JP2717812B2 - Load cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology is a so-called load converter that can convert a load such as weight acting on a product such as weight measurement into an electric signal and measure it. It belongs to the structure of a gauge attached to a strain body such as a load cell and the technical field of manufacturing.

<Summary of the Invention> Thus, the invention of this application relates to a heat-insulating organic resin such as polyimide, epoxy, amide imide, epoxy modified polyimide, etc. A heat-resistant insulating film made of stainless steel is applied, and a metal thin film layer consisting of only one layer of a gauge pattern and a conductor pattern that forms a Wheatstone bridge is formed by vapor deposition or sputtering. After being formed in a predetermined manner, the gauge pattern is formed in a single layer only by photolithography, etching, or the like, and the invention relates to a load cell and a method of manufacturing the load cell. , The conditions during the growth of the metal thin film or the processing conditions during the heat treatment are set to a predetermined value so as to be less than or equal to a predetermined value. The present invention relates to a load cell having a simple structure in which a pattern has only one layer and does not have two or more layers, and an invention relating to a method of manufacturing the load cell.

<Conventional technology> As is well known, in modern times, civil and industrial societies rely heavily on science and technology, and the use of machinery and equipment in various industries that support them is very large. Is also undeniable.

Thus, very many of these mechanical devices use an applied load such as gravity, and the load applied to not only the devices but also other manufacturing devices due to various mechanisms. In many cases, it is necessary to accurately measure.

For example, a load converter such as a so-called load cell that converts weight and the like into an electric signal in a weight weighing device for a commodity in a distribution market and the like which has recently become prosperous, and a control mechanism in various industrial facilities and the like. Is widely used.

As is well known to those skilled in the art, such a load converter such as a load cell changes the resistance value of the electric resistor in accordance with the strain of the beam or the like on a side portion of the strain-generating body such as a durable body where distortion is likely to occur. The technology of accurately measuring the load electrically using the change of the output voltage with respect to the input voltage using the principle has been used, and in the past, when manufacturing such load cells, polyimide, epoxy resin was used in the strain generating part of the beam. After attaching a resistor made of constantan, nickel, nichrome, or the like to an insulating film such as, the technology of bonding the insulating film to the strain-generating part has been used. Accordingly, it is strongly required that the pattern formation of the low antibody forming the Wheatstone bridge is micronized, and the gauge pattern of the resistor is changed. Called no longer cope on accuracy in shaping by machining, in order to cope with this, for example,
Japanese Patent Application Laid-Open No. 57-93220 discloses a method of forming a metal thin film layer on the insulating layer by vacuum deposition or sputtering after forming an insulating layer on the strain generating portion of the beam as shown in the invention. Elaborate advanced technology has been developed to form gauge patterns in units of micron thickness by means such as photolithography, etching, etc., and compact measurement of load cells, cost reduction by mass production system, and rapid measurement data due to weak current conduction have jumped. It has become possible to appear in such a way as to improve the performance.

However, recently, as the accuracy of electronic equipment has been improved, the demand for the accuracy of load transducers such as the above load cells has further increased, and fundamentally developed evaporation methods, sputtering, photolithography, and etching have been developed. For the gauge pattern of the metal thin film layer, the conductor pattern, etc., by means such as the above, the gauge associated with the temperature treatment for maintaining the stable fixing state at the final stage of the gauge pattern for the resistor or beam, such as zero point correction, etc. Ultra-precision technology such as interposing a trimming resistor for temperature correction of a pattern or the like in a gauge pattern has been required, and for this purpose, for example, a technology such as the invention of Japanese Patent Publication No. 62-25977 has been developed. Basically, it has become practical.

By the way, the thin film strain gauge in this kind of prior art is:
For example, as in the invention of Japanese Patent Publication No. 62-59767, an insulating layer is formed on a strain body, and a metal thin film having predetermined functions is laminated thereon by vacuum deposition, sputtering, photolithography, etching, or the like. This is a general technique.

As the seed thin film layer, for example, NiC
r, a gauge portion of metal such as Ta ₂ N, and a trimming pattern for zero balance (a trimming pattern for suppressing an output voltage at no load within a certain range) are formed. As the second layer, for example, A plurality of layers by forming a trimming pattern for zero-point temperature correction of a metal such as Ni and Cr, and forming a conductor pattern of a metal such as Cu, Al-Cu, and Au on the third layer. Are required for each function.

Furthermore, if there is a difference in the crystal structure between the layers in order to increase the adhesion strength between the pattern layers, since there is a possibility of peeling, provided with a buffer layer of a similar crystal structure interposed,
It has a multilayer structure of three or more layers in which metals that are easily compatible with each other are sequentially stacked.

<Problems to be Solved by the Invention> However, there are the following problems in manufacturing a load cell by such a conventional technique.

That is, first of all, it is necessary to perform temperature correction of the zero point.In order to do so, each load cell is housed in a constant temperature bath, and the output change of each bridge output due to the zero point temperature is measured. On the basis of the work of calculating the resistance value of the temperature correcting low antibody capable of compensating for the output change for each unit based on the single unit, and adjusting the resistance value of the temperature correcting resistor based on the calculated value by cutting or the like. Is complicated.

Secondly, it is necessary to laminate many thin-film metal tanks through vapor deposition or sputtering, and therefore, each metal substrate (eg, a target material for Cu, NiCr sputtering, etc.) must be prepared, It has the disadvantage of being expensive in terms of cost, and since the lamination of metal thin films is repeated sequentially, only a lamination thickness of about 100 angstroms per minute is possible. There is a problem that a sufficient amount of time is spent and work efficiency is deteriorated.

However, although this point can be solved by some means in the processing on the device side, thirdly, it is necessary to sequentially process by photolithography and an etching process from the upper side in order to form a pattern of each metal thin film layer. Next, a drying curing operation is performed, followed by a pattern baking exposure operation using a mask, and then, development and fixing are performed to remove the unexposed resist, to expose a metal surface for etching, and to perform a resist curing process. Perform the work of removing unnecessary resist by performing etching with an etchant, acid, or alkali,
I have to follow the same process by the number of the layers,
Therefore, there is a bottleneck that requires many steps and jig parts.

Fourth, in the process of processing the above-described layers, selective etching must be performed for each metal. Therefore, there is an inconvenience that an etching bath or the like must be prepared for each etchant. Disadvantage is that it is difficult to find an etchant for use.

In consideration of the fact that the metal is not originally violated by the etchant at all and that the traveling speed is usually slow, the first of the plurality of layers from the bottom side
This is because the third layer (uppermost layer) is etched by the etchant during the etching of the layer and the second layer, and has a disadvantage that characteristics are slightly affected.

In particular, as described in the invention of Japanese Patent Publication No. 62-25977,
When the layer is Cu and the Cu is violated by almost any etchant and the resistance value of the thin-film metal is significantly changed with time due to weak acid or insufficient alkali that has penetrated into the layer and is insufficiently washed, the conductive pattern layer is corroded. There was a problem that could develop to.

Then, there is a problem that the greater the number of times of using the etchant, the greater the trouble.

Fifth, since different types of thin-film metals are stacked in multiple layers, a weak signal current can be reproduced at the contact area at the boundary between them due to the presence of the contact potential due to the difference in ionization tendency. There is a Masunaus point that it cannot be taken out well, and a thermoelectromotive force is generated due to thermal behavior through temperature change over time, and it is likely that weak signal currents that are weak against temperature and cannot be taken out with good reproducibility as well .

Even if the thin-film metals are in close contact with each other, there is a problem that a delicate signal current cannot be taken out because the resistance value is not stable due to various vibrations and behaviors during operation because of the contact resistance.

Sixth, usually, the resistors in the gauge portion are not stable unless heat-treated in the final step. However, when two or more types of resistors are formed on the same strain-generating body, the optimum Generally, the heat treatment conditions are different. For example, it is not possible to set the optimum heat treatment conditions to match two resistors at the same time, and therefore, there is a disadvantage that one of the characteristics becomes a device characteristic. ,For this reason,
As a result, the characteristics of the load cell change with time and instability, and there are many disadvantages such as a disadvantage that good reproducibility cannot be maintained, and there are many points to be solved in terms of characteristics.

<Object of the Invention> The object of the invention of this application is a problem in a pattern processing process by photolithography and etching in forming a metal thin film layer of a gauge pattern attached to a strain generating element of a load converter such as a load cell based on the above-mentioned conventional technology. And the technical problem to be solved in the trimming of zero point temperature correction, to efficiently form only one layer forming the electric circuit of the gauge pattern and the conductor pattern, and to improve the forming efficiency. An excellent load cell that eliminates the need for trimming for the zero-point temperature correction and that is advantageous in measurement technology application fields in various industries by enabling low-cost, high-accuracy and highly reliable measurement data to be obtained with good reproducibility, and , And a manufacturing method thereof.

<Means and Actions for Solving the Problems> In order to solve the above-mentioned problems, the configuration of the invention of the present application having the above-mentioned claims in accordance with the above-mentioned objects has been described in the form of a flexure element of a load converter such as a load cell. Heat-insulating organic resin such as polyimide, epoxy, etc. is applied to the side surface of a predetermined strained part, heated and cured to form a thin insulating layer, and then the gauge of the Wheatstone bridge is formed by means such as evaporation or sputtering. The pattern, and the pattern for zero point correction and conductors are formed in only one layer, and then photolithography, etching, and resist removal are performed to form a predetermined metal thin film layer. For example, by maintaining the wattage of the input power of sputtering at a predetermined value, or by maintaining the flow rate and pressure of Ar at set conditions, or by controlling the temperature of the substrate. The temperature coefficient of the zero point of the bridge output is maintained by maintaining the predetermined value, or by maintaining the plasma density under the predetermined condition, or by controlling the heat treatment conditions in the post-process. In order to keep the metal thin film layer to only one layer by making the temperature coefficient value of the resistor of each gauge pattern equal to or below zero as much as possible. Since then, it is possible to accurately maintain high data reproducibility without performing zero point temperature compensation, reduce the man-hours required to manufacture gauge patterns and conductor patterns, and manufacture at low cost. It takes technical measures to make it possible.

<Basic Background of the Invention> Next, the basic background of the invention of this application will be described. The output equation of the Wheatstone bridge shown in FIG. It is well known to those skilled in the art, but if attention is focused only on the zero point where the strain is not applied to the flexure element, the resistances Ra, Rb, Rc, and Rd of Ra to Rd are included in the resistance. Temperature coefficients αa, αb,
It is known that only αc and αd enter as a variation factor due to the temperature T.

That is, Ra '= Ra (1 + αaT) Rb ′ = Rb (1 + αbT) Rc ′ = Rc (1 + αcT) Rd ′ = Rd (1 + αdT) Becomes

When this equation (2) is expanded with respect to the term of the temperature T (however, the square term of T is ignored), Becomes

The first and second items of [] in the expression (3) are the output expressions of the ordinary bridge balance, and the third and subsequent items are the temperature terms of the elements that fluctuate according to the temperature T.

Then, in equation (3), Is satisfied, the output becomes independent of temperature.

The following two methods are conceivable to make the third and fourth terms zero.

1) Each resistance value (Ra, Rb,
Rc, Rd).

2) Since the temperature coefficient is determined when the gauge is completed, the resistors of Ra to Rd are trimmed so as to satisfy the expression (4).

However, this method is not realistic in the following two points a) and b).

a) The initial output (zero point output) of the bridge is not guaranteed.

That is, it is not possible to satisfy the expression (4) while maintaining the bridge balance, and in practice, the trimming amount becomes very large.

b) Temperature coefficient of each resistor (Ra, Rb, Rc, Rd) (αa,
If all of αb, αc, and αd) are not measured independently, trimming cannot be performed, so that much time and labor is required for the measurement, and the management operation becomes extremely complicated.

Therefore, the invention of this application has examined the above point 1).

Since the bridge balance must be obtained from the first and second terms of the above equation (3), if trimming is performed so that Ra = Rb = Rc = Rd, the equation (3) is further simplified and Vout ′ = 1/4 (αa + αd-αb-αc) T × Vex
(5) where (αa + αd−αb−αc) in the equation (5) is defined as a temperature term.

That is, [αa + αd-αb-αc]
It is only necessary to form the resistors Ra, Rb, Rc, and Rd so as to reduce as much as possible.

Further, even if this number slightly exceeds the specified value, the resistance values (Ra, Rb, Rc, Rd) can be trimmed and corrected so that the balance is not lost.

For example, in order to suppress the zero point temperature coefficient to ± 100 ppm / ° C., it is necessary to make each resistor (Ra, Rb, Rc, Rd) such that [αa + αd−αb−αc] ≦ 0.8 ppm / ° C. or less. good.

In the case of Cu-Ni, α = −40 to 60 ppm / ° C. is usually used as the seed mode. Therefore, it is sufficient to find a condition for suppressing the variation.

The temperature coefficient (α
It has been found that it is feasible to control a, αb, αc, and αd) without variation by properly controlling the following two process conditions 1) and 2).

1) Processing process at the time of metal film growth 2) Processing process at the time of heat treatment First, regarding the processing process at the time of 1) metal film growth, there are various metal thin film fabrication processes. Power (input wattage per effective area) must be kept constant. Ar flow rate and pressure (ionized Ar condition for alloy pattern for device pattern) must be maintained. Substrate temperature must be maintained. Plasma density must be maintained. When various combinations of the above four conditions for keeping are made, there are conditions that can be made to satisfy the temperature coefficient condition [αa + αd−αb−αc] ≦ 0.8 ppm / ° C.

However, this alone cannot be said to be sufficient. In the heat treatment process of 2), the resistance value (Ra, Rb, Rc, Rd) and the temperature coefficient of resistance (αa, αb, αc, αd) can be controlled.

The optimum combination of the condition of the point 1) and the condition of the point 2) is determined. 1) [αa + αd−αb−αc] ≦ 0.8 or 2) αaαbαcαd0 The conditions need only be limited and this is possible at the state of the art and indeed it can be found.

<Example> Next, an example of the invention of this application will be described with reference to the drawings.

In the embodiment shown in FIG. 1, reference numeral 1 denotes a load cell used in a weighing device used in, for example, a backyard of a supermarket. Hole 3 is formed, and a strain-generating portion on one side is provided with a cleaning action after finishing polishing of the strain-generating body 2 in the same manner as in the conventional mode, and is made of a heat-resistant insulating organic resin such as polyimide or epoxy resin. After uniformly applying the coating solution of a predetermined thickness to a predetermined thickness, the coating solution is heated to a predetermined temperature in a nitrogen gas atmosphere and applied, and the resin is thermally cured to form a heat-resistant insulating film 4 of, for example, about 6 microns. Then, copper-nickel sputtering is performed, resist coating is performed in the same manner as in the conventional mode, pre-baked, exposed and developed, rinsed, post-baked, and subjected to photolithography and etching. It performs a removal, a gauge pattern 1
Only the layer is formed.

The basic process is similar to the process disclosed in the above-mentioned Japanese Patent Publication No. 62-25977, but as shown in the above-described basic background at the time of thin film growth at the time of forming a metal thin film, at the time of sputtering, Maintaining a constant wattage per unit effective area, maintaining a constant flow rate and pressure of ionized argon with respect to the copper-nickel alloy mass, maintaining a constant substrate temperature, and controlling plasma By combining conditions such as keeping the density constant, the absolute value of the temperature term in the above equation (5)
0.8 or less, and if the conditions during the growth of such a metal thin film are not sufficient, the temperature in the final heat-curing process and the holding time of the temperature are further controlled to control the temperature term. The absolute value is, for example, smaller or equal to 0.8.

Then, a protective film layer 7 is finally formed on the conductor pattern layer 6 in a predetermined manner to complete the process.

Further, in the embodiment of the load cell 1 'shown in FIG.
In this embodiment, only one layer of the gauge pattern 5 is formed on the absolute value 4 and the conductor pattern 6 is also formed in only one layer, so that the layer can be substantially made one layer.

In this embodiment as well, the protective film 7 finally covers the whole.

Thus, when forming the single layer, the conductor pattern 6 and the gauge pattern 5 are formed by adjusting the lateral width of the gauge pattern and the lateral width of the conductor pattern since both are of the same crystalline material. For example, if the gauge width of the normal gauge pattern is 10 to 50 μm mm and the width of the conductor pattern is 1 to 5 mm and a gauge of 5 kΩ is manufactured, the resistance value of the conductor pattern will be about 10 ohm, and it is sufficiently practical What can withstand.

It should be noted that the embodiments of the invention of this application are not limited to the above-described embodiments. For example, the load converter can be applied to other than the load cell. Various modes can be adopted, such as being applicable to various measuring devices other than the application to the weighing device.

<Effects of the Invention> As described above, according to the invention of this application, an insulating layer is basically applied to a strain-generating body made of duralumin at a strain-generating portion by applying and curing, and then a predetermined metal is formed by a vapor deposition method or a sputtering method. In a load cell in which a thin film is formed as a gauge pattern and a conductor pattern as only one layer, and further a final pattern is provided through a process such as photolithography and etching, the temperature coefficient of the zero point of the bridge output becomes a predetermined value or less. In addition, since the resistors of each gauge pattern are built, there is no need to perform temperature compensation for the zero point after completion, and since the same characteristics can be mass-produced without human intervention, the number of manufacturing steps is reduced and the characteristics are reduced. An excellent effect that extremely advantageous conditions in terms of surface and cost can be obtained.

Therefore, in the manufacturing method, the input power, the flow rate and the pressure of argon, the temperature of the substrate, the temperature of the substrate, and the plasma density are maintained at constant conditions during the growth of the continuous thin film or during the heat treatment process. Control the holding time of the bridge output so that the temperature coefficient of the zero point of the bridge output is equal to or less than a predetermined value,
In addition, by setting the temperature coefficient of each resistor to be as equal to zero as possible, a large amount of time and energy is required for photolithography during the formation of the metal thin film layer, reduction in man-hours in the etching process, measurement management in each process, and the like. An excellent effect is obtained in that weak measurement data with high accuracy and high reproducibility can be taken out.

Therefore, the number of steps is reduced by using only one thin-film metal layer attached to the strain-generating portion of the flexure element as in the prior art, complicated procedures for precision control are remarkably omitted, reliability in product precision is improved, and cost is reduced. The excellent effect that can be derived is produced.

In this way, the layer structure of the gauge pattern attached to the strain body and the conductor pattern is changed from the conventional structure of three or more layers to the structure of only one layer. It is possible to eliminate the necessity of forming the resistors for each gauge in a predetermined manner for each side of the bridge of each gauge.

In particular, if the photolithography process can be repeated twice to process and if you do not want to perform selective etching, the conductor pattern film should be formed by sputtering or the like with a shadow mask after gauge pattern processing and molding. The effect is obtained.

Thus, it is only necessary to form a conductor pattern and a trimming pattern for the gauge pattern portion using only the first layer. This has an effect that a change to a one-layer structure is possible.

[Brief description of the drawings]

The drawings are explanatory views of the embodiments of the invention of the present application.
FIG. 2 is a schematic side view of a load cell, and FIG. 3 is a circuit diagram of a Wheatstone bridge. 2 ... strain body, 5 ... gauge pattern, 1 ... load cell

Claims (1)

(57) [Claims] In a load cell, a metal thin film layer forming a gauge pattern for forming a Wheatstone bridge is formed on a side surface of a strained portion of a strain body via a heat-resistant insulating film.
The resistors of the two gauge patterns are built to a value at which the temperature coefficient of the zero point of the bridge output is equal to or less than a predetermined value,
A load cell, wherein the gauge pattern and the conductor pattern are formed of only one layer.