JP2019090721A - Strain gauge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce warpage in a strain gauge having a resistor formed on a flexible substrate. SOLUTION: A strain gauge is formed on a flexible base material 10, a resistor 30 formed of a material containing at least one of chromium and nickel on the base material 10, and a resistor 30. It has an insulating layer 50, and the expansion coefficient of the insulating layer 50 is the same as the expansion coefficient of the base material 10. [Selection diagram] Fig. 3

Description

  The present invention relates to strain gauges.

  There is known a strain gauge which is attached to a measurement object to detect a strain of the measurement object. The strain gauge includes a resistor that detects strain, and a material containing, for example, Cr (chromium) or Ni (nickel) is used as a material of the resistor. The resistor is formed on, for example, a base made of an insulating resin (see, for example, Patent Document 1).

JP, 2016-74934, A

  However, unlike the case of using a substrate made of a ceramic or the like having high mechanical strength, in the case of using a flexible substrate, warpage caused in the strain gauge becomes a problem. When warpage occurs in the strain gauge, the resistor may be cracked to deteriorate the gauge characteristics or may not function as a strain gauge.

  The present invention has been made in view of the above-described points, and an object of the present invention is to reduce warpage in a strain gauge having a resistor formed on a flexible base material.

  The present strain gauge comprises a flexible substrate, a resistor formed of a material containing at least one of chromium and nickel on the substrate, and an insulating layer formed on the resistor. And the expansion coefficient of the insulating layer is the same as the expansion coefficient of the substrate.

  According to the disclosed technology, warpage can be reduced in a strain gauge having a resistor formed on a flexible substrate.

It is a top view which illustrates the strain gauge concerning a 1st embodiment. It is a sectional view (the 1) which illustrates the strain gauge concerning a 1st embodiment. It is sectional drawing (the 2) which illustrates the strain gauge which concerns on 1st Embodiment. It is a figure which illustrates the manufacturing process of the strain gauge concerning a 1st embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

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, and shows a cross-section along the line A-A of FIG. FIG. 3 is a cross-sectional view illustrating the strain gauge according to the first embodiment, and shows a cross-section along the line B-B in FIG. Referring to FIGS. 1 to 3, the strain gauge 1 includes a base 10, a resistor 30, a terminal 41, and an insulating layer 50.

  In the present embodiment, for convenience, in the strain gauge 1, the side of the base material 10 on which the resistor 30 is provided is the upper side or one side, and the side on which the resistor 30 is not provided is the lower side or the other side. To the side. Further, the surface on the side where the resistor 30 of each part is provided is referred to as one surface or upper surface, and the surface on the side where the resistor 30 is not provided is referred to as the other surface or lower surface. However, the strain gauge 1 can be used in the upside-down state or can be disposed at any angle. Further, planar view refers to viewing the object in the normal direction of the upper surface 10a of the base material 10, and planar shape refers to a shape of the object viewed in the normal direction of the upper surface 10a of the base 10 I assume.

  The base 10 is a member to be a base layer for forming the resistor 30 and the like, and has flexibility. There is no restriction | limiting in particular in the thickness of the base material 10, Although it can select suitably according to the objective, For example, it can be about 5 micrometers-500 micrometers. In particular, when the thickness of the substrate 10 is 5 μm to 200 μm, in terms of the transmission of strain from the surface of the strain-generating body bonded to the lower surface of the substrate 10 via the adhesive layer etc., and dimensional stability to the environment. The thickness is preferably 10 μm or more, further preferably in terms of insulation.

  The substrate 10 is made of, for example, 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 insulating resin film of In addition, a film is about 500 micrometers or less in thickness, and points out the member which has flexibility.

  Here, "forming from an insulating resin film" does not prevent the base material 10 from containing a filler, an impurity, and the like in the insulating resin film. The substrate 10 may be formed of, for example, an insulating resin film containing a filler such as silica or alumina.

  The resistor 30 is a thin film formed in a predetermined pattern on the base material 10, and is a sensing part that receives a strain and causes a change in resistance. The resistor 30 may be formed directly on the upper surface 10 a of the substrate 10 or may be formed on the upper surface 10 a of the substrate 10 via another layer. In FIG. 1, for the sake of convenience, the resistor 30 is shown in a satin pattern.

  The resistor 30 can be formed of, 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 of a material containing at least one of Cr and Ni. As a material containing Cr, for example, a Cr multiphase film can be mentioned. As a material containing Ni, Ni-Cu (nickel copper) is mentioned, for example. As a material containing both Cr and Ni, Ni-Cr (nickel chromium) is mentioned, for example.

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

  The thickness of the resistor 30 is not particularly limited and may be appropriately selected according to the purpose. For example, the thickness may be about 0.05 μm to 2 μm. In particular, it is preferable that the thickness of the resistor 30 is 0.1 μm or more in that the crystallinity (for example, the crystallinity of α-Cr) of the crystals constituting the resistor 30 is improved, and the resistor of 1 μm or less It is further preferable in that it is possible to reduce the cracks of the film resulting from the internal stress of the film constituting 30 and the warpage from the base material 10.

  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 is a stable crystal phase, as a main component. In addition, when the resistor 30 contains α-Cr as the main component, the gauge factor of the strain gauge 1 is 10 or more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR are in the range of -1000 ppm / ° C to +1000 ppm / ° C. It can be done. Here, the main component means that the target substance occupies 50% by mass or more of all the substances constituting the resistor, but from the viewpoint of improving the gauge characteristics, the resistor 30 has 80% by weight of α-Cr. It is preferable to include the above. In addition, (alpha) -Cr is Cr of a bcc structure (body-centered cubic lattice structure).

  The terminal portion 41 extends from both ends of the resistor 30, and is wider than the resistor 30 and formed in a substantially rectangular shape in a plan view. The terminal portions 41 are a pair of electrodes for outputting a change in the resistance value of the resistor 30 caused by strain to the outside, and for example, a lead wire for external connection is joined. The resistor 30 extends, for example, from one of the terminal portions 41 in a zigzag manner and is connected to the other terminal portion 41. The upper surface of the terminal portion 41 may be coated with a metal having a better solderability than the terminal portion 41. In addition, although the resistor 30 and the terminal part 41 are made into another code | symbol for convenience, both can be integrally formed with the same material in the same process.

  The insulating layer 50 is formed on the substrate 10 so as to cover the upper surfaces (surfaces on the side opposite to the substrate 10) of the resistor 30 and the terminal portion 41 and to expose the side surfaces. The insulating layer 50 has an opening 50x, and a part of the upper surface of the terminal portion 41 is exposed in the opening 50x. However, the entire upper surface of the terminal portion 41 may be exposed in the opening 50x. The planar shape of the insulating layer 50 is substantially the same as the planar shape of the substrate 10.

  The material and thickness of the insulating layer 50 are selected such that the expansion coefficient of the insulating layer 50 is the same as the expansion coefficient of the substrate 10. The material of the insulating layer 50 can be appropriately selected, for example, from the materials exemplified as the material of the substrate 10. However, the insulating layer 50 does not necessarily have to be formed of the same material as the base material 10. For example, the base material 10 may be a polyimide resin, the insulating layer 50 may be an epoxy resin, or the like. The expansion coefficient of the insulating layer 50 may be adjusted by including the filler in the insulating layer 50 and selecting the material of the filler contained in the insulating layer 50 and adjusting the content thereof.

  In the present application, the expansion coefficient of the insulating layer 50 is the same as the expansion coefficient of the substrate 10, not only when the expansion coefficient of the insulating layer 50 is completely the same as the expansion coefficient of the substrate 10 It also includes the case where the coefficient is substantially the same as the expansion coefficient of the substrate 10.

  Here, when the expansion coefficient of the insulating layer 50 is substantially the same as the expansion coefficient of the base 10, the expansion coefficient of the insulating layer 50 is within ± 100 ppm / K with respect to the expansion coefficient of the base 10. Point to the case. This range is obtained experimentally by the inventors, and if it is within this range, the internal stress of the resistor 30 is reduced and the warpage of the strain gauge 1 is below the limit value at which the strain gauge 1 functions. It can be done.

  FIG. 4 is a view illustrating the manufacturing process of the strain gauge according to the first embodiment, and FIGS. 4 (a) to 4 (c) show cross sections corresponding to FIG. 3, and FIG. 4 (d) Shows a cross section corresponding to FIG.

  In order to manufacture the strain gauge 1, first, in the step shown in FIG. 4A, the base material 10 is prepared, and the metal layer 300 is formed on the upper surface 10 a of the base material 10. The metal layer 300 is a layer that is finally patterned to be the resistor 30 and the terminal portion 41. Accordingly, the material and thickness of the metal layer 300 are the same as the materials and thicknesses of the resistor 30 and the terminal portion 41 described above.

  The metal layer 300 can be formed, for example, by a magnetron sputtering method using a source capable of forming the metal layer 300 as a target. The metal layer 300 may be deposited using a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulse laser deposition method or the like instead of the magnetron sputtering method.

  From the viewpoint of stabilizing the gauge characteristics, before depositing the metal layer 300, for example, a functional layer having a thickness of about 1 nm to 100 nm is vacuum deposited on the upper surface 10a of the base 10 as a base layer by conventional sputtering. It is preferable to make a membrane.

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

  Since the insulating resin film constituting the substrate 10 contains oxygen and moisture, in particular when the metal layer 300 contains Cr, Cr forms a self-oxidized film, so that the functional layer has the function of preventing the metal layer 300 from being oxidized. Providing is effective.

  The material of the functional layer is not particularly limited as long as it has a function of promoting crystal growth of at least the upper metal layer 300 (resistor 30), and can be appropriately selected according to the purpose. Chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (C) Carbon), Zn (zinc), Cu (copper), Bi (bismuth), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (os) From osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), Al (aluminum) One or more metals selected from that group, one of the metal alloys of this group, or a compound of any one of metals of this group and the like.

As said alloy, FeCr, TiAl, FeNi, NiCr, CrCu etc. are mentioned, for example. As the above-mentioned compounds, _{e.g., TiN, TaN, Si 3 N} 4, TiO 2, Ta 2 O 5, SiO 2 , and the like.

  The functional layer can be vacuum deposited, for example, by a conventional sputtering method in which Ar (argon) gas is introduced into the chamber with a source capable of forming the functional layer as a target. By using the conventional sputtering method, the functional layer is formed while etching the upper surface 10a of the substrate 10 with Ar, so that the adhesion improvement effect can be obtained by minimizing the amount of the functional layer formed.

  However, this is an example of a method of forming a functional layer, and the functional layer may be formed by another method. For example, the adhesion improvement effect is obtained by activating the upper surface 10a of the substrate 10 by plasma treatment using Ar or the like before film formation of the functional layer, and then vacuum film formation of the functional layer by magnetron sputtering. Methods may be used.

  The combination of the material of the functional layer and the material of the metal layer 300 is not particularly limited and may be appropriately selected according to the purpose. For example, Ti is used as the functional layer and α-Cr (alpha chromium) is used as the metal layer 300 It is possible to form a Cr mixed phase film which is a main component.

  In this case, for example, the metal layer 300 can be formed by a magnetron sputtering method in which Ar gas is introduced into the chamber with a raw material capable of forming a Cr mixed phase film as a target. Alternatively, pure Cr may be used as a target, an appropriate amount of nitrogen gas may be introduced into the chamber together with Ar gas, and the metal layer 300 may be formed by reactive sputtering.

  In these methods, the growth surface of the Cr multiphase film is defined by the functional layer made of Ti as a trigger, and it is possible to form a Cr multiphase film mainly composed of α-Cr, which has a stable crystal structure. Further, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of the strain gauge 1 can be 10 or more, and the gauge factor temperature coefficient TCS and the resistance temperature coefficient TCR can be in the range of -1000 ppm / ° C to +1000 ppm / ° C. When the functional layer is formed of Ti, the Cr mixed phase film may contain Ti or TiN (titanium nitride).

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

  As described above, by providing the functional layer in the lower layer of the metal layer 300, crystal growth of the metal layer 300 can be promoted, and the metal layer 300 composed of a stable crystal phase can be manufactured. As a result, in the strain gauge 1, the stability of the gauge characteristics can be improved. Further, the material constituting the functional layer diffuses into the metal layer 300, whereby the gauge characteristics of the strain gauge 1 can be improved.

  Next, in the process shown in FIG. 4B, the insulating layer 50 covering the metal layer 300 is formed on the base material 10. The material and thickness of the insulating layer 50 are as described above. The insulating layer 50 can be produced, for example, by laminating a thermosetting insulating resin film in a semi-cured state so as to cover the metal layer 300 on the substrate 10 and heating and curing it. The insulating layer 50 may be produced by applying a liquid or paste-like thermosetting insulating resin on the substrate 10 so as to cover the metal layer 300 and heating and curing it.

  Next, in the step shown in FIG. 4C, the metal layer 300 is patterned to form the functional layer in the planar shape of FIG. 1, the resistor 30, and the terminal portion 41. For example, an unnecessary portion of the metal layer 300 can be removed by a laser processing method in which the metal layer 300 is irradiated with laser light having a wavelength that easily transmits the insulating layer 50 and is easily absorbed by the metal layer 300.

  By patterning the metal layer 300 by the laser processing method, the step of etching the metal layer 300 with the etching solution becomes unnecessary, so that the resistor 30 and the base material 10 can be prevented from being corroded by the etching solution.

  Next, in the process illustrated in FIG. 4D, the opening 50x is formed in the insulating layer 50, and a part of the upper surface of the terminal portion 41 is exposed in the opening 50x. However, the entire upper surface of the terminal portion 41 may be exposed in the opening 50x. The opening 50 x can be formed, for example, by a laser processing method using a laser beam having a wavelength that is easily absorbed by the insulating layer 50. The photosensitive resin may be used as the insulating layer 50, and the opening 50x may be formed by photolithography.

  Alternatively, in the step shown in FIG. 4B, the insulating resin film in which the opening 50x is formed in advance may be laminated, heated and cured to form the insulating layer 50 having the opening 50x. In this case, the process shown in FIG. 4D is unnecessary. The strain gauge 1 is completed by the above steps.

  As described above, the resistance body 30 is sandwiched between the base 10 and the insulating layer 50, and the warpage of the strain gauge 1 is reduced by making the expansion coefficient of the insulating layer 50 the same as the expansion coefficient of the base 10. It becomes possible. As a result, it is possible to prevent the occurrence of the crack of the resistor 30 due to the warpage of the strain gauge 1. Also, the warpage of the strain gauge 1 can be reduced, and the strain gauge 1 can function stably while maintaining good gauge characteristics.

  Moreover, since the insulating layer 50 is formed on the resistor 30, handling becomes easy.

  Also, by forming the insulating layer 50 and then patterning the metal layer 300 by laser processing to form the resistor 30, the heat generated at the time of laser processing is dissipated to the base 10 and the insulating layer 50, so that processing is performed. It is possible to prevent the formation of protrusions and the like on the resistor 30 later.

  In addition, since the metal layer 300 is patterned by the laser processing method to form the resistor 30, the step of etching the metal layer 300 with the etching solution becomes unnecessary, so that the resistor 30 and the base 10 are corroded by the etching solution. Can be prevented. As a result, disconnection of the resistor 30 due to corrosion can be prevented.

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

  For example, even when the resistor 30 is formed by patterning the metal layer 300 by a method other than that described in the step shown in FIG. 4C, the resistor 30 is sandwiched between the base 10 and the insulating layer 50. The warpage of the strain gauge 1 can be reduced by making the expansion coefficient of the insulating layer 50 the same as the expansion coefficient of the substrate 10.

1 strain gauge, 10 base materials, 10a top surface, 30 resistors, 41 terminals, 50 insulating layers, 50x openings

Claims (8)

A flexible substrate,
A resistor formed of a material containing at least one of chromium and nickel on the substrate;
And an insulating layer formed on the resistor.
The strain gauge in which the expansion coefficient of the said insulating layer is the same as the expansion coefficient of the said base material.   The strain gauge according to claim 1, wherein side surfaces of the resistor are exposed from the base and the insulating layer.   Each of the substrate and the insulating layer is formed of an insulating resin film selected from the group consisting of polyimide resin, epoxy resin, polyether ether ketone resin, polyethylene naphthalate resin, polyethylene terephthalate resin, polyphenylene sulfide resin, and polyolefin resin The strain gauge according to claim 1 or 2, which is   The strain gauge according to any one of claims 1 to 3, wherein the resistor contains alpha chromium as a main component.   The strain gauge according to claim 4, wherein the resistor contains 80% by weight or more of alpha chromium.   The strain gauge according to claim 4, wherein the resistor contains chromium nitride. It has a functional layer formed of a metal, an alloy, or a compound of a metal on one side of the substrate,
The strain gauge according to any one of claims 1 to 6, wherein the resistor is formed on one surface of the functional layer.   The strain gauge according to claim 7, wherein the functional layer has a function of promoting crystal growth of the resistor.

Images