strain gauge

Abstract

To improve the solderability of an electrode, in a strain gauge using as a resistor a material containing Cr (chromium) or Ni (nickel).SOLUTION: A strain gauge includes: a flexible base material made of resin; a functional layer formed directly on one surface of the base material and made of a metal, an alloy, or a metal compound; a resistor containing α-Cr as a main component, formed directly on one surface of the functional layer and made of a film containing Cr, CrN, and Cr2 N; and an electrode electrically connected to the resistor. The functional layer has a function of promoting crystal growth of the α-Cr to form a film containing the α-Cr as a main component. The resistor has a thickness of 0.05 μm or more and 2 μm or less, and the functional layer has a thickness of 1 nm or more and 100 nm or less. The electrode includes: a terminal portion extending from an end part of the resistor; a first metal layer formed on the terminal portion and made of copper, a copper alloy, nickel, or a nickel alloy; and a second metal layer formed on the first metal layer and made of a material more excellent in solder wettability than the first metal layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a strain gauge. [Background technology]

[0002] There is known a strain gauge that is attached to a measurement object to detect strain of the measurement object. The strain gauge has a resistor that detects strain, and the resistor is made of a material containing, for example, chromium (Cr) or nickel (Ni). Furthermore, for example, both ends of the resistor are used as electrodes, and lead wires for external connection are joined to the electrodes by soldering (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-74934 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because resistors have a thin film thickness, using both ends of the resistor as electrodes can easily cause solder erosion, resulting in poor solderability. Furthermore, when resistors are made of materials containing Cr (chromium) or Ni (nickel), solderability is further impaired. Cr, in particular, forms a self-oxidized film, which further impairs solderability.

[0005] The present invention has been made in consideration of the above points, and aims to improve the solderability of electrodes in strain gauges that use materials containing Cr (chromium) or Ni (nickel) for the resistor. [Means for solving the problem]

[0006] This strain gauge comprises a flexible resin substrate, a functional layer formed directly on one side of the substrate from a metal, alloy, or metal compound, a resistor whose main component is α-Cr and formed from a film containing Cr, CrN, and CrN directly on one side of the functional layer, and an electrode electrically connected to the resistor. The functional layer has the function of promoting crystal growth of the α-Cr and forming a film whose main component is α-Cr, the resistor having a thickness of 0.05 μm to 2 μm, and the functional layer having a thickness of 1 nm to 100 nm. The electrode comprises a terminal portion extending from an end of the resistor, a first metal layer formed on the terminal portion from copper, a copper alloy, nickel, or a nickel alloy, and a second metal layer formed on the first metal layer from a material with better solder wettability than the first metal layer. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to improve the solderability of electrodes in a strain gauge that uses a material containing Cr (chromium) or Ni (nickel) for the resistor. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment. [Figure 2] 1 is a cross-sectional view illustrating a strain gauge according to a first embodiment. [Figure 3] 3A to 3C are diagrams (part 1) illustrating a manufacturing process of the strain gauge according to the first embodiment; [Figure 4] 5A to 5C are diagrams (part 2) illustrating the manufacturing process of the strain gauge according to the first embodiment; [Figure 5] 1 is a cross-sectional view illustrating a strain gauge according to a first modified example of the first embodiment. [Figure 6] 10 is a cross-sectional view illustrating a strain gauge according to a second modification of the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] First Embodiment Fig. 1 is a plan view illustrating a strain gauge according to a first embodiment. Fig. 2 is a cross-sectional view illustrating the strain gauge according to the first embodiment, taken along line AA in Fig. 1. Referring to Figs. 1 and 2, the strain gauge 1 has a substrate 10, a resistor 30, and an electrode 40A.

[0011] In this embodiment, for convenience, the side of the strain gauge 1 on which the resistor 30 of the substrate 10 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. Furthermore, the surface on which the resistor 30 of each portion is provided is referred to as the one side or upper side, and the surface on which the resistor 30 is not provided is referred to as the other side or lower side. However, the strain gauge 1 can be used upside down or positioned at any angle. Furthermore, 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.

[0012] The substrate 10 is a flexible member that serves as a base layer for forming the resistor 30 and the like. The thickness of the substrate 10 is not particularly limited and can be appropriately selected depending on the purpose, but 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 transferability of strain from the surface of the strain generator bonded to the lower surface 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 properties.

[0013] 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, polyolefin resin, etc. The film refers to a flexible member having a thickness of about 500 μm or less.

[0014] 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, for example.

[0015] 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 strain is applied. 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 matte finish.

[0016] The resistor 30 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 30 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr 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).

[0017] Here, the Cr mixed phase film is a film containing a mixture of Cr, CrN, Cr2N, etc. The Cr mixed phase film may contain inevitable impurities such as chromium oxide.

[0018] The thickness of 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 resistor 30 of 0.1 μm or more is preferable because it improves the crystallinity of the crystals constituting resistor 30 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even more preferable because it reduces cracks in the film constituting resistor 30 and warpage from substrate 10 caused by internal stress in the film.

[0019] For example, when the resistor 30 is a Cr mixed-phase film, the stability of the gauge characteristics can be improved by using α-Cr (alpha chromium), which has a stable crystalline phase, as the main component. Furthermore, by using α-Cr as the main component of the resistor 30, the gauge factor of the strain gauge 1 can be 10 or more, and the temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be within the range of −1000 ppm / °C to +1000 ppm / °C. Here, “main component” means that the target substance accounts for 50 mass% or more of all materials constituting the resistor. From the viewpoint of improving the gauge characteristics, however, it is preferable that the resistor 30 contains α-Cr at 80 wt% or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0020] The electrodes 40A extend from both ends of the resistor 30 and are formed in a generally rectangular shape in plan view, wider than the resistor 30. The electrodes 40A are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and are joined to, for example, lead wires for external connection. The resistor 30 extends from one of the electrodes 40A while folding back in a zigzag pattern and is electrically connected to the other electrode 40A, for example.

[0021] The electrode 40A has a laminated structure in which multiple metal layers are stacked. Specifically, the electrode 40A has terminal portions 41 extending from both ends of the resistor 30, a metal layer 42 formed on the upper surface of the terminal portion 41, a metal layer 43 formed on the upper surface of the metal layer 42, and a metal layer 44 formed on the upper surface of the metal layer 43. Although the resistor 30 and the terminal portions 41 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. The metal layer 43 is a typical example of a first metal layer according to the present invention, and the metal layer 44 is a typical example of a second metal layer according to the present invention.

[0022] The material of the metal layer 42 is not particularly limited and can be selected appropriately depending on the purpose, for example, Cu (copper). The thickness of the metal layer 42 is not particularly limited and can be selected appropriately depending on the purpose, for example, it can be about 0.01 μm to 1 μm.

[0023] The material of the metal layer 43 is preferably Cu, a Cu alloy, Ni, or a Ni alloy. The thickness of the metal layer 43 is determined taking into consideration the solderability to the electrode 40A, and is preferably 1 μm or more, more preferably 3 μm or more. By using Cu, a Cu alloy, Ni, or a Ni alloy as the material of the metal layer 43 and making the thickness of the metal layer 43 1 μm or more, solder erosion is improved. Furthermore, by using Cu, a Cu alloy, Ni, or a Ni alloy as the material of the metal layer 43 and making the thickness of the metal layer 43 3 μm or more, solder erosion is further improved. Note that, for ease of electroplating, the thickness of the metal layer 43 is preferably 30 μm or less.

[0024] Here, solder erosion refers to the material that constitutes electrode 40A dissolving in the solder that is joined to electrode 40A, causing a decrease in the thickness of electrode 40A or even the disappearance of electrode 40A. If solder erosion occurs, there is a risk that the adhesive strength and tensile strength between electrode 40A and the lead wire or the like joined to electrode 40A may decrease, so it is preferable that solder erosion does not occur.

[0025] The material of the metal layer 44 can be selected from materials having better solder wettability than the metal layer 43. For example, if the material of the metal layer 43 is Cu, a Cu alloy, Ni, or a Ni alloy, Au (gold) can be used as the material of the metal layer 44. By coating the surface of Cu, a Cu alloy, Ni, or a Ni alloy with Au, oxidation and corrosion of the Cu, Cu alloy, Ni, or Ni alloy can be prevented and good solder wettability can be obtained. The same effect can be achieved by using Pt (platinum) instead of Au as the material of the metal layer 44. There are no particular limitations on the thickness of the metal layer 44 and it can be appropriately selected depending on the purpose, but it can be, for example, about 0.01 μm to 1 μm.

[0026] In plan view, the terminal portion 41 is exposed around the laminated portion of the metal layers 42, 43, and 44, but the terminal portion 41 may have the same planar shape as the laminated portion of the metal layers 42, 43, and 44.

[0027] A cover layer 60 (insulating resin layer) may be provided on the upper surface 10a of the substrate 10 so as to cover the resistor 30 and expose the electrodes 40A. By providing the cover layer 60, it is possible to prevent mechanical damage to the resistor 30. Furthermore, by providing the cover layer 60, it is possible to protect the resistor 30 from moisture and the like. The cover layer 60 may be provided so as to cover the entire portion except for the electrodes 40A.

[0028] The cover layer 60 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 or polyolefin resin). The cover layer 60 may contain a filler or a pigment. There are no particular restrictions on the thickness of the cover layer 60 and it can be appropriately selected depending on the purpose, but it can be, for example, about 2 μm to 30 μm.

[0029] 3 and 4 are diagrams illustrating the manufacturing process of the strain gauge according to the first embodiment, showing a cross section corresponding to FIG. 2. To manufacture the strain gauge 1, first, in the step shown in FIG. 3(a), a substrate 10 is prepared, and a metal layer 300 is formed on the upper surface 10a of the substrate 10. The metal layer 300 is a layer that will eventually be patterned to become the resistor 30 and the terminal portion 41. Therefore, the material and thickness of the metal layer 300 are the same as those of the resistor 30 and the terminal portion 41 described above.

[0030] The metal layer 300 can be formed by, for example, magnetron sputtering using a target made of a raw material capable of forming the metal layer 300. Instead of magnetron sputtering, the metal layer 300 may be formed by reactive sputtering, vapor deposition, arc ion plating, pulsed laser deposition, or the like.

[0031] From the viewpoint of stabilizing the gauge characteristics, it is preferable to vacuum-deposit a functional layer having a thickness of about 1 nm to 100 nm on the upper surface 10a of the substrate 10 as a base layer by, for example, conventional sputtering before depositing the metal layer 300.

[0032] In the present application, the functional layer refers to a layer having a function of promoting the crystal growth of at least the upper layer, the metal layer 300 (resistor 30). The functional layer preferably also has a function of preventing oxidation of the metal layer 300 due to oxygen and moisture contained in the substrate 10, and a function of improving adhesion between the substrate 10 and the metal layer 300. The functional layer may also have other functions.

[0033] The insulating resin film that constitutes the substrate 10 contains oxygen and moisture, and since Cr forms a self-oxidized film, it is effective for the functional layer to have the function of preventing oxidation of the metal layer 300, especially when the metal layer 300 contains Cr.

[0034] 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 300 (resistor 30), and can be appropriately selected depending on the purpose. For example, 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), Examples of the metals include one or more metals selected from the group consisting of copper (iron), iron (Fe), molybdenum (Mo), tungsten (W), ruthenium (Ru), rhodium (Rh), re (rhenium), osmium (Os), iridium (Ir), platinum (Pt), palladium (Pd), silver (Ag), gold (Au), cobalt (Co), manganese (Mn), and aluminum (Al), alloys of any of the metals in this group, and compounds of any of the metals in this group.

[0035] Examples of the alloys include FeCr, TiAl, FeNi, NiCr, CrCu, etc. Examples of the compounds include TiN, TaN, Si3N4, TiO2, Ta2O5, SiO2, etc.

[0036] The functional layer can be formed in vacuum by conventional sputtering, for example, using a target made of a material capable of forming the functional layer 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, thereby minimizing the amount of the functional layer formed and achieving an improvement in adhesion.

[0037] 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.

[0038] There are no particular restrictions on the combination of the material of the functional layer and the material of the metal layer 300, 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 300.

[0039] In this case, for example, the metal layer 300 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 300 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.

[0040] In these methods, the Ti functional layer defines the growth plane of the Cr mixed-phase film, allowing the formation of a Cr mixed-phase film primarily composed of α-Cr, which has a stable crystal structure. Furthermore, the Ti constituting 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 temperature coefficient of gauge factor (TCS) and temperature coefficient of resistance (TCR) can be set within the ranges of -1000 ppm / °C to +1000 ppm / °C. When the functional layer is made of Ti, the Cr mixed-phase film may contain Ti or TiN (titanium nitride).

[0041] When the metal layer 300 is a Cr mixed phase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of the metal layer 300, preventing oxidation of the metal layer 300 due to oxygen and moisture contained in the base material 10, and improving adhesion between the base material 10 and the metal layer 300. The same applies when Ta, Si, Al, or Fe is used as the functional layer instead of Ti.

[0042] In this way, by providing a functional layer below the metal layer 300, it is possible to promote crystal growth in the metal layer 300, and to produce a metal layer 300 consisting of a stable crystalline phase. As a result, it is possible to improve the stability of the gauge characteristics of the strain gauge 1. Furthermore, by diffusing the material that constitutes the functional layer into the metal layer 300, it is possible to improve the gauge characteristics of the strain gauge 1.

[0043] Next, in the step shown in FIG. 3(b), a seed layer 420 that will become the metal layer 42 is formed so as to cover the upper surface of the metal layer 300 by, for example, sputtering or electroless plating.

[0044] 3(c), a photosensitive resist 800 is formed on the entire upper surface of the seed layer 420, and is exposed and developed to form openings 800x that expose regions where the electrodes 40A will be formed. As the resist 800, for example, a dry film resist or the like can be used.

[0045] 3(d), a metal layer 43 is formed on the seed layer 420 exposed in the opening 800x by, for example, electrolytic plating using the seed layer 420 as a power supply path, and a metal layer 44 is then formed on the metal layer 43. Electrolytic plating is advantageous in that it has a high tact time and can form a low-stress electroplated layer as the metal layer 43. By forming a thick electroplated layer with low stress, warping of the strain gauge 1 can be prevented. Alternatively, the metal layer 44 may be formed on the metal layer 43 by electroless plating.

[0046] When forming the metal layer 44, the side surfaces of the metal layer 43 are covered with the resist 800, so the metal layer 44 is formed only on the top surface of the metal layer 43, and not on the side surfaces.

[0047] Next, in the step shown in Fig. 4(a), the resist 800 shown in Fig. 3(d) is removed. The resist 800 can be removed, for example, by immersing it in a solution that can dissolve the material of the resist 800.

[0048] 4(b), a photosensitive resist 810 is formed on the entire upper surface of the seed layer 420, and is exposed to light and developed to be patterned into a planar shape similar to that of the resistor 30 and the terminal portion 41 in FIG. 1. For example, a dry film resist or the like can be used as the resist 810.

[0049] Next, in the step shown in FIG. 4(c), the resist 810 is used as an etching mask to remove the metal layer 300 and seed layer 420 exposed from the resist 810, thereby forming the resistor 30 and terminal portion 41 having the planar shape shown in FIG. 1. For example, unnecessary portions of the metal layer 300 and seed layer 420 can be removed by wet etching. If a functional layer is formed below the metal layer 300, the functional layer is patterned by etching into the planar shape shown in FIG. 1, similar to the resistor 30 and terminal portion 41. At this point, the seed layer 420 is formed on the resistor 30.

[0050] 4(d), the metal layer 43 and the metal layer 44 are used as an etching mask to remove unnecessary seed layer 420 exposed from the metal layer 43 and the metal layer 44, thereby forming the metal layer 42. For example, the unnecessary seed layer 420 can be removed by wet etching using an etching solution that etches the seed layer 420 but does not etch the functional layer and the resistor 30.

[0051] 4(d), if necessary, a cover layer 60 that covers the resistor 30 and exposes the electrodes 40A is provided on the upper surface 10a of the substrate 10, thereby completing the strain gauge 1. The cover layer 60 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 and expose the electrodes 40A, and then heating and curing the film. The cover layer 60 may 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 and expose the electrodes 40A, and then heating and curing the resin.

[0052] In this way, as electrode 40A, metal layer 43 made of a thick film (1 μm or more) of Cu, Cu alloy, Ni, or Ni alloy is formed on terminal portion 41, and further metal layer 44 made of a material (Au or Pt) with better solder wettability than metal layer 43 is formed on the outermost layer, thereby preventing solder erosion and improving solder wettability.

[0053] <Modification 1 of the First Embodiment> In Modification 1 of the first embodiment, an example of an electrode having a layer structure different from that of Embodiment 1 is shown. Note that in Modification 1 of the first embodiment, the description of the same components as those of the already described embodiments may be omitted.

[0054] Fig. 5 is a cross-sectional view illustrating a strain gauge according to Modification 1 of the first embodiment, showing a cross section corresponding to Fig. 2. Referring to Fig. 5, strain gauge 1A differs from strain gauge 1 (see Fig. 2, etc.) in that electrode 40A is replaced with electrode 40B. Note that cover layer 60 may be provided so as to cover the entire portion excluding electrode 40B.

[0055] Electrode 40B has a laminated structure in which multiple metal layers are stacked. Specifically, electrode 40B has terminal portions 41 extending from both ends of resistor 30, metal layer 42 formed on the upper surface of terminal portion 41, metal layer 43 formed on the upper surface of metal layer 42, metal layer 45 formed on the upper surface of metal layer 43, and metal layer 44 formed on the upper surface of metal layer 45. In other words, electrode 40B has a structure in which metal layer 45 is provided between metal layer 43 and metal layer 44 of electrode 40A.

[0056] The material of the metal layer 45 is not particularly limited and can be selected appropriately depending on the purpose, but for example, Ni can be used. NiP (nickel phosphorus) or Pd may be used instead of Ni. The metal layer 45 may also be Ni / Pd (a metal layer formed by laminating a Ni layer and a Pd layer in this order). The thickness of the metal layer 45 is not particularly limited and can be selected appropriately depending on the purpose, but can be, for example, about 1 μm to 2 μm.

[0057] The metal layer 45 can be formed on the metal layer 43 in the step shown in FIG. 3(d) by, for example, electrolytic plating using the seed layer 420 as a power supply path.

[0058] In this way, the number of layers of the electrodes is not particularly limited, and may be increased as necessary. In this case, too, a metal layer 43 made of a thick film (1 μm or more) of Cu, a Cu alloy, Ni, or a Ni alloy is formed on the terminal portion 41, and further, a metal layer 44 made of a material (Au or Pt) having better solder wettability than the metal layer 43 is formed on the outermost layer. Therefore, as in the first embodiment, it is possible to prevent solder erosion and improve solder wettability.

[0059] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows another example of an electrode having a layer structure different from that of embodiment 1. Note that in Modification 2 of the first embodiment, the description of the same components as those in the already described embodiments may be omitted.

[0060] Fig. 6 is a cross-sectional view illustrating a strain gauge according to Modification 2 of the first embodiment, showing a cross section corresponding to Fig. 2. Referring to Fig. 6, strain gauge 1B differs from strain gauge 1A (see Fig. 5) in that electrode 40B is replaced with electrode 40C. Note that cover layer 60 may be provided so as to cover the entire portion excluding electrode 40C.

[0061] The electrode 40C has a laminated structure in which multiple metal layers are stacked. Specifically, the electrode 40C includes terminal portions 41 extending from both ends of the resistor 30, a metal layer 42 formed on the upper surface of the terminal portion 41, a metal layer 43 formed on the upper surface of the metal layer 42, a metal layer 45A formed on the upper and side surfaces of the metal layer 43 and the side surfaces of the metal layer 42, and a metal layer 44A formed on the upper and side surfaces of the metal layer 45A. The material and thickness of the metal layers 44A and 45A may be the same as those of the metal layers 44 and 45, for example. The metal layer 44A is a representative example of a second metal layer according to the present invention.

[0062] To form the electrode 40C, first, in the step shown in Fig. 3(d), for example, a metal layer 43 is formed by electrolytic plating using the seed layer 420 as a power supply path, and then the resist 800 is removed in the same manner as in the step shown in Fig. 4(a) without forming a metal layer 44. Thereafter, the same steps as in Figs. 4(b) to 4(d) are performed. Thereafter, for example, a metal layer 45A can be formed on the upper and side surfaces of the metal layer 43 and the side surfaces of the metal layer 42 by electroless plating. Furthermore, for example, a metal layer 44A can be formed on the upper and side surfaces of the metal layer 45A by electroless plating.

[0063] In this way, the electrode can be fabricated by appropriately combining electrolytic plating and electroless plating. In the structure of electrode 40C, metal layer 43 made of a thick film (1 μm or more) of Cu, Cu alloy, Ni, or Ni alloy is formed on terminal portion 41, and metal layer 44A made of a material (Au or Pt) with better solder wettability than metal layer 43 is further formed as the outermost layer. However, outermost metal layer 44A is formed not only on the top surface of metal layer 43 but also on the side surfaces of metal layers 42 and 43 via metal layer 45A. Therefore, compared to electrodes 40A and 40B, the effect of preventing oxidation and corrosion of Cu, Cu alloy, Ni, or Ni alloy constituting metal layer 43 can be further improved, and solder wettability can be further improved.

[0064] The same effect can be obtained by forming metal layer 44A directly on the upper and side surfaces of metal layer 43 and the side surfaces of metal layer 42 without forming metal layer 45A. That is, it is sufficient that metal layer 44A directly or indirectly covers the upper and side surfaces of metal layer 43 and the side surfaces of metal layer 42.

[0065] [Example 1] In Example 1, a plurality of strain gauges 1A each having an electrode 40B were fabricated.

[0066] First, a 3 nm thick Ti film was vacuum-formed as a functional layer by conventional sputtering on the upper surface 10a of the substrate 10 made of polyimide resin and having a thickness of 25 μm.

[0067] Next, a metal layer 300, which will eventually be patterned to form the resistor 30 and the terminal portion 41, was formed on the functional layer by magnetron sputtering.

[0068] 3(b) to 4(d) were modified as in Variation 1 of the first embodiment to fabricate strain gauges 1A equipped with electrodes 40B, and the presence or absence of solder erosion was confirmed. Specifically, Cu was used for metal layers 42 and 43, NiP was used for metal layer 45, and Au was used for metal layer 44. Ten types of samples (Samples No. 1 to No. 10) were fabricated with different thicknesses of each metal layer, and the presence or absence of solder erosion was confirmed.

[0069] The results are shown in Table 1. In Table 1, a film thickness of "0" indicates that the metal layer was not formed. Also, "x" indicates that solder erosion occurred during the first soldering. Also, "o" indicates that no solder erosion occurred during the first soldering, but some solder erosion occurred during the second soldering (assuming solder rework, etc.). Also, "◎" indicates that no solder erosion occurred during either the first or second soldering.

[0070] [Table 1] As shown in Table 1, it was confirmed that solder erosion was improved by increasing the Cu thickness to 1 μm or more, and that solder erosion was further improved by increasing the Cu thickness to 3 μm or more. Furthermore, the results of Samples 1 and 5 confirmed that the presence or absence of solder erosion depends only on the Cu thickness, and not on the presence or absence of NiP or Au. However, as mentioned above, a metal layer made of Au or an equivalent material (such as Pt) is necessary to prevent solder erosion and improve solder wettability.

[0071] Next, the gauge characteristics were measured for each sample of Example 1. As a result, the gauge factor of each sample of Example 1 was 14 to 16. Furthermore, the gauge factor temperature coefficient TCS and the temperature coefficient of resistance TCR of each sample of Example 1 were within the range of -1000 ppm / °C to +1000 ppm / °C.

[0072] In this way, by providing a functional layer made of Ti, the crystal growth of α-Cr is promoted and a Cr mixed-phase film containing α-Cr as the main component is formed, resulting in the fabrication of a strain gauge with a gauge factor of 10 or more and a temperature coefficient of gauge factor TCS and temperature coefficient of resistance TCR in the ranges of -1000 ppm / °C to +1000 ppm / °C. It is believed that the diffusion effect of Ti into the Cr mixed-phase film contributes to the improvement of the gauge characteristics.

[0073] The above describes in detail preferred embodiments, but 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. [Explanation of symbols]

[0074] 1, 1A, 1B strain gauge, 10 substrate, 10a upper surface, 30 resistor, 41 terminal portion, 40A, 40B, 40C electrodes, 42, 43, 44, 44A, 45, 45A metal layer, 60 cover layer

Claims

1. a flexible resin substrate; a functional layer formed directly on one surface of the substrate from a metal, alloy, or metal compound; Cr, CrN, and Cr are directly applied to one surface of the functional layer. ２ a resistor formed from a film containing N and containing α-Cr as a main component; an electrode electrically connected to the resistor; the functional layer has a function of promoting crystal growth of the α-Cr and forming a film containing the α-Cr as a main component; The resistor has a thickness of 0.05 μm or more and 2 μm or less, The thickness of the functional layer is 1 nm or more and 100 nm or less, The electrode is a terminal portion extending from an end of the resistor; a first metal layer formed on the terminal portion from copper, a copper alloy, nickel, or a nickel alloy; a second metal layer formed on the first metal layer from a material having better solder wettability than the first metal layer.

2. 2. The strain gauge according to claim 1, wherein the first metal layer is an electrolytic plated layer.

3. 3. The strain gauge according to claim 1, wherein the second metal layer directly or indirectly covers the top and side surfaces of the first metal layer.

4. 4. The strain gauge according to claim 1, wherein the first metal layer has a thickness of 1 [mu]m or more.

5. 5. The strain gauge according to claim 4, wherein the first metal layer has a thickness of 3 [mu]m or more.

6. The strain gauge according to claim 1 , wherein a seed layer is formed between the terminal portion and the first metal layer.

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