JP6500182B2 - Strain gauge - Google Patents

Description

  The present invention relates to a strain gauge for detecting strain, such as a load cell for performing load measurement and a pressure sensor used for a control device.

FIG. 5 is a plan view showing a pattern of a resistor in a conventional strain gauge.
The strain gauge 1 is formed by, for example, laminating a metal foil on the insulating base 2 and etching the metal resistive foil, or forming a metal layer on the insulating base 2 by a sputtering method, or the like. In general, a strain gauge is manufactured by forming a pattern, an electrode terminal pattern, a wiring pattern connecting these, and the like.

  When a metal foil is used as a resistor, unnecessary portions are removed from the metal foil by an etching step to insulate electrically conductive portions such as folded patterns for detecting distortion, wiring patterns, and connection terminal portions with the outside. It will be left on the base.

  The formation of these patterns is generally performed by photolithography. That is, an enlarged predetermined pattern is drawn on a screen in advance, and the pattern of this screen is formed on the mask in the original size by means such as projection, and is used as the original size photomask of strain gauge printing.

  Cover the metal foil laminated on the insulating base with a photoresist, expose the photoresist by UV irradiation through a full size photomask, and develop with a developer to form the photoresist in a shape corresponding to a predetermined pattern Do. Then, the metal foil is etched using the patterned photoresist as a mask, whereby a predetermined folded pattern or the like of the metal foil is formed. Thereafter, the photoresist is peeled and removed by a stripping solution for photoresist.

In actual manufacture, in order to manufacture a large number of strain gauges, a plurality of predetermined patterns are formed on a mask so that patterns of a plurality of strain gauges can be exposed at one time.

In the case of producing a strain gauge by this method, it is necessary to draw a strain gauge pattern on a screen and, further, perform multi-face baking etc. using a photo technology to make a mask. Next, contact exposure was performed using this mask to expose the photoresist on the metal foil.

As described above, since an optical method such as a photographic technique is performed, an error with a desired pattern occurs due to image distortion, blurring, and an uncertain factor of a chemical during development. Further, by repeating the optical method several times, the error will increase.

Furthermore, since metal foils are etched using a photoresist as a mask, errors in the concentration, temperature, time, etc. of the etching solution cause variations in pattern thickness, shape of edges, etc., resulting in variations in resistance as strain gauges. It was the result.

On the other hand, even if the resistor is formed by sputtering, since patterning is performed using a photoresist, the exposure conditions of the photoresist, variations in sectional shape of the developed photoresist and lift-off, sputtering discharge, target conditions, etc. Similarly, the result is that the resistance value as a strain gauge varies.

  The strain gauges produced by this process are used by being bonded to a measured object or strain generating body and connected to a predetermined Wheatstone bridge circuit, but the above-mentioned variations in resistance value create an equilibrium state as it is used It was difficult.

  Therefore, in order to correct the resistance so as to be in an equilibrium state, the correction is performed by inserting a suitable correction resistor in the Wheatstone bridge circuit to which the strain gauge is connected. As an example, a manganin wire or the like which is stable over a long period and whose temperature coefficient of resistivity is very small is cut out by a desired incremental resistance value and inserted in a Wheatstone bridge circuit as a correction resistance.

However, when the resistance value is corrected by this method, a place for inserting the correction resistance in the Wheatstone bridge circuit is also required, and not only the enlargement but also the structural restriction and the increase of the process occur. The
In addition, since the manganin line does not detect strain, a problem arises in that the sensitivity characteristic as a strain gauge and the temperature characteristic can not be stabilized.

Therefore, it has been practiced to form the resistance adjustment pattern 5 and cut it into a comb shape by laser trimming to provide a detour to increase the resistance value.
However, trial and error have been made to determine the cut pattern to be set to a desired resistance value, and it has been relied on experience. In addition, since errors occur due to processing variations such as output fluctuations due to aging of the laser element of the laser processing machine, and reductions in the processing amount due to dirt on the optical system, errors may eventually occur due to inability to adjust. It was

JP, 2001-108543, A

  According to Patent Document 1, there is described a method for obtaining a desired resistance value by separately providing a short pattern for resistance adjustment and selectively removing the short pattern by laser trimming or the like. However, in this method, since it is not a method to aim at the initial value before correction of the resistance value which becomes a pair basically in a Wheatstone bridge circuit to a desired value, if adjustment is impossible with the short pattern for resistance adjustment, separately Laser trimming is performed on the provided resistance adjustment region to adjust it to the desired resistance value by trial and error, and if it does not fall within the desired value, as described above, the manganin wire is inserted into the Wheatstone bridge circuit. Become.

Therefore, although it is relatively easy to adjust the degree of the short pattern for resistance adjustment, it is not a fundamental measure, so the problem is that trial and error occur in the number of steps of laser processing and adjustment member attachment for this resistance adjustment. It had become.

  The present invention has been made in view of the above-described points, and it is easy to configure the Wheatstone bridge circuit connected to this resistor by a method of making the variation of the resistance value very small in the initial manufacturing stage. It is an object of the present invention to provide a strain gauge which can realize high resistance value accuracy from an early stage by a method.

The strain gauge of the present invention is
Comprising a plurality of metal resistors comprising a folded pattern for sensing strain on each side of the Wheatstone bridge circuit forming a Wheatstone bridge circuit;
A pair of resistors disposed on two opposite sides of the four sides of the Wheatstone bridge circuit are provided facing each other in a substantial pattern .
Resistor groups formed of resistors arranged in series on each side of the Wheatstone bridge circuit and on opposing sides are arranged in rotational symmetry in a substantial pattern .

  The folded pattern of each resistor is preferably formed by etching or sputtering.

  It is desirable that the wiring portion connecting the resistors be made of a metal having a sufficiently low electrical resistance than the resistors.

  The wiring portion is preferably made of gold or copper and formed by sputtering or plating.

  It is desirable that the folded patterns of the respective resistors be provided alternately and that the lengths of the portions of the folded patterns that sense distortion be substantially the same in the strain sensing direction.

  With this configuration, the variation in resistance value of the strain gauge resistor can be greatly reduced, and the time required for adjusting the resistance value can be significantly reduced.

A plan view showing a pattern of a resistor in a strain gauge showing a first embodiment of the present invention Equivalent circuit diagram of a Wheatstone bridge in a strain gauge showing an embodiment of the present invention The physical wiring schematic diagram in the strain gauge which shows the embodiment of the present invention A plan view showing a resistor pattern in a strain gauge according to a second embodiment of the present invention Plan view showing a resistor pattern in a conventional strain gauge

  Hereinafter, a strain gauge according to an embodiment of the present invention will be described with reference to the attached drawings.

  FIG. 1 is a plan view showing a pattern of a resistor in a strain gauge showing a first embodiment of the present invention.

In FIG. 1, 1 is a strain gauge of the present invention, and 2 is an insulating base.
The insulating base 2 is a polyimide film in the present embodiment, for example, one having a thickness of 25 μm.

  The resistor 3 in the strain gauge is provided on the insulating base 2 and is formed by laminating metal foils to be the resistor 3. This metal foil is bonded to the insulating base 2 via an adhesive. In the present embodiment, the metal foil is a 2.5 μm thick alloy of 55% copper and 45% nickel. For adhesion, a polyimide-based adhesive is applied, and adhesion is performed by pressure and heat curing. In this state, the metal foil to be the resistor 3 covers substantially the entire upper surface of the insulating base 2, so that a predetermined resistor pattern is to be formed next.

  An enlarged image of a predetermined resistor pattern is drawn on a screen in advance, and the pattern of this screen is projected on a photomask to make a photomask of the full size.

  A photoresist (liquid resist) is formed on the surface of the metal foil stuck on the insulating base 2 by spin coat application, dip coater application, or lamination attachment such as dry film. Thereafter, the solvent remaining in the photoresist is evaporated by pre-baking to make the photoresist film dense, and then exposure is performed with UV light through a photomask of the original size. Then, it is immersed in a developer and developed to remove unnecessary portions.

The photoresist is removed and the exposed portion of the metal foil surface is etched away to form a predetermined resistor pattern. As the pretreatment, the photoresist is post-baked (heat treatment) to remove the remaining developing solution, rinse solution and moisture,
After improving the adhesion and etching resistance of the photoresist film, the photoresist film is introduced into an etching solution to remove the exposed metal foil portion.

  Since the photoresist remains on the surface of the resistor 3 left unetched, it is removed with a photoresist remover. Thus, resistors 3a to 3d having desired patterns are obtained.

  On the other hand, it is also possible to form the resistor 3 on the insulating base 2 by sputtering. As compared with the etching method, the photoresist has a negative-positive inverted structure, and a portion where a desired pattern is not formed is formed as a mask. That is, a photoresist (liquid resist) is formed on the insulating base 2 by spin coating and dip coating, and then prebaking is performed, followed by exposure to UV light through a photomask of the original size. Thereafter, it is immersed in a developing solution for development to remove unnecessary parts.

  The metal is then deposited on the photoresist side by sputtering to form the desired pattern. At this time, metal is also laminated on the photoresist, but since it has a lift-off resist shape, peeling is easily possible with a photoresist peeling material, and desired resistors 3a to 3d can be obtained.

  Further, a cover film is attached as a protective layer on the top surfaces of the resistors 3a to 3d. The cover film is a polyimide film having a thickness of 12.5 μm. In addition, in order to comprise a Wheatstone bridged circuit using resistance bodies 3a-3d, it is necessary to provide the electrode 4 for a connection. Therefore, predetermined opening holes are formed in the cover film in advance by laser processing, press punching, or the like, and this is attached. In this bonding, the above-mentioned polyimide type adhesive is applied, and adhesion is performed by pressing and heat curing.

  Of course, when forming the opening for the electrode 4, a method of forming a protective layer of photoresist by spin coating, removing a desired portion by exposure and development, and exposing the electrode 4 may be used. .

  In any case, the electrode 4 is electrically connected to the resistors 3a to 3d, and the metal is exposed on the surface, and this is used as a connection portion to constitute a Wheatstone bridge circuit.

  In addition, when the resistors 3a to 3d form a Wheatstone bridge circuit, the resistor adjustment pattern 5 removes a part of the resistor adjustment pattern 5 with a laser to change the resistance value, thereby making the Wheatstone bridge circuit It is provided to fine-tune the resistance value balance of

  The wiring portion 7 is a wiring that connects the respective resistors 3 or connects the resistor 3 and the electrode 4. Details of this will be described later.

  FIG. 2 is a Wheatstone bridge circuit diagram in a strain gauge illustrating an embodiment of the present invention.

In FIG. 2, the resistance of one side in each Wheatstone bridge circuit is divided into a plurality and expressed.
That is, in the circuit diagram, between the electrode 4a and the electrode 4f, the resistor 3a (R11) and the resistor 3a (R12),
Between the electrode 4b and the electrode 4f, a resistor 3b (R21) and a resistor 3b (R22),
Between the electrode 4c and the electrode 4e, a resistor 3c (R31) and a resistor 3c (R32),
Between the electrode 4c and the electrode 4d, the resistor 3d (R41) and the resistor 3d (R42) are shown separately.

The power source 6 is applied between the electrode 4c and the electrode 4f, and can be obtained as a terminal voltage of the electrode 4a (electrode 4e) and the electrode 4b (electrode 4d) as an output of strain detection.
The electrodes 4a and 4e and the electrodes 4b and 4d are electrically connected to each other and provided as output terminals.

FIG. 3 is a schematic diagram of physical wiring in a strain gauge showing an embodiment of the present invention.
The circuit diagram of FIG. 2 is compared with the plan view of FIG. 1 to show the state of the substantial wiring of the resistor 3 and the electrode 4.

  The resistor 3a (R11) of the Wheatstone bridge circuit shown in FIG. 2 and the resistor 3d (R41) opposed thereto are opposed and juxtaposed in the physical wiring diagram of FIG. When this is viewed in the plan view of FIG. 1, both of the resistor 3a (R11) and the resistor 3d (R41) are formed in a folded pattern, and are arranged in opposition to each other so as to sandwich each other. The pairing combination is expressed by being surrounded by an alternate long and two short dashes line for each opposing side in FIG.

  That is, all of the resistors 3c (R31) and 3b (R21), the resistors 3c (R32) and 3b (R22), and the resistors 3a (R12) and 3d (R42) are similarly turned back. It is formed in a pattern, and is formed in a form in which it is placed side by side facing each other.

  Therefore, those facing each other and forming sandwiches, for example, the resistor 3a (R11) and the resistor 3d (R41) are very close to each other, and each resistor has almost the same processing process conditions That is, it is manufactured under processing conditions of photolithography, etching or sputtering. When the strain gauge 1 has a relatively large size, for example, when the outer diameter is about 6 mm, the influence of the arrangement of the resistors 3 becomes a remarkable difference, and the resistors 3a (R11), 3a (R12), and 3b ( R21), the resistance 3b (R22), the resistance 3c (R31), the resistance 3c (R32), the resistance 3d (R41), and the resistance 3d (R42) vary, so the present invention is extremely effective. It becomes a thing.

  FIG. 4 is a plan view showing a resistor pattern in a strain gauge according to a second embodiment of the present invention. The arrangement of the electrodes 4 and the resistance adjustment pattern 5 is the same as that of the first embodiment, but the so-called grid lengths of the portions of the resistors 3a to 3d which sense distortion are equalized.

That is, the length grid lengths x of portions having high sensitivity to distortion in the resistor 3a (R11) and the resistor 3a (R41) are formed to have substantially the same dimensions.
The same applies to the resistors 3b (R21) and 3b (R22), the resistors 3c (R31) and 3c (R32), and the resistors 3d (R41) and 3d (R42). There is.

  By forming the length of the portion highly sensitive to distortion, that is, the grid length x to be the same dimension, the sensitivity to distortion becomes equal on opposite sides in the Wheatstone bridge circuit. The strain gauge 1 with extremely high accuracy can be realized.

  Now, by dividing and arranging the resistors 3 in this way, depending on the arrangement position of the resistors 3, there may be a case where the wiring connecting the resistors 3 becomes long. In the embodiments of FIGS. 1 and 4, since the resistor 3, the electrode 4, the resistance adjustment pattern 5 and the wiring 7 are disposed in rotational symmetry, an error in the resistance value is less likely to occur. There is. Of course, there are cases where the problem can be solved by increasing the wire width of these wiring portions 7 to lower the resistance value, but it is not difficult to imagine that it sometimes occurs that it is difficult to obtain a desired resistance value.

  In the present invention, the wiring portions 7 shown by hatching in FIG. 1 and FIG. 4 are formed of a metal having a small electric resistance such as gold or copper, thereby connecting the respective resistances 3 or the resistances 3 and electrodes The resistance value of the wiring connecting 4 can be reduced. In this case, the gold or copper may be formed on the metal of the resistor 3 or a single wiring as a bypass of gold or copper may be used. In the fabrication, it is easy to realize by masking unnecessary portions using the above-mentioned photolithography method and forming a gold or copper layer by sputtering or plating.

  Further, by forming the wiring portion 7 with a metal of low electric resistance such as gold or copper, there is also an effect that the soldering of the wiring drawn out from the electrode 4 becomes easy.

  In particular, by forming the wiring portion 7 of gold, it is possible to suppress oxidation of the exposed surface of the electrode portion 4 and withstand long-term storage use. Although not shown here, extending the arrangement length does not affect the characteristics of the strain gauge, so an additional extension of the wiring portion 7 is additionally provided, and the exposed surface portions of the electrodes 4 are arranged in a row. It is also possible to form it in the pattern fitted to the FPC connector. The insulating base 2 of the strain gauge 1 uses polyimide, and the connection portion in contact with the connector is gold-plated so that it can be compatible with a commonly available FPC connector. In this case, since there is no soldering or the like to the electrode 4, assembly can be facilitated.

  In the embodiment of the present invention, the four sided resistors in the Wheatstone bridge circuit are each divided into two and a strain gauge having a total of eight resistors is described, but the resistances on two opposite sides in the Wheatstone bridge circuit are described. In the case of a total of four resistors each divided into two in the body, it is effective in the other divisions.

  As an application example of the present invention, it can be applied to a load cell for measuring force and load, a pressure sensor for measuring pressure, etc., to a sensitive element of a transducer used for measuring physical quantities (load, pressure, displacement, acceleration, torque, etc.) is there.

Reference Signs List 1 strain gauge 2 insulating base 3, 3a to 3d resistor 4a to 4f electrode 5 resistance adjustment pattern 6 power supply 7 wiring portion

Claims (5)

A plurality of metal resistors having a folding pattern for sensing distortion on each side of the Wheatstone bridge circuit, which constitutes a Wheatstone bridge circuit,
A pair of each resistor disposed on two sides facing out of the four sides of the Wheatstone bridge circuit is provided to face with each sandwich form a substantive pattern,
A strain gauge characterized in that a resistor group composed of the respective resistors arranged in series on each side of the Wheatstone bridge circuit and arranged on opposite sides is arranged in rotational symmetry in a substantial pattern .
  The strain gauge according to claim 1, wherein the folded pattern of each resistor is formed by etching or sputtering.   The strain gauge according to any one of claims 1 to 2, wherein a wiring portion connecting the respective resistors is made of a metal whose resistance is sufficiently lower than that of the respective resistors.   The strain gauge according to claim 3, wherein the wiring portion is made of gold or copper and is formed by sputtering or plating. The folded patterns of the respective resistors are provided so as to be alternately sandwiched, and the lengths of the portions of the folded patterns that sense strain are substantially the same in the strain sensing direction. The strain gauge according to any one of Items 1 to 4.

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