge according to claim 1 , wherein the insulating resin layer has an opening through which at least a part of the wiring is exposed. The strain gauge according to claim 4, wherein a metal having a lower melting point than the second metal layer is laminated on the wiring exposed in the opening. a third metal layer disposed around the resistor and spaced apart from the resistor and the wiring;
The strain gauge according to claim 1 , wherein the third metal layer is made of the same material as the resistor. a pair of electrodes formed on the base material and electrically connected to the resistor;
The strain gauge according to claim 1 , wherein the electrodes are disposed on both sides of the resistor in a grid direction, with the resistor sandwiched between the electrodes. The strain gauge of claim 7, wherein the electrodes are wider in a direction perpendicular to the grid direction than in the grid direction. A strain gauge according to any one of claims 1 to 8, having a gauge factor of 10 or more.

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